Journal of Neurophysiology

Published by American Physiological Society
Online ISSN: 1522-1598
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Article
The surface electromyographic (EMG) signal from right and left trapezius muscles and the heart rate were recorded over 24 h in 27 healthy female subjects. The root-mean-square (RMS) value of the surface EMG signals and the heartbeat interval time series were calculated with a time resolution of 0.2 s. The EMG activity during sleep showed long periods with stable mean amplitude, modulated by rhythmic components in the frequency range 0.05-0.2 Hz. The ratio between the amplitude of the oscillatory components and the mean amplitude of the EMG signal was approximately constant over the range within which the phenomenon was observed, corresponding to a peak-to-peak oscillatory amplitude of approximately 10% of the mean amplitude. The duration of the periods with stable mean amplitude ranged from a few minutes to approximately 1 h, usually interrupted by a sudden change in the activity level or by cessation of the muscle activity. Right and left trapezius muscles presented the same pattern of FM. In supplementary experiments, rhythmic muscle activity pattern was also demonstrated in the upper extremity muscles of deltoid, biceps, and forearm flexor muscles. There was no apparent association between the rhythmic components in the muscle activity pattern and the heart rate variability. To our knowledge, this is the first time that the above-described pattern of EMG activity during sleep is documented. On reanalysis of earlier recorded trapezius motor unit firing pattern in experiments on awake subjects in a situation with mental stress, low-FM of firing with similar frequency content was detected. Possible sources of rhythmic excitation of trapezius motoneurons include slow-wave cortical oscillations represented in descending cortico-spinal pathways, and/or activation by monoaminergic pathways originating in the brain stem reticular formation. The analysis of muscle activity patterns may provide an important new tool to study neural mechanisms in human sleep.
 
Article
1. The pedunculopontine tegmental (PPT) cholinergic nucleus and the locus coeruleus (LC) noradrenergic nucleus were electrically stimulated to investigate their effects on the recently described slow oscillation (approximately 0.3 Hz) of neocortical neurons. Intracellular recordings of slowly oscillating, regular-spiking and intrinsically bursting neurons from cortical association areas 5 and 7 (n = 140) were performed in anesthetized cats. 2. Pulse trains to the PPT nucleus produced the blockage of rhythmic (approximately 0.3 Hz) depolarizing-hyperpolarizing sequences in 79% of tested cortical neurons and transformed this slow cellular rhythm into tonic firing. The latency of the cortical cellular response to PPT stimulation was 1.2 +/- 0.5 (SE) s and its duration was 15.9 +/- 1.9 s. The PPT-elicited suppression of the slow cellular oscillation was accompanied by an activation of the electroencephalogram (EEG) having a similar time course. Fast Fourier transform analyses of EEG activities before and after PPT stimulation showed that the PPT-evoked changes consisted of decreased power of slow rhythms (0-8 Hz) and increased power of fast rhythms (24-33 Hz); these changes were statistically significant. 3. The blockage of the slow cellular oscillation was mainly achieved through the diminution or suppression of the long-lasting hyperpolarizations separating the rhythmic depolarizing envelopes. This effect was observed even when PPT pulse trains disrupted the oscillation without inducing overt depolarization and increased firing rate. The durations of the prolonged hyperpolarizations were measured during a 40-s window (20 s before and 20 s after the PPT pulse train) and were found to decrease from 1.5 +/- 0.2 to 0.7 +/- 0.1 s. The values of the product resulting from the duration (in seconds), the amplitude (in millivolts), and number of such hyperpolarizing events within 20-s periods were 51.5 +/- 5 and 5.1 +/- 1.9 before and after PPT stimulation, respectively. 4. The PPT effect was suppressed by systemic administration of a muscarinic antagonist, scopolamine, but not by mecamylamine, a nicotinic antagonist. 5. The PPT effect on cellular and EEG cortical slow oscillation survived, although its duration was reduced, in animals with kainate-induced lesions of thalamic nuclei projecting to areas 5 and 7 (n = 3) as well as in animals with similar excitotoxic lesions leading to extensive neuronal loss in nucleus basalis (n = 2). These data indicate that the PPT effect is transmitted to neocortex through either thalamic or basal forebrain relays.(ABSTRACT TRUNCATED AT 400 WORDS)
 
Article
Responses to broadband Gaussian white noise were recorded in auditory-nerve fibers of deeply anesthetized chinchillas and analyzed by computation of zeroth-, first-, and second-order Wiener kernels. The first-order kernels (similar to reverse correlations or "revcors") of fibers with characteristic frequency (CF) <2 kHz consisted of lightly damped transient oscillations with frequency equal to CF. Because of the decay of phase locking strength as a function of frequency, the signal-to-noise ratio of first-order kernels of fibers with CFs >2 kHz decreased with increasing CF at a rate of about -18 dB per octave. However, residual first-order kernels could be detected in fibers with CF as high as 12 kHz. Second-order kernels, 2-dimensional matrices, reveal prominent periodicity at the CF frequency, regardless of CF. Thus onset delays, frequency glides, and near-CF group delays could be estimated for auditory-nerve fibers innervating the entire length of the chinchilla cochlea.
 
JTE-013 enhances the excitability of capsaicin-sensitive small-diameter sensory neurons. A : a representative recording in which the ramp of depolarizing current evoked 3 action potentials (APs) under control conditions, whereas after a 10-min exposure to 100 nM JTE-013 the number of APs increased to 10 ( right ). B summarizes the sensitizing actions of JTE-013 over a 15-min recording period. There was no significant difference between the number of APs at the 2, 5, 10, and 15 min time points. The number of neurons at each time point are as follows: control 11, 2 min 6, 5 min 11, 10 min 11, and 15 min 9. C : the number of evoked APs after exposure to JTE-013 normalized to their respective control values; these are the same neurons as shown in B . Note that there were no recordings obtained at 2 min for JTE-013-insensitive neurons. *Significant difference compared with the control condition ( P Ͻ 0.001, ANOVA on ranks). 
JTE-013 augments excitability in a time- and concentration-dependent manner. A : number of evoked APs for the different times and concentrations of JTE-013. The data shown represent only the mean values; the SE is not shown for clarity of presentation. The number of neurons comprising the results for each concentration are as follows: vehicle 5, 1 nM 4, 3 nM 5, 10 nM 10, 100 nM 11, 1,000 nM 8. B : number of evoked APs obtained for the different times and concentrations of JTE-013 normalized to their respective control values. The data were obtained from the neurons shown in A and represent means Ϯ SE. There was no difference in either the number of evoked APs or the normalized number of evoked APs over the recording periods for the vehicle ( P ϭ 0.20 and P ϭ 0.24 for the number and the normalized number, respectively, ANOVA), for 1 nM JTE-013 ( P ϭ 0.38 and P ϭ 0.27 for the number and the normalized number, respectively, ANOVA), and for 3 nM JTE-013 ( P ϭ 0.16 for both for the number and the normalized number, ANOVA on ranks). There was a significant difference in both the number and normalized number of APs for treatment times at 5, 10, and 15 min for 10, 100, and 1,000 nM JTE-013 compared with their control values ( P Ͻ 0.001 ANOVA on ranks, Dunn’s all pairwise test). C summarizes the increase in the normalized number of APs as a function of JTE-013 concentration for treatment times of 10 and 15 min. 
Sphingosine 1-phosphate (S1P) does not cause a further increase in AP firing after treatment with JTE-013. In a separate series of experiments, 7 sensory neurons were exposed to 100 nM JTE-013 over a 15-min recording period. After the recoding at 15 min, these neurons were exposed to 1 ␮ M S1P and recordings were obtained over the next 10 min. The data represent means Ϯ SE. *Significant difference from the control values [ P Ͻ 0.001, repeated-measures (RM) ANOVA]. 
Internal perfusion with guanosine 5 = - O -(2-thiodiphosphate) (GDP- ␤ -S) blocks the increased excitability produced by JTE-013. A demonstrates that internal perfusion with 3 mM GDP- ␤ -S prevents the increase in excitability produced by 1 ␮ M PGE 2 , which is known to act via the Gs-cAMP-PKA 
Pertussis toxin (PTX) and the S1P receptor 1 (S1PR 1 ) antagonist W146 
Article
Previously we demonstrated that sphingosine 1-phosphate receptor 1 (S1PR(1)) played a prominent, but not exclusive, role in enhancing the excitability of small-diameter sensory neurons, suggesting that other S1PRs can modulate neuronal excitability. To examine the potential role of S1PR(2) in regulating neuronal excitability we used the established selective antagonist of S1PR(2), JTE-013. Here we report that exposure to JTE-013 alone produced a significant increase in excitability in a time- and concentration-dependent manner in 70-80% of recorded neurons. Internal perfusion of sensory neurons with guanosine 5'-O-(2-thiodiphosphate) (GDP-β-S) via the recording pipette inhibited the sensitization produced by JTE-013 as well as prostaglandin E(2). Pretreatment with pertussis toxin or the selective S1PR(1) antagonist W146 blocked the sensitization produced by JTE-013. These results indicate that JTE-013 might act as an agonist at other G protein-coupled receptors. In neurons that were sensitized by JTE-013, single-cell RT-PCR studies demonstrated that these neurons did not express the mRNA for S1PR(2). In behavioral studies, injection of JTE-013 into the rat's hindpaw produced a significant increase in the mechanical sensitivity in the ipsilateral, but not contralateral, paw. Injection of JTE-013 did not affect the withdrawal latency to thermal stimulation. Thus JTE-013 augments neuronal excitability independently of S1PR(2) by unknown mechanisms that may involve activation of other G protein-coupled receptors such as S1PR(1). Clearly, further studies are warranted to establish the causal nature of this increased sensitivity, and future studies of neuronal function using JTE-013 should be interpreted with caution.
 
Glutamate pulses of the duration used in LTD experiments do not evoke Ca transients in acutely dissociated PNs, a preparation that lacks dendritic spines. A: image of a fura-2-filled acutely dissociated Purkinje cell illuminated with 380nm light. Analysis boxes for the soma (S) and dendritic stump (D) are superimposed. Scale bar Å 5 mm. B: acutely dissociated PN was stimulated in the same manner described for Fig. 2 B. These data are from the dendritic stump region of a single PN, representative of 4 tested. C: same measurements as in B, now reported from the somatic analysis box. D: to control for the order of presentation, an acutely dissociated PN received a set of 6 glutamate/depolarization conjunctive stimuli before depolarization alone. These data are from the somatic region of a single PN, representative of 3 tested. As seen in cultured PNs, glutamate pulses alone did not elicit a significant Ca transient, and the peak amplitudes and areas of Ca transients evoked by depolarization pulses and conjunctive glutamate/depolarization pulses were not significantly different and were independent of the order of presentation. 
Glutamate pulses do not contribute to Ca transients in acutely dissociated PNs through a synergistic action with depolarization. The ratio of the depolarization-evoked Ca transient to the glutamate/depolarization conjunction-evoked Ca transients is plotted for peak amplitude and area measures, for the 1st and 6th pulses of a 6 pulse stimulation set. Each data point (indicated by ) represents a single PN. The mean is indicated by /. Although there is a considerable range in these ratios, particularly for the area measures, it should be noted that there is no consistent bias toward ratios õ1 that would indicate that conjunction-evoked Ca transients are larger than those evoked by depolarization. 
Article
Cerebellar long-term depression (LTD) is a cellular model system of information storage in which coincident parallel fiber and climbing fiber activation of a Purkinje neuron (PN) gives rise to a sustained attenuation of parallel fiber-PN synaptic strength. Climbing fiber and parallel fiber inputs may be replaced by direct depolarization of the PN and exogenous glutamate pulses, respectively. The parallel fiber-PN synapse has a high-density of mGluR1 receptors that are coupled to phosphoinositide turnover. Several lines of evidence indicated that activation of mGluR1 by parallel fiber stimulation is necessary for the induction of cerebellar LTD. Because phosphoinositide hydrolysis has two initial products, 1,2-diacylglycerol and inositol-1,4,5- trisphosphate (IP3), we wished to determine whether IP3 signaling via IP3 receptors and consequent Ca mobilization were necessary for the induction of cerebellar LTD. First, ratiometric imaging of free cytosolic Ca was performed on both acutely dissociated and cultured PNs. It was determined that the threshold for glutamate pulses to contribute to LTD induction was below the threshold for producing a Ca transient. Furthermore, the Ca transients produced by depolarization alone and glutamate plus depolarization were not significantly different. Second, the potent and selective IP3 receptor channel blocker xestospongin C was not found to affect the induction of LTD in either acutely dissociated or cultured PNs at a concentration that was sufficient to block mGluR1-evoked Ca mobilization. Third, replacement of mGluR activation by exogenous synthetic diacylglycerol in an LTD induction protocol was successful. Taken together, these results suggest that activation of an IP3 signaling cascade is not required for induction of cerebellar LTD in reduced preparations.
 
Article
1. The effect of intracellular application of inositol 1,4,5-trisphosphate (IP3) from the patch pipette was analyzed in isolated rat olfactory neurons under whole-cell patch clamp. 2. Intracellular dialysis of 10 microM 1,4,5-IP3 in K(+)-internal solution induced a sustained depolarization of 35.8 +/- 10.5 (SD) mV (n = 16). The IP3-induced response was observed in 75% of the cells dialyzed with IP3 but not when 10 microM ruthenium red was also included in the pipette solution (4 cells). Lower concentrations (50-100 nM) of 2,4,5-IP3 induced similar responses to those produced by 1,4,5-IP3 in five of eight olfactory neurons. 3. Steady-state I-V relationships of IP3-gated currents with K(+)-internal solution were classified into two types: outwardly rectifying and N-shaped. In Cs(+)-internal solution outwardly rectifying and linear patterns were observed. 4. The IP3-induced currents were inhibited by external Cd2+ (1 mM). The reversal potentials of the Cd(2+)-inhibitable currents were -16.1 mV (n = 2) and -29.0 +/- 7.1 mV (n = 3) for the outwardly rectifying and N-shaped types, respectively, in K(+)-internal solution. The reversal potential was -5.9 +/- 6.8 mV (n = 5) in the Cs(+)-internal solution. 6. In contrast, the Ca(2+)-ionophore, ionomycin (5 microM) hyperpolarized the olfactory neurons and greatly potentiated the outward currents at positive holding membrane potential. 7. The data suggest that IP3 can depolarize rat olfactory neurons without mediation by intracellular Ca2+.
 
Article
1. The left upper-quadrant bursting neurons (cells L2, L3, L4, and L6) of the abdominal ganglion of Aplysia display a regular burst-firing pattern that is controlled by cyclic changes of intracellular Ca2+ that occur during the bursting rhythm. The characteristic bursting pattern of these neurons occurs within a range of membrane potentials (-35 to -50 mV) called the pacemaker range. 2. Intracellular pressure injection of inositol-1,4,5-trisphosphate (IP3) altered the bursting rhythm of the left upper-quadrant bursting (LUQB) cells for up to 15 min. Injection of IP3 induced a brief depolarization that was followed by a long-lasting (2-15 min) hyperpolarization. The hyperpolarizing phase of the response was accompanied by prolonged interburst intervals. 3. When cells were voltage-clamped at potentials within the pacemaker range, injection of IP3 generally induced a biphasic response that had a total duration of 2-15 min. An initial inward shift in holding current (Iin), which lasted 5-120 s, was followed by a slow outward shift in holding current (Iout). 4. At membrane potentials more negative than -40 mV, Iin was associated with a small and relatively voltage-independent increase in membrane conductance. Iin was not blocked by bath application of tetrodotoxin (TTX) or Co2+. Although Iin was activated by injection of IP3, we were unable to block it by iontophoretic injection of ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetra-acetic acid (EGTA) sufficient to block the Ca2+-activated inward tail current (IB). The ionic mechanism that produces Iin has not been analyzed. 5. In normal bathing solution, Iout was present at membrane potentials more positive than approximately -50 mV. Iout was not blocked by 50 mM tetraethylammonium (TEA), which is known to block Ca2+-activated K+ currents (IK,Ca) in these cells. However, it was blocked by 30 mM Co2+, which blocks ICa. These results indicate that a steady-state ICa is necessary for the generation of Iout following injection of IP3, suggesting that Iout is due to inactivation of ICa and not to activation of a K+ conductance. 6. Intracellular iontophoresis of EGTA abolished Iout indicating that elevation of intracellular Ca2+ is necessary.(ABSTRACT TRUNCATED AT 400 WORDS)
 
Article
The basolateral amygdala (BLA) is the major amygdaloid nucleus distributed with mu opioid receptors. The afferent input from the BLA to the central nucleus of the amygdala (CeA) is considered important for opioid analgesia. However, little is known about the effect of mu opioids on synaptic transmission in the BLA. In this study, we examined the effect of mu opioid receptor stimulation on the inhibitory and excitatory synaptic inputs to CeA-projecting BLA neurons. BLA neurons were retrogradely labeled with a fluorescent tracer injected into the CeA of rats. Whole cell voltage-clamp recordings were performed on labeled BLA neurons in brain slices. The specific mu opioid receptor agonist, (D-Ala2,N-Me-Phe4,Gly5-ol)-enkephalin (DAMGO, 1 microM), significantly reduced the frequency of miniature inhibitory postsynaptic currents (mIPSCs) in 77% of cells tested. DAMGO also significantly decreased the peak amplitude of evoked IPSCs in 75% of cells examined. However, DAMGO did not significantly alter the frequency of mEPSCs or the peak amplitude of evoked EPSCs in 90% and 75% of labeled cells, respectively. Bath application of the Kv channel blockers, 4-AP (Kv1.1, 1.2, 1.3, 1.5, 1.6, 3.1, 3.2), alpha-dendrotoxin (Kv1.1, 1.2, 1.6), dendrotoxin-K (Kv1.1), or tityustoxin-Kalpha (Kv1.2) each blocked the inhibitory effect of DAMGO on mIPSCs. Double immunofluorescence labeling showed that some of the immunoreactivities of Kv1.1 and Kv1.2 were colocalized with synaptophysin in the BLA. This study provides new information that activation of presynaptic mu opioid receptors primarily attenuates GABAergic synaptic inputs to CeA-projecting neurons in the BLA through a signaling mechanism involving Kv1.1 and Kv1.2 channels.
 
Article
Postinhibitory rebound (PIR) can play a significant role for producing stable rhythmic motor patterns, like locomotion, by contributing to burst initiation following the phase of inhibition, and PIR may also be a target for modulatory systems acting on the network. The current aim was to explore the PIR in one type of interneuron in the lamprey locomotor network and its dependence on low voltage-activated (LVA) calcium channels, as well as its modulation by 5-HT and dopamine. PIR responses in commissural interneurons, mediating reciprocal inhibition and left-right alternation in the network, were significantly larger than in motoneurons. The L-type calcium channel antagonist nimodipine reduced PIR amplitude by ∼ 50%, whereas the L-channel agonist BAY K 8644 enhanced PIR amplitude, suggesting that LVA calcium channels of the L-subtype (Ca(V)1.3) participate in the PIR response. The remainder of the response was blocked by nickel, indicating that T-type (Ca(V)3) LVA calcium channels also contribute. No evidence was obtained for the involvement of a hyperpolarization-activated current. Furthermore, 5-HT, acting via 5-HT(1A) receptors, reduced PIR, as did dopamine, acting via D(2) receptors. Coapplication of nimodipine caused no further PIR reduction, indicating that these modulators target Ca(V)1.3 channels specifically. These results suggest that PIR may play a prominent role in the generation of alternating network activity and that the Ca(V)1.3 and Ca(V)3 subtypes of LVA calcium channels together underlie the PIR response. 5-HT and dopamine both target PIR via Ca(V)1.3 channels, which may contribute significantly to their modulatory influence on locomotor network activity.
 
Article
We recently showed that spinal cord contusion injury (SCI) at the thoracic level induces pain-related behaviors and increased spontaneous discharges, hyperresponsiveness to innocuous and noxious peripheral stimuli, and enlarged receptive fields in neurons in the ventral posterolateral (VPL) nucleus of the thalamus. These changes are linked to the abnormal expression of Na(v)1.3, a rapidly repriming voltage-gated sodium channel. In this study, we examined the burst firing properties of VPL neurons after SCI. Adult male Sprague-Dawley rats underwent contusion SCI at the T9 level. Four weeks later, when Na(v)1.3 protein was upregulated within VPL neurons, extracellular unit recordings were made from VPL neurons in intact animals, those with SCI, and in SCI animals after receiving lumbar intrathecal injections of Na(v)1.3 antisense or mismatch oligodeoxynucleotides for 4 days. After SCI, VPL neurons with identifiable peripheral receptive fields showed rhythmic oscillatory burst firing with changes in discrete burst properties, and alternated among single-spike, burst, silent, and spindle wave firing modes. Na(v)1.3 antisense, but not mismatch, partially reversed alterations in burst firing after SCI. These results demonstrate several newly characterized changes in spontaneous burst firing properties of VPL neurons after SCI and suggest that abnormal expression of Na(v)1.3 contributes to these phenomena.
 
LER model fit comparison Fit LER Prediction LER 
WT and F1449V kinetics comparison WT F1449V 
WT and F1449V parameters comparison WT F1449V 
Action potentials generated by NaG.3e in WT and F1449V configuration in a single-compartment neuron. The passive conductance of the single compartment was set to 5 pS/m 2 and a reversal potential of 70 mV. A voltage-dependent potassium channel model (Mainen et al. 1995) with maximal conductance of 2,000 pS/m 2 and a reversal potential of 90 mV was incorporated into the membrane. The voltage-dependent sodium channel model was then incorporated with a reversal potential of 72 mV, and the maximal sodium conductance of the membrane was set at 561 pS/m 2. A: subthreshold responses and action potentials generated in response to 80-ms square current pulses varying in amplitude from 50 to 155 pA using the WT parameters for NaG.3e. B: subthreshold responses and action potentials generated in response to 80-ms square current pulses varying in amplitude from 50 to 65 pA using the F1449V parameters for NaG.3e. C: an action potential generated in response to a 500-ms square current pulse of 150 pA using the WT channel model of NaG.3e. D: a train of action potentials generated in response to a 500-ms square current pulse of 150 pA using the F1449V channel model of NaG.3e. 
Probabilities of state occupancy of the NaG.3e model. State occupancies of the NaG.3e model are coded by color: C 1 (black), C 2 (yellow), C 3 (blue), O (green), I 1 (red), and I 2 (purple). The inset in A shows the Markov model formalism with each state labeled in the appropriate color. A and B: results gained with the activation protocol at 10 mV for NaG.3e in WT (A) and F1449V configurations (B). For clarity, only the first 4 ms of the stimulus are shown. C and D: results for the inactivation protocol for NaG.3e with WT (C) and F1449V parameters (D) after a voltage prepulse to 75 mV, followed by a pulse to 10 mV. For clarity, only the last 3 ms of the prepulse and the first 5 ms of the following stimulus are shown. 
Article
Gain-of-function mutations of the voltage-gated sodium channel (VGSC) Na(v)1.7 have been linked to human pain disorders. The mutation F1449V, located at the intracellular end of transmembrane helix S6 of domain III, induces the inherited pain syndrome erythromelalgia. A kinetic model of wild-type (WT) and F1449V Na(v)1.7 may provide a basis for predicting putative intraprotein interactions. We semiautomatically constrained a Markov model using stochastic search algorithms and whole cell patch-clamp recordings from human embryonic kidney cells transfected with Na(v)1.7 and its F1449V mutation. The best models obtained simulated known differences in action potential thresholds and firing patterns in spinal sensory neurons expressing WT and F1449V. The most suitable Markov model consisted of three closed, one open, and two inactivated states. The model predicted that the F1449V mutation shifts occupancy of the closed states closer to the open state, making it easier for the channel pore to open. It also predicted that F1449V's second inactivated state is more than four times more likely to be occupied than the equivalent state in WT at hyperpolarized potentials, although the mutation still lowered the firing threshold of action potentials. The differences between WT and F1449V were not limited to a single transition. Thus a point mutation in position F1449, while phenotypically most probably affecting the activation gate, may also modify channel functions mediated by structures in more distant areas of the channel protein.
 
Article
Ethanol (EtOH) has powerful effects on GABA(A) receptor-mediated neurotransmission, and we have previously shown that EtOH-induced enhancement of GABA(A) receptor-mediated synaptic transmission in the hippocampus is developmentally regulated. Because synaptic inhibition is determined in part by the firing properties of interneurons, we have investigated the mechanisms whereby EtOH influences the spontaneous firing characteristics and hyperpolarization-activated cation current (Ih) of hippocampal interneurons located in the near to the border of stratum lacunosum moleculare and s. radiatum of adolescent and adult rats. EtOH did not affect current injection-induced action potentials of interneurons that do not exhibit spontaneous firing. However, in neurons that fire spontaneously, EtOH enhanced the frequency of spontaneous action potentials (sAPs) in a concentration-dependent manner, an effect that was more pronounced in interneurons from adolescent rats, compared with adult rats. EtOH also modulated the afterhyperpolarization (AHP) that follows sAPs by shortening the tau(slow) decay time constant, and this effect was more pronounced in slices from adolescent rats. EtOH increased Ih amplitudes, accelerated Ih activation kinetics, and increased the maximal Ih conductance in interneurons from animals in both age groups. These effects were also more pronounced in interneurons from adolescents and persisted in the presence of glutamatergic and GABAergic blockers. However, EtOH failed to affect sAP firing in the presence of ZD7288 or cesium chloride. These results suggest that Ih may be of mechanistic significance in the effect of EtOH on interneuron spontaneous firing.
 
Anticorrelated brain networks are replicable across datasets and statistical technique. A: anticorrelated brain networks reproduced from the dataset of Fox et al. (2005) using fixed effects analysis showed correlations within a system and negative correlations between systems. B: Z-score map from the current independent dataset shows voxels significantly correlated with a seed in the task-positive network (area MT) using random effects analysis. C: Z-score map from the current dataset shows voxels significantly correlated with a seed in the task negative network (posterior cingulate/precuneus) using random effects analysis.  
The impact of preprocessing and global regression on seed-based correlation maps. Z-score maps show voxels significantly correlated with various seed regions at 3 processing stages: no regression (left), movement, ventricle, and white matter regression (middle), and global regression (right). Histograms of voxel intensities for the 3 processing stages are shown to the right using blue (no regression), green (movement, vent and white matter), and red (global regression) lines. The location of each seed region is shown on the far left and include the posterior cingulate cortex/precuneus (Pcc), area MT (MT), the somatomotor cortex (MC), and primary visual cortex (V1). Talairach slice coordinates for Z-score maps: z 45 (Pcc); z 36 (MT); z 54 (MC); z 6 (V1).  
Global signal regression shows a unique distribution of negative correlations compared with post hoc distribution centering. Z-score maps showing voxels significantly correlated with seeds in the posterior cingulate (top) and area MT (bottom) after global signal regression (left) and post hoc distribution centering (right). Histograms show the distribution of voxel values across the entire brain (blue whole brain regression; green post hoc distribution centering images). Although both techniques center the distribution of correlations around 0, only global regression shows neuroanatomically specific negative correlations. Seed region locations are as shown in Fig. 1.  
Global signal regression mandates negative correlations at the single subject level but not at the population level. A: single-subject regression coefficients (beta maps) for seeds in the posterior cingulate (left, blue line) and in the white matter (right, green line) for a representative subject. B: random effects Z-score maps show voxels significantly correlated with seeds in the posterior cingulate (left) and white matter (right) across the population of 17 subjects. The sum of voxel values across the entire brain is shown below each image and voxel histograms are shown to the right. Although the voxelwise sum of beta maps must be 0 for each subject and histograms similar, these measures can vary greatly in the population level Z-score maps depending on the consistency across subjects.  
Article
Resting state studies of spontaneous fluctuations in the functional MRI (fMRI) blood oxygen level dependent (BOLD) signal have shown great promise in mapping the brain's intrinsic, large-scale functional architecture. An important data preprocessing step used to enhance the quality of these observations has been removal of spontaneous BOLD fluctuations common to the whole brain (the so-called global signal). One reproducible consequence of global signal removal has been the finding that spontaneous BOLD fluctuations in the default mode network and an extended dorsal attention system are consistently anticorrelated, a relationship that these two systems exhibit during task performance. The dependence of these resting-state anticorrelations on global signal removal has raised important questions regarding the nature of the global signal, the validity of global signal removal, and the appropriate interpretation of observed anticorrelated brain networks. In this study, we investigate several properties of the global signal and find that it is, indeed, global, not residing preferentially in systems exhibiting anticorrelations. We detail the influence of global signal removal on resting state correlation maps both mathematically and empirically, showing an enhancement in detection of system-specific correlations and improvement in the correspondence between resting-state correlations and anatomy. Finally, we show that several characteristics of anticorrelated networks including their spatial distribution, cross-subject consistency, presence with modified whole brain masks, and existence before global regression are not attributable to global signal removal and therefore suggest a biological basis.
 
Article
Taking advantage of transgenic mice with genetically labeled GABA-releasing interneurons, we examined the cell-specific patterns of mGluR expression in two broadly defined subtypes of inhibitory interneurons in layer IV of somatosensory cortex. Electrophysiological recording combined with application of specific agonists for specific mGluRs demonstrated different effects of mGluR activation in fast-spiking (FS) versus regular spiking nonpyramidal (RSNP) interneurons. Whereas activation of group I, II, and III mGluRs inhibited excitatory synaptic transmission in RSNP neurons predominantly via postsynaptic mechanisms, group I mGluR activation depolarized FS but not RSNP interneurons. Immunoreactivities of mGluR1, mGluR5, mGluR2/3, and mGluR8 exhibited different cellular expression patterns in the two groups of neurons that were not entirely consistent with physiological and pharmacological experiments. Taken together, our data indicate cell and circuit-specific roles for mGluRs in modulating inhibitory circuits in the somatosensory cortex. These results help to reinforce the concept that RSNP and FS cells represent morphologically, physiologically, and functionally distinct groups of interneurons. The results reported here help to increase our understanding of the roles of mGluRs in endogenous glutamatergic-induced plasticity of interneuronal networks.
 
A: photomicrograph of a gastric medial nucleus of the tractus solitarius (mNTS) neuron (*) visualized using infrared differential interference contrast optics. Scale bar equals 10 m. B: photomicrograph of the same gastric mNTS neuron visualized using fluorescence optics to demonstrate pseudorabies virus152 green fluorescent protein label. Scale bar equals 10 m. C: photomicrograph of a transverse section through the medulla at the level of the mNTS showing the position of both the recording electrode (left) and the Y-tubing (right). Scale bar equals 200 m. 
A: representative whole cell voltage clamp recording from a mNTS neuron. Focal application of [d-Ala(2),MePhe(4),Gly(ol)(5)]enkephalin (DAMGO; 100 nM) suppressed the I tonic and spontaneous IPSC (sIPSC) frequency, but produced no change in sIPSC amplitude or decay (upper panel). Graphical representation of the I tonic and root mean square (RMS) produced by DAMGO and changes in frequency, amplitude, and decay following DAMGO administration (lower panel). *P 0.05; n 8. B: representative whole cell voltage clamp recording from a mNTS neuron. Focal application of GBZ (100 M) significantly reduced the I tonic , and subsequent perfusion of DAMGO (100 nM) produced only a small further suppression of I tonic (upper panel). Graphical representation is shown of the I tonic produced by GBZ alone compared with GBZ following DAMGO pretreatment (lower left panel; *P 0.05; n 10 and 8, respectively) and of the I tonic produced by DAMGO alone compared with DAMGO following GBZ pretreatment (lower right panel; *P 0.05; n 8 and 11, respectively).
Effects of GABA A antagonists and THIP on I hold and RMS noise
Effects of TTX on GABAzine and THIP-induced changes in I hold and RMS Changes in I hold Change in RMS Noise
Article
Our laboratory previously reported that gastric activity is controlled by a robust GABA(A) receptor-mediated inhibition in the medial nucleus of the tractus solitarius (mNTS) (Herman et al. 2009), and that μ-opioid receptor activation inhibits gastric tone by suppression of this GABA signaling (Herman et al. 2010). These data raised two questions: 1) whether any of this inhibition was due to tonic GABA(A) receptor-mediated conductance in the mNTS; and 2) whether μ-opioid receptor activation suppressed both tonic and phasic GABA signaling. In whole cell recordings from rat mNTS neurons, application of three GABA(A) receptor antagonists (gabazine, bicuculline, and picrotoxin) produced a persistent reduction in holding current and decrease in population variance or root mean square (RMS) noise, suggesting a blockade of tonic GABA signaling. Application of gabazine at a lower concentration abolished phasic currents, but had no effect on tonic currents or RMS noise. Application of the δ-subunit preferring agonist gaboxadol (THIP) produced a dose-dependent persistent increase in holding current and RMS noise. Pretreatment with tetrodotoxin prevented the action of gabazine, but had no effect on the THIP-induced current. Membrane excitability was unaffected by the selective blockade of phasic inhibition, but was increased by blockade of both phasic and tonic currents. In contrast, activation of tonic currents decreased membrane excitability. Application of the μ-opioid receptor agonist DAMGO produced a persistent reduction in holding current that was not observed following pretreatment with a GABA(A) receptor antagonist and was not evident in mice lacking the δ-subunit. These data suggest that mNTS neurons possess a robust tonic inhibition that is mediated by GABA(A) receptors containing the δ-subunit, that determines membrane excitability, and that is partially regulated by μ-opioid receptors.
 
Article
Although evidence indicates that activation of presympathetic paraventricular nucleus (PVN) neurons contributes to the pathogenesis of salt-sensitive hypertension, the underlying cellular mechanisms are not fully understood. Recent evidence indicates that small conductance Ca(2+)-activated K(+) (SK) channels play a significant role in regulating the excitability of a key group of sympathetic regulatory PVN neurons, those with axonal projections to the rostral ventrolateral medulla (RVLM; i.e., PVN-RVLM neurons). In the present study, rats consuming a high salt (2% NaCl) diet were made hypertensive by systemic infusion of angiotensin II (AngII), and whole cell patch-clamp recordings were made in brain slice from retrogradely labeled PVN-RVLM neurons. To determine if the amplitude of SK current was altered in neurons from hypertensive rats, voltage-clamp recordings were performed to isolate SK current. Results indicate that SK current amplitude (P < 0.05) and density (P < 0.01) were significantly smaller in the hypertensive group. To investigate the impact of this on intrinsic excitability, current-clamp recordings were performed in separate groups of PVN-RVLM neurons. Results indicate that the frequency of spikes evoked by current injection was significantly higher in the hypertensive group (P < 0.05-0.01). Whereas bath application of the SK channel blocker apamin significantly increased discharge of neurons from normotensive rats (P < 0.05-0.01), no effect was observed in the hypertensive group. In response to ramp current injections, subthreshold depolarizing input resistance was greater in the hypertensive group compared with the normotensive group (P < 0.05). Blockade of SK channels increased depolarizing input resistance in normotensive controls (P < 0.05) but had no effect in the hypertensive group. On termination of current pulses, a medium afterhyperpolarization potential (mAHP) was observed in most neurons of the normotensive group. In the hypertensive group, the mAHP was either small or absent. In the latter case, an afterdepolarization potential (ADP) was observed that was unaffected by apamin. Apamin treatment in the normotensive group blocked the mAHP and revealed an ADP resembling that seen in the hypertensive group. We conclude that diminished SK current likely underlies the absence of mAHPs in PVN-RVLM neurons from hypertensive rats. Both the ADP and greater depolarizing input resistance likely contribute to increased excitability of PVN-RVLM neurons from rats with AngII-Salt hypertension.
 
Implication of K channels in D2 receptor-mediated presynaptic inhibition. A: whole-cell recordings from isolated DAergic neurons (V H 50 mV). A first application of quinpirole (5 M) inhibited EPSC amplitude. In the presence of barium (1 mM) the effect of quinpirole was slightly reduced. B: whole-cell recordings from a different DAergic neuron. A first application of quinpirole inhibited EPSC amplitude. In the presence of 4-aminopyridine (4-AP; 100 M) the effect of quinpirole was considerably reduced. C: whole-cell recordings from a different DAergic neuron. A first application of quinpirole inhibited EPSC amplitude. In the presence of 4-AP (1 mM) and Ba 2 (1 mM) the effect of quinpirole was almost completely blocked. D: lack of correlation between the effect of 4-AP or Ba 2 on EPSC amplitude and the ability of these blockers to reduce quinpirole-mediated inhibition of EPSC amplitude.  
Effect of K channels blockers on quinpirole-mediated inhibition. Summary diagram illustrating the average inhibition of autaptic EPSC amplitude by quinpirole in experiments performed with K channel blockers. The left column in each pair illustrates the effect of quinpirole under control conditions (). The right column in each pair illustrates the effect of quinpirole in the presence of the K channel blocker (). A combination of barium and 4-AP completely blocked the presynaptic effect of quinpirole (black columns) (**P 0.01).
Lack of effect of quinpirole on Ca 2 influx in DAergic neurons. A: phase contrast image of an isolated neuron. Note the presence of the extracellular stimulating pipette to the right of the image. B: TH immunofluorescent labeling confirming the DAergic phenotype of the neuron used for Fura-2 imaging. C: time course of Fura-2 ratio intensity measurements from three areas on the neuron shown in A and B. Extracellular stimulation trains (arrows) induced reproducible rises in intracellular Ca 2 as reflected by an increase in the 380/340 nm Fura-2 ratio. Quinpirole (5 M) failed to cause any detectable change in Ca 2 influx. D: summary diagram illustrating the normalized average amplitude of electrically evoked rises in Fura-2 ratios during the control period, in the presence of quinpirole and during washout of quinpirole.  
Article
Dopaminergic (DAergic) neurons possess D2-like somatodendritic and terminal autoreceptors that modulate cellular excitability and dopamine (DA) release. The cellular and molecular processes underlying the rapid presynaptic inhibition of DA release by D2 receptors remain unclear. Using a culture system in which isolated DAergic neurons establish self-innervating synapses ("autapses") that release both DA and glutamate, we studied the mechanism by which presynaptic D2 receptors inhibit glutamate-mediated excitatory postsynaptic currents (EPSCs). Action-potential evoked EPSCs were reversibly inhibited by quinpirole, a selective D2 receptor agonist. This inhibition was slightly reduced by the inward rectifier K(+) channel blocker barium, largely prevented by the voltage-dependent K(+) channel blocker 4-aminopyridine, and completely blocked by their combined application. The lack of a residual inhibition of EPSCs under these conditions argues against the implication of a direct inhibition of presynaptic Ca(2+) channels. To evaluate the possibility of a direct inhibition of the secretory process, spontaneous miniature EPSCs were evoked by the Ca(2+) ionophore ionomycin. Ionomycin-evoked release was insensitive to cadmium and dramatically reduced by quinpirole, providing evidence for a direct inhibition of quantal release at a step downstream to Ca(2+) influx through voltage-dependent Ca(2+) channels. Surprisingly, this effect of quinpirole on ionomycin-evoked release was blocked by 4-aminopyridine. These results suggest that D2 receptor activation decreases neurotransmitter release from DAergic neurons through a presynaptic mechanism in which K(+) channels directly inhibit the secretory process.
 
Article
Umami is considered to be the fifth basic taste quality and is elicited by glutamate. The mouse is an ideal rodent model for the study of this taste quality because of evidence that suggests that this species, like humans, may sense umami-tasting compounds as unique from other basic taste qualities. We performed single-unit recording of taste responses in the parabrachial nucleus (PbN) of anesthetized C57BL/6J mice to investigate the central representation of umami taste. A total of 52 taste-responsive neurons (22 sucrose-best, 19 NaCl-best, 5 citric acid-best, and 6 quinine-best) were recorded from stimulation period with a large panel of basic and umami-tasting stimuli. No neuron responded best to monopotassium glutamate (MPG) or inosine 5'-monophosphate (IMP), suggesting convergence of input in the central nervous system. Synergism induced by an MPG-IMP mixture was observed in all sucrose-best and some NaCl-best neurons that possessed strong sensitivity to sucrose. In more than half of sucrose-best neurons, the MPG-IMP mixture evoked stronger responses than those elicited by their best stimulus. Furthermore, hierarchical cluster analysis and multidimensional analysis indicated close similarity between sucrose and the MPG-IMP mixture. These results strongly suggest the mixture tastes sweet to mice, a conclusion consistent with previous findings that show bidirectional generalization of conditioned taste aversion between sucrose and umami mixtures, and suppression of taste responses to both sucrose and mixtures by the antisweet polypeptide gurmarin in the chorda tympani nerve. The distribution pattern of reconstructed recording sites of specific neuron types suggested chemotopic organization in the PbN.
 
Schematic of mechanically sensitive cutaneous sensory neurons and the specialized tactile cells they innervate in both hairy and glabrous skin. In hairy skin, guard hairs are innervated by light-touch rapidly adapting A ␤ -fibers (RA-A ␤ ), whereas down hairs are innervated by the very light-touch rapidly adapting Down-hair A ␦ -fibers (D-hair or DH). In glabrous skin only, Meissner’s corpuscles mediate the RA-A ␤ fiber response, positioned at the epidermal-dermal border and transduce rapidly adapting stimuli. Another light-touch organ found in both hairy and glabrous skin is the Merkel cell-neurite complex and is innervated by light-touch slowly adapting A ␤ -fibers (SA-A ␤ ) in the stratum basale layer of the epidermis. Slowly adapting A-mechanoreceptor (AM) A ␦ -fibers have lightly myelinated axons until the end termini in the dermis and epidermis where they lose their myelination. Many AM A ␦ -fibers and unmyelinated C-fibers, which terminate in the epidermis or near the epidermal-dermal border, are activated at higher mechanical forces and are predominately nociceptors. However, some C-fibers mediate gentle touch and others mediate warming sensations (Nordin 1990; Shea and Perl 1985). C-fibers can be further classified into two general populations, the non-peptidergic isolectin B4 positive (IB4 ϩ ) and the peptide-containing IB4 negative (IB4 Ϫ ) subtypes; these two C-fiber populations are associated with differential growth factor dependence, project to different regions of the spinal dorsal horn and may contribute to different nociceptive pathways 
Action potential firing is reduced in TRPC1-deficient mice in response to sustained mechanical force (10 s) in both A ␤ - and D-hair sensory neurons. Using the skin-nerve preparation, all recordings were performed in the saphenous nerve and hairy skin of the dorsal hindpaw. A : examples of responses of SA-A ␤ fibers from a wild-type and TRPC1 Ϫ / Ϫ mouse to sustained mechanical force at 20, 150, and 200 mN sustained for 10 s. Note that the TRPC1 Ϫ / Ϫ SA-A ␤ fibers fire fewer action potentials throughout the duration of the force. B : examples of responses of D-hair afferents from a wild-type and TRPC1 Ϫ / Ϫ mouse to sustained mechanical force at 40, 100, and 150 mN. Note that the TRPC1 Ϫ / Ϫ D-hair afferent fires fewer action potentials at the onset of force. C : overall, all SA-A ␤ fibers in TRPC1-deficient mice fired on average 40% fewer action potentials to mechanical forces (*** P Ͻ 0.001). Both high-threshold ( Ն 4 mN; D ) and low-threshold ( Ͻ 4 mN; E ) SA-A ␤ subtypes respond with fewer action potentials fired overall in TRPC1 Ϫ / Ϫ (* P Ͻ 0.05 and *** P Ͻ 0.001, respectively). TRPC1 Ϫ / Ϫ mice specifically had reduced action potential firing at 200 mN force in high-threshold SA-A ␤ (# P Ͻ 0.05). F : rapidly adapting A ␤ (RA-A ␤ ) fibers responded similarly at all mechanical forces between the two genotypes ( P Ͼ 0.05). G : in contrast, rapidly adapting D-hair fibers from TRPC1-deficient mice responded with markedly fewer action potentials (50%) at all force intensities (*** P Ͻ 0.001). Genotypes were compared across forces using a two-way ANOVA with a Bonferroni post hoc test. Error bars indicate SE. 
TRPC1-deficient mice exhibit decreased sensitivity to light-touch mechanical stimuli. All mechanical stimuli tests were administered by placing enclosed mice on an elevated mesh screen and applying mechanical force to the glabrous skin of the hindpaw. Left and right hindpaw responses were counted and averaged to calculate the percent response or paw withdrawal threshold. The experimenter was blinded to genotype. A and B : wild-type mice responded an average of 13.6 Ϯ 1.7% compared with 6.2 Ϯ 1.4% in TRPC1-deficient mice, resulting in a 55% decrease in mechanical sensitivity. TRPC1-deficient mice exhibited a 55% decreased response to a light 0.68 mN von Frey filament, responding an average of 6.2 Ϯ 1.4% compared with wild-type mice, which responded 13.6 Ϯ 1.7% of the time. TRPC1-deficient mice also exhibited a 45% decrease in paw withdrawal frequency in response to a Ͻ 1-s cotton swab stroke, responding an average of 19.6 Ϯ 2.5% compared with wild-type mice that responded an average of 35.9 Ϯ 4.6%. C : TRPC1-deficient mice had a similar mechanical threshold response to wild-type littermates using the 50% mechanical paw withdrawal threshold Up and Down method. D : TRPC1-deficient mice responded similarly to wild- type littermates, when stimulated with repeated application of a suprathreshold, 3.31 g von Frey filament. E : paw withdrawal latency to radiant heat applied to the glabrous hindpaw did not differ between genotypes. 
Article
The cellular proteins that underlie mechanosensation remain largely enigmatic in mammalian systems. Mechanically sensitive ion channels are thought to distinguish pressure, stretch, and other types of tactile signals in skin. Transient receptor potential canonical 1 (TRPC1) is a candidate mechanically sensitive channel that is expressed in primary afferent sensory neurons. However, its role in the mechanical sensitivity of these neurons is unclear. Here, we investigated TRPC1-dependent responses to both innocuous and noxious mechanical force. Mechanically evoked action potentials in cutaneous myelinated A-fiber and unmyelinated C-fiber neurons were quantified using the ex vivo skin-nerve preparation to record from the saphenous nerve, which terminates in the dorsal hairy skin of the hindpaw. Our data reveal that in TRPC1-deficient mice, mechanically evoked action potentials were decreased by nearly 50% in slowly adapting Aβ-fibers, which largely innervate Merkel cells, and in rapidly adapting Aδ-Down-hair afferent fibers compared with wild-type controls. In contrast, differences were not found in slowly adapting Aδ-mechanoreceptors or unmyelinated C-fibers, which primarily respond to nociceptive stimuli. These results suggest that TRPC1 may be important in the detection of innocuous mechanical force. We concurrently investigated the role of TRPC1 in behavioral responses to mechanical force to the plantar hindpaw skin. For innocuous stimuli, we developed a novel light stroke assay using a "puffed out" cotton swab. Additionally, we used repeated light, presumably innocuous punctate stimuli with a low threshold von Frey filament (0.68 mN). In agreement with our electrophysiological data in light-touch afferents, TRPC1-deficient mice exhibited nearly a 50% decrease in behavioral responses to both the light-stroke and light punctate mechanical assays when compared with wild-type controls. In contrast, TRPC1-deficient mice exhibited normal paw withdrawal response to more intense mechanical stimuli that are typically considered measures of nociceptive behavior.
 
Stimulated NE release before and after a localized ejection of AP and IDA. Shown is the current as a function of time at the oxidation potential for NE. A: representative baseline current trace for the stimulated release of NE. Boxes indicate the beginning and end of stimulation. B: representation of iontophoretic ejection of AP and IDA. The measured signal is due solely to AP and is used to estimate the concentration of IDA. Here, 5 M AP is the average concentration across the electrode and is equivalent to 12 M IDA. C: current trace for stimulated release 120 s after ejection seen in B. At the time of stimulation (open box), the concentration of AP has decreased to 2% of its original value, corresponding to a decrease in IDA concentration to 240 nM. The extracellular concentration of NE seen in C is significantly increased from that observed predrug. 
Effects on electrically evoked NE in the dmBNST and vBNST after iontophoretic delivery of RA, IDA, and DMI. A: effect on [NE] max. B: effect on t 1/2. *Significantly different from predrug (P 0.05); $significantly different from vBNST (P 0.05). 
Time course of drug effect onset due to systemic (ip, A) and iontophoretic (B) delivery of NE drugs DMI and IDA. Drugs were delivered either by ip injection or iontophoretically at t 0. Since washout of drugs is not possible for systemic delivery, IDA and DMI were evaluated in separate animals. In contrast, iontophoretic drug effects are short-lived; thus administration of DMI followed administration of IDA after evoked NE release returned to its predrug value. 
Article
Norepinephrine (NE) is an easily oxidized neurotransmitter that is found throughout the brain. Considerable evidence suggests that it plays an important role in neurocircuitry related to fear and anxiety responses. In certain subregions of the bed nucleus of the stria terminalis (BNST), NE is found in large amounts. In this work we probed differences in electrically evoked release of NE and its regulation by the norepinephrine transporter (NET) and the α(2)-adrenergic autoreceptor (α(2)-AR) in two regions of the BNST of anesthetized rats. NE was monitored in the dorsomedial BNST (dmBNST) and ventral BNST (vBNST) by fast-scan cyclic voltammetry at carbon fiber microelectrodes. Pharmacological agents were introduced either by systemic application (intraperitoneal injection) or by local application (iontophoresis). The iontophoresis barrels were attached to a carbon fiber microelectrode to allow simultaneous detection of evoked NE release and quantitation of iontophoretic delivery. Desipramine (DMI), an inhibitor of NET, increased evoked release and slowed clearance of released NE in both regions independent of the mode of delivery. However, the effects of DMI were more robust in the vBNST than in the dmBNST. Similarly, the α(2)-AR autoreceptor inhibitor idazoxan (IDA) enhanced NE release in both regions but to a greater extent in the vBNST by both modes of delivery. Since both local application by iontophoresis and systemic application of IDA had similar effects on NE release, our results indicate that terminal autoreceptors play a predominant role in the inhibition of subsequent release.
 
Article
The existence and role of fine-temporal structure in the spiking activity of central neurons is the subject of an enduring debate among physiologists. To a large extent, the problem is a statistical one: what inferences can be drawn from neurons monitored in the absence of full control over their presynaptic environments? In principle, properly crafted resampling methods can still produce statistically correct hypothesis tests. We focus on the approach to resampling known as jitter. We review a wide range of jitter techniques, illustrated by both simulation experiments and selected analyses of spike data from motor cortical neurons. We rely on an intuitive and rigorous statistical framework known as conditional modeling to reveal otherwise hidden assumptions and to support precise conclusions. Among other applications, we review statistical tests for exploring any proposed limit on the rate of change of spiking probabilities, exact tests for the significance of repeated fine-temporal patterns of spikes, and the construction of acceptance bands for testing any purported relationship between sensory or motor variables and synchrony or other fine-temporal events.
 
Article
1. Experimental studies have shown that a central pattern generator in the spinal cord of the lamprey can produce the basic rhythm for locomotion. This pattern generator interacts with the reticular neurons forming a spinoreticulospinal loop. To better understand and investigate the mechanisms for locomotor pattern generation in the lamprey, we examine the dynamic behavior of a simplified neural network model representing a unit spinal pattern generator (uPG) and its interaction with the reticular system. We use the techniques of bifurcation analysis and specifically examine the effects on the dynamic behavior of the system of 1) changing tonic drives to the different neurons of the uPG; 2) altering inhibitory and excitatory interconnection strengths among the uPG neurons; and 3) feedforward-feedback interactions between the uPG and the reticular neurons. 2. The model analyzed is a qualitative left-right symmetric network based on proposed functional architecture with one class of phasic reticular neurons and three classes of uPG neurons: excitatory (E), lateral (L), and crossed (C) interneurons. In the model each class is represented by one left and one right neuron. Each neuron has basic passive properties akin to biophysical neurons and receives tonic synaptic drive and weighted synaptic input from other connecting neurons. The neuron's output as a function of voltage is given by a nonlinear function with a strict threshold and saturation. 3. With an appropriate set of parameter values, the voltage of each neuron can oscillate periodically with phase relationships among the different neurons that are qualitatively similar to those observed experimentally. The uPG alone can also oscillate, as observed experimentally in isolated lamprey spinal cords. Varying the parameters can, however, profoundly change the state of the system via different kinds of bifurcations. Change in a single parameter can move the system from nonoscillatory to oscillatory states via different kinds of bifurcations. For some parameter values the system can also exhibit multistable behavior (e.g., an oscillatory state and a nonoscillatory state). The analysis also shows us how the amplitudes of the oscillations vary and the periods of limit cycles change as different bifurcation points are approached. 4. Altering tonic drive to just one class of uPG neurons (without altering the interconnections) can change the state of the system by altering the stability of fixed points, converting fixed points to oscillations, single oscillations to two stable oscillations, etc. Two-parameter bifurcation diagrams show the critical regions in which a balance between the tonic drives is necessary to maintain stable oscillations. A minimum tonic drive is necessary to obtain stable oscillatory output. With appropriate changes in the tonic drives to the L and C neurons, stable oscillatory output can be obtained even after eliminating the E neurons. Indeed, the presence of active E neurons in the biological system does not prove they play a functional role in the system, because tonic drive from other sources can substitute for them. On the other hand, very high excitation of any one class of neurons can terminate oscillations. Appropriate balance of tonic drives to different neuron classes can help sustain stable oscillations for larger tonic drives. Published experimental results concerning changes in amplitude and swimming frequency with increased tonic drives are mimicked by the model's responses to increased tonic drive. 5. Interconnectivity among the neurons plays a crucial role. The analysis indicates that the C and L classes of neurons are essential components of the model network. Sufficient inhibition from the L to C neurons as well as mutual inhibition between the left and right halves is necessary to obtain stable oscillatory output. When the E neurons are present in the model network, they must receive appropriate tonic drive and provide appropriate excitation
 
Article
Neuronal control with high temporal precision is possible with optogenetics, yet currently available methods do not enable to control independently multiple locations in the brains of freely moving animals. Here, we describe a diode-probe system that allows real-time and location-specific control of neuronal activity at multiple sites. Manipulation of neuronal activity in arbitrary spatiotemporal patterns is achieved by means of an optoelectronic array, manufactured by attaching multiple diode-fiber assemblies to high-density silicon probes or wire tetrodes and implanted into the brains of animals that are expressing light-responsive opsins. Each diode can be controlled separately, allowing localized light stimulation of neuronal activators and silencers in any temporal configuration and concurrent recording of the stimulated neurons. Because the only connections to the animals are via a highly flexible wire cable, unimpeded behavior is allowed for circuit monitoring and multisite perturbations in the intact brain. The capacity of the system to generate unique neural activity patterns facilitates multisite manipulation of neural circuits in a closed-loop manner and opens the door to addressing novel questions.
 
Article
1. Compartmental modeling experiments were carried out in an anatomically characterized neocortical pyramidal cell to study the integrative behavior of a complex dendritic tree containing active membrane mechanisms. Building on a previously presented hypothesis, this work provides further support for a novel principle of dendritic information processing that could underlie a capacity for nonlinear pattern discrimination and/or sensory processing within the dendritic trees of individual nerve cells. 2. It was previously demonstrated that when excitatory synaptic input to a pyramidal cell is dominated by voltage-dependent N-methyl-D-aspartate (NMDA)-type channels, the cell responds more strongly when synaptic drive is concentrated within several dendritic regions than when it is delivered diffusely across the dendritic arbor. This effect, called dendritic "cluster sensitivity," persisted under wide-ranging parameter variations and directly implicated the spatial ordering of afferent synaptic connections onto the dendritic tree as an important determinant of neuronal response selectivity. 3. In this work, the sensitivity of neocortical dendrites to spatially clustered synaptic drive has been further studied with fast sodium and slow calcium spiking mechanisms present in the dendritic membrane. Several spatial distributions of the dendritic spiking mechanisms were tested with and without NMDA synapses. Results of numerous simulations reveal that dendritic cluster sensitivity is a highly robust phenomenon in dendrites containing a sufficiency of excitatory membrane mechanisms and is only weakly dependent on their detailed spatial distribution, peak conductances, or kinetics. Factors that either work against or make irrelevant the dendritic cluster sensitivity effect include 1) very high-resistance spine necks, 2) very large synaptic conductances, 3) very high baseline levels of synaptic activity, and 4) large fluctuations in level of synaptic activity on short time scales. 4. The functional significance of dendritic cluster sensitivity has been previously discussed in the context of associative learning and memory. Here it is demonstrated that the dendritic tree of a cluster-sensitive neuron implements an approximative spatial correlation, or sum of products operation, such as that which could underlie nonlinear disparity tuning in binocular visual neurons.
 
Localization of conditional selection of grasp
Localization of movement related brain areas
Superior oblique view of left hemisphere demonstrating signifivation of dorsal premotor cortex and superior parietal cortex cant differences between execution (blue) and selection (yellow) tasks.
Apparatus used in position emission tomography (PET) experiment . Each of 3 stations can be grasped in 2 ways: power grasp of block (A) or precision pinch of 2 plates in groove ( B).  
Superior oblique view of left hemisphere demonstrating signifivation of dorsal premotor cortex and superior parietal cortex cant differences between execution (blue) and selection (yellow) tasks. Movement-related activity extends from primary sensorimotor cortex into when subjects were required to make a selection of  
Article
Positron emission tomography (PET) brain mapping was used to investigate whether or not human dorsal premotor cortex is involved in selecting motor acts based on arbitrary visual stimuli. Normal subjects performed four movement selection tasks. A manipulandum with three graspable stations was used. An imperative visual cue (LEDs illuminated in random order) indicated which station to grasp next with no instructional delay period. In a power task, a large aperture power grip was used for all trials, irrespective of the LED color. In a precision task, a pincer grasp of thumb and index finger was used. In a conditional task, the type of grasp (power or precision) was randomly determined by LED color. Comparison of the conditional selection task versus the average of the power and precision tasks revealed increased blood flow in left dorsal premotor cortex and superior parietal lobule. The average rate of producing the different grasp types and transport to the manipulandum stations was equivalent across this comparison, minimizing the contribution of movement attributes such as planning the individual movements (as distinct from planning associated with use of instructional stimuli), kinematics, or direction of target or limb movement. A comparison of all three movement tasks versus a rest task identified movement related activity involving a large area of central, precentral and postcentral cortex. In the region of the precentral sulcus movement related activity was located immediately caudal to the area activated during selection. The results establish a role for human dorsal premotor cortex and superior parietal cortex in selecting stimulus guided movements and suggest functional segregation within dorsal premotor cortex.
 
Article
1. Extracellular recordings from hippocampal area CA1 lasting 2-8 h posttetanus were used to evaluate the duration of long-term potentiation (LTP) at two key developmental ages. 2. At day 11 LTP consistently endured for approximately 1 h before declining to baseline by 2.5 h posttetanus. The response could then be repotentiated, and in some cases, the repotentiation lasted longer than the original potentiation. 3. At day 15 two patterns of potentiation were observed. The first pattern was similar to that observed at day 11 in that the potentiation did not persist; however, it did endure for approximately 2-2.5 h before declining to baseline by 4 h posttetanus. In the second pattern the potentiation persisted indefinitely; these responses were monitored for 6-8 h posttetanus. 4. These patterns are similar to the temporal phases of LTP that have been revealed in adult rat hippocampus through pharmacological manipulations. They may reflect developmental changes during which the different cellular mechanisms underlying LTP become sequentially activated. 5. These findings are important for several reasons. First, because the different temporal phases of LTP seem to be added stepwise during development, animals of different ages could be used explicitly to elucidate the underlying cellular mechanisms of these phases in LTP. Second, because LTP is a candidate mechanism for some forms of learning and memory, these results have implications for sequential steps in the ontogeny of learning and memory. Finally, because studies of LTP have used animals of widely varying ages, including these two ages, it is important to consider whether differences in the developmental properties of LTP could influence experimental observations.
 
Article
1. Substance P (SP) induces a slow neuronal excitation in cholinergic neurons from the nucleus basalis by suppressing an inwardly rectifying K+ current (Kir). We have determined which G protein alpha-subunit mediates this SP effect. 2. After intracellularly injecting antibody against each alpha-subunit of G proteins (Gq alpha/11 alpha, G12 alpha, and G13 alpha) with an Eppendorf microinjector, we examined, by using the whole cell patch-clamp and the ON-cell mode of single-channel recording, the effect of SP on Kir in cultured neurons of the nucleus basalis. The effect of SP on Kir was substantially reduced in neurons injected with antibodies to Gq alpha/11 alpha but not with antibodies to G12 alpha or G13 alpha. 3. The effects of antibodies against three isozymes of phospholipase C (PLC-beta 1, PLC-beta 2, and PLC-beta 3) were tested. The SP-induced suppression of Kir was reduced by antibody against PLC-beta 1 but not by antibodies against PLC-beta 2 or PLC-beta 3. 4. We conclude that the SP-induced inhibition of Kir in nucleus basalis neurons is mediated by Gq/11 and PLC-beta 1.
 
Article
To understand changes in motor behavior during development, kinematic measurements were made of the right leg during embryonic motility in chicks on embryonic (E) days 9, 11, and 13. This is an interesting developmental period during which the embryo first becomes large enough to be physically constrained by the shell. Additionally, sensory systems are incorporated at that time into the spinal motor circuitry. Previous electromyographic (EMG) recordings have shown that the basic pattern of muscle activity seen at E9, composed of half-center-type alternation of extensor and flexor activation, breaks down by E13. This breakdown in organization could be because of disruption of motor patterns by the immature sensory system and/or new spatial constraints on the embryo. The current article describes several changes in leg movement patterns during this period. Episodes of motility increase in duration and the intervals of time between episodes of motility decrease in length. The range of motion of the leg increases, but the overall posture of the leg becomes more flexed. It was found that in-phase coordination of movement among the hip, knee, and ankle decreased between E9 and E13 in agreement with the previous EMG recordings. However, it was also found that the decrease of in-phase coordination among the three joints was accompanied by an increase in the time any two joints were moving in the same manner. Furthermore, examination of in-phase coordination within pairs of joints showed that all three pairs were well coordinated at E9, but that at E13 the in-phase coordination of the ankle with the other two joints decreased, whereas the knee and hip coordination was maintained. This suggests that the hip-knee synergy was closely coupled and that coupling of the ankle with other joints was more labile. The authors conclude that embryos respond to the reduction of free space in the egg during this period not by decreasing the amplitude or coordination of leg movements in general, but instead by differentially controlling the movements of the ankle from those of the hip and knee. Additionally, the changes in movement patterns do not represent a decrease in organization, but rather an alteration of motor coordination possibly as the result of information from the newly acquired sensory systems. These data also support theories that limb central pattern generators (CPGs) are composed of unit CPGs for each joint that can be modulated individually and that this organization is already established early in embryogenesis.
 
Brain regions with significant negative covariations between normalized CBF and the number of TMS pulse-trains 
Article
Rapid-rate transcranial magnetic stimulation (rTMS) was used to stimulate the primary sensorimotor cortex in six healthy volunteers while regional changes in cerebral blood flow (CBF) were simultaneously measured by means of positron emission tomography. A figure-eight TMS coil (Cadwell Corticoil) was positioned, using frameless stereotaxy, over the probabilistic location of the left primary sensorimotor cortex, and a series of brief 10-Hz trains of TMS was delivered at subthreshold intensity during each of six 60-s scans. The scans differed in the number of trains delivered, namely 5, 10, 15, 20, 25, and 30 trains/scan, respectively. In the left primary sensorimotor cortex, CBF covaried significantly and negatively with the number of stimulus trains. These CBF decreases may reflect TMS-induced activation of local inhibitory mechanisms known to play a role in TMS-related phenomena, such as the electromyographic silent period.
 
Article
1. We investigated the electrical properties of globus pallidus neurons intracellularly using brain slices from adult guinea pigs. Three types of neurons were identified according to their intrinsic electrophysiological properties. 2. Type I neurons (59%) were silent at the resting membrane level (-65 ± 10 mV, mean ± SD) and generated a burst of spikes, with strong accommodation, to depolarizing current injection. Calcium-dependent low- frequency (1-8 Hz) membrane oscillations were often elicited by membrane depolarization (-53 ± 8 mV). A low-threshold calcium conductance and an A- current were also identified. The mean input resistance of this neuronal type was 70 ± 22 MΩ. 3. Type II neurons (37%) fired spontaneously at the resting membrane level (-59 ± 9 mV). Their repetitive firing (≤200 Hz) was very sensitive to the amplitude of injected current and showed weak accommodation. Sodium-dependent high-frequency (20-100 Hz) subthreshold membrane oscillations were often elicited by membrane depolarization. This neuronal type demonstrated a low-threshold calcium spike and had the highest input resistance (134 ± 62 MΩ) of the three neuron types. 4. Type III neurons (4%) did not fire spontaneously at the resting membrane level (-73 ± 5 mV). Their action potentials were characterized by a long duration (2.3 ± 0.6 ms). Repetitive firing elicited by depolarizing current injection showed weak or no accommodation. This neuronal type had an A-current and showed the lowest input resistance (52 ± 35 MΩ) of the three neuron types. 5. Stimulation of the caudoputamen evoked inhibitory postsynaptic potentials (IPSPs) in Type I and II neurons. In Type II neurons the IPSPs were usually followed by rebound firing. Excitatory postsynaptic potentials and antidromic responses were also elicited in some Type I and II neurons. The estimated conduction velocity of the striopallidal projection was <1 m/s (Type I neurons, 0.49 ± 0.37 m/s; Type II neurons, 0.33 ± 0.13 m/s).
 
Directional and spatio-temporal tuning of LM units. A: each arrow represents preferred direction for each unit, as calculated from peak of best-fit cosine to direction tuning curve. U, B, D, and F represent up, back (nasal to temporal), down, and forward (temporal to nasal) motion. B: filled circles represent locations of primary peaks from excitatory response (ER) contour plots. Dashed diagonal line represents stimulus velocity of 4°/s, which Ibbotson and Price (2001) used to distinguish "fast" and "slow" groups in both wallaby nucleus of the optic tract (NOT) and pigeon LM.
Directional tuning of LM units pretetrodotoxin (TTX) and post-TTX. Polar plots illustrating directional tuning of units in LM before and after nBOR was injected with TTX (pre-TTX, solid line; post-TTX, dashed line). Firing rate (spikes/s) relative to the spontaneous rate (SR; gray circle) is plotted as a function of direction of motion in polar coordinates (i.e., the SR has been set to zero; outside the gray circle excitation, inside inhibition). Solid and dashed arrows represent the unit's preferred direction pre-TTX and post-TTX, respectively, as calculated from best-fit cosines to tuning curves. [A cosine could not be fit to the tuning curves for the bidirectional unit (D)]. Spatial and temporal frequencies (SF and TF, respectively) of gratings used for directional tuning are illustrated for each case. U, B, D, and F represent up, back (nasal to temporal), down, and forward (temporal to nasal) motion.
, A and B, shows the effects of nBOR inactivation on the ER plots of two other LM units. The unit in Fig. 5A (case #10) showed two excitatory peaks in the pre-TTX ER plot (primary, 1 cpd/2 Hz; secondary, 0.06 cpd/16 Hz). Post-TTX the peak in the fast region was absent, but the peak in the slow region was unaffected. The difference ER plot showed a negative peak in the fast region, and a smaller positive peak to the lowest TFs. The unit in Fig. 5B (case #8) had two excitatory peaks in the fast region pre-TTX (primary, 0.125 cpd/0.5 Hz; secondary, 0.125 cpd/16 Hz). Post-TTX the primary peak is present, although at less than half the size, and the peak at 16 Hz disappeared. In addition, a second peak appeared in the slow region (0.5 cpd/0.5 Hz). All three examples (Figs. 4A, 5, A and B) are quite similar in that the difference ER plots had negative peaks in the fast region, indicating that LM units showed less excitation to low SF/high TF stimuli moving in the preferred direction post- TTX. This was the most common and dramatic effect that we observed in the ER plots. In column eight of Table 1 the presence of peaks in the difference ER plots for all 17 units tested is noted. Negative fast peaks (fast) and positive slow peaks (slow) are shown in bold and italics, respectively. In addition, the magnitude of the peak is indicated as the %change for that SF/TF combination [for ve peaks, %change (post- TTX pre-TTX)/pre-TTX; for ve peaks, (post-TTX pre-TTX)/post-TTX 100]. Of the 17 units tested, 14 had a negative peak in the fast region of the difference ER plots. For these 14 cells, there were four cases in which an excitatory peak in the fast region of the pre-TTX ER plot was virtually eliminated post-TTX (as in Fig. 5A). The average magnitude of these 14 peaks was 67%. For 7 cells there was a positive peak in the slow region of the difference ER plots (e.g., Fig. 4A) and the average magnitude was 61%. In Fig. 6A, the ER plots are averaged across all 17 cells. The responses for each cell were first normalized, using a common scale for the pre-TTX and post-TTX plots. Despite the averaging , two excitatory peaks were apparent pre-TTX, reflecting the spatio-temporal preferences of the fast and slow cells. Post-TTX both peaks were reduced in size, particularly the fast peak, and at the higher TFs. For the difference ER plot, based on the pooled variance of the associated with all points in the plot, values above 0.16 (and below 0.16) are statistically significant (P 0.05). [The critical difference (CD) was calculated as follows: CD t crit pooled variance/n.] The difference ER plot had a negative peak in the fast region, which was largest in magnitude (0.39) at 0.13 cpd/8 Hz (P 0.002, single-sample t-test). The positive peak (0.13) in the region of the highest SFs and lowest TFs was not significantly different from zero.  
Effects of inactivation of nBOR on the spatio-temporal tuning of LM units to gratings drifting in preferred (ER plots, A) and anti-preferred directions (IR plots, B). Normalized data averaged across all cases are shown. See caption to Fig. 4 and Results for additional details.  
Article
The nucleus of the basal optic root (nBOR) of the accessory optic system (AOS) and the pretectal nucleus lentiformis mesencephali (LM) are involved in the analysis of optic flow that results from self-motion and are important for oculomotor control. These neurons have large receptive fields and exhibit direction selectivity to large moving stimuli. In response to drifting sine wave gratings, LM and nBOR neurons are tuned to either low spatial/high temporal frequencies (SF, TF) or high SF/low TF stimuli. Given that velocity = TF/SF, these are referred to as "fast" and "slow" neurons, respectively. There is a heavy projection from the AOS to the pretectum, although its function is unknown. We recorded the directional and spatio-temporal tuning of LM units in pigeons before and after nBOR was inactivated by tetrodotoxin injection. After nBOR inactivation, changes in direction preference were observed for only one of 18 LM units. In contrast, the spatio-temporal tuning of LM units was dramatically altered by nBOR inactivation. Two major effects were observed. First, in response to motion in the preferred direction, most (82%) neurons showed a substantially reduced (mu = -67%) excitation to low SF/high TF gratings. Second, in response to motion in the anti-preferred direction, most (63%) neurons showed a dramatically reduced (mu = -78%) inhibition to high SF/low TF gratings. Thus the projection from the nBOR contributes to the spatio-temporal tuning rather than the directional tuning of LM neurons. We propose a descriptive model whereby LM receives inhibitory and excitatory input from "slow" and "fast" nBOR neurons, respectively.
 
Article
The subthalamic nucleus (STN) is considered to be one of the driving forces in the basal ganglia circuit. The STN is innervated by serotonergic afferents from the raphe nucleus and expresses a variety of 5-HT receptor subtypes. We investigated the effects of 5-HT and 5-HT receptor subtype agonists and antagonists on the firing properties of STN neurons in rat brain slices. We used cell-attached, perforated-patch, and whole cell recording techniques to detect changes in firing frequency and pattern and electrical membrane properties. Due to the depolarization of membrane potential caused by reduced potassium conductance, 5-HT (10 microM) increased the firing frequency of STN neurons without changing their firing pattern. Cadmium failed to occlude the effect of 5-HT on firing frequency. 5-HT had no effect on afterhyperpolarization current. These results indicated that the 5-HT action was not mediated by high-voltage-activated calcium channel currents and calcium-dependent potassium currents. 5-HT had no effect on hyperpolarization-activated cation current (I(H)) amplitude and voltage-dependence of I(H) activation, suggesting that I(H) was not involved in 5-HT-induced excitation. The increased firing by 5-HT was mimicked by 5-HT(2/4) receptor agonist alpha-methyl-5-HT and was partially mimicked by 5-HT2 receptor agonist DOI or 5-HT4 receptor agonist cisapride. The 5-HT action was partially reversed by 5-HT4 receptor antagonist SB 23597-190, 5-HT2 receptor antagonist ketanserin, and 5-HT2C receptor antagonist RS 102221. Our data indicate that 5-HT has significant ability to modulate membrane excitability in STN neurons; modulation is accomplished by decreasing potassium conductance by activating 5-HT4 and 5-HT2C receptors.
 
Article
The inferior frontal gyrus (IFG) of humans is known to play a critical role in speech production. The IFG is a highly convoluted and cytoarchitectonically diverse structure, classically forming 3 subgyri. It is reasonable to speculate that during speaking the IFG, or some portion of it, influences by corticocortical connections the orofacial representational area of primary motor cortex. To test the hypothesis that such corticocortical connections exist, electrical-stimulation tract tracing experiments were performed intraoperatively on 14 human subjects undergoing surgical treatment of medically intractable epilepsy. Bipolar electrical stimulation was applied to sites on the IFG, while the resulting evoked potentials were recorded from orofacial motor cortex, using a multichannel recording array. Stimulation of the IFG evoked polyphasic waveforms on motor cortex of both language-dominant and -nondominant hemispheres. The evoked waveforms had consistent features across subjects. The responses were seen in discrete regions on precentral cortex. Stimulation of motor cortex also evoked responses on portions of IFG. The data provide evidence for a functional connection between the human IFG and orofacial motor cortex.
 
Article
The high density of cannabinoid receptors in the cerebellum and the degradation of motor coordination produced by cannabinoid intoxication suggest that synaptic transmission in the cerebellum may be strongly regulated by cannabinoid receptors. Therefore the effects of exogenous cannabinoids on synapses received by Purkinje cells were investigated in rat cerebellar slices. Parallel fiber-evoked (PF) excitatory postsynaptic currents (EPSCs) were strongly inhibited by bath application of the cannabinoid receptor agonist WIN 55212-2 (5 microM, 12% of baseline EPSC amplitude). This effect was completely blocked by the cannabinoid CB1 receptor antagonist SR 141716. It is unlikely that this was the result of alterations in axonal excitability because fiber volley velocity and kinetics were unchanged and a cannabinoid-induced decrease in fiber volley amplitude was very minor (93% of baseline). WIN 55212-2 had no effect on the amplitude or frequency of spontaneously occurring miniature EPSCs (mEPSCs), suggesting that the effect of CB1 receptor activation on PF EPSCs was presynaptically expressed, but giving no evidence for modulation of release processes after Ca(2+) influx. EPSCs evoked by climbing fiber (CF) stimulation were less powerfully attenuated by WIN 55212-2 (5 microM, 74% of baseline). Large, action potential-dependent, spontaneously occurring inhibitory postsynaptic currents (sIPSCs) were either severely reduced in amplitude (<25% of baseline) or eliminated. Miniature IPSCs (mIPSCs) were reduced in frequency (52% of baseline) but not in amplitude, demonstrating suppression of presynaptic vesicle release processes after Ca(2+) influx and suggesting an absence of postsynaptic modulation. The decrease in mIPSC frequency was not large enough to account for the decrease in sIPSC amplitude, suggesting that presynaptic voltage-gated channel modulation was also involved. Thus, while CB1 receptor activation reduced neurotransmitter release at all major classes of Purkinje cell synapses, this was not accomplished by a single molecular mechanism. At excitatory synapses, cannabinoid suppression of neurotransmitter release was mediated by modulation of voltage-gated channels in the presynaptic axon terminal. At inhibitory synapses, in addition to modulation of presynaptic voltage-gated channels, suppression of the downstream vesicle release machinery also played a large role.
 
Article
1. We assessed the visual recognition abilities, as measured by delayed nonmatching-to-sample with trial-unique objects, of rhesus monkeys with hippocampectomy (i.e., removal of the hippocampal formation plus parahippocampal gyrus) combined with ablations of the rhinal cortex (i.e., entorhinal cortex plus perirhinal cortex). 2. Relative to unoperated controls, monkeys with combined hippocampectomy and rhinal cortex ablation (H+Rh) were significantly impaired in visual recognition. 3. Comparison of the scores of the monkeys in the present H+Rh group, which sustained near-complete rhinal cortex damage, with the scores of monkeys in an earlier H+Rh group in which the rostral part of the rhinal cortex had been spared indicates that the magnitude of the impairment is greater in the group with the more complete rhinal cortex damage. This finding is consistent with the idea that the rhinal cortex is critical for visual recognition. 4. Comparison of the present results with those from an earlier study on visual recognition that employed lesions limited to the rhinal cortex (Rh group) shows, paradoxically, that adding removal of the hippocampal formation and parahippocampal gyrus to a rhinal cortex lesion significantly reduces the recognition impairment produced by rhinal cortex lesions alone. 5. Our findings do not fit the view that the hippocampal formation, parahippocampal gyrus, and rhinal cortex constitute parts of a single functional system, such that the greater the damage to the entire system, the more severe the impairment. Instead, the results are consistent with the view that there are multiple functional subdivisions within the medial temporal lobe.
 
Article
1. We have previously identified face-selective areas in the mid-fusiform and inferior temporal gyri in electrophysiological recordings made from chronically implanted subdural electrodes in epilepsy patients. In this study, functional magnetic resonance imaging (fMRI) was used to study the anatomic extent of face-sensitive brain regions and to assess hemispheric laterality. 2. A time series of 128 gradient echo echoplanar images was acquired while subjects continuously viewed an alternating series of 10 unfamiliar faces followed by 10 equiluminant scrambled faces. Each cycle of this alternating sequence lasted 12 s and each experimental run consisted of 14 cycles. The time series of each voxel was transformed into the frequency domain using Fourier analysis. Activated voxels were defined by significant peaks in their power spectra at the frequency of stimulus alternation and by a 180 degrees phase shift that followed changes in stimulus alternation order. 3. Activated voxels to faces were obtained in the fusiform and inferior temporal gyri in 9 of 12 subjects and were approximately coextensive with previously identified face-selective regions. Nine subjects also showed activation in the left or right middle occipital gyri, or in the superior temporal or lateral occipital sulci. Cortical volumes activated in the left and right hemispheres were not significantly different. Activated voxels to scrambled faces were observed in six subjects at locations mainly in the lingual gyri and collateral sulci, medial to the regions activated by faces. 4. Face stimuli activated portions of the midfusiform and inferior temporal gyri, including adjacent cortex within occipitotemporal sulci.(ABSTRACT TRUNCATED AT 250 WORDS)
 
Article
1. The effect of intrathecal injection of the selective serotonin (5-HT)1B/1D receptor agonist CGS-12066B maleate (825 nmol) was assessed on stretch-evoked clasp knife inhibition of hindlimb ankle extensor muscle reflex force in precollicular decerebrate cats in which neural transmission in dorsolateral spinal pathways was blocked bilaterally by focal cooling. 2. During cold block, ramp and hold stretches of the medial gastrocnemius muscle (MG) evoked only a brief reflex excitation that was followed by powerful, long-lasting inhibition (the clasp knife reflex). Both the amplitudes of peak force evoked by the ramp and sustained force output during the last 500 ms of the hold phase of the stretch were depressed by > 50%. 3. Reflex force output during the hold portion of stretch was significantly improved on postdrug cold block trials, although peak force remained depressed. CGS-12066B did not significantly alter stretch-evoked force output in decerebrate cats when spinal cord neural transmission was unimpaired. 4. These data suggest that selective 5-HT1B/1D agonists may be of therapeutic usefulness in the treatment of reflex disorders arising from partial spinal cord injury.
 
Article
In the mechanically dissociated rat hippocampal CA1 neurons with native presynaptic nerve endings, namely "synaptic bouton" preparation, the purinergic modulation of spontaneous GABAergic miniature inhibitory postsynaptic currents (mIPSCs) was investigated using whole-cell recording mode under the voltage-clamp conditions. In immature neurons, adenosine (10 microM) reversibly decreased GABAergic mIPSC frequency without affecting the mean current amplitude. The inhibitory effect of adenosine transmission was completely blocked by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 100 nM), a selective Alpha(1) receptor antagonist, and was mimicked by N(6)-cyclopentyladenosine (CPA, 1 microM), a selective Alpha(1) receptor agonist. However, CPA had no effect on GABAergic mIPSC frequency in postnatal 30 day neurons. N-ethylmaleimide (10 microM), a guanosine 5'-triphosphate binding protein uncoupler, and Ca(2+)-free external solution removed the CPA-induced inhibition of mIPSC frequency. K(+) channel blockers, 4-aminopyridine (100 microM) and Ba(2+) (1 mM), had no effect on the inhibitory effect of CPA on GABAergic mIPSC frequency. Stimulation of adenylyl cyclase with forskolin (10 microM) prevented the CPA action on GABAergic mIPSC frequency. Rp-cAMPS (100 microM), a selective PKA inhibitor, also blocked the CPA action. It was concluded that the activation of presynaptic Alpha(1) receptors modulates the probability of spontaneous GABA release via cAMP- and protein kinase A dependent pathway. This Alpha(1) receptor-mediated modulation of GABAergic transmission may play an important role in the regulation of excitability of immature hippocampal CA1 neurons.
 
Article
1. The lateral intraparietal area (area LIP) of the macaque's posterior parietal cortex (PPC) lies in the dorsal stream of extrastriate visual areas. It receives extensive visual inputs and sends outputs to several eye movement centers. It contains neurons with visual and saccade-related responses suggesting a role of area LIP in programming saccadic eye movements to visual targets. Because primates can also orient to nonvisual stimuli, we investigated whether LIP neurons process stimuli of other modalities besides the visual one by comparing their activity in auditory and visual saccade tasks. 2. We recorded the activity of single neurons of Macaca mulatta monkeys while they performed memory saccades to acoustic and visual targets. We analyzed the activity during stimulus presentation (stimulus period, S) and during the delay (memory period, M) between stimulus presentation and the saccade to its remembered location. 3. Among 80 area LIP neurons tested, we found 44 that had S period and/or M period responses following presentation of the auditory stimulus. Most of these responses were spatially tuned, i.e., selective for the left or right stimulus location (27 of 29 S responses; 25 of 29 M responses). 4. The majority of neurons with responses in the auditory memory saccade task also responded in the visual version of the task. Eighty-nine percent (24/27) were clearly bimodal in the S period, and 88% (23/26) were bimodal in the M period. 5. Almost all the neurons with spatially tuned auditory responses that were bimodal were also spatially tuned in their visual responses (20/22 for S responses; 18/19 for M responses). The spatial tuning for the two modalities was the same in 85% (17/20) of the tested neurons for the S responses, and in 83% (15/18) of the tested neurons for the M responses. 6. Area LIP contains a population of neurons that respond to both visual and auditory stimuli. This result is consistent with our finding that the memory activity of many LIP cells encodes the next planned saccade. If cells are coding planned movements, they should be active independently of the sensory modality of the target for the movement, as was the case for most of the neurons described in the present study.
 
Compartmental distribution of calretinin- immunoreactive neurons in squirrel monkey striatum 
Comparison of neural distributions in simulation recordings in striatal interneurons and actual recordings of TANS 
Article
1. Tonically active neurons (TANs) in the primate striatum develop transient responses to sensory conditioning stimuli during behavioral training in classical conditioning tasks. In this study we examined the temporal characteristics of such TAN responses and mapped the sites of TANs responding to auditory and visual conditioned stimuli in the striatum in macaque monkeys. We further mapped the locations of TANs recorded acutely in the squirrel monkey striatum in relation to the neurochemically distinguished striosome and matrix compartments of the striatum, and made quantitative comparisons between the densities and compartmental distributions of TANs and those of four major types of striatal interneuron identified by histochemical and immunohistochemical staining. 2. We made recordings from 858 TANs at different sites in the striatum in two behaving macaque monkeys at different times during training with auditory (click) and visual (light-emitting diode flash) conditioning stimuli. TANs distributed across large parts of the striatum developed responses to the conditioning stimuli. The responses comprised a decrement of tonic firing (pause) followed by a rebound excitation. Measurements were made of the onsets, offsets, and durations of the pauses of individual TANs and of the interspike intervals (ISIs) of the same cells. 3. The mean duration of the pause responses (268.3 ms) was greater than the mean ISI of the same neurons (181 ms), suggesting that the pause represents an active suppression of TAN firing. The coefficient of variation (CV) for the pause responses was 0.28, compared with a CV of 0.63 for the same cells' ISIs. The population CV for the pauses was 0.16, compared with a population CV of 0.20 for the ISIs. These data, together with temporal analysis of the responses and population histograms, suggest that the pauses became temporally aligned across large parts of the striatum after learning. Analyses of variance (ANOVAs) were carried out to determine whether there were differences in the onset and offset latencies of the pause response or in the durations of the pause responses for TANs at different sites. These analyses suggested that, with rare exceptions, there was no difference in the timing of the TAN responses across large (> 10 mm3) parts of the striatum. 4. Comparisons of TAN responses in different regions of the striatum showed that, for responses to a given modality of conditioned stimulus, there were no significant differences in pause offset times for TANs recorded in the caudate nucleus or putamen, or for TANs recorded in more anterior or more posterior parts of these nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)
 
Article
The generation of neuronal diversity requires the coordinated development of differential patterns of ion channel expression along with characteristic differences in dendritic geometry, but the relations between these phenotypic features are not well known. We have used a combination of intracellular recordings, morphological analysis of dye-filled neurons, and stereological analysis of immunohistochemically labeled sections to investigate the development of characteristic electrical and morphological properties of functionally distinct populations of sympathetic neurons that project from the celiac ganglion to the splanchnic vasculature or the gastrointestinal tract of guinea pigs. At early fetal stages, neurons were significantly more depolarized at rest compared with neurons at later stages, and they generally fired only a single action potential. By mid fetal stages, rapidly and slowly adapting neurons could be distinguished with a topographic distribution matching that found in adult ganglia. Most rapidly adapting neurons (phasic neurons) at this age had a long afterhyperpolarization (LAH) characteristic of mature vasomotor neurons and were preferentially located in the lateral poles of the ganglion, where most neurons contained neuropeptide Y. Most early and mid fetal neurons showed a weak M current, which was later expressed only by rapidly-adapting and LAH neurons. Two different A currents were present in a subset of early fetal neurons and may indicate neurons destined to develop a slowly adapting phenotype (tonic neurons). The size of neuronal cell bodies increased at a similar rate throughout development regardless of their electrical or neurochemical phenotype or their topographical location. In contrast, the rate of dendritic growth of neurons in medial regions of the ganglion was significantly higher than that of neurons in lateral regions. The apparent cell capacitance was highly correlated with the surface area of the soma but not the dendritic tree of the developing neurons. These results demonstrate that the well-defined functional populations of neurons in the celiac ganglion develop their characteristic electrophysiological and morphological properties during early fetal stages of development. This is after the neuronal populations can be recognized by their neurochemical and topographical characteristics but long before the neurons have finished growing. Our data provide strong circumstantial evidence that the development of the full phenotype of different functional classes of autonomic final motor neurons is a multi-step process likely to involve a regulated sequence of trophic interactions.
 
Article
Optical methods for monitoring neuron activity were further developed with the aim of using these methods to study how groups of neurons interact to control behavior. The number of photodetectors was increased from 14 (22) to 124. The results suggest that the apparatus can monitor action-potential activity in a few hundred neurons if the cell bodies are large (>30 μm diameter) and they are fully invaded by the action potential. Pharmacologic effects of the dyes were troublesome. However, conditions were found where optical detection could be used to find neurons participating in a behavioral response while simultaneous electrode measurements suggested that there may not have been pharmacologic effects. In experiments where signal averaging could be used, potential changes as small as 1 mV were detected optically.
 
Article
The mechanosensory lateral line of fish is a hair cell based sensory system that detects water motion using canal and superficial neuromasts. The trunk lateral line of the plainfin midshipman fish, Porichthys notatus, only has superficial neuromasts. The posterior lateral line nerve (PLLn) therefore innervates trunk superficial neuromasts exclusively and provides the opportunity to investigate the physiological responses of these receptors without the confounding influence of canal organs. We recorded single-unit activity from PLLn primary afferents in response to a vibrating sphere stimulus calibrated to produce an equal velocity across frequencies. Threshold tuning, isovelocity, and input/output curves were constructed using spike rate and vector strength, a measure of phase locking of spike times to the stimulus waveform. All units responded maximally to frequencies of 20-50 Hz. Units were classified as low-pass, band-pass, broadly tuned, or complex based on the shapes of tuning and isovelocity curves between 20 and 100 Hz. A 100 Hz stimulus caused an increase in spike rate in almost 50%, and significant synchronization in >80%, of all units. Midshipman vocalizations contain significant energy at and below 100 Hz, so these results demonstrate that the midshipman peripheral lateral line system can encode these acoustic signals. These results provide the first direct demonstration that units innervating superficial neuromasts in a teleost fish have heterogeneous frequency response properties, including an upper range of sensitivity that overlaps spectral peaks of behaviorally relevant acoustic stimuli.
 
Article
1. Steady-state iodothyronine profiles in plasma are composed of thyroid gland-synthesized hormones (mainly thyroxine) and tissue iodothyronine metabolites (mainly triiodothyronine and reverse triiodothyronine) that have entered the bloodstream. The hormones circulate in noncovalently bound complexes with a panoply of carrier proteins. Transthyretin (TTR), the major high-affinity thyroid hormone binding protein in rat plasma, is formed in the liver. It is also actively and independently synthesized in choroid plexus, where its function as a chaperone of thyroid hormones from bloodstream to cerebrospinal fluid (CSF) is undergoing close scrutiny by several groups of investigators. Because TTR has high-affinity binding sites for both thyroxine and retinol binding protein, its potential role as a mediator of combined thyroid hormone and retinoic acid availability in brain is of further interest. 2. While they are in the free state relative to their binding proteins, iodothyronines in the cerebral circulation are putatively subject to transport across both the blood-brain barrier (BBB) and choroid plexus CSF barrier (CSFB) before entering the brain. Previous autoradiographic studies had already indicated that after intravenous administration the transport mechanisms governing thyroxine and triiodothyronine entry into brain were probably similar, whereas those for reverse triiodothyronine were very different, although the basis for the difference was not established at that time. Intense labeling seen over brain ventricles after intravenous administration of all three iodothyronines suggested that all were subject to transport across the CSFB. 3. To evaluate the role of the BBB and CSFB in determining iodothyronine access to brain parenchyma, autoradiograms prepared after intravenous administration of [125I]-labeled hormones (revealing results of transport across both barriers) were compared with those prepared after intrathecal (icv) hormone injection (reflecting only their capacity to penetrate into the brain after successfully navigating the CSFB). 4. Those studies revealed that thyroxine and triiodothyronine were mainly transported across the BBB. They shared with reverse triiodothyronine a generally similar, limited pattern of penetration from CSF into the brain, with circumventricular organs likely to be the main recipients of iodothyronines (with or without retinol) transported across the CSFB. 5. Analysis of all of the images obtained after intravenous and icv hormone administration clarified the basis for the unique distribution of intravenously injected reverse triiodothyronine. The hormone is excluded by the BBB but may be subject to limited penetration into brain parenchyma via the CSF. 6. Overall the observations single out reverse triiodothyronine as the iodothyronine showing the most distinctive as well as the most limited pattern of transport from blood to brain.(ABSTRACT TRUNCATED AT 400 WORDS)
 
Recording depth and baseline evoked responses of wide dynamic range neurons in SNL and uninjured rats SNL Uninjured
Effect of systemic A-1264087 on wind-up responses of WDR neurons to repeated electrical stimuli in SNL vs. uninjured rats. A: example recording of a WDR neuron displaying wind-up responses to a train of electrical stimuli applied at a frequency of 1.0 Hz. Stimulus number (1, 4, 8, 12) in the stimulation sequence is indicated. Systemic A-1264087 (4 mg/kg iv) reduced wind-up of WDR neurons in both SNL (B) and uninjured rats (C). Total number of action potentials in the C-fiber range (90 – 800 ms) to repetitive electrical stimulation (16 pulses) is plotted as a function of stimulus number in SNL (D) and uninjured (E) rats. n 5– 6 neurons per group. Results are expressed as means SE. *P 0.05, vs. baseline levels; P 0.05, P 0.01, vs. vehicle-treated group.  
Differential effect of systemic A-1264087 on mechanically evoked and spontaneous activity of WDR in SNL vs. uninjured rats. Example recording of a WDR neuron before and after A-1264087 injection in SNL (A) and uninjured rats (D). A-1264087 (4 mg/kg iv) inhibited the mechanical responses (10 g von Frey, 15 s; B) as well as the spontaneous activity (C) of WDR neurons in SNL rats. A-1264087 injection (4 mg/kg iv) did not effect mechanically evoked (E) or spontaneous activity (F) of WDR neurons in uninjured rats. n 5-8 neurons per group. t, tap; b, brush; p, pinch; vF, von Frey hair (10 g for 15 s). Results are expressed as means SE. **P 0.01, vs. baseline levels; P 0.05, P 0.01, vs. vehicle-treated group.
Site(s) of action of A-1264087 on WDR neuronal activity in SNL rats. Systemic A-1264087 (4 mg/kg iv) to spinally transected SNL rats decreased the mechanical responses (A) and the spontaneous activity (B) of WDR neurons comparable to the effects observed in intact SNL rats. Data from intact rats are shown for comparison. C: the responses of WDR neurons to 10 g von Frey hair stimulation was reduced by ipsilateral but not contralateral injection of A-1264087 (300 nmol/20 l) into the neuronal receptive field (RF) on the rat hindpaw. D: spontaneous activity of WDR neurons was not affected by either ipsilateral or contralateral injection of A-1264087 into the RF. Direct injection of A-1264087 (10 nmol/0.5 l) into the spinal cord reduced the mechanical evoked (E) and spontaneous activity (F) of WDR neurons in neuropathic rats. n 5-8 neurons per group. Results are expressed as means SE. *P 0.05, **P 0.01, vs. baseline levels; P 0.05, P 0.01 vs. vehicle-treated group.
Article
N-, T- and P/Q-type voltage-gated Ca(2+) channels are critical for regulating neurotransmitter release and cellular excitability and have been implicated in mediating pathological nociception. A-1264087 is a novel state-dependent blocker of N-, T- and P/Q-type channels. In the present studies, A-1264087 blocked (IC50 = 1.6 µM) rat DRG N-type Ca(2+) in a state dependent fashion. A-1264087 (1, 3 and 10 mg/kg, p.o.) dose-dependently reduced mechanical allodynia in rats with a spinal nerve ligation (SNL) injury. A-1264087 (4 mg/kg, i.v.) inhibited both spontaneous and mechanically evoked activity of spinal wide dynamic range (WDR) neurons in SNL rats but had no effect in uninjured rats. The inhibitory effect on WDR neurons remained in spinally transected SNL rats. Injection of A-1264087 (10 nmol/0.5 μl) into the spinal cord reduced both spontaneous and evoked WDR activity in SNL rats. Application of A-1264087 (300 nmol/20 μl) into the receptive field on the hindpaw attenuated evoked but not spontaneous firing of WDR neurons. Using electrical stimulation, A-1264087 (4 mg/kg, i.v.) inhibited Aδ-, C-fiber evoked responses and after-discharge of WDR neurons in SNL rats. These effects by A-1264087 were not present in uninjured rats. A-1264087 moderately attenuated WDR neuron windup in both uninjured and SNL rats. In summary, these results indicate that A-1264087 selectively inhibited spinal nociceptive transmission in sensitized states through both peripheral and central mechanisms.
 
Experimental setup. A : the custom- built apparatus allowed abduction and adduction of the index finger only. The index finger was abducted 5° from neutral at the beginning of each trial. B : the sinusoidal trace (target) was displayed as a red line on the monitor, and force feedback was provided to subjects as a blue line. 
Action potential identification from multi-motor unit recordings. A: multi-motor unit action potentials were identified using the first dorsal interosseus (FDI) intramuscular electromyographic (EMG) signal (top). Depicted in the bottom EMG trace, filled circles indicate the identified motor unit action potentials that exceeded the threshold (mean baseline EMG 2 SDs; represented by dotted line). B: the discharge times were identified. C: the interspike intervals (ISIs) were computed and and made into a continuous signal. D: the inverse of the smoothed ISI function was calculated, representing the modulation of the motor unit discharge rate (black trace).
Representative data of the index finger position (left) and detrended ISIs from the FDI EMG (right) during block 1, trial 4 (A) and block 8, trial 39 (B). The dashed line in left graphs represents the sinusoidal abduction-adduction trace subjects were asked to follow. C: detrended position data (top) and corresponding detrended ISIs (bottom) from the first 4 s of the data illustrated in the shaded areas within A and B. Greater position variability during early trials corresponded to greater ISI variability, whereas lower position variability corresponded to lower ISI variability.
Article
Practice of a motor task decreases motor output variability in older adults and is associated with adaptations of discharge activity of single motor units. In this paper we were interested in the practice-induced modulation of multiple motor units within 13-30 Hz because theoretically it enhances the timing of active motoneurons. Our purpose, therefore, was to determine the neural adaptation of multiple motor units and related improvements in movement control following practice. Nine healthy older adults (65-85 years) performed 40 practice trials of a sinusoidal task (0.12 Hz) with their index finger (10° range of motion). Multiple motor unit activity was recorded intramuscularly from the first dorsal interosseus muscle. The mean spike rate (MSR), spike rate variability (CVISI), and frequency modulation (5-60 Hz) of the spike rate were calculated from the multi-motor unit activity, and were correlated with movement accuracy and variability of index finger position. A decrease in movement trajectory variability was associated with an increase in MSR (R(2)=0.58), a decrease in CVISI (Christou et al. 2007b) (R(2)=0.58), and an increase in total power within 13-30 Hz band (R(2)=0.48). The increase in total power within 13-30 Hz band was associated significantly (P < 0.005) with an increase in MSR (R(2)=0.75) and the decrease in CVISI (R(2)=0.70). We demonstrate that practice-induced improvements in movement control are associated with changes in activity of multiple motor units. These findings suggest that practice-induced improvements in movement steadiness of older adults are associated with changes in the modulation of the motoneuron pool from 13-30 Hz.
 
Top-cited authors
Randy L Buckner
  • Harvard University
B.T. Thomas Yeo
  • National University of Singapore
Hesheng Liu
  • Harvard Medical School
Jordan W Smoller
  • Harvard Medical School
Jonathan R Polimeni
  • Massachusetts General Hospital