Journal of Neurophysiology

Published by American Physiological Society

Online ISSN: 1522-1598


Print ISSN: 0022-3077


Cholinergic and noradrenergic modulation of the slow (≃0.3 Hz) oscillation in neocortical cells
  • Article
  • Full-text available

November 1993


279 Reads

M Steriade



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)

Low-frequency oscillations (<0.3 Hz) in the electromyographic (EMG) activity of the human trapezius muscle during sleep

October 2002


87 Reads

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.

FIG. 3. Wiener-kernel analysis for a representative mid-CF ANF. ANF had a CF of 2.94 kHz. All panels represent the same train of 28,298 spikes evoked by a 192-s white-noise stimulus presented at 15 dB SPL/Hz (ERB pressure: 44 dB SPL). A: h 1 (blue) and normalized h 2 FSV (red). B and E: h 2 . E: h 2 as a 3-D object. B: projection of the h 2 onto a 2-D plane, with the 3rd (amplitude) dimension coded by hue; the magenta and black lines, respectively, indicate the diagonal 1 2 and the row with 1 2.29 ms. C: values of the h 2 at the diagonal 1 2 (magenta) and a slice through the h 2 maximum at fixed 2.29 ms (black line). Note different timescales for row (bottom) and diagonal (top). D: Fourier magnitudes of h 1 (blue) and of the h 2 FSV (red). Arrow indicates the CF. F: Fourier magnitudes of the h 2 , represented as its projection onto a 2-D plane, with the 3rd dimension coded by hue. Lines mark CF and CF. Th 11 dB SPL; SR 57.3/s; h 0 135.4/s.  
FIG. 6. Second-order Wiener kernels of the "sandwich" model system and their corresponding 2-D Fourier transforms. Left column: time-domain kernels. Right column: their Fourier transforms. [Note that only sections of the 1st and the 2nd quadrants of the complete 2-D Fourier transforms are shown here.]. In the case of the 500-Hz ("lowCF") system, the 2nd-order Wiener kernels computed preand post-low-pass filtering are the same and the corresponding Fourier transforms are also identical (top row). In the case of the 7-kHz ("high-CF") system, the 2nd-order Wiener kernel computed before low-pass filtering has a checkerboard pattern and the corresponding Fourier transform shows 7-kHz components in both quadrants. For the 7-kHz system, the 2nd-order Wiener kernel computed after lowpass filtering has a striped pattern and the corresponding Fourier transform shows a 7-kHz component only in quadrant II.
FIG. 7. Singular value decomposition of the 2nd-order kernels. Weights (diagonal elements of S in Eq. 13) of the 2ndand 3rd-rank singular vectors are expressed as a fraction of the FSV weights. A: relative weights of the 2nd-rank singular vector plotted against BF. Inset: averaged weights of the singular vectors with ranks 2-26, expressed as a fraction of the FSV weights for low-CF (CFs 2.7 kHz, downward triangles) and high-CF ANFs (CFs 2.7 kHz, upward triangles). Relative weights indicate that the FSVs almost fully characterize the h 2 s of low-CF ANFs (2nd-rank singular vector weights of low-CF ANFs are only about 0.26 of FSV weight). In the case of high-CF ANFs, the FSVs and 2nd-rank singular vectors have similar weights and jointly account for most properties of the 2nd-order kernels. Dashed line, a smoothed step function, fits very well the weights of the 2nd-rank singular vector relative to the weights of the h 2 FSVs (r 2 0.95). B: relative weights of the 2nd-and 3rd-rank singular vectors plotted against the signal-to-noise ratios of the 2nd-order kernels. There is a strong negative correlation between the signal-tonoise ratios of the 2nd-order kernels (abscissa) and the weights of the 3rd-rank singular vectors for all CFs (open symbols) and the 2nd-rank singular vectors of low-CF ANFs (closed circles). Signal-to-noise ratio was computed as 2nd-order kernel peakto-peak amplitude divided by baseline-noise amplitude. Exponential decay closely fits the variation of 3rd-rank singular vectors as a function of h 2 signal-to-noise ratio (r 2 0.81).
FIG. 8. First-and 2nd-order Wiener kernels of low-CF ANFs. Time-domain representations of the normalized h 1 s (blue) and h 2 FSVs (red) are shown to the left. Unit number on the left of each trace corresponds to the same ANF in Figs. 12, 15, and 17C. CF is indicated next to each tracing. Corresponding h 2 s, presented as color-coded projections are shown to the right. Note that timescales vary. Number of spikes (N) used for computation of kernels, stimulus duration (t), CF tone threshold , noise spectral level, and ERB pressure (between parentheses ): ANF No. 1: n 90,467 (t 759 s), 35 dB SPL, 18 dB SPL/Hz (37 dB SPL); 2: n 37,664 (t 540 s), 28 dB SPL, 18 dB SPL/Hz (41 dB SPL); 3: n 27,683 (t 180 s), 9 dB SPL, 6 dB SPL/Hz (18 dB SPL); 4: n 20,196 (t 240 s), 2 dB SPL, 17 dB SPL/Hz (9 dB SPL); 5: n 14,446 (t 170 s), 10 dB SPL, 18 dB SPL/Hz (9 dB SPL).  
FIG. 10. Windowing of 1st-order kernels. A: normalized raw h 1 (dashed line) and envelope of h 2 FSV (thin continuous line). Squares indicate the time interval within which the h 2 -FSV envelope was 6 dB higher than the h 2 -FSV root mean square (rms) computed for the 1st millisecond (horizontal dashed line). Circles indicate half the amplitude of the time window (thick continuous line). Duration of the flat part of the window was equal to (and varied with) the h2-FSV envelope width. Rise and fall ramps (0.5 period of a 1-kHz sinusoid) always had 0.5-ms durations. B: normalized h 2 FSV (thin line) and windowed h 1 (thick line). Note that the timescales are different in A and B. C: Fourier magnitudes of the raw h 1 (dashed line), windowed h 1 (thick line), and of the h 2 FSV (thin continuous line). D: phases of raw h 1 (dashed line), windowed h 1 (thick line), and of the h 2 FSV (thin continuous line). Phases at best frequencies (BFs) of h 1 and h 2 FSV, respectively, are indicated by circles. CF Th 33 dB SPL. Noise level: 17 dB SPL/Hz (47 dB SPL in ERB).  


doi:10.1152/jn.00882.2004. Wiener-Kernel Analysis of Responses to Noise of Chinchilla Auditory-Nerve Fibers

July 2005


210 Reads


Andrei N Temchin





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.

Fig. 1. 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). 
Fig. 2. 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. 
Fig. 3. 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]. 
Fig. 4. 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 
Fig. 5. Pertussis toxin (PTX) and the S1P receptor 1 (S1PR 1 ) antagonist W146 
Sphingosine 1-phosphate receptor 2 antagonist JTE-013 increases the excitability of sensory neurons independently of the receptor

June 2012


355 Reads

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.

Inositol 1,4,5-trisphosphate-gated conductance in isolated rat olfactory neurons

March 1994


11 Reads

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+.

Inositol 1,4,5-trisphosphate alters bursting pacemaker activity in Aplysia neurons: voltage-clamp analysis of effects on calcium currents

August 1988


14 Reads

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)

FIG. 4. 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. 
FIG. 5. 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. 
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Inositol-1,4,5-Trisphosphate Receptor-Mediated Ca Mobilization Is Not Required for Cerebellar Long-Term Depression in Reduced Preparations

January 1999


42 Reads

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.

Opioid Receptor Activation Inhibits GABAergic Inputs to Basolateral Amygdala Neurons Through Kv1.1/1.2 Channels

May 2006


81 Reads

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.

5-HT and dopamine modulates Ca(V)1.3 calcium channels involved in postinhibitory rebound in the spinal network for locomotion in lamprey

March 2011


48 Reads

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.

FIG. 1. Photomontage of a coronal section through the brain corresponding to bregma 3.14 mm, showing electrode penetration through the cortex and hippocampus, with termination (asterisk) and lesioning in the ventral posterolateral (VPL) nucleus of the thalamus (A). Two-dimensional distribution of 10 histologically identified recording sites plotted on a schematic diagram (Paxinos and Watson 1998) of the ventrobasal complex of the thalamus, which delineates the posterior nucleus group (Po), ventral posteromedial nucleus (VPM), and VPL. Units from intact (circles), spinal cord contusion injury (SCI) (squares), and SCI antisense (AS) (triangles) groups are shown. All units used in this analysis were confined to the VPL.
ISI burst analysis
Alterations in Burst Firing of Thalamic VPL Neurons and Reversal by Na v 1.3 Antisense After Spinal Cord Injury

July 2006


47 Reads

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.

Table 1 . LER model fit comparison Fit LER Prediction LER 
Table 2 . WT and F1449V kinetics comparison WT F1449V 
Table 3 . WT and F1449V parameters comparison WT F1449V 
Fig. 5. 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. 
Fig. 6. 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. 
Kinetic modeling of Na(v)1.7 provides insight into erythromelalgia-associated F1449V mutation

February 2011


199 Reads

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.

FIG. 1. 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.  
FIG. 2. 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).  
FIG. 5. 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.  
FIG. 6. 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.  
Fox MD, Zhang D, Snyder AZ, Raichle ME. The global signal and observed anticorrelated resting state brain networks. J Neurophysiol 101: 3270-3283

May 2009


1,137 Reads

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.

Yan H, Li Q, Fleming RL, Madison RD, Wilson WA, Swartzwelder HS. Developmental sensitivity of hippocampal interneurons to ethanol: involvement of the hyperpolarization-activated current, Ih. J Neurophysiol 101: 67-83

November 2008


110 Reads

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.

Sun QQ, Zhang Z, Jiao Y, Zhang C, Szabo G, Erdelyi F. Differential metabotropic glutamate receptor expression and modulation in two neocortical inhibitory networks. J Neurophysiol 101: 2679-2692

March 2009


219 Reads

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.

Fig. 1. 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. 
Fig. 6. 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
Herman MA, Gillis RA, Vicini S, Dretchen KL, Sahibzada N. Tonic GABAA receptor conductance in medial subnucleus of the tractus solitarius neurons is inhibited by activation of mu-opioid receptors. J Neurophysiol 107: 1022-1031

November 2011


33 Reads

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.

Hypertension Induced by Angiotensin II and a High Salt Diet Involves Reduced SK Current and Increased Excitability of RVLM Projecting PVN Neurons. (vol 104, pg 2329, 2010)

November 2010


24 Reads

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.

FIG. 2. 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.  
FIG. 3. 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).
FIG. 4. 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.  
Congar P, Bergevin A, Trudeau LE. D2 receptors inhibit the secretory process downstream from calcium influx in dopaminergic neurons: implication of K+ channels. J Neurophysiol 87: 1046-1056

March 2002


87 Reads

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.

Fig. 1. 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 
Fig. 3. 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. 
Fig. 5. 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. 
TRPC1 contributes to light-touch sensation and mechanical responses in low-threshold cutaneous sensory neurons. J Neurophysiol 107:913-922

November 2011


1,287 Reads

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.

Fig. 4. 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. 
Fig. 5. 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). 
Fig. 6. 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. 
Herr NR, Park J, McElligott ZA, Belle AM, Carelli RM, Wightman RM. In vivo voltammetry monitoring of electrically evoked extracellular norepinephrine in subregions of the bed nucleus of the stria terminalis. J Neurophysiol 107: 1731-1737

December 2011


93 Reads

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.

Conditional modeling and the jitter method of spike resampling. Journal of Neurophysiology, 107, 517-531

January 2012


72 Reads

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.

Tokita K, Yamamoto T, Boughter JD. Gustatory neural responses to umami stimuli in the parabrachial nucleus of C57BL/6J mice. J Neurophysiol 107: 1545-1555

December 2011


35 Reads

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.

Jung, R., Kimmel, T. & Cohen, A. H. Dynamical behavior of a neural network model of locomotor control in the lamprey. J. Neurophysiol. 75, 1074-1086

April 1996


20 Reads

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

Stark, E, Koos, T and Buzsáki, G. Diode probes for spatiotemporal optical control of multiple neurons in freely moving animals. J Neurophysiol 108: 349-363

April 2012


1,492 Reads

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.

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