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ABSTRACT: Sodium salicylate (NaSal), an aspirin metabolite, can cause tinnitus in animals and human subjects. To explore neural mechanisms underlying salicylate-induced tinnitus, we examined effects of NaSal on neural activities of the medial geniculate body (MGB), an auditory thalamic nucleus that provides the primary and immediate inputs to the auditory cortex, by using the whole-cell patch-clamp recording technique in MGB slices. Rats treated with NaSal (350 mg/kg) showed tinnitus-like behavior as revealed by the gap prepulse inhibition of acoustic startle (GPIAS) paradigm. NaSal (1.4 mM) decreased the membrane input resistance, hyperpolarized the resting membrane potential, suppressed current-evoked firing, changed the action potential, and depressed rebound depolarization in MGB neurons. NaSal also reduced the excitatory and inhibitory postsynaptic response in the MGB evoked by stimulating the brachium of the inferior colliculus. Our results demonstrate that NaSal alters neuronal intrinsic properties and reduces the synaptic transmission of the MGB, which may cause abnormal thalamic outputs to the auditory cortex and contribute to NaSal-induced tinnitus.
PLoS ONE 01/2012; 7(10):e46969. · 4.09 Impact Factor
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28th Politzer Society Meeting; 09/2011
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ABSTRACT: The medial geniculate body (MGB) receives ascending inputs from the inferior colliculus and descending inputs from the auditory cortex. In the present study, we intended to determine whether activation of presynaptic GABA(B) receptors modulates GABAergic and glutamatergic inputs to the MGB with whole-cell patch-clamp recordings in brain slices of the rat. To evoke a synaptic response, we electrically stimulated the ascending and descending inputs to MGB neurons with bipolar electrodes placed on the brachium of the inferior colliculus and the superior thalamic radiation. To isolate presynaptic mechanisms, we blocked the effects of postsynaptic GABA(B) receptors by filling recording electrodes with the internal solution containing cesium and QX-314. The activation of presynaptic GABA(B) receptors by exogenous agonist was shown to modulate synaptic inputs to the MGB as demonstrated by that (1) baclofen, a GABA(B) receptor agonist, reversibly suppressed both inhibitory postsynaptic currents (IPSCs) and excitatory postsynaptic currents (EPSCs) and this suppressive effect could be blocked by CGP35348, a GABA(B) receptor antagonist, (2) baclofen significantly increased the ratio of IPSCs or EPSCs elicited by paired-pulse stimulation, and (3) baclofen depressed EPSCs and IPSCs in response to repetitive stimulation. The activation of presynaptic GABA(B) receptors by endogenously released GABA was shown to modulate the synaptic transmission as demonstrated by that CGP55845, another GABA(B) receptor antagonist, increased the ratio of IPSCs to paired-pulse stimulation in young (P8-10) rats, although not in juvenile (P15-18) rats. Our study provides electrophysiological evidence for the presence of functional presynaptic GABA(B) receptors in the MGB and suggests an age-dependent role of these receptors in the synaptic transmission in this central auditory region.
Hearing research 05/2011; 280(1-2):157-65. · 2.18 Impact Factor
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ABSTRACT: Spatiotemporal variation in the species composition, relative abundance, and plant use by cicada nymphs were studied among continuous and fragmented forests and human-modified forestry plantations upon an uplifted reef-karst substrate in tropical East Asia. Nymphal emergence was concentrated in the rainy season but tended to begin earlier, end later, or both, on plantations. Species abundances fluctuated over time and among the types of forests, with greater variation in plantations and fragmented forests. Seven cicada species were present, but the overall similarity in species composition was low among the forest types. Higher mean numbers of species and mean abundances occurred on plantations than in fragmented and continuous forests, but the species heterogeneity was higher in continuous forests and lowest on plantations. Exuviae were found at various heights that were correlated positively with the abundance of exuviae and negatively with the diameter at breast height of trees, whereas coefficients of variation in the height distribution among trees were not correlated with the abundance of exuviae. The plant-use breadth was widest in the cicadas Chremistica ochracea (Walker) and narrowest in Cryptotympana takasagona Kato, Platypleura takasagona Matsumura, and Euterpnosia koshunensis Kato, with the other species intermediate, corresponding with their relative abundance. Among-species overlap was generally higher in the continuous forests but declined in forest fragments and plantations. Our results indicated that fragmenting tropical primary forests and creating plantations may generate higher richness and abundance of annual cicadas, but risk the loss of rare or endemic species that show a greater preference for tree species of the primary forests.
Annals of the Entomological Society of America 02/2010; 103(2):216-226. · 1.32 Impact Factor
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ABSTRACT: Fast glutamatergic and GABAergic transmission in the central nucleus of the inferior colliculus (ICC), a major auditory midbrain structure, is mediated respectively by alpha-amino-3-hydroxy-5-methylisoxazole-4 propionic acid (AMPA) and gamma-aminobutyric acid (GABA)(A) receptors. In this study, we used whole-cell patch clamp recordings in brain slices to investigate the effects of activation of metabotropic glutamate receptors (mGluRs) on synaptic responses mediated by AMPA and GABA(A) receptors in ICC neurons of young rats. Excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) mediated respectively by AMPA and GABA(A) receptors were elicited by stimulation of the lateral lemniscus, the major afferent pathway to the ICC. The agonists for groups I and II mGluRs, (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD), and for group III mGluRs, L-2-amino-3-hydroxypropanoic acid 3-phosphate (L-SOP), did not affect intrinsic membrane properties of the ICC neurons. The agonist for group II mGluRs, (1R,4R,5S,6R)-4-amino-2-oxabicyclo[3.1.0] hexane-4,6-dicarboxylic acid (LY379268), significantly reduced the AMPA receptor-mediated EPSCs and GABA(A) receptor-mediated IPSCs. The effects were reversed by the group II mGluR antagonist, (2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495). The agonists for groups I and III, (RS)-3,5-dihydroxyphenylglycine (DHPG) and L-SOP, respectively, did not affect AMPA or GABA(A) receptor-mediated responses. The reduction of the synaptic responses by LY379268 was accompanied by a substantial increase in a ratio of the second to the first AMPA receptor-mediated EPSCs and GABA(A) receptor-mediated IPSCs to paired-pulse stimulation. The results suggest that group II mGluRs regulate both fast glutamatergic and GABAergic synaptic transmission in the ICC, probably through a presynaptic mechanism due to reduction of transmitter release.
Brain research 02/2010; 1325:28-40. · 2.46 Impact Factor
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ABSTRACT: The inferior colliculus (IC) is a major center for neural integration in the auditory pathway. The IC processes inputs from the lower brainstem as well as from higher centers in the auditory system. To understand cellular mechanisms of IC neurons in auditory processing, we investigated physiological characteristics of the rebound depolarization (RD) following membrane hyperpolarization in neurons of the rat's dorsal cortex of the inferior colliculus (ICD). Whole-cell patch clamp recordings were made from ICD neurons in brain slices. In more than half of the ICD neurons, there was a RD accompanied by one or two anode break action potentials (APs) following membrane hyperpolarization. The RD was Ca(2+) mediated and primarily due to activation of low-threshold T-type Ca(2+) channels. Generation of the RD and anode break APs depended on the magnitude and duration of the preceding hyperpolarization. Larger and longer hyperpolarization induced a larger, shorter and faster rebound, and therefore earlier anode break APs. However, with further hyperpolarization the RD became constant in amplitude and duration despite increases in the strength or duration of the preceding hyperpolarization. Usually, membrane hyperpolarization as small as -15 mV for 100-200 ms was enough to induce a pronounced rebound of 15-20 mV. The RD in IC neurons may provide a neuronal mechanism for integrating excitatory inputs arriving soon after a period of synaptic inhibition and therefore processing specific aspects of auditory information.
Brain Research 07/2008; 1226:70-81. · 2.73 Impact Factor
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ABSTRACT: The diversity and spatiotemporal variation of avifauna in different settings of tropical coral reef-karst forests on the Hengchun Peninsula, Taiwan, were examined. The short-term effects on bird assemblages following two typhoons that severely impacted Hengchun were investigated. Line-transect census recorded 46 species of birds, dominated by forest-associated gleaning insectivores or omnivores, and 13% of the endemics of Taiwan. Prior to the typhoons, the continuous-canopy forest was close to the open forest setting in species evenness, but the species heterogeneity was lower and more variable. The continuous-canopy and open forests differed in overall avian composition, whereas two continuous-canopy forest settings were similar in composition. Typhoons did not significantly lower the mean numbers of either species or birds, nor affect the pattern of their spatial distribution in the forest settings. However, they did increase similarities in the species composition between the open and continuous-canopy settings, and caused a decrease in the similarity between forest edges and interiors. Overall, typhoons affected species composition more in the continuous-canopy forests than in the open setting, and more in interiors than in forest edges. This pattern corresponded to an increase in the species heterogeneity and species evenness in the forest interiors, indicating movements of birds from the edge toward the interior. Among different functional groups, gleaning omnivores tended to retain a pattern of higher abundance in the open forest setting than in the continuous-canopy forests, whereas the abundances of gleaning insectivores and cavity-nesting frugivores tended to decline in the latter or both settings.
ZOOLOGICAL SCIENCE 07/2008; 25(6):593-603. · 0.95 Impact Factor
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ABSTRACT: We investigated the composition, diversity, and patterns of spatial use of an anuran community following a wetland restoration project in a managed tropical monsoon forest in southern Taiwan. Anurans comprising eight species in seven genera and four families reached a mean density of 0.025+/-0.004 anurans m(-2) within a year. The three most important species in terms of frequency of occurrence and relative abundance all had an early appearance; only the most abundant Fejervarya limnocharis (62.2% of total accounts), however, remained present throughout the entire year. The distribution of anurans observed among habitat zones was non-random, with most records occurring in densely planted (42.8%) and running-water (23.9%) zones, and the fewest in a buffer zone adjacent to a paved road. Mean numbers of anurans were correlated with the mean percent vegetation cover among individually divided small pools. Microhyla ornate, M. heymonsi, Polypedates megacephalus, and F. limnocharis appeared to be more heterogeneous in their use of space than Buergeria japonicus. Species differed in their most frequently used habitat zones within the wetland site, with the pairs F. limnocharis and P. megacephalus, and M. ornate and Bufo melanostictus, exhibiting similar respective distributions among zones. Our study demonstrates the value of even a small, isolated wetland in contributing to and maintaining regional amphibian diversity. Patterns of spatial relationships of this anuran community have important implications for the conservation of local populations across species.
ZOOLOGICAL SCIENCE 11/2006; 23(10):883-91. · 0.95 Impact Factor
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ABSTRACT: Whole-cell patch clamp recordings were made from ICC neurons in brain slices of 9-16 day old rats. Postsynaptic currents were evoked by electrical stimulation of the lemniscal inputs. Excitatory postsynaptic currents (EPSCs) were isolated pharmacologically by blocking GABA(A) and glycine receptors. EPSCs were further dissected into AMPA and NMDA receptor-mediated responses by adding the receptor antagonists, APV and CNQX, respectively. The internal solution in the recording electrodes contained CsF and TEA to block K(+) channels that might be activated by postsynaptic GABA(B) receptors. The modulatory effects of GABA(B) receptors on EPSCs in ICC neurons were examined by bath application of the GABA(B) receptor agonist, baclofen, and the antagonist, CGP 35348. The amplitudes of EPSCs in ICC neurons were reduced to 34.4+/-3.2% of the control by baclofen (5-10 microM). The suppressive effect by baclofen was concentration-dependent. The reduction of the EPSC amplitude was reversed by CGP35348. The ratio of the 2nd to 1st EPSCs evoked by paired-pulse stimulation was significantly increased after application of baclofen. These results suggest that glutamatergic excitation in the ICC can be modulated by presynaptic GABA(B) receptors. In addition, baclofen reduced NMDA EPSCs more than AMPA EPSCs. The GABA(B) receptor-mediated modulation of glutamatergic excitation in the ICC provides a likely mechanism for preventing overstimulation and/or regulating the balance of excitation and inhibition involved in processing auditory information.
Neuroscience Letters 06/2006; 399(1-2):151-6. · 2.11 Impact Factor
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ABSTRACT: The synaptic pharmacology of the ventral nucleus of the lateral lemniscus (VNLL) was investigated in brain slices obtained from rats of 14-37 days old using intracellular recording techniques. Excitatory and inhibitory synaptic potentials (EPSPs and IPSPs) were elicited by electrical stimulation of the lemniscal pathway and recorded from neurons with five types of intrinsic firing patterns (onset, pause, adapting, regular and bursting types). Synaptic receptors that mediated the EPSPs and IPSPs were identified using AMPA, NMDA, GABA(A) and glycine receptor antagonists. The early/short EPSPs were mediated by AMPA receptors. The late/long EPSPs, encountered only in neurons of younger animals, were mediated by NMDA receptors. The IPSPs in most neurons were mediated by glycine receptors. In some neurons the IPSPs were mediated by GABA(A) receptors or both glycine and GABA(A) receptors. The temporal dynamics of fast AMPA EPSPs and glycinergic IPSPs were very similar. AMPA EPSPs and glycinergic (and/or GABAergic) IPSPs could be encountered in a single neuron. The results suggest that the VNLL not only relays incoming signals rapidly from the lower brainstem to the inferior colliculus, but also integrates excitatory and inhibitory inputs to modify and process auditory information.
Hearing Research 06/2005; 203(1-2):159-71. · 2.70 Impact Factor
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ABSTRACT: The central nucleus of the inferior colliculus (ICC) is a major site of synaptic interaction in the central auditory system. To understand how ICC neurons integrate excitatory and inhibitory inputs for processing temporal information, we examined postsynaptic responses of ICC neurons to repetitive stimulation of the lateral lemniscus at 10-100 Hz in rat brain slices. The excitatory synaptic currents mediated by AMPA and NMDA receptors and the inhibitory current mediated by GABA(A) receptors were pharmacologically isolated and recorded by whole-cell patch-clamp techniques. The response kinetics of AMPA receptor-mediated EPSCs and GABA(A) receptor-mediated IPSCs were similar and much faster than those of NMDA receptor-mediated EPSCs. AMPA EPSCs could follow each pulse of stimulation at a rate of 10-100 Hz but showed response depression during the course of repetitive stimulation. GABA(A) IPSCs could also follow stimulus pulses over this frequency range but showed depression at low rates and facilitation at higher rates. NMDA EPSCs showed facilitation and temporal summation in response to repetitive stimulation, which was most pronounced at higher rates of stimulation. GABA(A) inhibition suppressed activation of NMDA receptors and reduced both the degree of AMPA EPSC depression and the extent of temporal summation of NMDA EPSCs. The results indicate that GABA(A) receptor-mediated inhibition plays a crucial role in maintaining the balance of excitation and inhibition and in allowing ICC neurons to process temporal information more precisely.
Journal of Neuroscience 06/2004; 24(19):4625-34. · 7.11 Impact Factor
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ABSTRACT: The role of potassium channels in regulating spontaneous firing and sound-evoked responses in the central nucleus of the inferior colliculus was studied by recording single-unit activity before and during iontophoretic application of a nonspecific potassium channel blocker, tetraethylammonium (TEA). Tone bursts and sinusoidal amplitude-modulated tones were used to evoke auditory responses. Our results show that release of TEA increased the width of spikes for all neurons tested. There was an increase in spontaneous firing for most of the neurons. There was also an increase in responses to tone bursts for most of the neurons, although in some cases there was a reduction in the evoked responses. TEA also increased the firing rate in responses to sinusoidal amplitude-modulated sounds in the majority of the neurons tested. For some neurons, the change in firing reduced the selectivity of responses for particular rates of modulation. There was also a reduction in the synchrony of action potentials to the modulation envelope in many cells. Our results show that potassium channels are important for regulating the strength of sound-evoked responses and the level of spontaneous activity, and determining the temporal properties of responses to amplitude-modulated sounds.
Journal of Neurophysiology 06/2004; 91(5):2194-204. · 3.32 Impact Factor
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ABSTRACT: Whole-cell patch clamp recordings were made from neurons in the central nucleus of the inferior colliculus (ICC) in brain slices from rat (8-13 days old). ICC neurons were classified by their discharge pattern in response to depolarizing and hyperpolarizing current injection. Excitatory postsynaptic currents (EPSCs) were elicited by stimulation of synaptic inputs under the condition that the synaptic inhibition was suppressed by strychnine and picrotoxin. EPSCs in all tested types of ICC neurons showed posttetanic, long-term potentiation (LTP) and long-term depression with tetanic stimulation. The potentiated EPSCs consisted of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor and NMDA receptor mediated components. The magnitude of LTP was larger when the intracellular concentration of the calcium buffer ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetracetic acid (EGTA) was lower and stimulation frequency was higher in cells with rebound firing patterns. Blocking N-methyl-D-aspartate (NMDA) receptors in rebound cells prevented generation of LTP. These results suggest that excitatory synaptic transmission in ICC neurons can be modified. LTP in the auditory midbrain may be important for activity-dependent, adaptive changes in response to normal and pathological stimulus conditions.
Hearing Research 07/2002; 168(1-2):43-54. · 2.70 Impact Factor
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ABSTRACT: The synaptic mechanisms underlying excitation in the rat's central nucleus of the inferior colliculus (ICC) were examined by making whole-cell patch clamp recordings in brain slice preparations of the auditory midbrain. Responses were elicited by current pulse stimulation of the lateral lemniscus and recordings were made in ICC using either current clamp or voltage clamp methods. The excitatory postsynaptic responses in either current or voltage clamp mode consisted of two distinct components, an early component that could be blocked by bath application of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), and a later component that could be blocked by application of the N-methyl-D-aspartate (NMDA) receptor antagonists, (+/-)-2-amino-5-phosphonovaleric acid (APV) or (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP). Both AMPA and NMDA receptor-mediated responses were present at resting potential and could be isolated pharmacologically by application of receptor antagonists. Voltage clamp experiments revealed that the NMDA receptor-mediated current was voltage-dependent and increased in magnitude as the cell membrane was depolarized. This NMDA receptor-mediated response was enhanced at resting potential when Mg(2+) was eliminated from the bath solution. The ratio of response amplitudes associated with the late and early components, an estimate of the relative contribution of NMDA and AMPA receptor types, changed with age. There was a progressive decline in the ratio between 9 and 13 days of age, but no further reduction between days 13 and 16. The data show that both AMPA and NMDA receptors are important for determining excitatory responses in the ICC and that both receptor types probably play a role in auditory processing after the onset of hearing.
Hearing Research 07/2002; 168(1-2):25-34. · 2.70 Impact Factor
