It has been reported that the frequency modulation (FM) or FM direction sensitivity and forward masking of central auditory neurons are related with the neural inhibition, but there are some arguments, because no direct evidence of inhibitory synaptic input was obtained in previous studies using extracellular recording. In the present study, we studied the relation between FM direction sensitivity and forward masking of the inferior collicular (IC) neurons using in vivo intracellular recordings in 20 Mus musculus Km mice. Thirty seven with complete data among 93 neurons were analyzed and discussed. There was an inhibitory area which consisted of inhibitory postsynaptic potentials (IPSP) at high frequency side of frequency tuning of up-sweep FM (FMU) sensitive neurons (n = 12) and at low frequency side of frequency tuning of down-sweep FM (FMD) selective neurons (n = 8), while there was no any inhibitory area at both sides of frequency tuning of non-FM sweep direction (FMN) sensitive neurons (n = 17). Therefore, these results show that the inhibitory area at low or high frequency side of frequency tuning is one of the mechanisms for forming FM sweep direction sensitivity of IC neurons. By comparison of forward masking produced by FMU and FMD sound stimuli in FMU, FMD and FMN neurons, the selective FM sounds could produce stronger forward masking than the non-selective in FMU and FMD neurons, while there was no forward masking difference between FMU and FMD stimuli in the FMN neurons. We suggest that the post-action potential IPSP is a potential mechanism for producing stronger forward masking in FMU and FMD neurons.
Acoustic Stimulation ; Action Potentials ; Animals ; Inferior Colliculi ; cytology ; Inhibitory Postsynaptic Potentials ; Mice ; Neurons ; cytology

Experiments were performed to study the voltage-dependence of miniature inhibitory postsynaptic current (mIPSC) frequency and amplitude using patch-clamp technique with whole cell recording in optic tectal slices of Xenopus. The following results have been observed. (1) When the membrane potentials of a neuron were depolarized or hyperpolarized stepwise from a resting potential via recording pipette to inject a DC current, the frequency and/or amplitude of mIPSCs increased or decreased respectively. The frequency of mIPSCs increased gradually with depolarizing membrane potential and it attained to the maximum as the membrane potential was held at +10 mV. (2) The amplitude increased slightly as the neuron was depolarized. When the depolarization of membrane potential reached -30 or -40 mV, the amplitudes of mIPSCs were maximal. Further depolarization resulted in a decrease of amplitude. Meanwhile, the large mIPSCs appeared when the membrane potential depolarized to a range between -20 mV and +10 mV. (3) With Ca(2+)-free bath solution, the frequency and amplitude of mIPSCs also increased stepwise progressively on depolarization of membrane potential, but the increase was less marked as corresponding value in normal saline perfusion. (4) When the [K(+)](o) in bath solution increased, the frequency of mIPSCs decreased markedly and the amplitude of mIPSCs decreased slightly. If the external K(+) concentration increased further to higher than 20 mmol/L, the neuron produced a marked slow inward or outward membrane current. The possible mechanism underlying the voltage-dependence of mIPSC frequency and amplitude is discussed briefly.
Animals ; Brain ; cytology ; physiology ; Inhibitory Postsynaptic Potentials ; physiology ; Membrane Potentials ; physiology ; Miniature Postsynaptic Potentials ; physiology ; Neurons ; physiology ; Patch-Clamp Techniques ; Potassium Channels, Voltage-Gated ; physiology ; Xenopus

PURPOSE: Modafinil is a wake-promoting agent that has been proposed to improve cognitive performance at the preclinical and clinical levels. Since there is insufficient evidence for modafinil to be regarded as a cognitive enhancer, the aim of this study was to investigate the effects of chronic modafinil administration on behavioral learning in healthy adult rats. METHODS: Y-maze training was used to assess learning performance, and the whole-cell patch clamp technique was used to assess synaptic transmission in pyramidal neurons of the hippocampal CA1 region of rats. RESULTS: Intraperitoneal administration of modafinil at 200 mg/kg or 300 mg/kg significantly improved learning performance. Furthermore, perfusion with 1mM modafinil enhanced the frequency and amplitude of spontaneous postsynaptic currents and spontaneous excitatory postsynaptic currents in CA1 pyramidal neurons in hippocampal slices. However, the frequency and amplitude of spontaneous inhibitory postsynaptic currents in CA1 pyramidal neurons were inhibited by treatment with 1mM modafinil. CONCLUSIONS: These results indicate that modafinil improves learning and memory in rats possibly by enhancing glutamatergic excitatory synaptic transmission and inhibiting GABAergic (gamma-aminobutyric acid-ergic) inhibitory synaptic transmission.
Adult ; Animals ; CA1 Region, Hippocampal ; Excitatory Postsynaptic Potentials ; Humans ; Inhibitory Postsynaptic Potentials ; Learning* ; Memory ; Neurons ; Perfusion ; Rats* ; Synaptic Potentials ; Synaptic Transmission*

Isoliquiritigenin (ILTG) is a chalcone compound and shows various pharmacological properties, including antioxidant and anti-inflammatory activities. In recent study, we have reported a novel role of ILTG in sleep through a positive allosteric modulation of gamma-aminobutyric acid type A (GABA(A))-benzodiazepine (BZD) receptors. However, the effect of ILTG in GABA(A)R-mediated synaptic response in brain has not been tested yet. Here we report that ILTG significantly prolonged the decay of spontaneous inhibitory postsynaptic currents (sIPSCs) mediated by GABA(A)R in mouse hippocampal CA1 pyramidal neurons without affecting amplitude and frequency of sIPSCs. This enhancement was fully inhibited by flumazenil (FLU), a specific GABA(A)-BZD receptor antagonist. These results suggest a potential role of ILTG as a modulator of GABAergic synaptic transmission.
Animals ; Brain ; Chalcone* ; Flumazenil ; gamma-Aminobutyric Acid ; Inhibitory Postsynaptic Potentials ; Mice ; Neurons ; Synaptic Transmission

Previous studies have suggested that brain stem noradrenergic inputs differentially modulate neurons in the paraventricular nucleus (PVN). Here, we compared the effects of norepinephrine (NE) on spontaneous GABAergic inhibitory postsynaptic currents (sIPSCs) in identified PVN neurons using slice patch technique. In 17 of 18 type I neurons, NE (30-100microM) reversibly decreased sIPSC frequency to 41+/-7% of the baseline value (4.4+/-0.8 Hz, p<0.001). This effect was blocked by yohimbine (2-20microM), an alpha2-adrenoceptor antagonist and mimicked by clonidine (50 microM), an alpha2-adrenoceptor agonist. In contrast, NE increased sIPSC frequency to 248+/-32% of the control (3.06+/-0.37 Hz, p<0.001) in 31 of 54 type II neurons, but decreased the frequency to 41+/-7% of the control (5.5+/-1.3 Hz) in the rest of type II neurons (p<0.001). In both types of PVN neurons, NE did not affect the mean amplitude and decay time constant of sIPSCs. In addition, membrane input resistance and amplitude of sIPSC of type I neurons were larger than those of type II neurons tested (1209 vs. 736 M omega, p<0.001; 110 vs. 81 pS, p<0.001). The results suggest that noradrenergic modulation of inhibitory synaptic transmission in the PVN decreases the neuronal excitability in most type I neurons via alpha2-adrenoceptor, however, either increases in about 60% or decreases in 40% of type II neurons.
Brain Stem ; Clonidine ; Inhibitory Postsynaptic Potentials* ; Membranes ; Neurons ; Norepinephrine ; Paraventricular Hypothalamic Nucleus* ; Synaptic Transmission ; Yohimbine

Gamma-aminobutyric acid (GABA)-ergic inhibition is important in the function of the visual cortex. In a previous study, we reported a developmental increase in GABAA receptor-mediated inhibition in the rat visual cortex from 3 to 5 weeks of age. Because this developmental increase is crucial to the regulation of the induction of long-term synaptic plasticity, in the present study we investigated in detail the postnatal development of phasic and tonic inhibition. The amplitude of phasic inhibition evoked by electrical stimulation increased during development from 3 to 8 weeks of age, and the peak time and decay kinetics of inhibitory postsynaptic potential (IPSP) and current (IPSC) slowed progressively. Since the membrane time constant decreased during this period, passive membrane properties might not be involved in the kinetic changes of IPSP and IPSC. Tonic inhibition, another mode of GABAA receptor-mediated inhibition, also increased developmentally and reached a plateau at 5 weeks of age. These results indicate that the time course of the postnatal development of GABAergic inhibition matched well that of the functional maturation of the visual cortex. Thus, the present study provides significant insight into the roles of inhibitory development in the functional maturation of the visual cortical circuits.
Animals ; Electric Stimulation ; gamma-Aminobutyric Acid ; Inhibitory Postsynaptic Potentials ; Kinetics ; Membranes ; Plastics ; Rats ; Visual Cortex

The effects of Zn2+ on spontaneous glutamate and GABA release were tested in mechanically dissociated rat CA3 pyramidal neurons which retained functional presynaptic nerve terminals. The spontaneous miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs, respectively) were pharmacologically isolated and recorded using whole-cell patch clamp technique under voltage-clamp conditions. Zn2+ at a lower concentration (30 micrometer) increased GABAergic mIPSC frequency without affecting mIPSC amplitude, but it decreased both mIPSC frequency and amplitude at higher concentrations (> or =300 micrometer). In contrast, Zn2+ (3 to 100 micrometer) did not affect glutamatergic mEPSCs, although it slightly decreased both mIPSC frequency and amplitude at 300 micrometer concentration. Facilitatory effect of Zn2+ on GABAergic mIPSC frequency was occluded either in Ca2+ -free external solution or in the presence of 100 micrometer 4-aminopyridine, a non-selective K+ channel blocker. The results suggest that Zn2+ at lower concentrations depolarizes GABAergic nerve terminals by blocking K+ channels and increases the probability of spontaneous GABA release. This Zn2+ -mediated modulation of spontaneous GABAergic transmission is likely to play an important role in the regulation of neuronal excitability within the hippocampal CA3 area.
4-Aminopyridine ; Animals ; gamma-Aminobutyric Acid* ; Glutamic Acid ; Hippocampus ; Inhibitory Postsynaptic Potentials ; Neurons* ; Rats* ; Zinc*

OBJECTIVETo observe the microstructure of the cell membrane of epileptic neurons using atomic force microscopy (AFM).

METHODSModel of epileptic neurons was established by subjecting the neurons culture for 14 days in vitro to magnesium-free media treatment for 3 h. Patch clamp technique was applied to record the electrophysiological activity of the epileptic neurons. AFM was performed to observe and measure the microstructure of the cell membrane of the epileptic neuron.

RESULTSAfter a 3-hour treatment with magnesium-free media, the epileptic neurons displayed sustained epileptiform discharge, which continued after the neurons were returned to normal medium culture on day 14. Under AFM scanning size of 80 microm x 80 microm and 2 microm x 2 microm, no obvious difference in the morphology of the cell membrane was noted between epileptic and normal neurons; under the scanning size of 500 nm x 500 nm, small pits occurred in the cell membrane in both groups, but no significant difference was found in the dimension of the pits between the two groups (the diameter and depth of the pits was 114.86-/+9.33 nm and 5.71-/+0.69 nm in epileptic neurons, and 116.4-/+9.13 nm and 5.69-/+0.71 nm in the control neurons, respectively, P>0.05).

CONCLUSIONAFM provides a new method for observing neuronal membrane microstructure at nanometer resolutions. No significant alterations occur in the membrane of the neurons after a 3-hour magnesium-free media treatment.

Cell Membrane ; ultrastructure ; Cells, Cultured ; Culture Media ; Epilepsy ; pathology ; Excitatory Postsynaptic Potentials ; Inhibitory Postsynaptic Potentials ; Magnesium ; Microscopy, Atomic Force ; Neurons ; ultrastructure ; Patch-Clamp Techniques

Using whole cell current- and voltage-clamp recording we investigated the characteristics and pharmacology of group I metabotropic glutamate receptor (mGluR)-mediated responses in rat medial vestibular nucleus (MVN) neurons. In current clamp conditions, activation of mGluR I by application of the group I mGluR agonist (R,S)-3,5-dihydroxyphenylglycine (DHPG) induced a direct excitation of MVN neurons that is characterized by depolarization and increased spontaneous firing frequency. To identify which of mGluR subtypes are responsible for the various actions of DHPG in MVN, we used two subtype-selective antagonists. (S)-(+)-alpha-amino-a-methylbenzeneacetic acid (LY367385) is a potent competitive antagonist that is selective for mGluR1, whereas 2-methyl-6-(phenylethynyl)-pyridine (MPEP) is a potent noncompetitive antagonist that is selective for mGluR5. In voltage clamp conditions, DHPG application increased the frequency of spontaneous and miniature inhibitory postsynaptic currents (IPSCs) but had no effect on amplitude distributions. Antagonism of the DHPG-induced increase of miniature IPSCs required the blockade of both mGluR1 and mGluR5. DHPG application induced an inward current, which can be enhanced under depolarized conditions. DHPG-induced current was blocked by LY367385, but not by MPEP. Both LY367385 and MPEP antagonized the DHPG-induced suppression of the calcium activated potassium current (IAHP). These data suggest that mGluR1 and mGluR5 have similar roles in the regulation of the excitability of MVN neurons, and show a little distinct. Furthermore, mGluR I, via pre- and postsynaptic actions, have the potential to modulate the functions of the MVN.
Animals ; Benzoates ; Calcium ; Fires ; Glycine ; Inhibitory Postsynaptic Potentials ; Methoxyhydroxyphenylglycol ; Neurons ; Potassium ; Rats ; Receptors, Metabotropic Glutamate ; Vestibular Nuclei

BACKGROUND: gamma-Aminobutyric acid (GABA), the principal inhibitory neurotransmitter, activates persistent low amplitude tonic currents in several brain regions, in addition to conventional synaptic currents. Tonic conductance is highly sensitive to low concentrations of volatile anesthetics and therefore might contribute to amnestic properties. We compared the properties of GABAergic tonic currents mediated by sedative-amnestic midazolam and anesthetic propofol in rat hippocampal neurons. METHODS: Patch clamp techniques were used to characterize the GABAergic currents recorded in CA1 pyramidal neurons in rat hippocampal slices. The amplitude of the tonic currents and the decay of miniature inhibitory postsynaptic currents (mIPSCs) were measured after administration of midazolam or propofol. RESULTS: Both midazolam and propofol caused concentration dependent increases in the tonic currents. The enhancement of the tonic currents by midazolam concentrations of greater than 0.5 microM caused no further increase in current amplitude. Propofol continued to increase with concentrations over the range tested (0.1-10 microM). Low concentrations of midazolam 0.01 microM and propofol 0.5 microM selectively enhanced the tonic currents but failed to alter mIPSCs. CONCLUSIONS: Low concentrations of midazolam and propofol selectively enhanced the tonic currents but not synaptic currents of rat hippocampal pyramidal neurons. Unlike midazolam, the response to propofol did not become saturated and had a greater effect on the tonic currents.
Anesthetics ; Animals ; Brain ; gamma-Aminobutyric Acid ; Hippocampus ; Inhibitory Postsynaptic Potentials ; Midazolam ; Neurons ; Neurotransmitter Agents ; Patch-Clamp Techniques ; Propofol ; Rats