Botulinum toxin type A enhances the inhibitory spontaneous postsynaptic currents on the substantia gelatinosa neurons of the subnucleus caudalis in immature mice

Botulinum toxin type A (BoNT/A) has been used therapeutically for various conditions including dystonia, cerebral palsy, wrinkle, hyperhidrosis and pain control. The substantia gelatinosa (SG) neurons of the trigeminal subnucleus caudalis (Vc) receive orofacial nociceptive information from primary afferents and transmit the information to higher brain center. Although many studies have shown the analgesic effects of BoNT/A, the effects of BoNT/A at the central nervous system and the action mechanism are not well understood. Therefore, the effects of BoNT/A on the spontaneous postsynaptic currents (sPSCs) in the SG neurons were investigated. In whole cell voltage clamp mode, the frequency of sPSCs was increased in 18 (37.5%) neurons, decreased in 5 (10.4%) neurons and not affected in 25 (52.1%) of 48 neurons tested by BoNT/A (3 nM). Similar proportions of frequency variation of sPSCs were observed in 1 and 10 nM BoNT/A and no significant differences were observed in the relative mean frequencies of sPSCs among 1–10 nM BoNT/A. BoNT/A-induced frequency increase of sPSCs was not affected by pretreated tetrodotoxin (0.5 µM). In addition, the frequency of sIPSCs in the presence of CNQX (10 µM) and AP5 (20 µM) was increased in 10 (53%) neurons, decreased in 1 (5%) neuron and not affected in 8 (42%) of 19 neurons tested by BoNT/A (3 nM). These results demonstrate that BoNT/A increases the frequency of sIPSCs on SG neurons of the Vc at least partly and can provide an evidence for rapid action of BoNT/A at the central nervous system.

Effects of Modafinil on Behavioral Learning and Hippocampal Synaptic Transmission in Rats / 대한배뇨장애요실금학회지

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.

Involvement of stress-induced hippocampal synaptic potentiation in the novelty acquisition / 生理学报

To study the influence of behavioral stress on hippocampal spatial learning and memory, we used the freely moving rats that had undergone chronic implantation of a recording electrode in the hippocampus CA1 region and a bipolar stimulating electrode in the ipsilateral Schaffer collateral-commissural pathway. The field excitatory postsynaptic potentials (fEPSPs) were recorded in the absence of exogenous induction of high-frequency stimulation (HFS) or low-frequency stimulation (LFS) and reflected the effect of stress on the hippocampal spatial learning. And we also investigated the change of hippocampal synaptic plasticity when rats were re-exposed to the same environment at 24 h after novelty acquisition. We found that exploration of a novel environment induced the hippocampal synaptic depression in the rats with stress-adaption, whereas exposure to the novel environment induced the hippocampal synaptic potentiation in the behavioral stress rats. Furthermore, re-exposure to the same environment no longer elicited the hippocampal synaptic potentiation or depression at 24 h after the first novel acquisition in the behavioral stress rats. These results demonstrate that behavioral stress induces the hippocampal synaptic potentiation under novelty acquisition and further damages the hippocampal spatial learning and memory. However, the stress can be adapted by re-exposure to the novelty and thus does not further damage the hippocampal spatial learning and memory.

Effects of human growth hormone on gonadotropin-releasing hormone neurons in mice / 소아과

PURPOSE: Recombinant human growth hormone (rhGH) has been widely used to treat short stature. However, there are some concerns that growth hormone treatment may induce skeletal maturation and early onset of puberty. In this study, we investigated whether rhGH can directly affect the neuronal activities of of gonadotropin-releasing hormone (GnRH). METHODS: We performed brain slice gramicidin-perforated current clamp recording to examine the direct membrane effects of rhGH on GnRH neurons, and a whole-cell voltage-clamp recording to examine the effects of rhGH on spontaneous postsynaptic events and holding currents in immature (postnatal days 13-21) and adult (postnatal days 42-73) mice. RESULTS: In immature mice, all 5 GnRH neurons recorded in gramicidin-perforated current clamp mode showed no membrane potential changes on application of rhGH (0.4, 1 microgram/mL). In adult GnRH neurons, 7 (78%) of 9 neurons tested showed no response to rhGH (0.2-1 microgram/mL) and 2 neurons showed slight depolarization. In 9 (90%) of 10 immature neurons tested, rhGH did not induce any membrane holding current changes or spontaneous postsynaptic currents (sPSCs). There was no change in sPSCs and holding current in 4 of 5 adult GnRH neurons. CONCLUSION: These findings demonstrate that rhGH does not directly affect the GnRH neuronal activities in our experimental model.

Effects of human growth hormone on gonadotropin-releasing hormone neurons in mice / 소아과

PURPOSE: Recombinant human growth hormone (rhGH) has been widely used to treat short stature. However, there are some concerns that growth hormone treatment may induce skeletal maturation and early onset of puberty. In this study, we investigated whether rhGH can directly affect the neuronal activities of of gonadotropin-releasing hormone (GnRH). METHODS: We performed brain slice gramicidin-perforated current clamp recording to examine the direct membrane effects of rhGH on GnRH neurons, and a whole-cell voltage-clamp recording to examine the effects of rhGH on spontaneous postsynaptic events and holding currents in immature (postnatal days 13-21) and adult (postnatal days 42-73) mice. RESULTS: In immature mice, all 5 GnRH neurons recorded in gramicidin-perforated current clamp mode showed no membrane potential changes on application of rhGH (0.4, 1 microgram/mL). In adult GnRH neurons, 7 (78%) of 9 neurons tested showed no response to rhGH (0.2-1 microgram/mL) and 2 neurons showed slight depolarization. In 9 (90%) of 10 immature neurons tested, rhGH did not induce any membrane holding current changes or spontaneous postsynaptic currents (sPSCs). There was no change in sPSCs and holding current in 4 of 5 adult GnRH neurons. CONCLUSION: These findings demonstrate that rhGH does not directly affect the GnRH neuronal activities in our experimental model.

The correlation between the effects of propofol on the auditory brainstem response and the postsynaptic currents of the auditory circuit in brainstem slices in the rat / 대한마취과학회지

BACKGROUND: Although there have been reports showing the changes of the auditory brainstem response (ABR) waves by propofol, no detailed studies have been done at the level of brainstem auditory circuit. So, we studied the effects of propofol on the postsynaptic currents of the medial nucleus of the trapezoid body (MNTB)-lateral superior olive (LSO) synapses by using the whole cell voltage clamp technique and we compared this data with that obtained by the ABR. METHODS: 5 rats at postnatal (P) 15 days were used for the study of the ABR. After inducing deep anesthesia using xylazine 6 mg/kg and ketamine 25 mg/kg, the ABRs were recorded before and after intraperitoneal propofol injection (10 mg/kg) and the effects of propofol on the latencies of the I, III, and V waves and the I-III and III-V interwave intervals were evaluated. Rats that were aged under P11 were used in the voltage clamp experiments. After making brainstem slices, the postsynaptic currents (PSCs) elicited by MNTB stimulation were recorded at the LSO, and the changes of the PSCs by the bath application of propofol (100 microM) were monitored. RESULTS: We found small, but statistically significant increases in the latencies of ABR waves III and V and the interwave intervals of I-III and III-V by propofol. However, no significant changes were observed in the glycinergic or glutamatergic PSCs of the MNTB-LSO synpases by the application of propofol (100 microM). CONCLUSIONS: Glycinergic or glutamatergic transmission of the MNTB-LSO synapses might not contribute to the propofol-induced changes of the ABR.

Involvement of protein kinase C in NMDAR-dependent long-term potentiation in rat amygdala / 生理学报

The mechanism of long-term potentiation (LTP) in basolateral amygdala (BLA) was explored using field potential recording in rat brain slice preparation. Field potentials (field excitatory post-synaptic potentials, fEPSPs) in BLA were evoked with sharpened steel bipolar stimulating electrodes placed in the external capsule (EC). Two theta burst stimulations (TBS, interval=10 min) induced LTP in BLA. TBS-induced synaptic potentiation lasted for more than 30 min after the second TBS. LTP in BLA was input-specific and was blocked by N-methyl-D-aspartate receptor (NMDAR) antagonist 2-amino-5-phosphonovaleric acid (APV). The effect of protein kinase C (PKC) on LTP was then determined using PKC inhibitor chelerythrine chloride. Bath application of chelerythringe chloride had no effect on basic field potentials and paired-pulse ratio (PPR). However, in the presence of chelerythrine chloride, two TBS failed to induce LTP. In contrast, bath application of chelerythrine chloride 10 min after the second TBS did not affect the maintenance of LTP in BLA. These results indicate that LTP is NMDAR-dependent and PKC is involved in the induction and early maintenance of LTP in BLA.

Tetanus-induced LTD of Developing MNTB-LSO Synapses in Rat is Dependent on Postsynaptic Ca2+

Because synaptic refinement of medial nucleus of trapezoid body (MNTB) - lateral superior olive (LSO) synapses is most active during the first postnatal week and the long term depression (LTD) has been suggested as one of its mechanisms, LTD of MNTB-LSO synapses was investigated in neonatal rat brain stem slices with the whole cell voltage clamp technique. In Mg2+ free condition, tetanus (10 stimuli at 10 Hz for 2 min) in the current clamp mode induced a robust LTD of isolated D, L-APV-sensitive postsynaptic currents (PSCs) for more than 30 min (n=6, 2.4+/-0.4% of the control), while isolated CNQX-sensitive PSCs were not suppressed (n=6, 95.3+/-1.6%). Tetanus also elicited similar LTD in the isolated GABAergic/glycinergic PSCs (n=5, 3.6+/-0.5%) and mixed PSCs (GABAergic/glycinergic/glutamatergic) (n=4, 2.2+/-0.7%). However, such a strong LTD was not observed in the mixed PSCs when 10 mM EGTA was added in the internal solution (n=10), indicating that postsynaptic Ca2+ rise is needed for the strong LTD. This robust LTD might contribute to the active synaptic refinement occurring during the first postnatal week.

Basic Electrophysiology of the Electroencephalography

Although neuroimaging techniques and other diagnostic procedures has been developed, electroencephalography(EEG) is still very important for the evaluation of various brain diseases and functional studies of human brain. EEG is formed mainly by spatial and temporal summations of postsynaptic potentials generated from a large population of pyramidal cells that can be considered as a collection of oscillating dipoles. EEG shows continuous rhythmic oscillation depending on sleep-waking state. Alpha rhythms are generated in cortical areas acting as epicenters with local spread, although the precise cellular mechanism is still unknown. It's been known that neurons in the nucleus reticular thalami are the pacemakers of sleep spindle. Alterations in the circuit of the reticular nuclei-thalamocortical relay neuron-cortical neuron are responsible for generalized spike and wave complexes. At the intracellular level, large paroxysmal depolarizing shifts produce focal epileptic spikes. Slow waves of EEG appear to be related to thalamocortical and/or corticothalamic deafferentation. The interpretation of routine EEG requires a well training from a qualified EEG teacher and reading adequate amount of EEG under supervision. Frequent misinterpretations of routine EEG have been observed in both local clinics and general hospitals. The most common findings of normal routine EEG misinterpreted as abnormal are normal variants and artifacts of various sources. There are considerable variations of normal EEG rhythms and pseudoepileptiform discharges. Eyeball movements produce prominent or subtle EEG changes over the frontal regions that are sometimes hard to be differentiated from abnormal slow waves over that region. Systematic approach was described for a good interpretation of routine EEG.

Effect of GABA on Synaptic Currents in Cultured Hippocampal Neurons in Rats

GABA (-aminobutyric acid) is one of the important neurotransmitters in the central nervous system of mammals and its action is variable according to the maturation phases of neurons. The neurons of early cultural days (less than 7 days) have been used for a developing neuronal model, while the neurons of later days (over 3 weeks) used for a mature model. This study was performed to investigate the electrophysiological property of GABAergic synapses in the hippocampal neurons cultured for 10 to 14 days which are considered to be transitional period between the developing and the mature phases. Membrane potential was depolarized and a inward transmembrane current was induced by 20 M GABA infusion. Frequency and amplitude of spontaneous postsynaptic currents (PSCs) were inhibited during the GABA infusion, but decay time constant was not affected significantly. In most hippocampal neurons, no GABAergic PSCs were observed during the administration of 0.5 M TTX, 50 M APV and 10 M CNQX. In the neurons counting 25% approximately, however, small persisted PSCs showed the existence of GABAergic synapses which were blocked by 10 M bicuculine. As the functional property of isolated GABAergic synapses, amplitude of GABAergic PSCs were diminished, and decay time constants and rising times were prolonged during the 20 M GABA infusion in all recorded neurons. In conclusion, approximately 25% of the hippocmpal neurons cultured 10 to 14 days used GABA as well as glutamate as a neurotransmitter. It seems that the GABAergic synapses composed of functionally homogenous GABAA receptors act as inhibitory modulator of the excitatory signal transmission.