Intracellular calcium stores modulate miniature GABA-mediated synaptic currents in neonatal rat hippocampal neurons

The whole-cell configuration of the patch clamp technique was used to record miniature gamma-aminobutyric acidA (GABAA) receptor-mediated currents (in tetrodotoxin, 1 microM and kynurenic acid 1 mM) from CA3 pyramidal cells in thin hippocampal slices obtained from postnatal (P) day (P6-9) old rats. Switching from a Ca2+-containing to a nominally Ca2+-free medium (in which Ca2+ was substituted with Mg2+, in the presence or in the absence of 100 microM EGTA) did not change significantly the frequency or amplitude of miniature events. Superfusion of thapsigargin induced a concentration-dependent increase in frequency but not in amplitude of tetrodotoxin-resistant currents that lasted for the entire period of drug application. Mean frequency ratio (thapsigargin 10 microM over control) was 1.8+/-0.5, (n = 9). In nominally Ca2+-free solutions thapsigargin was ineffective. When bath applied, caffeine (10 mM), reversibly reduced the amplitude of miniature postsynaptic currents whereas, if applied by brief pressure pulses, it produced an increase in frequency but not in amplitude of spontaneous GABAergic currents. Superfusion of caffeine (10 mM) reversibly reduced the amplitude of the current induced by GABA (100 microM) indicating a clear postsynaptic effect on GABAA receptor. Superfusion of ryanodine (30 microM), in the majority of the cells (n = 7) did not significantly modify the amplitude or frequency of miniature events. In two of nine cells it induced a transient increase in frequency of miniature postsynaptic currents. These results indicate that in neonatal hippocampal neurons, mobilization of calcium from caffeine-ryanodine-sensitive stores facilitates GABA release.     

Activity-dependent response depression in rat hippocampal CA1 pyramidal neurons in vitro

1. A gradual and prolonged decrease of the response, termed here "depression," evoked by repeated activation with transmembrane current stimuli was analyzed in rat CA1 hippocampal pyramidal cells under single-electrode current clamp by the use of the in vitro slice technique. 2. Depression was induced by 2-s duration 0.3- to 0.7-nA current pulses presented as a sequence of 12 stimuli at 3- to 60-s intervals. Sinusoidal currents (0.5-1.0 nA) at 5-Hz or 200-ms pulses repeated at 0.3-0.5/s, which may be more natural stimulations, also induced depression. 3. Depression outlasted stimulation up to 170 s in all cells tested. The initial high rate spike burst changed little (< 20%), whereas the lower rate adapted response decreased markedly (> 40%). Thus neurons increased their rate of adaptation. The afterhyperpolarizations following pulse-evoked responses increased in duration and amplitude with depression. There were input resistance (Rin) reductions at depolarized membrane potentials and during pulses. However, Rin reductions were considerably smaller or altogether absent late during interpulse intervals. Sub-threshold current stimuli were ineffective, indicating that spike activity was necessary to elicit depression. 4. Depression was 1) insensitive to the toxin omega-Agatoxin-IVA (omega-Aga-IVA; 0.5 microM), which blocked synaptic transmission, revealing a key involvement of intrinsic properties and little if any synaptic participation; 2) insensitive to 4-aminopyrydine (2.00-4.00 mM), which greatly enhanced excitatory and inhibitory synaptic efficacy, again suggesting little synaptic involvement and a principal postsynaptic participation, and no participation of the K(+)-mediated currents IA and ID; 3) abolished by carbamalcholine (5.0-20.0 microM)- an effect blocked by atropine (1.0-10.0 microM)- and reduced by Ca(2+)-free solutions, and by intracellular injection of the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), suggesting that Ca(2+)-dependent K(+)-mediated currents are key factors, with a less important participation of the K(+)-mediated IM current. 5. We conclude that depression was due to activity-dependent modifications in intrinsic properties, with little if any synaptic participation. Depression may be functionally significant because it was induced by potentially natural stimulations. A model is proposed that accounts for the main traits of depression. In the model, depression was induced by a gradual decline of the speed at which Ca2+ was buffered intracellularly; an increase in the IK(Ca)S activation rate constant also simulated depression.     

Effects of hypertonia on voltage-gated ion currents in freshly isolated hippocampal neurons, and on synaptic currents in neurons in hippocampal slices

A NAD-dependent mannitol dehydrogenase (MtlD) was purified to homogeneity from P. fluorescens DSM50106 and the N-terminal amino acid sequence was determined. An oligonucleotide deduced from this peptide sequence was used as a probe to isolate the mannitol dehydrogenase gene (mtlD) from a genomic library of P. fluorescens. Nucleotide sequence analysis of a 1.8 kb NruI fragment containing the entire mtlD gene revealed an open reading frame of 1482 bp encoding a protein with a calculated molecular weight of 54.49 kDa. The enzyme shared a high similarity with a mannitol dehydrogenase from Rhodobacter sphaeroides and a putative mannitol dehydrogenase of Saccharomyces cerevisae with an overall identity in amino acid sequence of 44% and 42%, respectively, whereas the similarity to mannitol-1-phosphate dehydrogenases of Escherichia coli or Enterococcus faecalis was only about 23% of identical amino acids. By construction of inducible expression plasmids the specific activity of the mannitol dehydrogenase synthesized in E. coli was increased from 0.02 U (mg protein)(-1) to 10 U (mg protein)(-1). After fusion of six histidine codons to the 3' end of mtlD gene and expression in E. coli active mannitol dehydrogenase could be purified in a two-step procedure by affinity chromatography using a Ni2+ matrix column. The purified enzyme exhibited a specific activity of 46 U (mg protein)(-1) and was shown to be a polyol dehydrogenase with a broad substrate spectrum oxidizing efficiently mannitol, sorbitol and arabitol.     

Protracted treatment with diazepam reduces benzodiazepine1 receptor-mediated potentiation of gamma-aminobutyric acid-induced currents in dissociated rat hippocampal neurons

Tolerance to benzodiazepines (BZs) is thought to involve alterations of the gamma-aminobutyric acid (GABA)A receptor as a result of the prolonged occupancy of its modulatory BZ recognition site. We used the whole-cell patch-clamp technique to compare the functional and pharmacological properties of GABAA receptors in acutely dissociated hippocampal neurons from the control or diazepam-tolerant rats. Administration of diazepam (15 mg/kg p.o.) twice a day for 10 days induced tolerance as demonstrated by the decreased potency of acute diazepam i.p. injections to protect against pentylenetetrazole-induced clonictonic convulsions (10.5% of tolerant rats protected by 0.1 mg/kg of diazepam against 55% of nontreated rats, 48 hr after the last dose of the chronic treatment). The specific current induced by 1 microM GABA in acutely dissociated hippocampal neurons 48 hr after withdrawal (10.5 +/- 1.3 microA/cm2) was similar to that observed in the control rats (8.7 +/- 0.8 microA/cm2). The EC50 value for GABA was unchanged by the chronic treatment [6.3 (5.4-7.1) and 7.5 (6.2-8.7) microM in neurons from the control and treated rats, respectively]. The potency of the nonselective allosteric modulator diazepam to stimulate Cl- currents was identical in cells from treated rats [EC50 values of 25 (20-30) and 34 (26-41) nM in the control and treated rats, respectively; P < .05], but the potency of the selective BZ1-site ligand zolpidem was decreased [EC50 values of 99 (88-111) and 267 (221-313) nM in the control and treated rats, respectively; P < .05]. The maximal potentiation of the GABA-induced current was significantly decreased with diazepam (maximal potentiation: 168.0 +/- 16.2 and 124.0 +/- 8.9% in the control and treated rats, respectively). These results suggest that tolerance to diazepam is accompanied in hippocampal neurons by a decrease in BZ1 binding sites and in the functional coupling of BZ/GABA recognition sites.     

Optical imaging of hippocampal neurons with a chloride-sensitive dye: early effects of in vitro ischemia

We determined if changes in intraneuronal Cl- occur early after ischemia in the hippocampal slice. Slices from juvenile rats (14-19 days old) were loaded with the cell-permeant form of 6-methoxy-N-ethylquinolinium chloride (MEQ), a Cl(-)-sensitive fluorescent dye. Real-time changes in intracellular chloride concentration ([Cl-]i) were measured with UV laser scanning confocal microscopy in multiple neurons within each slice. In vitro ischemia (26-28 degrees C, 10 min) was confirmed by the loss of synaptic transmission (evoked field excitatory postsynaptic potentials) from pyramidal cells in area CA1. After ischemia and reoxygenation (10 min), MEQ fluorescence decreased significantly in CA1 pyramidal cells and interneurons. The decreased fluorescence corresponded to an ischemia-induced increase in [Cl-]i of approximately 10 mM. Pretreatment with the GABA(A)-gated Cl- channel antagonist picrotoxin (100 microM) blocked the ischemia-induced change in [Cl-]i. Analysis of the superfusates indicated that ischemia also caused a transient amino acid (GABA, glutamate, and aspartate) release that was maximal at approximately 10 min, returning to baseline shortly thereafter. Recovery from ischemia was confirmed by the return of synaptic transmission in area CA1, the return toward baseline of the ischemia-induced decrease in MEQ fluorescence, and exclusion of propidium iodide from MEQ fluorescent cells. Furthermore, pyramidal cells did not undergo cell swelling during this early phase of reoxygenation, as indicated by the volume-sensitive dye calcein. Thus, mild ischemia induces the accumulation of [Cl-]i secondary to GABA(A) receptor activation, in the absence of cellular swelling or death. In contrast, depolarization of the slice with K+ (50 mM) decreased MEQ fluorescence significantly but caused cell swelling. Picrotoxin did not prevent the K+-induced increase in [Cl-]i. It is possible that an increased [Cl-]i, following either an ischemic event or an episode of depolarization, would reduce the Cl- driving force and thereby limit synaptic transmission by GABA. To support this hypothesis, ischemia caused a reduction in the ability of the GABA agonist muscimol to increase [Cl-]i after 20-min reoxygenation.     

Differential effects of hippocampal ablations on dispositional and representational memory in the rat.

Long-Evans rats with electrolytic hippocampal ablations exhibited chronic impairment in performance on a spatial delayed nonmatching-to-sample task in the arms of a T-maze. The same rats exhibited only mild deficits, which disappeared with practice, in dispositional memory-dependent discrimination in the stem. Both types of discrimination were learned rapidly preoperatively with no marked positive or negative interaction between types of discrimination. The present results suggest that hippocampal lesions in rats have far more serious consequences on the performance of representational memory-dependent tasks than similar lesions in monkeys. In agreement with our past studies, the present experiment demonstrated that dispositional and representational memory systems in rodents have at least partially distinct anatomical substrates in brain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Glutamate-dependent astrocyte modulation of synaptic transmission between cultured hippocampal neurons

The idea that astrocytes merely provide structural and trophic support for neurons has been challenged by the demonstration that astrocytes can regulate neuronal calcium levels. However, the physiological consequences of astrocyte-neuron signalling are unknown. Using mixed cultures of rat hippocampal astrocytes and neurons we have determined functional consequences of elevating astrocyte calcium levels on co-cultured neurons. Electrical or mechanical stimulation of astrocytes to increase their calcium level caused a glutamate-dependent slow inward current (SIC) in associated neurons. Microinjection of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) into astrocytes to prevent the stimulus-dependent increase in astrocyte calcium level, blocks the appearance of the neuronal SIC. Pharmacological manipulations indicate that this astrocyte-dependent SIC is mediated by extracellular glutamate acting on N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors. Additionally, stimulation of astrocytes reduced the magnitude of action potential-evoked excitatory and inhibitory postsynaptic currents through the activation of metabotropic glutamate receptors. The demonstration that astrocytes modulate neuronal currents and synaptic transmission raises the possibility that astrocytes play a neuromodulatory role by controlling the extracellular level of glutamate.     

Activity regulates the synaptic localization of the NMDA receptor in hippocampal neurons

We describe here a novel effect of activity on the subcellular distribution of NMDA receptors in hippocampal neurons in culture. In spontaneously active neurons, NMDA receptors were clustered at a few synaptic and nonsynaptic sites. Chronic blockade of NMDA receptor activity induced a 380% increase in the number of NMDA receptor clusters and a shift to a more synaptic distribution. This effect was reversible. The distributions of the presynaptic marker synaptophysin, the AMPA-type glutamate receptor subunit GluR1, and the putative NMDA receptor clustering protein PSD-95 were not affected by blockade. Regulation of the synaptic localization of NMDA receptors by activity may define a novel mechanism by which input controls a neuron's ability to modify its synapses.     

Contribution of ATP-sensitive potassium channels to hypoxic hyperpolarization in rat hippocampal CA1 neurons in vitro

To investigate the mechanism of generation of the hypoxia-induced hyperpolarization (hypoxic hyperpolarization) in hippocampal CA1 neurons in rat tissue slices, recordings were made in current-clamp mode and single-electrode voltage-clamp mode. Superfusion with hypoxic medium produced a hyperpolarization and corresponding outward current, which were associated with an increase in membrane conductance. Reoxygenation produced a further hyperpolarization, with corresponding outward current, followed by a recovery to the preexposure level. The amplitude of the posthypoxic hyperpolarization was always greater than that of the hypoxic hyperpolarization. In single-electrode voltage-clamp mode, it was difficult to record reproducible outward currents in response to repeated hypoxic exposure with the use of electrodes with a high tip resistance. The current-clamp technique was therefore chosen to study the pharmacological characteristics of the hypoxic hyperpolarization. In 60-80% of hippocampal CA1 neurons, glibenclamide or tolbutamide (3-100 microM) reduced the amplitude of the hypoxic hyperpolarization in a concentration-dependent manner by up to approximately 70%. The glibenclamide or tolbutamide concentrations producing half-maximal inhibition of the hypoxic hyperpolarization were 6 and 12 microM, respectively. The chord conductance of the membrane potential between -80 and -90 mV in the absence of glibenclamide (30 microM) or tolbutamide (100 microM) was 2-3 times greater than that in the presence of glibenclamide or tolbutamide. In contrast, the reversal potential of the hypoxic hyperpolarization was approximately -83 mV in both the absence and presence of tolbutamide or glibenclamide. In approximately 40% of CA1 neurons, diazoxide (100 microM) or nicorandil (1 mM) mimicked the hypoxic hyperpolarization and pretreatment of these drugs occluded the hypoxic hyperpolarization. When ATP was injected into the impaled neuron, hypoxic exposure could not produce a hyperpolarization. The intracellular injection of the nonhydrolyzable ATP analogue 5'-adenylylimidodiphosphate lithium salt reduced the amplitude of the hypoxic hyperpolarization. Furthermore, application of dinitrophenol (10 microM) mimicked the hypoxic hyperpolarization, and the dinitrophenol-induced hyperpolarization was inhibited by either pretreatment of tolbutamide or intracellular injection of ATP, indicating that the hypoxic hyperpolarization is highly dependent on intracellular ATP. It is therefore concluded that in the majority of hippocampal CA1 neurons, exposure to hypoxic conditions resulting in a reduction in the intracellular level of ATP leads to activation of ATP-sensitive potassium channels with concomitant hyperpolarization.     

Differential effects of angiotensin II on the activities of suprachiasmatic neurons in rat brain slices

The effects of angiotensin II (AII) on the firing rates of suprachiasmatic neurons were determined in rat brain slices. AII in pmol ranges stimulated 25% and inhibited another 25% of 52 irregular firing neurons, while it stimulated 23% and inhibited 4% of 30 regular firing neurons. Three "oscillating" neurons whose firing rates oscillated with rather constant amplitudes and periods were recorded. AII induced the occurrence of oscillation in one unit and modulated the oscillation amplitude of the other two. Pretreatment with saralasin, an AII antagonist, effectively blocked (100%) the actions of AII (n = 5). The present findings suggest that AII may act as an important mediator in the suprachiasmatic nucleus and its mode of action may be variable in different neurons.     

Vasoactive intestinal polypeptide enhances the GABAergic synaptic transmission in cultured hippocampal neurons

The whole-cell mode of patch-clamp techniques was used to investigate the effect of vasoactive intestinal polypeptide (VIP) on spontaneous gamma-aminobutyric acid (GABA)-mediated inhibitory postsynaptic currents (IPSCs) of cultured hippocampal neurons. Application of VIP caused a significant increase in the frequency of spontaneous IPSCs with a reversible and dose-dependent manner. VIP had no effect on the mean amplitude and kinetic parameters of spontaneous IPSCs. In the presence of tetrodotoxin, VIP increased the frequency of miniature inhibitory postsynaptic currents (mIPSCs) without affecting their mean magnitude. Forskolin, but not its inactive analog 1,9-dideoxyforskolin, mimicked the stimulatory effect of VIP on spontaneous IPSCs and mIPSCs. VIP and forskolin failed to modulate GABAergic IPSCs in the presence of Rp-cAMPs, a cell permeable antagonist of cAMP-dependent protein kinase (PKA). Calcium channel blocker CdCl2 did not prevent VIP and forskolin from increasing the frequency of mIPSCs. These results suggest that the activation of presynaptic VIP receptor enhances the GABAergic synaptic transmission in cultured hippocampal neurons through the cAMP-PKA pathway and that VIP is likely to increase GABA release by directly stimulating the vesicular release apparatus.     

Mediation by intracellular calcium-dependent signals of hypoxic hyperpolarization in rat hippocampal CA1 neurons in vitro

In response to oxygen deprivation, CA1 pyramidal neurons show a hyperpolarization (hypoxic hyperpolarization), which is associated with a reduction in neuronal input resistance. The role of extra- and intracellular Ca2+ ions in hypoxic hyperpolarization was investigated. The hypoxic hyperpolarization was significantly depressed by tolbutamide (100 microM); moreover, the response was reversed in its polarity in medium containing tolbutamide (100 microM), low Ca2+ (0.25 mM), and Co2+ (2 mM), suggesting that the hypoxic hyperpolarization is mediated by activation of both ATP-sensitive K+ (KATP) channels and Ca(2+)-dependent K+ channels. The hypoxic depolarization in medium containing tolbutamide, low Ca2+, and Co2+ is probably due to inhibition of the electrogenic Na(+)-K+ pump and concomitant accumulation of interstitial K+. Hypoxic hyperpolarizations were depressed in either low Ca2+ (0.25 or 1.25 mM) or high Ca2+ (5 or 7.5 mM) medium (control: 2.5 mM), indicating that there is an optimal extracellular Ca2+ concentration required to produce the hypoxic hyperpolarization. Bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA)-AM (50-100 microM), procaine (300 microM), or ryanodine (10 microM) significantly depressed the hypoxic hyperpolarization, suggesting that Ca2+ released from intracellular Ca+ stores may have an important role in the generation of hypoxic hyperpolarization. The high-affinity calmodulin inhibitor N-(6-amino-hexyl)-5-chloro-1-naphthalenesulfonomide hydrochloride (W-7) (5 microM) completely blocked, whereas the low-affinity calmodulin inhibitor N-(6-aminohexyl)-1-naphthalenesulfonomide hydrochloride (W-5) (50 microM) did not affect, the hypoxic hyperpolarization. The calmodulin inhibitor trifluoperazine (50 microM) also suppressed the hypoxic hyperpolarization. In addition, calcium/ calmodulin kinase II inhibitor 1-[N,O-bis (1,5-isoquinol-inesulfonyl)-N-methyl-L-tyrosyl]-4-phenyl-pip erazine (KN-62) (10 microM) markedly depressed the amplitude and net outward current of the hypoxic hyperpolarization without affecting the reversal potential. In contrast, neither the myosin light chain kinase inhibitor 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexa-hydro-1,4-diazepin hydrochloride (ML-7) (10 microM) nor the protein kinase A inhibitor N-[2-(p-bromocinnamyl-amino) ethyl]-5-isoquinolinesulfonamide (H-89) (1 microM) significantly altered the hypoxic hyperpolarization. These results suggest that calmodulin kinase II, which is activated by calmodulin, may contribute to the generation of the hypoxic hyperpolarization. In conclusion, the present study indicates that, in the majority of hippocampal CA1 neurons, the hypoxic hyperpolarization is due to activation of both KATP channels and Ca(2+)-dependent K+ channels.     

The effects of temperature and synaptic blockade in vitro on neurons of the horizontal limb of the diagonal band of Broca in the rat basal forebrain

We studied the thermosensitivity of neurons in the rat horizontal limb of the diagonal band of Broca (HDB) in vitro under normal conditions and under conditions of a low calcium/high magnesium synaptic blockade (SB). Of 52 HDB neurons tested, 34 neurons (65%) were warm-sensitive (WS), three neurons (6%) were cold-sensitive (CS), 11 neurons (21%) were temperature-insensitive (TI) and four additional neurons (8%) were both warm- and cold-sensitive (WS/CS). Of 34 neurons tested for thermosensitivity under SB, 11 were WS, 4 were CS and 19 were TI. Nearly half (48%) of the WS neurons maintained warm sensitivity under SB, 43% became TI and 9% became CS. Baseline firing rates of neurons significantly decreased during SB and then increased during recovery from SB. In addition, a distinct anatomical distribution of thermosensitive neurons was found in the HDB. The most ventral aspect of the HDB (interaural +0.9-1.3 mm) had proportionally fewer temperature sensitive neurons (65% vs. 88%) than areas more dorsal (interaural +1.3-1.7 mm), and only one of seven ventral HDB neurons (14%) remained thermosensitive during SB. In the dorsal HDB, 65% of the neurons maintained thermosensitivity during SB. These results demonstrate that the HDB contains inherently thermosensitive neurons, and that a difference in thermal characteristics exists between the ventral and dorsal HDB neurons.     

Effects of the neuropeptide thyrotropin-releasing hormone on GABAergic synaptic transmission of CA1 neurons of the rat hippocampal slice during hypoxia

Thirty-six consecutive patients with 37 complete tears of the ulnar collateral ligament of the thumb metacarpophalangeal (MP) joint were treated with primary repair using a miniature intraosseous suture anchor. Thirty patients were evaluated by clinical examination or by questionnaire at an average of 11 months after repair. Loss of interphalangeal joint motion averaged 15 degrees on the involved side versus the other side, while loss of MP joint motion averaged 10 degrees. There was no significant difference on stress testing measurements between repaired and nonrepaired thumbs. There were no instances of nerve injury, infection, device failure, or reoperation. The authors concluded that this is a safe and effective method for repair of complete tears of the ulnar collateral ligament of the thumb MP joint.     

Excision-activated chloride channels in cultured postnatal rat hippocampal neurons

The non-enveloped picornaviruses, which are particularly resistant to physicochemical inactivation, include the aetiological agents of poliomyelitis, hepatitis A and E and infectious common cold (rhinovirus). In this work we used human rhinovirus type 5 (RV-5) cultivated in VERO cells to study the photoinactivating effects of several phthalocyanines and naphthobenzoporphyrazines. Free RV-5 was photoinactivated by aluminium trisulphonated naphthobenzoporphyrazine at 5 x 10(-8) M concentration. This photosensitizer was also active on replicating virus when the infected VERO cells were treated with 5 x 10(-6) M concentration followed by a very short illumination period. On the other hand, the ZnPc(3-MeO-Py)4 phthalocyanine, which possesses four positive charges, does not photoinactivate free rhinovirus, but this molecule protects VERO cells against RV-5 infection when added to the cultures before virus inoculation, in the presence or absence of subsequent illumination, and may therefore be considered as an antiviral agent in itself.     

异丙酚对大鼠海马神经元低电压激活钙电流的抑制作用

目的:观察异丙酚对大鼠海马锥体神经元低电压激活钙电流[low-voltage-activated calcium currents,ICa(LVA)]的影响.方法:培养Wistar大鼠海马锥体神经元,采用全细胞膜片钳技术测定ICa(LVA).加用不同浓度(3、10、30、100、300μmol/L)异丙酚后,计算ICa(LVA)抑制率,建立异丙酚的浓度-效应曲线,选择20μmol/L异丙酚作ICa(LVA)的激活及失活曲线.结果:3 μmol/L的异丙酚对ICa(LVA)的电流幅度无影响;10、30、100、300 μmol/L的异丙酚对ICa(LVA)的电流幅度抑制率分别为(12.6±4.1)%、(29.2±5.7)%、(36.6±5.3)%、(31.6±2.6)%.拟合后的浓度-效应曲线的IC50为16.8 μmol/L,Hill系数为0.15.激活曲线的半数最大激活膜电位(V1/2)由(-10±1)mV移动到(-11±2)mV;K分别为12±1和8±1;失活曲线的V1/2分别为(-25±1)mV和(-25±5)mV,K分别为15±1和16±3.20 μmol/L异丙酚均未使ICa(LVA)的激活曲线及稳态失活曲线发生明显移动.结论:异丙酚对ICa(LVA)通道有抑制作用,异丙酚对中枢神经系统的麻醉作用可能与ICa(LVA)抑制有关.     

Ethanol effects on synaptic neurotransmission and tetanus-induced synaptic plasticity in hippocampal slices of chronic in vivo lead-exposed adult rats

The interaction of chronic in vivo lead exposure and acute in vitro ethanol treatment on synaptic neurotransmission and plasticity were studied using extracellular electrophysiological techniques in CA1 region of hippocampal brain slices from adult rats. Neither chronic lead exposure nor acute ethanol treatment had any significant effect on field excitatory postsynaptic potentials (EPSPs). In vivo lead exposure enhanced short-term potentiation (STP, potentiation that decays within 30 min) by 21% shortly after 'weak' tetanus, but had no effect on long-term potentiation (LTP, sustained at least 1 h). In vitro bath application of 60 mM ethanol inhibited STP by 35% and blocked LTP induced by 'weak' tetanus in slices from Pb exposed rats (500 ppm lead acetate, 56-70 days), while having no effect on STP or LTP in slices from control counterpart Na-exposed rats (pair-fed 216 ppm sodium acetate). In contrast, 'strong'-tetanus-induced LTP was abolished in Pb-exposed slices, and 60 mM ethanol slightly inhibited STP and blocked LTP in slices from Na-exposed rats. These differences could not be explained by differences in ethanol inhibition of NMDA-mediated field EPSPs because they were similarly reduced in slices from Na-exposed (30%) and Pb-exposed (25%) rats. These findings suggest that the strength of the tetanus used determines whether or not synaptic plasticity is blocked by either chronic lead exposure or acute ethanol treatment, and that even in adult rats, hippocampal synaptic LTP can be compromised by combined exposure to ethanol and lead. More importantly, these findings suggest the consequences of combined lead exposure and alcohol abuse in the adult human population may not be fully recognized yet.     

Examination of persistent effects of repeated administration of pentylenetetrazol on rat hippocampal CA1: evidence from in vitro study on hippocampal slices

The early and long-lasting effects of pentylenetetrazol-kindling on hippocampal CA1 synaptic transmission were investigated. Experiments were carried out in the hippocampal slices from control and kindled rats at two post-kindling periods, i.e. 48-144 h (early phase) and 30-33 days (long-lasting phase). Field potentials, i.e. population excitatory postsynaptic potential (pEPSP) and population spike (PS) were recorded at the stratum pyramidale following stimulation of the stratum radiatum. Kindling-induced changes in synaptic transmission were assessed by stimulus-response functions and paired-pulse responses. The results showed that 48-144 h after kindling, the PS amplitude in the CA1 of kindled slices enhanced, and a second PS appeared compared to control slices. But at 30-33 days after kindling, the pEPSP slope in the CA1 of kindled slices enhanced without any change in the PS compared with those in the control slices. Evaluation of paired-pulse responses showed a significant reduction in paired-pulse inhibition for PS 48-144 h after kindling and a significant increase in paired-pulse inhibition for pEPSP 30-33 days after kindling. Our results suggest that pentylenetetrazol-kindling is accompanied by enhanced excitability and a reduction of paired-pulse inhibition in hippocampal CA1. The increased paired-pulse inhibition one month after kindling, may be interpreted as an adaptive process to cope with subsequent seizures.     

Modulation of synaptic GABAA receptor function by PKA and PKC in adult hippocampal neurons

Several protein kinases are known to phosphorylate Ser/Thr residues of certain GABAA receptor subunits. Yet, the effect of phosphorylation on GABAA receptor function in neurons remains controversial, and the functional consequences of phosphorylating synaptic GABAA receptors of adult CNS neurons are poorly understood. We used whole-cell patch-clamp recordings of GABAA receptor-mediated miniature IPSCs (mIPSCs) in CA1 pyramidal neurons and dentate gyrus granule cells (GCs) of adult rat hippocampal slices to determine the effects of cAMP-dependent protein kinase (PKA) and Ca2+/phospholipid-dependent protein kinase (PKC) activation on the function of synaptic GABAA receptors. The mIPSCs recorded in CA1 pyramidal cells and in GCs were differentially affected by PKA and PKC. In pyramidal cells, PKA reduced mIPSC amplitudes and enhanced the fraction of events decaying with a double exponential, whereas PKC was without effect. In contrast, in GCs PKA was ineffective, but PKC increased the peak amplitude of mIPSCs and also favored double exponential decays. Intracellular perfusion of the phosphatase inhibitor microcystin revealed that synaptic GABAA receptors of pyramidal cells, but not those of GCs, are continually phosphorylated by PKA and conversely, dephosphorylated, most likely by phosphatase 1 or 2A. This differential, brain region-specific phosphorylation of GABAA receptors may produce a wide dynamic range of inhibitory synaptic strength in these two regions of the hippocampal formation.     

Neurotrophic activity of organosulfur compounds having a thioallyl group on cultured rat hippocampal neurons

Several organosulfur compounds found in garlic extract promoted the survival of rat hippocampal neurons in vitro. From the analysis of structure-activity relationship, thioallyl group in these compounds is essential for the manifestation of neurotrophic activity. S-Allyl-L-cysteine (SAC), one of the organosulfur compounds having thioallyl group in garlic extract, also promoted the axonal branching of cultured neurons. These results suggest that thioallyl compounds make a unique group of neurotrophic factors.