Interaction of diazepam with synaptic transmission in the in vitro rat hippocampus

Summary Diazepam (5×10^–8–10^–6 M) was found to augment recurrent inhibition of pyramidal neuron firing in a dose-dependent manner in rat hippocampal slices. To determine possible loci of this effect, diazepam was locally administered by pressure ejection from a micropipette, while recording action potentials from single inhibitory (basket) interneurons. Diazepam induced reversible and reliable increases in interneuron firing in response to stimulation of Schaffer collateral and commissural afferents. Taken together with previous electrophysiological reports, these data suggest that benzodiazepines may augment central inhibition by increasing either the excitability of inhibitory interneurons, or by increasing the strength of excitatory afferents to these cells.     

肿瘤相关基因Cap43在胰腺癌中的表达及意义

目的研究肿瘤相关基因Cap43在胰腺癌组织中的表达情况,探讨其对胰腺癌的诊断价值。方法收集1999年4月～2002年8月长海医院外科手术切除胰腺癌标本和癌旁正常组织33例,诊断均由病理证实。男性22例,女性11例,年龄30～73岁,平均58．1岁。所有组织标本按肿瘤、癌旁(正常)配对。采用RT-PCR和Northern杂交方法研究Cap43 mRNA表达情况。结果 RT-PCR结果显示,Cap43在肿瘤组织中表达显著上调,其在肿瘤组织和癌旁正常组织的扫描值分别为4 033±1 986和2 244±1 145,有显著差异(P<0．001)。Northern杂交亦显示Cap43在肿瘤组织中表达显著上调,相同病例的RT-PCR结果与Northern杂交的结果有较好的一致性,经回归分析,没有显著性差异(P>0．1)。结论 Cap43在胰腺癌组织中呈显著高表达,其有可能成为胰腺癌早期诊断的重要标志物。     

N-methyl-D-aspartate receptor responses are differentially modulated by noncompetitive receptor antagonists and ethanol in inbred long-sleep and short-sleep mice: behavior and electrophysiology

BACKGROUND: Short-sleep (SS) mice exhibit higher locomotor activity than do long-sleep (LS) mice when injected with low doses of ethanol or the noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist MK-801 (dizocilpine). SS mice also have higher densities of brain NMDARs. However, two strains of LS X SS recombinant inbred (RI) mice also show differential activation to ethanol and MK-801, but have similar numbers of NMDARs. Here we used inbred LS (ILS) and SS (ISS) mice to investigate further the relationship between NMDARs and sensitivity to the stimulant effects of low doses of ethanol. METHODS: Open field activity and spontaneous alternations were measured after saline or drug injection. [3H]MK-801 binding parameters were determined in hippocampus, cortex, striatum, and nucleus accumbens. Extracellular field excitatory postsynaptic potentials (fEPSPs) were recorded in the CA1 region of hippocampal slices. RESULTS: Systemic injection of either ethanol or MK-801 increased locomotor activity to a greater extent in ISS mice than in ILS mice. The competitive NMDAR antagonist 2-carboxypiperazin-4-yl-propyl-1-lphosphonic acid (+/- CPP) depressed activity of ILS, but not ISS, mice. No strain differences were observed in spontaneous alternations or in the number or affinity of NMDARs in the brain regions examined. Likewise, the magnitudes of hippocampal NMDAR-mediated fEPSPs were similar in ILS and ISS mice and were inhibited to the same extent by a competitive NMDAR antagonist. However, both ethanol and the NMDAR NR2B receptor antagonist ifenprodil inhibited the late component of hippocampal NMDAR fEPSPs to a greater extent in ISS, than in ILS, mice. CONCLUSIONS: Differential ethanol- and MK-801-induced behavioral activation in ILS and ISS mice was not associated with differences in NMDAR number. Nonetheless, pharmacological differences in hippocampal NMDAR responsiveness suggest that ISS mice express NMDARs that have a greater sensitivity to noncompetitive, but not competitive, NMDAR antagonists. These differences, which may reflect differences in NMDAR subunit composition, could underlie the differential responsiveness to low doses of ethanol in ILS and ISS mice.     

Behavioural sensitivity to PIA in selectively bred mice is related to a number of A1 adenosine receptors but not to cyclic AMP accumulation in brain slices

In a dose of 0.1 mg/kg, PIA had marked behavioural effects in long-sleep mice (which show a high sensitivity to ethanol, while no significant effect was observed in short sleep mice (low sensitivity to ethanol). The number of [3H]PIA binding sites in cortex and subcortical brain regions was significantly higher in long-sleep than in short-sleep mice. The KD value was higher in cortex and cerebellum in the short-sleep mice, but there were no differences in the number of hippocampal beta-adrenoceptors or in the adenosine analogue-induced increase in cyclic AMP accumulation in slices of mouse hippocampus.     

Adenine nucleotides and synaptic transmission in the in vitro rat hippocampus

1 The effects of adenosine and various derivatives were examined in the in vitro hippocampal slice preparation from rat.

2 The amplitudes of extracellularly recorded field potentials from the CA1 region were depressed by adenosine, and this effect could be antagonized by methylxanthines. Because presynaptic field potentials were unaffected by adenosine, while the field e.p.s.p. was depressed, adenosine would appear to act at a synaptic site to depress transmission.

3 Adenosine deaminase, which breaks down adenosine to inosine, increased the amplitude of synaptic responses, while hexobendine, which blocks reuptake of adenosine, had a depressant effect. This strongly suggests that the endogenous release of adenosine from the hippocampal slice preparation is sufficient to exert a tonic inhibitory influence on the amplitude of synaptic responses.

4 Cyclic adenosine 3′,5′-monophosphate (cyclic AMP) and its dibutyryl derivative had depressant effects on the amplitude of field responses which were blocked by theophylline, suggesting that they are able to act at the extracellular adenosine receptor. (-)-Isoprenaline (which raises tissue cyclic AMP levels), and the 8-p-chlorophenylthio derivative of cyclic AMP both increased the amplitude of population spike responses, and these effects were not blocked by theophylline, suggesting that the physiological effects of adenosine are not mediated via a cyclic AMP-dependent mechanism.

5 Since adenosine is not the transmitter at this CA1 pyramidal cell synapse, but is apparently present in the extracellular compartment in sufficient concentrations to affect the synaptic physiology of this region, this provides strong evidence in favour of the concept of a neuromodulatory role for adenosine in the central nervous system.

     

A transient increase in temperature induces persistent potentiation of synaptic transmission in rat hippocampal slices

Previous studies have shown that increasing the temperature of rat hippocampal brain slices from 32.5 to 38.5 degrees C initiates a profound, adenosine-mediated decrease in excitatory synaptic transmission in the CA1 region. Here we found that upon lowering the temperature back to 32.5 degrees C, the amplitude of the field excitatory postsynaptic potential often recovers to a level that is significantly potentiated with respect to the initial baseline. This potentiation is rapid in onset (< 5min following return to 32.5 degrees C) and long lasting (>60min following the termination of the increase in temperature). Similar effects could not be induced by superfusion with adenosine alone, and adenosine receptor antagonists did not block the potentiation. Therefore, although an adenosine-mediated decrease in excitatory synaptic transmission occurs during the temperature increase, it is unrelated to the potentiation. Likewise, N-methyl-D-aspartate receptor activation is not required, as N-methyl-D-aspartate receptor antagonists do not influence this form of potentiation.In summary, we propose that transiently increasing brain slice temperature represents a novel way to induce synaptic plasticity in the hippocampus, and may provide a paradigm to elucidate additional cellular mechanisms involved in functional plasticity.     

Calcium-dependent chloride currents elicited by injection of ethanol into Xenopus oocytes

Electrophysiological techniques were used to study the response of native Xenopus laevis oocytes to intracellular injection and bath application of ethanol. Injection of ethanol produced dose-dependent transient inward currents accompanied by large current fluctuations, with estimated intracellular concentrations ranging from 10 to 300 mM. The response duration varied between 2 and 15 min, with an onset delay of 2-15 s. The inward current sometimes consisted of a fast and a slow component. Bath application of equivalent concentrations elicited similar but considerably smaller responses. The current showed a reversal potential of -20 +/- 10 mV, corresponding to an increase in chloride permeability. The response was eliminated in the presence of low chloride saline and was blocked by the chloride channel inhibitors SITS and DIDS. Ethanol responses were inhibited by the intracellular injection of the calcium chelator EGTA and were unaffected when the extracellular calcium was lowered. It is concluded that ethanol injection into Xenopus oocytes elicits a release of calcium from intracellular stores, which then activates an increased membrane permeability to chloride.     

Modulation of hippocampal glutamatergic transmission by ATP is dependent on adenosine a(1) receptors

Excitatory glutamatergic synapses in the hippocampal CA1 region of rats are potently inhibited by purines, including adenosine, ATP, and ATP analogs. Adenosine A(1) receptors are known to mediate at least part of the response to adenine nucleotides, either because adenine nucleotides activate A(1) receptors directly, or activate them secondarily upon the nucleotides' conversion to adenosine. In the present studies, the inhibitory effects of adenosine, ATP, the purportedly stable ATP analog adenosine-5'-O-(3-thio)triphosphate (ATPgammaS), and cyclic AMP were examined in mice with a null mutation in the adenosine A(1) receptor gene. ATPgammaS displaced the binding of A(1)-selective ligands to intact brain sections and brain homogenates from adenosine A(1) receptor wild-type animals. In homogenates, but not in intact brain sections, this displacement was abolished by adenosine deaminase. In hippocampal slices from wild-type mice, purines abolished synaptic responses, but slices from mice lacking functional A(1) receptors showed no synaptic modulation by adenosine, ATP, cAMP, or ATPgammaS. In slices from heterozygous mice the dose-response curve for both adenosine and ATP was shifted to the right. In all cases, inhibition of synaptic responses by purines could be blocked by prior treatment with the competitive adenosine A(1) receptor antagonist 8-cyclopentyltheophylline. Taken together, these results show that even supposedly stable adenine nucleotides are rapidly converted to adenosine at sites close to the A(1) receptor, and that inhibition of synaptic transmission by purine nucleotides is mediated exclusively by A(1) receptors.