Benzodiazepine selectively antagonize kainate-induced activation in the rat hippocampus

Histochemical and morphological changes in various regions of the rat hippocampus in swimming-induced stress

Swimming stress increased the functional activity of hippocampal pyramidal neurons in rats, as indicated by decreases in their glycogen contents and increases in their nucleic acid contents and the nucleus:cytoplasm ratio. These changes were most marked in hippocampal field CA1, while changes in other regions of the hippocampus were minimal.

Effect of 5,7-dihydroxytryptamine lesion on mianserin-induced conditioned place aversion and on 5-hydroxytryptamine1C receptors in the rat brain

The lesion of serotonergic neurons (by an intraventricular injection of 5,7-dihydroxytryptamine) potentiated the conditioned place aversion induced by the 5-hydroxytryptamine1C/5-hydroxytryptamine2 antagonist mianserin in rats. This effect was selective for mianserin as the same lesion suppressed the conditioned place aversion induced by the benzodiazepine inverse agonist FG-7142. Previous results had shown the involvement of the 5-hydroxytryptamine1C receptors in the conditioned place aversion induced by mianserin [Rocha et al. (1993) Behav. Pharmac. 4, 101-106]. It was thus of interest to investigate the effect of the lesion on these receptor binding sites. Autoradiographic binding studies showed that the lesion significantly increased the concentration of the 5-hydroxytryptamine1C binding sites in various brain regions, including the amygdala, the hippocampus and the nucleus accumbens. Contrastingly, in these same brain regions, in situ hybridization histochemistry did not reveal an alteration of the level of messenger RNA coding for these receptors. On the one hand, correlating potentiation of the aversive effects of mianserin and increase of 5-hydroxytryptamine1C binding sites in the limbic system represent an interesting step in the comprehension of the molecular and motivational effects of serotonergic drugs. On the other hand, showing a dissociation between the expression of 5-hydroxytryptamine1C receptors and their corresponding messenger RNA, suggest that post-transcriptional mechanisms are involved in the regulation of these receptors.

Seizure activity in pyridoxine-deficient adult rats

This investigation tested the hypothesis that the degree of pyridoxine depletion rather than the status of neuronal maturity determines seizure proneness in the pyridoxine-deficient rat. Dietary pyridoxine deficiency was induced in neuronally mature rats. Seizure activity was monitored using computerized EEG analysis. Dietary pyridoxine deficiency of 10 weeks' duration induced in neuronally mature rats led to spontaneous convulsive seizure activity. Even moderately pyridoxine-deficient adult rats (on the deficient diet for less than 8 weeks) exhibited seizure-like diffuse spike and wave activity and electrocortical inhibition. Picrotoxin-, pentylenetetrazol-, or domoic acid-induced seizure thresholds were significantly reduced in pyridoxine-deficient rats when compared with normal controls. Pyridoxine-deficient rats exhibited increased dominance of delta and theta activities and increased hemispherical asymmetries in response to convulsant treatment.

Effects of anticonvulsants on responses to excitatory amino acids applied topically to rat cerebral cortex

1. Five clinically used anticonvulsants were examined to find out if they block the effects of excitatory amino acids in the cerebral cortex of urethane anaesthetised rats. 2. Compounds were tested by topical application to the cortical surface and following their intraperitoneal injection at anticonvulsant doses. 3. Pentobarbital and diphenylhydantoin blocked the effect of quisqualic acid but only at concentrations higher than the therapeutically relevant levels. 4. Pentobarbital and diphenylhydantoin did not alter the effects of N-methyl-D,L-aspartic acid (NMDLA) or kainic acid. 5. Diazepam prevented the kainic acid-induced development of distorted somatosensory evoked potentials (SEPs) at therapeutically relevant levels. 6. Diazepam had no effect on NMDLA or quisqualic acid. 7. Carbamazepine and chlormethiazole had no effect on NMDLA, kainic acid or quisqualic acid. 8. The anticonvulsive effects of these drugs, with the exception of diazepam, probably do not involve antagonism of endogenous EAAs.

Attenuation of cerebral glucose use in kainic acid-treated rats by diazepam

Diazepam's impact on kainic acid seizure-induced local cerebral glucose utilization (LCGU) was assessed by a quantitative [14C]2-deoxyglucose method. Male rats were injected i.p. with either kainic acid (12 mg/kg) or its vehicle, 3 or 48 h before LCGU determination. Diazepam (3.2 mg/kg) or its vehicle were injected i.m. 15 min before, 1 and 2.5 h after kainic acid. Diazepam blocked kainic acid-induced overt convulsions, attenuated LCGU increases at 3 h and prevented 48 h LCGU decreases in piriform cortex and amygdala. LCGU in (% of vehicle): CA3 (438%), CA4 (537%) and CA1-ventral (340%) of hippocampus, interpeduncular nucleus (200%) and lateral lemniscus (213%) were still significantly above vehicle levels in the 3 h diazepam-kainic acid group. These results suggest that diazepam suppresses the spread of kainic acid-induced seizure activity from the proposed CA3 epileptogenic focus. In addition, diazepam reduces, but does not abolish, hypermetabolic activity at the foci itself.

Benzodiazepines antagonize cholecystokinin-induced activation of rat hippocampal neurones

Cholecystokinin (CCK) is a neuropeptide present in the mammalian central nervous system (CNS). In all species studied so far, the highest concentrations of this neuropeptide have been found in the cerebral cortex, the amygdala and the hippocampus. Five molecular forms of CCK having 39, 33, 13, 8 and 4 amino acid residues have been identified in the CNS, the sulphated octapeptide (CCK8) being the most abundant form detected. Specific CCK binding sites have been demonstrated in the rat, guinea pig and human brain. CCK8, applied by microiontophoresis to deep cortical neurones and hippocampal pyramidal neurones, has a powerful excitatory effect, whereas the non-sulphated CCK octapeptide has no such effect on these neurones. Low doses of benzodiazepines depress the spontaneous activity of hippocampal pyramidal neurones. We report here that benzodiazepines at very low doses antagonize selectively the CCK8-induced activation of rat hippocampal pyramidal neurones. This antagonistic action might be involved in the anxiolytic effect of these drugs.