Diphenylhydantoin potentiates the EEG and behavioural effects induced by N-methyl-D-aspartate antagonists in rats

Electroencephalographic spectral and coherence analysis of ketamine in rats: correlation with behavioral effects and pharmacokinetics

AIMS

This study was designed to evaluate the changes in EEG power spectra and EEG coherence in a ketamine model of psychosis in rats. Analyses of behavioral measurements--locomotion and sensorimotor gating--and the pharmacokinetics of ketamine and norketamine were also conducted.

METHODS

Ketamine and norketamine levels in rat sera and brains were analyzed by gas chromatography-mass spectrometry after ketamine 30 mg/kg (i.p.). Ketamine 9 and 30 mg/kg (i.p.) were used in the behavioral and EEG experiments. Locomotor effects in an open field test and deficits in prepulse inhibition of acoustic startle reaction (PPI ASR) were evaluated in the behavioral experiments. EEG signals were simultaneously recorded from 12 implanted active electrodes; subsequently, an EEG power spectral and coherence analysis was performed.

RESULTS

Ketamine had a rapid penetration into the brain; the peak concentrations of the drug were reached within 15 min after administration. Ketamine induced marked hyperlocomotion and deficits in the PPI ASR. EEG spectral analysis mainly showed increases in EEG power as well as coherence. These were most robust at 10-15 min after the administration and influenced all parts of the spectrum with ketamine 30 mg/kg.

CONCLUSIONS

Ketamine at behaviorally active doses induces a robust increase in EEG power spectra and coherence. The maximum levels of change correlated with the kinetics of ketamine.

Basis of the antiseizure action of phenytoin

1. Phenytoin has been used with much clinical success against all types of epileptiform seizures, except petit mal epilepsy, for over 50 years. Its mechanism of action, however, is still open to interpretation. 2. Several potential targets for phenytoin action have been identified within the central nervous system. These include the Na-K-ATPase, the GABAA receptor complex, ionotropic glutamate receptors, calcium channels and sigma binding sites. 3. To date, though, the best evidence hinges on the inhibition of voltage-sensitive Na+ channels in the plasma membrane of neurons undergoing seizure activity. Quieter nerve cells are far less affected. Moreover, the fact that phenytoin also has important cardiac antiarrhythymic effects and can inhibit Na+ influx into cardiac cells supports the idea that the primary target of phenytoin is, indeed, the Na+ channel.

The stimulation of cholecystokinin receptors in the rostral nucleus accumbens significantly antagonizes the EEG and behavioural effects induced by phencyclidine in rats

The influence of cholecystokinin (CCK), bilaterally injected into the rostral nucleus accumbens, on the EEG and behavioural effects induced by phencyclidine (PCP) has been studied in rats. CCK (10 ng) significantly inhibited PCP-induced EEG effects (increase of spectral power with respect to pre-drug tracing; increase of relative power distribution in the slowest frequency bands), and behavioural effects (circling and ataxia). The inhibitory effects of CCK were completely antagonized by 1 ng PD 135-158, a selective CCKB receptor antagonist, but not by lorglumide (1 microgram), a selective CCKA receptor antagonist. Since the effects induced by PCP in rodents have been proposed to be an experimental correlate of the psychotic symptoms it induces in humans, these results indicate that CCK may act as a neuroleptic. They also suggest that CCKB receptors located in the rostral nucleus accumbens may be involved in the neuroleptic-like activity of CCK.

Anticonvulsant Effects of Magnesium Sulfate in Hippocampal-Kindled Rats

The objective of the present study was to determine whether magnesium sulfate has anticonvulsant actions in the hippocampal-kindled rat model of epilepsy. Fully kindled rats received acute intraperitoneal injections of magnesium sulfate (270 mg/kg), phenytoin (20 mg/kg) or saline in random order. Electrical seizure duration, behavioral seizure stage and duration of postictal EEG depression were examined 15, 30 and 60 min after injection. In an additional group of rats, kindled seizures were measured before and after chronic (2 h) intraperitoneal injections of magnesium sulfate versus saline. There was a significant decrease in electrical seizure duration (p < 0.01) and behavioral seizure stage (p < 0.01) with acute magnesium sulfate injections compared to saline injections. Phenytoin had no statistically significant effects on hippocampal-kindled seizures. Chronic magnesium sulfate treatment significantly reduced behavioral seizure stage at 2, 24, and 48 h postinjection (p < 0.05), but did not affect seizure duration. There was a significant time by treatment effect for magnesium sulfate on postictal EEG depression (p < 0.01). We conclude that in this model of hippocampal epilepsy-induced (kindled) rats, magnesium sulfate has significant anticonvulsant effects. Copyright 1995 S. Karger AG, Basel