[Potentiation of metaphit-induced audiogenic epilepsy with N-methyl-D-aspartate in rats].

INTRODUCTION

Audiogenic seizures (AGS) are induced by high intensity sound stimulation in genetically susceptible rats or in animals subjected to chemical or electrical manipulation. Epileptic seizure may result from an impaired balance between excitation and inhibition in the CNS. The effect of NMDA (N-methyl-D-aspartic acid) on metaphit 1-(1(3-isothiocyanatophenyl-ciclohexyl)-piperidine) induced audiogenic seizures was evaluated in rats.

METHODS

Male Wistar albino rats were divided into 4 groups: 1) saline; 2) metaphit (10 mg/kg); 3) metaphit + NMDA; 4) NMDA (70 mg/kg). Animals were injected with metaphit intraperitoneally (i.p.) and exposed to sound stimulation (100 +/- 3 dB, 60 s) at hourly intervals. The incidence and severity (running, clonus and tonus) of seizures were analyzed. NMDA alone was administered i.p. to 6 rats. In group metaphit + NMDA only animals which did not exhibit any seizure during 8 hours were injected with NMDA i.p. after the 8th audiogenic testing. For electroencephalograph (EEG) recordings three gold-plated screws were used. Convulsive behaviour was assessed by incidence of motor seizure and by seizure severity grade, determined by use of a descriptive rating scale with range of 0-3; 0-no response; 1-wild running only; 2-wild running followed by clonic seizures of all four limbs with body rollover; 3-wild running progressing to generalized clonic convulsions and then a tonic extension of the fore and hind limbs and tail. Sound onset, seizure events, and sound offset, along with the animals behaviour (convulsive or other) were recorded as the correlates to the respective EEG responses.

RESULTS

In most animals the administration of metaphit (10 mg/kg) resulted in electrographic abnormalities, elicited epileptiform activity in the form of spikes, polyspikes and spikewave complexes (Fig. 1.). Maximum incidence and severity of metaphit convulsions occurred 8 h after the injection (9/12, 75%) (Fig. 2, 3.), then abated gradually and disappeared 30 h later. NMDA (70 mg/kg) alone induced no seizure response but isolated spiking activity, and sporadic slow-wave complexes were recorded (Fig. 4). NMDA induced stereotyped behaviour in the form of asymmetric posture, loss of righting reflex and tonic hindlimb extension, which lasted for 60-90 min. Subconvulsive dose of NMDA potentiated the metaphit-induced audiogenic seizures in rats. Two hours after NMDA administration 3 of 17 metaphit-treated rats convulsed, which in 8 previous testings never displayed seizures. Maximum incidence was 8 of 17 (53%), 5-6 h after NMDA administration and seizures lasted for 9 hours.

DISCUSSION

Several authors reported that metaphit dose of 10 mg/kg accompanied by some REM sleep deprivation (REM-D) procedures [4], or subconvulsive doses of NMDA [25] provoked seizures of higher intensity and incidence. Metaphit treatment (10 mg/kg) followed 24 h later by NMDA dose of 50 mg/kg provoked no spontaneous convulsions, while metaphit in combination with a higher NMDA dose of 70 mg/kg resulted in spontaneous and AGS-induced seizures only in one time point [25]. It was found that the incidence and severity of convulsive responses were highest 8-12 h after metaphit injection (10 mg/kg) [23, 24]. Although about 8 h after metaphit administration the power spectra increased and were more intense in the period of sound onset and seizure events.

CONCLUSION

The results of the present study strongly suggest that treatment of adult rats with the combination of metaphit and NMDA in the doses employed here followed by AGS provides a suitable animal model for examinations of epileptic seizures.