CHRONOBIOLOGICAL VARIATIONS IN THE CONVULSIVE EFFECT OF MONOSODIUM L-GLUTAMATE WHEN ADMINISTERED TO ADULT-RATS

Monosodium L-glutamate (MSG) when administered intraperitoneally (i.p. ) to rodents induces convulsions and has been used as a model to study various aspects of status epilepticus of multifocal origin, There are circadian variations of susceptibility to convulsions induced by vari ous factors in some animal species, The aim of this work was to learn whether the convulsive effect of MSG in rats would vary when the drug is given at different times of the day. Three subgroups of Wistar rats were given i.p. 5 mg/g MSG at 07:00, 15:00 and 23:00 h, whereas two g roups of rats divided into three subgroups of five animals each were u sed as controls, also being injected at 07:00, 15:00 and 23:00 h. One group was injected with NaCl solution, equimolar to that of MSG (eqNaC l); the other was injected with physiological saline solution (PSS) in proportional volumes to those of the experimental group. Motor behavi or was recorded for 4 h following injections in the three groups of an imals, Neither signs of brain hyperexcitability, nor convulsions appea red in animals injected with PSS or eqNaCl. With MSG, no variations we re seen in the latency period when data from the three subgroups studi ed were compared among them. Duration of convulsive period when rats w ere injected at 07:00 h was shorter than that seen at 15:00 and 23:00 h. No significant variations were seen in total number of convulsive e pisodes in the three subgroups, while the number of seizures per hour and their intensity were significantly greater when animals were injec ted at 07:00 h than those seen when rats were studied at 15:00 and 23: 00 h, Nearly 70% of animals injected at 07:00 h died in status epilept icus, whereas no deaths were recorded in animals injected at 15:00 and 23:00 h. Results could be explained in terms of variations of physiol ogical processes at both the brain and extracerebral tissues involved in MSG metabolism and cerebral excitability, related to circadian rhyt hms.