Central effects of the neurotropic mycotoxin fumitremorgin A in the rabbit. (II). Effects on the brain stem.

Abstract

In order to determine the main site of the convulsant action of the neurotropic mycotoxin fumitremorgin A, the role of the brain stem reticular formation was studied. In rabbits lightly anesthetized with urethane and chloralose, electrical stimulation of the reticular formation elicited burst discharges in the common peroneal nerve and in the tibial nerve. This facilitatory effect of electrical stimulation was markedly potentiated by intravenous administration of a small dose of FTA, before onset of actual convulsion. Under the influence of FTA, a remarkable increase in the spontaneous electrical activity of the midbrain reticular formation was observed. The firing pattern of some neurons in the reticular formation corresponded very well with abnormal burst discharges in the common peroneal nerve. These effects of FTA were inhibited by chlorpromazine (0.1-1.0 mg/kg, i.v.), diazepam (0.1-1.0 mg/kg, i.v.), mephenesin (5-10 mg/kg, i.v.) and pentobarbital (5-15 mg/kg, i.v.). It was concluded that FTA might activate some neurons in the midbrain reticular formation and that convulsive burst discharges in peripheral motor nerves resulted from abnormal activation of these neurons, although the role of the medullary reticular formation could not be excluded.