Modification of electroshock convulsive responses and thresholds in neonatal rats after brain monoamine reduction

Modification of electroshock (60 Hz; a.c.) convulsive responses and thresholds by monoamine-reducing drugs was investigated in developing rats. Throughout postnatal development, tetrabenazine (TBZ) reduced brain monoamines and increased the severity of motor responses to electroshock. The predominant maximal response in control pups progressed from hyperkinesia (day 1) to clonic convulsions (day 3) and tonic forelimb (day 7) and hindlimb (day 19) extension. The pattern in TBZ-treated pups progressed from tonic forelimb extension (day 1) to tonic hindlimb extension (day 7). On day 7, TBZ reduced the thresholds for clonic (CT) and tonic convulsions (TT) to 41 and 24% of control, respectively. Reserpine (1.25 mg/kg, 24 hours) decreased the TT but not the CT; TBZ, 4 hours before reserpine, prevented this decrease. A higher dose of reserpine (2.5 mg/kg) decreased both the CT and TT. On day 8, TBZ (25 mg/kg, 4 hours) decreased the TT (46% control); L-dihydroxyphenylalanine, but not 5-hydroxytryptophan prevented this decrease. Intracisternal 6-hydroxydopamine reduced the TT on day 8, while intracisternal 5,7-dihydroxytryptamine had no effect despite a 46% reduction in serotonin. The results indicate that in the neonatal rat brain, monoaminergic systems are sufficiently mature to attenuate electroshock convulsive responses, perhaps by limiting propagation of seizure discharge.