Blockade of photically induced epilepsy by 'dopamine agonist' ergot alkaloids.

The effect of the intravenous administration of ergot alkaloids on epileptic responses to intermittent photic stimulation )IPS) has been studied in adolescent baboons, Papio papio, from Senegal. Ergocornine, 1--2 mg/kg, produced marked autonomic and behavioural effects, slowed the EEG, and abolished myoclonic responses to IPS for 30--90 min. Ergometrine, 1 mg/kg, activated the EEG and blocked the induction of myoclonic responses for 1--3 h. Bromocriptine, 0.5--4 mg/kg, did not consistently prevent myoclonic responses to IPS. After pretreatment with a subconvulsant dose of allylglycine (180--200 mg/kg), lysergic acid diethylamide, 0.1 mg/kg, retained the capacity to block myoclonic responses to IPS, and ergocornine 1 mg/kg reduced such responses. The convulsant effect of allylglycine was enhanced, however, so that prolonged seizure sequences began 19--96 min after ergocornine administration. The protective action of ergot alkaloids against epileptic responses induced by sensory stimulation is interpreted in terms of effects at several sites, including dopaminergic and serotoninergic synapses.