Proconvulsant, convulsant and other actions of the D- and L-stereoisomers of allylglycine in the photosensitive baboon, Papio papio.

The effects of the intravenous or intracerebroventricular injection of the stereoisomers, and the racemic mixture, of allylglycine (2-amino-pent-4-enoic acid) have been studied in baboons, Papio papio, with photosensitive epilepsy. Enhancement of the natural syndrome of photosensitivy epilepsy is seen 1-12 h (maximally at 3-8 h) after L-allyglycine, 100 mg/kg, intravenously, or D,L-allyglycine, 200 mg/kg, intravenously. Such enhancement is seen with a slower onset, and to a lesser, and more variable, extent after D-allyglycine, 500-750 mg/kg, intravenously. Brief focal or generalised seizures occurred (in the absence of intermittent photic stimulation) after L-allyglycine, 150-200 mg/kg, intravenously. This effect is similar to that previously observed after D,L-allyglycine, 300-400 mg/kg. D-Allyglycine, 780 mg/kg, intravenously produced episodes of vertical nystagmus with increased extensor motor tone, but no 'spontaneous' seizures. Intracerebroventricular injection of L-allylglycine, D-allyglycine or D,L-allyglycine, 100 mg in 1 ml saline, did not modify the natural syndrome of photosensitive epilepsy. D-Allylglycine, or D,L-allyglycine, 100 mg intracerebroventricularly, after 1-2 h gave rise to a syndrome with vomiting, sustained vertical nystagmus, and intermittent extensor spasms. The results are interpreted in terms of regional differences in the metabolism of the two isomers to active compounds that can inhibit glutamic acid decarboxylase. D-Allylglycine is active only at the brain stem and cerebellum because D-amino acid oxidase is largely confined to these brain areas.