B. S Meldruma, R Naqueta,
Medical Research Council Neuropsychiatry Unit, Carshalton, Surrey, Great Britain
Département de Neurophysiologie appliquée, Institut de Neurophysiologie et de Psychophysiologie, C.N. R.S., 31, Chemin Joseph-Aiguier, 13-Marseille 9°, France
Following the demonstration that lysergic acid diethylamide (LSD) inhibits myoclonic responses to intermittent photic stimulation (ILS) in the baboon, some other hallucinogenic drugs and some “non-hallucinogenic” derivatives of lysergic acid have been tested for their effects on the EEG and on photically induced epilepsy in twenty-two adolescent baboons (Papio papio).
Psilocybin (1–4 mg/kg) and dimethyltryptamine (2–4 mg/kg) produced marked autonomic effects, EEG changes consistent with a severe disturbance of consciousness and a complete abolition of myoclonic or paroxysmal EEG responses to ILS (thus closely resembling the effect of LSD, 40–100 μg/kg). Mescaline (up to 32 mg/kg) was relatively ineffective on both the background EEG and on the myoclonic responses to ILS. After methysergide (2–5 mg/kg), although the autonomic effects were less severe than after psilocybin, there were muscular hypotonia, an abnormal EEG and reduction or abolition of the epileptic responses to ILS. BOL 148 and methergoline appeared less potent than methysergide, but, at 4 mg/kg, both drugs abolished ILS-induced myoclonus.
Averaged responses to flash stimulation showed that psilocybin resembled LSD 25 in modifying transmission in the afferent visual pathway, whereas methysergide, in doses blocking ILS-induced myoclonus, did not alter primary evoked responses in the visual cortex.
It is suggested that a serotoninergic system is probably involved in the epileptic responses of the baboon to ILS.