A possible antagonistic interaction between LSD and naloxone was investigated in rats. LSD (375 mcg/kg) administration in rats (280-320 g) elicited a diphasic reaction consisting of a brief excitable period (up to 8 min) followed by a prolonged catalepsy (8 min-1 hr). While the cataleptic response was antagonized by a single injection of naloxone (Endo, 0.2 mg/kg. i.m. given 30 min after LSD administration), pretreatment with nalaxone shortened the excitable phase and potentiated the catalepsy.
