The role of central serotoninergic neurotransmission in the morphine abstinence syndrome in rats.

It was found that 200 mg/kg of DL-p-chlorophenylalanine (PCPA) and 2 mg/kg of methergoline drugs inhibiting central serotoninergic transmission-decreased naloxone precipitated abstinence wet dog shakes in morphine-dependent rats. The inhibitory effect of PCPA was reversed by 200 mg/kg of 5-hydroxy-L-tryptophan (5-HTP) but not by the same amount of L-tryptophan (TP). 5-HTP alone (200 mg/kg) increased wet dog shakes epissodes, whereas TP alone in the same dosage practically did not have any influence on the wet dog shakes in morphine-dependent rats. These findings suggest that brain serotonin may play some role in the expression of wet dog shakes in morphine-dependent rats.