Involvement of neurotransmitter and neuropeptides in behavioural action of some neurohormones

Investigations were made of the action of ACTH and LH-RH on a number of behavioural paradigms and the possible involvement of neurotransmitters or opiates by pretreatment of receptor blockers in rats and mice. ACTH delayed the extinction of active avoidance behaviour. Atropine and haloperidol blocked this action, whereas phenoxybenzamine and propranolol were ineffective. LH-RH or a highly potent analogue of LH-RH (D-Trp6-LH-RH) decreased the rate of disappearance of dopamine in the hypothalamus following alpha-methyl- paratyrosine inhibition of catecholamine synthesis, and blocked the accumulation of serotonin following MAO inhibition. LH-RH or the analogue attenuated the consolidation of passive avoidance learning. Apomorphine-induced cage-climbing was also inhibited by the LH-RH analogue, but this action was not influenced by naloxone. Open-field activity (ambulation, rearing and grooming) was decreased by the analogue peptide. Naloxone blocked the action on ambulation and rearing, but was ineffective on grooming. The LH-RH analogue caused a dose-dependent increase in cataleptogenic activity. This action could not be blocked with naloxone. The LH-RH analogue suppressed picrotoxin-induced seizures. Naloxone restored the situation to the control level. The data suggested that the effects of some neurohormones are mediated by transmitters or endogenous opiates, and that both peptide-transmitter and peptide-peptide interactions have to be considered in the action of neurohormones.