Short-term behavioural effects of neurohypophyseal hormones: pharmacological characteristics

Neurohypophyseal hormones and related peptides cause behavioural alterations after intracerebroventricular injection in mice. In the present study, these effects, consisting of excessive grooming and scratching, and of escape-directed activity in stressful situations, could easily be distinguished from those of other centrally acting peptides and drugs by means of two different behavioural bioassays. The effects were not antagonized by drugs that block cholinergic or adrenergic receptors, but they were powerfully suppressed by some potent psychotropic agents. Some compounds with strong vasoconstrictor or vasodilatory actions did not mimick or antagonize the behavioural alterations, suggesting that vasoconstriction is not essential for the induction of these effects. A considerable degree of tolerance could be induced and cross-tolerance was observed between different neurohypophyseal hormones. In rats, behavioural alterations caused by oxytocin and vasopressin could be demonstrated as well, but they were by far less pronounced than those observed in mice. For comparison, some data on the behavioural effects of bombesin are included. This peptide caused behavioural alterations similar to those of the neurohypophyseal hormones, but these were apparently mediated by different mechanisms. It is suggested that centrally-released oxytocin and/or vasopressin might be physiologically involved in the regulation of animal behaviour.