Changes of enzyme activity in T-cells during induced maternal behaviour in rats

Continuous exposure to foster pups elicits specific behavioural patterns in adult naive female or male rats. The first exposure induces active avoidance of young. By day 2 or 3 adults show neutral behaviour. Next day complete maternal behaviour begins to develop; e.g. retrieving of pups, nursing and crouching. The avoidance reaction activates stress mechanisms, and the developed maternal behaviour is associated with moderate prolactin release. The question is raised whether pup-induced catecholamine and prolactin release is able to alter enzyme activity in T-cells. Using Arg-Pro-; Leu-Pro; and Pro-Pro-4-nitroanilide as substrates the activity of a marker enzyme dipeptidyl peptidase IV, DP IV, EC. 3.4.14.5., was measured in T-cell suspension prepared from the thymi of adrenalectomized female and male Wistar rats. We found that changes of DP IV activity during the pup-induced avoidance phase could be prevented by propranolol pretreatment indicating the role of catecholamines in this phenomenon. Prolactin released during artificial maternal behaviour in female rats resulted in an elevation of DP IV activity which failed to develop, if they were given daily injections of bromocriptine or apomorphine. It is concluded that pup-exposure is the most physiological way to influence hormonal mechanisms and immune functions, which are highly responsive to sensory stimuli.