[Neuroendocrine changes associated with corticotropic axis activity during lactation in rats].

Lactation in the rat is associated with a number of neuroendocrine and behavioural changes aimed at optimizing adequate development of the young. The present studies demonstrate that the suckling stimulus modifies both the adrenocortical system under basal and stimulated conditions, and reproductive functions. Despite tonically elevated concentrations of corticosterone in lactating females, we show that decreased stress-induced ACTH secretion is not caused by enhanced sensitivity to glucocorticoid negative feedback. Instead, it is postulated that lactation is associated with changes in stimulatory and/or inhibitory inputs converging to the CRF and/or vasopressin neurons of the hypothalamic paraventricular nucleus. In addition, central CRF release appears to mediate, at least in part, the inhibitory actions of suckling on LH and GnRH release. This action might be concerted with other neurotransmitters, neuropeptides and opioids systems and is likely to involve CRF populations outside the paraventricular nucleus.