Endocrine Abstracts

Around birth, beginning in mid-pregnancy and lasting until lactation, dramatic neuroendocrine and behavioural adaptations occur in the maternal organism as, for example, the reactivity of the HPA axis to various stressors is blunted. Further, state anxiety, the emotional evaluation of a stressorand the level of calmness are altered at this time. In addition to an attenuated feed forward drive to the HPA axis, reduced activity of the CRH system, and lack of excitatory inputs to the hypothalamus, activation of the brain oxytocin and prolactin systems may regulate these adaptations.Increased neuropeptide synthesis and local release within selected brain regions occurs not only in response to various stressors, but also during reproduction. Furthermore, manipulation of oxytocin and prolactin receptors within the brain using agonists, receptor antagonists or antisenseoligodesoxynucleotides revealed their involvement in regulating stress responses. Thus, oxytocin released, for example, within the amygdala, was found to exert an anxiolytic action in pregnant rats and to promote maternal aggressive behaviour in lactation. Also, brain oxytocin severely inhibitsthe (re)activity of the HPA axis as reflected by elevated secretion of ACTH and corticosterone into blood after oxytocin receptor antagonist treatment and attenuated responses after infusing oxytocin into the cerebral ventricles in virgin and male rats. Similarly, brain prolactin was found to be anxiolytic in virgin female, male and lactating rats, and to be significantly involved in the inhibition of the HPA axis activity in lactation. Thus, the elevated activity of these neuropeptides ensures not only essential reproductive functions and related behaviours, but plays also a major role in stress adaptations around birth. This is beneficial not only for the offspring preventing excessive plasma glucocorticoid concentrations, but also for the mother protecting the maternal brain against dramatic fluctuations in sexual steroids, which may otherwise trigger psychopathologies including post partum depression.