HYPOTHALAMIC METABOLISM OF NEUROTRANSMITTERS (SEROTONIN, NOREPINEPHRINE, DOPAMINE) AND NPY, AND GONADAL AND ADRENAL ACTIVITIES, DURING THE EARLY POSTNATAL-PERIOD IN THE RAT

It is noteworthy that in the rat the early postnatal life is marked by an activation of both the corticostimulating function of the adenohyp ophysis in neonates of both sexes acid of the gonadostimulating functi on mainly in males. In order to specify if such neuroendocrine variati ons are temporally correlated with changes in the hypothalamic metabol ism of neurotransmitters, the hypothalamic metabolism of serotonin (5 HT), norepinephrine (NE), and dopamine (DA) and the hypothalamic conte nt of neuropeptide Y (NPY) have been investigated in newborn rats of b oth sexes, delivered at term by cesarean section, as well as changes i n the activity of both the hypothalamo-pituitary adrenal axis (HPA) an d the hypothalamo-pituitary gonadal axis (HPG). Experimental data sugg ested that 1) in males a rise in hypothalamic metabolism of 5 HT, NE a nd DA occurs during the first two hours after delivery, whereas in fem ales, only the metabolism of NE increases. Moreover, the postnatal met abolism of NE was higher in females than in littermate males; 2) NPY c ontent of the hypothalamus, which was at birth significantly higher in males than in females, dropped in the former but not in the latter; 3 ) in newborn males, an early surge of plasma testosterone occurs, sugg esting postnatal activation of the HPG axis; on the other hand, in fem ales, a late and slight increase in plasma estradiol is observed; 4) i n early postnatal life, a sex-independent rise in plasma ACTH and adre nal and plasma corticosterone levels suggest a comparable activation o f the HPA axis in newborns of both sexes. In conclusion, the early pos tnatal activation of the corticostimulating function in neonates of bo th sexes and that of the gonadostimulating function, mainly in males, could be temporally correlated with a rise in the hypothalamic metabol ism of two neurotransmitters, 5 HT and NE, and of HPY content. Accordi ng to our data, a sex-dependent metabolism of neurotransmitters in the hypothalamus is already apparent in early postnatal life.