Neonatal hypermelatonemia and adult plasticity in terms of testis growth and functions and endocrine axes have been studied in rats. Melatonin was administered for 21 days post partum and adult rats at 90 days were evaluated for hormonal profile and germ cell dynamics by histometric enumeration. The results clearly suggest that, neonatal hypermelatonemia induces adult plasticity in body weight gain but not of testes and, permanently lowers the set point of the neuroendocrine reproductive axis and elevates the set point of the thyroid axis. Functionally, testicular germ cell number is increased by decreased apoptotic loss but there is a paradoxically increased loss of spermatids and spermatozoa by way of altered Sertoli-germ cell adhesive properties. Plasticity changes in the form of decreased tubular length, basement area and Sertoli cell number are also recorded. It can be concluded from the observations made herein that, neonatal melatonin perturbation can shape later phenotypic responses of male gonads and their controlling hormonal axes.
