Expression and physiological function of the neurotrophins BDNF, NT-3 and their receptors trkB, trkC and P75(LNTR) in the hen ovarian follicle

In recent years, studies have made it apparent that the role of the neurotrophin gene family is not limited to neuronal survival and differentiation, but extends to the function of non-neuronal cell types such as those of the ovary. To date, the presence or physiological role of neurotrophins within the avian ovary has not been described. Therefore, the present research was accomplished to further our understanding of neurotrophin expression and role in ovarian function in the post-hatch chick and laying hen.;Studies described herein demonstrate differential expression of mRNA levels, as well as mRNA and protein tissue distribution, for brain derived neurotrophin factor and neurotrophin-3, as well as the neurotrophin receptors, trkB, trkC and p75LNTR in hen ovarian follicles. The studies also demonstrate that changes in expression correlate to specific stages of ovarian follicular maturation. The data suggest that NT-3 and P75LNTR may play a role in follicle atresia or in mediating differentiation of prehierarchal follicle granulosa cells.;Moreover, a novel function of BDNF-mediated trkB signaling in granulosa cells of maturing avian ovarian follicles is proposed. Localization, in preovulatory follicles, of BDNF mRNA and protein to the theca interna immediately adjacent to granulosa cells expressing trkB mRNA and protein suggests a paracrine action by BDNF from the theca interna upon the granulosa layer. Furthermore, trkB mRNA levels can be modulated by pituitary LH and neuronal VIP in preovulatory follicles, as well as by FSH and VIP in prehierarchal follicles. Finally, expression of neurotrophins and receptors in the post-hatch chick ovary suggests a role in ovarian follicle organization, as levels of trkC and trkB are high during follicle organization, followed by a decrease by the end of primordial follicle assembly. Expression levels of NT-3 and BDNF remain essentially constant throughout the period of follicle assembly.;In summary, this dissertation characterizes the levels and distribution of neurotrophins and neurotrophin receptors in the adult hen and post-hatch chick ovary. Furthermore, a novel function is proposed for the BDNF-induced trkB signaling, as well as possible physiological regulators of ovarian follicle trkB mRNA expression.