Molecular and electrophysiological characterization of the GnRH systems in Atlantic cod

Teleosts are unique among vertebrates regarding neural control of the adenohypophysis. The cells are directly innervated instead of receiving their input through a portal system. Furthermore, the distribution of the different cell types in the adenohypoph ysis in teleosts is highly regionalized, whereas the distribution is scattered in mammals. This organization of the pituitary in fish makes it possible to obtain fairly homogenous primary cultures of the different cell types. In contrast to mammals, teleo sts have separate cells secreting FSH and LH. This suggests the possibility of a more finely tuned regulation of these hormones compared to mammals. So far there are no data on this, or on the general cell properties of the FSH and LH-secreting cells in t eleosts. We want to combine molecular neuroendocrinology and electrophysiology to obtain a thorough understanding of the GnRH systems and the effects on the gonadotropes in the Atlantic cod (Gadus morhua). Since nothing is known about the GnRH systems or the electrophysiological properties of gonadotropes in cod, and teleost gonadotropes are only roughly characterized so far, basic experiments are needed. Different forms of GnRHs and GnRH-Rs found in Atlantic cod will be cloned by my collaborator, Finn-Ar ne Weltzien. He will in his project investigate their distribution in the brain and pituitary by in situ hybridization. The different components of the GnRH signaling pathway in cod gonadotropes will be isolated by different patch-clamp methods and Fura-2 microfluorometry in combination with different pharmacological regimes; the electrophysiological response, the Ca2+ signaling and the second messengers. These approaches will help to understand the differential role of different forms of GnRH during the pubertal activation in cod.