Corticotropin-releasing hormone-immunopositive nerve elements in apposition to chicken gonadotropin-releasing hormone I-containing perikarya in Japanese quail (Coturnix coturnix japonica) brain

The neuroanatomic basis of how stress inhibits reproduction in birds is not understood. To address this question we used double-label immunofluorescence histochemistry to determine whether corticotropin-releasing hormone (CRH)-immunoreactive (ir) neuronal elements contact chicken gonadotropin-releasing hormone I (cGnRH I)-ir somata in brains of Japanese quail. The double-label system used a sheep anti-cGnRH I primary antibody with a secondary antibody conjugated to dichlorotriazinylaminofluorescein dihydrochloride for green fluorescence and a rabbit anti-CRH antibody with a secondary conjugated to Texas Red for red fluorescence. Immunohistochemical (IHC) distribution of both peptides resembled that in previous reports using single-label IHC. In four areas of the quail brain in which CRH nerve fibers and cGnRH I somata co-occurred (bed nucleus commissural pallii, nucleus preopticus medialis, nucleus septalis lateralis and nucleus accumbens), numerous instances were found of CRH-ir nerve fibers or terminals in apposition to cGnRH I cell bodies. These interactions provide a potential neuroanatomic route by which CRH may directly inhibit the activity of cGnRH-I-containing neurons, thereby inhibiting gonadotropin output and halting or slowing the progression of reproductive cycles. It remains to be demonstrated by electron microscopy whether these interactions, which appear abundant by IHC, represent instances of synaptic contact, as has been demonstrated to occur in analogous areas in mammalian species.