THE DISTRIBUTION OF HYPOTHALAMIC NITRIC-OXIDE SYNTHASE MESSENGER-RNA IN RELATION TO GONADOTROPIN-RELEASING-HORMONE NEURONS

Using probes for rat neural nitric oxide synthase (NOS) mRNA and GnRH mRNA, we performed in situ hybridization to survey NOS mRNA distributi on within the hypothalamus of the male and female rat and sought evide nce for its expression in GnRH neurons. The NOS cRNA probe was radiola belled with S-35, and a digoxigenin-labeled rat GnRH cRNA probe was us ed for double-label studies. NOS mRNA was localized in discrete hypoth alamic areas, in grain clusters suggestive of individual neurons. NOS mRNA-positive cells were located mainly in the supraoptic and paravent ricular nucleus, particularly overlying the magnocellular division. Ro strally, cells expressing NOS mRNA were especially prominent in the di agonal band of Broca, in a distribution very similar to GnRH neurons. Nevertheless, only one of 370 cells labeled for GnRH mRNA appeared to be positive for NOS mRNA. We conclude that NOS mRNA is located promine ntly in regions where CRH, AVP and oxytocin cells are located. NOS mRN A-positive cells are located in close proximity to GnRH neurons, but r arely do such neurons express NOS mRNA.