BURMEISTER, SS; MUNSHI, RG; FERNALD, RD; Stanford University; Stanford University; Stanford University: Afferents to the Preoptic Area in a Cichlid Fish with Socially Controlled Reproductive Phenotypes

Social signals regulate the reproductive axis in many vertebrates, and such regulation is central to the social system of the teleost Haplochromis burtoni. Territorial males suppress reproductive behavior and physiology of non-territorial males and social status governs growth rate. This is seen in the fact that territorial males have large preoptic gonadotropin-releasing hormone (GnRH) cells whereas non-territorial males have small GnRH cells. Loss of status causes loss of GnRH cell size and vice-versa. A detailed description of the connections to the preoptic area (POA), generally, and the preoptic GnRH neurons, specifically, will allow us to discover the neuroanatomical basis for the observed plasticity in reproductive phenotypes controlled by social interactions. We have mapped the afferents to the POA of sexually mature females and males by injecting biocytin into the rostral-most area of the POA in which resides the preoptic GnRH neurons. The largest population of labeled cells was in the ventral (subpallial) telencephalic area (V) with most of these cells located in the ventral nucleus of V (septal area). Labeled cells were also found in more caudal regions of the POA and the olfactory bulb. Although previous studies in teleosts identified a projection to the POA from the dorsal (pallial) division of the telencephalon and from thalamic nuclei, we observed no such projections to the GnRH-containing POA. Our results suggest that, although the POA receives pallial and thalamic projections, the GnRH neurons themselves do not. Rather, pallial and thalamic input to GnRH neurons may be indirect. Further work is underway to verify this interpretation. Supported by NRSA 1 F32 NS42984-01 to SSB & J. Javits Award NS 34950 to RDF.