ONTOGENY OF GONADOTROPIN-RELEASING HORMONE-CONTAINING NEURONS IN THE TELEOST BRAIN

We investigated changes in two gonadotropin releasing hormone (GnRH)-c ontaining neuronal populations during juvenile development in the Afri can teleost, Haplochromis burtoni. Juveniles were sampled at weekly in tervals and GnRHir neurons were identified through immunocytochemistry (ICC), then counted and measured on computer-captured video images. S oma size of GnRH neurons in the preoptic area (POA), which regulate go nadotropin release from the pituitary; is socially modulated in adults . Here we show that in juveniles the soma size of these neurons increa ses as a linear function of body weight. Terminal nerve (TN) GnRHir ne urons, in contrast, are not involved in pituitary regulation and their soma size is not socially modulated in adults. In juveniles, soma siz e of these neurons is a quadratic function of body size and the covari ance of soma size and body size is much less than in the POA GnRHir ne urons. In both populations, GnRHir neuronal number covaries with body size or age only in the earliest juvenile stages. Analysis of the deve lopment of these two distinct GnRHir neuronal populations provides ins ight into their functional differentiation in adults.