SOURCE OF SEXUALLY DIMORPHIC GALANIN-LIKE IMMUNOREACTIVE PROJECTIONS IN THE TELEOST FISH POECILIA-LATIPINNA

A galaninlike peptide has a sexually dimorphic distribution in the teleost fish, the sailfin molly. An extensive system of galanin-like immunoreactive (GAL-LI) fibers has been described in the brainstem and spinal cord of the male molly, which is absent in the female (Cornbrooks and Parsons, companion paper). As GAL-LI in the mammalian spinal cord has been localized to neurons of origin in the dorsal root ganglia and dorsal and ventral horns, the present study was undertaken to determine whether the sexually dimorphic GAL-LI in the male molly may originate in part from corresponding sources in this species. Colchicine treatments of the spinal cord and dorsal root ganglia did not result in GAL-LI staining in neuronal somata in these regions. Following complete transection of the spinal cord and at any level of the spinal cord, there was a complete absence of GAL-LI caudal to the lesion site. In fish that received unilateral spinal transection, there was a loss of GAL-LI ipsilateral and caudal to the lesion. Finally, in fish that received lesions in the rostral hypothalamus, there was a complete loss of GAL-LI in the sexually dimorphic fiber system in the brainstem and spinal cord, but not in non-dimorphic GAL-LI regions of the brainstem. Thus the sexually dimorphic fiber system in the male molly may originate in neurons of the preoptic nucleus that are sexually dimorphic for a GAL-LI peptide. This preoptico-spinal pathway may mediate sex-specific behaviors in this species.