The distribution of corticotropin-releasing factor immunoreactive neurons and nerve fibres in the brain of Gambusia affinis and Salmo trutta.

The study was carried out on the distribution of neurons and fibres which contain the Corticotropin releasing factor-like (CRF) immunoreactivity in the encephalon of two species of teleosts, Gambusia affinis and Salmo trutta. The peroxidase-antiperoxidase (PAP) immunocytochemical technique was employed. The present study has shown differences between both species. In Gambusia affinis, positive neurons were observed in the area ventralis telencephali pars lateralis (VLT), in the nucleus praeopticus (NPO) and in the nucleus lateralis tuberis (NLT). The immunoreactive fibres were in the area ventralis telencephali, in the preoptic hypophyseal tract and in the hypophysis. In Salmo trutta the immunoreactive cells were seen in the pars magnocellularis and pars parvocellularis of the NPO and in cerebrospinal fluid (CSF) contacting neurons of the NLT. The pattern of distribution of immunoreactive fibres in Salmo trutta was different from that in Gambusia affinis. In addition to the distribution of perikarya in Gambusia affinis (in the VLT and in the preoptic hypophyseal tract), fibres were also observed in the tubero-hypophyseal tract and in the posterior hypothalamus. The hypophysis of Salmo trutta also presents an extensive labelling. The interspecific differences shown in the present study should be due to the different degree of evolution in the two species studied and to other causes, such as environmental ones.