Neuronal organization of the supracommissural ventral telencephalon and the nucleus preopticus periventricularis in the himé salmon (landlocked red salmon, Oncorhynchus nerka): a Golgi study.

The neuronal organization of the supracommissural ventral telencephalon (Vs) and the nucleus preopticus periventricularis (NPP) of the medial preoptic area (MPOA) in the himé salmon (landlocked red salmon, Oncorhynchus nerka) was studied by means of the Nissl staining and the rapid Golgi methods. The Vs was composed of many laterally-orienting spiny neurons and a few sparsely-spined polymorphous neurons. Some of the laterally-orienting neurons extended their dendrites into the lateral forebrain bundle (LFB), suggesting that they may receive inputs from the telencephalofugal and telencephalopetal fibers in the LFB. The NPP consisted of five types of sparsely-spined neurons: laterally-orienting, bipolar, cerebrospinal fluid (CSF)-contacting, commissural, and multipolar neurons. Some of the laterally-orienting neurons extended their dendrites into the medial forebrain bundle (MFB) and regions near the LFB, suggesting that they may also receive inputs from the telencephalofugal and telencephalopetal fibers running there. The presence of the CSF-contacting neurons in the NPP suggests that the NPP may receive humoral informations from the CSF. Involvement of these CSF-contacting neurons in the control of the reproductive functions was discussed. The neuronal organization of the NPP in the himé salmon was compared with that of the MPOA in other vertebrates.