Afferent connections of the hypothalamic retrochiasmatic area in the rat.

The afferent projections to the retrochiasmatic area (RCA) of the rat hypothalamus have been studied by means of retrograde axonal transport of horseradish peroxidase. Iontophoretic deposit of the marker was used in most animals, and consistent projections from the hypothalamic ventromedial nucleus, the lateral part of the substantia nigra and the parabigeminal nucleus (NPB) were observed. A comparison between NPB projections and projections from the neighboring tegmentum suggests that some neurons of the NPB project to both the RCA and the superior colliculus. Consequently, these NPB neurons might link visual information on its way toward the retrochiasmatic area which, in view of its strategic position, could play a role in neuroendocrine processes.