The cells of origin of a sexually dimorphic serotonergic input to the medial preoptic nucleus of the rat.

The medial preoptic nucleus (MPN) is a sexually dimorphic complex composed of 3 distinct cytoarchitectonic subdivisions, and a sexually dimorphic distribution of presumably serotonergic fibers is associated with the lateral part of the nucleus (MPNl). In this study the probable cells of origin for these serotonergic fibers were identified by using a combined fluorescent retrograde tracer and immunofluorescence method. Serotonergic afferents to the MPN appear to arise exclusively from the dorsal raphe nucleus (B7), the median raphe nucleus (B8), and the region adjacent to the medial lemniscus (B9).