Efferents from the suprachiasmatic nucleus to basal forebrain nuclei in the green treefrog (Hyla cinerea)

Injections of horseradish peroxidase (HRP) into the eye, striatum, preoptic area, or ventral hypothalamus of the green treefrog (Hyla cinerea) demonstrated an indirect retinal pathway to each basal forebrain region via the suprachiasmatic nucleus (SCN). Intraocular injections resulted in HRP-filled fibers within the ventral portion of the SCN bilaterally. Apparent en passant and terminal swellings on these fibers were seen adjacent to SCN cells. Cells in both the ventral and dorsal portions of the SCN were retrogradely filled following each of the forebrain injections, but the relative distributions of filled cells were different. The striatum receives a bilateral projection mainly from cells in the ventral portion of the SCN. A small ipsilateral projection from this same SCN region reaches the ventral hypothalamus. The SCN projection to the preoptic area arises from a more uniform distribution of cells, with the majority located in the ipsilateral dorsal region of the nucleus. The striatum is believed to be involved in orientation responses, while the preoptic area and ventral hypothalamus regulate gonadal activity related to reproduction. Each of these areas receives auditory input carrying information about acoustic communication signals, social cues important for coordinating reproductive activity. Input from the SCN could provide these same basal forebrain centers with information about the photic environment, an important environmental cue regulating reproduction.