Serotonin-containing cell bodies in novel brain locations: effects of light input

Cell bodies staining positively for serotonin (5HT) appear in the suprachiasmatic nuclei (SCN) of hamsters that have been held in constant darkness (DD) for several months but are otherwise untreated. No such cell bodies are found in the SCN of animals that have been bilaterally enucleated for the same amount of time; however, in enucleated hamsters 5HT-containing cell bodies appear in the superior colliculus. These data provide the first indication that changes in sensory input can modulate 5HT levels in cells bodies outside of the raphe nuclei.