The distribution of 5-HT immunoreactive systems in the brain of a saurian, the chameleon

The distribution of serotonin immunoreactive cell bodies and fibers was studied in the chameleon brain by using the immunohistochemical technique with antisera against serotonin coupled to a carrier with glutaraldehyde. Serotonin perikarya were found in the caudal midbrain tegmentum, in the lateral part of the nucleus reticularis isthmi, the lateral part of the nucleus interpeduncularis and along the midline in the raphe superior. More caudally, the serotonin immunoreactive cell bodies were located along the nucleus raphe inferior and ventrolaterally in the vicinity of the olivary complex. No immunoreactive cell bodies were found in the spinal cord nor in the paraventricular organ (PVO) of the hypothalamus. Immunoreactive fibers were observed in the entire brain. Prominent concentrations were found in the dorsal cortex, lateral septum, lateral geniculate nucleus, median eminence, pretectal nucleus, nucleus interpeduncularis, vestibular nucleus and olivary complex. Descending serotonin immunoreactive fibers were found in particular in the ventral motoneuron area in the spinal cord. One of the most interesting findings in this study was the lack of immunoreactive CSF contacting neurons in the PVO and the observation of an extensive plexus of supraependymal fibers, a feature reported so far only in mammals.