Characterization of the raphe nuclei of the reptile Ctenosaura pectinata.

The brain stem of the lizard Ctenosaura pectinata was studied in 10 microns thick sections following the Nissl and eosin-hematoxilin techniques. Furthermore, the distribution of serotonin-containing neuronal somata in this encephalic region was determined by means of an indirect immunofluorescence technique using a specific antibody to serotonin. Two of the cellular groups of the brain stem were identified as the superior and inferior raphe nuclei, which show serotonergic cells of variable size (between 17 and 30 microns). The results obtained in the present study together with information coming from other authors, suggest that serotonergic neuronal systems placed at brain stem level of vertebrates are phylogenetically ancient.