IMMUNOHISTOCHEMICAL INVESTIGATION OF NEUROPEPTIDES IN THE CENTRAL-NERVOUS-SYSTEM OF THE AMPHIOXUS, BRANCHIOSTOMA-BELCHERI

The immunohistochemical localization of nine different neuropeptides w as studied in the central nervous system of the amphioxus, Branchiosto ma belcheri. In the brain, perikarya immunoreactive for urotensin I an d FMRFamide were localized in the vicinity of the central canal. One o f the processes of each of these perikarya was found to cross the dors oventral slit-like lumen of the central canal. Oxytocin-immunoreactive short fibers, but not perikarya, were detected in the ventral part of the brain. Perikarya immunoreactive for arginine vasopressin/vasotoci n, oxytocin and FMRFamide were widely distributed in the spinal cord. Arginine vasopressin/vasotocin-immunoreactive fibers often made contac ts with Rohde cell axons. Angiotensin II-immunoreactive perikarya were observed in the posterior half of the spinal cord, and urotensin I-im munoreactive perikarya were found in the caudal region of the spinal c ord. Cholecystokinin/gastrin-immunoreactive fibers, but not perikarya, were detected in the spinal cord; some extended as far as the ependym al layer of the cerebral ventricle. No colocalization of the peptides examined was observed. No immunoreactivity for atrial and brain natriu retic peptides nor for urotensin II was detected. The present study in dicates that there are at least six separate neuronal systems that con tain different peptides, respectively, in the central nervous system o f the amphioxus. Their functions remain to be determined.