DISTRIBUTION OF CALCITONIN-GENE-RELATED PEPTIDE-LIKE IMMUNOREACTIVITYIN THE BRAIN OF THE SMALL-SPOTTED DOGFISH, SCYLIORHINUS-CANICULA L

The distribution of neuropeptides has been useful in comparing neurona l aggregates of elasmobranchs with those in other vertebrates. The dis tribution of calcitonin gene-related peptide (CGRP)-like immunoreactiv ity in the brain of the dogfish was examined with an antiserum to rat alpha-CGRP. Western blot analysis confirms that our antiserum recogniz es a single peptide in the dogfish brain very similar to mammalian CGR P. CGRP-like immunoreactivity was located in discrete neuronal groups. CGRP-like-immunoreactive (CGRP-ir) neurons were found in the motor nu clei III, IV, V, VI, VII, IX, and X of the brainstem motor column and in the octavolateral efferent neurons. In the isthmal region, two grou ps of CGRP-ir neurons appeared in the parabrachial region and reticula r substance. Three other CGRP-ir cell groups were observed in the mese ncephalon: in the ventral tegmental area, in the substantia nigra, and one widely scattered but numerous population in superficial layers of the optic tectum. In the diencephalon, CGRP-ir cells were observed in the magnocellular preoptic nucleus and the organon vasculosum hypotha lami. A population of CGRP-ir cells was also observed in the entopedun cular nucleus in the impar telencephalon. CGRP-ir fibers of central or igin were widely distributed in the brain, but the most conspicuous ar eas were found in the ventral telencephalon, the hypothalamus, the mes encephalic lateral reticular area, and the dorsolateral isthmal region . The neurointermediate lobe of the hypophysis was also richly innerva ted by CGRP-ir fibers. CGRP-ir sensory fibers of cranial nerves IX and X and of dorsal spinal roots formed very conspicuous terminal fields in the lobus vagi and Cajal's nucleus commissuralis and in the dorsal region of the substantia gelatinosa, respectively. Comparison of the d istribution of fibers and perikarya in dogfish and other vertebrates s uggests that this CGRP-ir system has been well conserved during evolut ion. (C) 1995 Wiley-Liss, Inc.