CALCITONIN-GENE-RELATED PEPTIDE - DISTRIBUTION AND EFFECTS ON SPONTANEOUS RHYTHMIC ACTIVITY IN EMBRYONIC CHICK SPINAL-CORD

Immunohistochemical and in vitro electrophysiological techniques were utilized to examine the distribution and possible role of calcitonin g ene-related peptide (CGRP) in the spinal cord of the developing chick. CGRP-like immunoreactivity first appeared in the lateral motor column of the lumbosacral spinal cord at embryonic day 6 followed by the eme rgence of fiber immunoreactivity in the dorsal horn at embryonic day 1 1. A rostrocaudal survey of the cervical to lumbosacral spinal cord in embryonic day 18 chick demonstrated robust CGRP-like immunoreactivity at all levels in both putative motor neurons and dorsal horn fibers. Additionally, small immunoreactive lamina VII neurons were observed in sections of lumbosacral cord. In the embryonic day 10 (E10) in vitro reduced spinal cord preparation, bath application of the calcitonin ge ne-related peptide antagonist human alpha-CGRP fragment 8-37 decreased the frequency and increased the duration of episodes of spontaneously occurring rhythmic activity. Conversely, application of alpha or beta forms of calcitonin gene-related peptide increased the frequency of t he rhythmic episodes. The electrophysiological results suggest there i s a constitutive release of calcitonin gene-related peptide contributi ng to the spontaneous rhythmic activity. Immunohistochemical results f rom E10 animals suggest that CGRP-like immunoreactive putative motoneu rons may be the source of the released CGRP. (C) 1998 Elsevier Science B.V.