Immunocytochemical evidence for calcitonin gene-related peptide-like neurons in the dorsal horn and lateral spinal nucleus of the rat cervical spinal cord.

Calcitonin gene-related peptide (CGRP) in the dorsal horn of the rat spinal cord was assumed until now to be principally of primary afferent origin. It is shown here, on the basis of both light and electron microscopic immunocytochemical evidence, that some cell bodies of the dorsal horn and lateral spinal nucleus (LSn) of the rat cervical spinal cord contain a CGRP-like immunoreactivity. At the light microscopic level, immunoreactive cell bodies were observed in animals pretreated with colchicine injected intraventricularly, CGRP-like cell bodies were morphologically heterogeneous and distributed in the three superficial layers of the dorsal horn. They were very rare in lamina I and more numerous in laminae II and III. A group of immunoreactive cell bodies was also observed in the LSn. Using electron microscopic techniques, a few immunoreactive cell bodies were observed even in control animals. In addition, relatively numerous immunoreactive dendrites were observed in lamina II. The specificity of the reaction and the physiological implications of the results are discussed.