Development and distribution of substance P in the spinal cord and ganglia of embryonic and newly hatched chick: an immunofluorescence study.

The development and distribution of substance P (SP) immunoreactivity were studied in the spinal cord and ganglia of embryonic and newly hatched chick by using the indirect immunofluorescence method. Substance P immunoreactivity was first detected in the spinal cord at embryonic stages 18-20 (incubation day 3). Before stage 32 (day 7), it was mainly found in regions corresponding to the dorsolateral funiculus and Lissauer's tract. Subsequently, SP fibers appeared in the dorsal horn. By stage 38 (day 11), they were demonstrated almost throughout the gray matter, but mostly in laminae I and II. During this period, however, many SP-positive cells were found just ventral to the central canal at the thoracic level, although a few were also detected in other areas throughout the cord. In the white matter, very dense longitudinal SP fibers were observed in Lissauer's tract and the dorsolateral funiculus, where extremely dense plexuses of SP immunoreactivity were also detected around a group of nonimmunoreactive cell bodies. At later stages, no remarkable differences were noticed in the distribution of SP fibers, but the SP-positive cells decreased gradually in number and disappeared after hatching. However, they reappeared following colchicine treatment. In the spinal ganglia, SP immunoreactivity appeared initially at stage 25 (day 4). It was mostly located in small neurons of the mediodorsal region. These cells also decreased in number from later stages but increased by colchicine treatment after hatching. The development and distribution of SP immunoreactivity in the spinal cord and ganglia were generally comparable at all levels examined, except where indicated.