Distribution and development of VIP immunoreactive neurons in the spinal cord of the embryonic and newly hatched chick.

The distribution and development of vasoactive intestinal polypeptide (VIP) immunoreactive elements were studied in the spinal cord of embryonic and newly hatched chicks with the indirect immunofluorescence method. VIP neurons were first detectable in the presumed dorsal horn at stages 27-28 (incubation day 5). Subsequently they increased in number, and by stage 39 (day 12) many occurred in lamina I, in the nucleus of the dorsolateral funiculus, and in the lateral portion of the neck of the dorsal horn throughout the cord. However, at the thoracic level many were also situated lateral to the central canal, with their processes running to the ipsilateral lateral and contralateral ventral funiculi. The pattern described above remained visible in both embryonic and colchicine-pretreated newly hatched chicks. During development, VIP fibers appeared later than cell bodies. In the gray matter, they were mainly scattered in the intermediate zone, especially around the central canal at all levels examined. In the white matter, however, longitudinal fibers were observed in the lateral funiculus throughout the cord, but mostly at the cervical level, though some also occurred in the ventral funiculus. This finding supports the idea that spinal VIP neurons might project rostrally via the lateral funiculus. In addition, no VIP immunoreactivity was found in the spinal ganglia, but examination of the sympathetic paravertebral ganglia showed immunoreactivity as described by others.