Faculty Bibliography

Immunohistochemical studies using an antibody against pituitary adenylate cyclase activating polypeptide-38 (PACAP) were performed on spinal cords and dorsal root ganglia harvested from two human cadavers. PACAP-like immunoreactivity (PACAP-LI) was detected in nerve fibers of the superficial layers of the dorsal horn, a few of which extended into the deeper laminae and as far as the ventral horn. At the thoracic segments, additional PACAP-LI nerve fibers were seen in the lateral funiculus projecting into the intermediolateral cell column. Dorsal root ganglia contained numerous PACAP-LI cell bodies of varying intensity. As a control, immunoreactivity to calcitonin gene-related peptide (CGRP) and substance P(SP) was also studied and found to be in nerve fibers of the substantia gelatinosa of the dorsal horn and in dorsal root ganglion cells. These results show that the pattern of distribution of PACAP-LI in the human spinal cord and dorsal root ganglia is similar to that of rodents and further suggest that PACAP may participate in sensory and autonomic functions.

Rat adrenal chromaffin cells were invested by a dense network of nerve fibers immunoreactive to pituitary adenylate cyclase activating polypeptide-38 (PACAP-IR). Immunohistochemical studies demonstrated the presence of PACAP-IR in nodose and dorsal root ganglion cells, but not in neurons of the intermediolateral cell column and other autonomic nuclei of the thoracic and upper lumbar spinal cord. Somata of the T7 to T12 paravertebral ganglia were PACAP-negative. A few lightly labeled neurons were occasionally noted in the dorsal motor nucleus of the vagus. Injection of the retrograde tracer Fluorogold into the left adrenal medulla 3 days prior to sacrifice resulted in the labeling of a population of neurons in the ipsilateral spinal cord intermediolateral cell column (T1 to L1), ipsilateral and contralateral nodose ganglia and ipsilateral dorsal root ganglia from T7 to T10 inclusive. A small number of lightly labeled somata was occasionally noted in the dorsal motor nucleus of the vagus. Combined retrograde tracing and PACAP immunohistochemistry showed that a population of Fluorogold-containing nodose and dorsal root ganglion cells were also PACAP-positive. Pre-treatment of the rats with capsaicin caused a marked reduction of the PACAP-IR in the adrenal gland as well as in the superficial layers of the dorsal horn and caudal spinal trigeminal nucleus. These findings, in conjunction with the apparent absence of PACAP-IR in spinal sympathetic preganglionic neurons, sympathetic postganglionic neurons, and dorsal motor nucleus of the vagus, raise the possibility that PACAP-IR fibers observed in the adrenal medulla are primarily sensory in origin. As a corollary, catecholamine secretion from chromaffin cells may be modulated by the peptidergic sensory afferents in addition to the cholinergic sympathetic preganglionic nerve fibers.