Pituitary adenylate cyclase-activating polypeptide innervation of the mudpuppy cardiac ganglion.

The presence and potential origin of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) was determined in cardiac ganglia of the mudpuppy, Necturus maculosus. Although PACAP has been implicated in the regulation of cardiac function in several mammalian species, the presence of this peptide in the autonomic nervous system (ANS) of other species is unclear. Thus, this study is the first to characterize this highly conserved peptide in the ANS of a non-mammalian species. PACAP-immunoreactivity was observed in nerve fibers throughout the mudpuppy cardiac ganglia and often was co-localized with the sensory neuropeptides substance P and calcitonin gene-related peptide. Removal of all extrinsic inputs to the ganglia by organ culture eliminated PACAP-immunoreactivity in the cardiac ganglia, whereas bilateral vagotomies only partially reduced PACAP-labeling. PACAP-immunoreactive neurons were observed in both high thoracic dorsal root ganglia and in vagal sensory ganglia. While no PACAP-positive neurons were observed in caudal medulla brainstem regions, PACAP-containing nerve fibers were found in the region of the nucleus solitarius. These results suggest that, in the mudpuppy, PACAP is found primarily in visceral afferent fibers, originating from cells in either the dorsal root ganglia or vagal sensory ganglia. Based on their anatomic localization, these afferent fibers may function to transmit important sensory information to cardiovascular centers in the brain as well as serving as local reflex inputs to modulate postganglionic parasympathetic output within the cardiac ganglion itself.