The naris muscles in tiger salamander

Abstract.

The naris muscles control the aperature of the external naris in tiger salamanders, Ambystoma tigrinum, and may contribute to glandular secretion. Autonomic neurons of the palatine ganglion and possibly neurons associated with the nervus terminalis innervate these muscles. To elucidate the neural control of the naris muscles, neurotransmitters in nerve fibers supplying the naris muscles and in neurons of the palatine ganglion were examined using acetylcholinesterase enzyme histochemistry and immunocytochemistry to visualize possible peptide candidates for muscle innervation. The naris muscles, autonomic neurons, and associated nerve fascicles demonstrated strong acetylcholinesterase labeling, and the muscles were innervated by substance P fibers passing through the palatine ganglion from the trigeminal ganglion. Gonadotropin-releasing hormone and molluscan cardioexcitatory peptide-like immunoreactivities were found in secretory cell bodies and/or fibers in the palatine ganglion, and gonadotropin-releasing hormone was found in fiber projection pathways into the muscles. Vasoactive intestinal peptide was found in cell bodies and fibers of the palatine ganglion but appeared to provide a sparse innervation to the naris dilator muscle only. These findings suggest a typical autonomic cholinergic and sensory innervation of the naris muscles with some variations in peptide innervation. The presence of gonadotropin-releasing hormone in palatine ganglion and naris constrictor muscle suggests a potential modulation of autonomic neurons and perhaps even muscle fibers by this neuropeptide. We hypothesize that this reproductive hormone may modulate the activity of the naris constrictor muscle during reproductively appropriate events in order to provide access of pheromones to the vomeronasal organ.