Physiological studies have established that preganglionic sympathetic nerve fibers innervating the rat superior cervical ganglion release a second transmitter, in addition to
acetylcholine. Based on pharmacological and histochemical investigations, possible candidates for this non-
cholinergic neurotransmitter include
vasoactive intestinal peptide and
peptide histidine isoleucine amide. For example, previous immunohistochemical studies have demonstrated that
antisera raised against both of these
peptides stain neural processes in the rat preganglionic cervical sympathetic trunk and in the superior cervical ganglion. In the present study, it was found that, when the cervical sympathetic trunk was ligated,
vasoactive intestinal peptide- and
peptide histidine isoleucine amide-like immunoreactivities built up on both sides of the
ligature. In addition, examination of the thoracic spinal cord in
colchicine-treated animals revealed
vasoactive intestinal peptide- and
peptide histidine isoleucine amide-like immunoreactivies in neuronal cell bodies in the intermediolateral cell column and in the region of the lateral funiculus adjacent to it. In a second group of animals in which retrograde tracing techniques were used, these two regions of the spinal cord were shown to contain most of the cell bodies of the preganglionic neurons that project to the superior cervical ganglion. Smaller numbers of retrogradely labeled neurons were found dorsal to the central canal and in the nucleus intercalatus. When either
vasoactive intestinal peptide- or
peptide histidine isoleucine amide-like immunostaining and retrograde labeling were examined in the same animals, double-labeled neurons were found in the intermediolateral cell column and in the lateral funiculus. These data demonstrate that
vasoactive intestinal peptide- and
peptide histidine amide-like immunoreactivities are present in certain of the preganglionic neurons that project to the superior cervical ganglion, supporting the hypothesis that
vasoactive intestinal peptide and
peptide histidine isoleucine amide are released in the
ganglion when these preganglionic neurons are activated.