Substance P: Immunocytochemical Localization and Codistribution with Tyrosine Hydroxylase in the Vagal Nuclei of the Rat
The dorsal motor nucleus of the vagus (DMV) located in the hindbrain medulla of the brain is the origin of preganglionic parasympathetic outflow to the stomach. Neurotransmitters and neuropeptides contained within the DMV are ultimately responsible for innervation of the stomach. Innervation occurs through the vagus nerve which connects the DMV to the the stomach and causes gastric motility. In the present study, immunocytochemical labeling in the medulla of rats was used to determine the distribution pattern of substance P (SP) a neuropeptide, and its relationship to tyrosine hydroxylase (TH), an enzyme precursor to dopamine. Results showed a dense network of SP-immunoreactive (SP-ir) fibers and terminals throughout the levels of the DMV as well as in the adjacent nucleus tractus solitarius (NTS) which is the afferent vagal nuclei. Some SP-ir cell bodies were present in the DMV at caudal levels, however, none were observed in this nucleus at further rostral levels. This result is in contrast to the situation in the cat, where SP-ir neurons are dense throughout the DMV and, therefore, indicates a species difference regarding distribution of SP-ir cells in the vagal nuclei. To evaluate the distribution of SP in relation to that of tyrosine hydroxylase (TH) in the area of the DMV, dual-staining immunocytochemical techniques were used for both SP and TH. The pep tides were found to have similar distribution patterns in the caudal DMV and rostral NTS. Thus, SP and TH are said to be codistributed which suggests a functional interaction between the two neuromodulators. in controlling gastric motility; however, further experimental studies are necessary to elucidate the possibility of coexistence of the two peptides within the same neuron in the DMV and NTS.