The nucleus tractus solitarii of the cat: a comparison of Golgi impregnated neurons with methionine-enkephalin- and substance P-immunoreactive neurons.

Golgi-impregnated and methionine-enkephalin (ME)- and substance P (SP)-immunoreactive neurons were studied throughout the feline nucleus tractus solitarii. The majority of Golgi-impregnated neurons in the NTS range in size from 5 to 18 micron. A noticeable exception is the large (15-30 micron) neurons of the ventrolateral subdivision. The Golgi-impregnated neurons possess dendritic trees which remain within the nucleus and even at times within the particular subdivisions. Golgi-impregnated neurons had a variety of spine forms: pedunculated, sessile, filiform, and complex. A number of neurons exhibited axons originating from the cell and they could be followed for distances up to 100 micron. ME- and SP-immunoreactive neurons were found in commissural, medial, lateral, and parvocellular subdivisions while ME-immunoreactive neurons were situated additionally in the intermediate and ventrolateral subdivisions. Both types of immunostained neurons were similar in size (6-20 micron) and shape of dendritic arbor. One population of ME-immunoreactive neurons resembled the large ventrolateral neurons of the Golgi impregnations. Neither type of immunostained neuron possessed the extensive dendritic arbor, numbers of spines, or axons of the Golgi-impregnated neurons. The presence of ME- and SP-immunoreactive neurons in regions which are associated with autonomic regulation suggests that these two peptides are involved in this process.