Relationships between the morphology and function of gastric- and intestine-sensitive neurons in the nucleus of the solitary tract.

This study employed single cell recording and intracellular iontophoretic injection techniques to characterize and label gastric- and/or intestine-sensitive neurons in the rat nucleus of the solitary tract (NST). It was possible to divide our sample of NST neurons into three broad groups based on their response to increased intra-gastric and intra-duodenal pressure. Group 1 cells (N = 14) were excited by duodenal distention but were not responsive to gastric stimulation. Most of these intestine-sensitive neurons exhibited a delayed tonic response to the stimulus. Group 2 neurons (N = 13) were excited by gastric distention but were not sensitive to distention of the duodenum. The typical Group 2 neuron evidenced a rapid, phasic response to the distention stimulus. Group 3 neurons (N = 29) responded to both gastric and duodenal stimulation. We found that the Group 2 neurons had greater dendritic length and more dendritic branch segments than the Group 1 or Group 3 neurons. Most of the Group 1 neurons were found in the subpostremal/commissural region of the NST, while the majority of the Group 2 neurons were in the gelatinous subnucleus and a disproportionate number of the Group 3 neurons were located in the medial subnucleus. The results of this investigation demonstrate that 1) there are relationships between the morphology and physiology of distention-sensitive neurons in the NST, and 2) there are distinct functional differences between the gelatinous, medial and commissural subnuclei of this nucleus.