Neurons in the dorsal motor nucleus of the vagus may integrate vagal and spinal information from the GI tract.

Previous investigations have provided evidence that the activity of parasympathetic efferent neurons in the dorsal motor nucleus of the vagus (DMNV) may be influenced by either vagal afferent or spinal input from the gastrointestinal (GI) tract. Many questions remain, however, regarding the nature of this input and its integration by the brain stem. The present study was designed to examine one important aspect of this issue: the potential contribution of the spinal input to the brain stem in the generation of the response properties of intestine-sensitive neurons in the DMNV. Using intracellular recording and labeling techniques in adult rats, we found that ascending spinal pathways were capable of conveying both low- and high-threshold visceral information to the DMNV. We also determined that the neurons in the nucleus of the solitary tract failed to respond to intestinal distention when the vagal afferents to the brain stem had been severed, suggesting that the spinal projections terminate directly on the DMNV neurons. These data lend support to the emerging hypothesis that the spinal afferents that accompany the abdominal splanchnics are capable of responding to both innocuous and noxious stimuli. The results also suggest that the neurons in the DMNV play a larger role in the integration of visceral sensory information than was previously realized.