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 pa rasympathetic efferent neurons in the dorsal motor nucleus of the vagu s (DMNV) may be influenced by either vagal afferent or spinal input fr om the gastrointestinal (GI) tract. Many questions remain, however, re garding the nature of this input and its integration by the brain stem . The present study was designed to examine one important aspect of th is issue: the potential contribution of the spinal input to the brain stem in the generation of the response properties of intestine-sensiti ve neurons in the DMNV. Using intracellular recording and labeling tec hniques in adult rats, we found that ascending spinal pathways were ca pable of conveying both low- and high-threshold visceral information t o the DMNV. We also determined that the neurons in the nucleus of the solitary tract failed to respond to intestinal distention when the vag al afferents to the brain stem had been severed, suggesting that the s pinal projections terminate directly on the DMNV neurons. These data l end 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 neuro ns in the DMNV play a larger role in the integration of visceral senso ry information than was previously realized.