DIFFERENTIAL C-FOS EXPRESSION IN THE NUCLEUS OF THE SOLITARY TRACT AND SPINAL-CORD FOLLOWING NOXIOUS GASTRIC DISTENSION IN THE RAT

c-Fos has been used as a marker for activity in the spinal cord follow ing noxious somatic or visceral stimulation. Although the viscera rece ive dual afferent innervation, distention of hollow organs (i.e. esoph agus, stomach, descending colon and rectum) induces significantly more c-Fos in second order neurons in the nucleus of the solitary tract an d lumbosacral spinal cord, which receive parasympathetic afferent inpu t (vagus, pelvic nerves), than the thoracolumbar spinal cord, which re ceives sympathetic afferent input (splanchnic nerves). The purpose of this study was to determine the contribution of sympathetic and parasy mpathetic afferent input to c-Fos expression in the nucleus of the sol itary tract and spinal cord, and the influence of supraspinal pathways on Fos induction in the thoracolumbar spinal cord. Noxious gastric di stention to SO mmHg (gastric distension/80) was produced by repetitive inflation of a chronically implanted gastric balloon. Gastric distens ion/80 induced c-Fos throughout the nucleus of the solitary tract, wit h the densest labeling observed within 300 mu m of the rostral pole of the area postrema. This area was analysed quantitatively following se veral manipulations. Gastric distension/80 induced a mean of 724 c-Fos -immunoreactive nuclei per section. Following subdiaphragmatic vagotom y plus distention (vagotomy/80), the induction of c-Fos-immunoreactive nuclei was reduced to 293 per section, while spinal transection at T2 plus distention (spinal transection/80) induced a mean of 581 nuclei per nucleus of the solitary tract section. Gastric distension/80 and v agotomy/80 induced minimal c-Fos in the T8-T10 spinal cord (50 nuclei/ section), but spinal transection/80 induced 200 nuclei per section. Re petitive bolus injections of norepinephrine produced transient presser responses mimicking the presser response produced by gastric distensi on/80. This manipulation induced minimal c-Fos in the nucleus of the s olitary tract and none in the spinal cord. It is concluded that noxiou s visceral input via parasympathetic vagal afferents, and to a lesser extent sympathetic afferents and the spinosolitary tract, contribute t o gastric distention-induced c-Fos in the nucleus of the solitary trac t. The induction of c-Fos in the nucleus of the solitary tract is sign ificantly greater than in the viscerotopic segments of the spinal cord , which is partially under tonic descending inhibition, but is not sub ject to modulation by vagal gastric afferents. Distention pressures pr oduced by noxious gastric distention are much greater than those produ ced during feeding, suggesting that c-Fos induction in the nucleus of the solitary tract to noxious distention is not associated with physio logical mechanisms of feeding and satiety. The large vagal nerve-media ted induction of c-Fos in the nucleus of the solitary tract following gastric distension suggests that parasympathetic afferents contribute to the processing of noxious visceral stimuli, perhaps by contributing to the affective-emotional component of visceral pain. Copyright 1996 IBRO.