EFFECT OF VAGAL AND SPLANCHNIC NERVE-SECTION ON FOS EXPRESSION IN FERRET BRAIN-STEM AFTER EMETIC STIMULI

Previous studies have demonstrated that intraduodenal hypertonic salin e (IHS) induces dense Fos expression within two regions of the ferret dorsal vagal complex (DVC): the area postrema (AP) and the medial subn ucleus of the nucleus of the solitary tract (mn). The aims of the pres ent experiments were to determine the peripheral pathways involved in excitation of DVC neurons after IHS and the relative importance of mn and AP excitation in the emetic response to this stimulus. The emetic response and the distribution of Fos were examined after IHS in animal s that had received either vagotomy alone, vagotomy and splanchnic ner ve section, or sham operation. The emetic response was studied in both awake and anesthetized animals, and Fos induction was studied in anes thetized animals. Vagotomy alone or combined with splanchnic nerve sec tion abolished the emetic response and the area of dense labeling with in the mn and reduced but did not abolish the labeling in the AP. It w as concluded that both the emetic reflex and the dense expression of F os within the mn after IHS are dependent on an intact vagus nerve. The excitation of neurons in the AP after IHS is partially dependent on v agal afferents, and the residual labeling that: is present in the AP o f neurectomized animals may be mediated via a blood-borne route.