Effect of vagal and splanchnic nerve section on Fos expression in ferret brain stem after emetic stimuli.

Previous studies have demonstrated that intraduodenal hypertonic saline (IHS) induces dense Fos expression within two regions of the ferret dorsal vagal complex (DVC): the area postrema (AP) and the medial subnucleus of the nucleus of the solitary tract (mn). The aims of the present 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 animals that had received either vagotomy alone, vagotomy and splanchnic nerve section, or sham operation. The emetic response was studied in both awake and anesthetized animals, and Fos induction was studied in anesthetized animals. Vagotomy alone or combined with splanchnic nerve section abolished the emetic response and the area of dense labeling within the mn and reduced but did not abolish the labeling in the AP. It was concluded that both the emetic reflex and the dense expression of Fos 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 vagal afferents, and the residual labeling that is present in the AP of neurectomized animals may be mediated via a blood-borne route.