Canine salivary secretion from the submaxillary glands before and during retching

To investigate the changes in salivary secretion associated with emesis, salivary secretion from the submaxillary gland and centrifugal discharge from the parasympathetic postganglionic nerve fibers from the submandibular ganglion were measured after emetic stimulation in chloralose-anesthetized and paralyzed dogs. In the basal condition, saliva flow and the basal frequencies of single unit discharges from the parasympathetic nerve were very low. Esophageal and gastric distension and lingual nerve afferent stimulation generally increased salivary secretion and nerve activity. Administration of apomorphine (0.2-0.3 mg/kg im) or intragastric infusion of copper sulfate (10%, 50 ml) elicited an excitation of parasympathetic nerve activity, and salivary secretion was facilitated in parallel to this nerve activity. The excitatory responses induced by emetic stimulation were suddenly depressed in correspondence with retching activities. This depression in nerve activity appeared 200-400 ms after the beginning of retching volleys of the phrenic nerve and continued during retching. These results indicate that the salivary center receives excitatory and inhibitory inputs from two different sources before and during retching activities, respectively.