Parasympathetic reflex salivary secretion in the cat parotid gland

The aim of the present study was to compare and to characterize the secretory and vasodilator effects in the parotid gland of sympathectomized cats elicited reflexly by electrical stimulation of the central cut ends of the chorda tympani (or glossopharyngeal) nerves (physiologically conveying gustatory stimuli), vagus nerve (visceral stimuli), and the lingual nerve after cutting the chorda tympani nerve (somatic stimuli). The threshold stimulus-intensity needed to elicit the salivary secretion and a blood flow increase was markedly lower for stimulation of the chorda tympani nerve and glossopharyngeal nerve (2 V for each nerve) than for the lingual nerve, inferior alveolar nerve, and vagus nerve (10 V for each nerve). The salivary and vasodilator responses to stimulation of each afferent nerve were all abolished by prior treatment with hexamethonium at a dose of 5 mg/kg, i.v. Prior treatment with scopolamine completely abolished the salivary secretion elicited by lingual nerve and glossopharyngeal nerve stimulation, but had less effect on the vasodilator response in the parotid gland. These results indicate that the secretory and vasodilator responses evoked by afferent traffic in the above nerves are mediated via an activation of the autonomic nervous system, particularly by a parasympathetic mechanism. They suggest that there is a marked difference in the ability of different sensory modalities to induce reflex salivary secretion and vasodilatation, there being low threshold nerve fibers in the chorda tympani and glossopharyngeal nerves and high threshold nerve fibers in the lingual nerve, vagus nerve, and inferior alveolar nerve.