Parasympathetic vasodilator fibers in rat digastric muscle.

The present study examined whether parasympathetic vasodilator fibers exist in rat jaw-opening muscles such as the digastric muscle. The mental nerve was stimulated to activate the parasympathetic vasodilator nerve in the digastric muscle. Electrical stimulation of the mental nerve elicited intensity- and frequency-dependent increases of blood flow in this muscle. These increases were markedly reduced by hexamethonium in dose- and time-dependent manners, but pretreatment with phentolamine or propranolol had no effect. Pretreatment with atropine also attenuated the increase in blood flow in digastric muscle. When retrograde fluorogold was injected into the digastric muscle, labeled neurons were observed in the otic ganglion only on the ipsilateral side, but not in the pterygopalatine ganglion of either side. These results indicate that parasympathetic vasodilator fibers originate from cell bodies in the otic ganglion in rat digastric muscle.