Dopamine modulates carotid nerve responses induced by acetylcholine on thecat petrosal ganglion in vitro

We have recently reponed that application of acetylcholine (ACh) or nicotin e to the petrosal ganglion-the sensory ganglion of the glossopharyngeal ner ve-elicits a burst of discharges in the carotid nerve branch, innervating t he carotid body and sinus, but not in the glossopharyngeal branch, innervat ing the tongue and pharynx, Thus, the perikarya of sensory neurons for the carotid bifurcation exhibit selective cholinosensitivity. Since dopamine (D A) modulates carotid nerve chemosensory activity, we searched for the prese nce of DA sensitivity at the perikarya of these neurons in the cat petrosal ganglion superfused in vitro. Applications of DA in doses of up to 5 mg to the ganglion did not modify the rate of spontaneous discharges in the caro tid nerve, However, if DA was applied 30 s before ACh injections, ACh-evoke d reactions were modified: low doses of DA enhanced the subsequent response s to ACh, while high doses of DA depressed the responses to ACh. This depre ssant effect of DA on ACh responses was partially antagonized by adding spi roperone to the superfusate. Our results show that the response to ACh of p etrosal ganglion neurons projecting through the carotid nerve is modulated by DA acting on D-2 receptors located in the somata of these neurons. Thus, dopaminergic modulation of cholinosensitivity could be shared also by the membranes of peripheral endings and perikarya of primary sensory neurons in volved in arterial chemoreception. (C) 1999 Elsevier Science B.V. All right s reserved.