Effect of intracarotid injection of adenosine on the activity of RVLM neurons in barodenervated rats.

To observe the effect of intracarotid administration of adenosine on neurons in the rostral ventrolateral medulla (RVLM) region, 72 spontaneous active units were extracellularly recorded from 28 Sprague-Dawley rats with sino-aortic denervation. The results obtained are as follows: (1) intracarotid administration of Ado (25 micrograms/kg) reduced the discharge rate from (23.5 +/- 3.0) to (16.5 +/- 2.6) spikes/s (P < 0.001) in 31 out of 36 RVLM neurons, while the blood pressure and heart rate had no significant change (P > 0.05); (2) 8-phenyltheophylline (8-PT, 15 micrograms/kg), a nonselective adenosine receptor antagonist, and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 50 micrograms/kg), a selective A1 adenosine receptor antagonist, completely blocked the inhibitory effects of Ado in 24 units; and (3) in 12 units, glibenclamide (500 micrograms/kg), a blocker of ATP-sensitive potassium channel, abolished the effect of Ado. These results indicate that Ado can induce an inhibition of spontaneous electrical activity of RVLM neurons, an effect which is mediated by adenosine A1-receptor with the involvement of ATP-sensitive potassium channels.