VENTRICULAR SENSORY NEURONS IN CANINE DORSAL-ROOT GANGLIA - EFFECTS OF ADENOSINE AND SUBSTANCE-P

Effects elicited by adenosine and substance P on ventricular sensory e ndings of 14 dorsal root ganglion afferent neurons were studied in sit u in anesthetized dogs. Sensory-field application of adenosine (1 mu M ) increased the activity of these neurons by 179%. Application of a no nspecific adenosine antagonist to epicardial sensory fields suppressed ongoing activity in all 14 neurons by 39%. Application of an A(1)- or A(2)-adenosine-receptor antagonist suppressed activity generated by 1 0 of these neurons by 44 and 59%, respectively. Adenosine applied afte r A(1)- or A(2)-receptor blockade increased activity in 10 neurons by 131 and 145%, respectively, indicating that A(1)- and A(2)-receptor ef fects were not additive. Application of substance P (1 mu M) to identi fied sensory fields increased activity in 12 of these neurons by 169%, whereas application of a substance P-receptor antagonist reduced acti vity generated by these neurons by 75%. Myocardial ischemia increased activity of nine neurons associated with left ventricular sensory fiel ds by 320%, an effect that was counteracted by the nonspecific adenosi ne-receptor antagonist. It is concluded that A(1)- and A(2)-adenosine receptors, as well as substance Preceptors, are present on ventricular epicardial sensory nerve endings of dorsal root ganglion neurons that are tonically active during normal states, becoming further activated during ischemia.