Chemotransduction properties of nodose ganglion cardiac afferent neurons in guinea pigs

To determine the chemotransduction characteristics of ventricular sensory n eurites associated with nodose ganglion afferent neurons, various chemicals were applied individually to epicardial sensory neurites associated with i ndividual afferent neurons in anesthetized guinea pigs. The following ion c hannel-modifying agents were tested: barium chloride, cadmium chloride, cal cium chloride, the chelating agent EGTA, nickel chloride, potassium chlorid e, tetraethylammonium chloride, and veratridine. An acidic solution (pH 6.0 ) and oxygen-derived free radicals (H2O2) were tested. The following chemic als were also tested: adenosine, alpha- and beta-adrenergic agonists, angio tensin II, bradykinin, calcitonin gene-related peptide (CGRP), histamine, n icotine, the nitric oxide donor nitroprusside, substance P, and vasoactive intestinal peptide. A total of 102 cardiac afferent neurons was identified, of which similar to 66% were sensitive to mechanical stimuli applied to th eir epicardial sensory fields. Application of individual ion channel-modify ing agents to epicardial sensory fields modified most associated afferent n eurons, with barium chloride affecting each neuron studied. Ventricular sen sory neurites associated with most identified neurons were also responsive to the other tested chemicals, with hydrogen peroxide, adenosine, angiotens in II, bradykinin, CGRP, clonidine, and nicotine inducing responses from at least 75% of the neurons studied. It is concluded that 1) the ventricular sensory neurites associated with nodose ganglion afferent neurons transduce a much wider variety of chemical stimuli than considered previously, 2) th ese sensory neurites employ a variety of membrane ion channels in their tra nsduction processes in situ, and 3) adrenergic agents influence on sensory neurites associated with cardiac afferent neurons suggests the presence of a cardiac feedback mechanism involving local catecholamine release by adjac ent sympathetic efferent postganglionic nerve terminals.