Chemotransduction properties of nodose ganglion cardiac afferent neurons in guinea pigs

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Abstract
To determine the chemotransduction characteristics of ventricular sensory neurites associated with nodose ganglion afferent neurons, various chemicals were applied individually to epicardial sensory neurites associated with individual afferent neurons in anesthetized guinea pigs. The following ion channel-modifying agents were tested: barium chloride, cadmium chloride, calcium chloride, the chelating agent EGTA, nickel chloride, potassium chloride, tetraethylammonium chloride, and veratridine. An acidic solution (pH 6.0) and oxygen-derived free radicals (H2O2) were tested. The following chemicals were also tested: adenosine, α- and β-adrenergic agonists, angiotensin II, bradykinin, calcitonin gene-related peptide (CGRP), histamine, nicotine, the nitric oxide donor nitroprusside, substance P, and vasoactive intestinal peptide. A total of 102 cardiac afferent neurons was identified, of which ∼66% were sensitive to mechanical stimuli applied to their epicardial sensory fields. Application of individual ion channel-modifying agents to epicardial sensory fields modified most associated afferent neurons, with barium chloride affecting each neuron studied. Ventricular sensory neurites associated with most identified neurons were also responsive to the other tested chemicals, with hydrogen peroxide, adenosine, angiotensin 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) these sensory neurites employ a variety of membrane ion channels in their transduction 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 adjacent sympathetic efferent postganglionic nerve terminals.