The excitatory non-cholinergic, non-adrenergic nervous system of the guinea-pig airways

Guinea-pig airways, from the trachea to the hilus bronchi, were studied in vitro for the presence of excitatory nerves. Electrical field stimulation of the tissues demonstrated excitatory cholinergic nerves in the trachea and main bronchi; their effect was blocked by atropine. Field stimulation in the presence of atropine elicited contractions of the main and hilus bronchi. Tetrodotoxin blocked the field stimulation-induced contraction in all preparations; this indicated that nerves were stimulated. The contractions were, however, not blocked by any conventional receptor antagonists. These findings suggest that the non-adrenergic, non-cholinergic nerves are an important excitatory nervous system in the guinea-pig bronchi.