Expression of NADPH-diaphorase activity by guinea-pig paratracheal neurones

Pharmacological evidence suggests that nitric oxide (NO) is involved in non-adrenergic, non-cholinergic, nerve mediated responses seen in guinea-pig trachealis muscle. The synthetic enzyme for NO (NO synthase) has recently been shown to be responsible for neuronal NADPH-diaphorase activity. Therefore, to determine whether intrinsic paratracheal neurones could be a source of NO in the trachea, expression of NADPH-diaphorase activity was examined histochemically using whole mount preparations of the tracheal plexus. Many paratracheal neurones were found to express moderate to high levels of NADPH-diaphorase activity and are thus likely to be a source of NO in this tissue. This observation provides further evidence that NO is involved in the regulation of relaxation in airway smooth muscle.