NEURONAL NITRIC-OXIDE SYNTHASE IMMUNOREACTIVITY IN THE RESPIRATORY-TRACT OF THE FROG, RANA-TEMPORARIA

Physiological and histochemical studies have recently supported the no tion that nitric oxide (NO) is the transduction signal responsible for the non-adrenergic, non-cholinergic relaxation of the vasculature as well as the airways of the mammalian lung. We report the presence of i mmunoreactivity to NO synthase (NOS) in nerve cell bodies and nerve fi bres in the neural plexus of the buccal cavity and lungs of the frog, Rana temporaria, using the indirect immunocytochemical technique of av idin-biotin and the NADPH-diaphorase technique. The neural ganglia loc ated next to the muscle layer and within the connective tissue of the buccal cavity were partially immunoreactive for NOS. in the lungs, NOS immunoreactivity occurred in nerve cell bodies, as well as in both my elinated and unmyelinated nerve fibres. Fine nerve fibres immunoreacti ve to NOS were observed within the muscle fibre bundles and next to th e respiratory epithelium. Both the presence of NOS immunoreactivity an d the positive histochemical reaction for NADPH-diaphorase in the neur al plexus of amphibian respiratory tract suggests a broad evolutionary role for NO as a peripheral neurotransmitter.