Tracheal parasympathetic neurons of rat, mouse and guinea pig: partial expression of noradrenergic phenotype and lack of innervation from noradrenergic nerve fibres.

Noradrenergic nerves were studied in whole-mount preparations of the rat, mouse and guinea pig trachea by means of glyoxylic acid-induced catecholamine fluorescence and dopamine beta-hydroxylase immunoreactivity. In an effort to raise tissue levels of catecholamines, some specimens were also treated with the monoamine oxidase inhibitor pargyline, and with L-DOPA, a precursor of noradrenaline. Noradrenergic nerve fibres were detected around blood vessels, within the tracheal smooth muscle and in the mucosa, but never around or in the proximity of neurons of the tracheal ganglia, even after amine precursor loading. These parasympathetic ganglion cells did not show catecholamine fluorescence under control conditions. In the rat and mouse, but not in the guinea pig, some tracheal neurones were dopamine beta-hydroxylase immunoreactive and showed uptake and metabolism of amine precursors, thus expressing aspects of the catecholaminergic phenotype.