PREGANGLIONIC PARASYMPATHETIC SALIVATORY NEURONS IN THE BRAIN-STEM CONTAIN MARKERS FOR NITRIC-OXIDE SYNTHESIS IN THE RABBIT

The present study investigated the possible presence of markers for ni tric oxide synthesis in brainstem preganglionic parasympathetic neuron s involved in control of the submandibular and sublingual salivary gla nds of rabbits and rats. Retrograde axonal tracing was performed with biotinylated dextran to identify preganglionic parasympathetic salivat ory neurons and combined with NADPH diaphorase histochemistry or nitri c oxide synthase immunohistochemistry. The results of the double-label ling experiments demonstrated that most of the retrogradely labelled p reganglionic parasympathetic neurons in rabbits contained the markers for nitric oxide synthesis, whereas, in rats most retrogradely labelle d neurons lacked the markers for nitric oxide synthesis. These observa tions suggest that nitric oxide could influence ganglionic transmissio n in parasympathetic pathways controlling salivary secretion in the ra bbit, but not in the rat.