Projections and pathways of VIP- and nNOS-containing airway neurons in ferret trachea.

Airway ganglia in ferret trachea are organized into two identifiable plexuses, the longitudinal trunk (LT) ganglia and the superficial muscular plexus (SMP) ganglia. LT ganglia contain cholinergic neurons and neurons in SMP ganglia synthesize vasoactive intestinal peptide (VIP) and nitric oxide (NO). Both plexuses of ganglia project to airway smooth muscle, but communications between LT and SMP ganglia have not been extensively studied. Ganglia of the LT were injected with neural tracers, either rhodamine- or biotin-labeled dextran amines, and colocalized with VIP or neuronal NO synthase (nNOS) by immunocytochemistry. Anterograde tracers were found in nerve fibers that formed basket-like complexes associated with neurons of LT and SMP ganglia and were observed in the nerve fibers of smooth muscle and tracheal plexus. Some VIP or nNOS positive neurons in the SMP ganglia contained retrogradely transported tracer. The findings suggest that neurons in the SMP and LT ganglia communicate in a reciprocal fashion and that VIP and nNOS neurons both receive and send neural inputs to neurons of LT, presumably cholinergic, ganglia. These connections probably contribute to the integration of neural control of airway and vascular smooth muscle tone and glandular secretion in the airways.