NEUROCHEMICAL CHARACTERIZATION OF INTRINSIC NEURONS IN FERRET TRACHEAL PLEXUS

Although neuroanatomical and neurophysiological features of neurons in the ferret trachea have been studied, the neural mediators associated with this plexus have not been completely characterized. The purpose of this study was to examine the occurrence of choline acetyltransfera se (ChAT), nitric oxide synthase (NOS), vasoactive intestinal peptide (VIP), and substance P (SP) in the intrinsic neurons of this plexus. T he distribution of double- and triple-labeled neurons was quantified i n cryostat sections and in whole mounted specimens to evaluate the neu rochemical profiles. About 85 % of the nerve cell bodies with ChAT imm unoreactivity (ChAT-IR) were located in ganglia of the longitudinal tr unks or the closely associated bridge ganglia. Approximately 15 % of C hAT-positive neurons were in ganglia of the superficial muscular plexu s. Conversely, VIP-IR neurons were most frequent in the superficial mu scular plexus (> 75 %) and < 10 % were observed in the longitudinal tr unks or bridge neurons. Most NOS- and SP-IR neurons were also located in the superficial muscular plexus. The following distribution of neur ochemical profiles was determined for neurons of the superficial muscu lar plexus: 11 % only NOS, 20 % only VIP, 5 % only SP, 67 % NOS and VI P, and 40 % VIP and SP. NOS, VIP, and SP were frequently localized in the same nerve cell body. The occurrence of nerve terminals containing only SP located around the borders of individual NOS/VIP/SP-containin g neurons suggests possible sensory innervation to the airway neurons. The results demonstrate that: (1) most cholinergic nerves do not cont ain VIP, NOS, or SP; (2) cholinergic neurons are predominantly located in the longitudinal trunk ganglia; (3) VIP, NOS, and SP are predomina ntly located in the superficial muscular plexus ganglia; and (4) nerve terminals containing exclusively SP suggesting possible sensory origi n, are closely associated with some neurons in the plexus.