Nicotinic ACh receptor subtypes on gastrointestinally projecting neurones in the dorsal motor vagal nucleus of the rat

摘要

To determine the predominant nicotinic ACh receptor (nAChR) located on neurones in the dorsal motor nucleus of the vagus (DMV) that project to the gastrointestinal tract, we used the rat brainstem slice preparation and whole-cell recordings of DMV neurones identified by retrograde DiI tracing to pharmacologically characterize nAChRs. Pressure ejection of acetylcholine (ACh, 250 μm for 200 ms) from a patch pipette placed ≈10-20 μm from the surface of the recorded cell produced an inward current in most DMV neurones sampled. The average currents for neurones projecting to the fundus, antrum and caecum were 149 ± 38 (n = 25), 115 ± 18 (n = 29) and 117 ± 23 pA (n = 6), respectively. Blockade of the α7 subtype of nAChR with either α-bungarotoxin (α-BGT) or methyllycaconitine (MLA) counteracted 60-75 % of the ACh-evoked current in DMV neurones projecting to the fundus, antrum and caecum. In neurones projecting to the fundus and the antrum, currents resistant to α-BGT were significantly blocked by dihydro-β-erythroidine (10-20 nm), an antagonist of the α4β2 subtype of nAChR. In neurones projecting to the caecum, currents resistant to α-BGT were significantly depressed by a low concentration of mecamylamine (1 μm). Cytisine (100 μm), an agonist of nAChRs that contain the α7 or the β4 subunit, evoked significant currents in caecum-projecting neurones that were previously exposed to α-BGT. In contrast, cytisine had no effect on DMV neurones previously exposed to α-BGT that project to the fundus or antrum. Our data indicate that the prevailing nAChR subtype in DMV neurones projecting to the GI tract is the α7 subtype. In addition, we obtained evidence for the co-expression of the α4β2 nAChR subtype on DMV neurones projecting to the fundus and antrum, and the α3β4 nAChR subtype on DMV neurones projecting to the caecum.