Evidence of a functional α7-neuronal nicotinic receptor subtype located on motoneurons of the dorsal motor nucleus of the vagus

In vitro autoradiography using ¹²⁵I-α-bungarotoxin (αBGTx) and anti-α7 immunohistochemistry were performed on the dorsal motor nucleus of the vagus (DMV) of sham and chronically vagotomized rats to determine whether the α7-nicotinic acetylcholine receptor (nAChR) is located postsynaptically on DMV neurons whose axons contribute to the vagus nerve. Intense bilateral ¹²⁵I-α-BGTx binding and anti-α7 immunostaining were observed in coronal brain sections containing the DMV of sham-vagotomized animals. Unilateral cervical vagotomy resulted in ipsilateral losses of ¹²⁵I-α-BGTx binding and anti-α7 immunostaining from the DMV. Simultaneous staining of rat brainstem sections with anti-α7 and anti-choline acetyltransferase (ChAT) antibodies (to identify cholinergic DMV neurons that project into the vagus nerve) revealed that every DMV neuron that was stained for ChAT showed α7-staining as well. In vagotomized animals, no ChAT-positive neurons expressing α7-nAChRs remained in the ipsilateral DMV. We conclude that the α7-nAChR subtype is located postsynaptically on DMV neurons. To test whether the α7-nAChR is similar to the α7-homomeric nAChR, experiments were performed in anesthetized rats, and compounds were microinjected into the DMV while monitoring intragastric pressure (IGP). α-BGTx and strychnine antagonized nicotine-induced increases in IGP; no antagonism was observed with methyllycaconitine, a compound known to block the homomeric α7-nAChR subtype. Recovery from α-BGTx-induced antagonism of the nicotine response was observed. We conclude that there is a nAChR containing the α7-subunit in the DMV that is different from the homomeric α7-nAChR subtype.