Evidence of a functional alpha 7-neuronal nicotinic receptor subtype located on motoneurons of the dorsal motor nucleus of the vagus

In vitro autoradiography using I-125-alpha -bungarotoxin (alpha -BGTx) and anti-alpha7 immunohistochemistry were performed on the dorsal motor nucleus of the vagus (DMV) of sham and chronically vagotomized rats to determine w hether the alpha7-nicotinic acetylcholine receptor (nAChR) is located posts ynaptically on DMV neurons whose axons contribute to the vagus nerve. Inten se bilateral I-125-alpha -BGTx binding and anti-alpha7 immunostaining were observed in coronal brain sections containing the DMV of sham-vagotomized a nimals. Unilateral cervical vagotomy resulted in ipsilateral losses of I-12 5-alpha -BGTx binding and anti-alpha7 immunostaining from the DMV. Simultan eous staining of rat brainstem sections with anti-alpha7 and anti-choline a cetyltransferase (ChAT) antibodies (to identify cholinergic DMV neurons tha t project into the vagus nerve) revealed that every DMV neuron that was sta ined for ChAT showed alpha7-staining as well. In vagotomized animals, no Ch AT-positive neurons expressing alpha7-nAChRs remained in the ipsilateral DM V. We conclude that the alpha7-nAChR subtype is located postsynaptically on DMV neurons. To test whether the alpha7-nAChR is similar to the alpha7-hom omeric nAChR, experiments were performed in anesthetized rats, and compound s were microinjected into the DMV while monitoring intragastric pressure (I GP). alpha -BGTx and strychnine antagonized nicotine-induced increases in I GP; no antagonism was observed with methyllycaconitine, a compound known to block the homomeric alpha7-nAChR subtype. Recovery from alpha -BGTx-induce d antagonism of the nicotine response was observed. We conclude that there is a nAChR containing the alpha7-subunit in the DMV that is different from the homomeric alpha7-nAChR subtype.