Topographic distribution of nicotinic acetylcholine receptors in the cristae of a turtle

Abstract

The neurochemical basis of cholinergic efferent modulation of afferent function in the vestibular periphery remains incompletely understood; however, there is cellular, biochemical and molecular biological evidence for both muscarinic and nicotinic acetylcholine (ACh) receptors (nAChRs) in this system. This study examined the topographic distribution of α-bungarotoxin (α-BTX) nAChRs in the cristae of a turtle species. Cristae were perfusion-fixed, cut at 20 μm on a cryostat and incubated with α-BTX or polyclonal antibodies raised against Torpedo nAChR. Light microscopy showed abundant specific labeling of nAChR in the central zone of each hemicrista on the calyx-bearing afferents surrounding type I hair cells and on the base of the type II hair cells. Within the peripheral zone, dense labeling of type II hair cells near the torus and sparse or no label was observed on type II hair cells near the planum. The α-BTX binding showed a similar pattern within the cristae. The similarity between the topographic distribution of α-BTX binding nAChR and of efferent inhibition of afferents supports the notion that the inhibitory effect of afferents is mediated by nAChR.