Autoradiographic demonstration of quinuclidinyl benzilate binding sites inthe vestibular organs of the gerbil

Gerbil vestibular tissues were isolated by microdissection and incubated in vitro with H-3-quinuclidinyl benzilate (H-3-QNB). Control tissues were inc ubated in medium containing unlabeled atropine to differentiate non-specifi c from specific binding. Autoradiographic grain densities were determined b y morphometric techniques and evaluated by two-tailed t-test. The label den sities of sensory epithelia from experimental preparations of ampulla, utri cle and saccule were found to be significantly higher than those in the adj acent endolymphatic compartment and also higher than those of adjacent stro mal tissue comprising connective tissue, nerve fibers and capillaries. In c ontrast, no tissue region in atropine controls showed label density signifi cantly above that of the endolymphatic compartment. Label density of ampull ar sensory epithelium incubated with 3H-QNB alone was significantly higher than that of sensory epithelium from utricle or saccule. Grain density was greater in the peripheral regions of the ampullar crista compared to the ve rtex. Appreciable label was also present in nerve bundles beneath the senso ry epithelium of the ampulla. The current study demonstrates the existence of putative muscarinic neurotransmitter/neuromodulator receptor sites in ma mmalian vestibular sense organs at locations corresponding to efferent inne rvation, with particularly significant concentrations in the ampulla. (C) 1 999 Elsevier Science B.V. All rights reserved.