Effect of facial nerve transection on acetylcholinesterase, choline acetyltransferase and [3H]quinuclidinyl benzilate binding in rat facial nuclei.

Choline acetyltransferase activity and localization of acetylcholinesterase and [3H]quinuclidinyl benzilate binding sites (muscarinic receptors) in rat facial nuclei were examined 2 weeks after right facial nerve transection or sham control surgery. Choline acetyltransferase activity in the right facial nucleus of nerve-transected rats was only one-third of that in the left nucleus. Histochemical observations revealed loss of acetylcholinesterase from most motoneurons and neuropil of the right facial nucleus after axotomy. Autoradiographic grains, marking muscarinic receptors, were likewise depleted substantially from this region. Facial nuclei of control animals were identical with respect to all of these neurochemical measures and undistinguishable from the left facial nucleus of nerve-transected rats. Cholinergic enzymes are known to be synthesized by motoneurons, but the source of muscarinic receptors in the facial nucleus is not known. Since all three proteins are depleted from the facial nucleus after axotomy of motoneurons, it is concluded that these cells produce cholinergic enzymes and muscarinic receptors. Synthesis of muscarinic receptors by facial motoneurons could indicate these neurons are cholinoceptive. Axotomy should be a useful tool for determining which other neurotransmitter receptors are produced by facial motoneurons and efferent neurons in other cranial nerve nuclei.