The effect of selective lesions on vestibular nuclear complex choline acetyltransferase activity in the rat

Biochemical, physiological and behavioral evidence suggests that acetylcholine (ACh) may play a neurotransmitter role in central vestibular function. However, the anatomic basis for a possible cholinergic influence on the vestibular nuclear complex (VNC) is unknown. To investigate vestibular cholinergic anatomy, we have made selective lesions of neurons intrinsic to the VNC, and of most known afferents to the VNC, and we have measured the activity of choline acetyltransferase (ChAT), a specific marker for cholinergic neurons, following such lesions. We found that a kainic acid lesion of the VNC, and lesions of vestibular afferents, including the VIIth cranial nerve, cerebellum, spinal cord, vestibular commissure and the interstitial nucleus of Cajal, did not affect VNC ChAT activity. We conclude that there are no cholinergic neurons intrinsic to the VNC, and that these lesioned afferents are not cholinergic. It is likely, therefore, that a cholinergic projection to the VNC arises from a region other than those lesioned; possibilities include the nuclei of the reticular formation, the upper cervical cord and local pontomedullary nuclei.