Neurochemical changes in the cholinergic system of the rat lateral vestibular nucleus following hemilabyrinthectomy.

The neurochemistry of the cholinergic system in the lateral vestibular nucleus (LVN) of the hemilabyrinthectomized rat was studied in view of the previous findings of other research showing that the process of vestibular compensation (VC) following hemilabyrinthectomy can be influenced by the administration of cholinergic agents. At 15 min, 2 h, and 7 days after right hemilabyrinthectomy, animals were killed and the LVNs were removed from sections of the brain stem for various neurochemical measurements. The content of acetylcholine (ACh) and the activity of acetylcholinesterase in the LVN showed no significant changes at any time interval. In contrast, choline acetyltransferase activity decreased slightly in the nucleus on the unoperated side 15 min after the operation. These findings possibly implicate alterations in ACh synthesis in the LVN at an early stage of VC. However, there was no significant alteration in either high-affinity choline transport into the LVN or ACh release from the LVN 15 min after the operation. Furthermore, muscarinic ACh-receptor binding also showed no significant changes. These results suggest that the possible alterations in the function of cholinergic synapses in the course of VC indicated by previous pharmacological studies may take place in regions of the brain other than the LVN.