Vestibular nerve activation of a brain stem cholinergic system influencing the spinal cord

Abstract

In precollicular decerebrate cats the modification of effects of VIIth nerve stimulation on the spinal cord by physostigmine and atropine was studied. 1. 1. Repetitive stimulation of the VIIIth cranial nerve produces 2 phenomena in the lumbar cord: dorsal root potential and tension in extensor muscles, associated with facilitation of the corresponding monosynaptic reflex. 2. 2. Both cord effects of VIIIth nerve stimulation are depressed by physostigmine (0.1 mg kg i.V.). 3. 3. Atropine sulfate (1 or 2 mg kg i.v.) will reverse the effects of physostigmine. 4. 4. The cerebellum is not involved in either drug effect; the phenomena are repeatable after removal of the cerebellum. 5. 5. The monosynaptic vestibular responses to single shock stimulation of the ipsilateral VIIIth nerve, recorded from the ascending medial longitudinal fasiculus, is not altered by physostigmine. 6. 6. Neostigmine (0.1 mg kg i.v.) fails to produce the inhibitory effects of physostigmine. Physostigmine-produced effects are not reversed by atropine methylnitrate (1 mg kg i.v.).