Cholinergic properties of spino-bulbo-spinal reflex inhibition

Abstract

Experiments were performed to determine whether the inhibitory phase of the spino-bulbo-spinal (SBS) reflex had a cholinergic component and, if so, whether it was at the spinal or at the bulbar level. Cats were decerebrated under ether anesthesia and then two laminectomies were performed. One laminectomy was done over the lumbar cord exposing L 6 and L 7 for stimulating and recording; the other was done at T 10 for cold-blocking the cord. By stimulating the dorsal root of L 7 and recording from the ventral root, the L 7 monosynaptic reflex (MSR) obtained was used to test the effects of eserine and atropine, both directly and on the SBS inhibition produced by stimulating the dorsal root of L 6. Eserine (0–1 mg/kg, i.v.) was found to have an immediate effect of increasing SBS inhibition. It also produced, at a longer latency, a deep inhibitory phase of both the conditioned and unconditioned MSR. Atropine (4 mg/kg, i.v.), while having no effect when given alone, not only blocked the effects of a preceding dose of eserine, but usually abolished the SBS reflex altogether. The major effects of both eserine and atropine were found to be above the level of T 10.