CHEMICAL TRANSMITTER SUBSTANCES IN BRAIN STEM OF CAT

Abstract

Two or five-unit microelectrodes were employed to record activity in, and to apply a variety of chemical agents to individual neurones in the midbrain and medulla. Acetylcholine, 5-hydroxytryptamine, noradrena-lin, d-tubocurarine, and several amino acids were applied electro-phoretically into the extracellular fluid surrounding neurones in the brain stem of the unanesthetized decerebrate cat. The sensitivity of these cells to amino acids is similar to that of spinal interneurones. The other compounds failed to influence the responses of neurones in the medullary and mesencephalic reticular formation. Acetylcholine excited some of the neurones in the inferior colliculus. Many of these acetylcholine-sensitive cells responded to auditory stimulation. The characteristics of action of acetylcholine were not those expected of an excitatory transmitter.