Pharmacological properties of feline red nucleus

Biogenic amines and related compounds, and certain amino acids were applied by microelectrophoresis onto single red nucleus neurons. The cats were either lightly anesthetized or specially prepared in the unanesthetized state.l-Glutamic anddl-homoeysteic acids were potent excitants while gamma-aminobutyric acid was a strong depressant of neuronal activity. Acetylcholine and carbamylcholine, 5-hydroxytryptamine and lysergic acid diethylamide, noradrenaline and dopamine and other phenylethylamines stopped brachio-rubral synaptic transmission, reduced “spontaneous” firing and amino-acid evoked firing of RN neurons. Parenterally administered drugs which disturb motor coordination, such as lysergic acid diethylamide, bufotenine and mephenesin depress directly or indirectly rubral neuronal activity. 4-Methoxyphenylethylamine when applied locally did depress rubral neurons. However, when applied intravenously 4-methoxyphenylethylamine caused a hypokinetic rigid syndrome to develop; parallel to the increases in muscle tension and electromyogram activity were increases in rubral neuronal firing. The evidence presented and from a Preliminary Note (H. McLennan) indicates that the transmitter released from the brachium fibers to excite rubral neurons is not acetylcholine. The rubro-cerebellar fibers may be cholinergic.