Effects of ketamine and three other anaesthetics on spinal reflexes and inhibitions in the cat.

The effects of ketamine, alphaxalone/alphadolone, methohexitone and di-isopropylphenol have been compared on synaptic excitations and inhibitions in the spinal cord of decerebrate or pentobarbitone-anaesthetized cats. Ketamine selectively and reversibly decreased polysynaptic reflexes over a wide dose range. With the other three anaesthetic drugs decreases in reflex activity were accompanied by increases in the prolonged inhibition of reflexes, and in the amplitude and time course of dorsal root potentials. It was concluded that ketamine decreases synaptic transmission at terminals of excitatory interneurones, whereas the other three anaesthetics enhance synaptic inhibitions mediated by gamma-aminobutyric acid. Such specific effects of anaesthetics on particular synaptic processes do not support a unitary hypotheses of anaesthesia.