[Neuronal organization of coeruleo-spinal connections in the cat]

Electrical stimulation of locus coeruleus in anesthetized cats was accompanied by a decrease in the inhibitory action of flexor reflex afferents (FRA) on extensor motoneurons. No changes in excitatory reactions of spinal motoneurons were observed. Microinjections of aspartic acid or chlorpromazine depressed FRA inhibitory action; injection of procaine and noradrenaline potentiated this action. The responses of differente spinal interneurons during activation of locus coeruleus were also studied. A conclusion is made that the inhibitory action of FRA is depressed by coeruleo-spinal influences on the level of the last-order inhibitory interneuron of the FRA system.