[Effect of drugs potentiating or inhibiting the activity of locus coeruleus neurons on various types of spinal inhibition in the cat].

Microinjections of aspartate or chlorpromazine (which increase the background firing of many central neurons) into region of locus coeruleus of decerebellized cats anaesthetized with chloralose diminished the inhibitory action of flexor reflex afferents on the extensor monosynaptic reflexes but had no effect on the excitatory action from these afferents on the flexor reflexes. In some experiments the injections of these drugs decreased also recurrent inhibition of extensor motoneurons. Microinjections of procaine or norepinephrine (which reduce the background of firing of central neurons) in the same region increased the inhibitory action of the flexor reflex afferents and the recurrent inhibition of the extensor monosynaptic reflexes and had no effect on their excitatory action on the flexor reflex. The role of tonic activity of locus coeruleus in controlling the spinal inhibition evoked from the flexor reflex afferents is discussed.