Descending inhibitory influences exerted by the brain stem upon the activities of dorsal horn lamina V cells induced by intra-arterial injection of bradykinin into the limbs.

1. In order to study descending influences of the brain stem upon the transmission of nociceptive messages at the spinal level, the activities of lumbar lamina V dorsal horn cells, induced by intra-arterial injection of brandykinin into the limbs, were recorded in unanaesthetized cats in both decerebrate and temporary spinal states (reversible cold block applied at the thoracic level). 2. In the decerebrate state, the intra-arterial injection of bradykinin had little or no effect. 3. During the reversible spinalization, the effects of bradykinin were revealed or considerably enhanced. As described in a previous study, in the C1-transected cat, three types of effects were encountered: excitatory, inhibiitory and mixed (inhibitory-excitatory). 4. These modifications observed after spinalization were generally associated with a large increase of the spontaneous firing rate. 5. These results emphasize, in the decerebrate cat, the importance of descending inhibitory controls exerted by the brain stem upon the transmission of nonciceptive messages at the spinal cord level.