Decerebrate Control of Reflexes to Primary Afferents

Abstract Dorsal root potentials (DRP) have been compared in decerebrate cats before and after transection of the spinal cord. The DRPs evoked from group I muscle afferents of flexor and extensor muscle are either unchanged or slightly decreased after transection of the cord. In the spinal state the DRP evoked from cutaneous afferents has two components: 1) Component I, representing primary afferent depolarization (PAD) in cutaneous afferents, has brief latency and is of equal size in the decerebrate and spinal states. 2) Component II and the DRPs evoked from high threshold muscle and joint afferents are ascribed to the flexor reflex afferents (FRA) and represent PAD in the FRA. This action cannot be evoked in the decerebrate state. The FRA act on the same primary cutaneous afferents in which component I is evoked. It is concluded that there is a tonic inhibition in the decerebrate state of transmission from the FRA to the FRA but there is neither inhibition of the short latency path from cutaneous afferents to cutaneous afferents nor of the paths from group I muscle afferents to Ia, Ib and cutaneous afferents. The cord dorsum potentials (CDP) have also been compared before and after transection of the cord. The release after brain stem lesions of the CDPs and DRPs evoked from the FRA is compared with the release of actions from the FRA to motoneurones.