Cortical involvement in dorsal horn cell hyperactivity and abnormal behavior in rats with dorsal root section.

Abstract

Experiments were performed on rats using neurophysiological and behavioral techniques, in an attempt to study the role played by the somatosensory cortex in the abnormal spinal neuron activity and abnormal behavior observed after brachial plexus lesions. The onsets of both phenomena occur at the same postoperative period. Cortical controls exerted on spinal dorsal horn (DH) cells were studied using a transient and reversible cortical blockade, cortical spreading depression (CSD), applied contralateral to the spinal cord recording. In 28 intact animals, 55 cells were studied during the propagation of at least two CSDs. Only 4 of these cells presented a sustained decrease in their spontaneous activity during CSD, which may correspond to transient arrest of a descending tonic cortical facilitation. In 29 animals with dorsal root sections, 161 DH cells displayed abnormal burst activity, and 52 were examined with the CSD test. Thirty-five cells presented a long-duration change in their spontaneous activity during CSD; of these, 28 showed decreased activity (suppression of descending tonic facilitation) and 7 presented increased activity (suppression of descending tonic inhibition). More DH cells were influenced by the cortex in deafferented rats (67%) than in intact rats (7%). The cortical influence was also stronger, as the hyperactive cells were frequently rendered silent during CSD. These observations suggest that the abnormal activity is partly due to a descending cortical influence. Results of a behavioral study performed on 22 rats (one control group and two experimental groups with cortical ablations) showed that the self-mutilating behavior, which develops at the same time as the abnormal DH cell activity, was reduced by unilateral cortical ablation, independent of the cortical region removed. The possible pathways involved in this cortical influence are examined in the discussion.