THE MEDULLARY DORSAL RETICULAR NUCLEUS FACILITATES ACUTE NOCICEPTION IN THE RAT

The influence on pain processing caused by destruction or stimulation of the dorsal reticular nucleus (DRt) was studied using the tail-flick and the increasing temperature hotplate tests. Lesions of the DRt wer e obtained by injecting quinolinic acid (180 nmol/mu l) unilaterally o r bilaterally, and nociceptive responses were evaluated by both tests. Following unilateral lesions, the tail-flick latencies and the hot-pl ate response temperatures were increased, values differing statistical ly from controls in the latter test. Bilateral lesions resulted in sta tistically significant increases of both tail-flick latency and hot-pl ate response temperature. Stimulation of the DRt was performed by inje cting glutamate (100 nmol/mu l) unilaterally, which was followed 1 min later by a significant decrease in the tail-flick latency compared to saline injected controls. These results suggest that the DRt is invol ved in the facilitation of nociception after acute thermal noxious sti mulation. This effect may be mediated through a spino-DRt-spinal loop causing a rebound of excitation in lamina I cells receiving noxious in put from their own receptive field.