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 were obtained by injecting quinolinic acid (180 nmol/mu l) unilaterally or bilaterally, and nociceptive responses were evaluated by both tests. Following unilateral lesions, the tail-flick latencies and the hot-plate response temperatures were increased, values differing statistically from controls in the latter test. Bilateral lesions resulted in statistically significant increases of both tail-flick latency and hot-plate response temperature. Stimulation of the DRt was performed by injecting 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 involved in the facilitation of nociception after acute thermal noxious stimulation. This effect may be mediated through a spino-DRt-spinal loop causing a rebound of excitation in lamina I cells receiving noxious input from their own receptive field.