Characterization of stimulation-produced analgesia from the nucleus tractus solitarius in the rat

Electrical stimulation of the commissural region of the nucleus tractus solitarius (NTS) inhibits the tail-flick reflex evoked by noxious heat. This antinociception can be measured in the awake or pentobarbital anesthetized rat at current intensities that do not induce overt behavioral side effects. Glutamate microinjections into the NTS, but not immediately surrounding the NTS, also inhibit the tail-flick reflex, demonstrating that activation of NTS cell bodies, and not fibers of passage, mediates antinociception from this region. In contrast, morphine microinjections into the NTS have no effect on the tail-flick reflex in anesthetized rats. These findings provide further evidence that the NTS is involved in the modulation of nociception.