Dissociation of antinociception and escape deficits induced by stress in mice.

Several experiments with mice were conducted to assess the conditions under which stress would induce antinociception in a subsequent hot-plate test. Both footshock and tail shock produced the antinociception. This effect was apparent with as little as a single shock trial. The magnitude of the antinociception was maximal following 15 shock presentations and was largely reduced after 60 shocks. In contrast to the results of Jackson, Maier, and Coon, whether stress was escapable was not a necessary feature needed to produce the antinociception. Moreover, the magnitude of the antinociception induced by stress was not enhanced in mice that had previously been exposed to stress. Finally, morphine (10.0, 20.0, and 30.0 mg/kg) produced a pronounced antinociception but did not appreciably influence escape performance in a shuttle task in which performance is disrupted by inescapable shock. It is suggested that the antinociception and shuttle-escape deficits induced by uncontrollable shock are independent of one another.