Instrumental learning within the spinal cord: V. Evidence the behavioral deficit observed after noncontingent nociceptive stimulation reflects an intraspinal modification

Abstract

Spinally transected rats given leg shock whenever one hindlimb is extended learn to maintain the leg in a flexed position, which minimizes net shock exposure. Yoked rats, that receive an equal amount of shock independent of leg position (noncontingent shock), do not exhibit an increase in flexion duration. Yoked rats also fail to learn when response contingent shock is applied to the previously shocked leg, a behavioral deficit that resembles learned helplessness. This deficit could reflect either a peripheral (e.g. muscle fatigue) or central effect. Experiment 1 showed that spinalized rats given noncontingent shock to one hind limb fail to learn when response-contingent shock is applied to the contralateral leg. Experiment 2 demonstrated that blocking the afferent input to the spinal cord, by cutting the sciatic nerve, blocked the development of the deficit. Experiment 3 found that intrathecal lidocaine has a protective effect and prevents the deficit. These findings suggest that noncontingent nociceptive stimulation induces an intraspinal modification that undermines behavioral potential.