Effect of perinatal malnutrition on the inactive behavior induced by long-term shock and conditioned analgesia

Inactive behavior in response to long-term inescapable foot shock (IS) and conditioned analgesia were evaluated in adult rats perinatally undernourished. During the IS session, control rats exhibited first a period of vigorous activity and then inactive behavior, during which they accepted the shock more passively. Moreover, when these same animals were subsequently placed in the environment associated with shock application, they showed an increase in the paw lick latency. Conversely, in malnourished rats, this IS schedule induced lower behavioral inactivity and rats failed to develop conditioned analgesia. When undernourished rats were injected with morphine (MOR) before IS exposure, it was observed that both phenomena--inactivity during shock and analgesia conditioned by submission to the shock context--were normalized. A possible alteration in the activation of an opiate process implicated in the stress response in early undernourished rats is suggested.