Opiate antagonists overcome the learned helplessness effect but impair competent escape performance

Rats exposed to inescapable shocks exhibited deficiencies in learning to escape shock in a novel situation 24 hours later (learned helplessness). Opiate antagonists (naloxone or naltrexone) blocked the learned helplessness effect, allowing efficient escape performance on the subsequent test. In contrast, these drugs impaired the performance of rats pretrained with escapable shocks and animals with no previous exposure to shock. Both effects occurred at small doses and increased substantially with higher doses. The results suggest a significant role for endogenous opiates in the induction of learned helplessness as well as in the acquisition of efficient escape behavior.