Stress induced analgesia: its opioid nature depends on the strain of rat but not on the mode of induction

Gideon Urca*, Shlomo Segev, Yosef Sarne

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Reports by several investigators have shown that both opioid and non-opioid analgesia can be induced by non-pharmacological manipulations such as the administration of electric shock, and that such analgesia depends on shock parameters, the affective state of the animal and the region of the body shocked. We tested several manipulations which have been reported to induced opioid analgesia using a local strain of rats (CR). Such manipulations included the used of 30 min of intermittent footshock (3 mA, 1 s on, 5 s off), brief shock to the forepaws, transpineal electroconvulsive shock (ECS) and tail shock induced helplessness. Administration of either naloxone or naltrexone to rats of the CR strain failed to attenuate the analgesic effect of these manipulations and in some cases even enhanced analgesia. The existence of functional opioid analgesia systems in CR rats was evident from the fact that electrical stimulation of the periaqueductal gray area produced naloxone sensitive analgesia. In additional experiments we compared the analgesic effect of brief continuous (3 min) footshock, prolonged intermittent footshock (30 min) and ECS in young (< 75 days of age) and old (> 75 days of age) rats of the Sabra strain. Young Sabra rats showed naloxone sensitive analgesia following all 3 manipulations while adult rats displayed analgesia which was naloxone insensitive. Furthermore, no decrement in learning, indicative of helplessness, could be demonstrated in young Sabras following 3 min of shock which induced naloxone sensitive analgesia. We therefore propose that both opioid and non-opioid analgesia systems are coactivated by external stressors independent of the mode of stress or the indication of helplessness and that the determinants of their expression are genetically and ontogenetically determined.

Original languageEnglish
Pages (from-to)216-222
Number of pages7
JournalBrain Research
Issue number2
StatePublished - 23 Sep 1985


FundersFunder number
Israel Academy of Sciences and Humanities
Ministry of Health, State of Israel


    • analgesia
    • electroconvulsive shock analgesia
    • endorphin
    • opiate
    • rat
    • stress-induced analgesia


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