Electric footshock-induced changes in behavior and opioid receptor function

The present electric shock (ES) schedule produced significant behavioral changes, such as analgesia and motor suppression, and functional changes in binding capacities for opioid agonist and antagonist. In the naloxone (5 mg/kg, SC 15 min before ES application) pretreated rats, these behavioral and biochemical changes were blocked. In addition, when preincubation (37°C, 30 min) was not carried out in the process of preparation of synaptic membrane, the ES-induced functional changes in high affinity binding sites were not observed. Moreover, the present data indicated that preincubation may produce the destruction of [³H]-D-ala², L-met⁵-enkephalinamide ([³H]-DAMEA) specific binding sites with the forced dissociation of endogenous delta-type opioid peptides from delta opioid receptors. In addition, the significant decrease of [³H]-DAMEA specific binding in the ES membrane suggested that delta-type opioid peptides were released more than steady state level by ES application and bound to the delta opioid receptors. Therefore, these results suggest that ES-induced behavioral and biochemical changes were mediated by opioid peptides which were released by ES application. In addition, the ES-induced analgesia may be mediated by high affinity delta opioid receptor.