Unlike β-endorphin, dynorphin1–13 does not cause retrograde amnesia for shuttle avoidance or inhibitory avoidance learning in rats

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Abstract
Posttraining administration of the opioid peptides, β-endorphin or the enkephalins, is known to cause retrograde amnesia for a variety of tasks in rats. The present paper studies the effect of the posttraining administration of dynorphin1–13 on retention of a step-down inhibitory avoidance task and of a shuttle avoidance task. For the purpose of comparison, the effect of human β-endorphin was also studied. In confirmation of previous results, β-endorphin (1.0 or 10.0 μg/kg, IP) caused retrograde amnesia for the two tasks. Dynorphin1–13 had no effect at doses between 0.008–125.0 μg/kg IP or 1.25–125.0 ng/rat ICV in the inhibitory avoidance task, or at doses of 5.0, 25.0, or 125.0 μg/kg in the shuttle avoidance paradigm. These findings suggest that, in contrast to β-endorphin, dynorphin1–13 may not be involved in memory regulation at the posttraining period in rats.