Opposite effects of met-enkephalin and leu-enkephalin on a discriminated shock-escape task

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Leu-enkephalin was found to impair and met-enkephalin to enhance acquisition of a discriminated Y-maze shock-escape task in Swiss-Webster mice at equivalent doses (100 μg/kg, ip). Naloxone (1 and 10 mg/kg) also enhanced acquisition of the escape response and blocked the impairing actions of leu-enkephalin. Neither naloxone nor the enkephalins influenced shock-induced locomotor activity in an open field. Results suggest that enkephalin actions on escape conditioning are mediated through opioid receptors. (43 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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