peripheral administration of 30 and 100 micrograms/kg of [ leu5 ] enkephalin ( le ) and 11.6 micrograms/kg of [ d-pen2 , d-pen5 ] enkephalin ( dpdpe ) , a synthetic enkephalin analog with high delta-selectivity , impaired acquisition of avoidance responding .
C0525856
dpdpe
C0014298
enkephalin