morphine and the opioid peptides [ d-ala2 , d-leu5 ] -enkephalin ( dadl ) , beta-endorphin and tyr-d-ser-gly-phe-leu-thr ( a delta agonist ) caused a concentration-dependent shift to the left in the input-output curve constructed by plotting population spike amplitude ( a measure of evoked firing ) as a function of the dendritic field excitatory postsynaptic potential .
C0205753
opioid peptides
C0014298
enkephalin