morphine , normorphine and ethylketocyclazocine had no effect on the head-turn latency but met-enkephalin and d-ala2 , d-leu5-enkephalin , injected into the pallidum , and small doses of etorphine injected subcutaneously , produced a dose-related slowing of the response .
C0014295
met-enkephalin
C0014298
enkephalin