“Naloxone (75–…/paw); yohimbine (130–520 nmol/paw), BRL 44408 (50–200 nmol/paw), MK-912 (5–20 nmol/paw); caffeine (500–1500 nmol/paw), DPCPX (…–100 nmol/paw) and GR 127935 (50–200 nmol/paw); but not bicuculline (400 nmol/paw), significantly depressed the antihyperalgesic effects of levetiracetam (…).”