“Naloxone (75–300 nmol/paw), CTAP (1–5 nmol/paw); yohimbine (…–200 nmol/paw), MK-912 (5–20 nmol/paw); caffeine (500–1500 nmol/paw), DPCPX (3–30 nmol/paw); methysergide (10–100 nmol/paw) …/paw); but not bicuculline (400 nmol/paw), significantly depressed the antihyperalgesic effects of levetiracetam (…).”