[Effects of piracetam on pain sensitivity and levels of beta-endorphin in blood and cAMP in the cerebral cortex of rats].Biull Eksp Biol Med. 1990 Feb; 109(2):163-5.BE
It has been shown, that piracetam by i.p. injection (10, 100, 400 mg/kg) or by consumption with drinking water 10, 100, 1000 mg/kg/day during 12 days delays extinction of conditioned reflex of passive avoidance and dose-dependence elevates exploratory activity in "open field", pain sensitivity threshold reduces to 70-75%. Prolonged consumption of 1000 mg/kg/day piracetam results in 3-fold decrease of beta-endorphin concentration in plasma (p less than 0.01) and 100 mg/kg/day--in 35% increase of cAMP content in rat brain cortex.