Cortical alpha l-adrenergic regulation of acute and sensitized morphine locomotor effects

The role of alpha1-adrenergic transmission was tested on locomotor effects of acute or repeated morphine (5 mg/kg, i.p.) administration. Prazosin, an al-adrenergic antagonist, administered 30 min before morphine, either syste mically (0.5 mg/kg, Lp.) or locally and bitaterally into the prefrontal cor tex (200 pmol/side) reduced the stimulatory influence of morphine on locomo tion. The progressive increase of the locomotor response induced by repeate d morphine injections was blocked by a prazosin pretreatment but not the be havioral sensitization on the test day. These data suggest that blockade of cortical alpha1-adrenergic receptors reduces the expression of acute and s ensitized locomotor responses to morphine, but does not prevent the inducti on of behavioral sensitization. (C) 2001 Lippincott Williams & Wilkins.