Locus coeruleus and substantia nigra: involvement in morphine-induced behavior

Cats pretreated with morphine (5 mg/kg, IP) received naloxone into the area of the locus coeruleus (LC) or the area of the substantia nigra (SN). The LC-treated animals stopped the morphine-induced stereotyped behavior and showed normal but hyperactive behavior. The SN-treated animals, however, ceased their movements of the head and the forelegs, adopted a rigid posture with extended forelegs and became hypoactive. It is concluded that both the LC area, which contains noradrenergic cell bodies, and the SN area, which contains dopaminergic cell bodies, are sites of action of morphine on behavior.