Morphine and beta-endorphin antagonize posture and locomotor disorders induced by the injection of ACTH 1-24 in the rat locus coeruleus

The unilateral microinjection of ACTH 1-24 (20 nmol) into the locus coeruleus (LC) produced a long lasting (2-3 hr) posture asymmetry and movement disorder in all rats tested. This response was readily suppressed by the subsequent local microinjection of an equimolar dose of beta-endorphin or morphine or by the intraperitoneal injection of morphine sulphate (50 mg/kg). Microinjection of naloxone (20 nmol) into the LC produced the above syndrome in a lower percentage of animals. The results support the hypothesis that ACTH peptides and opioids play opposite roles in the control of different brain functions.