Morphine-induced tail erection: site of action

Acute ablation techniques were used to localize morphine-induced tail erection (MITE) within the central nervous system of mice. Morphine produced no elevation of tails in mice whose spinal cord had been transected at the lower thoracic or lumbar levels. Decortication and high-level precollicular decerebration did not prevent MITE while morphine caused no tail response at all in low-level inferior collicular decerebrate mice. Lesions in various portions of the mesencephalon revealed that the degree of MITE was closely related to the size of the lesions of the central gray matter. The larger the lesion, the smaller the degree of tail elevation. MITE could not be elicited in mice when the mesencephalic central gray matter had been completely destroyed. Results indicate that morphine acts on the mesencephalic central gray matter producing tail erection and the pathway responsible for the reaction descends from the midbrain downward to the spinal cord.