Contralateral circling induced by tegmental morphine: anatomical localization, pharmacological specificity, and phenomenology.
Unilateral morphine application to sites in the ventral tegmentum caused contralateral circling. Positive sites were restricted to the region of the dopamine-containing cells in the ventral tegmental area and substantia nigra; rates were highest with ventral tegmental application. The opiate receptor antagonists naltrexone and naloxone blocked morphine-induced circling whether given before or during the sessions. Pimozide pretreatment also blocked morphine-induced circling at doses that spared muscimol-induced circling. Morphine induced little postural asymmetry and induced forward locomotion in all 4 limbs. The radius of morphine-induced circling was large or small depending on the size of the test environment; thus the behavior was controlled by environmental (sensory) and not central (motor) constraints. These studies suggest that morphine-induced circling results from activation of dopaminergic circuitry involved in sensory-motor integration, particularly that involved in forward locomotion.
D000818:Animals; D008124:Locomotion / Q000187:drug effects; D008297:Male; D009020:Morphine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects*; D009118:Muscimol / Q000494:pharmacology; D009271:Naltrexone / Q000494:pharmacology; D010868:Pimozide / Q000494:pharmacology; D051381:Rats; D012399:Rotation; D013378:Substantia Nigra / Q000187:drug effects; D013681:Tegmentum Mesencephali / Q000187:drug effects*
D010868:Pimozide; D009118:Muscimol; D009271:Naltrexone; D009020:Morphine