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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.
L J Holmes, and
R A Wise
May 1988,
Brain research,
L J Holmes, and
R A Wise
November 1980,
Acta pharmacologica et toxicologica,
L J Holmes, and
R A Wise
January 1995,
Neuropharmacology,
L J Holmes, and
R A Wise
April 1980,
Acta pharmacologica et toxicologica,
L J Holmes, and
R A Wise
September 1985,
Brain research,
L J Holmes, and
R A Wise
May 2000,
Psychopharmacology,
L J Holmes, and
R A Wise
November 1977,
Psychopharmacology,
L J Holmes, and
R A Wise
April 1994,
Brain research,
L J Holmes, and
R A Wise
August 1988,
Pharmacology, biochemistry, and behavior,
L J Holmes, and
R A Wise
January 1984,
Psychopharmacology,
