Which is responsible for circling behavior in rats, locus coeruleus or dorsolateral pontine tegmentum?

Abstract

Unilateral electrolytic lesions restricted to the locus coeruleus (LC) in rats did not produce postural asymmetry or circling behavior, while similar lesions in the dorsolateral pontine tegmentum (DLPT) closely ventral to the LC caused a circling behavior toward the contralateral side. The circling behavior was potentiated by intraperitoneal injection of dopamine agonists, apomorphine or methamphetamine, and was abolished by the dopamine antagonist, haloperidol. Neurochemical analysis using a gas chromatographic-mass spectrometric method was made 4, 10 and 20 days after LC coagulation, resulting in a gradual decrease of noradrenaline level in the frontal cortex on the lesioned side. Dopamine content in the striatum in these rats was not significantly affected. Unilateral lesioning of the DLPT produced no significant change in contents of dopamine of homovanillic acid in the striatum or of noradrenaline in the frontal cortex. These results indicate that the LC is not involved in the circling behavior, without a modulatory effect on the dopamine metabolism in the striatum, whereas the DLPT closely ventral to the LC is responsible for circling behavior by subserving as a descending neural pathway conveying striopallidal function on the contralateral side.