Asymmetrical orientation to edges of an openfield: modulation by striatal dopamine and relationship to motor asymmetries in the rat
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Rats with unilateral 6-hydroxydopamine (6-OHDA, 4 or 8 micrograms) or sham lesions of the substantia nigra were examined (undrugged) for asymmetrical orientation to edges of a large openfield. Lesioned rats preferentially aligned with the edge such that the intact striatum was contralateral to the edge. The magnitude of this asymmetry was greatest in rats lesioned with the highest dose of 6-OHDA. There was no population left/right hemispheric asymmetry in the extent to which unilateral striatal dopamine (DA) depletion produces this behavioral bias. In sham-lesioned rats, endogenous imbalances in striatal DA activity (DOPAC/DA) were related to the direction of edge orientation, such that the more active striatum tended to be contralateral to the edge. Also in shams, the direction of this orientational asymmetry was not significantly related to the direction of motor bias measured as amphetamine- and apomorphine-induced turning behavior in rotometers (having no edges). However, the magnitudes of sensorimotor (edge behavior) and motor (turning) asymmetries were negatively correlated. The results extend previous findings that asymmetrical edge behavior is a sensitive index of imbalances in striatal DA activity, not only in DA-depleted rats, but in intact rats as well. Furthermore, sensorimotor and motor asymmetries, while both under DAergic influence, are largely independent processes.