Circling in normoxic or hypoxic rats with unilateral 6-OHDA nigrostriatal lesion. Part 2. Effects of d-amphetamine.

Unilateral administration of 6-hydroxydopamine into the rat nigrostriatal system induces a unilateral damage of the dopamine (DA) containing neurons. In such lesioned animals, d-amphetamine (AMPH) induces circling behavior (ipsiversive circling) in relation to its DA releasing property in the non-lesioned side. A preexposition to hypoxia potentiates the behavioral effect of AMPH: this can be related to an increase in the amount of substrate available for release, dopamine. Hypoxia occurring just after the administration of AMPH does not initially modify the AMPH induced circling behavior. This suggests that tyrosine hydroxylase inhibition by hypoxia is not a limiting factor of the releasing effect of AMPH. After 20 min of hypoxia, circling decreases. This impairment could be mediated by a decrease of the amount of available DA and/or by a decrease of release.