Effects of intranigral cannabinoids on rotational behavior in rats: interactions with the dopaminergic system.

The effect of unilateral intranigral cannabinoid receptor stimulation on rotational behavior was explored. The potent cannabinoid agonist CP 55,940 (5 and 10 micrograms/0.5 microliter) induced contralateral turning when microinjected unilaterally into the substantia nigra pars reticulata. In addition, the cannabinoid agonist markedly attenuated the contralateral rotation induced by the dopamine D1 agonist SKF 82958 and completely reversed the ipsilateral rotation induced by the dopamine D2 agonist quinpirole. In both cases, the coadministration of the cannabinoid agonist together with the D1 or D2 agonist induced contralateral rotation. It appears that cannabinoids may exert different effects depending on the state of the ongoing chemical activation of this brain circuitry.