Role of the superior colliculus in the motor effects of cannabinoids and dopamine

We studied the cellular distribution of CB1 cannabinoid receptors in the su perior colliculus of the rat using an antibody raised against the N-termina l of the receptor. The effect of unilateral cannabinoid receptor stimulatio n in the intermediate layers of the superior colliculus on rotational behav ior in rats was also explored. The antibody against CB1 receptors outlined the crossed descending system of the superior colliculus (predorsal bundle output system) as well as the collicular commisure. The potent cannabinoid agonist CP55,940 (5 mu g/0.25 mu l) induced strong contralateral turning wh en microinjected unilaterally into the lateral intermediate layers of the s uperior colliculus. The levels of turning obtained with the intracollicular administration of the cannabinoid were comparable to the highest levels ob tained with dopamine agonists in the basal ganglia. The D-2 dopamine agonis t quinpirole or the D-1 dopamine agonist SKF82958 reversed this contralater al rotation but failed to affect motor behavior on their own. A new motor p athway for cannabinoids is discussed. (C) 2000 Elsevier Science B.V. All ri ghts reserved.