Unilateral Injections of a D2 But Not D1 Agonist Into the Frontal Cortex of Rats Produce a

nipulations of frontocortical dopamine have been found in previous tudies to produce a directional bias in the circling behaviour of rats. Agonists produced contralateral circling and antagonists produced ipsilateral turning. To examine the role of dopamine recep-tor subtypes, the present studies investigated the ability of unilateral intrafrontal cortical microinjections of the D1 agonist, SKI: 38393 or the D2 agonist, quinpirole to produce contralateral circling in rats. The antagonist, cis-flupenthixol was also tested and was expected to produce ipsilateral circling. In 3 separate xperiments, rats received 7 50-min sessions in a circular arena separated by at least 48 hr. The first and final sessions were preceded by no injection, the second and sixth by saline [or the inactive trans isomer (25 p,g) in the flupenthixol experiment] and the middle 3 sessions by doses of cis-flupenthixol (1, 10, 25 wg in 0.5 i~1), quinpirole (3, 6, 12 ~,g) or SKF 38393 (2, 4, 8 p,g), the order being counterbalanced across rats. cis-Flupenthixol and quinpirole produced ose-dependent ipsi- and contralateral circling, respectively, whereas SKF 38393 was without significant effect. No reli-able directional bias was seen in any no-injection, saline or trans-flupenthixol sessions. Results suggested that the D2 receptor may mediate the motor effects of frontal cortical dopamine. Dopamine receptors SKF 38393 Quinpirole cis-Flupenthixol Circling Frontal cortex DOPAMINE (DA) contributes to the control of unconditioned motor activity. Numerous tudies have shown that increases and decreases in DA neurotransmission lead to respective increase