Effects of unilateral microinjections of sulpiride into the medial prefrontal cortex on circling behavior of rats.

Bilateral 6-OHDA lesions of rats' medial prefrontal cortex increased locomotor activity after 7-10 days suggesting that cortical DA may normally inhibit motor behaviour. However, hyperactivity may have resulted from enhanced subcortical DA function. Acute manipulation of frontal cortical DA neurotransmission in the present experiment avoided lesion-induced subcortical changes. Sulpiride (0, 6, 12, 24 micrograms in 1 microliter) was injected unilaterally into the medial prefrontal cortex of rats pretreated with (+)-amphetamine (1.5 mg/kg, i.p.). Circling behavior was scored during four 5-min intervals of a 60-min test session which began with injections and placement in a flat, circular arena. SUL resulted in ipsiversive circling whereas its vehicle did not. These results were consistent with those seen with other DA drugs and suggest an excitatory influence of frontal cortical DA on locomotor activity.