The blockade of D1 dopamine receptors in cat motor cortex causing an increase in the latency of conditioned forelimb placing reaction

Cat were trained to place a forepaw on a support in response to touching the ventral surface of the forepaw as a conditioned stimulus. A selective D1 receptor antagonist SCH23390 was injected under pressure into the region of pericruciate cortex just anterior and lateral to the end of the cruciate sulcus. Electrical microstimulation of this region evoked the elbow flexion and shoulder withdrawal that constitute the initial lifting--withdrawal phase of the forepaw placing. In contrast to control saline, the injection of SCH23390 caused a gradual increase in the latency of conditioned placing so that to the end of experiment it was, on the average, 200 ms longer than its preinjection level. The results obtained show that the local D1 receptor blockade in cat motor cortex significantly increases the latency of the simple instrumental conditioned reflex.