6-Hydroxydopamine lesion of the rat prefrontal cortex impairs motor initiation but not motor execution

We examined the effects of bilateral 6-hydroxydopamine (6-OHDA) lesions of the medial prefrontal cortex (PFC) in rats on motor initiation and execution in a simple reaction time task. Reaction times (RT) and movement times (MT) were measured in trained rats on four pre- and postoperative days. Animals with 6-OHDA lesions were selectively impaired on motor initiation as measured by a significant increase in RT on each postoperative day. Motor execution was intact postoperatively, since MT was not altered. Neurochemical analysis revealed a significant depletion of prefrontal dopamine (DA) and noradrenaline (NA) in lesioned animals. It was concluded that DA and, to a lesser extent, NA in the rat PFC were involved in monitoring RT performance.