Selective lesion of the substantia nigra pars reticulata reduces the cortical Fos expression induced by stimulation of striatal D1-like receptors, in the rat

We investigated the effects of a selective lesion of the substantia nigra pars reticulata (SNr), obtained by stereotaxic injection of ibotenic acid, on the cortical expression of Fos protein induced by striatal infusion of dopamine, D1-like agonist SKF 38393, in Sprague-Dawley rats. The specific aim was to clarify the role of the basal ganglia output structures - SNr in particular - in the cortical activation that follows a D1-dependent activation of the striatofugal, direct pathway, in freely moving animals. The striatal, unilateral infusion of 30 mM SKF 38393 induced consistent Fos expression throughout the whole ipsilateral cerebral cortex, including motor, sensorimotor, associative, and limbic areas; such expression was dramatically reduced by excitotoxic lesion of the ipsilateral SNr. These findings confirm the prominent role of the SNr in the transmission of striatofugal signals to functionally different cortical areas.