Subthalamic nucleus efferent projection to the cerebral cortex

A direct projection from the subthalamic nucleus to the dorsal cerebral cortex has been demonstrated in the rat using a retrograde axonal transport technique. Injections of horseradish peroxidase into the cerebral cortex gave rise to retrogradely-labelled neuronal cell bodies in the ipsilateral subthalamic nucleus. Labelled cells were restricted to the lateral half of the nucleus. In addition, retrograde-labelling was observed in the rostral and caudal portions of the entopeduncular nucleus. Injections of horseradish peroxidase into the striatum underlying the cortical region receiving subthalamic efferents failed to label any subthalamic nucleus or entopeduncular nucleus neurones. These findings add the cerebral cortex to the other known projection areas (globus pallidus, substantia nigra, nucleus tegmenti pedunculopontinus) of the subthalamic nucleus and might have implications for the way in which the subthalamic nucleus influences motor activity.