The basal ganglia function in motor control. Signals originating in the sensorimotor cortex are processed in the basal and then forwarded to other brain areas. Recent literature and our studies indicate that there are two parallel pathways between the sensorimotor cortex and the major output centers of the basal ganglia (i.e., pallidum and substantia nigra (SN)). One of the pathways involves the striatum (Str) and the other the subthalamic nucleus (STH). Since the importance of the striatal pathway has been well recognized, extensive electrophysiological study have been performed. On the other hand, the STH pathway has received less attention, and electrophysiological observations made on this pathway are controversial. The aim of this proposal is to study electrophysiological properties of STH and Str inputs to the pallidum and SN and the morphological characteristics of neurons recorded in these nuclei. The major questions to study are the following: 1) What is the postsynaptic action of the subthalamic inputs to the pallidum and SN? 2) How are the cortically derived striatal input and cortically derived STH input summated on pallidal and SN neurons? 3) What is the function of neuropeptides (enkephalin, substance P, substance K and dynorphin) localized in striato-pallidal and striato-SN systems? 4) What is the morphology of electrophysiologically identified neurons in the pallidum and SN? These questions will be studied, in anesthetized rats, using a combination of techniques including extracellular unit recording, intracellular recording, intracellular labeling with horseradish peroxidase, local application of agonists and antagonists of putative neuroactive substances, and electrical and chemical stimulation. Horseradish peroxidase reaction and immunocytochemistry of neuroactive substances will be performed on the recorded brain tissue after fixation. The intracellularly labeled and immunocytochemically labeled neuronal profiles will be analyzed at light and electron microscopic levels.