How do chemical inputs to the medial globus pallidus differ from inputs to the lateral globus pallidus?

The globus pallidus is divided into two segments, the lateral and the medial, both of which receive GABAergic terminals from the striatum. However, they differ in their additional chemical inputs:1

• Medial globus pallidus: In addition to GABAergic input, this segment receives fibers containing substance P.1
• Lateral globus pallidus: In addition to GABAergic input, this segment receives enkephalinergic projections.1

These distinct chemical inputs reflect the specialized roles of these segments within the basal ganglia circuitry, where the medial segment serves as a primary output nucleus to the thalamus, while the lateral segment maintains reciprocal connections with the subthalamic nucleus.21