In the direct pathway of the basal ganglia, cortical excitation of the striatum ultimately leads to increased thalamocortical output. What is the immediate effect of striatal output on the globus pallidus internus in this pathway, and which dopamine receptor mediates it?

• A Inhibition of GPi via D1 receptors ✓
• B Excitation of GPi via D2 receptors
• C Inhibition of GPi via D2 receptors
• D Excitation of GPi via D1 receptors

Explanation

Striatal neurons of the direct pathway express D1 receptors, are excited by dopamine, and send inhibitory GABAergic projections to the globus pallidus internus and substantia nigra pars reticulata. Suppressing GPi removes its tonic inhibition of the ventrolateral thalamus, thereby facilitating movement. The indirect pathway uses D2 receptors and excites GPi through the external segment and subthalamic nucleus, producing the opposite effect, which is why Parkinson disease causes hypokinesia.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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