Which is the most common excitatory neurotransmitter released by the thalamocortical neurons projecting to the motor cortex in the basal ganglia circuit?

Explanation

## Thalamocortical Neurotransmission in Basal Ganglia Circuits ### Anatomical Context The thalamus (particularly the ventral anterior [VA] and ventral lateral [VL] nuclei) receives inhibitory output from the basal ganglia and relays processed motor information back to the motor cortex. This is a critical feedback loop in motor control. ### Neurotransmitter Identity **Key Point:** Glutamate is the primary excitatory neurotransmitter used by thalamocortical projections. All thalamic relay neurons to cortex use glutamate as their main neurotransmitter, regardless of the specific thalamic nucleus. ### Functional Significance **High-Yield:** In the basal ganglia circuit: 1. Thalamus receives tonic inhibition (GABA) from substantia nigra pars reticulata (SNpr) and globus pallidus internus (GPi) 2. Glutamatergic input from cortex to striatum initiates the circuit 3. Thalamus releases glutamate to excite motor cortex, completing the loop **Clinical Pearl:** Disruption of this glutamatergic thalamocortical transmission contributes to movement disorders — in Parkinson disease, excessive GABAergic inhibition of the thalamus reduces glutamate output, impairing motor initiation. ### Why Glutamate? Glutamate is the universal excitatory neurotransmitter in the CNS. All thalamic relay neurons (sensory, motor, limbic) use glutamate to communicate with cortical targets. This ensures robust, rapid transmission of processed information back to cortex. [cite:Kandel & Schwartz Principles of Neural Science 6e Ch 41]