Using FoxP2 to Distinguish Direct and Indirect Basal Ganglia Pathways for Vocal Learning in Songbirds

Area of Science:

• Neuroscience
• Animal Behavior
• Genetics

Background:

• Vocal learning in songbirds relies on cortico-basal ganglia pathways.
• Area X, a specialized basal ganglia region, contains distinct neuronal circuits (CORE and SHELL) essential for vocal learning.
• Pallidal neurons in Area X are analogous to mammalian direct and indirect pathways, influencing thalamic activity.

Purpose of the Study:

• To investigate the role of the transcription factor FoxP2 in different neuronal populations within Area X of the zebra finch brain.
• To determine if FoxP2 is expressed in direct pallidal neurons projecting to the DLM or in other neuronal types within Area X.

Main Methods:

• Used tract-tracing to label Area X→DLM projection neurons.
• Employed immunohistochemistry to detect FoxP2 expression in adult and juvenile male zebra finches.
• Measured nuclear sizes and assessed co-localization with DARPP-32, a marker for striatal neurons.

Main Results:

• DLM-projecting neurons in Area X did not express FoxP2.
• A population of large neurons expressing FoxP2 was identified, which were not retrogradely labeled from DLM.
• FoxP2 did not co-localize with DARPP-32 in many of these large neurons, suggesting they are indirect pallidal neurons.

Conclusions:

• FoxP2 is not expressed in direct pallidal neurons projecting to the DLM in zebra finches.
• FoxP2 may serve as a marker for indirect pallidal neurons within Area X.
• These findings support the existence of distinct neuronal subpopulations corresponding to direct and indirect pathways in Area X, contributing to vocal learning.