Distinct afferents to internal and external pallidal segments in the squirrel monkey

Area of Science:

• Neuroscience
• Primate Neuroanatomy
• Basal Ganglia Circuits

Background:

• The globus pallidus, with its internal (GPi) and external (GPe) segments, plays a crucial role in motor control.
• Understanding the specific projections from the striatum and subthalamic nucleus to these pallidal segments is vital for deciphering basal ganglia function.
• Previous studies have suggested differential connectivity within the basal ganglia, but detailed mapping in primates remains essential.

Purpose of the Study:

• To investigate the distinct neuronal populations within the striatum and subthalamic nucleus that project to the internal (GPi) and external (GPe) segments of the globus pallidus in squirrel monkeys.
• To elucidate the topographical organization of these projections and identify any overlapping or segregated pathways.

Main Methods:

• Retrograde fluorescence double-labeling technique was employed in squirrel monkeys.
• Neuronal tracing was used to identify and map cells in the striatum and subthalamic nucleus projecting to GPi and GPe.

Main Results:

• Striatal neurons projecting to GPi and GPe formed distinct, non-overlapping, obliquely oriented cell bands within the putamen and caudate nucleus.
• Subthalamic nucleus neurons projecting to GPe were more numerous and located more laterally compared to those projecting to GPi.
• A small population of subthalamic neurons projected to both GPi and GPe, while no such cells were found in the striatum.

Conclusions:

• Distinct striatal and subthalamic neuronal populations differentially influence the GPi and GPe in primates.
• This segregation of projections suggests specialized roles for GPi and GPe in processing basal ganglia information.
• The findings contribute to a more refined understanding of the functional organization of the primate basal ganglia circuitry.