Monkey globus pallidus external segment neurons projecting to the neostriatum.

Experiments were performed to assess the number and parvalbumin (PV) immunoreactivity of neurons participating in the pallidostriatal projection in macaque monkeys. Injection of WGA-HRP into the right caudate nucleus and the left putamen of a Macaca mulatta and a M. fuscata labeled a large number of the globus pallidus external segment (GPe) neurons. Counting neurons labeled with WGA-HRP and those stained with neuronal markers indicated that approximately 30% of GPe neurons project to neostriatum. Approximately 2/3 of the pallidostriatal neurons are PV-immunoreactive. This study revealed that a significant number of primate GPe PV immunoreactive neurons project to the neostriatum, and suggest that the pallidostriatal projection should be taken into account in the analysis of functional roles of the basal ganglia circuitry.