Leading Toward a Unified Cortico-basal Ganglia Functional Model

Abstract

There is a large body of literature establishing the basal ganglia functional organization of cortical afferents projecting to the striatum to two different pathways: the direct and indirect pathways [1–4]. Consistent throughout this organization are the medium spiny neurons (MSNs) which account for approximately 90–95% of the cell population in the striatum [5, 6]. MSNs are GABAergic projection neurons that are comprised by two functionally distinct groups of neurons based on the expression of neuropeptides and dopamine (DA) receptors [7]. More specifically, striatal neurons in the direct pathway contain substance P and dynorphin, and preferentially express D1-class DA receptors [8–10]. On the other hand, MSNs from the indirect pathway are enkephalin positive neurons and preferentially express D2-class DA receptors [8–10].