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About the Authors:
Margaret I. Davis
* E-mail: [email protected]
Affiliation: Laboratory for Integrative Neuroscience, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland, United States of America
Henry L. Puhl III
Affiliation: Laboratory of Molecular Physiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland, United States of America
Introduction
Principle neurons in the telencephalon are organized into layers with distinct circuit and ensemble functions that can be surmised simply based on the location of the nuclei but the anatomical organization of the striatum has proven more challenging. This is because the striatum does not possess the readily identified laminar organization of most telencephalic structures and because the majority of striatal neurons are of one class, the GABAergic Medium Spiny Neuron (MSN) [1]. Recent studies have made use of the major distinction in MSN classes, differential expression of dopamine receptors (Drd1 or Drd2-GFP) in putative direct and indirect pathway neurons [2], respectively, to examine differential plasticity in the striatum but this technique only addresses one level of striatal complexity. The striatum is grossly divided into Dorsolateral (DLS), Dorsomedial (DMS) and ventral/Nucleus Accumbens (NAc). These divisions are roughly equivalent to motor, associative and limbic subdivisions but exist more as a dorsolateral to ventromedial gradient [3]. Regions can readily be identified for gross analysis but there is yet another layer of afferent-efferent and neurochemical heterogeneity within the striatum, the striosome-matrix organization.
Little is known about the differential function of the striosomes compared with the surrounding matrix. Existing data indicate that the dorsolateral matrix primarily serves motor functions [4] while partial ablation of dorsal striosomes impairs rotorod learning [5], suggesting cross talk between these regions during skill acquisition. Striosomes are a preferred striatal region for self-stimulation with implanted electrodes [6] and receive preferential and regionally selective innervation from the basolateral amygdala, prelimbic, infralimbic, orbitofrontal and anterior cingulate cortices and project primarily to the substantia nigra pars compacta (SNpc; reviewed in [7], [8], [9]). This is in contrast to dorsolateral matrix neurons, which receive innervation from sensorimotor cortex [4], [10], [11]. Matrix neurons are high in enkephalin, a marker of indirect pathway neurons, and project to the external segment of the globus pallidus (GPe) [2],[7]. The matrix neurons are also the...