The synaptic framework for chemical signaling in nucleus accumbens

Our knowledge of the organization of the nucleus accumbens has been greatly advanced in the last two decades, but only now are we beginning to understand the complex neural circuitry that underlies the mix of behaviors attributed to this nucleus. Superimposed on the neurochemically defined territories of the shell and core are four or more conduits for information flow. Each of these behaviorally relevant pathways can be characterized by the spatial distribution of inputs to its central unit: the GABAergic projection neuron, a spiny cell that also contains the opioid peptides, enkephalin or dynorphin. In this review, current models of accumbal circuits will be examined and, with the aid of recent anatomical findings, further extended to shed light on how functionally diverse information is processed in this nucleus. However complex, accumbal wiring is not fixed, and, as we will show, psychostimulants, dopamine-deleting lesions, and chronic blockade of dopaminergic receptors can alter the anatomical substrate, synaptology, and neurotrophic factors that govern circuits through the shell and core.