The structural basis for mapping behavior onto the ventral striatum and its subdivisions

Abstract

The striatum can be divided into dorsal (caudate-putamen) and ventral parts. In the ventral division, the nucleus accumbens, which subserves adaptive and goal-directed behaviors, is further subdivided into shell and core. Accumbal neurons show different types of experience-dependent plasticity: those in the core seem to discriminate the motivational value of conditioned stimuli, features that rely on the integration of information and enhanced synaptic plasticity at the many spines on these cells, whereas shell neurons seem to be involved with the release of predetermined behavior patterns in relation to unconditioned stimuli, and the behavioral consequences of repeated administration of addictive drugs. In the core, the principal neurons are medium sized and densely spiny, but in the medial shell, these same neurons are much smaller and their dendrites, significantly less spiny, suggesting that morphological differences could mediate unique neuroadaptations associated with each region. This review is focused on evaluating the structural differences in nucleus accumbens core and shell neurons and discusses how such different morphologies could underlie distinguishable behavioral processes.

Figure 1

Digitized reconstructions of principal neurons located in the (A) core – small to medium size densely spiny neuron, (B) lateral shell of nucleus accumbens – small to medium size densely spiny neuron, (C) medial shell of nucleus accumbens – small size sparsely spiny neuron. These reproductions were made from neurons reconstructed after intracellular filling with Lucifer yellow and then immunoreacted to produce a permanent record. Note the differences in the spread of the dendritic fields (Reproduced, with permission from psychobiology, Meredith and Totterdell 1996b).

Figure 2

Golgi-impregnated neurons in the (A) dorsal striatum, (B) core and (C) medial shell of the Acb. Note the differences in spine density and dendrite orientation of principal neurons in these regions