Elsevier

Neuroscience

Volume 136, Issue 4, 2005, Pages 1049-1071
Neuroscience

Neuroanatomy
Anatomical evidence for direct connections between the shell and core subregions of the rat nucleus accumbens

https://doi.org/10.1016/j.neuroscience.2005.08.050Get rights and content

Abstract

The nucleus accumbens is thought to subserve different aspects of adaptive and emotional behaviors. The anatomical substrates for such actions are multiple, parallel ventral striatopallidal output circuits originating in the nucleus accumbens shell and core subregions. Several indirect ways of interaction between the two subregions and their associated circuitry have been proposed, in particular through striato-pallido-thalamic and dopaminergic pathways. In this study, using anterograde neuroanatomical tracing with Phaseolus vulgaris-leucoagglutinin and biotinylated dextran amine as well as single-cell juxtacellular filling with neurobiotin, we investigated the intra-accumbens distribution of local axon collaterals for the identification of possible direct connections between the shell and core subregions.

Our results show widespread intra-accumbens projection patterns, including reciprocal projections between specific parts of the shell and core. However, fibers originating in the core reach more distant areas of the shell, including the rostral pole (i.e. the calbindin-poor part of the shell anterior to the core) and striatal parts of the olfactory tubercle, than those arising in the shell and projecting to the core. The latter projections are more restricted to the border region between the shell and core. The density of the fiber labeling within both the shell and core was very similar. Moreover, specific intrinsic projections within shell and core were identified, including a relatively strong projection from the rostral pole to the rostral shell, reciprocal projections between the rostral and caudal shell, as well as projections within the core that have a caudal-to-rostral predominance. The results of the juxtacellular filling experiments show that medium-sized spiny projection neurons and medium-sized aspiny neurons (most likely fast-spiking) contribute to these intra-accumbens projections. While such neurons are GABAergic, the intrastriatal projection patterns indicate the existence of lateral inhibitory interactions within, as well as between, shell and core subregions of the nucleus accumbens.

Section snippets

Animals

Twenty-six adult female Wistar rats (Harlan Centraal Proefdierbedrijf, Zeist, The Netherlands) weighing 180–250g were injected with BDA, and nine animals with PHA-L. All animals were fed ad libitum and housed in cages with enriched food. All experimental procedures were performed according to the guidelines of the ethical committee of animal experimentation, Vrije Universiteit, Amsterdam, that are in accordance with the European Community Council Directive 86/609/EEC. Special care was taken to

Delineation of the shell and core

For the delineation of the shell and core subregions on the basis of the pattern of CaB-immunoreactivity (IR), we refer to previous accounts (Zahm and Brog 1992, Jongen-Rêlo et al 1994; see also Fig. 1). To facilitate the descriptions of the distribution of labeled axons and terminals following anterograde tracer injections or juxtacellularly filling, the shell and core of the Acb have been subdivided on the basis of general anatomical planes that in each experimental case can be reproducibly

Discussion

This study provides the first systematic analysis of the organization of intrastriatal projections in the rat Acb. Using anterograde neuroanatomical tracing and single-cell juxtacellular filling, it was demonstrated that extensive intrastriatal projections exist (Fig. 13). These include reciprocal connections between specific parts of the shell and core. However, fibers originating in the core reached more widespread areas of the shell, including the rostral pole, than those arising in the

Acknowledgments

We thank Dirk de Jong for his support in making the illustrations and Jeroen van Zanten for his assistance with the data analysis. This study was supported by a Program Grant of the Dutch Medical Research Council NWO-ZonMW (903-42-092) and a NWO-ZonMW/INSERM travel grant (910-48-029).

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