Elsevier

Neuroscience

Volume 78, Issue 3, 27 March 1997, Pages 715-729
Neuroscience

Topographical organization of projections from the entorhinal cortex to the striatum of the rat

https://doi.org/10.1016/S0306-4522(96)00592-1Get rights and content

Abstract

The efferent projections of the entorhinal cortex to the striatum were studied with retrograde (horseradish peroxidase–wheat germ agglutinin) and anterograde (biocytin and biotinylated dextran amine) tracing methods. The bulk of the entorhinal cortical fibres were found to project to the nucleus accumbens in the ventral striatum, but the caudate–putamen is only sparsely and diffusely innervated, rostrally, along its dorsal and medial borders. Fibres arising from neurons in the lateral entorhinal cortex project throughout the rostrocaudal extent of the nucleus accumbens but are most abundant in the core and lateral shell of that nucleus. The rostral neurons of the medial entorhinal cortex were found to project sparsely to the striatum, whereas caudal neurons provide a dense input to the rostral one-third of the nucleus accumbens, especially to the rostral pole, where they concentrate more in the core than in the shell. Contralateral entorhinal projections, which are very sparse, were found in the same parts of the nucleus accumbens and the caudate–putamen as the ipsilateral terminal fields.

The present observations that entorhinal inputs to the nucleus accumbens are regionally aligned suggest that disruption of these connections could produce site-specific deficits with, presumably, specific behavioural consequences.

Section snippets

Experimental procedures

In this study, female Wistar rats (160–350 g) were anaesthetized either with Equithesin (0.25 M chloral hydrate: 9.7 mg/ml pentobarbitone sodium: 0.3 ml/100 g, i.p.) or a 4:3 mixture (1 ml/kg, i.m.) of 1% ketamine hydrochloride (Vetelar, U.K.) and 2% xylazine (Rompun, Bayer, Belgium). Each animal was placed in a stereotaxic apparatus and the skull opened. Using coordinates derived from the atlas of Paxinos and Watson,[42]microinjections of biocytin (n=12) or biotinylated dextran amine (BDA; n=20)

Results

The term entorhinal area, as used in this study, includes the medial (MEC) and lateral (LEC) entorhinal cortices and the perirhinal cortex.[29]MEC and LEC divisions, as determined by others,2, 22were identified in a series of Nissl-stained sections of our material (Fig. 1A). The MEC and rostral part of the EC have a less distinct lamination, due to a thinner layer II and clumping of neurons in layer III. The lamina dissecans is either small or absent. The LEC at the same level has a wider layer

Discussion

The main goal of this study was to examine, in detail, the fibre trajectories and topography of the terminal fields of entorhinal neurons in relation to the neostriatum and compartmental subdivisions of the nucleus accumbens in the ventral striatum. Anatomical evidence that the EC projects to the striatum has been presented in the past for rat,6, 28, 48, 55, 62cat[61]and guinea-pig.[54]The existence of these projections is also supported by physiological investigations.[13]All studies agree

Acknowledgements

The authors wish to thank Peter Kellaghan, and Drs Hong Lin and Thomas Farrell, for technical assistance and discussion. We are also indebted to Dr Ben Yee for helpful suggestions and advice, and to Professor Barry Roberts and Dr Richard Greene for critical comments on the manuscript. Further, we are grateful to the Media Services Department of the Royal College of Surgeons in Ireland for their assistance with the photomicrographs. The work was funded by a Wellcome Trust project grant, no.

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