Elsevier

Neuroscience

Volume 133, Issue 1, 2005, Pages 193-207
Neuroscience

Intrinsic connections of the cingulate cortex in the rat suggest the existence of multiple functionally segregated networks

https://doi.org/10.1016/j.neuroscience.2005.01.063Get rights and content

Abstract

The cingulate cortex is a functionally and morphologically heterogeneous cortical area comprising a number of interconnected subregions. To date, the exact anatomy of intracingulate connections has not been studied in detail. In the present study we aimed to determine the topographical and laminar characteristics of intrinsic cingulate connections in the rat, using the anterograde tracers Phaseolus vulgaris-leucoagglutinin and biotinylated dextran amine. For assessment of these data we further refined and compared the existing cytoarchitectonic descriptions of the two major cingulate constituents, the anterior cingulate and retrosplenial cortices. The results of this study demonstrate that rostral areas, i.e. the infralimbic and prelimbic cortices and the rostral one third of the dorsal anterior cingulate cortex are primarily interconnected with each other and not with other cingulate areas. The caudal two thirds of the dorsal anterior cingulate cortex project to the caudal part of the ventral anterior cingulate cortex, whereas the entire ventral anterior cingulate cortex projects to only the mid-rostro-caudal part of the dorsal anterior cingulate cortex. Dense reciprocal connections exist between the remaining, i.e. the supracallosal parts of the anterior cingulate and retrosplenial cortices with a general rostro-caudal topography, in the sense that the rostral part of the anterior cingulate cortex and caudal part of the retrosplenial cortex are interconnected and the same holds true for the caudal part of the anterior cingulate cortex and rostral part of the retrosplenial cortex.

This topographical pattern of intracingulate connections relates to the results of several functional studies, suggesting that specific cingulate functions depend on a number of interconnected cingulate subregions. Through their intricate associational connections, these subregions form functionally segregated networks.

Section snippets

Experimental procedures

Fifty-five female Wistar rats (weight: 180–220 g; Harlan Central Proefdier Bedrijf, Zeist, the Netherlands) were used in this study. All experiments were approved by the Animal Ethical Committee of the Vrije Universiteit concerned with ethical aspects of experiments and care for laboratory animals and were in accordance with national and EC guidelines. Care was taken to minimize the number of animals and their suffering as much as possible.

Cytoarchitectonics and flat map

Both the AC and RS can be divided into a ventral (ACv/RSv) and a dorsal (ACd/RSd) area. The RSv can be further subdivided into a ventral and dorsal part (RSv-a and RSv-b, respectively). The infralimbic cortex (IL), prelimbic cortex (PL) and AC lack a granular layer IV and are therefore referred to as agranular cortex (Uylings and Van Eden, 1990). The present description of cytoarchitectonic criteria of the cingulate cortex focuses on characteristic differences between the different subregions

Cytoarchitectonic map

A considerable variation appears to exist in the nomenclature for equivalent areas of the rodent cingulate cortex. The AC in the present study is equivalent to Brodmann’s area 24, whereas the RS can be equated with his area 29 (Brodmann, 1909). The RS is often referred to as the posterior cingulate cortex. In order to provide more clarity, a comparison between the nomenclature in this study with that of other major cytoarchitectonic studies in rodents is provided in Table 2 (Brodmann 1909, Rose

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