Rat's claustrum shows two main cortico-related zones

doi:10.1016/S0006-8993(97)00135-2

Brain Research

Volume 756, Issues 1–2, 9 May 1997, Pages 147-152

https://doi.org/10.1016/S0006-8993(97)00135-2 Get rights and content

Abstract

Methods of retrograde axonal transport were employed to evaluate the topography and overlap of claustroneocortical connections in the rat. Fluorescent tracers Fast Blue (FB) and Diamidino Yellow (DY) were injected simultaneously in various combinations into the motor, somatosensory, auditory and visual cortical areas. Experiments showed that claustroneocortical projections are organized in two main cortico-related zones: sensorimotor and visuoauditory. The sensorimotor zone occupies the anterodorsal part whereas the visuoauditory occupies the posteroventral part of the claustrum. Between these two main zones only a scanty overlap was observed. In the sensorimotor zone a large overlap between neurons projecting to the motor and somatosensory cortical areas exists. The visuoauditory zone is characterized by a full overlap of neuronal populations projecting to the visual and auditory areas.

Introduction

The claustrum is a brain structure present in all mammals from Insectivora to primates. In all examined species two parts of the claustrum can be distinguished: the insular which underlies the insular cortex and the prepiriform (endopiriform nucleus) 7, 11, 18, 26. For many years the claustrum has received little attention of investigators and its function, as well as organization of afferent and efferent connections, still remains in many respects unclear. As it has been shown in cat, monkey and men the claustrum shows the topographic organization of cortical connections 14, 15, 19, 21, 22, 26. The anterior part of the insular claustrum is linked mainly with the motor and prefrontal cortical areas, the central part with the somatosensory fields, whereas the posterior part is related to the visual cortex; neurons connected with the auditory cortex are located ventrally to the visual and somatosensory zones of the claustrum. Further studies have shown that subpopulations of claustral neurons projecting to various neocortical areas show a smaller or larger degree of overlap 22, 26. The prepiriform claustrum has no connections with neocortical areas but it is linked with prepiriform and entorhinal cortices 8, 16. These observations lead to the conclusion that the claustrum through its reciprocal limbic and neocortical connections may take part in the integration of motor, sensory, emotional and mnemonic information 3, 4, 5, 6, 12, 18, 20, 23, 26, 27.

Despite the accumulation of findings for many species the data about organization of claustroneocortical connections in more primitive animals are scanty and contradictory. Sloniewski et al. [28]having studied the rat as well as Dinopoulos et al. [7]the hedgehog reported that claustrocortical connections in these species showed anteroposterior topographic organization which was much less apparent than in cat or monkey. Li et al. [13]described another topographic relationship: the dorsal part of the insular claustrum sends fibers to the frontal cortex whereas the ventral part sends fibers to the occipital areas. On the contrary Shameem et al. [25]reported that the dorsal part of the claustrum projected to the visual cortex; other authors denied the existence of any topographic relationship between claustrum and neocortex of the rat [1]. In order to clarify the organization of the rat claustroneocortical connections we employed the retrograde fluorescent double labeling method using Fast Blue (FB) and Diamidino Yellow (DY). In the present study in each case FB and DY were injected in various combinations into two different cortical fields including primary motor, somatosensory, visual and auditory areas.

Section snippets

Material and methods

Fifteen adult Wistar rats (body weight 250–300 g) were used for this study. Animal care and use guidelines outlined by the National Institute of Health were followed. Rats were anesthetized with Nembutal (30 mg/kg) administered intraperitoneally. The surgical procedure was carried out under sterile conditions. Animals were fixed in the stereotaxic apparatus (Trend Wells, USA) and after skin incision the skull bone was extensively removed over the chosen cortical area. The dura was cut and

Results

(1) Injections of FB into the motor cortex and DY into the somatosensory cortex resulted in labeling of two intermingled populations of neurons localized anterodorsally in the claustrum (Fig. 1a,e, Fig. 2). The posterior part of the claustrum contained only a small number of labeled cells. Ipsilateral claustrum FB labeled neurons predominated in the anterior part of the claustrum. In the central and posterior parts of the claustrum DY-positive neurons were more numerous. In the contralateral

Discussion

The use of two different fluorescent retrograde tracers in the same animal allowed a detailed study of the interrelationship between neuronal populations of the claustrum projecting to various cortical areas. Double labeling experiments have shown that the claustroneocortical connections in the rat are arranged both in the rostrocaudal and in the dorsoventral axis. Neurons projecting to the motor cortex predominated in the anterior part of the claustrum, whereas those projecting to

Acknowledgements

The authors wish to thank Mrs. Aleksandra Arceusz, M.A., for copy-editing the manuscript. This research was supported by funds from the State Committee of Scientific Research, Grant PB 6P 207 03004.

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Research reportRat's claustrum shows two main cortico-related zones