Internal Subdivisions of the Marmoset Claustrum Complex: Identification by Myeloarchitectural Features and High Field Strength Imaging

Abstract

There has been a surge of interest in the structure and function of the mammalian claustrum in recent years. However, most anatomical and physiological studies treat the claustrum as a relatively homogenous structure. Relatively little attention has been directed toward possible compartmentalization of the claustrum complex into anatomical subdivisions, and how this compartmentalization is reflected in claustrum connections with other brain structures. In this study, we examined the cyto- and myelo-architecture of the claustrum of the common marmoset (Callithrix jacchus), to determine whether the claustrum contains internal anatomical structures or compartments, which could facilitate studies focused on understanding its role in brain function. NeuN, Nissl, calbindin, parvalbumin, and myelin-stained sections from eight adult marmosets were studied using light microscopy and serial reconstruction to identify potential internal compartments. Ultra high resolution (9.4T) post-mortem magnetic resonance imaging was employed to identify tractographic differences between identified claustrum subcompartments by diffusion-weighted tractography. Our results indicate that the classically defined marmoset claustrum includes at least two major subdivisions, which correspond to the dorsal endopiriform and insular claustrum nuclei, as described in other species, and that the dorsal endopiriform nucleus (DEnD) contains architecturally distinct compartments. Furthermore, the dorsal subdivision of the DEnD is tractographically distinguishable from the insular claustrum with respect to cortical connections.

A multifaceted architectural framework of the mouse claustrum complex

“…In general, MBP staining in the CC displayed intricate patterns that were highly useful for delineation. We observed clear differences in the amount of myelination within subregions of the CC, which is also the case in marmosets, where the CL is more myelinated than the DEn (Pham et al, 2019). Our motivation for studying MBP-labeling was also due to the evolutionarily preserved fiber-tracts encapsulating the CC in mammals (Bruguier et al, 2020; Buchanan & Johnson, 2011; Kowianski et al, 1999).…”

Regional and cell type-specific afferent and efferent projections of the mouse claustrum

“…The CLA is a more densely packed group of neurons compared to adjacent structures in the Nissl- ( Figure S1I ) and immunohistochemically (antibody against NeuN) stained specimens ( Figure S1K ) and in the transgenic mouse line Rorb-IRES2-Cre Ai110 with red nuclear-labeling ( Figure S1L ). The CLA is surrounded by densely labeled myelin fibers revealed by immunostaining with an antibody against SMI-99 (basic myelin protein, in red) ( Figure S1J ) and an antibody against NF-160 (Neurofilament-M, in green) ( Figure S1K), a characteristic used to define the CLA in mammals (Pham et al, 2019; Wang et al, 2017). Similarly, it is also surrounded by more darkly stained AchE-positive fibers (data not shown but see the Allen Reference Data portal http://connectivity.brain-map.org/static/referencedata/experiment/thumbnails/100140478?image_type=ACHE&popup=true).…”

Topographic gradients define the projection patterns of the claustrum core and shell in mice

“…As mice may now provide an essential model system to study the function of the claustrum, the data we present here will enable neural activity of specific claustrocortical pathways to be manipulated or measured while taking into consideration the crosstalk with other projection streams. However, there are species differences in the anatomical organization of the claustrum (Edelstein & Denaro, 2004; Orman et al, 2017; Pham et al, 2019; Smith et al, 2019; Witter et al, 1988) and therefore the results in mice may not generalize to other species.…”

“…In many cases, these different output streams are topographically organized (Gattass et al, 2014; Li, Takada, & Hattori, 1986; Minciacchi et al, 1985; Pearson, Brodal, Gatter, & Powell, 1982; Reser et al, 2017; Watson et al, 2017; Witter, Room, Groenewegen, & Lohman, 1988), whereas in others (particularly in rodents), a lack of topography is noted (Chia et al, 2020; White et al, 2017; Zingg et al, 2018). Discrepancies between studies likely arise from different claustrum projections being measured, and species‐specific differences in claustrocortical organization (Binks, Watson, & Puelles, 2019; Orman, Kollmar, & Stewart, 2017; Pham et al, 2019; Smith et al, 2019). As mice provide a powerful model system for studying cell types, circuits, and behavior, a comprehensive understanding of the mouse claustrocortical system is required.…”