Abstract
Accurate anatomical characterizations are necessary to investigate neural circuitry on a fine scale, but for the rodent claustrum complex (CC) this has yet to be fully accomplished. The CC is generally considered to comprise two major subdivisions, the claustrum (CL) and the dorsal endopiriform nucleus (DEn), but regional boundaries to these areas are highly debated. To address this, we conducted a multifaceted analysis of fiber- and cyto-architecture, genetic marker expression, and connectivity using mice of both sexes, to create a comprehensive guide for identifying and delineating borders to the CC. We identified four distinct subregions within the CC, subdividing both the CL and the DEn into two. Additionally, we conducted brain-wide tracing of inputs to the entire CC using a transgenic mouse line. Immunohistochemical staining against myelin basic protein (MBP), parvalbumin (PV), and calbindin (CB) revealed intricate fiber-architectural patterns enabling precise delineations of the CC and its subregions. Myelinated fibers were abundant in dorsal parts of the CL but absent in ventral parts, while parvalbumin labelled fibers occupied the entire CL. Calbindin staining revealed a central gap within the CL, which was also visible at levels anterior to the striatum. Furthermore, cells in the CL projecting to the retrosplenial-cortex were located within the myelin sparse area. By combining our own experimental data with digitally available datasets of gene expression and input connectivity, we could demonstrate that the proposed delineation scheme allows anchoring of datasets from different origins to a common reference framework.
Significance statement Mice are a highly tractable model for studying the claustrum complex (CC). However, without a consensus on how to delineate the CC in rodents, comparing results between studies is challenging. It is therefore important to expand our anatomical knowledge of the CC, to match the level of detail needed to study its functional properties. Using multiple strategies for identifying claustral borders, we created a comprehensive guide to delineate the CC and its subregions. This anatomical framework will allow researchers to anchor future experimental data into a common reference space. We demonstrated the power of this new structural framework by combining our own experimental data with digitally available data on gene expression and input connectivity of the CC.
Competing Interest Statement
The authors have declared no competing interest.
List of anatomical abbreviations
- rIns
- Insular cortex, rostral part
- LO
- Lateral orbital cortex
- VLO
- Ventrolateral orbital cortex
- VO
- Ventral orbital cortex
- MO
- Medial orbital cortex
- PL
- Prelimbic cortex
- IL
- Infralimbic cortex
- DPed
- Dorsal peduncular area
- dACC
- Anterior cingulate cortex, dorsal area
- vACC
- Anterior cingulate cortex, ventral area
- RSC
- Retrosplenial cortex
- LEC
- Lateral entorhinal cortex
- MEC
- Medial entorhinal cortex
- PER
- Perirhinal cortex
- POR
- Postrhinal cortex
- PrS
- Presubiculum
- PaS
- Parasubiculum
- CA1-3
- Cornu ammonis 1-3
- DG
- Dentate gyrus
- Sub
- Subiculum
- SSc
- Somatosensory cortex
- Aud c
- Auditory cortex
- Vis v
- Visual cortex
- M1
- Primary motor cortex
- rM2
- Secondary motor cortex, rostral part
- cM2
- Secondary motor cortex, caudal part
- cIns
- Insular cortex, caudal part
- TeA
- Temporal association área
- Par c
- Parietal cortex
- CPu
- Caudoputamen
- GP
- Globus pallidus
- VP
- Ventral pallidum
- NAc
- Nucleus accumbens
- NDB
- Nucleus of the diagonal band
- SIB
- Substantia innominata
- Th MNG
- Thalamic midline nuclear group
- Th ANG
- Thalamic anterior nuclear group
- Th LNG
- Thalamic lateral nuclear group
- Th VNG
- Thalamic ventral nuclear group
- Th IL
- Thalamic intralaminar nuclear group
- Th MD
- Thalamic mediodorsal nucleus
- Meta Th
- Metathalamus
- Hb
- Habenula
- LH
- Lateral hypothalamus
- MH
- Medial hypothalamus
- AH
- Anterior hypothalamus
- PH
- Posterior hypothalamus
- Sept
- Septal complex
- BNST
- Bed nucleus of the stria terminalis
- P.Opt
- Preoptic area
- STh
- Subthalamic nucleus
- ZI
- Zona incerta
- Mam.n
- Mammillary nucleus
- rPir
- Piriform cortex, rostral area
- cPir
- Piriform cortex, caudal area
- DPir
- Deep piriform area
- IEn
- Intermediate endopiriform nucleus
- VEn
- Ventral endopiriform nucleus
- AOL
- Anterior olfactory nucleus, lateral part
- AOM
- Anterior olfactory nucleus, medial part
- AOD
- Anterior olfactory nucleus, dorsal part
- AOV/P
- Anterior olfactory nucleus, ventral/posterior part
- VTT
- Ventral tenia tecta
- DTT
- Dorsal tenia tecta
- Tu
- Olfactory tubercle
- LOT
- Nucleus of the lateral olfactory tract
- OB
- Olfactory bulb
- AA
- Anterior amygdaloid area
- CxA
- Cortex amygdala transition zone
- ACo
- Anterior cortical amygdala
- PCo
- Posterior cortical amygdala
- APir
- Amygdala piriform transition zone
- IPAC
- Interstitial nucleus of the posterior limb of the anterior commissure
- BLA
- Basolateral amygdala, anterior
- BLP
- Basolateral amygdala, posterior
- BLV
- Basolateral amygdala, ventral
- LA
- Lateral amygdala
- BMA
- Basomedial amygdala
- CeA
- Central amygdala
- Med A
- Medial amygdala
- PAG
- Periaqueductal grey
- SN
- Substantia nigra
- VTA
- Ventral tegmental area
- Rn
- Raphe nucleus
- Rt
- Reticular formation
- Pn
- Pontine nuclei
- Other BS
- Other brain stem areas
