ANATOMICAL SUBDIVISIONS OF THE RAT AMYGDALOID COMPLEX: AN EMPIRICAL BASIS FOR UNIFYING MRI, DTI AND HISTOLOGY-BASED BOUNDARY CRITERIA IN THE WAXHOLM SPACE RAT BRAIN ATLAS

The amygdaloid complex is part of the limbic system governing emotion, learning, implicit memory and social behaviour. Its implication in neuropsychiatric disease has motivated extensive experimental preclinical research in animal models, particularly in rodents and non-human primates. For investigations in rat models, the Waxholm Space (WHS) rat brain atlas provides three-dimensional standardized representations of brain regions and is increasingly used for data integration, spatial analysis, and comparisons across studies. While this atlas includes detailed delineations for most major brain structures, it lacks subdivisions of the amygdaloid complex. Addressing this, we have manually delineated nuclei of the rat amygdala on the basis of high-resolution structural magnetic resonance imaging (sMRI) and diffusion tensor imaging (DTI) data, combined with co-registered cytoarchitectural, myeloarchitectural, and chemoarchitectural features derived from histological datasets. These multimodal data were interpreted and compared using available literature. We here present 3D delineations of the rat pallial and subpallial subdivisions of the amygdaloid complex, together with detailed documentation of delineation criteria. To facilitate cross-species translation, we also compared our delineation criteria and delineations to corresponding data from primates. This work represents an empirical basis for combining multimodal MRI and histological data to extend the anatomical delineations of the WHS rat brain atlas and to strengthen its role as a neuroinformatics resource for data integration, translational research, brain wide analyses and cross-species comparison particularly for future investigations into the neural mechanisms involving the amygdaloid complex.
Funded from the European Union’s Research and Innovation Program Horizon Grant Agreement No. 101147319 (EBRAINS 2.0).