Atlas of the developing brain of the marmoset monkey constructed using magnetic resonance histology

Abstract

The developmental anatomy of the brain is largely directed by neural-based cues. Despite this knowledge, the developmental trajectory of the primate brain has not yet been fully characterized. To realize this goal, the advance in noninvasive imaging methods and new brain atlases are essential. The common marmoset (Callithrix jacchus), a small New World primate, is widely used in neuroscience research. The recent introduction of transgenic techniques has enabled the marmoset to be used as a genetically modifiable primate model for brain development. Here, a magnetic resonance histology technique involving the use of ultra-high-resolution ex vivo magnetic resonance imaging (MRI) was performed to identify the developmental anatomy of the marmoset brain at different time points from gestational week 8 through to birth. The data allowed the generation of a multidimensional atlas of brain structures at different developmental stages. Furthermore, in utero MRI techniques were developed to noninvasively monitor brain development during the embryonic and fetal stages. The multidimensional atlas and the MRI tools developed herein are anticipated to further our understanding of the developing primate brain.

Introduction

The common marmoset (Callithrix jacchus) is a useful experimental animal because of its small size (250–400 g) (Power et al., 2001), high fertility (2–4 offspring per year) (Stevenson, 1976), and early sexual maturity (occurring at 1.5–2 years) (Mano et al., 1987). Most importantly, the central nervous system (CNS) of the marmoset is similar to that of humans in terms of its structural and cytoarchitectural organization, including a highly subdivided cortical area (Paxinos et al., 2011). Marmosets also display high cognitive function, as demonstrated by their abundant vocal communications (Epple, 1968, Bendor and Wang, 2007, Eliades and Wang, 2008, Sadagopan and Wang, 2009). Hence, compared to other higher order primates, the marmoset has characteristics, which makes this animal particularly suitable as a non-human primate model of CNS development. Moreover, we recently introduced novel transgenic techniques for the genetic manipulation of the marmoset (Sasaki et al., 2009), which raises new possibilities of employing these genetically modified primates to study normal brain development and neurodevelopmental disorders.

Assessment of the developing brain using conventional histological techniques requires the destruction of specimens (e.g., sectioning of the brain with a cryostat). Conventional histological techniques also fall short in terms of their ability to depict three-dimensional (3D) anatomical features that arise during development. For this reason, we have focused on two types of magnetic resonance imaging (MRI): (1) MR histology, which enables the generation of non-destructive 3D images of the brain with an isotropic resolution of several tens of micrometers (Petiet et al., 2008), and (2) in utero MRI, which enables the quantitative evaluation of longitudinal developmental changes via volumetric analysis.

Several studies have used MRI (Fujiyoshi et al., 2007, t Hart et al., 2008, Yamada et al., 2008, Bock et al., 2009, Bock et al., 2011) or positron emission tomography (Haneda et al., 2007, Yokoyama et al., 2010) to image adult marmoset brains. Moreover, atlases of the adult marmoset brain, including a web-based histological atlas (Tokuno et al., 2009), a combined histological/MRI atlas (Newman et al., 2009), and a population-averaged standard template atlas (Hikishima et al., 2011), have been published. However, studies of prenatal marmoset brain anatomy are limited to only a few gross observations at the early embryonic stages of CNS development (Phillips, 1976).

Therefore, the present study reports for the first time an atlas of the developing marmoset brain at various embryonic/fetal stages, which was generated using MR histology. Moreover, the obtained MR histology images were compared with in utero MR images and hematoxylin and eosin (H&E)-stained histological images. The data sets derived from ex vivo MRI are now freely available via a Marmoset database website at http://www.ciea.or.jp/marmoset/development.htm (ID = brain; password = database).