Kazuhiko Sawada

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

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.

Development of cerebral sulci and gyri in fetuses of cynomolgus monkeys ( Macaca fascicularis )

This study aimed to clarify the development of sulci and gyri on the external surface of the cerebrum of cynomolgus monkeys. Sulcus formation began with the appearance of the lateral fissure on embryonic day (ED) 70, followed by delineations of four cerebral lobes by the emergence of the parietooccipital sulcus, central sulcus, and preoccipital notch on EDs 80–90. The following primary sulci were then visible until ED 120: the superior temporal sulcus on ED 90; the intraparietal sulcus, lunate sulcus, inferior occipital sulcus, and arcuate sulcus on ED 100; and the principle sulcus on ED 110; the occipitotemporal sulcus, anterior middle temporal sulcus, and superior postcentral dimple on ED 120. These sulci demarcated the superior temporal gyrus on ED 90, the precentral gyrus, supramarginal gyrus, and angular gyrus on ED 100, and the inferior and middle temporal gyri, postocentral gyrus, superior parietal lobule, superior, middle and inferior frontal gyri, and inferior occipital gyrus on ED 120. Except for the intermediate and lateral orbitofrontal sulci, the sulci that appeared on ED 130 and thereafter were not related to the gyrus demarcations. Intriguingly, the brain markedly gained weight on EDs 100 and 120, corresponding to the embryonic ages when almost all gyri were visible. The results suggest that a rapid growth of the cerebrum involves convolutions of the gyri by a regular sequence of the sulcus formation in cynomolgus monkeys. This study further provides a standard of reference for normal development in the cerebral cortical morphology of cynomolgus monkeys.

Fetal Gyrification in Cynomolgus Monkeys: A Concept of Developmental Stages of Gyrification

Our article summarizes a series of studies about fetal gyrification and its relation to cerebral growth in cynomolgus monkeys. Based on the cerebral growth (i.e., brain weight, cerebral volume, and frontooccipital length of the cerebral hemisphere) and the developmental pattern of gyrification in each sulcus of cynomolgus monkeys, we divided the gyrification process into four stages: Stage 1. Demarcation of cerebral lobes and limbic gyri; Stage 2. Demarcation of neocortical gyri; Stage 3. Emergence of secondary and tertiary sulci; and Stage 4. Growth of sulcal length and depth. Each stage of those gyrification processes was influenced by different developmental events, such as the emergence of corticocortical long‐associative fiber tracts, cortical maturations, and subcortical white‐matter development. This is the first report to systematically propose gyrification processes closely related to the order of phyologenetical development of the cerebral cortex in primates. Anat Rec, 2012.

Ontogenetic pattern of gyrification in fetuses of cynomolgus monkeys

The ontogenetic pattern of gyrification and its relationship with cerebral cortical volume were examined in cynomolgus monkey fetuses. T(1)-weighted coronal magnetic resonance (MR) images at 7 T were acquired from the fixed cerebra of three male fetuses, each at embryonic days (EDs) 70 to 150, and the gyrification index (GI) of each slice was estimated. The mean GI was low (1.1-1.2) during EDs 70 to 90, and then increased dramatically on ED 100. The developmental profiles of the rostrocaudal GI distribution revealed that cortical convolution was more frequent in the parietooccipital region than in other regions during EDs 100 to 150, forming an adult-like pattern by ED 150. The mean GI was closely correlated with the volume of cortical gray matter (r=0.9877), and also with the volume of white matter/intermediate zone (r=0.8961). These findings suggest that cortical convolution is correlated with either the maturation of cortical gray matter or the development of white matter bundles. The characteristic GI distribution pattern of catarrhines was formed by ED 150 in correlation with the progressive sulcal infolding in the parietooccipital region of the cerebrum.

FETAL SULCATION AND GYRIFICATION IN COMMON MARMOSETS (CALLITHRIX JACCHUS) OBTAINED BY EX VIVO MAGNETIC RESONANCE IMAGING

The present study characterized fetal sulcation patterns and gyrification in the cerebrum of the New World monkey group, common marmosets, using a 3D T2-weighted high-resolution anatomical magnetic resonance imaging (MRI) sequence from the fixed brain at 7-tesla ex vivo. Fetal sulcation in the marmoset cerebrum began to indent the lateral fissure and hippocampal sulcus in gestational week (GW) 12, and then the following sulci emerged: the callosal and calcarine sulci on GW 15; the superior temporal sulcus on GW 17; and the circular and occipitotemporal sulci on GW 18. The degree of cortical convolution was evaluated quantitatively based on 2D MRI slices by the gyrification index (GI) and based on 3D MRI data by sulcation index (SI). Both the mean GI and SI increased from GW 16, and were closely correlated with the cortical volume and the cortical surface area during fetal periods (their correlation coefficients marked more than 0.95). After birth, both the mean GI and SI decreased slightly by 2years of age, whereas the cortical volume and surface area continuously increased. Notably, histological analysis showed that the outer subventricular zone (oSVZ) in non-sulcal regions was thicker than that in the presumptive calcarine sulcal region on GW 13, preceding the infolding of the calcarine sulcus. The present results showed definite sulcal infolding on the cerebral cortical surface of the marmosets, with similar pattern and sequence of their emergences to other higher-order primates such as macaques and humans. Differential expansion of the oSVZ may be involved in gyral convolution and sulcal infolding in the developing cerebrum.

Quantitative and Noninvasive Assessment of Prenatal X-Ray-Induced CNS Abnormalities Using Magnetic Resonance Imaging

Abstract Our purpose was to noninvasively assess formation of the microvasculature, blood-brain barrier (BBB) and blood-CSF barrier formation of prenatal X-ray-induced CNS abnormalities using quantitative MRI. Eight pregnant female Sprague-Dawley rats were divided into two groups consisting of control and X-irradiated animals. After birth, 20 neonatal male rats were divided into four groups of five rats. To evaluate the development of the BBB, changes in T1 induced by Gd-DTPA were compared quantitatively in normal and prenatally irradiated animals in the formative period 1 to 2 weeks after birth. To assess the abnormalities of the microvasculature, quantitative perfusion MRI and MR angiography were also used. Histology was also performed to evaluate the BBB (albumin) and vascular endothelial cells (laminin). Decreased cerebral blood flow (CBF) and angioarchitectonic abnormalities were observed in the prenatally irradiated rats. However, abnormalities of the BBB and blood-CSF barrier were not observed using Gd-enhanced MRI and albumin staining. Quantitative perfusion MRI, MR angiography and Gd-enhanced T1 mapping are useful for assessing CNS disturbance after prenatal exposure to radiation. These techniques provide important diagnostic information for assessing the condition of patients during the early stages of life after accidental or unavoidable prenatal exposure to radiation.

Sexual dimorphism of sulcal length asymmetry in the cerebrum of adult cynomolgus monkeys (Macaca fascicularis)

The present study aimed to quantitatively clarify the gross anatomical asymmetry and sexual dimorphism of the cerebral hemispheres of cynomolgus monkeys. While the fronto‐occipital length of the right and left cerebral hemispheres was not different between sexes, a statistically significant rightward asymmetry was detected in the cerebral width at the perisylvian region in females, but not in males (narrower width of the left side in the females). An asymmetry quotient of the sulcal lengths revealed a rightward asymmetry in the inferior occipital sulcus and a leftward asymmetry in the central and intraparietal sulci in both sexes. However, the laterality of the lengths of other sulci was different for males and females. The arcuate sulcus was directed rightward in males but there was no rightward bias in females. Interestingly, the principle sulcus and lateral fissure were left‐lateralized in the males, but right‐lateralized in the females. The results suggest that lateralization patterns are regionally and sexually different in the cerebrum of cynomolgus monkeys. The present results provide a reference for quantitatively evaluating the normality of the cerebral cortical morphology in cynomolgus monkeys.

Development of cerebral sulci and gyri in fetuses of cynomolgus monkeys (Macaca fascicularis). II. Gross observation of the medial surface.

This study aimed to clarify chronological sequences of the appearances of sulci and gyri on the medial cerebral surface and its relation to the regional development of the cerebrum in cynomolgus monkeys. The lengths of cingulate and calcarine sulci were measured, and the ratios of these lengths to fronto-occipital length were estimated as indices of the size of the “frontoparietal” and “occipital” regions, respectively. The relative length of cingulate sulcus showed a biphasic increase: a slow phase from EDs 100 to 110, and a rapid phase from EDs 110 to 130. The gyri in the “frontoparietal region” were convoluted in the limbic cortex during the initial slow phase and in the neocortical region during the rapid phase. The relative length of calcarine sulcus lineally increased between EDs 90 and 130, and the gyri in the “occipital region” generated in a dorso-ventral manner: the gyrus convolutions occurred first in the “phylogenetically older” striate and dorsal extrastriate cortices, and then in the “phylogenetically newer” ventral extrastriate cortex. The results suggest that the chronological order of appearance of sulci and gyri is closely associated with the order of phylogenetical development of the cerebral cortex. The present study provides a standard reference for the development of cerebral sulci and gyri of cynomolgus monkeys together with our previous study (Fukunishi et al. Anat Embryol 211:757–764, 2006).

MRI-based morphometric characterizations of sexual dimorphism of the cerebrum of ferrets (Mustela putorius)

The present study aimed to characterize cerebral morphology in young adult ferrets and its sexual dimorphism using high-field MRI and MRI-based morphometry. Ex vivo short TR/TE (typical T1-weighted parameter setting for conventional MRI) and T2W (long TR/TE) MRI with high spatial resolution at 7-tesla could visualize major subcortical and archicortical structures, i.e., the caudate nucleus, lentiform nucleus, amygdala and hippocampus. In particular, laminar organization of the olfactory bulb was identifiable by short TR/TE-MRI. The primary and secondary sulci observable in the adult ferret were distinguishable on either short TR/TE- or T2W-MRI, and the cortical surface morphology was reproduced well by 3D-rendered images obtained by short TR/TE-MRI. The cerebrum had a significantly lower volume in females than in males, which was attributed to region-specific volume reduction in the cerebral cortex and subcortical white matter in females. A sexual difference was also detected, manifested by an overall reduction in normalized signal ratios of short TR/TE-MRI in all cerebral structures examined in females than in males. On the other hand, an alternating array of higher and lower short TR/TE-MRI intensity transverse zones throughout the cortex, which was reminiscent of the functional cortical areas, was revealed by maximum intensity projection (MIP) in 3D. The normalized signal ratio of short TR/TE-MRI, but not T2W-MRI in the cortex, was negatively correlated with the density of myelin-basic protein immunoreactive fibers (males, r=-0.440; females, r=-0.481). The present results suggest that sexual differences in the adult ferret cerebrum are characterized by reduced volumes of the cerebral cortex and subcortical white matter in females, and by overall reductions in physiochemical characteristics, as obtained by short TR/TE-MRI, in females. It should be noted that short TR/TE-MRI-based MIP delineated functional cortical areas related to myeloarchitecture in 3D. Such an approach makes possible conventional investigation of the functional organization of the cerebral cortex and its abnormalities using high-field MRI.

Alternating array of tyrosine hydroxylase and heat shock protein 25 immunopositive Purkinje cell stripes in zebrin II-defined transverse zone of the cerebellum of rolling mouse Nagoya

The present study examined the spatial organization of tyrosine hydroxylase (TH) immunopositive Purkinje cells in the cerebellum of rolling mouse Nagoya with reference to the distribution pattern of the cerebellar compartmentation antigen, heat shock protein 25 (HSP25). Whole-mount immunostaining revealed a striking pattern of parasagittal stripes of TH staining in the rolling mouse cerebellum but not in the control cerebellum. Although the TH stripes resembled the zebrin II stripes in the rolling cerebellum, these two distributions did not completely overlap. The TH stripes were present in the lobules VI and VII (central zone), the lobule X (nodular zone), and the paraflocculus, where zebrin II immunostaining was uniformly expressed. Double immunostaining revealed that TH stripes were aligned in an alternative fashion with HSP25 stripes within the caudal half of lobule VIb, lobules IXb and X, and paraflocculus. Some, but not all, TH stripes shared boundaries with HSP25 stripes. These results revealed an alternating array of TH immunopositive Purkinje cell subsets with HSP25 immunopositive Purkinje cells in the zebrin II-defined transverse zone of the rolling mouse cerebellum. The constitutive expression of HSP25 may prevent the ectopic expression of TH in zebrin II immunopositive Purkinje cell subsets.