Regional difference in sulcal infolding progression correlated with cerebral cortical expansion in cynomolgus monkey fetuses

Preclinical magnetic resonance imaging and spectroscopy in the fields of radiological technology, medical physics, and radiology

Magnetic resonance imaging (MRI) is an indispensable diagnostic imaging technique used in the clinical setting. MRI is advantageous over X-ray and computed tomography (CT), because the contrast provided depends on differences in the density of various organ tissues. In addition to MRI systems in hospitals, more than 100 systems are used for research purposes in Japan in various fields, including basic scientific research, molecular and clinical investigations, and life science research, such as drug discovery, veterinary medicine, and food testing. For many years, additional preclinical imaging studies have been conducted in basic research in the fields of radiation technology, medical physics, and radiology. The preclinical MRI research includes studies using small-bore and whole-body MRI systems. In this review, we focus on the animal study using small-bore MRI systems as "preclinical MRI". The preclinical MRI can be used to elucidate the pathophysiology of diseases and for translational research. This review will provide an overview of previous preclinical MRI studies such as brain, heart, and liver disease assessments. Also, we provide an overview of the utility of preclinical MRI studies in radiological physics and technology.

Cerebral Sulcal Asymmetry in Macaque Monkeys

The asymmetry of the cerebral sulcal morphology is particularly obvious in higher primates. The sulcal asymmetry in macaque monkeys, a genus of the Old World monkeys, in our previous studies and others is summarized, and its evolutionary significance is speculated. Cynomolgus macaques displayed fetal sulcation and gyration symmetrically, and the sulcal asymmetry appeared after adolescence. Population-level rightward asymmetry was revealed in the length of arcuate sulcus (ars) and the surface area of superior temporal sulcus (sts) in adult macaques. When compared to other nonhuman primates, the superior postcentral sulcus (spcs) was left-lateralized in chimpanzees, opposite of the direction of asymmetry in the ars, anatomically-identical to the spcs, in macaques. This may be associated with handedness: either right-handedness in chimpanzees or left-handedness/ambidexterity in macaques. The rightward asymmetry in the sts surface area was seen in macaques, and it was similar to humans. However, no left/right side differences were identified in the sts morphology among great apes, which suggests the evolutionary discontinuity of the sts asymmetry. The diversity of the cortical lateralization among primate species suggests that the sulcal asymmetry reflects the species-related specialization of the cortical morphology and function, which is facilitated by evolutionary expansion in higher primates.

Asymmetry of Cerebellar Lobular Development in Ferrets

The ferret cerebellum is anteriorly right-lateralized and posteriorly left-lateralized. This study characterized the left/right difference in ferret cerebellar lobular morphology using 3D-rendered magnetic resonance images of fixed brains from seven male and seven female ferrets on postnatal day 90. Asymmetrical lobular morphology showed asymmetrical sublobular development in the anterior vermis, lobulus simplex, and ansiform lobules and additional grooves asymmetrically appearing in the paramedian lobule, lobule VI, and ansiform lobules. Although we observed these asymmetric hallmarks in four cerebellar transverse domains in both sexes, there was no left/right difference in their incidence in each domain. Males showed a significantly higher incidence of the additional grooves in the left side of the ansiform lobules than in females. Data were combined and classified as per the asymmetry quotient (AQ) into left- (AQ < 0) and right-dominant (AQ > 0) groups. There were significantly higher incidences of poor sublobular development of ansiform lobules and additional groove appearing in lobule VI on the right than on the left in the left-dominant group. Asymmetric hallmarks visible on the cerebellar surface of ferrets are relevant to the left-biased volume asymmetry of the central zone of cerebellar transversus domains containing lobule VI and ansiform lobules.

Follow-up study of subventricular zone progenitors with multiple rounds of cell division during sulcogyrogenesis in the ferret cerebral cortex

The subventricular zone (SVZ) of the developing cerebral cortex appears transiently during cortical neurogenesis and is known as the second proliferative zone that contains intermediate progenitor cells and self-renewable neuronal stem cells-the so-called basal radial glia (bRG). The present study attempted to track the differentiation and migration dynamics of SVZ progenitors undergoing multiple cell divisions at the late stage of neurogenesis in a course of sulcogyrogenesis in the ferret, a gyrencephalic mammal. Ferret pups were given a 5-ethynyl-2'-deoxyuridine (EdU) injection on postnatal day (PD) 5 followed by a 5-bromo-2'-deoxyuridine (BrdU) injection on PD 7. The 48 h interval between EdU and BrdU injections covered the minimum times for the first and second S-phase of self-renewing bRG. Two h after BrdU injection, EdU/BrdU-double labeled cells were found in the inner or outer SVZ (iSVZ and oSVZ), more than 80% of which were Sox2-positive. Furthermore, 95.8% of EdU/BrdU-double labeled Sox2-positive progenitors in the iSVZ and 84.2% in the oSVZ were also Pax6-positive, defining these progenitors as bRG. On PD 20, all EdU/BrdU-double labeled cells were NeuN-immunopositive, and more than 60% of these were parvalbumin-immunopositive. EdU/BrdU-double labeled neurons were distributed densely in the superficial portion of the outer cortical stratum. Cluster analysis divided the gyral and sulcal regions into higher and lower density groups, respectively, based on the diversity of the cortical density of EdU/BrdU-double labeled neurons. The higher density group included the gyral and sulcal regions of the prefrontal, parietooccipital and/or cingulate cortex, corresponding to cortical regions associated with evolutionary expansion. Although a limited population of neurons within a narrow time window of cortical neurogenesis was tracked, the present findings suggest that neurons derived from bRG at the late stage of neurogenesis express parvalbumin during corticohistogenesis. Due to the diversity of sulcogyral distributions, neurons derived from bRG may be implicated in evolutionary cortical expansion.