Male prevalent enhancement of leftward asymmetric development of the cerebellar cortex in ferrets (Mustela putorius)

Abstract

The present study was conducted in MRI-based volumetry to characterize the sexual dimorphism of the cerebellum in young adult ferrets. High spatial resolution 3D anatomical MRI at 7-tesla were acquired ex vivo from fixed cerebella of 90-day-old male and female ferrets. The 3D morphology and topology of cerebellar structures were reproduced well by volume-rendered images obtained from MRI. Volume of the whole cerebellum was significantly larger in males than in females. The cerebellar cortex was further divided into five transverse domains: the anterior zone (AZ; lobules I-V), central zone anterior (lobule VI), central zone posterior (CZp; lobule VII), posterior zone (PZ; lobules VIII-IXa) and nodular zone (NZ; lobules IXb -X). Significantly greater volumes in males than in females were detected bilaterally in the AZ, CZp, and NZ, and leftward in PZ. Notably, the significant volume asymmetry was detected leftward in the CZp of males. By asymmetry quotient analysis, the counterclockwise torque asymmetry of the cerebellum was revealed, and it was more striking in males than in females. The present results suggest that sexual dimorphism of the ferret cerebellum is characterized by enhancing the leftward laterality in the CZp in males, forming the distinctive counterclockwise torque asymmetry.

Age-Dependent Sexually-Dimorphic Asymmetric Development of the Ferret Cerebellar Cortex

“…A similar clockwise torque pattern was seen in the cerebellum of chimpanzees [14]. In contrast, a counterclockwise cerebellar torque (rostrally leftward biased, and caudally rightward biased or symmetrical) was revealed in the cerebellum of ferrets [15]. The present AQ analysis revealed that the anticlockwise torque asymmetry is archived in both sexes of ferrets during PDs 42 to 90, although the leftward laterality is more enhanced in males.…”

“…Our recent Magnetic Resonance Imaging (MRI)-based volumetric analysis revealed that sexual dimorphism of the ferret cerebellum was characterized by increasing the whole volume with an enhancement of counterclockwise torque asymmetry in more males than in females [15]. That report was the first to show sexually-dimorphic asymmetric development of the cerebellum.…”

“…We further segmented four transverse domains of the cerebellar cortex, primarily based on the expression pattern of zebrin II/aldolase C [29,30]: left and right sides of the anterior zone (AZ) (vermal lobules I-V), central zone (CZ) (vermal lobules VI-VII, lobules simplex, and crura I and II of ansiform lobules), posterior zone (PZ) (vermal lobules VIII-IXa, and paramedian lobule), and the nodular zone (NZ) (vermal lobules IXb-X, paraflocculus and flocculus). Boundaries of those domains were defined by major fissures/sulci (Supplemental Figure S1) primarily according to our previous study [15]. During PDs 4 to 10, boundaries of each domain were unclear on MRI images.…”

“…The volumetric analysis was carried out primarily in accordance with our previous procedure [15,32]. Segmented areas of each cerebellar region were measured using SliceOmatic software.…”

“…The cerebellar torque asymmetry was reportedly clockwise in primates such as humans [13] and chimpanzees [14], but counterclockwise torque asymmetry was observed in carnivores, such as ferrets [15].…”