Effects of Brain Size on Adult Neurogenesis in Shrews.

Katarzyna Bartkowska,Peter Vogel,Ruzanna Djavadian,Krzysztof Turlejski,Beata Tepper,Leszek Rychlik

doi:10.3390/ijms22147664

Abstract

Shrews are small animals found in many different habitats. Like other mammals, adult neurogenesis occurs in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus (DG) of the hippocampal formation. We asked whether the number of new generated cells in shrews depends on their brain size. We examined Crocidura russula and Neomys fodiens, weighing 10–22 g, and Crocidura olivieri and Suncus murinus that weigh three times more. We found that the density of proliferated cells in the SVZ was approximately at the same level in all species. These cells migrated from the SVZ through the rostral migratory stream to the olfactory bulb (OB). In this pathway, a low level of neurogenesis occurred in C. olivieri compared to three other species of shrews. In the DG, the rate of adult neurogenesis was regulated differently. Specifically, the lowest density of newly generated neurons was observed in C. russula, which had a substantial number of new neurons in the OB compared with C. olivieri. We suggest that the number of newly generated neurons in an adult shrew’s brain is independent of the brain size, and molecular mechanisms of neurogenesis appeared to be different in two neurogenic structures.

Highlights

Shrews are small eutherian mammals found in Eurasia, Africa and both Americas.A total of 461 living shrew species of different metabolism and habits are classified into the family Soricidae, encompassing three extant subfamilies; Crocidurinae, Myosoricinae and Soricinae
BrdU administration, the number of newly generated cells in the subventricular zone of the lateral ventricle (SVZ) and RMS wasvery very high, with the exception of C. olivieri that had a low number of proliferated cells in the RMS
The manew cells were located in the olfactory bulb (OB), and the highest number of new neurons was observed jority of new cells were located in the OB, and the highest number of new neurons was in N. fodiens that we classified as a small-mass animal

Summary

Introduction

Shrews are small eutherian mammals found in Eurasia, Africa and both Americas.A total of 461 living shrew species of different metabolism and habits are classified into the family Soricidae, encompassing three extant subfamilies; Crocidurinae, Myosoricinae and Soricinae. Shrews are generally small animals, the difference in body mass between species is huge. The smallest species have the small brain mass, and larger animals have larger brains. The brain and body mass relationship is not linear between different mammalian species, and in addition, not always the larger brain manifests in evolutionary progress [3,4]. Brains of larger species have more neurons than smaller brains within each mammalian order [5]. The cellular scaling rules have been identified to describe changes in brain structures for different mammalian species. These cellular rules were applied for rodents and primates [6,7]. Larger brains have more neurons, smaller neuronal densities and larger glia/neuron ratios than smaller brains

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Results

Conclusion