Biology subjects

Naumann, R. K.

Publications and source records attributed to Naumann, R. K..

3 recordsLinked to original sources

bioRxiv2024

Genomic evolution reshapes cell type diversification in the amniote brain

Over 320 million years of evolution, amniotes have developed complex brains and cognition through largely unexplored genetic and gene expression mechanisms. We created a comprehensive single-cell atlas of over 1.3 million cells from the telencephalon and cerebellum of turtles, zebra finches, pigeons, mice, and macaques, employing single-cell resolution spatial transcriptomics to validate gene expression patterns across species. Our study revealed significant species-specific variations in cell types, highlighting their conservation and diversification in evolution. We found pronounced differences in telencephalon excitatory neurons (EX) and cerebellar cell types between birds and mammals. Birds predominantly express SLC17A6 in EX, whereas mammals expressed SLC17A7 in neocortex and SLC17A6 elsewhere, possibly due to loss of SLC17A7 function loss in birds. Additionally, we identified a novel bird-specific Purkinje cell subtype (SVIL+), implicating the LSD11/KDM1A pathway in learning and circadian rhythms, and related numerous positively selected genes in birds, suggesting an evolutionary optimization of cerebellar functions for ecological and behavioral adaptation. Our findings elucidate the complex interplay between genetic evolution and environmental adaptation, underscoring the role of genetic diversification in the development of specialized cell types across amniotes.

evolutionary biology↗

bioRxiv2022

Cortical synapses of the world's smallest mammal: an FIB/SEM study in the Etruscan shrew

The main aim of the present study was to determine if synapses from the exceptionally small brain of the Etruscan shrew show any peculiarities compared to the much larger human brain. This study constitutes the first description of the Etruscan shrew synaptic characteristics using Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM). We analyzed the synaptic density and a variety of structural characteristics of 7,239 3D reconstructed synapses, obtaining the following major results: (i) cortical synaptic density was very high, particularly in layer I; (ii) the vast majority of synapses were excitatory, with the highest proportion found in layer I; (iii) excitatory synapses were larger than inhibitory synapses in all layers except in layer VI; and (iv) synapses were either randomly distributed in space or showed a slight tendency to be organised in a regular arrangement. Some of these general synaptic characteristics are remarkably similar to those found in the human cerebral cortex. However, the cortical volume of the human brain is about 50,000 times larger than the cortical volume of the Etruscan shrew, while the total number of cortical synapses in human is only 20,000 times the number of synapses in the shrew, and synaptic junctions are 35% smaller in the Etruscan shrew. Thus, the differences in the number and size of synapses cannot be attributed to a brain size scaling effect but rather to adaptations of synaptic circuits to particular functions. The present work provides a quantitative dataset from the Etruscan shrew synapses -- not only contributing to the knowledge of the ultrastructure of the mammalian cortex, but also identifying common and differing principles of synaptic organization.

neuroscience↗

bioRxiv2018

Estrus-Cycle Regulation of Cortical Inhibition

Female mammals experience cyclical changes in sexual receptivity known as the estrus-cycle. Little is known about how estrus affects the cortex although alterations in sensation, cognition and the cyclic occurrence of epilepsy suggest brain-wide processing changes. We performed in vivo juxtacellular and whole-cell recordings in somatosensory cortex of female rats and found that the estrus-cycle potently altered cortical inhibition. Fast-spiking interneurons strongly varied their activity with the estrus-cycle and estradiol in ovariectomized females, while regular-spiking excitatory neurons did not change. In vivo whole-cell recordings revealed a varying excitation-to-inhibition-ratio with estrus. In situ hybridization for estrogen receptor {beta} (Esr2) showed co-localization with parvalbumin-positive interneurons in deep cortical layers, mirroring the laminar distribution of our physiological findings. In vivo and in vitro experiments confirmed that estrogen acts locally to increase fast-spiking interneuron excitability through an estrogen receptor {beta} mechanism. We conclude that sex hormones powerfully modulate cortical inhibition in the female brain.

neuroscience↗