Species-specific differences in synaptic transmission and plasticity

Prateep Beed,Saikat Ray,Laura Moreno Velasquez,Daniel Parthier,Noam Nitzan,Liora Las,Jörg Breustedt,Michael Brecht,Dietmar Schmitz,Aarti Swaminathan,Alexander Stumpf

doi:10.1038/s41598-020-73547-6

Abstract

Synaptic transmission and plasticity in the hippocampus are integral factors in learning and memory. While there has been intense investigation of these critical mechanisms in the brain of rodents, we lack a broader understanding of the generality of these processes across species. We investigated one of the smallest animals with conserved hippocampal macroanatomy—the Etruscan shrew, and found that while synaptic properties and plasticity in CA1 Schaffer collateral synapses were similar to mice, CA3 mossy fiber synapses showed striking differences in synaptic plasticity between shrews and mice. Shrew mossy fibers have lower long term plasticity compared to mice. Short term plasticity and the expression of a key protein involved in it, synaptotagmin 7 were also markedly lower at the mossy fibers in shrews than in mice. We also observed similar lower expression of synaptotagmin 7 in the mossy fibers of bats that are evolutionarily closer to shrews than mice. Species specific differences in synaptic plasticity and the key molecules regulating it, highlight the evolutionary divergence of neuronal circuit functions.

Highlights

Synaptic transmission and plasticity in the hippocampus are integral factors in learning and memory
For DAPI showing the hippocampus of (a) shrew and (b) mice indicating the different subregions of the hippocampus—dentate gyrus (DG), CA1, CA3 and the pyramidal (Py), Stratum Radiatum (Sr) and Stratum
Lucidum (SL) layers. (c) Relative cell densities in different hippocampal subregions do not differ between shrews and mice, indicating conserved cytoarchitectonic layout (p-values based on Mann–Whitney two tailed test.). (d,f) Saggital section of an Etruscan shrew hippocampus labelled for calbindin (CB, green) and DAPI indicating the different hippocampal subregions—CA1, CA2, CA3, dentate gyrus (DG) and mossy fibers. (e) Mossy fibers visualized by the presence of synaptic zinc in a sagittal section of an Etruscan shrew brain, and CA2 labelled by the presence of the protein PCP4 show that the mossy fibers are present in CA3 and terminate at the CA2 region. (g) Sagittal section of a mouse, marked same as (f). (h)

Summary

Introduction

Synaptic transmission and plasticity in the hippocampus are integral factors in learning and memory. (d,f) Saggital section of an Etruscan shrew hippocampus labelled for calbindin (CB, green) and DAPI (blue) indicating the different hippocampal subregions—CA1, CA2, CA3, dentate gyrus (DG) and mossy fibers (mf). We recorded mossy fiber fEPSPs from sagittal slices of shrews using the same solutions and slicing procedure as used for mice (Fig. S1a).

Results

Conclusion