Optogenetically Controlled Activity Pattern Determines Survival Rate of Developing Neocortical Neurons.

I Emeline Wong Fong Sang,Heiko J Luhmann,Jonas Schroer,Anne Sinning,Jenq-Wei Yang,Werner Kilb,Davide Warm,Lisa Halbhuber

doi:10.3390/ijms22126575

Abstract

A substantial proportion of neurons undergoes programmed cell death (apoptosis) during early development. This process is attenuated by increased levels of neuronal activity and enhanced by suppression of activity. To uncover whether the mere level of activity or also the temporal structure of electrical activity affects neuronal death rates, we optogenetically controlled spontaneous activity of synaptically-isolated neurons in developing cortical cultures. Our results demonstrate that action potential firing of primary cortical neurons promotes neuronal survival throughout development. Chronic patterned optogenetic stimulation allowed to effectively modulate the firing pattern of single neurons in the absence of synaptic inputs while maintaining stable overall activity levels. Replacing the burst firing pattern with a non-physiological, single pulse pattern significantly increased cell death rates as compared to physiological burst stimulation. Furthermore, physiological burst stimulation led to an elevated peak in intracellular calcium and an increase in the expression level of classical activity-dependent targets but also decreased Bax/BCL-2 expression ratio and reduced caspase 3/7 activity. In summary, these results demonstrate at the single-cell level that the temporal pattern of action potentials is critical for neuronal survival versus cell death fate during cortical development, besides the pro-survival effect of action potential firing per se.

Highlights

The main observations of the present study are as follows: (i) Physiological and nonphysiological patterns of neuronal activity can be reinstalled in ChR2-expressing neurons in cell-cultures silenced by GABAergic and glutamatergic blockers. (ii) Reinstalling a physiological burst pattern reduced the number of apoptotic neurons, in contrast to a non-physiological stimulation paradigm using the same number of stimuli at equidistant repetitions. (iii) Burst pattern stimulation-induced larger Ca2+ transients, a higher expression of BDNF, and decreased Bax/BCl-2 ratio, which can contribute to the anti-apoptotic effect of this physiological stimulation paradigm
Our results indicate that the temporal pattern of neuronal activity in the immature brain can directly influence the regulation of apoptosis in neurons during development and highlight the importance of highly correlated bursting activity for the structural development of the central nervous system
The transition from sparse, uncorrelated firing of neurons to highly-correlated bursting activity of neurons is a general and well-conserved developmental feature of cortical networks before neuronal activity enters the mature phase that is again dominated by decorrelated network activity [41,42,43]

Summary

Introduction

Neurons are produced in excess, and neuronal population sizes are only later reduced by apoptotic cell death This fundamental process is important for the maturation of functional neuronal networks and has to be tightly regulated [1,2,3]. Population-based approaches with pharmacological or electrical stimulation suggest correlations of distinct neuronal activity patterns with respective apoptotic rates [13,23,24] From these experiments, the contribution of intrinsic electrical activity states of individual neurons remains indistinguishable from the role of its network-dependent synaptic inputs

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