The Effect of Optogenetically Activating Glia on Neuronal Function

Cecilia Pankau,Robin L Cooper,Shelby Mccubbin

doi:10.3390/neuroglia2010007

Abstract

Glia, or glial cells, are considered a vital component of the nervous system, serving as an electrical insulator and a protective barrier from the interstitial (extracellular) media. Certain glial cells (i.e., astrocytes, microglia, and oligodendrocytes) within the CNS have been shown to directly affect neural functions, but these properties are challenging to study due to the difficulty involved with selectively-activating specific glia. To overcome this hurdle, we selectively expressed light-sensitive ion channels (i.e., channel rhodopsin, ChR2-XXL) in glia of larvae and adult Drosophila melanogaster. Upon activation of ChR2, both adults and larvae showed a rapid contracture of body wall muscles with the animal remaining in contracture even after the light was turned off. During ChR2-XXL activation, electrophysiological recordings of evoked excitatory junction potentials within body wall muscles of the larvae confirmed a train of motor nerve activity. Additionally, when segmental nerves were transected from the CNS and exposed to light, there were no noted differences in quantal or evoked responses. This suggests that there is not enough expression of ChR2-XXL to influence the segmental axons to detect in our paradigm. Activation of the glia within the CNS is sufficient to excite the motor neurons.

Highlights

From insects to mammals, the general role of glia in neural function is to serve as an electrical insulator and a protective barrier from the interstitial media or hemolymph
Adults of upstream activating sequence (UAS)-channelrhodopsin 2 (ChR2) and glia > Chr2 XXL were fed All trans-Retinal (ATR) for 2 days prior to being examined in a vial and switched to a vial without food in order to examine the effect of blue light
Glial activation of intact larvae via channel rhodopsin activation results in the depolarization of the motor neurons and produces muscle contraction and paralysis, which was documented in direct recordings of muscle fibers in dissected larvae

Summary

Introduction

The general role of glia in neural function is to serve as an electrical insulator and a protective barrier from the interstitial (extracellular) media or hemolymph (i.e., blood in insects and crustaceans). Considering that the mitochondrial types and densities vary within myelinated axons in the paranodes and nodes, it appears that this is related to homeostasis with ATP dependent pumps [2] These regional differences impact the local ionic flux at nodes and internodes differentially over the Schwann cell. The physiological function of glial cells being influenced by neural activity was demonstrated in the leech ganglion as K+ efflux from the neurons’ depolarized glia [3]. This is assumed to be one of the major functions for oligodendrocytes and Schwann cells. Since there is such a dynamic interplay of the terminal Schwann cell, neuron and muscle, the NMJ is referred to as a tripartite synapse [8,9]

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