Tag Archives: Toxicity

Long-term channelrhodopsin-2 expression can induce abnormal axonal morphology and targeting in cerebral cortex

When using optogenetics to study circuit function or animal behavior, a critical prerequisite is that optogenetic protein expression does not, in itself, perturb the circuit being studied. While short-term expression is very commonly used without observable circuit disruption, whether this is also true for long-term expression is less clear. A recent paper by Miyashita et al. in Frontiers in Neural Circuits shows that long-term, high-level expression of ChR2 can induce abnormal axonal morphology and targeting in cerebral cortex. This underscores the importance of using the lowest expression possible, particularly for long-term studies.

Miyashita et al. expressed a common construct, CAG::hChR2 (H134R)-EYFP-WPRE, in L2/3 pyramidal neurons in rat somatosensory cortex via in utero electroporation (IUE). This same strategy was used in several prior studies of S1 circuit function, with one important difference: Miyashita et al. expressed hChR2 that was codon-optimized for mammalian expression, while prior studies expressed native ChR2 (discussed below). This strategy successfully conferred light-evoked spiking in vivo and in in vitro brain slices. However, long-term expression (> 40 d) also caused major abnormalities in axonal morphology, which included cylinders of axonal membrane that enveloped pyramidal cell proximal dendrites, and spherical, calyx-like axonal swellings that surrounded neuron cell bodies. These … Continue reading

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