Impact of volume and expression time in an AAV-delivered channelrhodopsin

Optogenetics has revolutionised neuroscience research, but at the same time has brought a plethora of new variables to consider when designing an experiment with AAV-based targeted gene delivery. Some concerns have been raised regarding the impact of AAV injection volume and expression time in relation to longitudinal experimental designs. In this study, we investigated the efficiency of optically evoked post-synaptic responses in connection to two variables: the volume of the injected virus and the expression time of the virus. For this purpose, we expressed the blue-shifted ChR2, oChIEF, employing a widely used AAV vector delivery strategy. We found that the volume of the injected virus has a minimal impact on the efficiency of optically-evoked postsynaptic population responses. The expression time, on the other hand, has a pronounced effect, with a gradual reduction in the population responses beyond 4 weeks of expression. We strongly advise to monitor time-dependent expression profiles when planning or conducting long-term experiments that depend on successful and stable channelrhodopsin expression.

Automated summary

Optogenetics has transformed neuroscience research and introduced new considerations for AAV-based targeted gene delivery experiments. This study examined the impact of virus injection volume and expression time on optically evoked post-synaptic responses. The findings suggest that injection volume has minimal effect, while expression time gradually reduces population responses beyond 4 weeks. Time-dependent expression profiles should be carefully monitored for long-term experiments relying on stable channelrhodopsin expression.