If you are doing an experiment where you inject AAV into a specific region, e.g. AAV-DIO-ChR2-eYFP in a Cre driver line for optogenetics, will the AAV transduce the axons passing through the region in addition to the cell bodies? This would compromise a conclusion saying, "Region X neuronal activity is sufficient for Process Y", because really you are activating both Region X and axons from unknown regions.
In my experience such retrograde infection with AAV (frox the axon to the cell body) is very hard to achieve, at least with most available serotypes. However, this highly depends on your preparation so an empirical examination (e.g., look at nearby areas projecting to your injection site) would be advised in any case.
Hi Cassey,
the short answer is yes, AAVs are able to infect axon terminals and produce retrograde transport (towards the cell body). The slightly longer answer is that this process is highly biased based on the seropype you are using. There are a number of papers reporting AAV6 (and maybe AAV6.2) is the main serotype to produce retrograde transport. There are however reports of many other serotypes producing retrograde transport with a much smaller rate. Keep in mind that there are many other considerations related to your experimental design that will help you minimize the consequences of this possible off target effect. One of the most obvious, since you talk about a cre line, is that if the axons that get infected are from a Cre- cell then the expression of your gene of interest won't take place; for example if you use a Dat Cre of a Gad Cre mouse line, terminals from pyramidal cells could be infected but they won't be able to express. Moreover, if you are interested in activate a specific cell population in many cases you apply the light stimulation (in the case of optogenetics) in the area where the neurons you infect project, and not in the area of injection itself since this approach increases the specificity of the manipulation. Finally retrograde transport, with AAV, HSV or CAV2, can be used to your advantage as it allows you to be much more selective in your manipulations. There are numerous recent papers taking advantage of this approach.
Hope this helps,
Ezequiel
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