you can use the activated caspase 3 gene delivered by AAV. there is a Cre-dependent version available at the UNC. You just need to inject it together with an AAV expressing Cre recombinase under hSyn (neuron-specific) promoter, or just inject it in a suitable Cre line. Cell death takes places within 10-15 days.

Indeed as Francesco suggested, you can use AAV-hSyn-DIO-Capase3 and inject it to a cre line. I heard a talk recently describing the success of this approach, so it should be good to try. Also, you can try AAV-hSyn-DTA injection, expressing diphteria toxin that will also kill cells (neurons specifically thanks to the promoter).

Thanks everyone for the insightful comments. Well i am injecting in WT mice. So it shall not be a cre line. AAV-hSYn-DTA as suggested by Boaz Barak could be the best approach. Do you know any vendor who provides this specific construct?

I checked with UNC and all they offer is cre version. I dont want a cre line. I would appreciate all your comments.

I know Dymecki lab at Harvard work with this kind of stuff, but you should ask them if they have no cre-dependent version.

http://genepath.med.harvard.edu/~dymecki/

you can make it cre-independent just by co-injecting an AAV expressing Cre under CMV (or any other) promoter. they are easy to find.