Small dose (100 micrograms) of exosomes (cell derived vesicles) from mesenchymal stem cells improved functional recovery and enhanced neurite remodeling, neurogenesis, and angiogenesis in a rat stroke model.  A single treatment given by tail vein.
http://www.ncbi.nlm.nih.gov/pubmed/23963371

Systemic administration of exosomes released from mesenchymal stromal cells promote functional recovery and neurovascular plasticity after stroke in rats.

J Cereb Blood Flow Metab. 2013 Aug 21. doi: 10.1038/jcbfm.2013.152.