In an article (it costs money to read it) in the European Journal of Cell Biology, one Doctor William Frey and some colleagues describe work in which rats sniff tiny amounts of adult rat stem cells as a method of implanting therapeutic cells into the brain. The point is that snorting gets the stuff to your brain pretty directly and pretty quickly and is better than boring a hole into your brain, just ask Keith Richards. ("I’ve been trepanned. That’s quite an interesting experience, especially for my brain surgeon, who saw my thoughts flying around in my brain.")
The report was covered in the University of Minnesota News (UMNews): "If you had a brain malady that could be treated with stem cells, how would you like them delivered—by having surgeons cut open your skull to implant the cells, or by snorting them like a nasal decongestant? Not really a hard choice, is it?"