Montelukast (singular)

#1

https://www.newscientist.com/article/dn28384-old-rat-brains-rejuvenated-and-new-neurons-grown-by-asthma-drug/ 

Interesting - and as a potential re-purposing option, maybe slightly more near-term than some others (if proven)

#2

It doesn't say what will happen next, just the usual, heart-sinking disclaimer at the end.

#3

Like everything, it needs funding to go to the next level (initial and phase II trials)