This Notice informs potential applicants that the National Institute of Neurological Disorders and Stroke (NINDS) will no longer accept applications under PAR-09-251, "Optimization of Small Molecule Probes for the Nervous System (R21)," beginning with the February 16, 2012 receipt date. Researchers seeking support for chemical optimization of small molecules probes for preclinical, in vivo proof-of-concept experiments for the purposes of drug discovery should consider PAR-12-060, "Solicitation of Validated Hits for the Discovery of in vivo Chemical Probes (R01)."