A self-administered nasal spray is really gonna get appreciable amounts to the brain? I'm skeptical. Why not an infusion into the cerebrospinal fluid, or a topical ultrasound guided injection through a thinner, softer area of the skull?
Yes, if it has the 'right' properties to pass through mucosa and the BBB, it's absolutely possible. How else would insufflated drugs like cocaine work? There are a number of nasal sprays that act on the CNS. Bupreborphine nasal spray is pretty common as a fast acting overdose treatment that also acts on the central nervous system.