Hey Tomas - funny you should ask this, I just came upon it today
(12/9/94) in my pharmacology textbook. "Although there have been
intensive efforts to isolate an endogenous Valium-like substance from
brain tissue, so far none has succeeded." However, it goes on to mention
diazepam-binding inhibitor which, when administered "has effects opposite
to those of diazepam... producing excitement and increased anxiety." So
you know, this is from "Drug, Society & Human Behavior" by O. Ray and C.
Ksir, copyright 1993. Hope this helps!
- Hannah
