In mice that performed poorly on a maze test, the peptide semax raised levels of a brain protein called BDNF in both the hippocampus and cortex, while it didn’t change BDNF in mice that already did well. This suggests semax might boost brain health mainly when there’s a cognitive deficit, but the evidence is from animal studies only.

The influence of subchronic administration of nootropic drugs (piracetam, phenotropil, meclophenoxate, pantocalcine, semax, nooglutil) on the brain-derived neurotrophic factor (BDNF) content in hippocampal and cortical tissues in mice with different exploratory behavior--high efficacy (HE) against low efficacy (LE)--in cross-maze test has been studied. The initial BDNF concentration in hippocamp (but not in cortex) of control HE mice was higher than that in LE mice (LE, 0.091 +/- 0.005 pg/microg; HE, 0.177 +/- 0.005 pg/microg; p < 0.0005). After drug administration, changes in the BDNF level were only observed in the hippocamp of LE mice, where it reached (pg/microg) 0.115 +/- 0.004 (for piracetam); 0.119 +/- 0.006 (for phenotropil); 0.123 +/- 0.007 (for semax); and 0.122 +/- 0.009 (for meclophenoxate). In the LE mice cortex, the BDNF content increased only after piracetam and semax injections (to 0.083 +/- 0.003 and 0.093 +/- 0.008, respectively, vs. 0.071 +/- 0.003 pg/microg in the control group; p < 0.0005). No changes were observed in the cortex of HE mice. Thus, the obtained results demonstrate that clinically used drugs piracetam, phenotropil, meclophenoxate, and semax realize their nootrope effects, at least partially, via increase in hippocampal BDNF level, which is achieved only under conditions of cognitive deficiency.