BDNF and bipolar disorder: For example, butyrate was shown to reverse the reduction in BDNF, NGF and GDNF levels in the hippocampus and frontal cortex of rats subjected to a model of bipolar disorder [62] and to improve cognitive decline, loss of neuronal spines and the reduction in BDNF induced by the NMDA receptor agonist quinolinic acid both in vitro and in vivo [209].