In schizophrenia, the protein reelin, which promotes neural plasticity, is decreased, but these are postmortem findings, hard to disentangle from drug action. However, making rats/mice "depressed" by constantly stressing them out or injecting with corticoids -> and then suddenly adding some reelin into their brains - makes their depression suddenly vanish, as fast as it vanished upon ketamine injection.
pubmed.ncbi.nlm.nih.gov/37550058