Researchers led by David Nutt, University of Bristol, UK, have homed in on a mode of action of psilocybin, a classic psychedelic found in magic mushrooms. Psilocybin is quickly converted by the body to psilocin, which has mind-altering effects similar to those of LSD and mescaline.

The UK team has shown using functional magnetic resonance imaging (fMRI) that a component of Psilocybe cubensis and other species of magic mushrooms that is first metabolized to psilocin, appears to decrease brain “connectivity”. Experiments involving pre-treatment with antagonists for the 5-HT_2A receptor and tests with knock-out mice lacking the gene for this protein allowed the researchers to show that this receptor, which belongs to the serotonin receptor family, is the source of the psychedelic action of “shrooms”.

• Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin,
  R. L. Carhart-Harris, D. Erritzoe, T. Williams, J. M. Stone, L. J. Reed, A. Colasanti, R. J. Tyacke, R. Leech, A. L. Malizia, K. Murphy, P. Hobden, J. Evans, A. Feilding, R. G. Wise, D. J. Nutt,
  Proc. Natl Acad. Sci. 2012, 109(6), 2138–2143.
  DOI: 10.1073/pnas.1119598109