Mood elevation with ketamine via rapid change in synaptic spines?

Rapid antidepressant effects of ketamine (an NMDA receptor antagonist) have been observed in treatment-resistant depressed patients. The mechanism for this action is unknown. Li and coworkers now show that ketamine increases the number of new synaptic spines. Blockade of mTOR (rapamycin) signaling blocked ketamine induction of synaptogenesis and behavioral responses in animal models of depression. These effects of ketamine are opposite to the synaptic changes occurring in response to stress and may contribute to the fast antidepressant actions of ketamine.
Li N et al.: mTOR-dependent synapse formation underlies the rapid antidepressant effects of NMDA antagonists. Science 329: 959-964 (2010).
http://www.ncbi.nlm.nih.gov/pubmed/20724638