Recent studies indicate that eCB-CB1 signaling is not the only system that can initiate presynaptic LTD at striatal synapses. Indeed, presynaptically-expressed LTD can be induced by activation of serotonin, opiate, and group II metabotropic glutamate receptors, among those that have been examined to date (Kahn, Alonso et al. 2001, Mathur, Capik et al. 2011, Atwood, Lovinger et al. 2014). Some of these LTD forms show mutual occlusion with eCB-LTD, indicating that they probably occur at the same synapses, and involve similar downstream signaling mechanisms (Atwood, Lovinger et al. 2014). It will be interesting to determine how chronic EtOH exposure affects these other presynaptic forms of LTD, and if similar mechanisms underlie these effects.
