Hunting for synaptic tagging and capture in memory formation.

Editor's Note: These short reviews of a recent paper in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to mimic the journal clubs that exist in your own departments or institutions. For more information on the format and purpose of the Journal Club, please see Long-term potentiation (LTP) and some forms of long-term memory share a number of properties, such as associativity, durability , and protein synthesis dependence. These similarities suggest that LTP could be the cellular substrate for memory (Bliss and Collingridge, 1993). The recently reported changes in synaptic transmission caused by learning in behaving animals (Gruart et al., 2006; Whitlock et al., 2006) have provided significant support to this view and attracted attention to additional properties of LTP potentially relevant in memory formation. Ten years ago, Frey and Morris (1997, 1998) performed a series of two-pathway stimulation experiments that led them to propose the synaptic tagging and capture hypothesis. In their seminal work, Frey and Mor-ris (1997, 1998) showed that early-LTP, a transient form of LTP, which is induced by a weak stimulus, could be converted into late-LTP, a more persistent form of LTP, if the weak and the strong stimuli were applied temporally close to each other on different synapses of the same neuron. These results suggested an interaction between the molecular events connecting early-and late-LTP in different pathways. Thus, the authors speculated that such a mechanism might explain why inconsequential events are remembered for much longer if they occur around the same time as relevant well remembered events. A decade later, a recent study by Moncada and Viola (2007) in The Journal of Neuroscience tested the validity of this prediction in vivo. By combining two behavioral tasks, Moncada and Viola (2007) investigated whether a behavioral experience could extend the duration of the memory for an independent task and whether this interaction displayed properties consistent with synaptic capture. In the inhibitory avoidance paradigm (IA), a hippocampal-dependent task (Whitlock et al., 2006), rodents receive an electrical foot shock immediately after they step down from a platform, so they suppress the step-down behavior the next time they are placed on the platform. Thus, the step-down latency can be used as a parameter to assess memory retention. To answer the question of whether this memory could be promoted by its coincidence with an independent task, the authors combined this paradigm with the exploration of a novel …