, 2009, Clopath et al., 2008, Frey, 2001, Frey and Morris, 1997 and Okada et al., 2009). This, in turn, buy LY294002 would lead to a memory engram being formed, at the single-cell level, at synapses dispersed throughout the dendritic arbor. However, an alternative model combining STC with the phenomenon of local activity-induced protein synthesis (Martin and Kosik, 2002 and Steward and Schuman, 2001), namely the Clustered Plasticity Hypothesis (CPH) (Govindarajan et al., 2006), predicts that STC is biased toward
occurring between spines that are close together. This would result in memory engrams being preferentially formed at synapses clustered within dendritic compartments, such as a branch (Govindarajan et al., 2006). Competition
among synapses for limiting PrPs would further restrict the engram to such a dendritic compartment because spines close to the site of translation would use up limiting PrPs and reduce their concentration at more distant spines (Govindarajan et al., 2006). The advantages of the CPH include increased efficiency of long-term memory formation and retrieval, as well as a greater capacity for memory storage for an individual neuron (Govindarajan et al., 2006). A study of the link between the level of E-LTP at a given spine and the strength of its synaptic tag, the spatial limits over which STC can occur, and selleck the temporal dynamics of the STC at individual stimulated competing spines require ADP ribosylation factor a
method that permits stimulations and response monitoring of single spines. However, the field stimulation and field recording methods that have been used in the past to study STC measure the average response of a population of unidentified stimulated synapses. Thus, we developed a method using two-photon glutamate uncaging at single spines on proximal apical dendritic branches of CA1 pyramidal neurons to examine the relationship between spines that participate in STC. The expression of L-LTP was assayed by examining spine volume using two-photon imaging of the fluorescent protein Dendra (Gurskaya et al., 2006), along with perforated patch-clamp electrophysiology in some experiments to measure the change in the postsynaptic response to the uncaging of glutamate. We found that STC is temporally asymmetric, is spatially localized, and is biased toward occurring between stimulated spines that reside on the same dendritic branch. In addition, while strongly stimulated spines facilitate induction of L-LTP at neighboring weakly stimulated spines, the stimulated spines then compete for expression of L-LTP. Lastly, we demonstrated that there is a bias toward L-LTP being induced at a single dendritic branch, as opposed to across branches.