Previous studies, using in vitro hippocampal slices to measure LTP, also point to the rapidity, e.g., within 15 minutes, with which GluR1-containing AMPARs can be delivered to synapses to mediate postsynaptic potentiation (Shi, 2001; Shi et al., 1999). Whether LA synapses of our in vivo preparation would also have shown increased levels of endogenous GluR1 immunoreactivity at the synaptic junction within 15 minutes and whether these arise through lateral diffusion from nonsynaptic plasma membrane or through exocytosis from the cytoplasmic pool is a question that can be addressed in the future.
