A spaced HFS paradigm was used to induce non-decremental protein synthesis-dependent LTP in urethane-anesthetized rats (Messaoudi et al., 2002, 2007). As shown in Fig. 1, HFS resulted in a robust and stable increase in the slope of field excitatory postsynaptic potential (fEPSP) and amplitude of the population Epigenetics inhibitor spike (Fig. 1A–C). A second group of rats received HFS following

systemic (i.p.) injection of the competitive NMDAR antagonist, CPP. As previously shown (Williams et al., 1995; Messaoudi et al., 2002), LTP of the fEPSP and population spike was inhibited in CPP-treated rats. No changes in synaptic efficacy were observed in a third group of rats receiving LFS only. As a positive control for NMDAR-dependent gene regulation, we examined expression of immediate-early gene zif268 (also known as Egr1) in homogenate samples from microdissected dentate gyrus (Cole et al., 1989; Havik et al., 2003). At 2 h post-HFS, zif286 mRNA levels

in the HFS-treated dentate gyrus were significantly elevated 2.8-fold above the contralateral, control dentate gyrus (Fig. 1D). This increase was abolished in the CPP group and absent in the LFS group. These results confirmed generation of stable NMDAR-dependent LTP associated with robust changes in gene expression. Microarray expression profiling was performed to screen for LTP-regulated miRNAs 2 h post-HFS. MirVana-purified RNA from the HFS-treated and contralateral control dentate gyrus from two animals was differentially hybridized to rat miRNA chips (MiRat_8.0_060307) representing all miRNA transcripts find more listed in Sanger miRBase Release 8.0. Figure 2A

shows miRNAs exhibiting mean changes of at least 20%. By this arbitrary criterion 10 miRNAs showed increased expression (rno-miRNA-28, -103, -107, -125a, -132, -151*, -212, -320, -485, -543) and 11 miRNAs showed decreased expression (rno-miRNA-17, -19b, -21, -23a, -23b, -138, -181b, -219, -247, -338, -494), of a total of 237 probes on the Carbohydrate chip. Real-time RT-PCR analysis was used for independent validation and further study of three candidate regulated miRNAs (Fig. 2B). In agreement with the array data, miR-132 and miR-212 levels were significantly elevated, while miR-219 levels were significantly decreased at 2 h post-HFS in treated dentate gyrus relative to untreated control dentate gyrus. This regulation was HFS dependent, as no changes in miRNA expression were observed in rats receiving LFS only. We anticipated that blockade of LTP by CPP would eliminate or reduce the changes in miRNA expression. Instead, each of the three miRNAs exhibited enhanced expression when HFS was applied in the presence of CPP. Thus, miR-132 levels were elevated from 1.38-fold in the HFS group to 1.83-fold in the HFS + CPP group, miR-212 levels increased from 1.26- to 1.59-fold, and miR-219 levels flipped from a decrease of 0.68-fold in the HFS group to an increase of 1.27-fold in the HFS + CPP group (Fig. 2C).