Quantitative proteomic analysis of histone variants following contextual conditioning. A. Single ion chromatograms of peptides from core H2A (HLQLAIR, 453.780 m/z) or the H2AB variant (HLQLAVR). B. MS/MS spectra positively identifying the peak at 453.780 m/z as containing the HLQLAIR sequence (core H2A). C. MS/MS spectra identifying the peak at 466.772 m/z as containing the HLQLAVR sequence (H2AB). D. Quantification of histone variants following contextual conditioning. Values represent average normalized percentage (n = 4 per group) of the total for each variant for cage controls (CC) and contextual fear conditioning (FC). Statistical significance was determined using two-tailed t-tests.