Abnormal circadian oscillation of hippocampal MAPK activity and power spectrums in NF1 mutant mice

Abstract

Studies have implied that the circadian oscillation of mitogen-activated protein kinase (MAPK) signal pathways is crucial for hippocampus-dependent memory. NF1 mouse models (Nf1 heterozygous null mutants; Nf1 ^+/-) displayed enhanced MAPK activity in the hippocampus and resulted in memory deficits. We assumed a link between MAPK pathways and hippocampal rhythmic oscillations, which have never been explored in Nf1 ^+/- mice. We demonstrated that the level of extracellular signal-regulated kinases 1 and 2 (ERK1/2) phosphorylation in Nf1 ^+/- mice were significantly higher at nighttime than at daytime. Moreover, the in vivo recording revealed that for the Nf1 ^+/- group, the power spectral density of theta rhythm significantly decreased and the firing rates of pyramidal neurons increased. Our results indicated that the hippocampal MAPK oscillation and theta rhythmic oscillations in Nf1 ^+/- mice were disturbed and hinted about a possible mechanism for the brain dysfunction in Nf1 ^+/- mice.

Keywords: Hippocampal rhythmic oscillations; Local field potentials; MAPK oscillation; Nf1 +/− mouse model; Spike activity.

Fig. 1

In vivo recording in CA1 demonstrates alterations in hippocampal rhythmic oscillations and firing rates in Nf1 ^+/− mice. a The timeline of the in vivo recording experiments. The typical local field potentials (LFPs) recordings and unit spikes in CA1, the diagram of mice in recording with 16-channel microelectrode array were shown. b Histograms show the averaged power spectral density of the neuronal rhythmic oscillations (theta). Data are expressed as mean ± SEM (WT, n = 5; Nf1 ^+/−, n = 5). Two-way analysis of variance with repeated measures and post hoc Bonferroni tests was used to evaluate differences in local field potential power spectrum density in day and night recordings in Nf1 ^+/− and WT groups. *** p < 0.001. c The differences in the spike waveforms of hippocampal pyramidal neurons between day and night in WT and Nf1 ^+/− groups (WT, N = 5, n_day = 38, n_night = 37; Nf1 ^+/−, N = 5, n_day = 31, n_night = 25). d The spike firing rates of pyramidal cells. Comparison of the firing rates of pyramidal cells during day and night recordings (WT, N = 5, n_day = 38, n_night = 37; Nf1 ^+/−, N = 5, n_day = 31, n_night = 25). Paired t-test was used to evaluate differences in firing rates of pyramidal cells. **p < 0.01, ***p < 0.001

Fig. 2

The level of P-MAPK activity of Nf1 ^+/− mice in hippocampus shows different circadian oscillations compared with WT mice. a pErk1/2 expression in Nf1 ^+/− mice and littermates WT mice were evaluated by western blot analysis at day and night. pErk1/2, normalized to Erk, the statistical quantification is shown in the right panel (Nf1 ^+/− mice: n = 6 mice per time point, WT mice: n = 3 mice per time point, all groups normalized to WT in day), *p < 0.05, **p < 0.01. b pErk1/2 expression in C57BL/6 mice were evaluated by western blot analysis at day and night (10:30–11:00 a.m. and 10:30–11:00 p.m.). pErk1/2, normalized to Erk, the statistical quantification is shown in the right panel (n = 10 mice per time point, all groups normalized to C57BL/6in day), **p < 0.01. c pErk1/2 protein expression in 129 T2/SvEmsJ mice. pErk1/2 expression level, normalized to total Erk protein in the hippocampus (n = 7 mice per time point, all groups normalized to129T2/SvEmsJ in day). d pErk1/2 expression in mice with hybrid background of 129 T2/SvEmsJ-C57BL/6 mice were evaluated by western blot analysis at day and night. pErk1/2 expression level, normalized to total Erk protein in the hippocampus (n = 3 mice per time point, all groups normalized to mice in day)