Article Figures & Data
Figures
- Figure 1.
L-IFD induces an enhancement of learning and memory processes. A, Motor learning was assayed using a rotarod over four sessions. The percentage of mice (ordinate) and the number of trials required (abscissa) to complete 5 min on a 60 rpm rotating cylinder is shown (n = 13 and 14 for AL and L-IFD mice, respectively). B, Number of conditioning responses per session after training in 12 s fixed-interval operant conditioning. C, Percentage of conditioned responses per session across the whole training using a trace electrical shock-SHOCK eyeblink classical conditioning paradigm (n = 10 and 8 for the two groups in operant and classical conditioning, respectively). D, The object recognition memory test was performed for 5 min and 15 min training sessions (n = 8 for both groups). Discrimination indices during training, STM, and LTM sessions (1 and 24 h after training, respectively) are shown for each experimental procedure. Black and gray colors represent AL and L-IFD mice, respectively. +Statistical significance of AL and L-IFD mice in the same session; *statistical significance of the different session with respect to habituation in the same group. +,*p ≤ 0.05; ++,**p ≤ 0.01; +++,***p ≤ 0.001. H, Habituation session; C1–C8, conditioning sessions 1–8.
- Figure 2.
L-IFD induces alterations in basal electric oscillations and synaptic transmission in the hippocampus. A, Schematic representation of sites at which the stimulating and recording electrodes, aimed to activate CA3–CA1 synapses in the hippocampus, were implanted. Two seconds of basal electrocorticogram recordings, from two selected AL and L-IFD mice, are also shown (black for AL and gray for L-IFD mice). A, Anterior; P, posterior. B, Mean power spectra of hippocampal local field activity recorded from the CA1 pyramidal layer of AL and L-IFD mice during exploratory behavior. C, Relative spectrum quantification (mean ± SEM) in the low-theta and theta ranges for AL and L-IFD mice. D, Basal neurotransmission was measured by paired pulses with interpulse intervals from 20 to 200 ms. The percentage of maximum paired-pulse facilitation in each interpulse interval in AL and L-IFD mice is represented (n = 6 for each group). +Statistical significance of AL and L-IFD mice in the same session; *statistical significance of the different session with respect to 50 ms paired pulse (PP) interval in the same group. +p ≤ 0.05; **p ≤ 0.01; +++,***p ≤ 0.001.
- Figure 3.
Early and late LTP is enhanced in L-IFD mice. A, A single HFS train [arrow; five pulses (200 Hz, 100 ms) at a rate of 1/s] evoked LTP that lasts for up to 2 h in L-IFD mice (gray), but not in AL mice (black). B, Summary of the changes in fEPSP slope (mean ± SEM) at different times after a single HFS train. Representative fEPSP recordings, collected at the same time, from AL and L-IFD mice are also shown. C, Three HFS trains (arrows) induced indistinguishable LTP (lasting >2 h) in AL and L-IFD mice. D, Summary of changes in fEPSP slope (mean ± SEM) at different times after three HFS trains. Representative fEPSP recordings, collected at the same time, in AL and L-IFD mice are also shown (n = 6 for each group). +Statistical significance of AL and L-IFD mice in the same session; *statistical significance of the different session with respect to baseline recording in the same group. *p ≤ 0.05; **p ≤ 0.01; +++,***p ≤ 0.001.
- Figure 4.
L-IFD induces overexpression of the NR2B subunit of NMDAR in the hippocampus. A–C, Basal expression of genes encoding different NMDAR subunits in hippocampal (A), somatosensory (B), and perirhinal (C) cortices of AL and L-IFD mice as assessed by semiquantitative RT-PCR. The GAPDH mRNA served as an internal control. The graphs represent the relative presence of specific PCR products in AL (black bars) and L-IFD (gray bars) mice. The NMDAR NR2B/2A subunit ratio in each area for AL and IFD mice is also shown. D, Photomicrographs and immunohistochemical analyses of the NR2B expression pattern in the hippocampus of AL and L-IFD mice. The graphs represent the densitometric analysis of NR2B expression in the different areas of hippocampus (n = 5 animals per group in all tests). s luc, Stratum lucidum; mol, molecular layer; l mol, lacunosum moleculare layer; Molec, molecular layer; Lac mol, lacunosum moleculare layer; O.D., optical density. *p ≤ 0.01; **p ≤ 0.01; ***p ≤ 0.001.
- Figure 5.
The NMDAR NR2B subunit antagonist, Ro25-6981 (Ro), partially restores the altered basal hippocampal activity induced by L-IFD. A, Averages of the relative power spectra of CA1 pyramidal layer field activity during exploratory behavior of AL and L-IFD mice 30 min after administration of either vehicle or Ro25-6981 (5 mg/kg, s.c.). Inset, Two-second samples of basal field activity recorded in AL and L-IFD mice under the same conditions (black for AL and gray for L-IFD mice). B, Relative spectral power (mean ± SEM) of low-theta and theta bands in AL and L-IFD mice 30 min after administration of either vehicle or Ro25-6981 (5 mg/kg, s.c.). C, Basal excitatory neurotransmission was measured using paired-pulse facilitation with interpulse intervals from 50 to 200 ms in the presence or absence of Ro25-6981. Bars represent the percentage of maximum paired-pulse facilitation as a function of interpulse interval in AL and L-IFD mice (n = 6 for each group). PP, Paired pulse. **p ≤ 0.01; ***p ≤ 0.001.
- Figure 6.
Ro25-6981 (Ro) reverses the facilitation of synaptic plasticity induced by L-IFD. A, A single HFS train [arrow; five pulses (200 Hz, 100 ms) at a rate of 1/s] evokes an LTP at the CA3–CA1 synapse that lasts for up to 2 h in L-IFD mice (gray circles). Ro25-6981 administration (gray squares) reverses this effect but does not affect the same synapse in AL mice (black circles and squares). B, Summary of percentage change in fEPSP slope (mean ± SEM) at different times after a single HFS train in AL and L-IFD mice, in either the presence or absence of the specific NR2B antagonist. C, Three HFS trains (arrows) induce an indistinguishable LTP (lasting >2 h) in AL and L-IFD mice, in either the presence or absence of Ro25-6981. D, Summary of the percentage change in fEPSP slope (mean ± SEM) at different times after three HFS trains in AL and L-IFD mice, in either the presence or absence of the specific NR2B antagonist (n = 6 for each group). *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001.
- Figure 7.
Ro25-6981 (Ro) reverses learning and consolidation facilitation induced by L-IFD. A, B, Administration of Ro25-6981 before each training session blocks the facilitation of trace eyeblink classical conditioning (A) and object recognition memory (B) induced by L-IFD. AL mice were not affected by Ro25-6981 administration. C, The effects of Ro25–6951 infusion directly in hippocampus or perirhinal cortex of AL and L-IFD mice before a 5 min training session were evaluated for the object recognition memory test. Also, schematic representation of cannula localization in hippocampus (top) and perirhinal cortex (bottom) is shown. D, Administration of Ro25-6981 after STM test with a 5 min training in the object recognition memory paradigm blocks memory consolidation in L-IFD mice (n = 8 and 10 mice per group for eyeblink classical conditioning and ORM, respectively). *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001. Hp, Hippocampus; PRN, perirhinal cortex; sal, saline.
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