The Effect of a High-Fat Diet on Brain Plasticity, Inflammation and Cognition in Female ApoE4-Knockin and ApoE-Knockout Mice

<div><p>Apolipoprotein E4 (ApoE4), one of three common isoforms of ApoE, is a major risk factor for late-onset Alzheimer disease (AD). ApoE-deficient mice, as well as mice expressing human ApoE4, display impaired learning and memory functions and signs of neurodegeneration. Moreover, ApoE protects against high-fat (HF) diet induced neurodegeneration by its role in the maintenance of the integrity of the blood-brain barrier. The influence of a HF diet on the progression of AD-like cognitive and neuropathological changes was assessed in wild-type (WT), human ApoE4 and ApoE-knockout (ApoE^-/-) mice to evaluate the modulatory role of ApoE in this process. From 12 months of age, female WT, ApoE4, and ApoE^-/- mice were fed either a standard or a HF diet (19% butter, 0.5% cholate, 1.25% cholesterol) throughout life. At 15 months of age mice performed the Morris water maze, evaluating spatial learning and memory. ApoE^-/- showed increased spatial learning compared to WT mice (<i>p</i> = 0.009). HF diet improved spatial learning in WT mice (<i>p</i> = 0.045), but did not affect ApoE4 and ApoE^-/- mice. Immunohistochemical analyses of the hippocampus demonstrated increased neuroinflammation (CD68) in the cornu ammonis 1 (CA1) region in ApoE4 (<i>p</i> = 0.001) and in ApoE^-/- (<i>p</i> = 0.032) mice on standard diet. HF diet tended to increase CD68 in the CA1 in WT mice (<i>p</i> = 0.052), while it decreased in ApoE4 (<i>p</i> = 0.009), but ApoE^-/- remained unaffected. A trend towards increased neurogenesis (DCX) was found in both ApoE4 (<i>p</i> = 0.052) and ApoE^-/- mice (<i>p</i> = 0.068). In conclusion, these data suggest that HF intake induces different effects in WT mice compared to ApoE4 and ApoE^-/- with respect to markers for cognition and neurodegeneration. We propose that HF intake inhibits the compensatory mechanisms of neuroinflammation and neurogenesis in aged female ApoE4 and ApoE^-/- mice.</p></div

Immunohistochemistry.

<p>Representative images of (<b>A</b>) DCX staining (2.5x objective), (<b>B</b>) PSD95 staining (2.5x objective). Black = visual cortex, white = sensory cortex, yellow = stratum radiatum, blue = inner molecular layer, red = outer molecular layer, green = stratum lucidum, (<b>C</b>) GLUT-1 staining (5x objective), and (<b>D</b>) CD68 staining (5x objective). Scale bars represent 500μm.</p

GLUT-1 immunoreactivity.

<p>GLUT-1 density was analyzed as a measure for capillary density. No differences in capillary density, caused by either genotype nor diet, were observed (<i>p</i>>0.05). Values represent mean±SEM; WT CTRL n = 6, WT HF n = 6, ApoE4 CTRL n = 6, ApoE4 HF n = 6, ApoE^-/- CTRL n = 4, ApoE^-/- HF n = 4. ApoE = apolipoprotein E; CA1 = cornu ammonis 1; CA3 = cornu ammonis 3; CTRL = control; DG = dentate gyrus; GLUT = glucose transporter; HF = high-fat; WT = wild-type.</p

CD68 immunoreactivity.

<p>In the CA1, we observed a genotype × diet interaction (p = 0.001), there was a trend for increased inflammation in WT after HF supplementation (p = 0.052). Inflammation in ApoE4 mice significantly decreased after HF supplementation (p = 0.009). ApoE4 mice on CTRL demonstrated increased inflammation compared to WT mice on CTRL (p = 0.001). ApoE-/- compared to WT mice showed a genotype × diet interaction (p = 0.010). ApoE-/- on CTRL demonstrated increased inflammation when compared to WT mice on CTRL (p = 0.032). In the CA3, a genotype × diet interaction was observed (p = 0.024) but no significant effect on inflammation caused by genotype or diet when comparing ApoE4 to WT mice. Furthermore, ApoE-/- compared to WT mice showed a genotype × diet interaction (p = 0.023). No significant effects on inflammation caused by genotype or diet were found though. In the DG, we observed a genotype × diet interaction (p = 0.047) when comparing ApoE4 to WT mice. There was a trend for increased inflammation in ApoE4 mice on CTRL diet compared to WT mice on CTRL (p = 0.063). In addition, ApoE-/- displayed increased inflammation when compared to WT mice (p = 0.029). Values represent mean±SEM; WT CTRL n = 5, WT HF n = 7, ApoE4 CTRL n = 7, ApoE4 HF n = 5, ApoE-/- CTRL n = 4, ApoE-/- HF n = 6. *p≤0.05, #0.05</p

DCX-positive cells in the DG.

<p>ApoE4 and ApoE-/- mice display a trend for increased adult neurogenesis compared to WT mice (p = 0.052 and p = 0.068 respectively). Values represent mean±SEM; WT CTRL n = 4, WT HF n = 6, ApoE4 CTRL n = 4, ApoE4 HF n = 7, ApoE-/- CTRL n = 4, ApoE-/- HF n = 7. #0.05</p

Brain weights for immunohistochemistry.

<p>Brain weights for immunohistochemistry.</p

MWM acquisition and probe (0-30s).

<p><b>(A)</b> Both groups displayed a learning effect (p = 0.000). HF fed mice showed improved spatial learning compared to CTRL diet (p = 0.045). <b>(B)</b> Both groups displayed a learning effect (p = 0.000). ApoE-/- demonstrated improved spatial learning compared to WT mice (p = 0.009). There was no difference in spatial learning between diets. <b>(C)</b> No significant differences were found in the probe phase of the MWM caused by either genotype or diet (<i>p</i>>0.05). <b>(D)</b> No significant differences were found in the probe phase of the MWM caused by either genotype or diet (<i>p</i>>0.05). ApoE-/- mice displayed a trend for increased time spent in platform area (p = 0.059). Values represent mean±SEM; WT CTRL n = 6, WT HF n = 7, ApoE4 CTRL n = 8, ApoE4 HF n = 8, ApoE-/- CTRL n = 6, ApoE-/- HF n = 6. *p≤0.05. ApoE = apolipoprotein E; CTRL = control; HF = high-fat; MWM = Morris water maze; WT = wild-type.</p

PSD95 immunoreactivity.

<p>PSD95 was analyzed as a synaptic marker in the VIS, SEN, IML, OML, SL and SR of the hippocampus. No significant genotype nor diet effects were found (<i>p</i>>0.05). In the SEN, ApoE^-/- mice showed a slight trend (<i>p</i> = 0.064) for decreased PSD95 expression. Values represent mean±SEM; WT CTRL n = 8, WT HF n = 8, ApoE4 CTRL n = 8, ApoE4 HF n = 7, ApoE^-/- CTRL n = 5, ApoE^-/- HF n = 7. #0.05</p

Ⅵ PAIN AND REGIONAL ANESTHESIA Pulsed and Continous Radiofrequency Current Adjacent to the Cervical Dorsal Root Ganglion of the Rat Induces Late Cellular Activity in the Dorsal Horn

Background: Pulsed radiofrequency treatment has recently been described as a non-neurodestructive or minimally neurodestructive alternative to radiofrequency heat lesions. In clinical practice long-lasting results of pulsed radiofrequency treatment adjacent to the cervical dorsal root ganglion for the management of chronic radicular spinal pain have been reported without neurologic complications. However, the mode of action is unclear. An early (3 h) effect of pulsed radiofrequency as measured by an increase of c-Fos in the pain-processing neurons of the dorsal horn of rats has been described in the literature. This effect was not mediated by tissue heating. The authors investigated a possible late or long-term effect of three different radiofrequency modalities. Methods: Cervical laminectomy was performed in 19 male Wistar rats. The cervical dorsal root ganglion was randomly exposed to one of the four interventions: sham, continuous radiofrequency current at 67 centigrades, or pulsed radiofrequency current for 120 s or 8 min. The animals were sacrificed and the spinal cord was prepared for c-Fos labeling 7 days after the intervention. Results: The number of c-Fos immunoreactive cells in the dorsal horn was significantly increased in the three different radiofrequency modalities as compared with sham. No significant difference was demonstrated between the three active intervention groups. Conclusions: The authors demonstrated a late neuronal activity in the dorsal horn after exposure of the cervical dorsal root ganglion to different radiofrequency modalities, which was not temperature dependent

Representative images of the amyloid-β plaque load in the brain of a 12-month-old AβPP-PS1 mouse.

<p>A: The Aβ plaque load was quantified in the prelimbic area at level +1.98 up to +1.78 anterior to bregma, B: in the anterior cingulate gyrus at level +1.10 up to +0.86 anterior to bregma, and C: in the dentate gyrus (DG), CA1 and CA3 areas of the hippocampus at level −2.18 up to −2.46 posterior to bregma, using one appropriate section per animal. Images were taken using a 2.5× objective. Scale bar = 500 µm.</p