Figure 3. ArcKR expression prevents GI-mGluR-mediated priming of
long-term potentiation (LTP)
A, Graph plotting mean normalised (to the baseline) fEPSP slope
against time for WT (n = 10 slices, 5 mice) and ArcKR mice
(n = 12 slices, 6 mice). After a 20-minute baseline, LTP was
induced with high frequency stimulation (1s, 100 Hz). Inset, example
fEPSP waveforms before and after LTP induction from WT and ArcKR mice.
B, Bar chart plotting the mean potentiation of fEPSP slope (between
55-60 minutes post LTP induction). There was no significant difference
(p = 0.3791, Z =-0.89, U = 46, Mann Whitney) in the amplitude of
long-term potentiation between WT (mean potentiation 60.2 ± 17.9 %) and
ArcKR slices (74.0 ± 14.9 %). C, Graph plotting mean normalised (to the
baseline) fEPSP slope against time for WT (n = 7 slices, 4 mice) and
ArcKR mice (n = 7 slices, 5 mice). Following a 20-minute baseline, a low
concentration of DHPG (20 µM) was applied for 10 minutes to activate
GI-mGluRs (mean peak inhibition in WT 41.9 ± 4.8 %; ArcKR 42.8 ± 4.7
%). Following a 20-minute wash, LTP was induced by high frequency
stimulation (1s, 100 Hz). Inset, example fEPSP waveforms before and
after LTP induction (average of waveforms at 55-60 minutes) from WT and
ArcKR mice. D, Bar chart plotting mean potentiation (55-60 minutes post
LTP induction). There was a significant difference (p = 0.022, U =37, Z
= 2.2) in the amplitude of LTD following GI-mGluR priming in WT (mean
potentiation 76.6 ± 8.6 %) compared to ArcKR slices (mean potentiation
36.6 ± 8.3 %). Data points are the mean potentiation from individual
experiments. E, Graph plotting mean normalised (to the baseline) fEPSP
slope against time for WT (n = 7 slices, 4mice) and ArcKR mice
(n = 7 slices, mice) illustrating the actions of 20 µM DHPG. F,
Bar chart plotting the mean inhibition after 20 minutes following DHPG
wash. There was no significant difference in the amount of inhibition in
WT compared to ArcKR mice (P = 0.069, Z = -1.78, U =14.5, Mann Whitney).
The points (B, D and F) are the means from individual experiments. G,
Western blot showing Arc protein expression in hippocampal lysates
obtained from WT (n = 4) and ArcKR (n = 4) mice. Slices
were incubated in control (vehicle), 20 µM DHPG and 100 µM DHPG for 10
min. H, Bar chart analysis show a significant increase in Arc expression
after DHPG (100 µM) exposure compared to control in WT (*p=0.012) and
ArcKR (**p=0.008), but not after 20 µM DHPG exposure (WT: p=0.26 and
ArcKR: p=0.75). GAPDH was used as loading control. The data points are
the Arc/GAPDH ratios from individual experiments. Error bars indicate ±
S.E.M. Statistical comparisons were performed with one-way analysis of
variance (ANOVA) followed by Tukey’s multiple comparisons.