Search tips
Search criteria 


Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
J Alzheimers Dis. Author manuscript; available in PMC 2011 January 1.
Published in final edited form as:
PMCID: PMC2915889

Alzheimer's Disease and Down Syndrome Rodent Models Exhibit Audiogenic Seizures


Amyloid β-protein precursor (AβPP) is overexpressed in Alzheimer's disease (AD), Down syndrome (DS), autism and fragile × syndrome (F×S). Seizures are a common phenotype in all of these neurological disorders; yet, the underlying molecular mechanism(s) of seizure induction and propagation remain largely unknown. We demonstrate that Alzheimer's disease (AD) and Down syndrome (DS) mice exhibit audiogenic seizures (AGS), which can be attenuated with antagonists to metabotropic glutamate receptor 5 (mGluR5) or by passive immunization with anti-Aβ antibody. Our data strongly implicates AβPP or a catabolite in seizure susceptibility and suggests that mGluR5 mediates this response.

Keywords: Alzheimer's disease (AD), amyloid β-protein precursor (AβPP), audiogenic seizure (AGS), amyloid beta (Aβ), Down syndrome (DS), metabotropic glutamate receptor 5 (mGluR5)

Fmr-1-/- mice lack expression of fragile × mental retardation protein (FMRP), overproduce AβPP and amyloid beta (Aβ) and are highly susceptible to audiogenic seizures (AGS) [1-3]. FMRP binds to and represses the dendritic translation of AβPP mRNA [2], thus, we hypothesized that increased levels of AβPP or a catabolite of AβPP near synaptic connections in fmr-1-/- mice contributed to AGS sensitivity and that other mouse models that overexpress AβPP would exhibit AGS. Seizures and myoclonus are prevalent phenotypes in AD and DS [4-5]. In this study, we employed established AD (Tg2576) [6] and DS (Ts65Dn) [7] mouse models as well as FRA×AD mice, which overexpress human AβPP with the Swedish familial mutation (hAβPPSWE) in an fmr-1-/- background [8], to study the role of AβPP on AGS susceptibility.

We assessed AGS in WT, fmr-1-/-, Tg2576 and FRA×AD mice all in a C57BL/6 background. Mice were generated, bred and housed as previously described [8]. All strains were tested at postnatal day 21 (P21), the peak of AGS sensitivity [9]. Mice were transferred to a Plexiglas box (13″L × 8″W × 7″H) and exposed to a high-pitched siren (118 dB) from a personal body alarm (LOUD KEYTM). We scored the number of mice exhibiting wild running (WR), tonic seizures (AGS) and death, and statistical significance was assessed by Chi Square analyses. All husbandry, seizure and euthanasia procedures were performed in accordance with NIH guidelines and an approved University of Wisconsin animal care protocol.

Pure C57BL/6 mice are resistant to AGS [10] and we observed only a 5% seizure rate in WT mice (Figure 1). In fmr-1-/- mice, 56% exhibited WR, 44% AGS and 38% death resulting from seizures. Thus, as seen previously, fmr-1-/- mice exhibit a strong AGS phenotype and WT controls do not [9,11-13]. Tg2576 exhibited very similar susceptibility to AGS as fmr-1-/- mice. This is the first report that an AD mouse model is susceptible to AGS, although elevated susceptibility to PTZ-induced seizures has been reported [14]. FRA×AD mice showed nearly double the AGS susceptibility as the parental fmr-1-/- and Tg2576 lines. The increased susceptibility to audiogenic stimulation in the FRA×AD compared to the Tg2576 is also apparent by the decreased latency time to onset of WR (data not shown). ELISA analyses of brain lysates revealed the highest levels of Aβ in FRA×AD mice followed by Tg2576, fmr-1-/- and WT [2,8]. Thus, there was a significant increase in seizure sensitivity in all of the AD and F×S mouse strains tested compared to WT controls, which correlated with aggregate Aβ levels.

Figure 1
WR, AGS and Death Rates in WT, fmr-1-/-, Tg2576, FRA×AD and Ts65Dn Mice. Mice (age P21) were exposed to 118 dB siren and the percentage exhibiting WR, AGS and death was plotted versus genotype for WT (Wt, n=39), fmr-1-/- (Fm, n=16), Tg2576 (Tg, ...

To further strengthen our hypothesis, we tested AGS susceptibility in Ts65Dn mice, which like fmr-1-/- over-express mouse AβPP (mAβPP) and mAβ. Trisomic mice displayed 75% WR, 56% AGS and 50% death rates (Figure 1). The Ts65Dn and littermate control (Cn) mice are in a mixed background (mothers: B6EiC3Sn a/A-Ts(1716)65Dn; fathers: B6EiC3Sn (C57BL/6JEi × C3H/HeSnJ) F1. The WT controls in the mixed background exhibited an increased propensity for WR and AGS compared to the C57BL/6 WT mice, but significantly less than their trisomic littermates. In aggregate these results suggest that AβPP over-expression contributes to AGS.

Antagonists to mGluR5 have been shown to revert many fmr-1-/- phenotypes [9,15-17]. MPEP is a specific and potent noncompetitive antagonist of mGluR5 that is capable of crossing the blood brain barrier [18-19], attenuating AGS in fmr-1-/- mice [9], and blocking mGluR5-mediated up-regulation of AβPP synthesis [2]. We treated WT, Tg2576 and FRA×AD mice with 30 mg/kg body weight MPEP 30 minutes prior to AGS induction. mGluR5 blockade completely attenuated WR, AGS and death in Tg2576 and reduced these phenotypes in FRA×AD mice (Table 1). FRA×AD mice produce significantly more Aβ1-40 by 2 weeks of age than Tg2576 as assessed by ELISA of whole brain lysates [8], which may account for the inability of a single treatment with MPEP to completely attenuate AGS. To corroborate these results, we tested a second mGluR5 antagonist, fenobam, which can be orally administered in chow to rodents. Pups were weaned at P18 and transferred to the fenobam-supplemented feed for 3 days prior to AGS testing at P21. Fenobam significantly reduced the number of deaths in Tg2576 and Ts65Dn mice (Table 1). For the mice that did exhibit seizures, the latency times to WR and AGS were longer (at least 1.8-fold) after fenobam treatment (data not shown). This data demonstrates that mGluR5 blockade significantly reduces AGS in mice that overexpress AβPP.

Table 1
Attenuation of AGS in APP/Aβ-Overexpressing Mice

Finally, we assessed AGS rates in Tg2576 mice after passive immunization with an anti-AβPP/Aβ antibody, sc-28365LS (Santa Cruz Biotechnology, Inc., Santa Cruz, CA). This monoclonal antibody was generated against amino acids 672-714 of hAβPP, but epitope information is not available. Thus, sc-28365LS recognizes AβPP and Aβ and possibly sAβPPα if the antigen recognition site is amino-terminal to the α-secretase cleavage site within Aβ. The antibody (12.5 μg) was administered by I.P. injection to 18-day-old Tg2576 and AGS sensitivity was tested at P21. Passive immunization with the anti-Aβ antibody significantly reduced the death rate in Tg2576 mice (Table 1).

Due to the heterogeneity of seizures, the underlying cellular and molecular mechanisms that induce and propagate these abnormal electrical discharges in the brain remain poorly understood. An increased incidence of seizure activity or lower thresholds to chemically-induced seizures are apparent in multiple AD mouse models [8,14,20-25]. MPEP reduces the severity of chemically-induced seizures in Tg2576 and FRA×AD mice [26]. Herein, we demonstrate that AD, FRA×AD and DS mice are highly susceptible to audiogenic-induced seizures at rates that match or exceed fmr-1-/- mice and that mGluR5 blockade or passive immunization with anti-Aβ reduces AGS and deaths. These data support roles for AβPP, or an AβPP catabolite, in seizure induction as well as FMRP-dependent and independent mGluR5 signaling pathways [9] in signal propagation. AβPP plays critical physiological roles in synapse formation and maturation and altered expression or processing likely contributes to lower seizure threshold. Our data strongly suggests that therapies that reduce AβPP expression, block mGluR5 signaling or increase clearance of Aβ could be beneficial in controlling seizures.


We acknowledge the expert technical assistance provided by the University of Wisconsin-Madison animal care staffs at the Waisman Center and Rennebohm Pharmacy buildings. We thank Levi Stodola for assistance with genotyping. MPEP and fenobam were kind gifts from FRA×A Research Foundation (Newburyport, MA). This work was supported by National Institutes of Health Grants R01 DA026067 (J.S.M.) and P30 HD03352 (Waisman Center), the Alzheimer's Drug Discovery Foundation (J.S.M. & C.J.W.), FRA×A Research Foundation (C.J.W. & J.S.M.), Wisconsin Comprehensive Memory Program and a private donation by Bill and Doris Willis (Waisman Center).


1. The Dutch-Belgian fragile × consortium. Fmr1 knockout mice: A model to study fragile × mental retardation. Cell. 1994;78:23–33. [PubMed]
2. Westmark CJ, Malter JS. FMRP mediates mGluR5-dependent translation of amyloid precursor protein. PLoS Biol. 2007;5:e52. [PMC free article] [PubMed]
3. Musumeci SA, Bosco P, Calabrese G, Bakker C, De Sarro GB, Elia M, Ferri R, Oostra BA. Audiogenic seizures susceptibility in transgenic mice with fragile × syndrome. Epilepsia. 2000;41:19–23. [PubMed]
4. Mendez M, Lim G. Seizures in elderly patients with dementia: Epidemiology and management. Drugs Aging. 2003;20:791–803. [PubMed]
5. Pueschel SM, Louis S, McKnight P. Seizure disorders in Down syndrome. Arch Neurol. 1991;48:318–320. [PubMed]
6. Hsiao K, Chapman P, Nilsen S, Eckman C, Harigaya Y, Younkin S, Yang F, Cole G. Correlative memory deficits, Abeta elevation, and amyloid plaques in transgenic mice. Science. 1996;274:99–102. [PubMed]
7. Davisson MT, Schmidt C, Akeson EC. Segmental trisomy of murine chromosome 16: A new model system for studying Down syndrome. Prog Clin Biol Res. 1990;360:263–280. [PubMed]
8. Westmark CJ, Westmark P, Beard A, Hildebrandt S, Malter JS. Seizure susceptibility and mortality in mice that over-express amyloid precursor protein. Int J Clin Exp Pathol. 2008;1:157–168. [PMC free article] [PubMed]
9. Yan QJ, Rammal M, Tranfaglia M, Bauchwitz RP. Suppression of two major fragile × syndrome mouse model phenotypes by the mGluR5 antagonist MPEP. Neuropharmacology. 2005;49:1053–1066. [PubMed]
10. Schlesinger K, Griek BJ. The Genetics and Biochemistry of Audiogenic Seizures. Pleton-Centry-Crofts; New York: 1970.
11. Chen L, Toth M. Fragile × mice develop sensory hyperreactivity to auditory stimuli. Neuroscience. 2001;103:1043–1050. [PubMed]
12. Qin M, Kang J, Smith CB. A null mutation for Fmr1 in female mice: Effects on regional cerebral metabolic rate for glucose and relationship to behavior. Neuroscience. 2005;135:999–1009. [PubMed]
13. Dolen G, Osterweil E, Rao BS, Smith GB, Auerbach BD, Chattarji S, Bear MF. Correction of fragile × syndrome in mice. Neuron. 2007;56:955–962. [PMC free article] [PubMed]
14. Del Vecchio RA, Gold LH, Novick SJ, Wong G, Hyde LA. Increased seizure threshold and severity in young transgenic CRND8 mice. Neurosci Lett. 2004;367:164–167. [PubMed]
15. Bear MF, Huber KM, Warren ST. The mGluR theory of fragile × mental retardation. Trends Neurosci. 2004;27:370–377. [PubMed]
16. de Vrij FM, Levenga J, van der Linde HC, Koekkoek SK, De Zeeuw CI, Nelson DL, Oostra BA, Willemsen R. Rescue of behavioral phenotype and neuronal protrusion morphology in Fmr1 KO mice. Neurobiol Dis. 2008;31:127–132. [PMC free article] [PubMed]
17. McBride SM, Choi CH, Wang Y, Liebelt D, Braunstein E, Ferreiro D, Sehgal A, Siwicki KK, Dockendorff TC, Nguyen HT, et al. Pharmacological rescue of synaptic plasticity, courtship behavior, and mushroom body defects in a drosophila model of fragile × syndrome. Neuron. 2005;45:753–764. [PubMed]
18. Gasparini F, Lingenhohl K, Stoehr N, Flor PJ, Heinrich M, Vranesic I, Biollaz M, Allgeier H, Heckendorn R, Urwyler S, et al. 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a potent, selective and systemically active mGlu5 receptor antagonist. Neuropharmacology. 1999;38:1493–1503. [PubMed]
19. Varney MA, Cosford ND, Jachec C, Rao SP, Sacaan A, Lin FF, Bleicher L, Santori EM, Flor PJ, Allgeier H, et al. SIB-1757 and SIB-1893: Selective, noncompetitive antagonists of metabotropic glutamate receptor type 5. J Pharmacol Exp Ther. 1999;290:170–181. [PubMed]
20. Lalonde R, Dumont M, Staufenbiel M, Strazielle C. Neurobehavioral characterization of APP23 transgenic mice with the SHIRPA primary screen. Behav Brain Res. 2005;157:91–98. [PubMed]
21. Moechars D, Lorent K, De Strooper B, Dewachter I, Van Leuven F. Expression in brain of amyloid precursor protein mutated in the alpha-secretase site causes disturbed behavior, neuronal degeneration and premature death in transgenic mice. EMBO J. 1996;15:1265–1274. [PubMed]
22. Steinbach JP, Muller U, Leist M, Li ZW, Nicotera P, Aguzzi A. Hypersensitivity to seizures in beta-amyloid precursor protein deficient mice. Cell Death Differ. 1998;5:858–866. [PubMed]
23. Kobayashi D, Zeller M, Cole T, Buttini M, McConlogue L, Sinha S, Freedman S, Morris RG, Chen KS. BACE1 gene deletion: Impact on behavioral function in a model of Alzheimer's disease. Neurobiol Aging. 2008;29:861–873. [PubMed]
24. Palop JJ, Chin J, Roberson ED, Wang J, Thwin MT, Bien-Ly N, Yoo J, Ho KO, Yu GQ, Kreitzer A, et al. Aberrant excitatory neuronal activity and compensatory remodeling of inhibitory hippocampal circuits in mouse models of Alzheimer's disease. Neuron. 2007;55:697–711. [PubMed]
25. Vogt DL, Thomas D, Galvan V, Bredesen DE, Lamb BT, Pimplikar SW. Abnormal neuronal networks and seizure susceptibility in mice overexpressing the APP intracellular domain. Neurobiol Aging. 2009 In Press. [PMC free article] [PubMed]
26. Westmark CJ, Westmark PR, Malter JS. MPEP reduces seizure severity in fmr-1 KO mice over expressing human Abeta. Int J Clin Exp Pathol. 2009;3:56–68. [PMC free article] [PubMed]