Elsevier

Neuroscience

Volume 171, Issue 1, 24 November 2010, Pages 268-283
Neuroscience

Neurodegeneration, Neuroprotection, and Disease-Oriented Neuroscience
Research Paper
Cortico-hippocampal hyperexcitability in synapsin I/II/III knockout mice: age-dependency and response to the antiepileptic drug levetiracetam

https://doi.org/10.1016/j.neuroscience.2010.08.046Get rights and content

Abstract

Synapsins (SynI, SynII, SynIII) are a multigene family of synaptic vesicle (SV) phosphoproteins implicated in the regulation of synaptic transmission and plasticity. Synapsin I, II, I/II and I/II/III knockout mice are epileptic and SYN1/2 genes have been identified as major epilepsy susceptibility genes in humans. We analyzed cortico-hippocampal epileptiform activity induced by 4-aminopyridine (4AP) in acute slices from presymptomatic (3-weeks-old) and symptomatic (1-year-old) Syn I/II/III triple knockout (TKO) mice and aged-matched triple wild type (TWT) controls and assessed the effect of the SV-targeted antiepileptic drug (AED) levetiracetam (LEV) in reverting the epileptic phenotype. Both fast and slow interictal (I-IC) and ictal (IC) events were observed in both genotypes. The incidence of fast I-IC events was higher in presymptomatic TKO slices, while frequency and latency of I-IC events were similar in both genotypes. The major age and genotype effects were observed in IC activity, that was much more pronounced in 3-weeks-old TKO and persisted with age, while it disappeared from 1-year-old TWT slices. LEV virtually suppressed fast I-IC and IC discharges from 3-weeks-old TWT slices, while it only increased the latency of fast I-IC and IC activity in TKO slices. Analysis of I-IC events in patch-clamped CA1 pyramidal neurons revealed that LEV increased the inhibitory/excitatory ratio of I-IC activity in both genotypes. The lower LEV potency in TKO slices of both ages was associated with a decreased expression of SV2A, a SV protein acting as LEV receptor, in cortex and hippocampus. The results demonstrate that deletion of Syn genes is associated with a higher propensity to 4AP-induced epileptic paroxysms that precedes the onset of epilepsy and consolidates with age. LEV ameliorates such hyper excitability by enhancing the inhibition/excitation ratio, although the effect is hindered in TKO slices which exhibit a concomitant decrease in the levels of the LEV receptor SV2A.

Section snippets

Experimental animals

Homozygous Syn TKO mice (Gitler et al., 2004) were kindly provided by Drs. H.T. Kao (Brown University, Providence, RI, USA) and Paul Greengard (The Rockefeller University, NY, USA). TKO mice were rederived on a C57BL/6J background (Charles River, Calco, Italy) obtaining single and multiple Syn KO strains up to TKO and matching TWT mice. For genotyping, tail DNA was extracted and analyzed by PCR using the previously described primers (Gitler et al., 2004). Mice were housed (2–4 per cage) under

Ontogeny of epilepsy in TKO mice

Deletion of SynI, SynII, SynI/II or SynI/II/III (TKO) gives rise to an epileptic phenotype that is not present at birth and develops with age (Li et al., 1995, Rosahl et al., 1995, Gitler et al., 2004, Corradi et al., 2008, Etholm and Heggelund, 2009). Similar to the other strains, TKO mice did not show either spontaneous or stimuli-evoked seizures until 8–9 weeks of age. After this time, mice started to suffer of generalized tonic-clonic attacks which persisted in the adulthood: although

Discussion

Genetically-engineered mouse lines have provided a number of valuable epilepsy models with the potential to link epileptogenesis to changes in both specific genes and neuronal function (Noebels, 2003). The genetic deletion of the Syns in mice is of particular interest in this respect, because it represents the first model of epilepsy based on concomitant alterations of the release of excitatory and inhibitory neurotransmitters and because of the widespread distribution of these SV proteins in

Acknowledgments

We thank drs. Paul Greengard (The Rockefeller University, New York, NY) and Hung-Teh Kao (Brown University, Providence, RI) for providing us with the TKO mutant mouse strain and for invaluable discussions and Giacomo Gaggero for technical help. This study was supported by research grants from the Italian Ministry of University and Research (PRIN to FB and PB), the Italian Ministry of Health Progetto Giovani (to PB), the Compagnia di San Paolo, Torino (to FB, FV and PB), UCB SA Brussels-Belgium

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