ABSTRACT
Title
Reduction of SNAP-25 expression enhances evoked glutamatergic transmission and induces epileptiform activity associated with memory defects
Authors
I. Corradini1,2,3, F. Antonucci1,2, A. Donzelli1, S. De Astis1,2 , R. Martucci1 , D. Braida1, C. Verderio1,2, M. Sala1 and M. Matteoli1,2,3
1. Dept of Medical Pharmacology, University of Milan, Italy
2. CNR Institute of Neuroscience, Milan, Italy
3. Fondazione Filarete per le Bioscienze e l’Innovazione, Milan, Italy
1. Dept of Medical Pharmacology, University of Milan, Italy
2. CNR Institute of Neuroscience, Milan, Italy
3. Fondazione Filarete per le Bioscienze e l’Innovazione, Milan, Italy
Abstract
SNAP-25 is a member of the SNARE protein complex that participates in synaptic vesicle exocytosis. Alterations of SNAP-25 expression have been associated to several neurological diseases, such as schizophrenia, ADHD and epilepsy (reviewed in Corradini et al., 2009). We have previously proposed that differential SNAP-25 expression may be at the root of a different regulation of intracellular calcium dynamics in distinct neuronal populations (Verderio et al., Neuron 2004). Accordingly, exogenously expressed SNAP-25 negatively modulates neuronal voltage-gated calcium channels, through a process which requires SNAP25 activity-dependent phosphorylation on Ser187 (Pozzi et al., PNAS 2008). Moreover, we recently demonstrated that endogenous SNAP-25 negatively regulates voltage-gated calcium channel (VGCC) activity in glutamatergic but not GABAergic rat hippocampal neurons in culture. Consistent with these data, VGCC current densities in glutamatergic neurons from Snap-25 +/- mice were significantly elevated compared to wild type glutamatergic neurons, whileno such effect could be observed in GABAergic heterozygous neurons (Condliffe et al., 2010). In this study, we aimed at investigating at which extent reductions of SNAP-25 levels of expression impact synaptic function and network excitability using wild type or SNAP-25 heterozygous mice.
Patch-clamp paired recordings on primary hippocampal neurons revealed an increased amplitude of evoked EPSCs and a reduction in evoked IPSCs amplitude in SNAP-25 +/- neurons, in the absence of changes in miniature activity or in synaptic density. A switch from paired pulse facilitation (PPF) to paired pulse depression (PPD) occurred at glutamatergic terminals, while the total charge transferred by calcium independent sucrose hypertonic stimulation was comparable in wt and het cultures. Behavioral analysis revealed that SNAP-25 het mice were moderately hyperactive and displayed defects in different paradigms of associative memory. Moreover, EEG recordings on freely moving animals showed frequent spikes in both cortex and hippocampus, and the mice were more susceptible to treatment with convulsant agents, in the absence of brain anatomical alterations. Treatment with antiepileptic drugs normalized the EEG profile and potently improved the cognitive defects.
These results indicate that reduction of SNAP-25 expression produces an imbalance in excitatory versus inhibitory neurotransmission which is associated to the generation of subclinical epileptiform discharges and cognitive impairment. They open new perspectives for the use of antiepileptic drugs for the treatment of neuropsychiatric diseases characterized by reductions of SNAP-25 expression, such as ADHD.
Verderio et al. (2004). Neuron. 41 (4): 599-610.
Pozzi et al. (2008). PNAS. 105 (1): 323-328.
Corradini et al. (2009). Ann N Y Acad Sci. 1152: 93-99.
Condliffe et al. (2010). J Biol Chem. 285 (32): 24968-76.
Patch-clamp paired recordings on primary hippocampal neurons revealed an increased amplitude of evoked EPSCs and a reduction in evoked IPSCs amplitude in SNAP-25 +/- neurons, in the absence of changes in miniature activity or in synaptic density. A switch from paired pulse facilitation (PPF) to paired pulse depression (PPD) occurred at glutamatergic terminals, while the total charge transferred by calcium independent sucrose hypertonic stimulation was comparable in wt and het cultures. Behavioral analysis revealed that SNAP-25 het mice were moderately hyperactive and displayed defects in different paradigms of associative memory. Moreover, EEG recordings on freely moving animals showed frequent spikes in both cortex and hippocampus, and the mice were more susceptible to treatment with convulsant agents, in the absence of brain anatomical alterations. Treatment with antiepileptic drugs normalized the EEG profile and potently improved the cognitive defects.
These results indicate that reduction of SNAP-25 expression produces an imbalance in excitatory versus inhibitory neurotransmission which is associated to the generation of subclinical epileptiform discharges and cognitive impairment. They open new perspectives for the use of antiepileptic drugs for the treatment of neuropsychiatric diseases characterized by reductions of SNAP-25 expression, such as ADHD.
Verderio et al. (2004). Neuron. 41 (4): 599-610.
Pozzi et al. (2008). PNAS. 105 (1): 323-328.
Corradini et al. (2009). Ann N Y Acad Sci. 1152: 93-99.
Condliffe et al. (2010). J Biol Chem. 285 (32): 24968-76.