BEHAVIOURAL PHENOTYPE AND ELECTROENCEPHALOGRAPHIC PROFILE OF ADOLESCENT AND ADULT SNAP-25+/- MUTANT MICE.

Synaptosomal-associated protein of 25 kDa (SNAP-25) is a protein that participates in the regulation of synaptic vesicle exocytosis through the formation of the soluble N-ethylmaleimide-sensitive proteine (NSF) attachment protein receptor complex and modulates voltage-gated calcium channels activity. Snap25 gene has been associated with schizophrenia, and bipolar disorder, and lower levels of SNAP-25 have been described in patients with schizophrenia. In particular several SNAP-25 intronic single polymorphisms were linked to attention deficit hyperactivity disorder, one of the most common neuropsychiatric diseases among children and adolescents. The most animal models of this pathology, available until now, are characterized by reduced SNAP-25 level in the CNS: the coloboma mice, and the spontaneously hypertensive rats (SHR). However none of them can completely ricapitulate all the core features of the human patology. Thus we used adult SNAP-25 heterozygous (SNAP-25+/−) mice in comparison with age-matched wild type mice (SNAP-25+/+) to investigate at which extent the reduction of the protein levels affects neuronal network function and mouse behavior, and the possible therapeutic effect of antiepileptic drugs. We also characterized adolescent SNAP-25+/- mice (6-7 weeks) in order to evaluate if they can be considered a new ADHD animal model. Firstly we analysed general health, sensory and motor abilities, and emotional behaviour in our animals, without finding any abnormalities in heterozygous mice. Since altered SNAP-25 level were associated with cognitive deficit, we performed T-maze test for the evaluation of spatial memory, latent inhibition test for attention, conditioned taste aversion and object recognition for associative memory. SNAP-25+/- resulted impaired in associative but not in spatial memory, probably because of the heterogeneous protein expression levels in different hippocampal areas, being more expressed in CA3, known to play a key role in associative memory, than in CA1, critical for long-term spatial memory. SNAP-25+/- has been associated to disease characterized by altered social behaviour, such as schizophrenia and bipolar disorder. We tested SNAP-25 mutant mice in sociability and social novelty test. Heterozygous showed impairment both in sociability and in social recognition. Pathologies characterized by SNAP-25 alterations show significantly higher incidence of epilepsy. For this reason we recorded the cortical electric activity of mice and we found that SNAP-25 levels reduction was associated with network hyperexcitability, in terms of spike activity, which did not lead to spontaneous epileptiform behaviour. Acute treatment with antiepileptic drugs and Ca2+ antagonist normalized cerebral activity. Among these drugs, sodium valproate was more effective in blocking EEG and behavioural deficits. Since it is known the correlation between EEG alteration and cognitive deficits we can hypothesize that the mnemonic and social deficit are due to the abnormal EEG profile. Adolescents SNAP-25+/- mice showed the same deficits found in the adults. They also were hyperactivite, and were not susceptible to d-amphetamine treatment. These results are in line with the characteristic phenotype of ADHD children, that display cognitive deficits, problems in socialization and hyperactivity, normalized by stimulants. Recently EEG analysis was used as diagnostic tool to discriminate ADHD from other neuropsychiatric diseases. EEG in ADHD children is characterized by spikes and alteration in spectral power bands frequency. Spectral analysis heterozygous mice EEG recordings was caharacterized by spikes, a decrease in fast waves and a parallel increase in slow waves, as occur in ADHD children. Repeated exposition to a VLP solution (0.1%) reduced all the behavioural deficit and was effective in blocking spike activity for two weeks, when discontinued. SNAP-25+/- mice seem to be a promising ADHD animal model, able to recapitulate almost all the core symptoms of the human disease. Repeated treatment with VLP resulted effective in all the tests carried out in adolescents mice, in line with recent findings of its therapeutic effects on ADHD symptoms in x-fragile syndrome.