It has recently been proposed that extracellular signalregulated kinases 1 and 2 (ERK1/2) are one of the factors mediating seizure development. We hypothesized that inhibition of ERK1/2 activity could prevent audiogenic seizures by altering GABA and glutamate release mechanisms. Krushinsky-Molodkina rats, genetically prone to audiogenic seizure, were recruited in the experiments. Animals were i.p. injected with an inhibitor of ERK1/2 SL 327 at different doses 60 min before audio stimulation. We demonstrated for the first time that inhibition of ERK1/2 activity by SL 327 injections prevented seizure behavior and this effect was dose-dependent and correlated with ERK1/2 activity. The obtained data also demonstrated unchanged levels of GABA production, and an increase in the level of vesicular glutamate transporter 2. The study of exocytosis protein expression showed that SL 327 treatment leads to downregulation of vesicle-associated membrane protein 2 and synapsin I, and accumulation of synaptosomal-associated protein 25 (SNAP-25). The obtained data indicate that the inhibition of ERK1/2 blocks seizure behavior presumably by altering the exocytosis machinery, and identifies ERK1/2 as a potential target for the development of new strategies for seizure treatment. Temporal lobe epilepsy is one the most common chronic neurological diseases, and there is no available treatment capable of fully preventing the development of epilepsy or ensuring complete recovery.Recently, it has been proposed that extracellular signalregulated kinases 1 and 2 (ERK1/2), members of the MAPK family, are one of the factors mediating seizure development (Nateri et al. 2007). ERK1/2 are activated by dual-specificity MAP/ERK kinases (MEK1/2), which use ERK1/2 kinases as the only known substrates (Shaul and Seger 2007). Mice with over-expression of constitutively active brain-specific form of MEK1 demonstrate spontaneous seizures (Nateri et al. 2007). It has been reported that ERK1/2 activity is also upregulated following pilocarpine treatment (Berkeley et al. 2002) or by electric stimulation of seizures (Baraban et al. 1993;Kang et al. 1994;Bhat et al. 1998). However, little is known about the role of ERK1/2 in epileptiform seizure progression in animals genetically prone to seizures. Address correspondence and reprint requests to Dr Margarita Glazova, Group of Molecular mechanisms of neuronal functioning, Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 44 Thorez pr., 194223 Saint-Petersburg, Russia. E-mail: marglazova@gmail.com Abbreviations used: ERK1/2, extracellular signal-regulated kinases 1 and 2; GAD65 and GAD67, glutamic acid decarboxylases 65 and 67; KM, Krushinsky-Molodkina rats; MEK1/2, dual-specificity MAP/ERK kinases; SNAP-25, synaptosomal-associated protein 25; SNARE, soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor; VAMP2, vesicle-associated membrane protein 2; VGLUT2, vesicular glutamate transporter 2.

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Obtained results demonstrated a decrease activity in synapsin I, and accumulation of VGLUT2 in the striatum after blockade of audiogenic seizure (AGS) by SL 327 that could lead to inhibition of glutamate release. While in the striatum GAD65/67 level was diminished, in the substantia nigra GAD65/67 was increased showing enhanced inhibitory output to the compact part of the substantia nigra. Analysis of dopaminergic system showed a significant reduction of tyrosine hydroxylase activity and expression in the substantia nigra, and decreased D1 and D2 receptor expression in the striatum. In summary, we propose that changes in the nigrostriatal system could be mediated by inhibitory effect of SL 327 on AGS expression.

The role of apoptotic signaling proteins for long-lived neurons in the mature brain is poorly understood. Recently, we have shown that water deprivation leads to the activation of vasopressin (VP) secretion and expression of Bcl-2 and caspase-9 apototic proteins in the hypothalamus of the rat brain. In the present work, we continued to study a possible relationship between the functional activity of neurosecretory cells of the hypothalamus and apoptosis related proteins. We found that water deprivation leads to simultaneous activation of synthesis of VP and p53 and Bcl-2 apoptotic proteins in the mouse brain. To study a possible effect of apoptotic proteins on the functional state of hypothalamic neurons, the VP and tyrosine hydroxylase (TH) synthesis were analyzed in p53, p21(Waf1/Cip1) and Bcl-2 deficient mice. Loss of p53 and Bcl-2 significantly reduced VP synthesis in paraventricular and supraoptic nuclei and TH expression in arcuat, periventricular and zona incerta nuclei of the hypothalamus. Surprisingly, in contrast with the loss of p53, the inactivation of p21(Waf1/Cip1) up-regulates the expression of VP and TH. These data indicate that p53, p21(Waf1/Cip1) and Bcl-2 proteins, besides affecting cell cycle, tumor suppression and apoptosis, may act as modulators of neurosecretory activity of hypothalamic neurons; however, this problem remains to be determined more detailed.