NEUROSYSTEMS Altered distribution and function of A 2A adenosine receptors in the brain of WAG/Rij rats with genetic absence epilepsy, before and after appearance of the disease Iolanda D’Alimonte, 1, * Mariagrazia D’Auro, 1, * Rita Citraro, 2, * Francesca Biagioni, 3 Shucui Jiang, 4 Eleonora Nargi, 1 Silvana Buccella, 1 Patrizia Di Iorio, 5 Patricia Giuliani, 5 Patrizia Ballerini, 1 Francesco Caciagli, 1 Emilio Russo, 2 Giovambattista De Sarro 2 and Renata Ciccarelli 1 1 Department of Biomedical Sciences, Section of Pharmacology, University of Chieti, Medical School, Via dei Vestini 29, pal. B. 66013 Chieti, Italy 2 Department of Experimental and Clinical Medicine, ‘Magna Graecia’ University, Catanzaro, Italy 3 Istituto Neurologico Mediterraneo (Neuromed), Pozzilli, Venafro, Italy 4 Department of Surgery (Neurosurgery, Neurobiology), McMaster University, Health Sciences Centre, Hamilton, ON, Canada 5 Department of Human Movement Sciences, ‘G. D’Annunzio’ University, Chieti, Italy Keywords: cAMP levels, electroencephalographic (EEG) recordings, glutamate release, MAPK system, spike-wave discharge (SWD) Abstract The involvement of excitatory adenosine A 2A receptors (A 2A Rs), which probably contribute to the pathophysiology of convulsive seizures, has never been investigated in absence epilepsy. Here, we examined the distribution and function of A 2A Rs in the brain of Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats, a model of human absence epilepsy in which disease onset occurs 2–3 months after birth. In the cerebral areas that are mostly involved in the generation of absence seizures (somatosensory cortex, reticular and ventrobasal thalamic nuclei), A 2A R density was lower in presymptomatic WAG/Rij rats than in control rats, as evaluated by immunohistochemistry and western blotting. Accordingly, in cortical/thalamic slices prepared from the brain of these rats, A 2A R stimulation with the agonist 2-[4-(-2-carboxyethyl)-phenylamino]-5¢-N-ethylcarboxamido-adenosine failed to modulate either cAMP formation, mitogen-activated protein kinase system, or K + -evoked glutamate release. In contrast, A 2A R expression, signalling and function were significantly enhanced in brain slices from epileptic WAG/Rij rats as compared with matched control animals. Additionally, the in vivo injection of the A 2A R agonist CGS21680, or the antagonist 5-amino-7-(2-phenylethyl)-2-(2-fuyl)-pyrazolo-(4,3- c)1,2,4-triazolo(1,5-c)-pyrimidine, in the examined brain areas of epileptic rats, increased and decreased, respectively, the number/ duration of recorded spontaneous spike–wave discharges in a dose-dependent manner during a 1–5 h post-treatment period. Our results support the hypothesis that alteration of excitatory A 2A R is involved in the pathogenesis of absence seizures and might represent a new interesting target for the therapeutic management of this disease. Introduction Adenosine and related analogues exert anti-epileptic effects in convulsive seizure models (Maitre et al., 1974; Von Lubitz et al., 1994; Malhotra & Gupta, 1997) by decreasing neuronal membrane excitability and neurotransmitter release (Dunwiddie, 1985) via A 1 receptors (A 1 Rs). A 2A receptors (A 2A Rs) are less abundant in brain than A 1 Rs, and their activation generally produces effects opposite to those mediated by A 1 R; this favours epileptic attacks in pharmaco- logically induced convulsive seizures (Morgan & Duncan, 1990; Giraldez et al., 1999; El Yacoubi et al., 2001) or animal models of temporal lobe epilepsy (Zeraati et al., 2006; Hosseinmardi et al., 2007). Although some results are controversial (Adami et al., 1995; De Sarro et al., 1999), recent data indicate that A 2A R antagonists may be promising anticonvulsant drugs (Rebola et al., 2005). Little is known about the role of adenosine in absence seizures, a disorder characterized in humans and homologous animal models by bilateral synchronous spike–wave discharges (SWDs) in electroen- cephalographic (EEG) recordings, associated with behavioural arrest. A lower A 1 R density was shown in the reticular thalamic nucleus (RTN) (Ekonomou et al., 1998) of Genetic Absence Epilepsy Rats from Strasbourg, an animal model of absence epilepsy. The RTN, together with the ventrobasal thalamic nucleus (VBTN) and the perioral region of the somatosensory cortex (S1po), forms a network, the dysfunction of which underlies the pathophysiology of absence seizures (Van Luijtelaar & Sitnikova, 2006). Neurobiological changes in neocortical neurons are currently believed to initiate pathological oscillatory rhythms, recorded as SWDs, whereas RTN and thalamic relay cells contribute to the maintenance of this paroxysmal activity (Van Luijtelaar & Sitnikova, 2006). As adenosine, via presynaptic Correspondence: Dr R. Ciccarelli, as above. E-mail: r.ciccarelli@dsb.unich.it *Contributed equally to this work. Received 12 November 2008, revised 10 July 2009, accepted 13 July 2009 European Journal of Neuroscience, Vol. 30, pp. 1023–1035, 2009 doi:10.1111/j.1460-9568.2009.06897.x ª The Authors (2009). Journal Compilation ª Federation of European Neuroscience Societies and Blackwell Publishing Ltd European Journal of Neuroscience