Selective changes in thalamic and cortical GABA A receptor subunits in a model of acquired absence epilepsy in the rat Huifang Li a, * , Alli Kraus a , Jie Wu b , John R. Huguenard a , Robert S. Fisher a a Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Room A343, Stanford Medical Center, 300 Pasteur Drive, Stanford, CA 94305-5235, USA b Department of Neurology, Barrow Neurological Institute, Phoenix, AZ, USA Received 22 September 2005; received in revised form 6 March 2006; accepted 7 March 2006 Abstract Neonatal treatment of LongeEvans Hooded rats with the cholesterol synthesis inhibitor (CSI) AY9944 has been shown to increase occur- rence of spike-waves in EEG recordings and decrease benzodiazepines sensitivity of GABA A receptor-mediated responses in neurons from the thalamic reticular nuclei (nRt, Wu et al., 2004). The present experiments were designed to investigate the changes in the g2 and a1 subunits of the GABA A receptor in CSI model rats as possible mechanisms of these changes. Western blot, immunohistochemistry and real-time PCR tech- niques were performed to measure the levels of GABA A receptor g2 and a1 subunit transcripts and protein in the nRt and ventrobasal (VB) relay nuclei of thalamus and in somatosensory cortex. In CSI model animals, Western blot results showed that g2 subunit expression significantly decreased in thalamus (control, n ¼ 6: 0.17  0.02 relative to actin vs. CSI model, n ¼ 6: 0.11  0.01, P < 0.05) but neither in cortex nor in hippocampal tissues. Conversely, a1 subunit expression decreased in CSI model somatosensory cortex, but not in nRt and VB. The present results demonstrate that neonatal block of cholesterol synthesis produces region- and subunit-specific decreases in GABA A receptor subunits in thalamus and cortex. Selective reductions in GABA A receptor subunits in thalamus may play a role in pathophysiology of absence epilepsy. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Cholesterol synthesis inhibitor; GABA A receptor subunit; Thalamic reticular nucleus; Ventrobasal relay nucleus; Somatosensory cortex; Absence epilepsy 1. Introduction Absence seizures, previously referred to as petit mal sei- zures, are important clinical entities in children and in some adults. Atypical absence seizures present with frequent episodes of lost awareness, may be associated with falls and injuries, and are especially difficult to treat (Dreifuss and Ogunyemi, 1992). Much work has elucidated the mechanisms of the genetically-transmitted absence epilepsies in animal model systems (Danober et al., 1998), and this work has high- lighted the key role played by the reticular nucleus of thalamus (nRt) in generation of thalamocortical spike-waves. Until recently, no good animal models have existed for study of acquired absence epilepsy, which usually results from a cere- bral insult early in a child’s life. However, a model of acquired absence epilepsy now can be derived from inhibition of cho- lesterol synthesis in neonatal rats (CSI model). The inhibitor, AY9944 (trans-1,4-bis(2-chlorobenzylaminoethyl) cyclohex- ane 2HCl), was shown to produce long-standing absence epi- lepsy after a single injection, or a small series of injections in the first few weeks of life (Smith and Fisher, 1996). In distinc- tion to the many drugs that can produce seizures, AY9944 can produce epilepsy (Cortez et al., 2001). Study of the CSI model might lead to insights about the mechanisms of epilepsy sec- ondary to intrauterine or neonatal insults. This paper focuses on the potential stoichiometric changes in heteromeric GABA A receptors in thalamus. The g2 subunit is of particular interest. Benzodiazepine and muscimol binding is * Corresponding author. Tel.: þ1 650 724 7560; fax: þ1 650 498 6327. E-mail address: huifang@stanford.edu (H. Li). 0028-3908/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropharm.2006.03.003 Neuropharmacology 51 (2006) 121e128 www.elsevier.com/locate/neuropharm