Pilocarpine-induced epilepsy alters the expression and daily variation of the nuclear receptor RORα in the hippocampus of rats Anna Karynna Alves de Alencar Rocha a , Eliangela de Lima a,b , Fernanda Gaspar do Amaral b, ⁎, Rafael Peres b , José Cipolla-Neto b , Débora Amado a a Department of Neurology and Neurosurgery, Universidade Federal de São Paulo (UNIFESP), São Paulo, Brazil b Department of Physiology and Biophysics, Institute of Biomedical Science, Universidade de São Paulo, São Paulo, SP, Brazil abstract article info Article history: Received 19 August 2015 Revised 16 November 2015 Accepted 24 November 2015 Available online 28 December 2015 It is widely known that there is an increase in the inflammatory responses and oxidative stress in temporal lobe epilepsy (TLE). Further, the seizures follow a circadian rhythmicity. Retinoic acid receptor-related orphan recep- tor alpha (RORα) is related to anti-inflammatory and antioxidant enzyme expression and is part of the machin- ery of the biological clock and circadian rhythms. However, the participation of RORα in this neurological disorder has not been studied. The aim of this study was to evaluate the RORα mRNA and protein content profiles in the hippocampus of rats submitted to a pilocarpine-induced epilepsy model at different time points through- out the 24-h light–dark cycle analyzing the influence of the circadian rhythm in the expression pattern during the acute, silent, and chronic phases of the experimental model. Real-time PCR and immunohistochemistry results showed that RORα mRNA and protein expressions were globally reduced in both acute and silent phases of the pilocarpine model. However, 60 days after the pilocarpine-induced status epilepticus (chronic phase), the mRNA expression was similar to the control except for the time point 3 h after the lights were turned off, and no differences were found in immunohistochemistry. Our results indicate that the status epilepticus induced by pilocarpine is able to change the expression and daily variation of RORα in the rat hippocampal area during the acute and silent phases. These findings enhance our understanding of the circadian pattern present in sei- zures as well as facilitate strategies for the treatment of seizures. © 2015 Elsevier Inc. All rights reserved. Keywords: Epilepsy Pilocarpine RORα receptor 1. Introduction The retinoic acid receptor-related orphan receptor alpha (RORα) is a member of a nuclear receptor superfamily with biological functions not fully known [1]. It has been described that RORα is constitutively active, being found in several areas of the central nervous system such as the hypothalamus, pituitary, thalamus, neocortex [2], and hippocampus [3]. Moreover, it presents a daily pattern of expression in both neurons and astrocytes of the hippocampus [4]. Retinoic acid receptor-related orphan receptor alpha is essential for the regulation of the circadian rhythm [5]. It has been shown that RORα acts in a coordinated fashion with REVERB on the same promoter ele- ment, leading to the circadian rhythm of BMAL1 transcription. The mas- ter gene BMAL1 drives rhythmic gene expression and regulates biological functions under circadian control [6,7]. Therefore, RORα in- fluences the period length and stability of the biological clock and, con- sequently the circadian rhythm [8]. Retinoic acid receptor-related orphan receptor alpha has been asso- ciated with antioxidant enzyme expression [9], and its upregulation prevents the expression of important markers of the inflammatory re- sponse such as TNFα, IL-6, IL-8, and COX-2 [1]. Moreover, RORα is a binding site for melatonin, a hormone that is considered a chemical messenger of the light–dark cycle (a circadian and circannual pacemak- er) with anti-inflammatory, antioxidant, and neuroprotective effects [10,11]. In fact, melatonin exerts neuroprotective effects in temporal lobe epilepsy by decreasing inflammation and promoting antioxidant actions [12–17], which could be related to RORα activation in the hippocampus. In this context, it is known that temporal lobe epilepsy (TLE) is asso- ciated with high rates of tissue inflammation which affect temporal lobe regions (especially the hippocampus). Some studies have demonstrated an increase of free radical levels as well as of inflammatory cytokines and tumor necrosis factor-α during epileptogenesis [18–21]. Furthermore, the seizures of temporal lobe epilepsy follow a circadian rhythmicity as demonstrated in several studies in both humans [22, 23] and animals [24–30]. These seizures are more prevalent during the day regardless of whether the species is diurnal or nocturnal. Considering that (1) RORα is related to the inflammatory response and antioxidant enzyme expression and is a part of the machinery of Epilepsy & Behavior 55 (2016) 38–46 ⁎ Corresponding author at: Av. Prof. Lineu Prestes, 1524, Cid. Universitária, 05508-000 São Paulo, SP, Brazil. E-mail address: fgamaral@gmail.com (F.G. Amaral). http://dx.doi.org/10.1016/j.yebeh.2015.11.026 1525-5050/© 2015 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Epilepsy & Behavior journal homepage: www.elsevier.com/locate/yebeh