Contents lists available at ScienceDirect Behavioural Brain Research journal homepage: www.elsevier.com/locate/bbr Orexin-A promotes EEG changes but fails to induce anxiety in rats Víctor Manuel Magdaleno-Madrigal a , Sandra Morales-Mulia b , Humberto Nicolini c , Alma Genis-Mendoza c,d , Elizabeth Cázares-Martínez Claudia a , Manuel Pérez-Luna José e , Marcela Morales-Mulia f, ⁎ a Neurofisiología del Control y la Regulación, Dirección de Neurociencias, INPRFM, México D.F., Mexico b Departamento de Biología, Facultad de Ciencias, UNAM, México D.F., Mexico c Laboratory of Genomics of Psychiatric Diseases, Neurodegenerative and Addictions, National Institute of Genomic Medicine, Mexico City, Mexico d Hospital Psiquiátrico Infantil “Dr. Juan N. Navarro” Psychiatric Attention Services, Mexico City, Mexico e Departamento de Genética, Subdirección de Investigaciones Clínicas, INPRFM, México D.F., Mexico f Bases Moleculares de las Adicciones, Subdirección de Investigaciones Clínicas, INPRFM, México D.F., Mexico ARTICLE INFO Keywords: Orexins system Electroencephalographic-activity Anxiety Dopamine-D 2 -receptor ABSTRACT Orexins (OXs) system has been suggested to play a key role in regulate processes related to arousal, including anxious behaviors. However, until now, the contribution of OXs in anxiogenic-like effects has not been com- pletely clear, particularly in rats, whose results are not yet conclusive in behavioral-tests such as elevated-plus- maze test (EPM-test). The goal of this study was to explore the anxiogenic-like effect induced by orexin-A (OX-A) using two different paradigms; the EPM-test and simultaneously a quantitative index in vivo, the cortical-elec- troencephalographic-(EEG)-record. This index proposes that a low-frequency domain EEG, particularly 0.5–5-Hz (delta and low portion of theta-waves), is a key indicator to evaluate anxiety levels. We also explored whether the anxious effect of OX-A could be altered by an antagonist of dopamine-D2-receptor (D 2 R) sulpiride (SUL). Our results showed that intracerebroventricular (i.c.v.) injection of a low dose of OX-A (140 pmol) did not increase anxiety levels in rats. On the other hand, cortical-EEG-activity showed only a decrease in delta-spectral-power but no changes in theta-potency. These data suggest that the reduction in delta-power induced by OX-A only keeps the animals awake and alert without changes in anxiety levels. 1. Introduction The orexin-A (OX-A) and orexin-B (OX-B) (also known as hypo- cretin-1 and hypocretin-2, respectively) regulate arousal-related pro- cesses including sleep/wake function and reinforcing effects of diverse drugs of abuse as well as motivated behavior along with anxiety-related disorders. Both orexins (OXs) come from a precursor (prepro-orexin) that undergoes enzymatic processing, they are produced in neurons residing in the lateral (LH) and dorsomedial (DMH) hypothalamus and perifornical area (PFA) [1,2]. The OXs interact with two G-protein- coupled receptors, the OX 1 R and OX 2 R[2,3]. Orexin-receptors are ex- pressed widely throughout the brain although their expression levels vary based on location [4,5]. Orexin-containing-neurons project from the LH to diverse areas of the mesocorticolimbic pathway including ventral tegmental area (VTA), nucleus accumbens (NAc), prefrontal cortex (PFC), hippocampus and amygdala [6], where orexin-receptors are expressed. Intracerebroventricular (i.c.v.) injection of OXs increase the firing- rate of dopaminergic (DAergic)-neurons in the VTA [7,8] and augment the dopamine (DA) release and its metabolites in NAc and PFC [9,10]. The inhibition of OX 1 R reduces DA cell-firing [11], as well as decreases the amphetamine- and, cocaine-induced DA release in NAc [12,13]. Furthermore, OX-A stimulates stress-related behaviors like grooming, stereotypy and hyperlocomotion [14,15], actions that were blocked by dopamine-D1-receptor (D 1 R) or dopamine-D2-receptor (D 2 R) antago- nists in rodents [15]. These data provide strong evidence that OXs contribute to the regulation of DAergic-neurons and that the actions of OXs in these neurons could be involved in a diversity of abuse drug- induced behaviors known to be regulated by DA. Dysfunction in the OXs system can lead to the pathology of anxiety and addiction to drugs of abuse which is commonly associated with stress and/or impaired fear processing. Increase in orexin mRNA levels have been observed in an- imals exposed to different stressors such as immobilization [16], cold stress [16], or hypoglycemia [17]. These findings indicate that high https://doi.org/10.1016/j.bbr.2018.12.037 Received 19 September 2018; Received in revised form 3 December 2018; Accepted 20 December 2018 ⁎ Corresponding author at: Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz, Calzada México-Xochimilco 101, San Lorenzo Huipulco, Tlalpan, CP. 14370. México, D.F., Mexico. E-mail address: mmulia@imp.edu.mx (M. Morales-Mulia). Behavioural Brain Research 361 (2019) 26–31 Available online 21 December 2018 0166-4328/ © 2018 Published by Elsevier B.V. T