Contents lists available at ScienceDirect Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet Research article NMDA receptor and nitric oxide synthase activity in the central amygdala is involved in the acquisition and consolidation of conditioned odor aversion Héctor González-Sánchez a , Jorge Tovar-Díaz a,b , Jean-Pascal Morin a , Gabriel Roldán-Roldán a, ⁎ a Department of Physiology, Faculty of Medicine, National Autonomous University Mexico, Mexico City, Mexico b Faculty of Medicine and Psychology, Autonomous University of Baja California, Tijuana, BC, Mexico ARTICLE INFO Keywords: Conditioned odor aversion Central amygdala Lithium chloride Nitric oxide synthase NMDA receptors ABSTRACT Rats readily learn to avoid a tasteless odorized solution if they experience visceral malaise after consuming it. This phenomenon is referred to as conditioned odor aversion (COA). Several studies have shown that COA depends on the functional integrity of the amygdala, with most studies focusing on the basolateral nucleus. On the other hand, the role of the central amygdala (CeA) which is known to be involved in the consolidation of conditioned taste aversion (CTA) remains to be established. To address this issue, we evaluated the effect of inhibiting NMDA receptor activity in this structure on COA memory formation. Intra-CeA infusions of non- competitive NMDA receptor inhibitor MK-801 prevented memory formation both when administered before and up to 15 min after COA conditioning, while no effect of this drug was observed when given before long-term memory test. We next evaluated the role of one of the main downstream effectors of brain NMDA receptor signaling, nitric oxide synthase (NOS), known to play a key role in a wide variety learning tasks including some types of olfactory conditioning. Similar results were obtained with inhibition of either NOS or neuron-specific NOS; which proved to be required both during and after COA training, though for a shorter time span than NMDA receptors. Also, neither isoform showed to be required to memory retrieval. These results suggest that the US signaling during acquisition and the initial consolidation step of COA depends on glutamate-NO system activation in the CeA. 1. Introduction Conditioned Odor Aversion (COA) is a form of classical conditioning in which rats learn to avoid the consumption of an odorized tasteless solution (conditioned stimulus, CS) that was previously paired with visceral toxicosis (unconditioned stimulus, US) [1]. As with many other aversively-motivated behaviors, it is well established that the amygdala (AMY) plays a critical role in COA and taste-potentiated odor aversion (TPOA) conditioning, a behavioral paradigm in which the compound presented as the CS is an odorized novel taste [1]. Permanent (elec- trolytic or excitotoxic) lesions [2] or reversible (novocaine) inactivation of the whole AMY [3] disrupt the acquisition of both COA and TPOA learning. Moreover, small electrolytic, NMDA or ibotenic acid-induced lesions of the basolateral nucleus of AMY (BLA) induced an impairment of potentiated odor aversion learning [4–6]. Glutamatergic neuro- transmission has also been implicated in TPOA; intra-cerebroven- tricular [7] or intra-BLA [8,9] infusion of D(–)-2-amino-5-phosphono- valeric acid (d-APV), an NMDA receptor antagonist before, but not after CS impairs TPOA. Considerably less is known about the role of the central nucleus of AMY (CeA) in associative memory and its role in COA remains un- known. The CeA is the striatum-like AMY which contains mainly in- hibitory, GABAergic neurons that receive abundant glutamatergic af- ferent from the BLA, cortex, thalamus, and brainstem, making it the major output nucleus of the AMY [10]. Interestingly, whereas rats with permanent lesions in the BLA had a stronger impairment of Conditioned Taste Aversion (CTA) acquisition than those with CeA lesions [11], protein synthesis inhibition after conditioned stimulus presentation in the CeA abolished CTA consolidation while the same treatment in the BLA left CTA intact [12]. On the other hand, studies have shown that temporary inactivation of the CeA with GABAergic receptor agonist muscimol or the AMPA receptor antagonist NBQX impairs both the acquisition and the expression of auditory and context-fear con- ditioning tasks [13,14]. Moreover, while NMDA-type glutamate re- ceptors in the BLA were shown to be required for both acquisition and extinction of conditioned fear [14,15], their activity in the CeA has been shown to be required for the conditioned fear acquisition only [14,16]. https://doi.org/10.1016/j.neulet.2019.134327 Received 22 February 2019; Received in revised form 22 May 2019; Accepted 9 June 2019 ⁎ Corresponding author at: Department of Physiology, Faculty of Medicine, UNAM, PO Box 70-250, 04510, D.F., Mexico. E-mail address: gabrielr.roldan@gmail.com (G. Roldán-Roldán). Neuroscience Letters 707 (2019) 134327 Available online 11 June 2019 0304-3940/ © 2019 Elsevier B.V. All rights reserved. T