RETRIEVAL AND RECONSOLIDATION OF OBJECT RECOGNITION MEMORY ARE INDEPENDENT PROCESSES IN THE PERIRHINAL CORTEX I. BALDERAS,   C. J. RODRIGUEZ-ORTIZ   AND F. BERMUDEZ-RATTONI * Divisio ´n de Neurociencias, Instituto de Fisiologı´a Celular, Universidad Nacional Auto ´noma de Me ´ xico, A.P. 70-253, Me ´xico D.F. 04510, Mexico Abstract—Reconsolidation refers to the destabilization/re- stabilization process upon memory reactivation. However, the parameters needed to induce reconsolidation remain unclear. Here we evaluated the capacity of memory retrieval to induce reconsolidation of object recognition memory in rats. To assess whether retrieval is indispensable to trigger reconsolidation, we injected muscimol in the perirhinal cor- tex to block retrieval, and anisomycin (ani) to impede recon- solidation. We observed that ani impaired reconsolidation in the absence of retrieval. Therefore, stored memory under- went reconsolidation even though it was not recalled. These results indicate that retrieval and reconsolidation of object recognition memory are independent processes. Ó 2013 IBRO. Published by Elsevier Ltd. All rights reserved. Key words: reconsolidation, updating, retrieval, object recognition memory, perirhinal cortex, rats. INTRODUCTION Memories turn stable in the long term through a protein synthesis-dependent process known as consolidation (McGaugh, 2000). However, after consolidation, memories can become labile (Nader et al., 2000). Reconsolidation theory posits that upon retrieval, consolidated memories are destabilized and once again require a protein synthesis-dependent process to be retained in long-term storage (Nader and Einarsson, 2010). Nevertheless, some results indicate that inhibition of retrieval in the amygdala does not impede fear or taste-conditioned memory to undergo reconsolidation (Yasoshima et al., 2005; Ben Mamou et al., 2006; Rodriguez-Ortiz et al., 2012). Since it has been observed that different types of memory differ on the conditions that render them labile (Finnie 2012), the aim of the present study was to evaluate whether retrieval is indispensable for declarative memory to reconsolidate. The object recognition task is useful to evaluate declarative memory. This task relies on rodents’ natural tendency to explore for a longer time novel than familiar objects when presented together (Ennaceur and Delacour, 1988). It has been suggested that this task maintains a close analogy to recognition memory tasks used in humans to evaluate impairments in declarative memories (Reed and Squire, 1997). Previous studies have demonstrated that the perirhinal cortex is specifically involved in long-term formation of object recognition memory (Brown and Aggleton, 2001; Mumby et al., 2007; Balderas et al., 2008; Winters et al., 2008; Tinsley et al., 2011; Brown et al., 2012). Therefore, the present study focused on retrieval and reconsolidation processes taking place in the perirhinal cortex during object recognition memory reactivation. By infusing the GABA A receptor agonist muscimol (musc), previous reports have shown that temporal inactivation of brain structures, like the hippocampus and prefrontal cortex, effectively reveals whether these structures are mandatory for the retrieval process of different kinds of memories (Moser and Moser, 1998; Holt and Maren, 1999; Blum et al., 2006; Jo et al., 2007). Moreover, it has been shown that musc infusions into the hippocampus impaired retrieval of spatial memory without affecting new learning processing (Moser and Moser, 1998; Holt and Maren, 1999; Blum et al., 2006; Jo et al., 2007). Consequently, in order to assess retrieval we used musc to temporally inactive the perirhinal cortex and, anisomycin (ani) was applied to unveil effects over reconsolidation. EXPERIMENTAL PROCEDURES Subjects The general protocol used for animal manipulation and object recognition memory task have been described in detail elsewhere [see (Balderas et al., 2012)]. Briefly male Wistar rats from our Institute breeding colony, (270–310 g) were used. All manipulations were carried out in accordance to the National Institutes of Health Guide for the Care and Use of Laboratory Animals (eighth edition). The institutional Bio Safety and Ethics Committee approved these protocols, aimed to minimize the number of animals used and their suffering. All experiments were carried out in independent groups (for the detailed number of subjects in each group please see the figure legends). 0306-4522/13 $36.00 Ó 2013 IBRO. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.neuroscience.2013.09.001 * Corresponding author. Tel: +525-556225626; fax: +525- 556225607. E-mail addresses: fbermude@ifc.unam.mx, bermudez@unam.mx (F. Bermudez-Rattoni).   These authors contributed equally to this work. Abbreviations: ani, anisomycin; ANOVA, analysis of variance; ACSF, artificial cerebrospinal fluid; musc, muscimol; sal, saline; veh, vehicle. Neuroscience 253 (2013) 398–405 398