Behavioural Brain Research 260 (2014) 101–110 Contents lists available at ScienceDirect Behavioural Brain Research j ourna l h om epage: www.elsevier.com/locate/bbr Research report Spatial memory extinction: A c-Fos protein mapping study M. Méndez-Couz a , N.M. Conejo a,∗ , G. Vallejo b , J.L. Arias a a Laboratory of Neuroscience, Department of Psychology, Instituto de Neurociencias del Principado de Asturias (INEUROPA), University of Oviedo, Plaza Feijóo s/n, 33003 Oviedo, Spain b Methodology Area, Department of Psychology, Instituto de Neurociencias del Principado de Asturias (INEUROPA), University of Oviedo, Plaza Feijóo s/n, 33003 Oviedo, Spain h i g h l i g h t s • The medial prefrontal cortex is required for spatial memory extinction. • The amygdala complex was activated after spatial memory extinction. • The lateral mammillary nucleus is involved in spatial memory extinction. a r t i c l e i n f o Article history: Received 3 October 2013 Received in revised form 18 November 2013 Accepted 22 November 2013 Available online 4 December 2013 Keywords: Spatial memory Extinction c-Fos Mammillary body Prefrontal cortex Rat a b s t r a c t While the neuronal basis of spatial memory consolidation has been thoroughly studied, the substrates mediating the process of extinction remain largely unknown. This study aimed to evaluate the functional contribution of selected brain regions during the extinction of a previously acquired spatial memory task in the Morris water maze. For that purpose, we used adult male Wistar rats trained in a spatial reference memory task. Learning-related changes in c-Fos inmunoreactive cells after training were evaluated in cortical and subcortical regions. Results show that removal of the hidden platform in the water maze induced extinction of the previously reinforced escape behavior after 16 trials, without spontaneous recovery 24 h later. Extinction was related with significantly higher numbers of c-Fos positive nuclei in amygdala nuclei and prefrontal cortex. On the other hand, the lateral mammillary bodies showed higher number of c-Fos positive cells than the control group. Therefore, in contrast with the results obtained in studies of classical conditioning, we show the involvement of diencephalic structures mediating this kind of learning. In summary, our findings suggest that medial prefrontal cortex, the amygdala complex and diencephalic structures like the lateral mammillary nuclei are relevant for the extinction of spatial memory. © 2013 Elsevier B.V. All rights reserved. Abbreviations: Ba, amygdala basal nucleus; Ce, amygdala central nucleus; Me, amygdala medial nucleus; ANOVA, analysis of variance; CG, cingulate cortex; CS, conditioned stimulus; N, control naïve group; CA1d, cornu ammonis 1 of the dorsal hippocampus; CA1v, cornu ammonis 1 of the ventral hippocampus; CA3d, cornu ammonis 3 of the dorsal hippocampus; CA3v, cornu ammonis 3 of the ventral hip- pocampus; df, degrees of freedom; DGd, dentate gyrus of the dorsal hippocampus; DGv, dentate gyrus of the ventral hippocampus; EX, extinction group; EXR, extinc- tion plus retention probe group; FWE, familywise error rate; IEGs, immediate early expression gene; IL, infralimbic cortex; LM, mammillary bodies lateral nucleus; MM, mammillary bodies medial nucleus; MWM, Morris water maze; PBS-T, PBS solution containing triton; PBS, phosphate-buffered saline; PL, prelimbic cortex; RSA, ret- rosplenial agranular cortex; RSG, retrosplenial granular cortex; US, unconditioned stimulus. ∗ Corresponding author at: Laboratorio de Neurociencias, Instituto de Neurocien- cias del Principado de Asturias (INEUROPA), Plaza Feijóo s/n, E-33003 Oviedo, Spain. Tel.: +34 985 10 41 88; fax: +34 985 10 41 44. E-mail address: conejonelida@uniovi.es (N.M. Conejo). 1. Introduction Most adaptive behavior in complex organisms is learned behav- ior driven by the availability of positive or negative reinforcers. However, withdrawal of positive reinforcers leads to the extinc- tion of the previously learned behavior. Over trials of extinction, the organism learns that the former adaptive response is no longer effective in conducting to reinforcement and it will gradually desist to emit this behavior. During standard Pavlovian tasks, repeated presentations of the conditioned stimulus (CS), but in the absence of the unconditioned stimulus (US) previously paired with the CS results in the extinction of the previously conditioned response. The effect of this procedure had been assumed to decrease the CS’s ability to evoke the conditioned response established during early phases, when both stimuli (CS and US) were paired [1,2]. See also the review by Delamater [3]. According to Huston et al. [4], learning and extinction pro- cesses in the water maze follow the classical rules that govern 0166-4328/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bbr.2013.11.032