Elsevier

Brain Research Bulletin

Volume 117, August 2015, Pages 16-23
Brain Research Bulletin

Research report
c-Fos expression correlates with performance on novel object and novel place recognition tests

https://doi.org/10.1016/j.brainresbull.2015.07.004Get rights and content

Highlights

  • Levels of c-fos in brain correlate with performance on the novelty preference tests.

  • Fos expression depends on the magnitude of novel object or novel place exploration.

  • c-Fos in CA1 correlate with exploration(d2) on novel place recognition.

  • c-Fos in perirhinal cortex correlate with exploration(d2) on novel object recognition.

Abstract

In rodents, many studies have been carried out using novelty-preference paradigms. The results show that the perirhinal cortex and the hippocampus are involved in the recognition of a novel object, “what”, and its new position, “where”, respectively. We employed these two variants of a novelty-preference paradigm to assess whether the expression of the immediate-early gene c-fos in the dorsal hippocampus and perirhinal cortex correlates with the performance discrimination ratio (d2), on the respective versions of the novelty preference tests. A control group (CO) was added to explore c-fos activation not specific to recognition. The results showed different patterns of c-Fos protein expression in the hippocampus and perirhinal cortex. The Where Group presented more c-Fos positive nuclei than the What and CO groups in the CA1 and CA3 regions, whereas in the perirhinal cortex, the What Group showed more c-Fos positive nuclei than the Where and CO groups. The correlation results indicate that levels of c-Fos in the CA1 area and perirhinal cortex correlate with effective exploration, d2, on the respective versions of the novelty preference tests, novel place and novel object recognition. These data suggest that the hippocampal CA1 and perirhinal cortex are specifically related to the level of recognition of place and objects, respectively.

Introduction

When rats are exposed to a previously-encountered object and a novel object, they frequently approach and spend more time exploring the novel object than the familiar one. This preference for a novel object indicates that rats maintain a representation of the familiar object in memory (Ennaceur, 2010). This spontaneous behaviour is the basis for one-trial object recognition tests (Dere et al., 2005, Ennaceur and Delacour, 1988, Ennaceur et al., 2005, Ennaceur et al., 2009), which have been widely used to study recognition memory in mice and rats. Tests assessing this type of memory, which consists of the ability to judge a previously encountered item as familiar, have often been used in basic research to investigate the neural basis of recognition memory (Winters et al., 2008). The most well-known recognition test is the one-trial object recognition test, which assesses the ability of rats to identify a particular object as novel or familiar based on the memory of an earlier experience with one of the two objects encountered in the same open-field (memory of “what”). However, this novelty preference paradigm has also been used to assess memory of the location of an object. This test assesses to what extent animals recognize the non-displaced object and, thus, spend more time exploring the displaced one (memory for “where”).

There is a large body of evidence about the role of the perirhinal cortex and the hippocampus in these two tasks. Many studies using a variety of methods and techniques have indicated that the perirhinal cortex is fundamental in novel object recognition (“what”). Lesion and electrophysiological studies suggest that the perirhinal cortex is critical for encoding object information, maintaining the object memory trace during the consolidation period and retrieving object information during the test trial (Brown and Aggleton, 2001, Winters and Bussey, 2005, Winters et al., 2008). At the same time, the hippocampus plays a fundamental role in place memory (“where”). Damage to the hippocampal system affects tasks involving the recognition of stimuli rearranged within a scene (Gaffan and Parkerm, 1996). Other studies, using measures of neuronal activation, also reveal an important role of the hippocampus in remembering what particular objects are located in specific locations (Manns and Eichenbaum, 2009, Castilla-Ortega et al., 2012).

Functional evidence about the role of the perirhinal cortex and hippocampus in the recognition of objects and places, respectively, has also been provided by imaging experiments using the products of the immediate early gene c-fos as an index of neuronal activation in response to stimulus exposure. The c-fos-encoded protein, c-Fos, is the product of the c-fos oncogene, an immediate-early gene. c-Fos can provide information about the neuronal plasticity required for memory processes and object recognition tests. Specifically, c-Fos studies showed increasing activity in rats’ perirhinal cortex following exposure to novel objects, whereas novel spatial arrangements of familiar objects significantly activated area CA1 of the hippocampus (Aggleton and Brown, 2005, Wan et al., 1999, Zhu et al., 1995, Zhu et al., 1996).

Therefore, perirhinal cortex involvement has been clearly shown in the representation of individual object information useful for recognition processes, whereas the hippocampus plays a specific role in more spatial functions (for review, see Winters et al., 2008). However, these studies do not explore whether levels of c-Fos in these brain areas correlate with performance on the respective versions of the novelty preference tests. For this purpose, in this study we employed novelty-preference tests similar to those developed by Ennaceur and Delacour (1988) and Mitchell and Laiacona (1998), which distinguish “what” and “where” information in order to assess whether c-Fos expression in these specific brain areas depends on the magnitude of novel object or novel place exploration.

Section snippets

Animals

We used 24 male Wistar rats from the vivarium of the University of Oviedo that weighed 290–330 gm at the beginning of the study. Rats were housed in groups of 4 three weeks prior to the beginning of the experiments and maintained under standard laboratory conditions (20–22 °C, 65–70% relative humidity and a 12 h light/dark cycle). Food and water were available ad libitum throughout all the experiments, and sessions were performed during the light phase, between 9:00 a.m. and 13:00 p.m. All

What

The results showed that rats were able to discriminate between a previously-encountered object and a novel object, as the means for d1 and d2 were both significantly higher than zero (d1: t7 = 4.663, p = 0.002; d2: t7 = 5.407, p = 0.001) (Fig. 3B). There were no significant differences in exploration between the sample and test phases (e1 = 0.496 ± 0.021, e2 = 0.485 ± 0.032: t7 = 0.276, p = 0.791) (Fig. 3A).

Where

The results showed that rats were able to discriminate between a location within the open field that had

Discussion

We assess whether the expression of the immediate-early gene c-fos in the dorsal hippocampus and perirhinal cortex correlates with the performance discrimination ratio (d2) on the “what” and “where” variants of a novelty-preference paradigm. This study related c-fos activity and the level of effective recognition in rats performing the test trial of novelty-preference tests of object and place discrimination. The results of this study reveal that CA1 is specifically involved in the recognition

Conflict of interest

All authors declare that there are no actual or potential conflicts of interest including any financial, personal or other relationships with other people or organizations that could inappropriately influence this work.

Acknowledgements

This research was supported by Project Grants of the Spanish Ministry of Economy and Competitiveness: PSI 2010-19348 and PSI 2013-45924; MEC Grant AP2009-1714 and Alfonso Martín Escudero Foundation to NA and USE-07750-E to SU.

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