The role of the medial prefrontal cortex in the ontogeny of the Object-in-Place
Date
2017
Authors
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Publisher
University of Delaware
Abstract
The Object-in-Place (OiP) task is a variant of the novel object recognition paradigm, which relies on a rat’s natural tendency to explore novel stimuli. The OiP task requires rats to learn the identity of an object in conjunction with its spatial location. Past research in our lab has shown that the object recognition task, which relies on perirhinal circuitry, emerges at Postnatal day (PD) 17, whereas the spatial variants of the novel object recognition paradigm, which require hippocampal involvement, such as the object location and object-place-context tasks emerge at PD21 and PD31 respectively (Westbrook, Brennan & Stanton, 2014; Ramsaran, Sanders & Stanton, 2016). This study sought to characterize the ontogenetic profile of the OiP task using the 2 variants of the Object-in-Place task currently used in the literature: the 2-Object and 4-object task, which rely on a differential neural circuitry. While both tasks are believed to require the medial prefrontal and perirhinal cortices, recent research suggests that the 4-Object OiP task requires the hippocampus, while the egocentric 2-Object OiP task does not (Langston & Wood, 2010; Barker & Warburton, 2011). The present study examined ontogenetic differences in the performance of these tasks (Experiment 1) and the role of the medial prefrontal cortex (mPFC) in OiP task performance, across the two task variants in juvenile rats (Experiment 2). In Experiment 1, rats were run at PD17, PD21, PD26 or PD31 in either the 2-object or 4-object variants of the task. This study found that both the 2-object and 4-object OiP tasks emerged between postnatal day 21 and 26. In Experiment 2, PD26 rats received the bilateral insertion of cannula into the mPFC, through which they received bilateral microinfusions of either the GABAergic agonist muscimol or a phosphate buffered saline solution 15 minutes prior to training on the 2-object, 4-object or novel object recognition task. The results in Experiment 2 show that the medial prefrontal cortex is involved in the 2-Object and 4-Object OiP tasks. This study is the first to identify the ontogenetic profile of object recognition tasks that depend on mPFC at the age when task performance first emerges.
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Keywords
Medial prefrontal cortex, Object-in-place paradigm, Ontogeny