Circuitos neurais e mecanismos moleculares subjacentes à separação de padrões de objetos em uma tarefa de múltiplas tentativas

Abstract

The neural bases involved in the processing of recognition memory have been the focus of various molecular studies. Research has pointed to the pattern separation function for spatial and object information in underlying structures of the cortex (Perirhinal and Lateral Entorhinal Cortex) and hippocampus (Dentate Gyrus and CA3). It is noteworthy that this is one of the first circuits to undergo changes during aging. However, it remains unclear how the anteroposterior axis of the hippocampus and parahippocampal cortex are engaged in solving processes involving the recognition and separation of objects. Additionally, there is a need for standardizing tasks that allow for the collection of a larger amount of data, particularly for studies focused on electrophysiology. Thus, this study aims to standardize an object recognition and discrimination task with multiple trials and investigate c-Fos expression in regions of the temporal cortex and hippocampal subregions, considering them along the anteroposterior axis. Initially, a behavioral pilot study was conducted to standardize the task, with 6 animals. Following this, animals divided into 5 groups for immunofluorescence underwent: an Object Recognition task (C1), n=8; a discrimination task with all levels of similarity (C2), n=8; and a discrimination task with a specific similarity degree (25%, 50%, and 75%), with 7, 7, and 6 animals respectively. The task consists of 4 trials, each containing a sample phase and a test phase. During each trial, a new set of objects was used. In each sample, two identical pairs of objects constructed from Legos were presented. During the test phase, one of the objects was replaced by a different object, varying its similarity depending on the experimental group. To control object similarity, a Cartesian plane was constructed so that the amount of overlap between them could be quantified and shared features controlled. Sections were subjected to an immunofluorescence protocol for c-Fos labeling. Counting was performed manually using ImageJ. For behavioral data, cumulative indices (D2) were calculated throughout the trials. For immunofluorescence data, ANOVA for independent measures and planned contrasts were performed. Kruskal-Wallis tests and post hoc Dunn tests were also conducted. Graph analyses were guided by the igraph package. Our results indicate that for the behavioral pilot, animals discriminate new objects from different ones with similarity degrees of 25% and 50%. For immunofluorescence, significant differences were found in c-Fos expression in different portions of the horizontal axis of CA3R and Hilos R, with higher similarity conditions showing greater c-Fos expression, with no difference between the higher similarity conditions (50% and 75%). Moreover, under higher similarity conditions, c-Fos expression in different hippocampal regions was strongly correlated with the discrimination index. Graph analysis showed that the functioning of the hippocampal network is highly dynamic depending on the condition. As the level of similarity increases, so do the network interconnections; therefore, the networks are more densely interconnected and more efficient for high similarity conditions. Furthermore, depending on the level of similarity, different forms of organization and cluster division are found. Therefore, HilosR and CA3cR are activated differently depending on the level of similarity, having a central role in pattern separation. The hippocampus functions as a more densely integrated network as the demand for overlap between memories increases. These findings contribute to elucidating the mechanisms surrounding the neurobiological bases of recognition memory acquisition, consolidation, and pattern separation.