Reduction in locomotor activity and freezing time: A dual measure for more accurate fear response in rats

Abstract

Fear conditioning serves as a cornerstone behavioural test for modelling disorders, such as Post-Traumatic Stress Disorder (PTSD) and clinical anxiety, and for evaluating memory. The traditional measure of fear response, namely freezing time, might not encompass all expressions of fear behaviours, leading to potential exclusion of animals demonstrating 'resilient' responses. In this study, we sought to assess the combined utility of reduced locomotor activity and freezing time as a dual-measure for a more accurate evaluation of the fear response in Sprague-Dawley rats. Both cued and contextual conditioning paradigms were employed. Behavioural outcomes were meticulously recorded via a state-of-the-art, fully automated Multi-Conditioning System. The results indicated a significant correlation between freezing time and diminished locomotor activity, underscoring that both measures represent congruent facets of the fear response. Each conditioning paradigm led to a notable reduction in locomotor activity in response to the conditioned cues. A pivotal insight from our findings is the risk associated with solely relying on freezing time, which could inadvertently overlook animals manifesting alternate fear responses. Conversely, gauging reduced locomotor activity facilitates a more precise discernment of animals that are genuinely resilient to fear conditioning. Our research champions the concurrent assessment of reduced locomotor activity and freezing time as a refined method to interpret fear response in rodents, particularly for identifying animals that exhibit fear-related behaviors but do not meet traditional freezing thresholds, promising to bolster the integrity of fear conditioning investigations and offer a deeper insight into fear behaviours.