Efeitos do isolamento social sobre a extinção da memória de medo condicionado

Abstract

Fear memory exhibits great relevance to our survival. However, its permanence and retrieval for prolonged periods and in non-aversive situations can characterize a maladaptive attribute. Considering the fact that social isolation (SI) can cause deleterious effects on cognitive and emotional functions, such as memory impairment, we investigated whether SI can facilitate or impair the extinction of an aversive memory. Male and female C57BL/6 mice were kept grouped or subjected to a 7-day IS, followed by a Pavlovian contextual fear conditioning task with 3 unconditioned stimuli (US). Males and females extinguished memory, however, isolated females had a worse extinction compared to isolated males. Then, another group of animals under the same experimental conditions was exposed to conditioning with 1US, which is milder. To confirm that even with 1US the animals consolidated the fear memory, we added naïve groups. Males and females conditioned and presented freezing behaviour superior to their respective naïve groups. Although we did not observe any difference between the groups, in general, the isolated male animals showed a lower level of freezing, which may indicate a facilitated extinction or impaired learning. To better characterize fear memory in males, we used auditory fear conditioning, with 1 or 3 US. However, we did not observe differences between the grouped and isolated animals. Finally, there was no difference between the groups regarding anxious-like behaviour in the elevated plus maze. While in locomotor activity, isolated females covered a greater distance in the open field compared to isolated males. Taken together, the results suggest that the effect of S on the extinction of fear memories is manifested, albeit mildly, only in females.