The impact of trait anxiety and visual perception on nesting expression in deer mice

Abstract

From these mice, 24 NNB1- and 24 LNB2-expressing mice were identified and used in further study. Mice of each cohort were again divided into either a standard 12-h light-dark (SL)3 or visually deprived (visual deprivation; VD)4 group and reassessed for nesting expression during a second phase (P2). Specifically, approximately half of the mice in each cohort were maintained under a SL cycle, with the other half under conditions of utter VD applied during the dark cycle. After completion of P2, all mice were euthanised, the frontal-cortical and hippocampal tissues removed, and analysed for serotonin and noradrenaline concentration. From these experiments, our main findings were that 1) in contrast to NNB, LNB represents an inflexible and excessive behavioural phenotype that is not dependent on visually guided action-outcome processing, and 2) despite fronto-limbic noradrenaline concentrations not being influenced by VD, LNB associates with increased frontal-cortical and hippocampal noradrenaline, a neurobiological signature which may contribute to its expression. The first main finding of this investigation points to separation between the neurocognitive underpinnings of NNB and LNB, whereby NNB, but not LNB, inflates over time. Such a response cannot be related to overt limbic activation (see below) and thus, we propose NNB behaviour to be founded on evolutionary conserved mechanisms that enable nesting, but that is in the same sense, subject to improvement based on prior experience. In contrast, LNB is excessive, rigid, and representative of maximal habit-like behavioural activation that is not subject to temporal or experiential influences. Further, while mice of both cohorts were sensitive to VD so that nesting sizes varied less between different days, the consistency with which nest construction was executed relied less on visual feedback in LNB, than in NNB mice. These results are in line with theories pointing to a role of behavioural rigidity and habitual engagement in compulsive symptom expression, both of which are linked with cortico-striatal hyperactivation. The second main finding of this study was particularly striking and potentially indicates a novel noradrenergic mechanism which may underlie compulsive-like behavioural expression. To explain, LNB expressing mice showed increased fronto-limbic noradrenaline concentrations that, although not traditionally associated with OCD5, may play a profound role in promoting limbic activation and compromising frontal-cortical regulation of executive goal-directed decision making. These findings contribute in a meaningful way to our understanding of LNB and how this naturalistic phenotype could 1 normal nest building 2 large nest building 3 standard 12-h light-dark 4 visual deprivation 5 obsessive-compulsive disorder be positioned to elaborate our understanding of how fronto-limbic mechanisms may underlie compulsive symptom promulgation.