Maternal separation disrupts noradrenergic control of adult coping behaviors

Early life stress (ELS) profoundly impacts the brain and correlates with negative affective behaviors in adulthood. The locus coeruleus (LC), a stress-responsive brainstem nucleus that supplies most of the brain with norepinephrine (NE), is known to modulate negative affect. Using repeated maternal separation stress (MSS), we investigated the impact of ELS on the LC and stress-related behaviors in adulthood. We performed ex vivo cell-attached electrophysiology across the lifespan to reveal that MSS significantly increased LC firing during early development and adulthood but not in pre-adolescence and adolescence. We next examined potential changes in the expression of genes linked to LC function. In adulthood, MSS decreased mRNA levels for both the alpha-2A adrenergic receptor and dopamine beta-hydroxylase, the enzyme necessary for NE synthesis. At the behavioral level, MSS increased locomotion in approach-avoidance exploratory assays and increased immobility in the forced swim test. While forced swim increased LC cFos expression, a marker for neuronal excitation, in both No MSS and MSS mice, this increase was significantly lower in MSS mice than in No MSS controls. We further showed that MSS decreased the number of LC cells, possibly underlying the difference in cFos induction and gene expression between MSS and No MSS mice. Finally, we showed that inhibiting the LC in No MSS mice increased immobility time, but did not affect MSS immobility. Instead, LC inhibition in MSS mice increased climbing time. Together, this study demonstrates that MSS dysregulates LC-NE activity across the lifespan and disrupts LC regulation of coping strategies during stressful events.