Disturbing sleep in adolescent mice

Disturbing sleep in female adolescent mice does not increase vulnerability to depression triggers later in life.

Egebjerg et al. Brain Behaviour and Immunity, 2025

Overview

- This study investigates the long-term effects of sleep disturbance (SD) during adolescence on vulnerability to depression triggers later in life, using a female adolescent mouse model.

- The primary objectives were to determine whether SD in adolescence induces lasting behavioral or molecular changes that increase susceptibility to depression-like behaviors after exposure to known triggers such as social isolation (SI) or inflammation (LPS).

- The research aims to clarify if adolescent SD acts as a "second hit" in the development of depression, which is highly relevant given the high prevalence of sleep issues and depression during human adolescence.

Key Concepts

Adolescence as a vulnerable period: Characterized by ongoing neurodevelopment, especially in brain regions involved in mood regulation.

Sleep disturbance (SD): Disruption of normal sleep patterns, which has been linked to structural and functional brain changes.

Two-hit hypothesis: Suggests that a combination of genetic vulnerability and environmental insults (e.g., SD, stress) increases risk for neuropsychiatric disorders like depression.

Microglia and neuroinflammation: Microglial morphology and cytokine expression as markers of neuroinflammatory processes potentially involved in depression.

Gene expression markers: Focus on molecules such as Cx3cr1, Dnmt3b, Htr1a, Bdnf, Ntrk2, and Tnf related to neuroplasticity, methylation, serotonin regulation, and inflammation.

Conclusions

- Adolescent sleep disturbance induces specific molecular alterations in the hippocampus and mPFC but does not lead to persistent behavioral deficits or increased vulnerability to depression-like triggers in adulthood.

- The findings challenge the assumption that SD during adolescence acts as a "first hit" for depression development, at least under the less stressful SD model used.

- The study emphasizes the importance of stress levels associated with SD protocols; less stressful methods may not produce the behavioral phenotypes seen with more stressful deprivation paradigms.

- Results suggest that sleep disturbance alone during adolescence may not be sufficient to predispose individuals to depression triggered by social isolation or inflammation later in life.

Methodology

Research design: Experimental study with longitudinal assessments involving adolescent female mice subjected to SD, followed by adult exposure to depression triggers.

Subjects: Female C57BL/6J mice, starting at post-natal day (P)36.

SD protocol: 7 days of voluntary sleep disturbance for 4 hours daily during light phase (ZT2-6), with novel objects introduced to minimize stress.

Data collection:

- Gene expression: Quantitative PCR (qPCR) analysis of hippocampus and medial prefrontal cortex (mPFC) tissues immediately after SD.

- Microglia morphology: Fractal analysis of Iba-1 stained microglia in cortex.

- Behavioral tests: Open Field Test (OFT) and Tail Suspension Test (TST) conducted post-SD and after adult triggers.

  - Home-cage activity: Monitored via Digital Ventilated Cages (DVC) system during social isolation and post-LPS.

Triggers of depressive behaviour: Social isolation (SI) for 7 days and lipopolysaccharide (LPS) injection (250 µg/kg) to induce inflammation.

Key Findings

Molecular changes: SD acutely decreased hippocampal Cx3cr1 and Dnmt3b expression and mPFC Htr1a expression; no significant changes in Tnf, Dnmt3a, Bdnf, Ntrk2.

Microglia morphology: Slight non-significant trend toward increased fractal dimension; no significant differences in circularity, span ratio, density, or lacunarity.

Behavioral outcomes: No significant differences in home-cage activity, anxiety-like behavior (OFT), or despair-like behavior (TST) following adolescent SD alone.

Vulnerability to triggers:

- SI in adulthood did not exacerbate behavioral deficits in SD mice.

- LPS reduced activity initially but did not differentially affect SD vs. control mice; no increase in depression-like behaviors was observed after SD plus LPS.

Overall pattern: While molecular effects of SD were evident acutely, these did not translate into increased behavioral susceptibility to depression triggers later in life.

Limitations

- The SD protocol was designed to be less stressful by using voluntary wakefulness; thus, it may not replicate stress-inducing SD models that show behavioral effects.

- The study focused solely on female mice; sex differences might influence outcomes.

- The timing of SD during mid-adolescence (P36) may not capture effects occurring earlier or later in development.

- The sample size for some measures may limit detection of subtle effects.

- Potential confounding factors include stress from shipment and housing conditions that could influence neurobiological responses.