Combined Prenatal Environmental Stressors Induce Suprachiasmatic Degeneration with Unexpected Behavioural Resilience in Long-Evans Rats.

INTRODUCTION

Environmental heat stress and displacement adversity during pregnancy pose significant risks to neurodevelopment, particularly in regions with high maternal mortality and population displacement. The suprachiasmatic nucleus (SCN), the brain's master circadian pacemaker, is vulnerable to prenatal environmental insults, yet the combined impact of thermal and psychosocial stressors on SCN development remains unexplored. We examined the effects of prenatal heat stress and displacement-like conditions on SCN morphology and behaviour across two critical developmental stages.

METHODS

Twenty-five timed-pregnant Long-Evans rats were exposed to heat stress (38-40°C, 2h daily), displacement conditions (overnight food/water restriction plus overcrowding), combined stressors, or control conditions from gestational days 15-20. Male offspring were assessed at postnatal days 10 (neonatal) and 30 (juvenile).

RESULTS

Heat exposure induced significant maternal hyperthermia (2.5-2.9°C elevation). Histological analysis revealed marked SCN cellular degeneration across stress groups at both developmental stages, characterised by reduced cell counts, pyknotic nuclei, and disrupted tissue architecture. Despite structural damage, juvenile behavioural testing revealed paradoxical outcomes: combined stress exposure reduced anxiety-like behaviour in the elevated plus maze, enhanced sociability in three-chamber testing, while preserving recognition memory. Growth analysis demonstrated preferential brain sparing despite reduced somatic growth, with significantly elevated brain-to-body weight ratios in stress-exposed animals.

CONCLUSION

These findings demonstrate that prenatal environmental stressors cause lasting SCN damage but trigger adaptive behavioural responses. The dissociation between structural vulnerability and functional adaptation suggests complex neurodevelopmental programming with implications for populations experiencing heat exposure and displacement adversity.