Hippocampal developmental vulnerability to methylmercury extends into prepubescence.

Area of Science:

• Neuroscience
• Toxicology
• Developmental Biology

Background:

• The developing brain is susceptible to environmental toxicants like methylmercury (MeHg).
• Prenatal MeHg exposure is linked to cognitive deficits in children, potentially due to hippocampal dysfunction.
• The specific vulnerable cell populations and developmental periods to MeHg remain unclear.

Purpose of the Study:

• To investigate the long-term effects of early methylmercury exposure on hippocampal neurogenesis.
• To define the developmental window of vulnerability to MeHg in the rat brain.
• To explore the mechanisms underlying age-dependent MeHg neurotoxicity.

Main Methods:

• Postnatal day 7 (P7) rat model for third-trimester human gestation.
• Assessed neurogenesis markers (BrdU, Tbr2+, Doublecortin, Sox2+) at different ages (P7, P14, P21).
• Measured mercury levels in the hippocampus to evaluate blood-brain barrier transfer.

Main Results:

• P7 MeHg exposure led to long-term reductions in adolescent neurogenesis and stem cell populations.
• Higher MeHg exposure at P14 significantly reduced neural stem cells (Sox2+) and mitotic cells (BrdU+).
• MeHg levels in the hippocampus were similar at P14 and P21, indicating age-dependent vulnerability is tissue-based.

Conclusions:

• Methylmercury vulnerability in the developing brain decreases with age.
• Early-life MeHg exposure can impair later neurogenesis and cognitive development.
• Targeted interventions during critical developmental windows may mitigate MeHg's neurotoxic effects.