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Long-Term Space Flights May Impede Learning & Memory in the Hippocampus

A recent study found that the Earth’s magnetic field plays an important role in neurogenesis, learning & memory mediated by the hippocampus.

Neurogenesis in the Hippocampus

The adult hippocampus continuously generates new neurons throughout life. These are then functionally integrated into hippocampal circuits and contribute to memory and learning. However, this process of adult neurogenesis has been shown to be strongly influenced by physiological conditions and environmental factors. 

A Hypomagnetic Field (HMF)

Living on Earth, we are exposed to the Earth’s geomagnetic field. Many organisms use the field for orientation and long distance navigation. However, we can also be exposed to a hypomagnetic field (HMF) in some artificial environments, such as during long-term deep space flights.

This HMF may trigger central nervous system dysfunction-like behaviours. In fact, previous studies have demonstrated nervousness and stress-induced analgesia reduction in adult mice, amnesia in chickens and impairments of cognitive processes in humans. However, these previous studies were mostly based on behavioural analyses, thus the underlying mechanisms are still elusive. 

The Mechanistic Impact on the Hippocampus

A recent study sought to determine whether and how HMF exposure affects adult hippocampal neurogenesis and cognition. They found that long-term HMF exposure impaired neurogenesis through decreasing adult neural stem/progenitor cells (aNSCs) proliferation. It also altered cell lineage in crucial development stages of neurogenesis and impeded dendritic development of new-born neurons.

Mechanistically, a gene ontology analysis revealed that genes related to cellular response to reactive oxygen species (ROS), ROS metabolic processes and cellular response to hypoxia were downregulated following HMF exposure. Similarly, a differential gene expression analysis revealed that stem cells of HMF mice expressed lower levels of ROS synthesis and metabolism related genes. 

The Role of Reactive Oxygen Species (ROS)

Proliferative, self renewing neural stem cells need to maintain high ROS levels. ROS generation and oxidative stress have previously been shown to regulate the behaviour of neural stem cells to ensure proper neurogenesis in the mammalian brain. This study suggests that exposure to HMF disrupts this process. Low ROS levels are also known to impair learning and memory, cell proliferation and migration. 

Encouragingly, these deficits were reversible by returning mice back to GMF, which was accompanied by increased ROS levels. Furthermore, inhibition of ROS depleting enzymes increased ROS levels in HMF mice back to their natural levels and rescued any defects in learning and memory. Their results suggest the Earth’s magnetic field plays an important role in neurogenesis, learning and memory. With our growing advances in space exploration, these factors may need deeper investigation.

Image Credit: Pixabay


More on these topics

Gene Ontology / Hippocampus / Learning / Memory / Space