GFAP and Hyponatremia: The water overload on RIH induced hypotonic hyponatremia, progressively decreased ADC values in the whole brain (less pronounced than in controls), and increased GFAP and MBP's expression in the white matter (similar increase found in controls).<h4>Conclusion</h4>RIH is a novel animal model that suggests there can be significant water retention after only a few hours of hyponatremia a day provided this situation is repeated over time.