Time Course of Astrocyte Activation in Mouse Nucleus Tractus Solitarius During Exposure to Hypoxia

Abstract

Chronic sustained hypoxia (CH) occurs in populations living at high altitude and in patients with chronic pulmonary disease. Exposure to CH produces ventilatory acclimatization to hypoxia (VAH) and increases the hypoxic ventilatory response (HVR) by mechanisms that involve areas of the brainstem that control breathing. The nucleus tractus solitarius (NTS) is a sensory integrative center in the medulla receiving carotid body afferents and known to be crucial for VAH. Our previous results demonstrated that glia cells in the rat NTS contribute to VAH but these mechanisms have not been studied in mice exposed to CH beyond 24 hours. We hypothesized that CH produces an early transient activation of astrocytes and microglia in the mouse brainstem as observed in rats. To study the activation of glial cells with CH, we exposed mice to normobaric hypoxia (10% FiO2) for 0.5, 1 and 4 hours and 1 and 7 days. Mice were perfused with 4% paraformaldehyde and brainstem sections were obtained. We quantified astrocyte activation by measuring glial fibrillary acidic protein (GFAP) intensity with immunofluorescence, and microglial activation by measuring branch morphology using Iba‐1 marker. Exposure to CH significantly increased GFAP intensity after 30 minutes and 1day while microglia morphology did not change significantly. The results differ from those in rats (J. Neurophysiol.117: 1625–1635, 2017) and suggest that time‐dependent astrocyte activation in the NTS may contribute to VAH.Support or Funding InformationSupported by NIH RO1 HL‐081823