Altered astrocyte-neuronal interactions after hypoxia-ischemia in the neonatal brain in female and male rats

Abstract

BACKGROUND AND PURPOSE: Increased susceptibility to excitotoxicity of the neonatal brain after hypoxia-ischemia (HI) may be caused by limited capacity of astrocytes for glutamate uptake, and mitochondrial failure probably plays a key role in the delayed injury cascade. Male infants have poorer outcome than females after HI, possibly linked to differential intermediary metabolism. METHODS: [1-(13)C]glucose and [1,2-(13)C]acetate were injected at zero, 6, and 48 hours after unilateral HI in 7-day-old rats. Intermediary metabolism was analyzed with magnetic resonance spectroscopy. RESULTS: Mitochondrial metabolism was generally reduced in the ipsilateral hemisphere for ≤6 hours after HI, whereas contralaterally, it was reduced in neurons but not in astrocytes. Transfer of glutamate from neurons to astrocytes was increased in the contralateral, but not in the ipsilateral hemisphere at 0 hour, and reduced bilaterally at 6 hours after HI. The transfer of glutamine from astrocytes to glutamatergic neurons was unaltered in both hemispheres, whereas the transfer of glutamine to GABAergic neurons was increased ipsilaterally at 0 hour. Anaplerosis (astrocytes) was decreased, whereas partial pyruvate recycling (astrocytes) was increased directly after HI. Male pups had lower astrocytic mitochondrial metabolism than females immediately after HI, whereas that of females was reduced longer and encompassed both neurons and astrocytes. CONCLUSIONS: The prolonged depression in mitochondrial metabolism indicates that mitochondria are vulnerable targets in the delayed injury after neonatal HI. The degree of astrocytic malfunction may be a valid indicator of outcome after hypoxic/HI brain injury and may be linked to the differential outcome in males and females.