TrkB receptor agonist 7, 8 dihydroxyflavone triggers profound gender- dependent neuroprotection in mice after perinatal hypoxia and ischemia.

In this study, we investigated the effects of a bioactive high-affinity TrkB receptor agonist 7,8- dihydroxyflavone (7,8 DHF) on neonatal brain injury in female and male mice after hypoxia ischemia (HI). HI was induced by exposure of postnatal day 9 (P9) mice to 10% O2 for 50 minutes at 37°C after unilateral ligation of the left common carotid artery. Animals were randomly assigned to HI-vehicle control group [phosphate buffered saline (PBS), intraperitoneally (i.p.)] or HI + 7,8 DHF-treated groups (5 mg/kg in PBS, i.p at 10 min, 24 h, or with subsequent daily injections up to 7 days after HI). The HI-vehicle control mice exhibited neuronal degeneration in the ipsilateral hippocampus and cortex with increased Fluoro-Jade C positive staining and loss of microtubule associated protein 2 expression. In contrast, the 7,8 DHF-treated mice showed less hippocampal neurodegeneration and astrogliosis, with more profound effects in female than in male mice. Moreover, 7,8 DHF-treated mice improved motor learning and spatial learning at P30-60 compared to the HI-vehicle control mice. Diffusion tensor imaging of ex vivo brain tissues at P90 after HI revealed less reduction of fractional anisotropy values in the ipsilateral corpus callosum of 7,8 DHF-treated brains, which was accompanied with better preserved myelin basic protein expression and CA1 hippocampal structure. Taken together, these findings strongly suggest that TrkB agonist 7,8 DHF is protective against HI-mediated hippocampal neuronal death, white matter injury, and improves neurological function, with a more profound response in female than in male mice.

Chronic neurological deficits in mice after perinatal hypoxia and ischemia correlate with hemispheric tissue loss and white matter injury detected by MRI.

We investigated the effects of perinatal hypoxia-ischemia (HI) on brain injury and neurological functional outcome at postnatal day (P)30 through P90. HI was induced by exposing P9 mice to 8% O(2) for 55 min using the Vannucci HI model. Following HI, mice were treated with either vehicle control or Na(+)/H(+) exchanger isoform 1 (NHE1) inhibitor HOE 642. The animals were examined by the accelerating rotarod test at P30 and the Morris water maze (MWM) test at P60. T(2)-weighted MRI was conducted at P90. Diffusion tensor imaging (DTI) was subsequently performed in ex vivo brains, followed by immunohistochemical staining for changes in myelin basic protein (MBP) and neurofilament protein expression in the corpus callosum (CC). Animals at P30 after HI showed deficits in motor and spatial learning. T(2) MRI detected a wide spectrum of brain injury in these animals. A positive linear correlation was observed between learning deficits and the degree of tissue loss in the ipsilateral hemisphere and hippocampus. Additionally, CC DTI fractional anisotropy (FA) values correlated with MBP expression. Both FA and MBP values correlated with performance on the MWM test. HOE 642-treated mice exhibited improved spatial learning and memory, and less white matter injury in the CC. These findings suggest that HI-induced cerebral atrophy and CC injury contribute to the development of deficits in learning and memory, and that inhibition of NHE1 is neuroprotective in part by reducing white matter injury. T(2)-weighted MRI and DTI are useful indicators of functional outcome after perinatal HI.