Stroke and hypoxia frequently cause seizures or myoclonus, disorders of excessive neuronal excitability. Hypoxia-induced hyperexcitability is linked to dysfunction of inhibitory GABAA receptors (GABAARs), but the underlying mechanisms are poorly understood. GABAARs are chloride channels activated by gamma-aminobutyric acid (GABA), composed of subunits that determine their pharmacology and kinetic properties. We have studied the effects of hypoxia on GABAAR function and subunit mRNA expression in NT2-N neuronal cells and primary cortical neurons in vitro. Maximal GABA-evoked currents increased 1 h after transient hypoxia but then decreased to 60% of control after 48 h, associated with reductions in alpha-1, alpha-5, beta-2 and gamma-2 subunit mRNAs. These changes are associated with induction of the bHLH transcription factor, hypoxia-inducible factor-1alpha (HIF1a) and calcium entry via voltage-gated channels opened by hypoxia-induced depolarizaton. Our long-term goal is to understand the mechanisms of hypoxia-induced GABAAR neuroplasticity, with these specific aims: 1. Determine the mechanisms underlying the early increase in GABAAR current after hypoxia. Hypothesis 1 is that the initial increase in GABAAR current is related to increased GABAAR channel density or phosphorylation. We will use whole-cell, perforated patch and single channel recordings to measure GABAAR currents, pharmacology, and single channel properties of post-hypoxic GABAAR currents. 2. Determine whether transcriptional changes account for the late reduction in GABAAR currents. Hypothesis 2 is that the reduction in GABAAR currents 48 h after hypoxia is related to altered GABAAR subunit transcription, and that specific subunit changes account for altered GABAAR pharmacology. We will use whole-cell recordings and RT-PCR to assess changes in GABAAR pharmacology and subunit expression. 3. Determine whether HIF-1a is involved in altered GABAAR subunit expression. Hypothesis 3 is that hypoxic induction of HIF-1a participates in regulating GABAAR subunit expression in concert with other signaling mechanisms. We will determine a. whether hypoxia alters HIF-1a expression, b. whether elevated HIF-1a reproduces hypoxia-related GABAR changes, and c. whether voltage-gated calcium channels mediate GABAAR regulation. These studies implicate a novel mechanism underlying post- hypoxic hyperexcitability, and could result in new treatments for post-hypoxic seizures and myoclonus. ? ? ?
| Greenfield Jr, L John (2013) Molecular mechanisms of antiseizure drug activity at GABAA receptors. Seizure 22:589-600 |
| He, Zhen; Ferguson, Sherry A; Cui, Li et al. (2013) Role of neural stem cell activity in postweaning development of the sexually dimorphic nucleus of the preoptic area in rats. PLoS One 8:e54927 |
| He, Zhen; He, Bei; Behrle, Brian L et al. (2012) Ischemia-induced increase in microvascular phosphodiesterase 4D expression in rat hippocampus associated with blood brain barrier permeability: effect of age. ACS Chem Neurosci 3:428-32 |
| Xiang, Kun; Earl, Damien; Dwyer, Trisha et al. (2012) Hypoxia enhances high-voltage-activated calcium currents in rat primary cortical neurons via calcineurin. Epilepsy Res 99:293-305 |
| Wang, Liping; Greenfield Jr, L John (2009) Post-hypoxic changes in rat cortical neuron GABA A receptor function require L-type voltage-gated calcium channel activation. Neuropharmacology 56:198-207 |
