Reduced neurosteroid potentiation of GABAA receptors in epilepsy and depolarized hippocampal neurons. Issue 4 (3rd April 2020)

• Record Type: Journal Article
• Authors: Joshi, Suchitra; Roden, William H.; Kapur, Jaideep; Jansen, Laura A.
• Is Part Of: Annals of clinical and translational neurology. Volume 7:Issue 4(2020)
• Page Start: 527
• Page End: 542
• Publication Date: 2020-04-03
• Subjects: Nervous system -- Diseases -- Periodicals; Neurology -- Periodicals; 616.8005
• DOI: 10.1002/acn3.51023
• Languages: English
• ISSNs: 2328-9503

Abstract

Abstract: Objective: Neurosteroids regulate neuronal excitability by potentiating γ ‐aminobutyric acid type‐A receptors (GABARs). In animal models of temporal lobe epilepsy, the neurosteroid sensitivity of GABARs is diminished and GABAR subunit composition is altered. We tested whether similar changes occur in patients with epilepsy and if depolarization‐induced increases in neuronal activity can replicate this effect. Methods: We determined GABAR α 4 subunit expression in cortical tissue resected from pediatric epilepsy patients. Modulation of human GABARs by allopregnanolone and Ro15‐4513 was measured in Xenopus oocytes using whole‐cell patch clamp. To extend the findings obtained using tissue from epilepsy patients, we evaluated GABAR expression and modulation by allopregnanolone and Ro15‐4513 in cultured rat hippocampal neurons exposed to high extracellular potassium (HK) to increase neuronal activity. Results: Expression of α4 subunits was increased in pediatric cortical epilepsy specimens encompassing multiple pathologies. The potentiation of GABA‐evoked currents by the neurosteroid allopregnanolone was decreased in Xenopus oocytes expressing GABARs isolated from epilepsy patients. Furthermore, receptors isolated from epilepsy but not control tissue were sensitive to potentiation by Ro15‐4513, indicating higher expression of α 4 β x γ 2 subunit‐containing receptors. Correspondingly, increasing the activity of cultured rat hippocampal neurons reduced allopregnanolone potentiation of miniature inhibitory postsynaptic currents (mIPSCs), increased modulation of tonic GABAR current by Ro15‐4513, upregulated the surface expression of α 4 and γ 2 subunits, and increased the colocalization of α 4 and γ 2 subunit immunoreactivity. Interpretation: These findings suggest that seizure activity‐induced upregulation of α 4 β x γ 2 subunit‐containing GABARs could affect the anticonvulsant actions of neurosteroids.