Brimonidine enhances inhibitory postsynaptic activity of OFF- and ON-type retinal ganglion cells in a Wistar rat chronic glaucoma model

Xujiao Zhou; Ting Zhang; Jihong Wu

doi:10.1016/j.exer.2019.107833

Brimonidine enhances inhibitory postsynaptic activity of OFF- and ON-type retinal ganglion cells in a Wistar rat chronic glaucoma model

Exp Eye Res. 2019 Dec:189:107833. doi: 10.1016/j.exer.2019.107833. Epub 2019 Oct 13.

Authors

Xujiao Zhou¹, Ting Zhang², Jihong Wu³

Affiliations

¹ Eye Institute, Eye & ENT Hospital, State Key Laboratory of Medical Neurobiology, Institutes of Brain Science and Collaborative Innovation Center for Brain Science, Shanghai Medical College, Fudan University, Shanghai, 200032, China; Shanghai Key Laboratory of Visual Impairment and Restoration, Shanghai, 200032, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences (Fudan University), Shanghai, 200032, China. Electronic address: xujiaozhou@126.com.
² Shanghai Key Laboratory of Visual Impairment and Restoration, Shanghai, 200032, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences (Fudan University), Shanghai, 200032, China; Research Center, Eye & ENT Hospital, Fudan University, Shanghai, 200032, China. Electronic address: tee_eent@foxmail.com.
³ Eye Institute, Eye & ENT Hospital, State Key Laboratory of Medical Neurobiology, Institutes of Brain Science and Collaborative Innovation Center for Brain Science, Shanghai Medical College, Fudan University, Shanghai, 200032, China; Shanghai Key Laboratory of Visual Impairment and Restoration, Shanghai, 200032, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences (Fudan University), Shanghai, 200032, China; Department of Ophthalmology and Vision Science, Eye & ENT Hospital, Fudan University, Shanghai, 200032, China. Electronic address: jihongwu@fudan.edu.cn.

PMID: 31618613
DOI: 10.1016/j.exer.2019.107833

Abstract

Glaucoma is a multifactorial disease in which retinal ganglion cells (RGCs) undergo excitotoxic damage, leading to their degeneration. The α2-adrenoceptor (α2-AR) agonist brimonidine exerts a neuroprotective effect by regulating postsynaptic excitatory N-methyl-D-aspartate (NMDA) receptor activity in RGCs. However, researchers have not clearly determined whether or how brimonidine regulates inhibitory synaptic transmission in rat models of chronic glaucoma. Whole-cell voltage-clamp and current-clamp recordings were performed in ON- and OFF-type RGCs in retinal slices. Brimonidine directly and acutely enhanced γ-aminobutyric acidergic (GABAergic) transmission mediated by ionotropic GABA_A receptors in ON- and OFF-type RGCs in rat retinal slices; this effect occurred at the synaptic terminals and was independent of action potentials and multi-synaptic connections. The highly selective α2-AR antagonist yohimbine blocked the effects of brimonidine. Regarding the postsynaptic GABA receptor sensitivity, brimonidine also increased the amplitude of the GABA-induced current. Additionally, compared to RGCs from the control group, the frequencies and amplitudes of spontaneous excitatory postsynaptic currents (sEPSCs) and miniature excitatory postsynaptic currents (mEPSCs) did not change after brimonidine gravity perfusion. Brimonidine significantly decreased the spontaneous firing frequency of rat RGCs with intact synaptic inputs and decreased the resting membrane potential of RGCs, changes that were blocked by the highly selective GABA_A receptor antagonist SR95531. SR95531 alone increased spontaneous action potentials and the resting membrane potential. Based on these findings, an α2-AR agonist facilitated the frequency of the GABAergic inhibitory postsynaptic currents (IPSCs), directly increased the amplitude of the postsynaptic GABA-induced current (GABA receptor reactivity/sensitivity), suppressed the firing frequency of spontaneous action in RGCs with intact synaptic inputs and decreased the resting membrane potential of RGCs, thus deactivating RGCs from the neural network level and reducing the excitotoxic damage occurring during the pathological process of chronic glaucoma.

Keywords: Brimonidine; Chronic glaucoma; GABA release; Neuroprotection; Retinal ganglion cells.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adrenergic alpha-2 Receptor Agonists / pharmacology
Animals
Brimonidine Tartrate / pharmacology*
Chronic Disease
Disease Models, Animal
Excitatory Postsynaptic Potentials
Glaucoma / drug therapy*
Glaucoma / metabolism
Glaucoma / physiopathology
Intraocular Pressure / drug effects*
Intraocular Pressure / physiology
Male
Membrane Potentials / drug effects*
Membrane Potentials / physiology
Patch-Clamp Techniques
Presynaptic Terminals
Rats
Rats, Wistar
Retinal Ganglion Cells / drug effects
Retinal Ganglion Cells / metabolism*
Retinal Ganglion Cells / pathology
Synaptic Transmission

Substances

Adrenergic alpha-2 Receptor Agonists
Brimonidine Tartrate