Alpha7 nicotinic acetylcholine receptor agonist promotes retinal ganglion cell function via modulating GABAergic presynaptic activity in a chronic glaucomatous model

Abstract

Alpha-7 nicotinic acetylcholine receptor (α7-nAChR) agonists can prevent glutamate-induced excitotoxicity in cultured retinal ganglion cells (RGCs). However, the neuroprotective effects and the mechanism of action of PNU-282987, an α7-nAChR agonist, in a chronic in vivo rat glaucoma model are poorly understood. We found that elevated intraocular pressure (IOP) downregulated retinal α7-nAChR expression. Electroretinography revealed that the amplitude of the photopic negative response (PhNR) decreased in parallel with the loss of RGCs caused by elevated IOP. PNU-282987 enhanced RGC viability and function and decreased terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive signals in RGCs. Patch-clamp recordings revealed differences in the baseline frequencies and decay times of the miniature GABAergic inhibitory postsynaptic currents (mIPSCs) of RGCs between control and glaucomatous retinal slices. The results of western blotting and immunostaining showed that glutamic acid decarboxylase 65/67 and GABA deficits persisted in glaucomatous retinas and that these deficits were reversed by PNU-282987. Patch-clamp recordings also showed that PNU-282987 significantly increased the frequency and amplitude of the GABAergic mIPSCs of RGCs. The protective effects of PNU-292987 were blocked by intravitreal administration of selective GABAA receptor antagonists. The modulation of GABAergic synaptic transmission by PNU-282987 causes de-excitation of ganglion cell circuits and suppresses excitotoxic processes.

Activation of 5-HT1A Receptors Promotes Retinal Ganglion Cell Function by Inhibiting the cAMP-PKA Pathway to Modulate Presynaptic GABA Release in Chronic Glaucoma

“…Rat model of ocular hypertension. As described previously (Mittag et al, 2000;Wu et al, 2010;, episcleral veins located near the superior and inferior rectus muscles of the right eye were precisely isolated and cauterized. The left eye underwent a sham operation isolating the veins without cauterization.…”

“…Western blotting. Protein preparation and Western blotting were performed according to our previously described methods (Wu et al, 2010). Briefly, retinal lysates were centrifuged at 12,000 ϫ g for 10 min at 4°C.…”

“…Immunohistochemistry. Immunohistochemistry was performed as described previously (Wu et al, 2010). Briefly, 10-m-thick cryosections were fixed in 4% paraformaldehyde for 20 min at room temperature and then incubated in 0.1% Triton X-100/PBS for 20 min at 37°C, followed by incubation in 3% bovine serum albumin/PBS for 1 h at room temperature.…”

“…Communication between retinal neurons is dominated by the neurotransmitter-mediated chemical signaling (Yang, 2004) that occurs at the synaptic terminals in the outer and inner plexiform layers. Glutamate excitotoxicity leads to retinal degeneration in the pathogenesis of glaucoma and retinal ischemia (Ishikawa, 2013).…”

“…Glutamate excitotoxicity leads to retinal degeneration in the pathogenesis of glaucoma and retinal ischemia (Ishikawa, 2013). Clinically validated anticonvulsants, including valproic acid, tiagabine, and topiramate, can also prevent NMDA and glutamate-induced excitotoxic damage to neural ganglion cells in the inner retina (Yoneda et al, 2003;Pisani et al, 2006;Biermann et al, 2010;Kimura et al, 2015). Inhibitory signaling progresses via amacrine and horizontal cells and is primarily mediated by GABA.…”