Streptozotocin-induced diabetes modulates GABA receptor activity of rat retinal neurons
Introduction
Diabetic retinopathy is a common complication of diabetes and is a leading cause of blindness in the United States (EDIC, 1999). Although diabetic retinopathy is typically diagnosed by abnormalities in the retinal microvasculature after prolonged hyperglycemia, there is well-documented evidence to indicate that neural deficits occur early in the course of the disease (see Fletcher et al., 2005; Barber, 2003 for review). Particularly relevant to this study is that diabetes alters the GABA signaling pathway of the inner retina. For example, electroretinographic recordings from diabetic patients often exhibit reductions in the amplitude and implicit time of the oscillatory potentials (Tzekov and Arden, 1999), a GABA-sensitive component of the flash ERG (Wachtmeister, 1998, Tzekov and Arden, 1999, Wachtmeister, 2001). An altered GABA inhibitory signal in the diabetic retina is also supported by evidence of disrupted processing of lateral inhibition (Davies and Morland, 2002), and the fact that GABA levels are elevated in the vitreous of patients with proliferative diabetic retinopathy (Ambati et al., 1997).
Studies of diabetic animal models also reveal aberrations in GABA activity. Changes in the content and localization of GABA are evident in the diabetic retina, with both amacrine and Müller cells accumulating high concentration of GABA (Ishikawa et al., 1996a, Ishikawa et al., 1996b, Takeo-Goto et al., 2002). In addition, the activities of metabolic enzymes for GABA are also modified (Ishikawa et al., 1996a, Vilchis and Salceda, 1996, Honda et al., 1998), and the diabetic rat retina exhibits an enhanced capacity to transport GABA (Vilchis and Salceda, 1996). However, despite the substantial evidence indicating that GABA signaling within the inner retina is affected in diabetes, there is little information about the activity of GABA receptors in response to hyperglycemia.
In a previous study (Ramsey et al., 2006), we established a streptozotocin-induced diabetes model in pigmented (Long Evans) rats, and characterized the global changes in neuronal activity in the retina by means of electroretinography. The results indicated that pathways mediating inhibitory signaling in the inner retina are affected by the disease. In addition, our results provided preliminary evidence that the GABA responses of rod-bipolar cells were altered in diabetes. In the present study, we investigated the modulatory effects of hyperglycemia on the GABAC receptors present on retinal neurons, with a focus on the GABAC receptor activity of rod-driven bipolar cells. The GABAC receptors on retinal bipolar cells have a simple molecular composition that primarily consists of GABA ρ1 and ρ2 subunits (Qian and Ripps, 2001, Zhang et al., 2001). These receptors are expressed predominately on the axon terminals of retinal bipolar cells to control signal outflow from the second order neuron in the retina. Patch-clamp recordings from isolated retinal neurons revealed a number of changes in GABAC receptor activity in the diabetic retina; in particular, an enhanced sensitivity to GABA, slower response kinetics, and a smaller single channel conductance. These results, and those obtained by real time RT-PCR, suggest that hyperglycemia affects the GABA ρ subunit composition of GABAC receptors on retinal neurons.
Section snippets
Materials and methods
All experimental procedures conformed to the statement on animal care of the Association for Research in Vision and Ophthalmology, and adhered to the guidelines for the Care and Use of Laboratory Animals formulated by the Animal Committee of the University of Illinois, College of Medicine.
GABA-mediated responses of bipolar cells
To extend our previous observations on the diabetic modification of the GABAC receptor activity on retinal bipolar cells (Ramsey et al., 2006), we examined the property of GABA-elicited responses from retinal bipolar cells derived from STZ-induced diabetic and normal rats. Rod bipolar cells in the rat retina display a characteristic morphology, i.e., a rounded cell body from which extends several dendrites and a long axon that terminates in a prominent expansion (Fig. 1A). In agreement with
Discussion
GABAC receptors are prominently expressed in the vertebrate retina, and they constitute the majority of the GABA receptor population on rod bipolar cells in the rat retina (Feigenspan et al., 1993, Euler and Wassle, 1998, Lukasiewicz et al., 2004). The GABAC receptors are thought to be formed by GABA ρ subunits, and each of the three ρ subunits cloned thus far is expressed in retina (Zhang et al., 1995, Ogurusu and Shingai, 1996). The GABA ρ1 and ρ2 subunits have been detected on bipolar cells,
Acknowledgments
The authors would like to thank Dr Ralph Enz for a generous gift of the GABAC receptor antibody, Dr Stuart Lipton for providing rat GABA ρ1 and ρ2 subunits and Ms Ruth Zelkha for her expert assistance with imaging and fluorescence analysis. This work was supported by grants from the National Eye Institute (EY-12028, EY-06516, and EY-01792), an unrestricted departmental award from Research To Prevent Blindness (RPB) to the Department of Ophthalmology and Visual Sciences, and a Medical Student
References (55)
A new view of diabetic retinopathy: a neurodegenerative disease of the eye
Prog. Neuropsychopharmacol. Biol. Psychiatry
(2003)- et al.
Regional variations in NMDA receptor downregulation in streptozotocin-diabetic rat brain
Brain Res.
(2006) - et al.
ZIP3, a new splice variant of the PKC-ζ-interacting protein family, binds to GABAC receptors, PKC-ζ, and Kvβ2
J. Biol. Chem.
(2003) - et al.
Increase of cannabinoid CB(1) receptor density in the hippocampus of streptozotocin-induced diabetic rats
Exp. Neurol
(2007) - et al.
Synaptic transmission changes in the pyramidal cells of the hippocampus in streptozotocin-induced diabetes mellitus in rats
Brain Res.
(2006) - et al.
Retinal glutamate in diabetes and effect of antioxidants
Neurochem. Int
(2001) - et al.
GABAC receptor-mediated inhibition in the retina
Vis. Res.
(2004) - et al.
Expression of glutamate receptors and calcium-binding proteins in the retina of streptozotocin-induced diabetic rats
Brain Res.
(2004) - et al.
Cloning of a putative gamma-aminobutyric acid (GABA) receptor subunit rho 3 cDNA
Biochim. Biophys. Acta
(1996) - et al.
The GABAC receptors of retinal neurons
Co-assembly of GABA ρ subunits with the GABAA receptor γ2 subunit cloned from white perch retina. Brain Res
Mol. Brain Res.
High glucose and diabetes increase the release of [3H]-D-aspartate in retinal cell cultures and in rat retinas
Neurochem. Int
The GABA ρ1 subunit interacts with a cellular retinoic acid binding protein in mammalian retina
Neuroscience
The electroretinogram in diabetic retinopathy
Surv. Ophthalmol
Oscillatory potentials in the retina: what do they reveal
Prog. Retin. Eye Res.
Some aspects of the oscillatory response of the retina
Prog. Brain Res.
Structure and function of GABAC receptors: a comparison of native versus recombinant receptors
Trends Pharmacol. Sci.
A single amino acid in the second transmembrane domain of GABA rho receptors regulates channel conductance
Neurosci. Lett.
Functional characterization of rat ρ2 subunits expressed in HEK 293 cells
Eur. J. Neurosci
Enhancement of L-type Ca(2+) current from neonatal mouse ventricular myocytes by constitutively active PKC-betaII
Am. J. Physiol. Cell Physiol
Elevated gamma-aminobutyric acid, glutamate, and vascular endothelial growth factor levels in the vitreous of patients with proliferative diabetic retinopathy
Arch. Ophthalmol
Biochemistry and molecular cell biology of diabetic complications
Nature
Channel opening locks agonist onto the GABAC receptor
Nat. Neurosci
The Hermann-Hering grid illusion demonstrates disruption of lateral inhibition processing in diabetes mellitus
Br. J. Ophthalmol
Risk factors for high-risk proliferative diabetic retinopathy and severe visual loss: Early Treatment Diabetic Retinopathy Study Report #18
Invest. Ophthalmol. Vis. Sci.
Epidemiology of Diabetes Interventions and Complications (EDIC). Design, implementation, and preliminary results of a long-term follow-up of the Diabetes Control and Complications Trial cohort
Diabetes Care
GABAC receptor ρ subunits are heterogeneously expressed in the human CNS and form homo- and heterooligomers with distinct physical properties
Eur. J. Neurosci
Cited by (38)
Design and synthesis of new benzylidene-quinazolinone hybrids as potential anti-diabetic agents: In vitro α-glucosidase inhibition, and docking studies
2022, Journal of Molecular StructureCitation Excerpt :Found: C, 62.68; H, 4.36; N, 12.23%. Anti-hyperglycemic activity evaluation of the title compounds was determined in vivo using STZ induced hyperglycemic rats according to biological method described by Ramsey et al. [34]. ( Supplementary data)
Design, synthesis, molecular modeling and anti-hyperglycemic evaluation of phthalimide-sulfonylurea hybrids as PPARγ and SUR agonists
2019, Bioorganic ChemistryCitation Excerpt :They were kept in clean and dry cages and maintained in well-ventilated animal house with 12 h light-12 h dark cycle. A freshly prepared solution of streptozotocin (STZ) dissolved in 0.1 M sodium citrate buffer (pH 4.5) just before use and injected intraperitoneally in a dose of 55 mg/kg body weight to overnight fastening rats [36]. Control animals (n = 6) received an equivalent volume of citrate buffer.
Neurodegeneration in diabetic retinopathy: Potential for novel therapies
2017, Vision ResearchDesign, synthesis, molecular modeling and anti-hyperglycemic evaluation of quinazolin-4(3H)-one derivatives as potential PPARγ and SUR agonists
2017, Bioorganic and Medicinal ChemistryCitation Excerpt :For C22H24BrN5O5S (549.07): C, 48.01; H, 4.40; N, 12.72; Found: C, 48.23; H, 4.49; N, 12.97%. Anti-hyperglycemic activity evaluation of the title compounds was determined in vivo using STZ induced hyperglycemic rats according to biological method described by Ramsey et al.39 as follows. Swiss albino adult male rats, weighing 200–300 g, were used as test animals, conducted with approval from the Ethics Committee (approval#23PD/3/12/8R) of Al-Azhar University, Nasr City, Cairo, Egypt.