Sun-Sook Paik

Anthocyanins from the seed coat of black soybean reduce retinal degeneration induced by N-methyl-N-nitrosourea☆

Anthocyanins are known to have antioxidant effects and thus may play an important role in preventing various degenerative diseases. In this study, we examined the effect of anthocyanins extracted from the seed coat of black soybean on an animal model of retinal degeneration (RD), a leading cause of photoreceptor cell death resulting in blindness. RD was induced in rats by an intraperitoneal injection of N-methyl-N-nitrosourea (MNU) (50mg/kg), a DNA-methylating agent that causes photoreceptor damage. Anthocyanins extracted from black soybean seed coat (50mg/kg) were daily administered, orally, for 1, 2, and 4 weeks after MNU injection. Electroretinographic (ERG) recordings and morphological analyses were performed. In control rats with MNU-induced retinal damage, the ERG recordings showed a gradual significant time-dependent reduction in both a- and b-wave amplitudes compared with those of normal animals. In the MNU-induced RD rats given anthocyanins for 4 weeks, ERG responses were significantly increased compared with untreated RD rats, more apparently in scotopic stimulation than in the photopic condition. However, in the MNU-injected rats given anthocyanins for 1 and 2 weeks, the increase in ERG responses was not significant. Morphologically, the outer nuclear layer, where photoreceptors reside, was well preserved in the anthocyanin-treated rat retinas throughout the experimental period. In addition, retinal injury, evaluated by immunolabeling with an antibody against glial fibrillary acidic protein, was markedly reduced in anthocyanin-treated retinas. These results demonstrate that anthocyanins extracted from black soybean seeds can protect retinal neurons from MNU-induced structural and functional damages, suggesting that anthocyanins from black soybean seed coat may be used as a useful supplement to modulate RD.

Cyanidin-3-glucoside Extracted from Mulberry Fruit Can Reduce N-methyl-N-nitrosourea-Induced Retinal Degeneration in Rats

Abstract Purpose: To investigate the effect of cyanidin-3-O-glucoside (C3G) on a rat retinal degeneration (RD) model. Materials and methods: Experimental RD was induced in rats by the intraperitoneal injection of N-methyl-N-nitrosourea (MNU) at 50 mg/kg. C3G extracted from mulberry (Morus alba L.) fruit (50 mg/kg) was orally administered, daily for 1, 2 and 4 weeks after MNU injection. The effects of C3G administration on MNU-induced RD retinas were histologically and functionally assessed by hematoxylin and eosin staining and electroretinography (ERG), respectively. The degree of retinal injury in C3G-administered RD rats was evaluated by immunohistochemistry with an antibody against glial fibrillary acidic protein (GFAP). The preferential protective effect of C3G on scotopic vision was examined by western blot analysis. Results: Marked loss of photoreceptors in the outer nuclear layer (ONL) was observed in RD rats at 2 and 4 weeks after MNU injection, while the ONL in the MNU-induced RD rats given C3G was relatively well preserved. Immunohistochemistry with anti-GFAP showed that retinal injury was also reduced in the retinas of the rats given C3G. Functional assessment by using ERG recordings showed that scotopic ERG responses were significantly increased in RD rats given C3G for 4 weeks (p < 0.01) compared with that of untreated RD rats. In the RD rats given short-term C3G (for 1 and 2 weeks), the increase in ERG responses was not significant. In addition, western blot analysis showed that rhodopsin level in the C3G-administered RD retinas significantly increased compared to that in the non-administered RD retinas (p < 0.05), whereas red/green opsin level did not show any significant difference. Conclusions: Long-term administration of C3G extracted from mulberry fruit could structurally reduce photoreceptor damage and functionally improve scotopic visual functions in the RD rat model induced by MNU.

Run-up of γ-aminobutyric acidC responses in catfish retinal cone-horizontal cell axon-terminals is modulated by protein kinase A and C

Using whole-cell voltage-clamp techniques, we investigated the protein kinase modulation of gamma-aminobutyric acid(C) (GABA(C))-activated currents relating to run-up regulation in dissociated cone-horizontal cell (HC) axon-terminals from catfish retina. GABA induced an inward chloride current in cells voltage-clamped at -70 mV. With repetitive applications of 10 microM GABA, the peaks of the GABA responses increased up to approximately 135% of the control responses during a period of 10 min. Intracellular application of forskolin, an adenylate cyclase activator, decreased the run-up of GABA(C) responses. H8 dihydrochloride, a cAMP inhibitor, enhanced this run-up to 190% of the control responses. 1-oleoyl-2-acetyl-sn-glycerol, a protein kinase C activator, accelerated the run-up of GABA(C) responses. GF 109203X, a PKC inhibitor, decreased the run-up. These results suggest that retinal GABA(C) responses in cone-HC axon-terminals are modulated by both protein kinase A and C.

GABA receptors on horizontal cells in the goldfish retina

We investigated the localization of GABA(A) and GABA(C) receptors in horizontal cells (HCs) and HC axon terminals (ATs) dissociated from goldfish retina, using whole-cell patch-clamping recordings. Applications of GABA on HCs induced two groups with inward currents at the holding potential of -50 mV: One was a sustained inward current in the H1 cell, with one type of HCAT (AT1), and the other was a transient inward current in other HC soma and HCAT (AT2). Co-application of GABA with bicuculline or SR95531, GABA(A) receptor antagonists, showed a non-blocking effect in the sustained current, but a blocking effect in the transient current. The sustained current was evoked by cis-4-aminocrotonic acid (CACA), a GABA(C) receptor agonist, while the transient current was not induced by CACA, but mimicked by muscimol, a GABA(A) receptor agonist. Both the sustained and transient currents were completely blocked by picrotoxin and not mimicked by baclofen, a GABA(B) receptor agonist. Thus H1 cell and AT1 have GABA(C) receptors, while H2, H3 cells and AT2 have GABA(A) receptors.

The GABAC receptor is present in cone-horizontal cell axon terminals isolated from catfish retina

Whole cell voltage-clamp recordings were performed on isolated terminals and somata from catfish retina to compare the distribution of excitatory and inhibitory receptors in both structures. Saturating concentrations of glutamate or kainate produced small currents in axon terminals, averaging less than 8% of the current evoked in the soma. In contrast, application of high concentrations of gamma-aminobutyric acid (GABA) produced approximately similar current amplitudes in both structures. Based on estimates of membrane surface area, GABA-induced current densities were around 0.05 pA/microm2 for both structures. The GABA-activated current in the axon terminal was not blocked by bicuculline or SR95531, but was completely inhibited by picrotoxin. Baclofen did not mimic the GABA effect, but trans-4-aminocrotonic acid (TACA, 300 microM) and muscimol (1 mM) elicited currents of 100 and 40 pA, respectively. These results suggest that the axon terminals of cone-horizontal cells possess GABA(C) receptors at a high density, do not possess GABA(A) or GABA(B) receptors, and have few glutamate receptors. The GABA(C) receptors could function as postsynaptic receptors in the inner plexiform layer or as autoreceptors.

Neuroprotective effect of NecroX-5 against retinal degeneration in rodents.

NecroX-5 is a derivative of cyclopentylamino carboxymethylthiazolylindole (NecroX), an inhibitor of necrosis/necroptosis. NecroX-5 has been shown to scavenge mitochondrial reactive oxygen and nitrogen species, and thus preventing necrotic cell death against various kinds of oxidative stress in several tissues, including the brain. To examine the effect of NecroX-5 on retinal degeneration (RD), RD was induced in Sprague–Dawley rats by an intraperitoneal injection of N-methyl-N-nitrosourea and in BALB/c mice by blue light-emitting diode exposure. Scotopic electroretinography recording was used to evaluate retinal function. For histological evaluation, hematoxylin and eosin staining, terminal deoxynucleotidyl transferase dUTP nick end labeling, and immunohistochemistry were performed. Electroretinography recordings showed that a-waves and b-waves were significantly reduced in both RD rats and mice, whereas the amplitudes of both waves were significantly increased in both NecroX-5-treated RD rats and mice compared with untreated RD animals. In hematoxylin and eosin staining and terminal deoxynucleotidyl transferase dUTP nick end labeling assay, the outer nuclear layer where photoreceptors reside appeared to be more preserved, and there were fewer apoptotic cells in NecroX-5-treated RD retinas than in untreated RD retinas. In addition, immunohistochemistry with antiglial fibrillary acidic protein and anti-8-hydroxy-2′-deoxyguanosine showed lower levels of retinal injury and oxidative stress in NecroX-5-treated RD retinas than in untreated RD retinas. These results indicated that NecroX-5 protects retinal neurons from experimentally induced RD, suggesting that NecroX-5 may have a potential for the treatment of RD as a medication.

The functional roles of chemical coupling and gap junction between horizontal cells in the catfish retina

Abstract For the investigation of the roles of chemical coupling and gap junction between horizontal cells, the spatio-temporal properties of horizontal cell network were studied using conventional physiological recording techniques and computer simulations. Our results show that the spatial integration of light signal may be mainly performed by electrical junctions, and the temporal integration may be regulated by chemical coupling between horizontal cells. This means that visual information can be modulated spatio-temporally by pathways involving both electrical coupling composed of gap junctions and chemical coupling composed of GABAergic synapses in outer retina of the low vertebrate.