Blue-on-Green Flash Induces Maximal Photopic Negative Response and Oscillatory Potential and Serves as a Diagnostic Marker for Glaucoma in Rat Retina

The purpose of this study was to investigate the application of various electroretinography (ERG) to the diagnosis of inner retinal dysfunction induced by mild intraocular pressure (IOP) elevation in a rat glaucoma model. For inner retinal function measurements, available photopic ERG protocols were applied under various light conditions including monochromatic combinations, which complement conventional scotopic ERG. Three episcleral veins in the right eyes of Sprague-Dawley rats were cauterized to induce an experimental model of glaucoma, leading to mild IOP elevation. ERG responses were measured before surgery and at 1, 2, 4, and 8 weeks after cauterization. We first confirmed that the amplitude reduction in the standard photopic b-wave was almost comparable to the amplitudes of scotopic a- and b-waves in glaucomatous eyes over time. We have implemented additional photopic ERG protocols under different stimulus conditions, which consisted of a longer duration and different monochromatic combinations. Such a change in the stimulations resulted in more pronounced differences in response between the two groups. Especially in normal animals, blue stimulation on a green background produced the largest b-wave and photopic negative response (PhNR) amplitudes and caused more pronounced oscillatory potential (OP) wavelets (individual components). In glaucomatous eyes, blue stimulation on a green background significantly reduced PhNR amplitudes and abolished the robust OP components. These results, by providing the usefulness of blue on green combination, suggest the applicable photopic ERG protocol that complements the conventional ERG methods of accessing the progression of glaucomatous damage in the rat retina.

Changes in transcript and protein levels of calbindin D28k, calretinin and parvalbumin, and numbers of neuronal populations expressing these proteins in an ischemia model of rat retina / 대한해부학회지

Excessive calcium is thought to be a critical step in various neurodegenerative processes including ischemia. Calbindin D28k (CB), calretinin (CR), and parvalbumin (PV), members of the EF-hand calcium-binding protein family, are thought to play a neuroprotective role in various pathologic conditions by serving as a buffer against excessive calcium. The expression of CB, PV and CR in the ischemic rat retina induced by increasing intraocular pressure was investigated at the transcript and protein levels, by means of the quantitative real-time reverse transcription-polymerase chain reaction, western blot and immunohistochemistry. The transcript and protein levels of CB, which is strongly expressed in the horizontal cells in both normal and affected retinas, were not changed significantly and the number of CB-expressing horizontal cells remained unchanged throughout the experimental period 8 weeks after ischemia/reperfusion injury. At both the transcript and protein levels, however, CR, which is strongly expressed in several types of amacrine, ganglion, and displaced amacrine cells in both normal and affected retinas, was decreased. CR-expressing ganglion cell number was particularly decreased in ischemic retinas. Similar to the CR, PV transcript and protein levels, and PV-expressing AII amacrine cell number were decreased. Interestingly, in ischemic retinas PV was transiently expressed in putative cone bipolar cell types possibly those that connect with AII amacrine cells via gap junctions. These results suggest that these three calcium binding proteins may play different neuroprotective roles in ischemic insult by their ability to buffer calcium in the rat retina.

Maturation of the Neurokinin 1 (NK1) Receptor Immunoreactive Amacrine Cells in the Rat Retina during Postnatal Development / 대한해부학회지

We examined the morphological maturation of amacrine cells expressing neurokinin 1 (NK1) receptor, whose ligand is substance P, in the rat retina, focusing on the period from postnatal day 5 (P5) when the outer plexiform layer is formed, to postnatal day 13 (P13) when the eyes open, with immunohistochemistry using a specific antiserum against NK1 receptor, and we compared maturing NK1 receptor-immunoreactive (NK1 receptor-IR) amacrine cells with adult one. In the adult retina, numerous NK1 receptor-IR amacrine cells were located in the inner part of the inner nuclear layer (INL) adjacent to the inner plexiform layer (IPL), and their processes emerging from the somata branched and stratified at 1, 2, and 5 strata of within the IPL. NK1 receptor-IR amacrine cells were already observed at P5. The cell bodies were located in the inner INL away from the IPL and their processes branched and formed two distinct bands in the IPL. Afterwards, somata of NK1 receptor-IR amacrine cells moved toward the inner part of the INL, and thus, were located in the INL adjacent to the IPL. Their processes formed three distinct bands at P10 and then, at P13, three bands occupied the same strata as those of the adult, which were posed at 1, 2, and 5 strata of the IPL. During the postnatal development, most of NK1 receptor-IR amacrine cells directly extended one or a few primary dendrites toward the IPL and formed the strata. However, some of the labeled cells located at the outermost row had horizontal processes emerging from their primary dendrites, and these horizontal processes branched and formed plexuses in the INL. The NK1 receptor-IR amacrine cells with horizontal processes were frequently observed at P7, rarely at P10, and not at P13 and in the adult. These results indicate that the NK1 receptor-IR amacrine cells of the rat retina morphologically mature by way of migration of their somata within the INL and formation of distinct processes during postnatal development, and suggest that they morphologically and functionally complete the maturation process about the time of P13.

NADPH Diaphorase Staining Retinal Cells in Streptozotocin-induced Diabetic Rat Retina

Nitric oxide(NO) is a free radical which serves a wide variety of functions on vascular tone, neurotransmission, immune cytotoxicity, and many others. Nitric oxide synthase(NOS) is the biosynthetic enzyme of NO and colocalized with NADPH diaphorase(NADPH-d) activity in many tissues. The author aimed to assess the changes that occur in this populations of neurons in the streptozotocin-induced diabetic rat where the retinal vasculature is known to be dysfunctional. The 8 rats was a diabetic group and the other 8 was a control group. Diabetes was induced with a single intraperitoneal injection of streptozotocin(65mg/kg). Four weeks later, the retina was flat mounted and stained with NADPH-d. Counting of the stained cells was made. There was a 20.6% decrease in the total number of positively staining cells in the retinas of the diabetic group(2532+/-192) compared with those of the control group(3188+/-176)(p<0.001). It is worth to suggest the close correlation between NO released from retinal neurons and the microcirculatory dysfunction in diabetic retinopathy.