Tae-Hoon Kang

Changes in retinal neuronal populations in the DBA/2J mouse

DBA/2J (D2) mice develop a form of progressive pigmentary glaucoma with increasing age. We have compared retinal cell populations of D2 mice with those in control C57BL/6J mice to provide information on retinal histopathology in the D2 mouse. The D2 mouse retina is characterized by a reduction in retinal thickness caused mainly by a thinning of the inner retinal layers. Immunocytochemical staining for specific inner retinal neuronal markers, viz., calbindin for horizontal cells; protein kinase C (PKC) and recoverin for bipolar cells, glycine, γ-aminobutyric acid (GABA), choline acetyltransferase (ChAT), and nitric oxide synthase (NOS) for amacrine cells, and osteopontin (OPN) for ganglion cells, was performed to detect preferentially affected neurons in the D2 mouse retina. Calbindin, PKC, and recoverin immunoreactivities were not significantly altered. Amacrine cells immunoreactive for GABA, ChAT, and OPN were markedly decreased in number, whereas NOS-immunoreactive amacrine cells increased in number. However, no changes were observed in the population of glycine-immunoreactive amacrine cells. These findings indicate a significant loss of retinal ganglion and some amacrine cells, whereas glycinergic amacrine cells, horizontal, and bipolar cells are almost unaffected in the D2 mouse. The reduction in amacrine cells appears to be attributable to a loss of GABAergic and particularly cholinergic amacrine cells. The increase in nitrergic neurons with the consequent increase in NOS and NO may be important in the changes in the retinal organization that lead to glaucomain D2 mice. Thus, the D2 mouse retina represents a useful model for studying the pathogenesis of glaucoma and mechanisms of retinal neuronal death and for evaluating neuroprotection strategies.

Expression of Interferon Inducible Genes Following Hantaan Virus Infection as a Mechanism of Resistance in A549 Cells

Hantaan virus (HTN) is a causative agent of hemorrhagic fever with renal syndrome (HFRS). Little is known of its pathogenesis or the molecular mechanisms underlying resistance to HTN infection. In the present study, DNA microarray technology was used to monitor changes in mRNA levels after HTN infection, to elucidate resistance mechanisms to viral infection by understanding virus–host interactions. We found that several interferon (IFN)-inducible genes were up-regulated in host cells infected with HTN. According to previous available data, IFNs have been reported to be inhibitory, but their mode of action has not been yet clear. In this study, the 2′,5′-oligoadenylated synthetase (OAS) and Mx1 genes, not a double-stranded RNA-dependent protein kinase R (PKR), of the IFN response pathways are associated with antiviral activity during HTN infection. Furthermore, A549 cells treated with IFN-α were protected against HTN infection. Taken together, these results confirmed that IFN plays a role in cellular defenses against HTN infection at an early stage of the infection and revealed the resistance mechanism for HTN infection.

Comparative study of cholinergic cells in retinas of various mouse strains.

We examined cholinergic cells in the retinas of BALB/C albino, C57BL/6J black, and 129/SvJ light chinchilla mice by using immunocytochemistry with specific antisera against choline acetyltransferase (ChAT). Two types of ChAT-immunoreactive amacrine cell bodies were found in the inner nuclear layer (INL) and ganglion cell layer in the retinas of all three mouse strains. They were distributed with mirror-image symmetry and their processes ramified in strata 2 and 4 of the inner plexiform layer. A distinct type of ChAT-immunoreactive cell was found only in C57BL/6J mouse retina. The somata of this third type of ChAT-immunoreactive cell were located in the outermost part of the INL, with their processes extending toward the outer plexiform layer. Double-labeling experiments demonstrated that these were not horizontal cells and that they were GABA-immunoreactive. The results suggested that these cells were probably “misplaced” cholinergic amacrine cells showing GABA immunoreactivity. This feature of the C57BL/6J mouse retina should be taken into account in studies of mutant mice having a mixed genetic background with a C57BL/6J contribution.

Identification and characterization of an aquaporin 1 immunoreactive amacrine-type cell of the mouse retina

Using immunocytochemistry, a type of amacrine cell that is immunoreactive for aquaporin 1 was identified in the mouse retina. AQP1 immunoreactivity was found in photoreceptor cells of the outer nuclear layer (ONL) and in a distinct type of amacrine cells of the inner nuclear layer (INL). AQP1‐immunoreactive (IR) amacrine cell somata were located in the INL and their processes extended through strata 3 and 4 of the inner plexiform layer (IPL) with thin varicosities. The density of the AQP1‐IR amacrine cells increased from 100/mm2 in the peripheral retina to 350/mm2 in the central retina. The AQP1‐IR amacrine cells comprise 0.5% of the total amacrine cells. The AQP1‐IR amacrine cell bodies formed a regular mosaic, which suggested that they represent a single type of amacrine cell. Double labeling with AQP1 and glycine, γ‐aminobutyric acid (GABA) or GAD65 antiserum demonstrated that the AQP1‐IR amacrine cells expressed GABA or GAD65 but not glycine. Their synaptic input was primarily from other amacrine cell processes. They also received synaptic inputs from a few cone bipolar cells. The primary synaptic targets were ganglion cells, followed by other amacrine cells and cone bipolar cells. In addition, gap junctions between an AQP1‐IR amacrine process and another amacrine process were rarely observed. In summary, a GABAergic amacrine cell type labeled by an antibody against AQP1 was identified in the mouse retina and was found to play a possible role in transferring a certain type of visual information from other amacrine or a few cone bipolar cells primarily to ganglion cells. J. Comp. Neurol. 488:352–367, 2005.

Morphological analysis of the hyperpolarization-activated cyclic nucleotide-gated cation channel 1 (HCN1) immunoreactive bipolar cells in the rabbit retina.

Hyperpolarization‐activated cation currents (Ih) have been identified in neurons in the central nervous system, including the retina. There is growing evidence that these currents, mediated by the hyperpolarization‐activated cyclic nucleotide‐gated cation channel (HCN), may play important roles in visual processing in the retina. This study was conducted to identify and characterize HCN1‐immunoreactive (IR) bipolar cells by immunocytochemistry, quantitative analysis, and electron microscopy. The HCN1‐IR bipolar cells were a subtype of OFF‐type cone bipolar cells and comprised 10% of the total number of cone bipolar cells. The axons of the HCN1‐IR cone bipolar cells ramified narrowly in the border of strata 1 and 2 of the inner plexiform layer (IPL). These cells formed a regular distribution, with a density of 1,825 cells/mm2 at a position 1 mm ventral to the visual streak, falling to 650 cells/mm2 in the ventral periphery. Double‐labeling experiments demonstrated that their axons stratified narrowly within and slightly proximal to the OFF‐starburst amacrine cell processes. In the IPL, they were presynaptic to amacrine cell processes. The most frequent postsynaptic dyads formed of HCN1‐IR bipolar cell axon terminals are pairs composed of both amacrine cell processes. These results suggest that these HCN1‐IR cone bipolar cells might be the same as the DAPI‐Ba1 bipolar population, and might therefore be involved in a direction‐selective mechanism, providing inputs to the OFF‐starburst amacrine cells and/or the OFF‐plexus of the ON–OFF ganglion cells. J. Comp. Neurol. 467:389–402, 2003.

Synaptic connections of calbindin-immunoreactive cone bipolar cells in the inner plexiform layer of rabbit retina

In the mammalian retina, information concerning various aspects of an image is transferred in parallel, and cone bipolar cells are thought to play a major role in this parallel processing. We have examined the synaptic connections of calbindin-immunoreactive (IR) ON cone bipolar cells in the inner plexiform layer (IPL) of rabbit retina and have compared these synaptic connections with those that we have previously described for neurokinin 1 (NK1) receptor-IR cone bipolar cells. A total of 325 synapses made by calbindin-IR bipolar axon terminals have been identified in sublamina b of the IPL. The axons of calbindin-IR bipolar cells receive synaptic inputs from amacrine cells through conventional synapses and are coupled to putative AII amacrine cells via gap junctions. The major output from calbindin-IR bipolar cells is to amacrine cell processes. These data resemble our findings for NK1 receptor-IR bipolar cells. However, the incidences of output synapses to ganglion cell dendrites of calbindin-IR bipolar cells are higher compared with the NK1-receptor-IR bipolar cells. On the basis of stratification level and synaptic connections, calbindin-IR ON cone bipolar cells might thus play an important role in the processing of various visual aspects, such as contrast, orientation, and approach sensing, and in transferring rod signals to the ON cone pathway.

Synaptic connections of cone bipolar cells that express the neurokinin 1 receptor in the rabbit retina

We have investigated and further characterized, in the rabbit retina, the synaptic connectivity of the ON-type cone bipolar cells that are immunoreactive for an antibody against the neurokinin-1 receptor (NK1R). NK1R-immunoreactive bipolar cell axons terminate in stratum 4 of the inner plexiform layer. The axons of NK1R-positive bipolar cells receive synaptic inputs from amacrine cells through conventional synapses and from putative AII amacrine cells via gap junctions. The major outputs from NK1R-positive bipolar cells make contacts with amacrine cell processes. The most frequent postsynaptic dyads comprise two amacrine cell processes. Double-labeling experiments with antibodies against NK1R and either calretinin or glycine have demonstrated that NK1R-immunoreactive bipolar cells form gap junctions with AII amacrine cells. Thus, NK1R-positive cone bipolar cells, together with calbindin-positive cone bipolar cells, may play an important role in transferring rod signals to the ON-type ganglion cells of the cone pathway in the rabbit retina.