Horizontal, bipolar, and amacrine cells in the zebrafish retina were morphologically characterized using DiOlistic techniques. In this method, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-coated microcarriers are shot at high speed onto the surfaces of living retinal slices where the DiI then delineates axons, somata, and dendrites of isolated neurons. Zebrafish retinal somata were 5-10 microm in diameter. Three horizontal cell types (HA-1, HA-2, and HB) were identified; dendritic tree diameters averaged 25-40 microm. HA somata were round. Cells classified as HA-2 were larger than HA-1 cells and possessed an axon. HB somata were flattened, without an axon, although short fusiform structure(s) projected from the soma. Bipolar cells were separated into 17 morphological types. Dendritic trees ranged from 10 to 70 microM. There were six B(on) types with axon boutons only in the ON sublamina of the inner plexiform layer (IPL), and seven B(off) types with axon boutons or branches only in the OFF sublamina. Four types of bistratified bipolar cells displayed boutons in both ON and OFF layers. Amacrine cells occurred in seven types. A(off) cells (three types) were monostratified and ramified in the IPL OFF sublamina. Dendritic fields were 60-150 microM. A(on) pyriform cells (three types) branched in the ON sublamina. Dendritic fields were 50-170 microM. A(diffuse) cells articulated processes in all IPL strata. Dendritic fields were 15-90 microM. These findings are important for studies examining signal processing in zebrafish retina and for understanding changes in function resulting from mutations and perturbations of retinal organization.

Diabetes affects over 16 million Americans yearly, resulting in hyperglycaemia and microvascular complications, including retinopathy, neuropathy and nephropathy. Animal models have been developed to examine the immunological aspects of type 1 diabetes and the pathogenic mechanisms associated with diabetic retinopathy, but the methods of diabetes induction raise concerns regarding these models. Zebrafish (Danio rerio) have been used extensively to study developmental processes and mutant zebrafish strains have been used to examine vision disease present in humans. In this paper, we have induced hyperglycaemia in zebrafish by alternately immersing the fish in glucose solution or water. Eyes from untreated fish or fish exposed to alternating glucose/water solutions for 28 days were dissected, sectioned and stained to visualise cell bodies in the retina. In untreated fish retinas, the inner plexiform layer (IPL) and inner nuclear layer (INL) were approximately the same thickness, whereas in fish repeatedly exposed to glucose solutions the IPL was approximately 55% the thickness of the INL. Both the IPL and INL were significantly reduced in retinas of treated fish, compared to untreated fish, similar to that seen in other animal models of diabetes and in diabetic patients. These results suggest that zebrafish may be used as an animal model in which to study diabetic retinopathy.

Retinal bipolar cells are physiologically separated into ON_ and OFF_subtypes based on responses to light andÏor glutamate, the photoreceptor neurotransmitter. OFF_bipolar cells are depolarized by glutamate release in the dark. ON_bipolar cells, in contrast, are hyperpolarized by the very same glutamate release. The division of the light signal into ON_ and OFF_pathways is achieved through a variety of glutamate receptors mediating these responses. OFFbipolar cells express ionotropic glutamate receptors (iGluRs) that are directly activated by glutamate or the glutamate agonists, kainate and á_amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). Glutamate responses restricted to the kainate receptor family were recently described in OFF_bipolar cells of ground squirrel (DeVries & Schwartz, 1999). Kainate receptor currents are typically characterized by slower desensitization and recovery than AMPA receptor currents. Glutamate responses of the N-methyl-ª_aspartate (NMDA) family are not seen in retinal bipolar cells.Journal of Physiology (2000)

Connaughton VP, Nelson R. Spectral responses in zebrafish horizontal cells include a tetraphasic response and a novel UV-dominated triphasic response. J Neurophysiol 104: 2407-2422, 2010. First published July 7, 2010 doi:10.1152/jn.00644.2009. Zebrafish are tetrachromats with red (R, 570 nm), green (G, 480 nm), blue (B, 415 nm), and UV (U, 362 nm) cones. Although neurons in other cyprinid retinas are rich in color processing neural circuitry, spectral responses of individual neurons in zebrafish retina, a genetic model for vertebrate color vision, are yet to be studied. Using dye-filled sharp microelectrodes, horizontal cell voltage responses to light stimuli of different wavelengths and irradiances were recorded in a superfused eyecup. Spectral properties were assessed both qualitatively and quantitatively. Six spectral classes of horizontal cell were distinguished. Two monophasic response types (L1 and L2) hyperpolarized at all wavelengths. L1 sensitivities peaked at 493 nm, near the G cone absorbance maximum. Modeled spectra suggest equally weighted inputs from both R and G cones and, in addition, a "hidden opponency" from blue cones. These were classified as RϪ/GϪ/(bϩ). L2 sensitivities were maximal at 563 nm near the R cone absorbance peak; modeled spectra were dominated by R cones, with lesser G cone contributions. B and UV cone signals were small or absent. These are RϪ/gϪ. Four chromatic (C-type) horizontal cells were either depolarized (ϩ) or hyperpolarized (Ϫ) depending on stimulus wavelength. These types are biphasic (Rϩ/GϪ/BϪ) with peak excitation at 467 nm, between G and B cone absorbance peaks, UV triphasic (rϪ/Gϩ/ UϪ) with peak excitation at 362 nm similar to UV cones, and blue triphasic (rϪ/Gϩ/BϪ/uϪ) and blue tetraphasic (rϪ/Gϩ/BϪ/uϩ), with peak excitation at 409 and 411 nm, respectively, similar to B cones. UV triphasic and blue tetraphasic horizontal cell spectral responses are unique and were not anticipated in previous models of distal color circuitry in cyprinids.