The dendritic architecture of the cholinergic plexus in the rabbit retina: Selective labeling by glycine accumulation in the presence of sarcosine

The cholinergic amacrine cells in the rabbit retina slowly accumulate glycine to very high levels when the tissue is incubated with excess sarcosine (methylglycine), even though these cells do not normally contain elevated levels of glycine and do not express high-affinity glycine transporters. Because the sarcosine also depletes the endogenous glycine in the glycine-containing amacrine cells and bipolar cells, the cholinergic amacrine cells can be selectively labeled by glycine immunocytochemistry under these conditions. Incubation experiments indicated that the effect of sarcosine on the cholinergic amacrine cells is indirect: sarcosine raises the extracellular concentration of glycine by blocking its re-uptake by the glycinergic amacrine cells, and the excess glycine is probably taken-up by an unidentified low-affinity transporter on the cholinergic amacrine cells. Neurobiotin injection of the On-Off direction-selective (DS) ganglion cells in sarcosine-incubated rabbit retina was combined with glycine immunocytochemistry to examine the dendritic relationships between the DS ganglion cells and the cholinergic amacrine cells. These double-labeled preparations showed that the dendrites of the DS ganglion cells closely follow the fasciculated dendrites of the cholinergic amacrine cells. Each ganglion cell dendrite located within the cholinergic strata is associated with a cholinergic fascicle and, conversely, there are few cholinergic fascicles that do not contain at least one dendrite from an On-Off DS cell. It is not known how the dendritic co-fasciculation develops, but the cholinergic dendritic plexus may provide the initial scaffold, because the dendrites of the On-Off DS cells commonly run along the outside of the cholinergic fascicles. J. Comp. Neurol. 421:1-13, 2000. (C) 2000 Wiley-Liss, Inc.

The fountain amacrine cells of the rabbit retina

We have characterized a distinctive type of bistratified amacrine cell in the rabbit retina at both the single cell and population levels. These cells correspond to the fountain amacrine cells recently identified by MacNeil and Masland (1998). The fountain cells can be distinguished in superfused retinal wholemounts labeled with nuclear dyes, thus enabling them to be targeted for intracellular injection with Neurobiotin. This revealed that the primary dendrites ascend steeply to sublamina b of the inner plexiform layer, where they form an irregular arbor at the border of strata 4 and 5. These dendrites then give rise to multiple varicose processes that descend obliquely to sublamina a, where they form a more extensive arbor in stratum 1. The fountain amacrine cells show strong homologous tracer coupling when injected with Neurobiotin, and this has enabled us to map their density distribution across the retina and to examine the dendritic relationships between neighboring cells. The fountain amacrine cells range in density from 90 to 360 cells/mm(2) and they account for 1.5% of the amacrine cells in the rabbit retina. The thick tapering dendrites in sublamina b form highly territorial arbors that tile the retina with minimal overlap, whereas the thin varicose processes intermingle in sublamina a. The fountain cells are immunopositive for gamma-aminobutyric acid and immunonegative for glycine. We further propose that these cells are homologous to the substance P-immunoreactive (SP-IR) amacrine cells in the cat retina and that they may account for a subset of the SP-IR amacrine cells in the rabbit retina.

Transversal and longitudinal images from the retina of the living eye using low coherence interferometry

An optical coherence tomography (OCT) system to produce both longitudinal and transversal images of the in vivo human eye is presented. For the first time, OCT transversal images collected from the living eye at 50-µm depth steps show details unobtainable with the state-of-the-art scanning laser ophthalmoscope. Images of up to 3×3?mm are produced from the retina in less than a second. For images larger than 1.6×1.6?mm, a path modulation is introduced by the galvanometric scanning mirror and is used as an effective phase modulation method.

Simultaneous en-face imaging of two layers in human retina by low-coherence reflectometry

We show that with a fiberized multiple Michelson-interferometer-type configuration, transverse images from several layers in the human eye can be simultaneously obtained. We demonstrate the principle by producing simultaneous 100×100 pixel en-face images of a 4 mm×4 mm region on a postmortem retina for two depth positions 250 µm apart.

Optical imaging of retina in response to grating stimuli in cats

We examined the intrinsic signals in response to grating stimuli in order to determine whether the light-evoked intrinsic signals of the retina are due to changes in the photoreceptor activities induced by the image projected on to the retina or are due to neural activities of the inner retina. The retinas of the left eye of 12 cats under general anesthesia were examined by a functional imaging fundus camera. Near infrared light was used to monitor the reflectance changes (RCs) of the retina. Vertical grating were used to stimulate the retina at 4 Hz. The spatial frequencies of the gratings were 0.05, 0.11, 0.22, 0.43, 0.86, 1.73, and 3.46 cycles/degree (cpd). Ten images were averaged and used to analyze the RCs to obtain the peak value (PV) of a two dimensional fast Fourier transfer of the RCs. The wavefront aberrations (WA) were measured with a compact wavefront aberrometer and the spatial modulation transfer function (MTF) of the eye was calculated. The retinal reflectance image had a grating pattern. The PV of the spatial sensitivity curve was highest at low spatial frequencies (0.05 and 0.11 cpd), and the sensitivity decreased steeply with an increase in the spatial frequency. RCs were not detectable at 3.46 cpd. The MTF decreased gradually with increases in the spatial frequencies and was 0.68 at 3.46 cpd. The reflectance pattern of the retinal intrinsic signal elicited by grating stimuli of different spatial frequencies was different from that of the MTF. This suggests that the intrinsic signal represents not only the response of the photoreceptors but also other neuronal or vascular changes in the retina.