Biomedical subjects

Peter Gouras

Publications and source records attributed to Peter Gouras.

21 records · Page 2Linked to original sources

PubMed2002

Retinal degeneration and RPE transplantation in Rpe65(-/-) mice.

PURPOSE: To determine whether transplanting normal retinal pigment epithelium (RPE) into the subretinal space influences photoreceptor function and degeneration in Rpe65(-/-) mice. METHODS: RPE cells were isolated from eyes of normal mice and transplanted to the subretinal space of one eye of Rpe65(-/-) mice. The other eye received a subretinal injection of saline or was not touched. Corneal electroretinograms (ERGs) from both eyes were monitored before and after surgery to follow progression of the degeneration. The width of the outer nuclear layer was measured in the area of transplantation and compared with a similar area in control retinas. RESULTS: Transplantation of RPE increased ERG amplitude maximally at 3.7 weeks after surgery. This rescue effect slowly diminished with time. Sham surgery had little effect on the ERG. The width of the outer nuclear layer in the area receiving RPE transplants was slightly greater than in control subjects. Evidence of the presence of RPE transplants in the subretinal space decreased with time after transplantation without signs of inflammation. CONCLUSIONS: Retinal degeneration in the Rpe65(-/-) mice is slowly progressive. Photoreceptor function can be transiently increased for several months and anatomic degeneration slightly reduced in Rpe65(-/-) mice by RPE cell transplantation. Loss of the rescue effect may be due to degeneration of the transplanted RPE.

Animals↗

PubMedDate not supplied

Co-expression of murine opsins facilitates identifying the site of cone adaptation.

Murine cones contain two opsins in the same cone, one ultraviolet (UV) and the other middle-wavelength sensitive (M). A long-wavelength flash only affecting M-opsin suppresses the cone electroretinogram (ERG) produced by light absorption of UV-cone opsin raising the hypothesis that activation of M-cone opsin suppresses UV-cone opsin responses in the same cone. Here we show that pharmacologic blockade of synaptic transmission in the superfused murine retina, which eliminates interaction from second-order neurons, fails to prevent suppression of the UV-opsin driven pathway by long-wavelength stimuli. This proves that the antagonism must be occurring in the same cone, co-expressing both opsins. Our results show that UV-opsin suppression successively ceases in presence of the M-opsin activating background light, which implies that cone light adaptation is controlled at the opsin stage, before activation of transducin. It also reveals the time course of a transient desensitization of cones due to post-opsin factors in the transduction cascade.

Adaptation, Ocular↗

PubMedDate not supplied

Cone and rod inputs to murine retinal ganglion cells: evidence of cone opsin specific channels.

To identify ultraviolet (UV) and middle- (M) wavelength-sensitive cone and rod signals in murine retinal ganglion cells, single ganglion cell responses were studied in anesthetized, light-adapted C57/BL6 mice with tungsten microelectrodes driven through the sclera and vitreous to the neural retina. One hundred fifty-four ganglion cells were examined in 43 retinas of 34 mice. The retina was stimulated with diffuse flashes and/or pulses of ultraviolet (360 nm) or green (520 nm) light in the presence and absence of a strong steady orange adapting light. Twelve ganglion cells were studied in the dark-adapted retina in order to identify the signals of rods. Three functionally different types of ganglion cells were found: (1) phasic responding cells (31%) with no spontaneous activity and large impulse amplitudes; (2) tonic responding cells (60%) with irregular, low frequency (5-10 Hz) spontaneous activity and smaller impulse amplitudes; and (3) metronome-like cells (9%) with regular, relatively high-frequency (20-40 Hz) spontaneous activity. A few cells (1%) had habituating responses. Every cell encountered was affected by diffuse stimulation. The more common two types were excited at either the ON or OFF or at both the ON and OFF phases of stimulation. Type III cells had weaker responses, sometimes only inhibited by turning off a light. In the light-adapted state, most cells received signals of the same polarity from UV- and M-cones but UV-cone inputs were usually more dominant, especially in ventral retina. A fraction of cells received signals from only UV- (18%) or only M- (3%) cones. In rare cases (2%) these cone inputs had an opposite polarity on the same cell. In the dark-adapted state, all cells were at least four or five logarithmic units more sensitive and more to green than ultraviolet light. The results indicate that co-expression of both UV-and M-cone opsins cannot be ubiquitous in murine retina. Some cones, especially UV cones, exist without the presence of any functional M-cone opsin. This must be the case to explain the presence of ganglion cells that receive inputs only from UV-cones and others that receive inputs of opposite polarity from UV- and M-cones. The results support the hypothesis that murine retina has the physiological capacity to relay signals to the brain that allow the sensing of chromatic contrast and color vision.

Adaptation, Physiological↗