Genetic Dissection of Rod and Cone Pathways in the Dark-Adapted Mouse Retina

Abstract

A monumental task of the mammalian retina is to encode an enormous range (>10(9)-fold) of light intensities experienced by the animal in natural environments. Retinal neurons carry out this task by dividing labor into many parallel rod and cone synaptic pathways. Here we study the operational plan of various rod- and cone-mediated pathways by analyzing electroretinograms (ERGs), primarily b-wave responses, in dark-adapted wildtype, connexin36 knockout, depolarizing rod-bipolar cell (DBCR) knockout, and rod transducin alpha-subunit knockout mice [WT, Cx36(-/-), Bhlhb4(-/-), and Tralpha(-/-)]. To provide additional insight into the cellular origins of various components of the ERG, we compared dark-adapted ERG responses with response dynamic ranges of individual retinal cells recorded with patch electrodes from dark-adapted mouse retinas published from other studies. Our results suggest that the connexin36-mediated rod-cone coupling is weak when light stimulation is weak and becomes stronger as light stimulation increases in strength and that rod signals may be transmitted to some DBCCs via direct chemical synapses. Moreover, our analysis indicates that DBCR responses contribute about 80% of the overall DBC response to scotopic light and that rod and cone signals contribute almost equally to the overall DBC responses when stimuli are strong enough to saturate the rod bipolar cell response. Furthermore, our study demonstrates that analysis of ERG b-wave of dark-adapted, pathway-specific mutants can be used as an in vivo tool for dissecting rod and cone synaptic pathways and for studying the functions of pathway-specific gene products in the retina.

Possible roles of glutamate transporter EAAT5 in mouse cone depolarizing bipolar cell light responses

“…To facilitate dissection of the rod/cone pathways the stimulus strength is divided into four different zones (Abd-El-Barr, Pennesi et al 2009), which correspond to the operating ranges of different retinal neurons including rod, cone, DBC R , DBC C and AII amacrine cells (Fig. 1B).…”

“…To facilitate dissection of the rod and cone pathways, the scotopic ERG protocol which was comprised of progressively increasing stimuli strength, was used to measure the b- and a- waves in different zones as defined previously (Abd-El-Barr, Pennesi et al 2009). At the lowest intensity, 25 responses were averaged with a delay of 2 sec between each ash.…”

Trehalose reduces retinal degeneration, neuroinflammation and storage burden caused by a lysosomal hydrolase deficiency

“…Half-millisecond square flashes for scotopic a-wave and b-wave measurements were produced by cyan light-emitting diodes of 503-nm peak wavelength, calibrated with a photometer (International Light Technology, ILT1700) and converted to the unit photoisomerizations/rod (R*/rod) [75,76] where 1 scot cd m^2 = 581 photoisomerizations/rod/sec. At the lowest intensity, 25 responses were averaged with a delay of 2 sec between each flash.…”

Loss of Scotopic Contrast Sensitivity in the Optomotor Response of Diabetic Mice

“…This conclusion is based upon the assumption that rod signals at mean illumination rates of 0.02 R*/rod/s are transmitted largely by rod bipolar cells along the primary rod pathway, 37 whereas rod and cone signals at mesopic and photopic illumination levels are transmitted largely by cone bipolar cells and the secondary rod pathway. 38,39 The observed spatial vision deficits in the optomotor contrast sensitivity may thus arise from impaired function at or proximal to sites where rod and cone pathways converge, which include the rod-cone gap junctions 40 and the retinal inner plexiform layer. 41 In the inner plexiform layer, synaptic interactions between amacrine, bipolar, and ganglion cells shape the antagonistic center-surround receptive fields of FIGURE 3.…”