Photoreceptor synaptic structure and function in the dfcr retina. (
A,
B) Rod photoreceptor synapses (spherules) in a 3-week-old dfcr retina (
A) and a 2-month-old dfcr retina (
B) show the typical synaptic arrangement observed in mouse retina. Scale bars: (
A) 50 nm; (
B) 100 nm. Horizontal cell (HC) and bipolar cell (BC) processes, arciform densities (
thin arrow), and the density of vesicles (

) associated with the ribbon (
thick arrow) are indicated. (
C,
left) The percentage of rod spherules, shown in ultrathin section, in which an arciform density, a bipolar cell process, and two horizontal processes were evident, and (
right) the density of ribbon-associated vesicles in the rod photoreceptor synapses of dfcr and WT retinas. Data shown in (
C) were obtained from four dfcr and four wild-type littermates that had been used to obtain the ERG data in (
D–
F). Bars, mean ± SD. There is no significant difference between dfcr mice and controls for all measurements; according to Student’s
t-test (
n = 4 for each), the probability of no significant difference was calculated as 0.97, 0.89, 0.79, and 0.30 for the number of arciform densities, bipolar cell processes, horizontal processes, and synaptic vesicle density, respectively. (
D–
F) ERGs and waveform analyses in dfcr mice. (
D) Dark-adapted ERGs elicited with increasing intensities of a blue light stimulus in a representative dfcr mouse compared to an age-matched (2-month-old) WT mouse. Stimulus luminance is to the left of key traces; traces start at stimulus onset. ERG waveforms from the dfcr mouse are indistinguishable from those of WT. (
E) B-wave amplitude plotted as a function of stimulus intensity in five dfcr mice.
Shaded region: normal range (mean ± SD) for wild-type animals (
n = 20). The b-wave amplitudes for all animals tested fell within the normal range across a wide range of stimulus intensities. (
F) Ratio of the amplitude of the postreceptoral component of the ERG (b-wave) to the receptoral component (a-wave) in response to a +0.1 log scot-cd · s · m
−2 stimulus in dfcr compared with results from wild-type. There is no significant difference between dfcr mice and controls (
P > 0.05).