Figure 1.
Blood glucose levels and body weights of control and STZ-induced diabetic mice.
A. Blood glucose levels of control and diabetic mice are shown as a function of time after the induction of diabetes. Control and diabetic mice had similar blood glucose levels before injection of STZ. Control mice maintained blood glucose levels ∼5 mM over the course of the study, whereas blood glucose levels in the STZ-treated mice were increased by more than threefold at all three time points (*** P<0.001, Student's t-test).The grey dashed line indicates the blood glucose level of 11.1 mM. B. Age-matched control mice gained weight over the course of 3 months. In contrast, no weight increase was seen in diabetic mice. White bars show the age-matched control group (Ctrl); black bars indicate the STZ-treated group (STZ).
Figure 2.
Spontaneous and light-evoked spike activity of retinal ganglion cells.
A. A DIC image taken from the ganglion cell layer in a whole-mount mouse retina (scale bar indicates 10 µm). The arrow and arrowhead point to the soma of a representative α-type ganglion cell and the recording pipette, respectively. B. Spontaneous activity of an α-type ganglion cell. The cell exhibited a mixture of single spikes (left inset) and bursts (right inset). Typical recordings of representative ganglion cells showing ON (C), OFF (D), and ON-OFF (E) responses to 4-s full-field light stimuli (indicated by square wave above response traces; light intensity: 1.06×109 photons/cm2/s).
Figure 3.
Spontaneous firing rates of ON-type ganglion cells were increased in diabetic mice.
A. The percentages of ON- and OFF-type ganglion cells in both control and diabetic mice. B. Box and whisker charts illustrating the distribution of average spontaneous firing rates of ON-type ganglion cells in control and diabetic mice. In the charts, the middle line in the box represents the median, the box ends represent the first and third quartiles, whiskers indicate the 5% and 95% margins, and crosses indicate the data margins. In addition, the mean value is indicated by a small square. The diabetic ON-type ganglion cells showed a significant increase in spontaneous firing rate (*P<0.05, Mann-Whitney U test). C. Box and whisker charts illustrate the distribution of the average spontaneous firing rates of OFF-type ganglion cells in control and diabetic retinas. No difference was detected in spontaneous activity in OFF-type ganglion cells between control and diabetic groups (P>0.05). D. Histograms showing the percentage of all ON-type ganglion cells recorded as a function of firing frequency. The first band includes firing rates from 0–5 Hz, the middle band includes firing rates of 5–25 Hz, and the right band represents the firing rates >25 Hz. In diabetic mice, a considerable decrease was observed in the percentage of cells with an average firing frequency <5 Hz, but in the other two frequency bands (≥5 Hz) the percentage of diabetic cells were larger than the control group.
Figure 4.
Enhanced bursting activity of diabetic ON-type ganglion cells.
Histograms show that the bursting frequency (A) and time spent bursting (B) of ON-type ganglion cells were significantly increased in diabetic mice (*P<0.05, Student's t-test).
Figure 5.
Effect of synaptic blockers on ON-type ganglion cell spontaneous activity.
The cocktail of blockers contained (in μM): 50 L-AP4, 10 bicuculline, 10 strychnine, 50 D-AP5, and 10 CNQX. A. Representative traces show that spontaneous activity was completely eliminated in a control ON-type ganglion cell (upper panel) and a diabetic ON-type ganglion cell (middle panel), but was maintained to some extent in another diabetic ON-type ganglion cell (lower panel). Summarized data show that spontaneous firing rate of each ON-type cell was recorded before and after application of the synaptic blockers in control (B) and diabetic retinas (C). Grey circles show firing rate of each cell.
Figure 6.
Suppression of inhibitory inputs to ON-type ganglion cells during diabetes.
A. Typical traces of spontaneous activity show the effects of an inhibitory input blockade using bicuculline and strychnine on a control ON-type ganglion cell (upper panel) and a diabetic ON-type ganglion cell (bottom panel). B. Box and whisker plots show the distribution of average spontaneous firing rates of ON-type ganglion cells in control and diabetic mice before and after inhibitory input blockade. The difference in spontaneous firing rate between normal and diabetic ON-type ganglion cells in normal Ringer's solution (*P<0.05, Mann-Whitney U test) was eliminated in the presence of bicuculline and strychnine (P>0.05).