Cone-Driven Retinal Responses Are Shaped by Rod But Not Cone HCN1.

Signal integration of converging neural circuits is poorly understood. One example is in the retina where the integration of rod and cone signaling is responsible for the large dynamic range of vision. The relative contribution of rods versus cones is dictated by a complex function involving background light intensity and stimulus temporal frequency. One understudied mechanism involved in coordinating rod and cone signaling onto the shared retinal circuit is the hyperpolarization activated current (Ih) mediated by hyperpolarization-activated cyclic nucleotide-gated 1 (HCN1) channels expressed in rods and cones. Ih opposes membrane hyperpolarization driven by activation of the phototransduction cascade and modulates the strength and kinetics of the photoreceptor voltage response. We examined conditional knock-out (KO) of HCN1 from mouse rods using electroretinography (ERG). In the absence of HCN1, rod responses are prolonged in dim light which altered the response to slow modulation of light intensity both at the level of retinal signaling and behavior. Under brighter intensities, cone-driven signaling was suppressed. To our surprise, conditional KO of HCN1 from mouse cones had no effect on cone-mediated signaling. We propose that Ih is dispensable in cones because of the high level of temporal control of cone phototransduction. Thus, HCN1 is required for cone-driven retinal signaling only indirectly by modulating the voltage response of rods to limit their output.SIGNIFICANCE STATEMENT Hyperpolarization gated hyperpolarization-activated cyclic nucleotide-gated 1 (HCN1) channels carry a feedback current that helps to reset light-activated photoreceptors. Using conditional HCN1 knock-out (KO) mice we show that ablating HCN1 from rods allows rods to signal in bright light when they are normally shut down. Instead of enhancing vision this results in suppressing cone signaling. Conversely, ablating HCN1 from cones was of no consequence. This work provides novel insights into the integration of rod and cone signaling in the retina and challenges our assumptions about the role of HCN1 in cones.

Rod Photoreceptors Signal Fast Changes in Daylight Levels Using a Cx36-Independent Retinal Pathway in Mouse.

Temporal contrast detected by rod photoreceptors is channeled into multiple retinal rod pathways that ultimately connect to cone photoreceptor pathways via Cx36 gap junctions or via chemical synapses. However, we do not yet understand how the different rod pathways contribute to the perception of temporal contrast (changes in luminance with time) at mesopic light levels, where both rods and cones actively respond to light. Here, we use a forced-choice, operant behavior assay to investigate rod-driven, temporal contrast sensitivity (TCS) in mice of either sex. Transgenic mice with desensitized cones (GNAT2 cpfl3 line) were used to identify rod contributions to TCS in mesopic lights. We found that at low mesopic lights (400 photons/s/µm2 at the retina), control and GNAT2 cpfl3 mice had similar TCS. Surprisingly, at upper mesopic lights (8000 photons/s/µm2), GNAT2 cpfl3 mice exhibited a relative reduction in TCS to low (<12 Hz) while maintaining normal TCS to high (12-36 Hz) temporal frequencies. The rod-driven responses to high temporal frequencies developed gradually over time (>30 min). Furthermore, the TCS of GNAT2 cpfl3 and GNAT2 cpfl3 ::Cx36-/- mice matched closely, indicating that transmission of high-frequency signals (1) does not require the rod-cone Cx36 gap junctions as has been proposed in the past; and (2) a Cx36-independent rod pathway(s) (e.g., direct rod to OFF cone bipolar cell synapses and/or glycinergic synapses from AII amacrine cells to OFF ganglion cells) is sufficient for fast, mesopic rod-driven vision. These findings extend our understanding of the link between visual circuits and perception in mouse.SIGNIFICANCE STATEMENT The contributions of specific retinal pathways to visual perception are not well understood. We found that the temporal processing properties of rod-driven vision in mice change significantly with light level. In dim lights, rods relay relatively slow temporal variations. However, in daylight conditions, rod pathways exhibit high sensitivity to fast but not to slow temporal variations, whereas cone-driven responses supplement the loss in rod-driven sensitivity to slow temporal variations. Our findings highlight the dynamic interplay of rod- and cone-driven vision as light levels rise from night to daytime levels. Furthermore, the fast, rod-driven signals do not require the rod-to-cone Cx36 gap junctions as proposed in the past, but rather, can be relayed by alternative Cx36-independent rod pathways.

Rod Photoresponse Kinetics Limit Temporal Contrast Sensitivity in Mesopic Vision.

The mammalian visual system operates over an extended range of ambient light levels by switching between rod and cone photoreceptors. Rod-driven vision is sluggish, highly sensitive, and operates in dim or scotopic lights, whereas cone-driven vision is brisk, less sensitive, and operates in bright or photopic lights. At intermediate or mesopic lights, vision transitions seamlessly from rod-driven to cone-driven, despite the profound differences in rod and cone response dynamics. The neural mechanisms underlying such a smooth handoff are not understood. Using an operant behavior assay, electrophysiological recordings, and mathematical modeling we examined the neural underpinnings of the mesopic visual transition in mice of either sex. We found that rods, but not cones, drive visual sensitivity to temporal light variations over much of the mesopic range. Surprisingly, speeding up rod photoresponse recovery kinetics in transgenic mice improved visual sensitivity to slow temporal variations, in the range where perceptual sensitivity is governed by Weber's law of sensation. In contrast, physiological processes acting downstream from phototransduction limit sensitivity to high frequencies and temporal resolution. We traced the paradoxical control of visual temporal sensitivity to rod photoresponses themselves. A scenario emerges where perceptual sensitivity is limited by: (1) the kinetics of neural processes acting downstream from phototransduction in scotopic lights, (2) rod response kinetics in mesopic lights, and (3) cone response kinetics as light levels rise into the photopic range.SIGNIFICANCE STATEMENT Our ability to detect flickering lights is constrained by the dynamics of the slowest step in the visual pathway. Cone photoresponse kinetics limit visual temporal sensitivity in bright (photopic) lights, whereas mechanisms in the inner retina limit sensitivity in dim (scotopic) lights. The neural mechanisms underlying the transition between scotopic and photopic vision in mesopic lights, when both rods are cones are active, are unknown. This study provides a missing link in this mechanism by establishing that rod photoresponse kinetics limit temporal sensitivity during the mesopic transition. Surprisingly, this range is where Weber's Law of Sensation governs temporal contrast sensitivity in mouse. Our results will help guide future studies of complex and dynamic interactions between rod-cone signals in the mesopic retina.

Onecut1 is essential for horizontal cell genesis and retinal integrity.

Horizontal cells are interneurons that synapse with photoreceptors in the outer retina. Their genesis during development is subject to regulation by transcription factors in a hierarchical manner. Previously, we showed that Onecut 1 (Oc1), an atypical homeodomain transcription factor, is expressed in developing horizontal cells (HCs) and retinal ganglion cells (RGCs) in the mouse retina. Herein, by knocking out Oc1 specifically in the developing retina, we show that the majority (∼80%) of HCs fail to form during early retinal development, implying that Oc1 is essential for HC genesis. However, no other retinal cell types, including RGCs, were affected in the Oc1 knock-out. Analysis of the genetic relationship between Oc1 and other transcription factor genes required for HC development revealed that Oc1 functions downstream of FoxN4, in parallel with Ptf1a, but upstream of Lim1 and Prox1. By in utero electroporation, we found that Oc1 and Ptf1a together are not only essential, but also sufficient for determination of HC fate. In addition, the synaptic connections in the outer plexiform layer are defective in Oc1-null mice, and photoreceptors undergo age-dependent degeneration, indicating that HCs are not only an integral part of the retinal circuitry, but also are essential for the survival of photoreceptors. In sum, these results demonstrate that Oc1 is a critical determinant of HC fate, and reveal that HCs are essential for photoreceptor viability, retinal integrity, and normal visual function.

Restoration of cone vision in a mouse model of achromatopsia.

Loss of cone function in the central retina is a pivotal event in the development of severe vision impairment for many prevalent blinding diseases. Complete achromatopsia is a genetic defect resulting in cone vision loss in 1 in 30,000 individuals. Using adeno-associated virus (AAV) gene therapy, we show that it is possible to target cones and rescue both the cone-mediated electroretinogram response and visual acuity in the Gnat2 ( cpfl3 ) mouse model of achromatopsia.

Signal detection theoretic estimates of the murine absolute visual threshold are independent of decision bias.

Decision bias influences estimates of the absolute visual threshold. However, most psychophysical estimates of the murine absolute visual threshold have not taken bias into account. Here we developed a one-alternative forced choice (1AFC) assay to assess decision bias of mice at the absolute visual threshold via the theory of signal detection, and compared our approach with the more conventional high-threshold theoretic approach. In the 1AFC assay, mice of both sexes were trained to signal whether they detected a flash stimulus. We directly measured both Hit and False Alarm rates, which were used to estimate d' Using the theory of signal detection we obtained absolute thresholds by interpolating the intensity where d' = 1 from d' psychometric functions. This gave bias-independent estimates of the absolute visual threshold which ranged over 6-fold, averaging ∼1R* in 1,000 rods (n = 7 mice). To obtain high-threshold theoretic estimates of absolute visual threshold from the same mice, we estimated threshold intensities from frequency of seeing curves, corrected for guessing. This gave us thresholds that were strongly correlated with decision bias, ranging over 13-fold and averaged ∼1 R* in 2,500 rods. We conclude that the theory of signal detection uses False Alarms to overcome decision bias and narrow the range of threshold estimates in mice, providing a powerful tool for understanding detection behavior near absolute visual threshold.Significance statement The detection of dim flashes of light depends both on the number of photons delivered by the flash and on the level of spontaneous neural activity, which observers can misclassify as incident photons. Such ambiguity introduces decision biases, which can make observers appear more, or less sensitive to light, increasing the range of sensitivity estimates. We found that the theory of signal detection provides a framework for dealing with these biases in mice by taking spontaneous neural activity into account, reducing the range of sensitivity estimates during the detection of dim, brief, flashes of light.

The relationship between slow photoresponse recovery rate and temporal resolution of vision.

The rate at which photoreceptors recover from excitation is thought to be critical for setting the temporal resolution of vision. Indeed, mutations in RGS9 (regulator of G-protein signaling 9) and R9AP (RGS9 anchor protein) proteins mediating rapid photoresponse recovery impair patients' ability to see moving objects. In this study, we analyzed temporal properties of retinal sensitivity and spatiotemporal aspects of visual behavior in R9AP knock-out mice. Surprisingly, we have found that this knock-out does not affect dim-light vision mediated by rods acting as single-photon counters. Under these conditions, vision was also unaffected in mice overexpressing R9AP in rods, which causes accelerated photoresponse recovery. However, in brighter light, slow photoresponse recovery in rods and cones impaired visual responses to high temporal frequency stimuli, as reported for the daylight vision of human patients. Therefore, the speed of photoresponse recovery can affect temporal resolution and motion detection when photoreceptors integrate signals from multiple photons but not when they act as single-photon counters.

Long-term retinal function and structure rescue using capsid mutant AAV8 vector in the rd10 mouse, a model of recessive retinitis pigmentosa.

The retinal degeneration 10 (rd10) mouse is a well-characterized model of autosomal recessive retinitis pigmentosa (RP), which carries a spontaneous mutation in the ß subunit of rod cGMP-phosphodiesterase (PDEß). Rd10 mouse exhibits photoreceptor dysfunction and rapid rod photoreceptor degeneration followed by cone degeneration and remodeling of the inner retina. Here, we evaluate whether gene replacement using the fast-acting tyrosine-capsid mutant AAV8 (Y733F) can provide long-term therapy in this model. AAV8 (Y733F)-smCBA-PDEß was subretinally delivered to postnatal day 14 (P14) rd10 mice in one eye only. Six months after injection, spectral domain optical coherence tomography (SD-OCT), electroretinogram (ERG), optomotor behavior tests, and immunohistochemistry showed that AAV8 (Y733F)-mediated PDEß expression restored retinal function and visual behavior and preserved retinal structure in treated rd10 eyes for at least 6 months. This is the first demonstration of long-term phenotypic rescue by gene therapy in an animal model of PDEß-RP. It is also the first example of tyrosine-capsid mutant AAV8 (Y733F)-mediated correction of a retinal phenotype. These results lay the groundwork for the development of PDEß-RP gene therapy trial and suggest that tyrosine-capsid mutant AAV vectors may be effective for treating other rapidly degenerating models of retinal degeneration.

Impaired cone function and cone degeneration resulting from CNGB3 deficiency: down-regulation of CNGA3 biosynthesis as a potential mechanism.

The cone cyclic nucleotide-gated (CNG) channel is essential for central and color vision and visual acuity. This channel is composed of two structurally related subunits, CNGA3 and CNGB3; CNGA3 is the ion-conducting subunit, whereas CNGB3 is a modulatory subunit. Mutations in both subunits are associated with achromatopsia and progressive cone dystrophy, with mutations in CNGB3 alone accounting for 50% of all known cases of achromatopsia. However, the molecular mechanisms underlying cone diseases that result from CNGB3 deficiency are unknown. This study investigated the role of CNGB3 in cones, using CNGB3(-/-) mice. Cone dysfunction was apparent at the earliest time point examined (post-natal day 30) in CNGB3(-/-) mice. When compared with wild-type (WT) controls: photopic electroretingraphic (ERG) responses were decreased by approximately 75%, whereas scotopic ERG responses were unchanged; visual acuity was decreased by approximately 20%, whereas contrast sensitivity was unchanged; cone density was reduced by approximately 40%; photoreceptor apoptosis was detected; and outer segment disorganization was observed in some cones. Notably, CNGA3 protein and mRNA levels were significantly decreased in CNGB3(-/-) mice; in contrast, mRNA levels of S-opsin, Gnat2 and Pde6c were unchanged, relative to WT mice. Hence, we show that loss of CNGB3 reduces biosynthesis of CNGA3 and impairs cone CNG channel function. We suggest that down-regulation of CNGA3 contributes to the pathogenic mechanism by which CNGB3 mutations lead to human cone disease.

Temporal Contrast Sensitivity Increases despite Photoreceptor Degeneration in a Mouse Model of Retinitis Pigmentosa.

The detection of temporal variations in amplitude of light intensity, or temporal contrast sensitivity (TCS), depends on the kinetics of rod photoresponse recovery. Uncharacteristically fast rod recovery kinetics are facets of both human patients and transgenic animal models with a P23H rhodopsin mutation, a prevalent cause of retinitis pigmentosa (RP). Here, we show that mice with this mutation (RhoP23H/+) exhibit an age-dependent and illumination-dependent enhancement in TCS compared with controls. At retinal illumination levels producing ≥1000 R*/rod/s or more, postnatal day 30 (P30) RhoP23H/+ mice exhibit a 1.2-fold to 2-fold increase in retinal and optomotor TCS relative to controls in response to flicker frequencies of 3, 6, and 12 Hz despite significant photoreceptor degeneration and loss of flash electroretinogram (ERG) b-wave amplitude. Surprisingly, the TCS of RhoP23H/+ mice further increases as degeneration advances. Enhanced TCS is also observed in a second model (rhodopsin heterozygous mice, Rho+/-) with fast rod recovery kinetics and no apparent retinal degeneration. In both mouse models, enhanced TCS is explained quantitatively by a comprehensive model that includes photoresponse recovery kinetics, density and collecting area of degenerating rods. Measurement of TCS may be a non-invasive early diagnostic tool indicative of rod dysfunction in some forms of retinal degenerative disease.

Molecular and functional architecture of the mouse photoreceptor network.

Mouse photoreceptors are electrically coupled via gap junctions, but the relative importance of rod/rod, cone/cone, or rod/cone coupling is unknown. Furthermore, while connexin36 (Cx36) is expressed by cones, the identity of the rod connexin has been controversial. We report that FACS-sorted rods and cones both express Cx36 but no other connexins. We created rod- and cone-specific Cx36 knockout mice to dissect the photoreceptor network. In the wild type, Cx36 plaques at rod/cone contacts accounted for more than 95% of photoreceptor labeling and paired recordings showed the transjunctional conductance between rods and cones was ~300 pS. When Cx36 was eliminated on one side of the gap junction, in either conditional knockout, Cx36 labeling and rod/cone coupling were almost abolished. We could not detect direct rod/rod coupling, and cone/cone coupling was minor. Rod/cone coupling is so prevalent that indirect rod/cone/rod coupling via the network may account for previous reports of rod coupling.

Speed, spatial, and temporal tuning of rod and cone vision in mouse.

Rods and cones subserve mouse vision over a 100 million-fold range of light intensity (-6 to 2 log cd m(-2)). Rod pathways tune vision to the temporal frequency of stimuli (peak, 0.75 Hz) and cone pathways to their speed (peak, approximately 12 degrees/s). Both pathways tune vision to the spatial components of stimuli (0.064-0.128 cycles/degree). The specific photoreceptor contributions were determined by two-alternative, forced-choice measures of contrast thresholds for optomotor responses of C57BL/6J mice with normal vision, Gnat2(cpfl3) mice without functional cones, and Gnat1-/- mice without functional rods. Gnat2(cpfl3) mice (threshold, -6.0 log cd m(-2)) cannot see rotating gratings above -2.0 log cd m(-2) (photopic vision), and Gnat1-/- mice (threshold, -4.0 log cd m(-2)) are blind below -4.0 log cd m(-2) (scotopic vision). Both genotypes can see in the transitional mesopic range (-4.0 to -2.0 log cd m(-2)). Mouse rod and cone sensitivities are similar to those of human. This parametric study characterizes the functional properties of the mouse visual system, revealing the rod and cone contributions to contrast sensitivity and to the temporal processing of visual stimuli.

Monitoring mouse retinal degeneration with high-resolution spectral-domain optical coherence tomography.

Progression of retinal degeneration in a mouse model was studied in vivo with high-resolution spectral-domain optical coherence tomography (SD-OCT). Imaging in 3D with high depth resolution (<3 mum), SD-OCT resolved all the major layers of the retina of control C57BL/6J mice. Images of transgenic mice having a null mutation of the rhodopsin gene revealed the anatomical consequences of retinal degeneration: thinning of the outer retina, including the outer plexiform layer (OPL), outer nuclear layer (ONL), and inner and outer segments (IS/OS). We monitored the progression of retinal degeneration in rd1 mice (C3H/HeJ) by periodically imaging the same mice from the time the pups opened their eyes on P13 to P34. SD-OCT images showed that the outer retina (OPL, ONL, IS/OS) had already thinned by 73% (100 to 27 mum) at eye opening. The retina continued to degenerate, and by P20 the outer retina was not resolvable. The thickness of entire retina decreased from 228 mum (control) to 152 mum on P13 and to 98 mum by P34, a 57% reduction with the complete loss in the outer retina. In summary, we show that SD-OCT can monitor the progression of retinal degeneration in transgenic mice.

Visual Temporal Contrast Sensitivity in the Behaving Mouse Shares Fundamental Properties with Human Psychophysics.

The mammalian visual system has a remarkable capacity to detect differences in contrast across time, which is known as temporal contrast sensitivity (TCS). Details of the underlying neural mechanisms are rapidly emerging as a result of a series of elegant electrophysiological studies performed largely with the mouse as an experimental model. However, rigorous psychophysical methods are necessary to pair the electrophysiology with temporal visual behavior in mouse. The optomotor response is frequently used as a proxy for retinal temporal processing in rodents. However, subcortical reflexive pathways drive the optomotor response rather than cortical decision-making areas. To address this problem, we have developed an operant behavior assay that measures TCS in behaving mice. Mice were trained to perform a forced-choice visual task and were tested daily on their ability to distinguish flickering from nonflickering overhead lights. Correct responses (Hit and Correct Rejections) were rewarded. Contrast, temporal frequency, and mean illumination of the flicker were the independent variables. We validated and applied the theory of signal detection to estimate the discriminability factor (d´), a measure of performance that is independent of response bias and motivation. The empirical contrast threshold was defined as the contrast necessary to elicit d´ = 1 and TCS as the inverse of the contrast threshold. With this approach, we established in the mouse a model of human vision that shares fundamental properties of human temporal psychophysics such as Weber adaptation in response to low temporal frequency flicker and illumination-dependent increases in critical flicker frequency as predicted by the Ferry-Porter law.

A system to measure the pupil response to steady lights in freely behaving mice.

BACKGROUND: Transgenic mice are widely used for the study of basic visual function and retinal disease, including in psychophysical tests. Mice have a robust pupillary light reflex that controls the amount of light that enters the eye, and the attenuating effects of the pupil must be considered during such tests. Measurement of the size of pupils at various luminance levels requires that mice remain stable over prolonged periods of time; however, sedation of mice with anesthesia and/or manual restraint can influence the size of their pupils. NEW METHOD: We present a system to measure the pupillary light response to steady lights of freely behaving mice using a custom-built, portable device that automatically acquires close-up images of their eyes. The device takes advantage of the intrinsic nature of mice to inspect objects of interest and can be used to measure pupillary responses in optomotor or operant behavior testing chambers. RESULTS: The size of the pupils in freely behaving mice decreased gradually with luminance from a maximal area in the dark of 3.8mm2 down to a minimum 0.14mm2 at 80 scotopic cd/m2. The data was well fit with a Hill equation with Lo equal to 0.21cd/m2 and coefficient h=0.48. COMPARISON WITH EXISTING METHODS: These values agree with prior measurements of the pupillary response of unrestrained mice that use more laborious and time consuming approaches. CONCLUSIONS: Our new method facilitates practical, straightforward and accurate measurements of pupillary responses made under the same experimental conditions as those used during psychophysical testing.

Spatial and temporal patterns of distribution of the gap junctional protein connexin43 during retinal regeneration of adult newt.

Newts possess the ability to regenerate a functional retina after complete removal of the original retina. We performed immunoblot and immunohistochemical analyses of newt retinas at different stages of regeneration by using an antibody against a gap junction channel protein, connexin43 (Cx43). The specificity of the antibody was shown on immunoblots as well as immunohistochemical staining pattern in the normal retina. Punctate Cx43 immunolabeling was detected intensely between proliferating cell nuclear antigen-immunoreactive progenitor cells in the regenerating retinas, and the amount of this labeling tended to be prominent along both scleral and vitreal sides. The amount of Cx43 became less abundant as regeneration proceeded. This temporal loss of Cx43 during regeneration was also shown on the immunoblot analysis. Furthermore, the loss of Cx43 was observed in a spatial manner in the peripheral retina, where progenitor cells clustered at the ciliary marginal zone (CMZ) are adding new cells of all types in order toward the central retina. Immunolabeling often extended longitudinally throughout the retina when regenerating retinas became thick. Double immunolabeling with Cx43 and glial fibrillary acidic protein indicated the overlapping between the Cx43 and Müller cell processes. At the beginning of the synaptic formation, immunolabeling almost disappeared in the entire retina. However, in the completely regenerated retina, Cx43 reappeared in the distal end of Müller cells and pigment epithelial cells in the same pattern as in the normal retina. The above observations lead us to speculate that Cx43-mediated gap junctions may play an important role in regenerating events. Possible roles of Cx43 during regeneration are discussed.

Morphological and functional organization of ON and OFF pathways in the adult newt retina.

Morphological and functional organization of ON and OFF pathways in the adult newt retina were examined by intracellular recording and staining techniques and immunohistochemistry. Synaptotagmin immunoreactivity discriminated three broad bands within the IPL: the distal band (sublamina I), the middle band (sublamina II) consisting of two dense punctate bands (sublaminae II(a) and II(b)), and proximal band (sublamina III). The Lucifer-yellow labeled OFF amacrine and ganglion cells send their processes mainly in sublamina I and/or II(a) where OFF bipolar cells extend their axon terminals, while ON amacrine and ganglion cells send their processes in sublamina III and/or II(b) where ON bipolar cells extend their axon terminals. Processes of ON-OFF amacrine and ganglion cells ramify broadly in the whole thickness of the IPL. Many bipolar cells responded to light spot with a transient hyperpolarization at both light onset and offset. They are probably subtypes of ON bipolar cells, because their axon terminals branch mainly in sublaminae III and/or II(b), although a few cells ramified the axon at both sublaminae II(a) and III. Two immunohistochemical markers for bipolar cells, PKC and RB-1, identified axon terminals in sublaminae III and/or II(b). From the ramification pattern of axon terminal, they are probably subtypes of ON bipolar cells. ChAT-ir amacrine cells ramified their dendrites in either sublamina I or II(b). Altogether, present studies support the general idea of segregation of ON and OFF pathways in sublaminae a and b of the IPL.

Loss of scotopic contrast sensitivity in the optomotor response of diabetic mice.

PURPOSE: Diabetes reduces retinal and visual sensitivity to dim light flashes. However, the impact of diabetes on contrast sensitivity in dim light is unknown. Based on the lowered visual sensitivity previously observed, we hypothesized that contrast sensitivity would similarly be reduced. We therefore examined scotopic contrast sensitivity of the optomotor response in the Ins2(Akita/+) mouse model of type 1 diabetes. METHODS: A longitudinal study of spatial and temporal contrast sensitivity in Ins2(Akita/+) mice and wild-type Ins2(+/+) littermates was conducted. Contrast sensitivity of the optomotor response to rotating gratings of various spatial and temporal frequencies was measured at a dim luminance level (2.6 · 10(-5) cd/m2) known to elicit rod- but not cone-driven responses. RESULTS: An early, progressive loss in scotopic contrast sensitivity was observed in Ins2(Akita/+) mice that was absent from Ins2(+/+) littermate controls. The loss in contrast sensitivity developed over a 3- to 4-month period after the onset of hyperglycemia. Ins2(Akita/+) mice exhibited a nonselective 40% loss in sensitivity to all spatial frequencies and a selective loss in sensitivity to fast but not to slow varying gratings (temporal frequencies > 0.1 Hz or, equivalently, speeds > 3 deg/s). Such losses in sensitivity were prevented by glycemic control with insulin treatment. CONCLUSIONS: An association between a model of type 1 diabetes and scotopic contrast sensitivity of the optomotor response is indicated. Ins2(Akita/+) mice exhibit a uniform loss in optomotor contrast sensitivity to all spatial frequencies that, unexpectedly, can be explained as being secondary to a retinal or central loss in sensitivity to high temporal frequencies.