Differential gene expression between central and peripheral retinal regions in dogs and comparison with humans.

The dog retina contains a central macula-like region, and there are reports of central retinal disorders in dogs with shared genetic etiologies with humans. Defining central/peripheral gene expression profiles may provide insight into the suitability of dogs as models for human disorders. We determined central/peripheral posterior eye gene expression profiles in dogs and interrogated inherited retinal and macular disease-associated genes for differential expression between central and peripheral regions. Bulk tissue RNA sequencing was performed on 8 mm samples of the dog central and superior peripheral regions, sampling retina and retinal pigmented epithelium/choroid separately. Reads were mapped to CanFam3.1, read counts were analyzed to determine significantly differentially expressed genes (DEGs). A similar analytic pipeline was used with a published bulk-tissue RNA sequencing human dataset. Pathways and processes involved in significantly DEGs were identified (Database for Annotation, Visualization and Integrated Discovery). Dogs and humans shared the extent and direction of central retinal differential gene expression, with multiple shared biological pathways implicated in differential expression. Many genes implicated in heritable retinal disorders in dogs and humans were differentially expressed between central and periphery. Approximately half of genes associated with human age-related macular degeneration were differentially expressed in human and dog tissues. We have identified similarities and differences in central/peripheral gene expression profiles between dogs and humans which can be applied to further define the relevance of dogs as models for human retinal disorders.

Consensus guidelines for nomenclature of companion animal inherited retinal disorders.

Companion animals, namely dogs, cats, and horses, can be affected with many forms of hereditary retinal disease. The number of such diseases characterized in the last decade has increased substantially, and nomenclature is nonstandardized, heterogenous, and confusing. We provide in this viewpoint article consensus guidelines for naming of companion animal hereditary retinal diseases, either prospectively or retrospectively. These consensus guidelines have been developed with the purpose of standardizing nomenclature. We provide examples for the iterative nomenclature process and a comprehensive File S1 on proposed renaming of previously described diseases.

Quantifying refractive error in companion dogs with and without nuclear sclerosis: 229 eyes from 118 dogs.

OBJECTIVE: To evaluate the relationship between nuclear sclerosis (NS) and refractive error in companion dogs. ANIMALS STUDIED: One hundred and eighteen companion dogs. PROCEDURES: Dogs were examined and found to be free of significant ocular abnormalities aside from NS. NS was graded from 0 (absent) to 3 (severe) using a scale developed by the investigators. Manual refraction was performed. The effect of NS grade on refractive error was measured using a linear mixed effects analysis adjusted for age. The proportion of eyes with >1.5 D myopia in each NS grade was evaluated using a chi-square test. Visual impairment score (VIS) was obtained for a subset of dogs and compared against age, refractive error, and NS grade. RESULTS: Age was strongly correlated with NS grade (p < .0001). Age-adjusted analysis of NS grade relative to refraction showed a mild but not statistically significant increase in myopia with increasing NS grade, with eyes with grade 3 NS averaging 0.58-0.88 D greater myopia than eyes without NS. However, the myopia of >1.5 D was documented in 4/58 (6.9%) eyes with grade 0 NS, 12/91 (13.2%) eyes with grade 1 NS, 13/57 (22.8%) eyes with grade 2 NS, and 7/23 (30.4%) eyes with grade 3 NS. Risk of myopia >1.5 D was significantly associated with increasing NS grade (p = .02). VIS was associated weakly with refractive error, moderately with age, and significantly with NS grade. CONCLUSIONS: NS is associated with visual deficits in some dogs but is only weakly associated with myopia. More work is needed to characterize vision in aging dogs.

Subjective vision assessment in companion dogs using dogVLQ demonstrates age-associated visual dysfunction.

Introduction: Dim light vision as assessed by proxy and clinical tools is commonly impaired in older humans and impacts quality of life. Although proxy visual assessment tools have been developed for dogs, it is unclear if they are sensitive enough to detect subtle visual dysfunction in older dogs. We sought to determine if a newly designed proxy visual function questionnaire could detect age-associated differences in visual behaviors in varying lighting conditions in dogs. Methods: A 27-item questionnaire (the dog variable lighting questionnaire, dogVLQ) was designed to assess visual behavior in dogs in different lighting settings. We conducted the dogVLQ, a previously validated visual function questionnaire the dog vision impairment score and performed light- and dark-adapted electroretinography (ERG) on a subset of dogs. Questionnaire scores were analyzed for dog age associations using correlation analysis. Results: Questionnaire responses from 235 dog owners were obtained (122 female, 112 male dogs), 79 of which underwent ERG (43 female, 36 male dogs). Bright light visual behavior was significantly associated with light-adapted bright flash ERG amplitudes, visual behavior in near darkness was associated with dark-adapted ERG amplitudes. The dogVLQ identified worse vision in older dogs in bright light, dim light, and darkness; predicted onset was younger for vision in near darkness. Older dogs had more difficulty navigating transitions between lighting conditions. Discussion: Subjective dog owner assessment of visual function associates with objective measurement of retinal function in dogs and supports reduced vision-mediated behaviors in older dogs.

Peroxisome Proliferator-Activated Receptor Gamma Coactivator-1Alpha (PGC-1α): A Transcriptional Regulator at the Interface of Aging and Age-Related Macular Degeneration?

Human age-related macular degeneration (AMD) is a prevalent age-related disease which causes retinal dysfunction and disability. Genetic and cell culture studies from AMD patients have implicated impaired activity of peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α). PGC-1α is a transcriptional co-regulator that acts to control a plethora of metabolic processes relevant to AMD pathophysiology including gluconeogenesis, oxidative phosphorylation, and response to oxidative injury. Perturbation of PGC-1α activity in mice causes AMD-like RPE and retinal pathology. There is potential for therapeutic modulation of the PGC-1α pathway in AMD treatment.

Age-associated changes in electroretinography measures in companion dogs.

PURPOSE: To determine the association between age and retinal full-field electroretinographic (ERG) measures in companion (pet) dogs, an important translational model species for human neurologic aging. METHODS: Healthy adult dogs with no significant ophthalmic abnormalities were included. Unilateral full-field light- and dark-adapted electroretinography was performed using a handheld device, with mydriasis and topical anaesthesia. Partial least squares effect screening analysis was performed to determine the effect of age, sex, body weight and use of anxiolytic medication on log-transformed ERG peak times and amplitudes; age and anxiolytic usage had significant effects on multiple ERG outcomes. Mixed model analysis was performed on data from dogs not receiving anxiolytic medications. RESULTS: In dogs not receiving anxiolytics, median age was 118 months (interquartile range 72-140 months, n = 77, 44 purebred, 33 mixed breed dogs). Age was significantly associated with prolonged peak times of a-waves (dark-adapted 3 and 10 cds/m2 flash p < 0.0001) and b-waves (cone flicker p = 0.03, dark-adapted 0.01 cds/m2 flash p = 0.001). Age was also significantly associated with reduced amplitudes of a-waves (dark-adapted 3 cds/m2 flash p < 0.0001, 10 cds/m2 flash p = 0.005) and b-waves (light-adapted 3 cds/m2 flash p < 0.0001, dark-adapted 0.01 cds/m2 flash p = 0.0004, 3 cds/m2 flash p < 0.0001, 10 cds/m2 flash p = 0.007) and flicker (light-adapted 30 Hz 3 cds/m2 p = 0.0004). Within the Golden Retriever breed, these trends were matched in a cross-sectional analysis of 6 individuals that received no anxiolytic medication. CONCLUSIONS: Aged companion dogs have slower and reduced amplitude responses in both rod- and cone-mediated ERG. Consideration of anxiolytic medication use should be made when conducting ERG studies in dogs.

Hemostatic profiles in dogs with sudden acquired retinal degeneration syndrome.

BACKGROUND: Sudden acquired retinal degeneration syndrome (SARDS) is a common cause of irreversible blindness in dogs. It bears clinical resemblance to hypercortisolism, which can be associated with hypercoagulability. The role of hypercoagulability in dogs with SARDS is unknown. OBJECTIVE: Determine hemostatic profiles in dogs with SARDS. ANIMALS: Prospective pilot study: Dogs with a history of SARDS (n = 12). Prospective case-control study: Dogs with recent onset of SARDS (n = 7) and age-, breed-, and sex-matched controls (n = 7). METHODS: Prospective pilot study: We performed thromboelastography (TEG). Prospective case-control study: Dogs had CBC, serum biochemistry, urinalysis, TEG, fibrinogen concentration, antithrombin activity, D-dimers, thrombin-antithrombin complexes, and optical platelet aggregometry performed. RESULTS: Prospective pilot study: 9/12 dogs with a history of SARDS were hypercoagulable with increased TEG G value and 2/3 had hyperfibrinogenemia. Case-control study: All dogs with SARDS and 5/7 controls were hypercoagulable based on TEG G value. Dogs with SARDS had significantly higher G values (median, 12.7 kdynes/s; range, 11.2-25.4; P = .04) and plasma fibrinogen concentration (median, 463 mg/dL; range, 391-680; P < .001) compared to controls. CONCLUSIONS AND CLINICAL IMPORTANCE: Hypercoagulability was common in both dogs with SARDS and controls, but dogs with SARDS were significantly more hypercoagulable on TEG. The role of hypercoagulability in the pathogenesis of SARDS remains to be determined.

An unusual inherited electroretinogram feature with an exaggerated negative component in dogs.

OBJECTIVES: To assess an inherited abnormal negative response electroretinogram (NRE) that originated in a family of Papillon dogs. ANIMALS STUDIED: Thirty-eight dogs (Papillons, or Papillon cross Beagles or Beagles). PROCEDURES: Dogs underwent routine ophthalmic examination and a detailed dark-adapted, light-adapted and On-Off electroretinographic study. Vision was assessed using a four-choice exit device. Spectral-domain optical coherence tomography (SD-OCT) was performed on a subset of dogs. Two affected males were outcrossed to investigate the mode of inheritance of the phenotype. RESULTS: The affected dogs had an increased underlying negative component to the ERG. This was most pronounced in the light-adapted ERG, resulting in a reduced b-wave and an exaggerated photopic negative response (PhNR). Changes were more pronounced with stronger flashes. Similarly, the On-response of the On-Off ERG had a reduced b-wave and a large post-b-wave negative component. The dark-adapted ERG had a significant increase in the scotopic threshold response (STR) and a significant reduction in the b:a-wave ratio. Significant changes could be detected at 2 months of age but became more pronounced with age. Vision testing using a four-choice device showed affected dogs had reduced visual performance under the brightest light condition. There was no evidence of a degenerative process in the affected dogs up to 8.5 years of age. Test breeding results suggested the NRE phenotype had an autosomal dominant mode of inheritance. CONCLUSIONS: We describe an inherited ERG phenotype in Papillon dogs characterized by an underlying negative component affecting both dark- and light-adapted ERG responses.

Use of Cognitive Testing, Questionnaires, and Plasma Biomarkers to Quantify Cognitive Impairment in an Aging Pet Dog Population.

BACKGROUND: Aging dogs may suffer from canine cognitive dysfunction syndrome (CCDS), a condition in which cognitive decline is associated with amyloid pathology and cortical atrophy. Presumptive diagnosis is made through physical examination, exclusion of systemic/metabolic conditions, and completion of screening questionnaires by owners. OBJECTIVE: This study aimed to determine whether cognitive function could be quantified in aging pet dogs, and to correlate cognitive testing with validated questionnaires and plasma neurofilament light chain (pNfL) concentration. METHODS: Thirty-nine dogs from fifteen breeds were recruited (9.3 to 15.3 years). Owners completed the Canine Dementia Scale (CADES) and Canine Cognitive Dysfunction Rating scale (CCDR). Executive control and social cues were tested, and pNfL was measured with single molecule array assay. Comparisons were made between cognitive testing scores, CADES, CCDR scores, and pNfL. RESULTS: CADES scoring classified five dogs as severe CCDS, six as moderate, ten as mild, and eighteen as normal. CCDR identified seven dogs at risk of CCDS and thirty-two as normal. Cognitive testing was possible in the majority of dogs, although severely affected dogs were unable to learn tasks. CADES score correlated with sustained attention duration (r = -0.47, p = 0.002), inhibitory control (r = -0.51, p = 0.002), detour (r = -0.43, p = 0.001), and pNfL (r = 0.41, p = 0.025). Concentration of pNfL correlated with inhibitory control (r = -0.7, p≤0.001). The CCDR scale correlated with performance on inhibitory control (r = -0.46, p = 0.005). CONCLUSION: Our findings suggest that a multi-dimensional approach using a combination of questionnaires, specific cognitive tests, and pNfL concentration can be used to quantify cognitive decline in aging pet dogs.

A Comprehensive Study of the Retinal Phenotype of Rpe65-Deficient Dogs.

The Rpe65-deficient dog has been important for development of translational therapies of Leber congenital amaurosis type 2 (LCA2). The purpose of this study was to provide a comprehensive report of the natural history of retinal changes in this dog model. Rpe65-deficient dogs from 2 months to 10 years of age were assessed by fundus imaging, electroretinography (ERG) and vision testing (VT). Changes in retinal layer thickness were assessed by optical coherence tomography and on plastic retinal sections. ERG showed marked loss of retinal sensitivity, with amplitudes declining with age. Retinal thinning initially developed in the area centralis, with a slower thinning of the outer retina in other areas starting with the inferior retina. VT showed that dogs of all ages performed well in bright light, while at lower light levels they were blind. Retinal pigment epithelial (RPE) inclusions developed and in younger dogs and increased in size with age. The loss of photoreceptors was mirrored by a decline in ERG amplitudes. The slow degeneration meant that sufficient photoreceptors, albeit very desensitized, remained to allow for residual bright light vision in older dogs. This study shows the natural history of the Rpe65-deficient dog model of LCA2.

Canine sudden acquired retinal degeneration syndrome: Owner perceptions on the time to vision loss, treatment outcomes, and prognosis for life.

BACKGROUND: Canine sudden acquired retinal degeneration syndrome (SARDS) causes blindness for which there are no proven effective treatments. We aimed to clarify the time to vision loss, treatment response/side effects, and prognosis for life in dogs with SARDS. METHODS: An online questionnaire was administered to owners of dogs with a historical diagnosis of SARDS. Mortality data were compared with a published purebred reference population. Select parameters were analyzed statistically using general linear model with least square means, two-sample t tests, and chi-squared or Fisher's exact tests. RESULTS: Responses from owners that stated that their dog visited an ophthalmologist and had electroretinography performed (n = 434) were analyzed. The majority of owners (65.4%) reported the time from vision disturbance to complete vision loss as <2 weeks; 19.4% reported >4 weeks. Onset of systemic clinical signs to complete vision loss was >4 weeks in 44.5% of responses. A higher proportion of owners reported some vision recovery with combination treatment (14.4%) compared with monotherapy (3.2%, P = .0004). Side effects of treatment were commonly reported. Dogs with SARDS did not have a shorter lifespan than the reference population but had higher incidence of kidney disease (P = .0001) and respiratory disease (P = .0004) at death. CONCLUSIONS: Dogs with SARDS have a rapid onset of vision loss. In the owner's opinion, treatment is unlikely to restore vision and is associated with systemic side effects. The potential for systemic pathologies that arise after SARDS diagnosis warrants further study.

Retinal cone photoreceptor distribution in the American black bear (Ursus americanus).

The distribution of cone photoreceptor subtypes (important for color vision and vision quality) varies widely in different carnivore species, but there have been limited studies on bear (ursid) cone distribution. A previous behavioral study suggests that American black bears (Ursus americanus) are dichromatic, indicating that they possess two cone subtypes, although the retinal distribution of cones is unknown. The purpose of this study was to examine the subtype and topography of cones in American black bear retinas to further predict the nature of their color vision and image resolution. We studied 10 eyes from seven individual legally hunted black bears in northeastern North Carolina. Cryosections and retinal wholemounts were labeled using antibodies targeting two cone opsin subtypes: long/medium (L/M) wavelength sensitive and short (S) wavelength sensitive. Cones in fluorescent microscopy images were counted and density maps were created for retinal wholemounts. The black bear retina contains both cone subtypes and L/M cones outnumber S cones by at least 3:1, a finding confirmed in retinal frozen sections. There are higher concentrations of S cones present than typically seen in other carnivores with some evidence for co-expression of L/M and S cones. A cone-dense area centralis is present dorsotemporal to the optic nerve, similar to other carnivores. These results confirm that American black bears are predicted to have a dichromatic vision with high acuity indicated by the presence of a dorsotemporally located area centralis.

Plasma Amyloid Beta Concentrations in Aged and Cognitively Impaired Pet Dogs.

Longevity-associated neurological disorders have been observed across human and canine aging populations. Alzheimer's disease (AD) and canine cognitive dysfunction syndrome (CDS) represent comparable diseases affecting both species as they age. Translational diagnostic and therapeutic research is needed for these incurable diseases. The amyloid ß (Aß) peptide family are AD-associated peptides with identical amino acid sequences between dogs and humans. Plasma Aß42 concentration increases with age and decreases with AD in humans, and cerebrospinal fluid (CSF) concentration decreases in AD and correlates inversely with the amyloid load within the brain. Similarly, CSF Aß42 concentrations decrease in dogs with CDS but there is limited and conflicting information on plasma Aß42 concentrations in aging dogs and dogs with CDS. We measured plasma concentrations of Aß42 and Aß40 with an ultrasensitive single-molecule array assay (SIMOA) in a population of healthy aging dogs of different life stages (n = 36) and dogs affected with CDS (n = 11). In addition, the ratio of Aß42/ß40 was calculated. The mean plasma concentrations of Aß42 and Aß40 increased significantly with age (r2 = 0.27, p = 0.001; and r2 = 0.42, p < 0.001, respectively) and with life stage: puppy/junior group (0.43-2 years): 1.23 ± 0.95 and 38.26 ± 49.43 pg/mL; adult/mature group (2.1-9 years): 10.99 ± 5.45 and 131.05 ± 80.17 pg/mL; geriatric/senior group (9.3-14.5 years): 18.65 ± 16.65 and 192.88 ± 146.38 pg/mL, respectively. Concentrations of Aß42 and Aß40 in dogs with CDS (11.0-15.6 years) were significantly lower than age-matched healthy dogs at 11.61 ± 6.39 and 150.23 ± 98.2 pg/mL (p = 0.0048 and p = 0.001), respectively. Our findings suggest the dynamics of canine plasma amyloid concentrations are analogous to that found in aging humans with and without AD.

Plasma Neurofilament Light Chain as a Translational Biomarker of Aging and Neurodegeneration in Dogs.

Age is a primary risk factor for multiple comorbidities including neurodegenerative diseases. Pet dogs and humans represent two populations that have experienced a significant increase in average life expectancy over the last century. A higher prevalence of age-related neurodegenerative diseases has been observed across both species, and human diseases, such as Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), have canine analogs, canine cognitive dysfunction (CCD), and degenerative myelopathy (DM) respectively. In humans, protein biomarkers have proved useful in the prediction and diagnosis of neurodegeneration. Molecular signatures of many proteins are highly conserved across species. In this study, we explored the potential of the neuronal cytoskeletal protein neurofilament light chain (NfL) as a biomarker of neuro-aging in dogs using an ultrasensitive single-molecule array assay to measure plasma concentrations. Healthy dogs of different ages and dogs affected with CCD and DM were evaluated. The mean plasma NfL concentrations in the different age groups of the healthy population were as follows: 4.55 ± 1.70 pg/mL in puppy/junior group (0.43-2 years), 13.51 ± 6.8 pg/mL in adult/mature group (2.1-9 years), and 47.1 ± 12.68 pg/mL in geriatric/senior group (9.3-14.5 years). Concentrations in dogs with DM (7.5-12.6 years) and CCD (11.0-15.6 years) were 84.17 ± 53.57 pg/mL and 100.73 ± 83.72 pg/mL, respectively. Plasma NfL increases in an age-dependent manner and is significantly elevated in dogs diagnosed with neurodegenerative disease. This work identified plasma NfL as a key clinical index of neuro-aging and neurodegeneration in pet dogs. Our findings mirror recent reports from human neurodegenerative diseases.

Detection of circulating anti-retinal antibodies in dogs with sudden acquired retinal degeneration syndrome using indirect immunofluorescence: A case-control study.

Sudden acquired retinal degeneration syndrome (SARDS) in dogs is proposed to have an immune-mediated etiology. However, there is conflicting evidence regarding the presence of antiretinal antibodies, as assessed by western blotting, in the serum of SARDS patients. Because of the possibility that antibodies recognize only conformational epitopes, we hypothesized that a more sensitive method to investigate circulating retinal autoantibodies in SARDS is immunofluorescence. Sera from 14 dogs with early SARDS, and 14 age- and breed-matched healthy control dogs were screened for circulating antiretinal IgG, IgM, IgE and IgA using indirect immunofluorescence on lightly fixed frozen sections of normal canine retina. Controls without canine serum were also performed. A nuclear counterstain was used to identify cellular retinal layers. Images were obtained using a fluorescence microscope, and 2-3 separate masked observers graded retinal layers for fluorescence staining intensity using a 0-3 scale. Total circulating IgG and IgM was assessed by radial immunodiffusion. Statistical analysis was performed using 2-way ANOVA, paired 2-tailed student's t-test and correlation analysis. Intensity of IgG staining of photoreceptor outer segments was significantly higher using serum from dogs with SARDS compared with healthy controls in 2/3 observers (P < 0.05). Intensity of IgM staining throughout the retina was higher in SARDS dogs compared to matched healthy controls (P < 0.0001), although no specific retinal layer was statistically significant. There were no differences in staining intensity for IgE or IgA. Dogs with SARDS had a comparably lower circulating IgG and higher IgM than healthy controls (P = 0.01 and 0.001 respectively) and IgG and IgM were negatively correlated (r = -0.69, P = 0.007). Despite having decreased serum IgG compared with healthy controls, circulating IgG in dogs with SARDS binds photoreceptor outer segments to a greater extent. Dogs with SARDS have a relatively higher circulating IgM than matched healthy controls. The pathogenic nature of these antibodies is unknown.

MOLECULAR PREVALENCE OF SELECTED VECTOR-BORNE ORGANISMS IN CAPTIVE RED WOLVES (CANIS RUFUS).

The red wolf (Canis rufus) is a critically endangered North American canid, with surviving conspecifics divided between a captive breeding population and a reintroduced free-ranging population. The goal of this study was to assess the prevalence of selected vector-borne pathogens in captive red wolves. Whole blood samples were collected from 35 captive red wolves. Quantitative polymerase chain reaction (PCR) assays were performed on extracted DNA to identify infection by Trypanosoma cruzi and vector-borne organisms within the following genera: Anaplasma, Babesia, Bartonella, Ehrlichia, Mycoplasma, Neoehrlichia, Neorickettsia, and Rickettsia. All red wolves sampled were PCR-negative for all tested organisms. These pathogens are unlikely to constitute threats to red wolf conservation and breeding efforts under current captive management conditions. The results of this study establish a baseline that may facilitate ongoing disease monitoring in this species.

Naturally Occurring Inherited Forms of Retinal Degeneration in Vertebrate Animal Species: A Comparative and Evolutionary Perspective.

The ability to noninvasively monitor retinal abnormalities using imaging and cognitive and electrophysiological assessment has made it possible to carefully characterize genetic influences on retinal health. Because genetic retinal traits in animal species are not commonly detrimental to survival beyond birth, it is possible to document the natural history of retinal disease. Human quality of life is greatly impacted by retinal disease, and blindness carries a significant financial burden to society. Because of these compelling reasons, there is an ongoing medical need to study the effect of genetic mutations on retinal health and to develop therapies to address them. Transgenic animal models have aided in these missions, but there are opportunities for novel gene discovery and a development of greater understanding of retinal physiology using animal models that develop naturally occurring heritable retinal disorders. In this chapter, the advantages and disadvantages of transgenic and spontaneous vertebrate animal models of human inherited retinal disease are debated, in particular those of carnivore species, and the potential resource of spontaneous heritable retinal disorders in inbred nondomestic carnivore species is discussed.

Circulating neurohormone imbalances in canine sudden acquired retinal degeneration syndrome and canine pituitary-dependent hypercortisolism.

BACKGROUND: Sudden acquired retinal degeneration syndrome (SARDS) has clinical similarity to pituitary-dependent hypercortisolism (PDH) in dogs. Some studies have identified a greater frequency of SARDS in seasons with reduced daylight hours. Neurohormone imbalances contribute to retinal lesions in other species, warranting further study in dogs with SARDS. HYPOTHESIS: Dysregulation of circulating melatonin concentration is present in dogs with SARDS but not in dogs with PDH. ANIMALS: Fifteen client-owned dogs with spontaneous SARDS (median time of vision loss 18 days), 14 normal dogs, and 13 dogs with confirmed PDH. PROCEDURES: Prospective case-control study. ELISA on samples (obtained in the morning) for measurement of plasma melatonin and dopamine, serum serotonin, urine 6-sulfatoxymelatonin (MT6s), and creatinine. Statistical analysis was performed using 1-way ANOVA, Spearman correlation and receiver operator characteristic area under the curve analysis. RESULTS: There were no significant differences in circulating melatonin, serotonin or dopamine concentrations between the 3 groups, although the study was underpowered for detection of significant differences in serum serotonin. Urine MT6s:creatinine ratio was significantly higher in dogs with PDH (4.08 ± 2.15 urine [MT6s] ng/mL per mg of urine creatinine) compared with dogs with SARDS (2.37 ± .51, P < .01), but not compared with normal dogs. CONCLUSIONS AND CLINICAL RELEVANCE: We have identified neurohormone differences between dogs with SARDS and PDH.

In vivo electroretinographic differentiation of rod, short-wavelength and long/medium-wavelength cone responses in dogs using silent substitution stimuli.

The canine species has dichromatic color vision comprising short-wavelength (S-) and long/medium (L/M-) wavelength-sensitive cones with peak spectral sensitivity of 429-435 nm and 555 nm respectively. Although differentiation of rod- and cone-mediated responses by electroretinogram (ERG) in dogs is commonly performed, and standards have been developed based on standards for human observers, methods to differentiate S- and L/M-cone responses in dogs have not been described. We developed flicker protocols derived from previously published rod and cone spectral sensitivities. We used a double silent substitution paradigm to isolate responses from each of the 3 photoreceptor subclasses. ERG responses were measured to sine-wave modulation of photoreceptor excitation at different temporal frequencies (between 4 and 56 Hz) and mean luminance (between 3.25 and 130 cd/m2) on 6 different normal dogs (3 adult female, and 3 adult male beagles) and one female beagle dog with suspected hereditary congenital stationary night blindness (CSNB). Peak rod driven response amplitudes were achieved with low frequency (4 Hz, maximal range 4-12 Hz) and low mean luminance (3.25 cd/m2). In contrast, peak L/M-cone driven response amplitudes were achieved with high frequency (32 Hz, maximal range 28-44 Hz) and high mean luminance (32.5-130 cd/m2). Maximal S-cone driven responses were obtained with low frequency stimuli (4 Hz, maximal range 4-12 Hz) and 32.5-130 cd/m2 mean luminance. The dog with CSNB had reduced rod- and S-cone-driven responses, but normal/supernormal L/M cone-driven responses. We have developed methods to differentiate rod, S- and L/M-cone function in dogs using silent substitution methods. The influence of temporal frequency and mean luminance on the ERGs originating in each photoreceptor type can now be studied independently. Dogs and humans have similar L/M cone responses, whereas mice have significantly different L/M responses. This work will facilitate a greater understanding of canine retinal electrophysiology and will complement the study of canine models of human hereditary photoreceptor disorders.

Diagnostic utility of clinical and laboratory test parameters for differentiating between sudden acquired retinal degeneration syndrome and pituitary-dependent hyperadrenocorticism in dogs.

OBJECTIVE: To identify discriminating factors, using clinical ophthalmic examination findings and routine laboratory testing, that differentiate dogs with early sudden acquired retinal degeneration (SARDS; vision loss <6 weeks' duration), age- and breed-matched control dogs, and dogs with pituitary-dependent hyperadrenocorticism (PDH). ANIMALS: Client-owned dogs: 15 with SARDS with <6 weeks duration of vision loss, 14 age- and breed-matched control dogs, and 13 dogs with confirmed PDH. PROCEDURES: Dogs underwent ophthalmic examination, electroretinography (ERG) fundus photography, and spectral-domain optical coherence tomography (SD-OCT) in addition to physical examination, urinalysis, serum biochemistry, complete blood count, and adrenocorticotrophic hormone (ACTH) stimulation testing. Statistical analysis was performed using receiver operating curve area under the curve analysis, principal component analysis with sparse partial least squares analysis, and one-way ANOVA. RESULTS: Dogs with SARDS all had absent vision and ERG a- and b-waves. SD-OCT demonstrated that dogs with SARDS had significantly thicker inner retina, thinner outer nuclear layer, and thicker photoreceptor inner/outer segment measurements than either controls or dogs with PDH. Discriminating laboratory parameters between dogs with SARDS and PDH with high specificity included post-ACTH serum cortisol (<19.3 µg/dL), AST:ALT ratio (>0.343), and urine specific gravity (>1.030). CONCLUSIONS AND CLINICAL RELEVANCE: We have identified significant discriminators between SARDS and PDH. This work provides the basis for future studies that could identify and examine dogs with SARDS prior to vision loss, which may extend the potential therapeutic window for SARDS.