Early morphometry of a retinal dystrophy in Labrador retrievers

Photoreceptor cell dysplasia in two Tippler pigeons

Two 12-week-old Tippler pigeons were evaluated for ocular abnormalities associated with congenital blindness. The pigeons were emaciated and blind. Biomicroscopy and direct and indirect ophthalmoscopy findings of the Tippler pigeons were normal with the exception of partially dilated pupils at rest. Scotopic (blue stimuli) and photopic monocular electroretinograms were extinguished in the blind Tippler pigeons. Histological and electron microscopy studies revealed reduced numbers of rods and cones, and an absence of the double cone complex. The photoreceptor cells' outer segments were absent, and the inner segments were short and broad. The number of cell nuclei in the outer and inner nuclear layers was decreased, and the internal and external plexiform layers were reduced in width. Photoreceptor cell endfeet with developing synaptic ribbons were present in the external plexiform layer. Inflammatory cell and subretinal debris was not seen. The electroretinographic, histopathological, and ultrastructural findings of the blind Tippler pigeons support the diagnosis of a photoreceptor cell dysplasia.

Genetic animal models for retinal degeneration

Inherited retinal degenerations are a common cause of blindness in Western countries. A mechanism for most retinal degenerations is still unknown; hence, a suitable treatment for most of these diseases has yet to be found. Before one can rationally design a treatment, it is necessary to understand the pathway from a gene mutation to the phenotype in patients. Animal models are crucial to understand this process and to develop a treatment. Some naturally occurring animal models are known. However, over the past few years, transgenic engineering has allowed the generation of a rapidly growing number of animal models. In this review, we give an overview of the broad variety of genetic animal models for retinal degeneration.

Cloning of the cDNA encoding rod photoreceptor cGMP-phosphodiesterase alpha and gamma subunits from the retinal degenerate Labrador retriever dog

The nucleotide (nt) sequence of the cDNA encoding the retinal rod cyclic 3'5'-GMP phosphodiesterase (PDE) alpha and gamma subunits from two strains of dogs-(i) Labrador Retrievers homozygous for autosomally recessively inherited rod-cone degeneration and (ii) the wild-type Beagle-are reported. Cloning of these subunits was accomplished by polymerase chain reaction using retinal cDNA libraries as templates. The nt sequence of alpha PDE predicts a 861-amino-acid polypeptide which is 97.7 per cent and 96.9 per cent identical to the bovine and human counterparts, respectively. PDE gamma encodes an 87-amino-acid polypeptide differing from bovine and murine gamma subunits by only one amino acid. Since no differences were found between these two strains of dogs, the cause of the Labrador Retriever's degeneration remains to be determined.

Impaired retinal function in young labrador retriever dogs heterozygous for late onset rod-cone degeneration

Xenon-flash d.c.-electroretinograms were recorded from dark adapted, rod-cone degenerate homozygote affected (n = 6), heterozygote carrier (n = 3) and control retinas (n = 4) at 3 and 4 months of age, starting at 0.6 log units below control PII threshold. One log unit higher stimuli were necessary to evoke PII in heterozygote and affected retinas compared to controls. Unique to the heterozygotes, double peaked PII responses that were evoked by -2 log relative units intensity stimulation were significantly (P = 0.028) lower in amplitude than those of controls. PII amplitudes of homozygotes were significantly (P = 0.005) lower in amplitude than those of controls at both ages examined in response to -2 and 0 log relative intensity stimulation. No differences were found in scotopic threshold response amplitudes or times to peak between the three groups. Homozygote affected PII times to peak were significantly (P = 0.005) shorter in relation to controls at -2 log units. Findings suggest that heterozygotes exhibit an impaired retinal function which can be demonstrated at 3 and 4 months in this mutant.