Congenital stationary night blindness: An animal model

Investigative Ophthalmology &amp Visual Science (Impact Factor: 3.4). 09/1978; 17(8):788-95.
Source: PubMed


Electroretinographic studies of myctalopic Appaloosa horses demonstrated photopic and scotopic abnormalities similar to those in humans with congenital stationary night blindness (CSNB) of the Schubert-Bornschein type. The phototopic abnormalities consisted of reduced b-wave amplitudes and slower than normal b-wave implict time. The dark-adapted ERG's consisted of a simple negative potential; the scotopic b-wave was nonrecordable. However, a normal c-wave was present in the dark-adapted response. Histologic studies demonstrated no structural abnormalities that could explain the functional defect.

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Available from: Gustavo David Aguirre, Feb 25, 2014
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    • "Congenital stationary night blindness is a nonprogressive disease of the retina that occurs in Appaloosas and rarely in other breeds such as the Thoroughbred and Paso Fino. Affected animals characteristically show poor vision in dim light and normal vision in bright light, but a wide variation in the severity of visual deficits has been observed (Nunnery et al. 2005; Witzel et al. 1978). More recently clinical diagnosis of CSNB has been reported in the Danish Knabstrupper (de Linde Henriksen et al. 2007). "
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    • "In these horses, there is a link between a specific pattern of coat coloration and congenital stationary night blindness (Sandmeyer et al., 2007). Animals with this coloration lack the ERG b-wave, indicating a loss of function of On bipolar cells, although the structure of the retina appears normal (Witzel et al., 1978). Genetic analysis of this phenotype revealed decreased expression of mRNA encoding TRP channel TRPM1 (Bellone et al., 2008). "
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    ABSTRACT: On bipolar cells are connected to photoreceptors via a sign-inverting synapse. At this synapse, glutamate binds to a metabotropic receptor which couples to the closure of a cation-selective transduction channel. The molecular identity of both the receptor and the G protein are known, but the identity of the transduction channel has remained elusive. Here, we show that the transduction channel in mouse rod bipolar cells, a subtype of On bipolar cell, is likely to be a member of the TRP family of channels. To evoke a transduction current, the metabotropic receptor antagonist LY341495 was applied to the dendrites of cells that were bathed in a solution containing the mGluR6 agonists L-AP4 or glutamate. The transduction current was suppressed by ruthenium red and the TRPV1 antagonists capsazepine and SB-366791. Furthermore, focal application of the TRPV1 agonists capsaicin and anandamide evoked a transduction-like current. The capsaicin-evoked and endogenous transduction current displayed prominent outward rectification, a property of the TRPV1 channel. To test the possibility that the transduction channel is TRPV1, we measured rod bipolar cell function in the TRPV1(-/-) mouse. The ERG b-wave, a measure of On bipolar cell function, as well as the transduction current and the response to TRPV1 agonists were normal, arguing against a role for TRPV1. However, ERG measurements from mice lacking TRPM1 receptors, another TRP channel implicated in retinal function, revealed the absence of a b-wave. Our results suggest that a TRP-like channel, possibly TRPM1, is essential for synaptic function in On bipolar cells.
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    ABSTRACT: ERG findings in five sisters are reported. By pedigree analysis, four of the five must be obligate carriers for I- CSNB since their sons were affected (impaired night vision, reduced visual acuity, variable ametropia, congenital nystagmus and ERG with both scotopic and photopic b-wave reduced amplitude). The fifth was childless at the time of examination and her ERG analysis was normal. Three of the four obligate carriers showed significant reduction in the sum of the OPs amplitude as previously reported as being an electrophysiological signs in female carriers: two without alteration in other ERG components and the third with association with a flicker ERG amplitude significantly increased. The fourth female carrier showed a normal sum of the OPs amplitude whereas the other b-wave ERG or flicker amplitudes were significantly decreased. These last two ERG results suggest a possible modifications of synaptic transmission at a post-receptoral site (outer plexiform layer or involvement of the bipolar pathways) in these two carriers.
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