Postnatal refractive development in the Brown Norway rat: limitations of standard refractive and ocular component dimension measurement techniques.

PURPOSE: The genetic tractability of the rat and its larger eye size as compared to the mouse make it an attractive model for studies of ocular development and emmetropisation. This study aimed to provide normative data in the strain of rat being used for the rat genome sequencing project whilst also evaluating standard measurement techniques. METHODS: Ocular refraction (retinoscopy, Hartinger coincidence optometry) and ocular component dimensions (keratometry, A-scan ultrasonography, calliper measures, eye weight) were measured at intervals from eye-opening to adulthood. RESULTS: There was no convincing evidence of visually guided emmetropisation during normal development. Key measurement techniques such as high-resolution A-scan ultrasonography, which work effectively in several other animal species, were unusable or inaccurate in the rat. CONCLUSIONS: This study found no evidence of emmetropisation during normal development in rat. As in mice, technical difficulties prevent accurate measurement of ocular refraction and vitreous chamber depth and may complicate tests of emmetropisation to imposed blur.

Genetic Models in Applied Physiology. HXB/BXH rat recombinant inbred strain platform: a newly enhanced tool for cardiovascular, behavioral, and developmental genetics and genomics.

This review deals with the largest set of rat recombinant inbred (RI) strains and summarizes past and recent accomplishments with this platform for genetic mapping and analyses of divergent and complex traits. This strain, derived by crossing the spontaneously hypertensive rat, SHR/Ola, with a Brown Norway congenic, BN-Lx, carrying polydactyly-luxate syndrome, is referred to as HXB/BXH. The RI strain set has been used for linkage and association studies to identify quantitative trait loci for numerous cardiovascular phenotypes, including arterial pressure, stress-elicited heart rate, and pressor response, and metabolic traits, including insulin resistance, dyslipidemia and glucose handling, and left ventricular hypertrophy. The strain's utility has been enhanced with development of a new framework marker-based map and strain distribution patterns of polymorphic markers. Quantitative trait loci for behavioral traits mapped include loci for startle motor response and habituation, anxiety and locomotion traits associated with elevated plus maze, and conditioned taste aversion. The polydactyly-luxate syndrome Lx mutation has allowed the study of alleles important to limb development and malformation phenotypes as well as teratogens. The RI strains have guided development of numerous congenic strains to test locus assignments and to study the effect of genetic background. Although these strains were originally developed to aid in studies of rat genetic hypertension and morphogenetic abnormalities, this rodent platform has been shown to be equally powerful for a wide spectrum of traits and endophenotypes. These strains provide a ready and available vehicle for many physiological and pharmacological studies.