Cataract has been defined by Bourne as any pathological condition of the lens which alters its normal transparency. More specifically, a cataract is regarded as a loss of transparency of the lens, or an opacification occurring at any place in the lens or its capsule. Since the lens is an intricate physico-chemical system, changes in the physical and chemical state of the lens proteins which result in loss or transparency or opacification may be brought about by many agents: interference with the normal metabolic processes, alteration in hydrogen ion concentration, disturbance of osmotic equilibrium, and the harmful action of heat, light, and radiation. As a result, cataract presents many complexities with respect to clinical manifestations. [...]

No description available.

No description available.

Several aspects of the physiology of the fat mouse Steatomys pratensis natalensis were studied in the laboratory using standard techniques and custom-made data-logging equipment. The fat was studied both from a morphological and functional point of view. The measurement of metabolic rates showed that euthermic S.pratensis have very low basal metabolic rates of 36% of expected, with torpor saving up to 69% of expended energy. Body temperatures, oxygen consumption, and activity patterns monitored over 24 hour periods with a data-logging system showed that Sipratensis have very low body temperatures of 31.3 to 35.0°C which fluctuate on a circadian rhythm with activity and oxygen consumption, all being lower during the day and higher at night. Torpor started very early in the morning and lasted for 5.5 to 11.7 hours. Huddling with a mate could reduce energy expenditure by 18%. Torpid body temperatures lay just above ambient from 15 to 35°C, below which all animals tried to arouse. Forced arousal at 10 to 30°C was slow and depended on ambient temperature while no mouse could arouse at O°C. Thermal conductance was 97.4 % of expected but cooling rates of dead S.pratensis were slow due to the heavy fat layer. Non-shivering thermogensis (measured after noradrenaline injection) was normal at 369% of BMR but maximum metabolism was twice as much, indicating other means of thermogenesis used additively with NST. Dissection showed extremely heavy fat deposits in the normal mammalian positions and also three additional deposits. Histological studies revealed most deposits as white fat but there was brown fat in the interscapular region. Soxhlet analysis showed an extremely wide range of body fat content from normal mammalian levels to contents higher than in hibernating rodents. Deprivation of food and water, or food alone, was found to induce torpor and cause the mice to become non-reproductive. Deprivation of water but not food, and deprivation of a cage mate, triggered torpor in only 40 - 44% of the cases studied. The mice took 5 to 12 days to lose 30% of their mass, but theoretically could survive longer. Weekly measurements showed no annual mass fluctuations in the laboratory but the mice became reproductively active mid-summer to early winter while torpor was at a maximum around late winter. All animals showed torpor, young more than adults and females more than males. It is suggested that the low body temperature and metabolism of S.pratensis may have evolved to prevent overheating caused by their inability to lose heat through the heavy fat layer. The species could then disperse into areas where their low energetic demands would permit them to compete successfully with high metabolic rate rodents. / Thesis (M.Sc.)-University of Natal, Durban, 1990.

Following fertilization, the embryo undergoes a sequence of precisely timed cleavage cycles to produce a blastocyst. The timing of these cycles likely depends in part on appropriate levels of gene activity. I have investigated whether high mobility group (HMG) proteins 14 and 17, which are associated with chromatin containing transcribed genes, are expressed in mouse embryos and are required to maintain normal early developmental timing. As assayed using RT-PCR, mRNAs encoding both HMG-14 and HMG-17 were present throughout preimplantation development to the blastocyst stage. By immunofluorescence, both proteins were detected in the nuclei of prophase I-arrested oocytes and embryos beginning at the 2-cell stage. To investigate their function, antisense oligonucleotides targeting the 5' end of each mRNA species were injected into 1-cell stage embryos which were then cultured to develop to the blastocyst stage. At the 2- and 4-cell stages, only weak nuclear immunofluorescence was observed; however, by the 8-cell stage, the staining pattern of injected embryos was indistinguishable from controls. Thus, the injected antisense oligonucleotides transiently depleted the cellular supply of HMG-14 and HMG-17. Furthermore, the embryos in which both HMG-14 and MAG-17 had been depleted progressed significantly more slowly through successive stages of preimplantation development, as compared with embryos in which the proteins were individually depleted or injected with nonsense oligonucleotides. Therefore, it can be concluded that depletion of HMG-14 and HMG-17 from embryonic chromatin transiently delays preimplantation development, demonstrating a crucial role for these proteins in maintaining the normal temporal coordination of development.

To investigate the lineage relationships that are postulated to underlie the origins of phenotypically different neurons, Thy-1.1 $ leftrightarrow$ Thy-1.2 and hNF-L $ leftrightarrow$ +/+ mouse chimeras were examined for the distribution of the two neuron genotypes. Throughout the nervous system, a finely variegated pattern of mosaicism was always observed and, in each chimera, similar genotype proportions were found in all analysed neuronal populations of the peripheral and central nervous system. These findings require that the chimera neuroectoderm was a homogeneous mix of the two genotypes and that different neuronal phenotypes do not arise clonally from a small number of prespecified progenitors. Rather it would seem that all progenitors contribute daughter cells to all of the neuronal subpopulations at each level of the neuroaxis.

The BxH recombinant inbred strains of mice were used to undertake a genetic analysis of the maternal factors controlling the survival of trisomy 16 fetuses. The data presented indicate that the prevalence of trisomic fetuses on day 15 of gestation varies significantly with the genetic background of the mother. The strain difference in the frequency of trisomy appears to be the result of selective elimination of trisomic fetuses. Various statistical methods to elucidate the genetic architecture of the trait from the recombinant inbred strains data indicate that the number of loci involved in the selection process ranges from one to five. Linkage association with two loci have been found; however, with a low probability level (p = 0.292).

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No description available.

Firstly, exposure of compacted morulae (CM) and early blastocysts (EB) to methanol (M) or glycerol (G) for 1 h at room temperature followed by culture in standard culture medium showed that the embryos tolerated up to 12 to 24% methanol or 24 to 48% glycerol. Next, the effects of stage of embryo (CM vs EB), preservation temperature and concentration of 1:1 M:G on embryo survival were tested. EB survived longer than CM under all conditions. Increased concentrations of cryoprotectants (M and G) increased the survival of supercooled embryos, but survival was decreased with the storage temperature. Replacing G with propanediol (P) significantly increased blastocyst survival at lower temperatures. / Exposure for 1 h to $>$ 0.6 M of sucrose or trehalose at room temperature suppressed growth in culture, but dehydration in up to 0.4M sucrose before supercooling (in M:P) increased survival at $-$5 or $-$10$ sp circ$C, survival increasing with dehydration. / Finally, demi-embryos and intact embryos were cultured to the blastocyst stage, stored at $-$5$ sp circ$ for 48 h, then cultured for 24 h and transferred into pseudopregnant recipients.