Local regeneration in the retina of the goldfish

We have studied regeneration of the retina in the goldfish as a model of regenerative neurogenesis in the central nervous system. Using a transsclearal surgical approach, we excised small patches of retina that were replaced over several weeks by regeneration. Lesioned retinas from three groups of animals were studied to characterize, respectively, the qualitative changes of the retina and surrounding tissues during regeneration, the concomitant cellular proliferation, and the quantitative relationship between regenerated and intact retina. The qualitative and quantitative analyses were done on retinas prepared using standard methods for light microscopy. The planimetric density of regenerated and intact retinal neurons was computed in a group of animals in which the normal planimetric density ranged from high to low. Cell proliferation was investigated by making intraocular injections of 5-bromo-2′-deoxyuridine (BUdr) at various survival times to label proliferating cells and processing retinal sections for BUdr immunocytochemistry. The qualitative analysis showed that the surgery created a gap in the existing retina that was replaced with new retina over the subsequent weeks. The BUdr-labeling experiments demonstrated that the excised retina was replaced by regeneration of new neurons. Neuroepithiallike cells clustered on the wound margin and migrated centripetally, appositionally adding new retina to the old. The quantitative analysis showed that the planimetric density of the regenerated neurons approximated that of the intact ones.     

Photoreactivation and repair replication in rat kangaroo cells

Potorous tridactylis cells can perform photoreactivation, i.e., the visible light- catalyzed reversal of UV-induced pyrimidine dimers in DNA. UV-induced inhibitions of total RNA and DNA synthesis can also be partially reversed by exposure to visible light. P. tridactylis cells can also perform repair replication, but the extent of the latter is reduced if the cells are exposed to visible light (VL). None of these effects are observed in mouse L cells, which cannot perform photoreactivation. The results are consistent with the concept of pyrimidine dimers are one of the main substrates for repair replication.     

24R,25-dihydroxyvitamin D stimulates creatine kinase BB activity in chick cartilage cells in culture

In chick limb-bud cartilage cell cultures 24R,25-dihydroxycholecalciferol (24R,25(OH)2D3), but not 24S,25(OH)2D3, 1 alpha,25(OH)2D3 or 25(OH)D3, stimulates the activity of the brain type (BB) isozyme of creatine kinase (EC 2.7.3.2), the 'estrogen-induced protein' first identified in rat uterus. Cultures treated with bromodeoxyuridine, in which cartilage formation is inhibited, show no stimulation of creatine kinase BB by 24R,25(OH)2D3.     

A comparison of diameters of micronuclei induced by clastogens and by spindle poisons

To compare the size of micronuclei induced by clastogens and by spindle poisons, bone-marrow smears were prepared 24 h after a single intraperitoneal injection of triethylenemelamine (TEM) (0.3 mg/kg) or vincristine (VCR) (0.125 mg/kg) into male mice. 100 micronucleated erythrocytes (MNEs) were randomly selected from each group and photomicrographed. Diameters of the cytoplasm (D) and the micronucleus (d) of each MNE were measured on the photographs. Relatively large micronuclei (d?D/4) were frequent (74%) in the VCR-treated group, and infrequent (2%) in the TEM-treated group. The frequencies of MNEs resulting in d?D/4 were determined for several other mutagens. All clastogens tested could be classified as TEM type, and all spindle poisons as VCR type.These findings indicate that it is possible to analyze the action site of micronucleus-inducing agents on the basis of the relative sizes of micronuclei.