Genotypic influences on reproductive aging of inbred female mice: effects of H-2 and non-H-2 alleles

The H-2 (major histocompatibility) complex of mice influences a variety of physiologic parameters. This study describes the influences of H-2 polymorphisms and other genetic influences on age-related changes (5-20 mo) in estrous cycles and fecundity. We monitored estrous cycles of virgin or retired-breeder mice of congenic strains on the background of C57BL/10Sn (B10):B10.BR/Sg (B10.BR) and B10.RIII/Sn (B10.RIII). For another comparison, we examined the C57BL/6J (B6) strain, which has the same H-2 haplotype as the B10. Estrous cycles were categorized by length during 10 mo of observations. From 5 to 15 mo of age, B10 and B10.RIII mice displayed a preponderance of 5-day cycles, B10.BR mice displayed a preponderance of 4-day cycles, and B6 mice had diminishing numbers of 4-day cycles. Age-related acyclicity differed with strain, particularly among retired breeders; B6 mice had an earlier onset and more rapid increase of acyclicity with age than the B10 congenic mice. Litters/female, maternal age at last litter, and total pups/female differed with strain; B10.BR and B10.RIII were similar and both had greater values than B10 mice. In conclusion, reproductive senescence of female mice was influenced by genes at the H-2 locus and elsewhere.     

Prolongation and cessation of estrous cycles in aging C57BL/6J mice are differentially regulated events

The relative contributions of ovarian failure and hypothalamic-pituitary dysfunction to the prolongation and cessation of estrous cycles were assessed by measuring the ability of acutely ovariectomized (OVX) middle-aged (12 mo) mice to cycle after receiving grafts (under the renal capsule) of ovaries from young (2 mo) mice. The potentially disruptive effect of the acyclic state on the cycling response to grafted, young ovaries was avoided restricting grafting to middle-aged hosts that were still cycling. The effect of chronic exposure to ovarian secretions before the cessation of cyclicity on age-related hypothalamic-pituitary dysfunction was also assessed. The cycling ability of long-term OVX middle-aged mice (i.e., OVX at 3 mo) bearing grafts of young ovaries was compared to that of age-matched acutely OVX controls. Grafted young ovaries extended the cycling lifespan of acutely OVX middle-aged hosts by 60%. The length of this extended cycling lifespan, however, was only 80% of that achieved by young hosts bearing grafts of young ovaries. Young ovaries in middle-aged mice markedly lowered the incidence of long cycles (greater than 5 days), shifting the modal cycle length to 5 days. However, young ovaries in middle-aged mice failed to increase the incidence of 4-day cycles, the modal cycle of young controls. Middle-aged ovaries grafted into young hosts lengthened their cycles and shortened their cycling lifespan to middle-aged values. Long-term ovariectomy failed to increase the cycling lifespan of middle-aged hosts bearing grafts of young ovaries beyond that achieved in acutely OVX mice. Long-term ovariectomy did shorten the modal cycle length of middle-aged mice to 4 days, although the duration of 4-day cycling was only one-third (2 mo) that of young controls. These results indicate that the relative contributions of ovarian and neuroendocrine factors to three major events of reproductive aging vary with each event. Whereas the hypothalamic-pituitary unit appears to play an important role in the initial shift from 4- to 5-day cycles, the aging ovary plays the major role in the subsequent shift to longer cycles and in the ultimate cessation of cyclicity. Although chronic exposure to ovarian secretions during the period of cyclicity does not play a major role in the cessation of cyclicity, it appears to contribute to the hypothalamic-pituitary changes responsible for the initial shift from 4- to 5-day cycles.     

The effect of transferrin saturation on internal iron exchange

Radioiron was introduced into the intestinal lumen to evaluate absorption, injected as nonviable red cells to evaluate reticuloendothelial (RE) processing of iron, and injected as hemoglobin to evaluate hepatocyte iron processing. Redistribution of iron through the plasma was evaluated in control animals and animals whose transferrin was saturated by iron infusion. Radioiron introduced into the lumen of the gut as ferrous sulfate and as transferrin-bound iron was absorbed about half as well in iron-infused animals, and absorbed iron was localized in the liver. The similar absorption of transferrin-bound iron suggested that absorption of ferrous iron occurred via the mucosal cell and did not enter by diffusion. The decrease in absorption was associated with an increase in mucosal iron and ferritin content produced by the iron infusion. An inverse relationship (r = -0.895) was shown between mucosal ferritin iron and absorption. When iron was injected as nonviable red cells, it was deposited predominantly in reticuloendothelial cells of the spleen. Return of this radioiron to the plasma was only 6% of that in control animals. While there was some movement of iron from spleen to liver, this could be accounted for by intravascular hemolysis. Injected hemoglobin tagged with radioiron was for the most part taken up and held by the liver. Some 13% initially localized in the marrow in iron-infused animals was shown to be storage iron unavailable for hemoglobin synthesis. These studies demonstrate the hepatic trapping of absorbed iron and the inability of either RE cell or hepatocyte to release iron in the transferrin-saturated animal.     

Enzymes of pyrimidine deoxyribonucleotide metabolism in Mycoplasma mycoides subsp. mycoides.

Cell-free extracts of Mycoplasma mycoides subsp. mycoides were assayed for enzymes associated with the salvage synthesis of pyrimidine deoxyribonucleotides. They possessed kinases for deoxycytidine, (d)CMP, thymidine (deoxyuridine), dTMP, and nucleoside diphosphates; dCTPase and dUTPase; dCMP deaminase; thymidine (deoxyuridine) phosphorylase; and dUMP (dTMP) phosphatase. The existence of these enzymic activities together with ribonucleoside diphosphate reductase explains the capacity of cytidine to provide M. mycoides with deoxyribose for the synthesis of thymidine nucleotides from thymine.     

Completion of diapause in field populations of the cabbage root fly (Delia radicum)

The various diapause and post-diapause stages entered by cabbage root fly pupae during the overwintering period are shown schematically. Although diapause induction started in mid-Aug., the early-pupating insects did not develop further but were maintained in diapause by the warm autumn temperatures. Therefore, diapause development was simultaneous in all Wellesbourne pupae, whether of second or third generation origin. Diapause development started only in mid-Oct., when mean soil temperatures fell below 10°. In the field, 90% of the overwintering population of cabbage root fly pupae had completed pleted diapause by 5 March 1980, 17 Feb. 1981 and 18 Feb. 1982. This was equivalent to a duration of 19 weeks from mid-Oct. onwards, during the winters of 1979–80, 1980–81 and 1981–82 respectively. A further break between the completion of diapause and the warm conditions required to start post-diapause development also helps to condense the emergence of flies in the spring. Hence, an accurate forecast of the time of spring attack by populations of flies similar to those at Wellesbourne should be possible.This study was financed partly by the Commission of the European Communities as CEC Contract No. 0771.     

Imminent oocyte exhaustion and reduced follicular recruitment mark the transition to acyclicity in aging C57BL/6J mice

Quantitative cytological analyses of aging C57BL/6J mouse ovaries revealed that the populations of primordial and growing follicles were nearly exhausted by 13-14 months, the average age of ovulatory failure. Anovulatory animals of this age had, on the average, half the follicle number of their counterparts which were still ovulating. This result suggests that follicular depletion is a factor which contributes to the loss of ovarian cyclicity during aging. However, the considerable overlap of follicle number between the two groups suggests that other, possibly extraovarian, factors also influence the loss of ovulatory function. Although the numbers of follicles recruited for growth was much lower in ovaries from old cycling animals, the number of ova shed cyclically was generally within the range of younger individuals. The observed reduction in incidence of morphological atresia among medium-sized follicles may explain how ovulatory constancy is maintained virtually throughout the cyclical life of the ovary.     

Small-field, binocular neurons in the superficial layers of the frog optic tectum

Binocular neurons with receptive fields about 5 degrees across were recorded just beneath the pia. Most of them responded to dark stimuli in the lower half of their receptive field and to light stimuli above. There was almost no vertical disparity between the left and right fields and the modal value of the horizontal disparity of the population of cells was 1.7 degrees. Because frogs do not verge their eyes it is possible to calculate at what distance the receptive fields through the two eyes are superimposed. This calculation suggests that the neurons are tuned to detect features in the external world about 50 cm away. This is too far for the neurons to be involved in the frog's everyday distance vision. It is more likely that they are concerned with assessing the vertical position of a horizontal surface.     

Enzymic methods for the micro assay of D-mannose,D-glucose,D-galactose,and L-fucose from acid hydrolyzates of glycoproteins

Enzymic methods of micro assay have been described for four neutral sugars commonly present in glycoproteins and glycolipids. These assays can be applied to glycoprotein hydrolyzates without prior purification of individual sugars.d-Mannose is assayed by first phosphorylating the sugar in the presence of hexokinase and then measuring the formation of ADP by the use of pyruvate kinase and lactic dehydrogenase. This assay is not specific for d-mannose since both d-glucose and d-glucosamine can be phosphorylated by hexokinase. It is possible to remove d-glucosamine prior to hexokinase treatment by passage through a Dowex 50-X8 (H⁺) column. The effect of d-glucose in the sample can be corrected for by measuring d-glucose with d-glucose-6-phosphate dehydrogenase, an assay which is highly specific for d-glucose.d-Galactose and l-fucose are measured by their respective dehydrogenases. Neither of these dehydrogenases is affected by sugars commonly found in glycoproteins or glycolipids, nor by the presence of a partial acid hydrolyzate of bovine serum albumin. The methods described enable detection of 0.025 μmole of d-mannose, d-glucose, d-galactose, or l-fucose in a glycoprotein digest. The methods can theoretically be made even more sensitive by the use of fluorometric techniques.     

Treatment with recombinant IFN-gamma decreases cell surface CD4 levels on peripheral blood monocytes and on myelomonocyte cell lines

The human cell surface protein CD4 is not only an important accessory molecule in the activation of MHC class-II-restricted T cells, but has also been implicated to be a receptor for the human immunodeficiency virus HIV-I on lymphoid and monocytic cells. We have found that a 24-h treatment of the promonocytic leukemia cell line U937 with rIFN-gamma decreases the expression of the CD4 Ag by 50% as measured by cytofluorographic analysis. The decrease in CD4 expression was dependent on the concentration of rIFN-gamma, with maximal effects occurring at 20 to 200 U/ml. The decrease appeared to be due to actual loss of the CD4 molecule from the cell surface rather than masking of a particular epitope, inasmuch as similar results were obtained with the OKT4 and OKT4A antibodies. The effect of rIFN-gamma to decrease CD4 expression was not due to a general loss of cell surface Ag, because the binding of OKM1 and anti-HLe-1 increased after rIFN-gamma treatment. Treatment of rIFN-gamma also decreased cell surface CD4 expression on the promyelocytic leukemia cell line HL-60, and on the monocytic cell line THP-1, although the extent of the decrease was less than on U937 cells. Freshly isolated normal peripheral blood monocytes treated for 48 h with rIFN-gamma bound much less OKT4 or OKT4A antibody than cells incubated in the absence of rIFN-gamma. Moreover, treatment with rIFN-gamma reduced the percentage of peripheral blood monocytes that were positive for the CD4 Ag. In contrast with the decrease in CD4 levels on rIFN-gamma-treated monocytes, treatment with rIFN-gamma had no effect on CD4 levels on peripheral blood T lymphocytes or T cell lines.     

Prospects for research on the modulation of gene activity during brain aging

This brief review is concerned with prospects of the role of modulated gene expression in the brain during aging and in two age-related neurological diseases: Parkinson's and Alzheimer's diseases. Two key mechanisms involved in the disturbance of neuronal function during aging, i. e. deafferentation syndromes (as a result of the impairment of afferent influences) and steroid-induced neuronal changes, have been studied. The author suspects that many aspects of cell aging in the brain represent the influence of the environmental factors. The conception of new therapeutic approaches to the treatment of Alzheimer's disease has been developed.