Retinal photoreceptor damage produced in guinea pigs by tunicamycin.

Corynetoxins, members of the tunicamycin group of antibiotics, produce a severe and frequently fatal neurological disorder in ruminant livestock, and guinea pigs are a useful model to study the pathology and pathogenesis of this disease. The aim of this study was to determine whether tunicamycin produced ocular damage in this species, which could have pharmacotherapeutic and diagnostic value. Four 8-week-old guinea pigs were treated with tunicamycin, and two control animals were given the drug vehicle only. Guinea pigs were injected subcutaneously with 400 µg/kg of tunicamycin, in dimethyl sulphoxide, and killed 48 h post-injection. The eyes were then examined by light microscopy. Immunohistochemistry for rhodopsin was also performed. The principal pathological finding was marked retinal photoreceptor damage, which was characterised by disruption and disorganisation of rods, sometimes progressing to necrosis and separation of the outer segment. The cytoplasm of some rods was focally distended by accumulated, proteinaceous material. Rhodopsin immunopositivity in injured rods was markedly diminished and associated with shrinkage and shortening of the injured rod's outer segment. Ocular pathology, in the form of reproducible and extensive retinal photoreceptor damage, was found in guinea pigs given tunicamycin, extending the range of species found to be susceptible to this toxic injury. The guinea pig could prove to be a good animal model to test potential therapeutic interventions, and as brain lesions are often minimal and liver pathology non-specific in intoxicated ruminants, any spontaneously arising ophthalmic injury found in these species could be diagnostically useful.

How old is old? Revising the definition based on life table criteria.

PIP: "Sixty-five has long been thought of as the point of entry into ¿old age'. We propose a number of life table criteria for answering the following questions: If 65 was considered appropriate four decades ago, what is the corresponding age today? If 65 was (implicitly) a male-oriented definition four decades ago, as we believe it was, what would have been the appropriate definition for women at that time, and what is it today? We address these questions by applying our criteria to Canada, using 1951 and 1991 life tables, but the criteria could be applied equally well to other countries. For other developed countries we would expect broadly similar results." (EXCERPT)^ieng

The response of aggregate production to fertility-induced changes in population age distribution.

PIP: With a particular focus upon long-term supply effects, the authors explored the implications of different population age distributions for the productive capacity of an economy. A multilevel aggregate production process was specified, plausible values assigned to its parameters, and steady-state solutions obtained under a range of alternative fertility assumptions. The theoretical model was calibrated to conform with Canadian data and published estimates of age-sex substitution elasticities. The study found productive capacity to be related to age distribution, although the output effects exceed 8%, regardless of the structure of the economy, only when total fertility rate is less than 1.6 or well above 3.0; within the range of variation, productive capacity and output per capita are lower for both younger and older populations; altering the elasticity of substitution between different tasks has negligible effects upon the sensitivity of the economy to changes in age distribution; altering the elasticity of substitution between different age-sex groups for a given task has a markedly greater effect; introducing either increasing or decreasing returns to scale has only a minor effect upon the sensitivity of the economy to changes in age distribution; and marginal products are quite sensitive to changes in age distribution for both younger and older workers, but far less sensitive for middle-aged workers.^ieng

Physician supply in Ontario: further observations on SHARP and the SHARP projections.

In this issue (see pages 1395 to 1398) Eva Ryten questions the validity of the data that supported the projection of a surplus of physicians in Ontario over the next two decades, as presented in an earlier article in CMAJ by Denton, Gafni and Spencer. The authors maintain that the data they used were appropriate. Although the average annual growth rate for the early 1990s calculated from Ontario Health Insurance Plan (OHIP) billing data is somewhat lower than the rate they projected for the decade as a whole, the OHIP-based rate is much closer to their figure than Ryten's rate. They also disagree with Ryten in their belief that the recent reduction of medical school enrollment will have a negligible effect on the physician population by the year 2000. They argue too that Ryten misunderstands the nature of the imbalance they project between the availability of intern and resident services and the requirements for those services. Finally, the authors note that there is an argument for setting requirements for practising physicians at levels lower than they had assumed. For that reason, even if the supply of practising physicians were to grow less rapidly than projected, a substantial surplus could still result by the year 2000.

Who signs China's one-child certificate, and why?

PIP: A policy of 1 child/family was initiated in China in 1979 to help control population growth. An estimation model is presented using 1985 fertility survey data to estimate characteristics associated with deciding to comply with the policy. After accounting for place of residence, woman's education, husband's occupation, marriage duration, presence of a son, family structure, and house size were found to significantly influence compliance. Age, child mortality experience, husband's education, and woman's occupation, however, did not. No conclusions could be made on the influence of income and wealth in adhering to policy.^ieng

Macro-effects of changes in household preferences for children: simulated history and future time paths.

The basic ideas underlying the analysis in this paper are that family size can be viewed as an economic life cycle decision and that there are decision trade-offs among fertility, consumption, and leisure. A micro-model of life cycle choice is developed and embedded in an economic-demographic macro-model. The macro-model is then used in a series of computer experiments to assess the effects on the population and the economy of changes in household preferences for children. The experiments include factual and counterfactual simulations of Canadian historical demographic experience and simulations of alternative future scenarios. The analysis and conclusions have general relevance for countries that have been through a fertility boom-and-bust sequence.

Potential savings from the adoption of nurse practitioner technology in the Canadian health care system.

An investigation is reported of the potential for reducing aggregate medical costs by the introduction of nurse practitioners into the Canadian health care system to an extent consistent with demonstrated safety and effectiveness. A cost model is developed for this purpose and estimates of its parameters are provided. The cost model is coupled with a demographic projection model and potential cost reductions are simulated over the period 1980-2050, under alternative assumptions. Results suggest that savings could have been in the range 10-15% in 1980 for medical services as a whole, and 16-24% for ambulatory services. The estimated savings percentages are quite insensitive to projected changes in the age structure of the Canadian population.

Some demographic consequences of changing cohort fertility patterns: An investigation using the Gompertz function.

Abstract In this paper are formulated some convenient summary measures of fertility patterns. These measures, which are based on the Gompertz function, are total lifetime fertility, median age of mothers at childbirth, and inter-quartile range of age of mothers at childbirth. Estimates of the parameters of Gompertz function, based on Canadian data, are used to derive, for each of the summary measures, values which reflect historical fertility experience, and thus give an impression about the range of realistic values for these measures. A simple model of demographic activity which includes the Gompertz function is also considered, and this model is used in computer simulation experiments to determine the macro-demographic effects of changes in each of the three summary measures.