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Biomedical subjects

M Tatar

Publications and source records attributed to M Tatar.

51 records · Page 3Linked to original sources
PubMed1998

Mutation and senescence: where genetics and demography meet.

Two evolutionary genetic models-mutation accumulation and antagonistic pleiotropy-have been proposed to explain the origin and maintenance of senescence. In this paper, we focus our attention on the mutation accumulation model. We re-examine previous evidence for mutation accumulation in light of new information from large-scale demographic experiments. After discussing evidence for the predictions that have been put forth from models of mutation accumulation, we discuss two critical issues at length. First, we discuss the possibility that classical fruit fly stock maintenance regimes may give rise to spurious results in selection studies of aging. Second, we consider evidence for the assumptions underlying evolutionary models of aging. These models assume that mutations act additively on age-specific survival rate, that there exist mutations whose effects are confined to late age-classes, and that all mutations have equal effects. Recent empirical evidence suggests that each of these three assumptions is unlikely to be true. On the basis of these results, we do not conclude that mutation accumulation is no longer a valid explanation for the evolution of aging. Rather, we suggest that we now need to begin developing more biologically realistic genetic models for the evolution of aging.

Aging↗
PubMed1997

Heat-induced longevity extension in Drosophila. I. Heat treatment, mortality, and thermotolerance.

Survival data were collected on a total of 28,000 Drosophila melanogaster adults in order to investigate mortality patterns and induced physiological responses after a mild thermal stress. A brief, nonlethal heat treatment extends adult life span at normal temperatures by an average of 2 days (64), compared to nontreated controls of the same genotypes. Life expectancy is extended as a demographic consequence of reduced age-specific mortality over a period of up to several weeks after the heat treatment. Heat treatment also increases tolerance to subsequent, more severe thermal stress. Observations on single-sex populations suggest that heat-induced longevity extension is independent of the suppression of reproductive activity.

Acclimatization↗
PubMed1997

Primary health care in Turkey: a passing fashion?

The Alma-Ata Declaration has long been regarded as a watershed in the health policy arena. The global goal of the World Health Organization, 'Health for All by the Year 2000' through primary health care, has attracted many countries both in the developed and the developing world and commitments to this end have been made at every level. However, albeit this consensus on the paper, a common and explicit definition of the concept has not been reached yet. This paper aims at discussing various definitions of primary health care that emerged after the Declaration and also presenting a case study from Turkey, a country that advocates primary health care in her recent health policy reform attempts. After setting the conceptual framework for discussion the Turkish case is presented by using research carried out among Turkish policy-makers at different levels of the State apparatus. It has been concluded that application of primary health care principles as defined in the broad definition of the concept requires major changes or rather shake-ups in Turkey. These areas are outlined briefly at the end of the paper.

Comprehensive Health Care↗
PubMed1996

Community participation in health care: the Turkish case.

World Health Organization's global goal of Health for All by the Year 2000 (HFA) and achievement of this laudable goal through the Primary Health Care (PHC) approach has been accepted unanimously by participant countries of the Alma-Ata Conference in 1978. Turkey is also among the countries that showed their approval to the concept. However, that approval of the policy did not generate particular attention among the policy-makers until the 1990s. The year 1990 can be regarded as a watershed in the Turkish health policy-making environment as attempts at producing a National Health Policy document that centred around the global goal of HFA and PHC commenced. This paper aims at discussing the commitment of Turkey to one of the prerequisites of the approach, or heart of the PHC as regarded by some: community participation. After a brief presentation of community participation the Turkish commitment to the concept is analyzed based on a research carried out among Turkish health policy-makers. It is concluded that the prospect for community participation in Turkey does not look good mainly because of the medical approach adopted by the policy-makers. The need for more discussion of the topic among the academic circles has been emphasized.

Community Health Planning↗
PubMed1996

Age-specific patterns of genetic variance in Drosophila melanogaster. I. Mortality.

PETER MEDAWAR proposed that senescence arises from an age-related decline in the force of selection, which allows late-acting deleterious mutations to accumulate. Subsequent workers have suggested that mutation accumulation could produce an age-related increase in additive genetic variance (VA) for fitness traits, as recently found in Drosophila melanogaster. Here we report results from a genetic analysis of mortality in 65,134 D. melanogaster. Additive genetic variance for female mortality rates increases from 0.007 in the first week of life to 0.325 by the third week, and then declines to 0.002 by the seventh week. Males show a similar pattern, though total variance is lower than in females. In contrast to a predicted divergence in mortality curves, mortality curves of different genotypes are roughly parallel. Using a three-parameter model, we find significant VA for the slope and constant term of the curve describing age-specific mortality rates, and also for the rate at which mortality decelerates late in life. These results fail to support a prediction derived from MEDAWAR's "mutation accumulation" theory for the evolution of senescence. However, our results could be consistent with alternative interpretations of evolutionary models of aging.

Aging↗
PubMed1996

Age-specific patterns of genetic variance in Drosophila melanogaster. II. Fecundity and its genetic covariance with age-specific mortality.

Under the mutation accumulation model of senescence, it was predicted that the additive genetic variance (VA) for fitness traits will increase with age. We measured age-specific mortality and fecundity from 65,134 Drosophila melanogaster and estimated genetic variance components, based on reciprocal crosses of extracted second chromosome lines. Elsewhere we report the results for mortality. Here, for fecundity, we report a bimodal pattern for VA with peaks at 3 days and at 17-31 days. Under the antagonistic pleiotropy model of senescence, it was predicted that negative correlations will exist between early and late life history traits. For fecundity itself we find positive genetic correlations among age classes > 3 days but negative nonsignificant correlations between fecundity at 3 days and at older age classes. For fecundity vs. age-specific mortality, we find positive fitness correlations (negative genetic correlations) among the traits at all ages > 3 days but a negative fitness correlation between fecundity at 3 days and mortality at the oldest ages (positive genetic correlations). For age-specific mortality itself we find overwhelmingly positive genetic correlations among all age classes. The data suggest that mutation accumulation may be a major source of standing genetic variance for senescence.

Aging↗
PubMed1995

Genetic variation and aging.

Life span is subject to genetic modification in yeasts, nematodes, fruit flies, mice, humans, and other vertebrates and invertebrates. There are a few single-gene mutants known that extend life span in yeast and nematodes; in other experimental systems the character is treated quantitatively, and generally has a low to moderate heritability. Life span responds to artificial selection in Drosophila and Caenorhabditis. There are many candidate genes presently under investigation, including the anti-oxidizing enzymes and heat-shock proteins. The main evolutionary models of senescence are antagonistic pleiotropy and mutation accumulation, neither of which has substantial experimental support. The incorporation of analytical techniques from demography is playing an increasing role in research on aging.

Aging↗
PubMed1994

Laryngeal and tracheobronchial cough in anesthetized dogs.

Tussigenic sensitivity of laryngeal and tracheobronchial regions to mechanical and chemical stimuli was compared in 22 urethan-alpha-chloralose-anesthetized dogs. In addition, the contribution of myelinated and unmyelinated vagal fibers in mediating laryngeal and tracheobronchial cough was investigated. The intensity of cough was evaluated from changes in esophageal pressure. Whereas all mechanical stimulations and citric acid inhalations into tracheobronchial region elicited cough, only 56.7% of mechanical stimulation and 33.3% of citric acid challenges to larynx were effective. The intensity of tracheobronchial cough was significantly higher than that of laryngeal cough. When mechanical stimulation was conducted under visual control (bronchofiberscope), cough elicitability was found to be higher from tracheal bifurcation and main stem bronchi (62.5-87.5%) than from any laryngeal structure (0-42.9%). During partial block of vagal conduction (cooling to 6 degrees C), mechanical and citric acid tracheobronchial stimulations failed to elicit cough and mechanical laryngeal stimulation was effective only in 1 of 10 dogs. Intensity of cough was strongly decreased when mechanical stimulation followed capsaicin administration into trachea (0.3 ml; 100 micrograms/ml) or intravenously (10 micrograms/kg). We conclude that, in anesthetized dogs, stimulation of tracheobronchial region is more effective and prompt in eliciting cough than stimulation of larynx, myelinated vagal afferent fibers play an important role in mediating mechanically and citric acid-induced tracheobronchial cough and mechanically induced laryngeal cough, and stimulation of tracheobronchial and pulmonary capsaicin-sensitive receptors strongly inhibits mechanically induced cough.

Anesthesia↗
PubMed1991

Veratrine-induced reflexes and cough.

With cats anaesthetized with sodium pentobarbital we studied how veratrine-induced reflexes interact with cough. Cough was elicited by mechanical stimulation of tracheobronchial mucosa and its intensity was evaluated from the changes in oesophageal pressure. Veratrine injected intravenously produced apnoea, bradycardia and long-lasting hypotension. With each dose the intensity of cough was significantly decreased during the apnoea. When the mechanical stimulus was repeated during the breathing following apnoea with remaining hypotension, cough intensity parameters were not changed from control. Veratrine injected intracardially caused bradycardia, hypotension, and decreases in respiratory rate and tidal volume. The intensity of cough elicited just after injection of veratrine was also significantly decreased. We suggest that veratrine-induced reflexes depress the cough reflex mainly by inhibitory reflexes arising from cardiac receptors. The inhibition of cough is probably mediated indirectly via the inhibition of medullary respiratory neurons.

Animals↗
PubMed1988

Lung C-fibre receptor activation and defensive reflexes in anaesthetized cats.

1. With pentobarbitone-anaesthetized cats we have elicited cough reflexes from the tracheobronchial tree and the larynx, and the aspiration and sneeze reflexes from the nasopharynx and the nose respectively. The reflexes were induced by mechanical stimulation of the mucosa, before and during activation of pulmonary C-fibre receptors by intravenous injections of capsaicin or phenylbiguanide. 2. During the 20-30 s apnoea due to C-fibre stimulation, the cough reflex from both sites and the sneeze reflex were completely abolished, whereas the aspiration reflex response was approximately halved. Reflex contractions of genioglossus muscle still occurred at this time, but were far weaker than in the control state. 3. During the rapid shallow breathing that immediately followed apnoea due to C-fibre receptor stimulation, the defensive reflexes recovered: the aspiration and sneeze reflexes fully and the cough reflexes to about half of the control response. 4. Acute hypotension due to haemorrhage, of a size considerably greater than that due to stimulation of the pulmonary C-fibre receptors, caused no significant inhibition of the cough reflex from the tracheobronchial tree. 5. We conclude that the pulmonary C-fibre reflex powerfully inhibits airway defensive reflexes, and that its activation is unlikely to contribute positively to coughing induced by aerosols of capsaicin and similar agents.

Action Potentials↗
PubMed1983

[Respiratory center function in the course of the cough reflex in normoxia and hypoxia].

Impulse activity of the medulla respiratory neurons and electrical activity of the diaphragm and intercostal muscles were studied prior to, during and after coughing fit in anesthetized cats under conditions of normoxia and hypoxia. Simultaneously the intrapleural pressure was recorded and O2, paCO2, SaO2 were determined in arterial blood. Massive excitation of inspiratory and expiratory neurons as well as considerable augmentation of respiratory muscles electrical activity occurred during coughing fit. Soon after the fit the activity of neurons and muscles restored to initial level. During acute hypoxia the coughing fit shortened, the coughing seizures weakened as compared with the normoxic conditions. After the coughing fit, in result of hyperventilation during the fit, the paCO2 sharply dropped in arterial blood, the neuronal volley activity and the muscles rhythmic activity became disorganized, and apnea occurred. Within 20-40 sec rhythmic volley activity of the medulla inspiratory neurons disrupted the apnea.

Animals↗