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Biomedical subjects

D G Smith

Publications and source records attributed to D G Smith.

At least 271 records · Page 15Linked to original sources
PubMed1984

Calibrating the molecular clock: estimates of ground squirrel divergence made using fossil and geological time markers.

According to 5-Myr-old fossil evidence, ground squirrels within the genus Spermophilus had diverged into subgenera Spermophilus and Otospermophilus by late Miocene times. Radiometric dating has also provided a precise time for the sudden onset of a geological event, occurring 0.725 Myr ago, that initiated the complete and permanent reproductive isolation of two subspecies within the subgenus Otospermophilus. Since these two subspecies (S. beecheyi beecheyi and S. b. douglasii) readily hybridize with each other under laboratory conditions, allopatric subspeciation is unlikely to have occurred prior to 0.725 Myr ago. We employed Nei's model for estimating genetic distance in units which are linear in time, calibrated on the 0.725-Myr-ago date for initiation of S. b. subspeciation, to test its ability to generate a time scale for subgeneric divergence in keeping with the minimum estimate provided by the fossil record. This represents the most valid test to date of the utility of Nei's model for estimating genetic distance in units which are linear in time. Nei's model was found to underestimate this minimum time by 1 Myr, but it approximated this date after correcting values of D for variation in rates of evolution among loci.

Animals↗
PubMed1984

Bilirubin binding by variant albumins in Yanomama Indians.

Sera of Yanomama Indians homozygous for the common albumin allele exhibited greater total effective-binding capacities for bilirubin than did sera of individuals homozygous for the Yan-2 albumin variant in the in vitro experiments described herein. Total effective binding capacities of heterozygous samples were close to those of homozygotes for AlA. Individuals homozygous for Yan-2 might experience a higher risk of bilirubin toxicity and related disorders during the neonatal period. Further studies of binding and displacement of bilirubin by competitors, such as dietary or medicinal coumarins, might help explain the existence of these polymorphisms and the significance of phenotypic differences in binding to bilirubin.

Alleles↗
PubMed1983

Sustained branchial apnea in the Australian short-finned eel, Anguilla australis.

Branchial and cutaneous O2 uptake as well as branchial ventilatory stroke volume and frequency were measured by twin-chamber respirometry in conscious unoperated eels (Anguilla australis) at 20 degrees C. The branchial ventilatory pattern comprised alternating periods of apnea and eupnea, together constituting a "Standard Breathing Cycle" (SBC = 1 apneic period plus the ensuing period of eupnea). SBC time in 17 eels averaged 15.5 min of which only 23% was devoted to eupnea. Reduction of the PO2 of inspired water from 155 to 80 torr significantly increased the proportion of time devoted to eupnea to 49% of SBC time without significantly changing SBC time. Absolute cutaneous O2 uptake (5.8 ml O2 X h-1 X kg-1) was largely independent of the frequency or occurrence of eupnea, with the relative contribution of the skin to total O2 uptake averaging 47%. The histological appearance of the skin in A. australis is very similar to that described in A. anguilla: eel skin is only poorly vascularized. It was concluded that the skin may contribute to O2 requirements other than its own, and that this adaptation is a consequence of the unusual intermittent pattern of gill ventilation.

Animals↗
PubMed1982

Segregation distortion at the transferrin locus in Macaca mulatta.

The transferrin phenotypes of 256 rhesus monkeys and their parents were identified by polyacrylamide gel electrophoresis. The segregation ratio for phenotypes involving only alleles of high electrophoretic mobility was statistically significantly higher than expected and suggests that selection favors these more negatively charged transferrins. Electrostatic-dependent processes associated with the binding and transportation of iron might be responsible for this outcome.

Alleles↗
PubMed1982

Inbreeding in three captive groups of rhesus monkeys.

Using electrophoretic and serological genetic markers each of 17 potentially inbred matings in three groups of rhesus monkeys could be classified as either inbred or noninbred matings. Although nine of these 17 matings involved either father-daughter or paternal half-sib matings, only 7.4 were expected by chance alone. At least two, and possibly as many as three, of the nine cases of inbreeding involved father-daughter matings. Thus, no evidence of avoidance of inbreeding was observed in the closed captive groups of rhesus monkeys studied. Colony management policies must be developed to minimize the opportunity for or the deleterious effects of both father-daughter and half-sib matings. Furthermore, kin selection theory should consider why kin recognition, if it occurs, does not lead to avoidance of inbreeding.

Animals↗
PubMed1982

Binding of a bacteriophage to wall-membrane adhesion in proteus mirabilis.

A bacteriophage was shown to adsorb to plasmolyzed non-swarming cells of Proteus mirabilis preferentially at the sites of adhesion between the inner membrane and outer cell wall membrane; 75% of phage particles were adsorbed at these sites, while 25% were not. Differences in outer membrane composition between swarming and non-swarming cells were reflected in altered phage-binding properties, with only 33% of phage absorbed at these adhesion sites in swarming cells. On the basis of their phage distribution, cross-sections of swarm cells could be distinguished from sections of short non-swarming cells.

Adsorption↗
PubMed1982

Selection and the transferrin polymorphism in rhesus monkeys (Macaca mulatta).

Rates of survival, infant growth and fertility of rhesus monkeys with two, one and no C allele(s) at the transferrin locus are compared. Infants with no C allele experience slower growth rates than animals with either one or two C allele(s). While heterozygous females exhibit the highest infant growth rates among females, their fertility is lower and incidence of abortions and stillbirths is higher than for females with two or no C alleles. It is hypothesized that opposing directions of selection at different life-cycle stages maintain a stable equilibrium at the transferrin locus.

Abortion, Veterinary↗
PubMed1982

Use of genetic markers in the colony management of nonhuman primates: a review.

Genetic markers in blood were used to identify paternity and reconstruct genealogical relationships in six captive breeding groups of rhesus monkeys (Macaca mulatta) using paternity exclusion analysis. The theoretical and observed incidence of inbreeding and its deleterious effects were discussed and colony management alternatives proposed for minimizing these effects. Genetic markers for disorders and both desirable and undesirable phenotypic characteristics have been sought so as to maximize the reproductive success and vitality of the colony by selective breeding. A sound genetic component such as that described here is a necessary adjunct to any successful long-term program for breeding nonhuman primates.

Animals↗
PubMed1982

[Electrophoretic distances between the three gibbon sub-genera (author's transl)].

The three gibbon sub-genera : Symphalangus, Nomascus, and Hylobates are compared for 18 loci coding for serum proteins and enzymes. They are equally distant from each other on the basis of six discriminating electrophoretics markers. These results are compared with those of a similar study based on erythrocyte markers.

Alkaline Phosphatase↗
PubMed1982

Iron binding and transferrin polymorphism in Rhesus monkeys (Macaca mulatta).

Transferrin binds with and delivers serum iron to bone marrow where it is used in heme production. Total iron binding capacities and serum total iron levels were estimated for rhesus monkeys with different transferrin genotypes. Monkeys homozygous for the Tf-D or Tf-G alleles were found to have higher total iron binding capacities and lower serum total iron levels than those homozygous for the Tf-C allele. This difference might be responsible for or associated with differences in fertility and infant growth rates which have previously been reported for these animals.

Alleles↗
PubMed1981

Localization of smooth-muscle myosin in branchial pillar cells of snapper (Chrysophys auratus) by immunofluorescence histochemistry.

Smooth muscle myosin was localized in pillar cells by immunofluorescence histochemistry of gills from snapper (Chrysophys auratus). The amount of myosin present is comparable to that seen in mammalian vascular smooth muscle. No differences in the distribution of myosin-containing pillar cells, either within or between different secondary lamellae, were noted. The possibility that contractile proteins in pillar cells could function as autoregulators of blood flow, by responding with changes in active tension to alterations in the rate of change of pressure with each cardiac cycle, is discussed.

Animals↗
PubMed1981

Immunofluorescent and structural features of cells in the intervascular stroma of the amphibian carotid labyrinth.

The amphibian carotid labyrinth consists of a pars cavernosa, the main chamber of which is in communication with both the base of the external carotid artery, and the vessels of the labyrinthine pars capillaris. On the walls of the main chamber is a network of thick strands of connective tissue and modified smooth muscle cells surrounding the openings into the p. capillaris. These openings lead into wide-diameter atrial vessels, which in turn branch to form the short narrow-diameter vessels. The short vessels form the major component of the labyrinth. A few extremely narrow-diameter vessels are also present. The short vessels open into the roots of the internal carotid artery on the ventral aspect of the carotid labyrinth. The intervascular stroma of the p. capillaris contains numerous stellate and bipolar cells. These cells give a positive response to an immunofluorescent technique specific for smooth muscle myosin and tropomyosin. As the ultrastructural features of these cells are comparable in many respects to smooth muscle, they have been designated as modified smooth muscle cells. It is proposed that these cells act in both an active and passive fashion in maintaining the luminal dimensions of the short vessels relatively constant.

Animals↗
PubMed1981

Baroreceptor control of heart rate in the conscious toad Bufo marinus.

Perivascular balloons were used to elicit heart rate (HR) responses to imposed changes in mean arterial pressure (Pa) in conscious unrestrained toads (Bufo marinus). It is clear that functional baroreceptors lie in the pulmocutaneous arteries of B. marinus, and that these can elicit compensatory heart rate responses to perturbations of blood pressure. Functional baroreceptors were not present in the carotid circulation and are probably absent from the lateral aortae and conus arteriosus as well. Normalized gain of the baroreceptor-heart rate reflex (delta HR%/delta Pa) in five toads was 13%/kPa, which is considerably less than that found in other vertebrates to date.

Animals↗