Model For Other Species Research Articles

A base-age invariant site index model for aspen stands in north central Ontario

A time series version of the Chapman-Richards function was used to develop a base-age invariant site index model for aspen ( Populus tremuloides Michx.) stands in north central Ontario. The model developed was compared with a base-age invariant and a base-age specific site index model. It proved to be superior to both for estimating the height at Age 40 years from all other heights, but somewhat less accurate than the base-age specific model for estimating all other heights from the height at Age 40 years. The time series version of the Chapman-Richards function described here may be used to develop base-age invariant site index models for other species.

Method for obtaining accurate geometrical coordinates of nasal airways for computer dosimetry modeling and lesion mapping

Recently, finite-element computer simulation of airflow in rat nasal airways has been used to predict local and global xenobiotic mass transport. These computer simulations have the capability to facilitate the extrapolation of experimental data from rats to humans for risk assessment. Implementation of similar models of other species requires accurate and detailed geometrical coordinates of airways. This article presents a sectioning method for the acquisition of airway coordinates and morphometric data from fixed tissues. Using this method, airway tissue specimens are embedded in a frozen, contrast-enhancing medium and serially sectioned. Video images are digitized from photographs of the block face, and image analysis is used to obtain geometrical coordinates of the nasal passage perimeters. Calibration images and embedded alignment marks are used to scale and align sequential sections. Data resulting from the application of this method to a rhesus monkey specimen are reported, including a three-dimensional computer reconstruction of the data. Airway coordinates are also used to generate a set of diagrams suitable for lesion mapping for comparison with local dosimetry data derived from numerical simulations. This method improves on previously reported methods. Undistorted airway geometry is obtained by photographing the cut block face. Automatic thresholding to obtain coordinates during image analysis is made possible by the contrast-enhancing medium. Automatic scaling and alignment of sections is facilitated by the use of calibration images and alignment marks. This coordinate acquisition method has applicability to other complex biological passageways.

A Model of Cultural Evolution of Chaffinch Song Derived with the Meme Concept

The cultural evolution of song in populations of chaffinches from New Zealand was analyzed using the meme concept. Songs were broken down into their constituent memes (individual syllable types, their variants, or groups of linked syllables), and patterns of geographical variation for memes of different length were assessed. Multivariate spatial-autocorrelation analyses revealed a clinal pattern of variation, with close populations sharing more memes than would be expected at random and the inverse for populations that are far apart. Univariate spatial autocorrelation of syllable variants showed a random pattern attributable to high levels of mutation and random drift at this level. Syllable types, by contrast, are significantly correlated in their frequencies across populations and therefore have similar patterns. This is probably due to a major migrational event during colonization. Using Slatkin's method of rare alleles, we estimated that approximately 10 syllables per generation enter each population as a result of immigration. Rates of mutation vary for different units of cultural transmission, being highest for larger memes of sets of syllables and lowest for single syllable types. Approximately 20-30 new variants of syllables arise in a population each generation. Overall, the rate of cultural mutation and drift of apparently neutral song memes in New Zealand populations of chaffinches is high enough to swamp any homogenizing effect of meme flow, thus allowing the meme pools of these populations to diverge significantly in about the last 100 years. This is the first quantitative attempt to explain the process of cultural evolution of bird song in terms of the interaction of the mutation, flow, and random drift of memes within and among populations, and the task for the future is to assess the generality of this model in other species.

Analysis of Steady‐State Populations With the Gamma Abundance Model: Application to Tribolium

We develop a stochastic model for the abundance of adult populations of the four beetle Tribolium. The model is in the form of a stochastic differential equation containing adult recruitment and mortality rates perturbed by multiplicative noise. A deterministic version of the model (an ordinary differential equation) predicts a fixed, stable equilibrium; by contrast, the stochastic model predicts a stationary probability distribution for population size. The model can be approximated closely by a stochastic logistic equation having a gamma distribution as a stationary solution. We develop or clarify various practical aspects of making statistical inferences for the resulting gamma abundance model, including estimation of parameters, testing goodness of fit, obtaining confidence intervals for functions of parameters, and testing to compare two gamma distributions. Analyses of 11 data sets on Tribolium suggest that the gamma model deserves more widespread consideration as an equilibrium abundance model for other species.

Developmental genetics.

Of particular concern to the human geneticist are the effects of genetic abnormalities on development. To gain an understanding of these effects it is necessary to engage in a reciprocal process of using knowledge of normal developmental events to elucidate the mechanisms operative in abnormal situations and then of using what is learned about these abnormal situations to expand our understanding of the normal. True developmental genes have not been described in man, although it is likely that they exist, but many developmental abnormalities are ascribable to mutations in genes coding for enzymes and structural proteins. Some of these even produce multiple malformation syndromes with dysmorphic features. These situations provide a precedent for asserting that not only monogenic developmental abnormalities, but also abnormalities resulting from chromosome imbalance must ultimately be explicable in molecular terms. However, the major problem confronted by the investigator interested in the pathogenesis of any of the chromosome anomaly syndromes is to understand how the presence of an extra set of normal genes or the loss of one of two sets of genes has an adverse effect on development. Several molecular mechanisms for which limited precedents exist may be considered on theoretical grounds. Because of the difficulties in studying developmental disorders in man, a variety of experimental systems have been employed. Particularly useful has been the mouse, which provides models for both monogenic and aneuploidy produced abnormalities of development. An example of the former is the mutation oligosyndactylism which in the heterozygous state causes oligosyndactyly and in the homozygous state causes early embryonic mitotic arrest. All whole arm trisomies and monosomies of the mouse can be produced experimentally, and of special interest is mouse trisomy 16 which has been developed as an animal model of human trisomy 21 (Down syndrome). In the long run, the most direct approach to elucidating the genetic problems of human development will involve not only the study of man himself but also of the appropriate experimental models in other species.

Macrophages and glomerular crescent formation. Studies with rat nephrotoxic nephritis

A model of crescentic glomerulonephritis in the rat was developed, based upon an augmented form of nephrotoxic nephritis. The glomerular lesions were relatively mild, permitting an analysis of the morphologic events in crescent formation to an extent not possible in models in other species in which the sequence of changes is obscured by the severity of the inflammatory process. Monocytes and macrophages accumulated in glomerular capillary lumens and walls. Crescents were composed of cells with ultrastructural features indistinguishable from those of the intracapillary mononuclear cells. The findings support the view that the crescent cells are predominantly composed of macrophages derived from circulating monocytes.

Naloxone or TRH fails to improve neurologic deficits in gerbil models of “stroke”

The effects of naloxone or thyrotropin releasing hormone (TRH) upon neurologic outcome were evaluated in gerbil models of cerebral ischemia. Following temporary bilateral carotid occlusion, hypotension was transiently reversed by these endorphin antagonists. However, neither drug altered time to awaken, time to death, or the severity of neurologic signs (ptosis, movement, retracted paws, circling, righting reflexes, seizures, or opisthotonus) when evaluated by a blinded rater. Hot plate escape and roto-rod performance were also unaltered by naloxone or TRH; TRH, but not naloxone, increased respiratory rates. Thus, the transient improvement of cardiorespiratory function produced by these drugs is unrelated to the morbidity and mortality associated with temporary cerebral ischemia in the gerbil. Additional studies evaluating the effects of naloxone or TRH upon neurologic outcome following permanent unilateral carotid occlusion also failed to show any therapeutic effects of these drugs. Both morphine and TRH exacerbated the effects of ischemia. Of gerbils which developed neurologic impairment, the deficit was usually ipsilateral to the occluded carotid. Collectively, these results indicate that neither naloxone nor TRH prevents ischemic deficits in the gerbil. Further studies with different cerebral ischemia models in other species are required to clarify the possible therapeutic effects of these drugs in experimental stroke.

A technique for the intubation of the parotid duct in rats

Recently there has been an increased interest to develop specialised dosage forms that are better suited to specific patient populations, such as paediatrics and geriatrics. In these patient populations the acceptability of the oral dosage form can be paramount to the products success. However, many Active Pharmaceutical Ingredients (APIs) are known to cause an aversive taste response. One way to increase the acceptability and to enhance the palatability of the formulation is to design coated taste-masked particulate-based dosage forms. The masking of poorly tasting drugs with physical barriers such as polymer coatings can be utilised to prevent the release of drug within the oral cavity, thus preventing a taste response. However, currently, there are few assessment tools and models available to test the efficiency of these particulate-based taste-masked formulations. The rat brief access taste aversion model has been shown to be useful in assessment of taste for liquid dosage forms. However, the applicability of the rat model for particulate-based taste masked formulations is yet to be assessed. It is not understood whether dissolution, solubility and thus exposure of the drug to taste receptors would be the same in rat and human. Therefore, rat saliva must be compared to human saliva to determine the likelihood that drug release would be similar within the oral cavity for both species. In this study rat saliva was characterised for parameters known to be important for drug dissolution, such as pH, buffer capacity, surface tension, and viscosity. Subsequently dissolution of model bitter tasting compounds, sildenafil citrate and efavirenz, in rat saliva was compared to dissolution in human saliva. For all parameters characterised and for the dissolution of both drugs in rat saliva, a substantial difference was observed when compared to human saliva. This discrepancy in saliva parameters and dissolution of model drugs suggests that preclinical taste evaluation of particulate-based taste-masked formulations suggests rat is not a good model for predicting taste of solid dosage forms or undissolved drug where dissolution is required. Alternative preclinical in vivo models in other species, or improved biorelevant in vitro models should be considered instead.