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D L MacMillan

Publications and source records attributed to D L MacMillan.

At least 19 recordsLinked to original sources
PubMed1995

Heightened concerns over the 1992 AAMR definition: advocacy versus precision.

We reiterated our earlier concerns (MacMillan et al., 1993) regarding the 1992 AAMR definition of mental retardation and replied to a defense of the definition (Reiss, 1994). Our major point here is that definitional precision should not be sacrificed to advance a particular ideological position. The result of such a compromise is a definition lacking precision and necessitating identification dependent upon assessment of behavioral dimensions for which there is currently no reliable measurement. We explored the varied purposes served by classification systems and criticized the new AAMR definition for lack of precision needed to serve research. In addition, we attempted to reduce confusion over the concepts of reliability, assessment, test bias, and use of factor analysis to establish the independence of adaptive skill domains. Some factual errors and incorrect representations in Reiss's article were pointed out.

Activities of Daily Living↗
PubMed1994

Morphology, physiology, and homology of the N-cell and muscle receptor organs in the thorax of the crayfish Cherax destructor.

The serial homology of arthropods, together with our ability to identify individual neurons from segment to segment, and from animal to animal, provides opportunities for studying the changes wrought by natural selection on specific neural elements when functional requirements change in different parts of the trunk. Using this concept as a guide, we studied the morphology and physiology of the thoracic N-cells and muscle receptor organs (MROs) of the crayfish Cherax destructor for evidence of serial homology and functional plasticity. Methylene blue staining, together with anterograde and retrograde filling with cobalt through cut axons, revealed the morphology of the receptors, disposition of their endings, and the pathways of their axons from receptor to ganglion. The seventh thoracic segment has tonic and phasic MROs with receptor muscles in parallel with different heads of the deep thoraco-abdominal extensor muscle. The sixth segment has a tonic MRO with a receptor muscle in parallel with one head of the abdominal abductor. These three receptors are typical MROs complete with accessory nerves. Thoracic segments 1-5 each give rise to one mechanosensory N-cell with a small cell body and long processes ramifying in a target muscle. N-cell 5 is associated with the abdominal-thoracic abductor muscle, and the other four are associated with parts of the epimeral attractor. The responses of N-cells 1-4 range from tonic to phasico-tonic and show a range of thresholds to passive muscle stretch and active contraction. Cobalt introduced into bundles of nerve fibers known to include N-cell axons reveals projections with branching patterns and morphology similar to abdominal MROs. The present findings, together with information on thoracic MROs and N-cells from other species, were tabulated according to neurotome. The clear pattern revealed leads us to propose that N-cells are derivatives of segmentally repeating MROs modified to monitor postural and locomotory movements in the less mobile thorax.

Animals↗
PubMed1993

Caloric restriction and intervention in pancreatic carcinogenesis in the rat.

In two experiments, the effects of caloric restriction during the postinitiation phase of pancreatic carcinogenesis were evaluated. Male Lewis rats were given injections of azaserine at 14 days of age and weaned to the postinitiation test protocols at 21 days of age. In the first experiment, the caloric content of the diets was restricted by 10, 15, 20, and 30% of the intakes of the ad libitum-fed rats. A sixth group was fed diet ad libitum for only 5-6 h/day; i.e., they were "meal-fed". The development of putative preneoplastic lesions (henceforth termed foci) was evaluated by quantitative stereological (morphometric) analysis of the pancreas. Caloric restriction during the 4-month postinitiation phase resulted in a significant reduction in focal development beginning at 10% caloric restriction and increasing with more severe restriction. The caloric intake of the meal-fed group closely matched the caloric intake of the 10 or 15% caloric restriction groups and the focal response of the meal-fed rats was similar to the groups restricted in calories by 15 to 20%. In the second experiment, rats were initiated with azaserine and weaned to one of four groups: ad libitum; meal-fed; meal-fed for 2 months and ad libitum thereafter; or ad libitum for 2 months and meal-fed thereafter. Foci were evaluated at 2 and 4 months; neoplasm incidence and multiplicity were determined at 14 months postinitiation. Compared to the ad libitum group, the meal-fed group had significantly fewer foci at all times of evaluation and significantly fewer neoplasms. When rats were meal fed for 2 months and then switched to ad libitum feeding for the remainder of the experiment, the focal outcome at 4 months was similar to the group meal fed for all 4 months; and at 14 months the neoplastic outcome was intermediate between the ad libitum and the meal-fed group. Intervention in the ad libitum feeding regimen at 2 months by meal feeding for the remainder of the experiment resulted in a significant decrease in the focal and neoplastic development, as compared to the group fed ad libitum continuously. These two intervention groups were intermediate in response between the meal-fed and ad libitum-fed groups. These results indicate that the postinitiation phase of pancreatic carcinogenesis can be modulated by relatively simple dietary interventions such as moderate caloric restriction.

Animals↗
PubMed1993

Evaluation of the post-initiation effects of oltipraz on aflatoxin B1-induced preneoplastic foci in a rat model of hepatic tumorigenesis.

Previous studies have demonstrated that ingestion of 5-(2-pyrazinyl)-4-methyl-1,2-dithiole-3-thione (oltipraz) during the aflatoxin B1 (AFB1) treatment phase completely prevented hepatic cancer. In this study we evaluated the effect of feeding oltipraz during the post-AFB1 treatment phase. Fifty-five male F344 rats were divided into five groups. All rats were gavaged with 25 micrograms AFB1/rat, five times a week for two successive weeks. The rats were fed the oltipraz-supplemented diet according to three different feeding regimes: during the AFB1 treatment phase (1 week prior to, during and 1 week after the last gavage with AFB1); during the post-treatment phase; or throughout the entire time of the experiment. Phenobarbital-supplemented diet was fed during post-treatment phase to one group and this was used as a positive control for the promotion of AFB1-induced focal growth. The burden of putative, preneoplastic, hepatic glutathione S-transferase P-positive foci was evaluated at 13 weeks after the AFB1 treatment phase. As seen previously, oltipraz fed during the AFB1 treatment phase significantly inhibited focal development, i.e. the volume percent of the liver occupied with foci was reduced by 87%. Oltipraz when fed during the post-treatment phase neither inhibited nor enhanced focal development.

Aflatoxin B1↗
PubMed1993

Conceptual and psychometric concerns about the 1992 AAMR definition of mental retardation.

The new American Association on Mental Retardation (AAMR) definition of mental retardation (Luckasson et al., 1992) represents a radical departure from previous definitions. In the present paper we examined the extent to which the new definition provides decision rules to guide clinicians and researchers in classification efforts. We concluded that the IQ criterion of 75 will increase the proportion of the general population eligible near the cut-off score. Moreover, the 10 adaptive skill areas adopted fail to consider developmental factors and cannot be assessed reliably with current scales. Proposed differentiation by levels of needed supports is also challenged as being imprecise and not amenable to reliable measurement. Implications of this new definition for diagnostic practices and research endeavors were explored.

Activities of Daily Living↗
PubMed1992

Differences in adolescents' self-concept as a function of academic level, ethnicity, and gender.

The relations of dimensions of self-concept of adolescents with their academic level, ethnicity, and gender were investigated. A self-concept inventory assessing 11 aspects of self-concept was administered to a sample of 1,140 eight-grade students stratified with regard to academic level (regular class, educationally marginal, learning handicapped), ethnicity (white, black, and Hispanic), and gender. Results showed that regular class students had higher levels of self-concept on most scales than did students who were educationally marginal or learning handicapped; the latter two groups showed few differences. Black students had higher self-concept ratings than did white and Hispanic students on most scales. An interaction on two academically related dimensions of self-concept revealed that white students who were educationally marginal had the lowest level of academic and verbal self-concept. Implications of the results for theories of self-concept formation were discussed.

Achievement↗
PubMed1990

Evaluation of promotion of pancreatic carcinogenesis in rats by benzyl acetate.

Benzyl acetate was found to induce liver tumours and gastric squamous neoplasms in mice in a chronic bioassay conducted through the National Toxicology Program. An increased incidence of acinar cell adenomas of the pancreas of F344 rats was noted in the bioassay, but the significance of these lesions was confounded because the benzyl acetate was given by gavage in corn oil. The use of corn oil as a vehicle has been shown to enhance the growth of such lesions in the rat pancreas. The current studies were undertaken to evaluate benzyl acetate alone as an initiator and promoter of carcinogenesis in the pancreas. Alkaline elution analysis of acinar cell DNA showed no evidence of damage 1 hr after administration of benzyl acetate. Significant stimulation of growth of azaserine-induced foci was observed in a 6-month study, and a low but significant incidence of carcinoma in situ was observed in rats fed benzyl acetate in the diet for 2 yr. These experiments suggest that benzyl acetate is a weak promoter of the growth of carcinogen-induced and spontaneous pre-neoplastic foci in the pancreas.

Adenoma↗
PubMed1984

Modulation of azaserine-induced pancreatic foci by phenolic antioxidants in rats.

Effects of the dietary phenolic antioxidants butylated hydroxyanisole [(BHA) CAS: 25013-16-5; (1,1-dimethylethyl)-4-methoxyphenol] and butylated hydroxytoluene [(BHT) CAS: 128-37-0; 2,6-di-tert-butyl-p-cresol] on pancreatic tumorigenesis were examined. Male LEW inbred rats were given injections of 30 mg azaserine [CAS: 115-02-6; diazoacetate (ester) serine] per kg body weight once a week for 3 weeks and maintained on either a control diet or 0.45% BHA- or 0.45% BHT-supplemented control diet throughout the initiation and post-initiation phases of the experiment. At 4 months post initiation, pancreatic tissue sections were quantitatively examined for the number and size of preneoplastic foci. BHT and BHA treatments reduced the number of acidophilic foci per pancreas by 32 and 48%, respectively, but were without effect on focal size. By contrast, basophilic foci were not subject to modulation by these antioxidants. A constellation of enzyme activities involved in carcinogen inactivation and known to be perturbed by antioxidant treatment was examined in liver and pancreas. The hepatic activities of glucose-6-phosphate dehydrogenase, glutathione reductase, and glutathione-S-transferases were markedly elevated while catalase and superoxide dismutase activities were unchanged. Glutathione peroxidase activity was diminished. In the pancreas, only glutathione peroxidase activity was affected, and it was reduced in both the BHA and BHT treatment groups. Although the pancreas is refractory to the enzyme inductive effects of these antioxidants, morphometric analysis of foci demonstrated chemoprevention by BHA and BHT of azaserine-induced foci. Whether this reduction reflected inhibition of an initiation, postinitiation , or a combination of effects was not known.

Animals↗
PubMed1983

Influence of the EMR label on initial expectations of regular-classroom teachers.

Regular-classroom elementary teachers (N = 1,114) were queried as to their initial expectations for mainstreamed handicapped children. Subjects were randomly assigned to treatment conditions and told that the experimenter was interested in assessing their initial expectations for a child being considered for placement in their class. Each teacher was shown a photograph and read a vignette about a particular child who was portrayed as varying in attractiveness, school-related traits, and labeled background (i.e., educable mentally retarded). Subjects then completed a questionnaire on which they indicated their initial expectations regarding: (a) academic ability, (b) the child's behavioral potential, (c) their ability to work with the child, and (d) their general impressions of that child. Results indicated that the label EMR differentially influenced teacher expectations across the four areas rated. Data also showed that a child's attractiveness and school-related traits significantly influenced initial expectations of regular-classroom teachers. Ramifications of the findings were discussed.

Achievement↗
PubMed1980

Convergent and discriminant validity of project PRIME's Guess Who?

Two forms of the Guess Who?, a peer-assessment instrument, were administered to 1,095 mildly handicapped learners and 143 teachers. Factor analysis of the student and teacher ratings yielded three factors--disruptive, bright, and dull--for both sets of data. Factor scores for the student and teacher forms were then intercorrelated in a multitrait-multimethod matrix, and the results established the convergent and discriminant validity of the instrument. The finding that teachers could provide valid estimates of student perceptions of the three traits was interpreted as promising for future research.

Child↗
PubMed1980

System-identification of mildly mentally retarded children: implications for interpreting and conducting research.

The position was taken that the system identification of EMR children is designed to find children for service delivery and is not intended to identify a population with known parameters. Variability in the system derives from several sources: teacher judgment of academic failure, teacher referral, screening of referrals, and factors related to the assessment process. Moreover, recent litigation and sociopolitical forces have compounded this variability to the point of obscuring the population parameters of EMR or mildly mentally retarded children. The implications of such variability in characteristics of mildly retarded children were discussed in terms of interpreting past research and conducting future research.

Child↗