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Biomedical subjects

J D Skinner

Publications and source records attributed to J D Skinner.

At least 37 records · Page 2Linked to original sources
PubMed1997

Distribution and morphology of luteinising hormone-releasing hormone neurones in a species of wild antelope, the springbok (Antidorcas marsupialis).

The distribution and morphology of luteinising hormone-releasing hormone (LHRH) neurones varies between species. The primary purpose of this study was to characterize the distribution and morphology of the LHRH system in a species of antelope, the springbok. This wild antelope has a well-defined social structure in which reproductive activity is confined to a few dominant, territorial rams. We also sought to determine whether social or reproductive status could be accounted for by differences in the distribution or morphology of hypothalamic LHRH neurones. Eleven anoestrous female, nine breeding territorial male (TM) and eight "bachelor" male (BM) springbok were obtained, and their reproductive and body conditions were assessed. By using standard immunocytochemical techniques, the LHRH system was visualised in the brains of four animals from each group. Immunoreactive neurones were located in a continuum from the septum to the arcuate nucleus, with the majority at the level of the organum vasculosum of the lamina terminalis. Neither the distribution nor the number of cells differed among the three groups. Furthermore, the area of LHRH perikarya was similar in both groups of males, suggesting that reproductive differences between TMs and BMs lie at another level of the neuroendocrine axis. The anoestrous females had significantly larger neurones than males (TM plus BM). This may reflect a sex difference in the LHRH system of this wild antelope. However, an alternative explanation is that the male/female difference is related to the comparatively inactive reproductive neuroendocrine state of the females.

Analysis of Variance↗
PubMed1997

Longitudinal study of nutrient and food intakes of infants aged 2 to 24 months.

OBJECTIVE: To determine the nutrient and food intakes of healthy, white infants from families of middle and upper socioeconomic status and to compare intakes to current recommendations. DESIGN: Using an incomplete random block design, we interviewed 98 mother-infant pairs longitudinally when infants were 2, 3, 4, 6, 8, 10, 12, 16, 20, and 24 months old. Data obtained included 24-hour dietary recalls, usual food intake, and food likes and dislikes. SETTING: Interviews were conducted in the mother's home by registered dietitians. Subjects resided in two urban areas of Tennessee. SUBJECTS: Of the original 98 subjects, 94 completed the 2-year study. RESULTS: Mean energy and nutrient intakes generally met or exceeded the Recommended Dietary Allowance (RDA). Exceptions were zinc and vitamin D, which were each below 100% of the RDA at 9 of the 10 data points, and vitamin E, which was below the RDA in the infants' second year. Fat intake decreased from more than 40% of energy in the first 6 months to 30% to 32% from 10 to 24 months. One third of the infants drank reduced-fat milks at 12 months and more than half drank them at 24 months. Although infants ate a variety of foods, vegetables often were the least favorite foods. A variety of dairy products provided calcium for the infant but lacked vitamin D. CONCLUSIONS: Several nutritional issues about infant feeding before 2 years of age arose. Low intakes of zinc, vitamin D, and vitamin E were observed. In the second year, low fat intake, use of reduced-fat milks, and dislike of vegetables were areas of concern.

Age Factors↗
PubMed1997

A Food Variety Index for Toddlers (VIT): development and application.

OBJECTIVE: To develop a variety index based on the Food Guide Pyramid that is specific to toddlers and is indicative of dietary adequacy. DESIGN: Subjects' mothers were assigned randomly to two in-home interviews with a registered dietitian at four possible collection periods: 24, 28, 32, or 36 months. Three days of dietary information were collected at each period. A Variety Index for Toddlers (VIT) was developed to assess variety within and among food groups based on the number of servings from the food groups in the Food Guide Pyramid. SUBJECTS: White children aged 24 to 36 months (n = 124) and their mothers who were participants in an ongoing longitudinal study. STATISTICAL ANALYSES: Descriptive statistical procedures were performed on VIT scores. Mean adequacy ratio (MAR) scores were calculated for all subjects and compared with VIT scores. RESULTS: Bread group scores were consistently the highest of the individual food groups (mean score = 0.94 to 0.96 on the 0.0 to 1.0 scale); the vegetable and meat groups were generally the lowest (mean score = 0.68 to 0.73 and 0.73 to 0.76, respectively). Mean VIT scores (an average of the five food group scores) over the four collection periods ranged from 0.79 +/- 0.14 to 0.81 +/- 0.15; a score of 1.00 represented intake of at least the minimum number of recommended servings from each food group. VIT scores were strongly correlated to the MAR score of nutrient adequacy (r = +.74, P < .01). APPLICATIONS: The VIT can provide a numeric description of dietary variety specific to toddlers. VIT scores can be compared with other characteristics of children, and this index has the potential to be adapted for use with other age groups and populations.

Adult↗
PubMed1997

Developmental and food profiles of infants born to adolescent and adult mothers.

OBJECTIVE: To compare developmental markers and dietary intake of infants born to lower socioeconomic adolescent and adult mothers. DESIGN: Sixty-one adolescent (age 14-18 years) and 60 adult (age 22-28 years) mothers met inclusion criteria of comparable socioeconomic status, age range, urban/rural residence, and distribution of infants by gender. SAMPLE/SETTING: Adolescent subjects were recruited in last trimester and adult mothers postpartum. Interviews were conducted when infants were about 6 and 12 months of age. Data included age of occurrence for eight markers, age at adding complementary foods, two 24-h dietary recalls, and two measurements of growth. RESULTS: Adolescent mothers reported a significantly earlier age at which the infant "holds a spoon by self" and "drinks alone from a trainer cup." Six other markers were not significantly different between groups. Adolescent mothers fed cereal significantly earlier than did adult mothers, but there were no significant differences for fruit, vegetables, and meat. At 12 months, infants of adolescents had intakes of vitamin D and iron which were < 100% of recommended allowances, as did infants of adult mothers for vitamin D, iron, and zinc. Dietary fat was significantly higher at 6 and 12 months and vitamin C was lower at 12 months for infants of adolescents compared to the adult group. CONCLUSIONS: Compared to adult mothers, adolescent mothers reported earlier mean ages for developmental markers related to self-feeding, and introduced cereal earlier. In each group, selected nutrient intakes decreased from recommended amounts in the 6-12-month period. Fat intakes were significantly different between groups at 6 and 12 months.

Adolescent↗
PubMed1997

Transitions in infant feeding during the first year of life.

OBJECTIVE: To document ages at which transitions in infant feeding occur, to compare these transitions to literature reports from the 1970s and 80s, and to identify maternal characteristics related to the age of the infant when solid food was first introduced. METHODS: Ninety-eight mother/infant pairs (middle and upper socioeconomic status) participated in the longitudinal study. Using a randomized, incomplete block design, in-home interviews were conducted by trained personnel when infants were 2, 3, 4, 6, 8, 10, and 12 months of age; each mother/infant pair was seen four or five times. Information on food intake, including breast milk/formula, was collected at each interview. Means +/- SD and frequencies were calculated, and least squares analysis of variance was used to develop a predictive model related to the introduction of cereal. RESULTS: Most mothers decided on the initial feeding mode (breastfeeding or formula) prior to pregnancy; 83% breastfed initially although most (76%) totally discontinued breastfeeding by 6 months. Infants' ages varied greatly when each of the seven categories of food was introduced, cereal was added to the infants' diets at a mean age of 3.8 +/- 1.4 (SD) months, juice 4.7 +/- 2.2, fruit 4.9 +/- 1.6, vegetables 5.2 +/- 1.3, mixed foods 7.8 +/- 2.1, table foods 8.2 +/- 2.1, and meat 8.2 +/- 2.1. The multivariate model explained 59% of the variability in ages of infants when cereal (generally the first solid food) was added. Significant variables (p < or = 0.05) were feeding mode, recommendation by the physician, and the interaction between feeding mode and education of the mother. Mother's employment and sibling rank of the infant contributed to the model (p = 0.06 and p = 0.09, respectively). Infants' age when cereal was added was not related to the variables of gender or birth weight. CONCLUSIONS: The finding that the mothers' decision whether or not to breastfeed was made prior to conception supports the importance of population-based education aimed at women in the child-bearing years as well as patient instruction early in the pregnancy. However, the duration of breastfeeding was shorter than was reported in the 1980s. Infants varied greatly in ages when the seven categories of complementary foods were added to their diets. Although recommendations for delaying introduction of solid foods until the infant is 4 to 6 months of age have been in place for more than a decade, about half the mothers in this study did so earlier. Characteristics of mothers who introduced cereal earliest (i.e., mean age of infants < 4 months) were more likely to be formula feeding when cereal was added, to feed cereal via the bottle, to be primiparous, to be employed outside the home, and/or not to cite the physician as a source for guiding the infant's transition to supplemental food.

Adult↗
PubMed1996

Summer torpor in African woodland dormice Graphiurus murinus (Myoxidae:Graphiurinae).

We determined the effect of food availability (presence/absence) and ambient temperature (25/10 degrees C) on daily energy expenditure and the use of activity and torpor in summer-acclimated captive Graphiurus murinus. Daily energy expenditure declined logarithmically with duration of food deprivation at a mean rate of 11 and 31% per day at 25 and 10 degrees C, respectively. The incidence of torpor in the presence of food at 25 degrees C was low (one in seven individuals) and increased on a single day's exposure to 10 degrees C and with duration of food deprivation. Use of torpor was highest during the day, varied between individuals, and torpor bouts of greater than 24 h duration were not noted. With food deprivation, individuals at 25 degrees C initially responded by reducing activity but remained euthermic while the same individuals at 10 degrees C responded by increasing their use of torpor during the light period: this difference in response probably reflects a difference in the relative energetic benefits of torpor at different temperatures.

Animals↗
PubMed1994

Interactive effects of temperature and photoperiod on the daily activity and energy metabolism of pouched mice (Saccostomus campestris: Cricetidae) from southern Africa.

The daily activity and energy metabolism of pouched mice (Saccostomus compestris) from two localities in southern Africa was examined following warm (25 degrees C) and cold (10 degrees C) acclimation under long (LD 14:10) and short (LD 10:14) photoperiod. There was no differential effect of photoperiod on the daily activity or metabolism of pouched mice from the two localities examined, which suggests that reported differences in photoresponsivity between these two populations were not the result of differences in daily organisation. Nevertheless, there was a significant increase in metabolism at 10 degrees C, irrespective of photoperiod, even though seven cold-acclimatized animals displayed bouts of spontaneous torpor and saved 16.4-36.2% of their daily energy expenditure. All but one of these bouts occurred under short photoperiod, which suggests that short photoperiod facilitated the expression of torpor and influenced the daily energy metabolism of these individuals. As expected for a nocturnal species, the amount of time spent active increased following acclimation to short photoperiod at 25 degrees C. However, there was a reduction in mean activity levels under short photoperiod at 10 degrees C, possibly because the stimulation of activity by short photoperiod was masked by a reduction in activity during bouts of spontaneous torpor. Cold temperature clearly had an overriding effect on the daily activity and metabolism of this species by necessitating an increase in metabolic heat production and eliciting spontaneous torpor which over-rode the effect of short photoperiod on activity at an ambient temperature of 10 degrees C.

Activity Cycles↗
PubMed1994

Morphology of intestinal villi in African antelope (Artiodactyla: Bovidae).

Villous morphology in 16 species of African antelope varied from finger-like and leaf-like to ridge-like forms. Some species showed uniform villi whereas it was variable in others. There was a slight indication that leaf-like and finger-like forms become more frequent in the distal regions of the small intestine. The variation in morphology was not associated with body size or phylogeny, but did show a significant correlation with diet: species with high moisture content and/or high fibre levels (equivalent to low bulk values) in the digesta were more likely to have ridges, which were the lowest of the villi.

Animals↗
PubMed1992

Avian species-specific tandem repeats contain nuclear protein binding sites.

Three avian highly repetitive tandem repeats were identified and examined. These repeats had similar unit lengths (about 42 bp long) but completely different sequences each containing particular protein binding sites. Each of these repeats was found within only one of the five closely related genera studied.

Animals↗
PubMed1992

The relative importance of photoperiod and temperature as cues for seasonal acclimation of thermoregulation in pouched mice (Saccostomus campestris: Cricetidae) from southern Africa.

The effect of short photoperiod and cold on metabolism and thermoregulation was investigated in pouched mice (Saccostomus campestris: Cricetidae) from three localities in southern Africa which experience contrasting climatic conditions. Mice were initially acclimated to long photoperiod (14L: 10D) at 25 degrees C, followed first by a decline in photoperiod (to 10L: 14D) and then by a fall in temperature (to 10 degrees C). Minimum observed metabolic rate (identical to basal metabolic rate) was unaffected by the decline in photoperiod but increased significantly following cold acclimation. Because minimal thermal conductance remained constant throughout the study the increase in minimum observed metabolic rate caused a decline in lower critical temperature to around 26 degrees C. In contrast to minimum observed metabolic rate, regulatory non-shivering thermogenesis improved significantly following the decline in both photoperiod and temperature. However, pouched mice from the warmest locality were significantly less responsive to photoperiod than those from the other two localities whose survival might depend upon their ability to accurately predict seasonal changes in temperature. Neither photoperiod nor temperature had any effect on body mass, yet pouched mice from the most arid locality, where food supply might be unpredictable, were significantly smaller and had lower total energy requirements than those from areas experiencing higher annual rainfall. These results indicate that S. campestris displays considerable geographical variation in energy requirements together with differences in the use of photoperiod as an anticipatory cue for predicting the onset of winter. These differences appear to be related to the availability of energy and the relative severity of climatic conditions in each locality.

Africa↗
PubMed1992

Burrowing and huddling in newborn porcupine: the effect on thermoregulation.

The newborn cape porcupine Hystrix africaeaustralis is a precocial rodent. However, the newborn spends its first 9 weeks in the burrow. Heat production (oxygen consumption--VO2) and body temperature (Tb) were measured at various ambient temperatures (Ta) in newborn (4-8-week-old) porcupines, with a body mass between 1340-1993 g during summer, from the colony kept at the Mammal Research Institute, University of Pretoria. To assess the effect of huddling, these parameters were also measured in adult pairs of porcupines (Ta = 15 and 25 degrees C) kept together in the metabolic chamber and the values were compared with those obtained from single porcupines. Overall minimal thermal conductance was calculated for newborn and paired adult porcupines. The newborn porcupines can regulate their body temperature at Tas between 10-28 degrees C. VO2 measured at lower critical point is 0.602 +/- 0.08 ml/O2/g.h. At Ta = 10 degrees C, VO2 oscillated with a characteristic amplitude and frequency, while body temperature was well regulated. Huddling decreases the lower critical point. The overall minimal thermal conductance (0.044 +/- 0.002 ml O2/g.h.1 degree C) is higher than expected from body mass, so that the young are liable to lose heat rapidly. It is well known that the newborn porcupine spends a long period in the burrow and the results of this study suggest that this may be in order to conserve energy and presumably allocate it to growth. Apart from decreasing vulnerability, delaying foraging also avoids heat loss in the newborn porcupine.

Animals↗
PubMed1992

Adrenocortical responsiveness to immobilization stress in spotted hyenas (Crocuta crocuta).

1. The adrenocortical responsiveness to an induced stressor was monitored in free-living spotted hyenas belonging to a number of social and reproductive categories. 2. No significant differences between sexes, or changes in mean cortisol concentrations during serial sampling within the sexes, could be demonstrated. 3. The extreme individual variance in temporal cortisol profiles recorded in this study is inexplicable, as it was not related to differences in immobilization procedure, sex, age, reproductive or social category. 4. Females, which are the dominant sex in this species, generally showed larger percentage increases in cortisol concentrations during serial sampling. 5. Significant correlations between initial cortisol concentrations, as well as cortisol responsiveness and androgen concentrations, in a number of social and reproductive categories, suggest that these categories do not provide sufficient resolution for the identification of specific dominance-related trends.

Adrenal Cortex↗
PubMed1992

Sex-specific androgen binding in spotted hyaena (Crocuta crocuta) plasma.

1. A charcoal adsorption assay demonstrated a large variance in androgen binding ability in female spotted hyaenas. 2. A positive correlation between plasma androgen binding ability and ovarian steroid concentrations was demonstrated in adult females. 3. The strong plasma binding affinity for testosterone and dihydrotestosterone (DHT) (nM) together with the lack of cortisol and weaker oestradiol-17 beta binding suggests that a specific androgen binding substance, possibly a protein, is present in adult females of this species. 4. The lack of high affinity binding in male spotted hyaenas is unusual and deserves further investigation. 5. Some androgen binding in all, including males and immature animals suggests that albumin may bind some plasma androgens in this species.

Androgens↗
PubMed1992

Changes in concentration of serum prolactin during social and reproductive development of the spotted hyaena (Crocuta crocuta).

A homologous radioimmunoassay system developed for humans was used to measure prolactin concentrations in spotted hyaenas. Concentrations of prolactin showed a significant (P < 0.05) decrease in lactating females, which is consistent with the infrequent suckling pattern of this species. This lack of hyperprolactinaemic conditions during lactation may explain the ability of females to resume reproductive activity soon after the loss of a litter, or even during lactation. Prolactin concentrations did not increase significantly during dispersion in male spotted hyaenas. This conforms to the pattern observed for cortisol, but differs from that for androgen, which fluctuates significantly with social suppression. Although comparative data from other species provide some circumstantial evidence for hyperprolactinaemic conditions during male dispersal, no obvious deductions regarding the recorded inverse relationship between prolactin and cortisol concentrations in mature males could be made.

Androstenedione↗
PubMed1992

Cravings and aversions of pregnant adolescents.

Adolescents from 31 eastern Tennessee counties were interviewed during the third trimester of pregnancy (n = 97) and at 1-year postpartum (n = 64) to assess cravings and aversions, beliefs about dietary cravings, and how these factors influence dietary intake. Characteristics of cravings and aversions were assessed using a semistructured interview. Beliefs about cravings during pregnancy were measured with a 13-item Likert-type scale (alpha = 0.79). Two 24-hour recalls and 2 days' food records provided dietary data. Most adolescents (86%) reported cravings during pregnancy. They most frequently reported cravings for sweets, especially chocolate; fruits and fruit juices; fast foods; pickles; ice cream; and pizza. Many participants (66%) experienced aversions during pregnancy toward previously liked foods. The most common aversions were to meats, eggs, and pizza. Fewer cravings and aversions were noted during the first year postpartum. No significant relationship existed between craving and aversions and belief scores. Adolescents craving sweets during pregnancy consumed more sugar and energy than those who did not crave sweets. Cravings generally resulted in increased intake, and aversions led to decreased food consumption. On the basis of these results, we suggest that nutritional assessment of pregnant adolescents include questions about cravings and aversions.

Adolescent↗
PubMed1991

Phosphorylation and chromatin mechanics: the central importance of substrate conformation in determining the patterns of HL-60 nuclear phosphorylation.

HL-60 nuclear autophosphorylation was studied in vitro under circumstances in which the conformation of chromatin was manipulated with both polyamines and DNAse-I. A general re-arrangement of the phosphorylation patterns occurred as polyamines were removed and nuclei were observed to expand. DNAse-I treatment reduced these phosphorylation patterns to a much simpler configuration indicating that the responding substrates were DNA-associated. It was concluded that substrate conformation was the main determining factor in the control of nuclear protein phosphorylation. These results suggest a method of general utility for the identification of truly nuclear proteins by the characteristics of their phosphate acceptor activity.

Cell Line↗