Search PubMed⌕ Search

Biomedical subjects

R W Rice

Publications and source records attributed to R W Rice.

32 records · Page 2Linked to original sources
PubMed1976

Sex differences in the effects of surgical isolation of the medial basal hypothalamus on linear growth and plasma growth hormone levels in the rat.

The effects of surgical isolation of the medial basal hypothalamus (MBH) on linear growth and plasma growth hormone (GH) levels were studied in adult male and female rats. Whereas MBH isolation resulted in reduced linear growth in males, increased growth resulted in females. These effects were apparent in males 4 weeks after surgery and in females at 10 weeks. The altered growth rates persisted throughout the 28 weeks of the study. MBH isolation in both sexes led to increased food intake, obesity, and atrophy of reproductive tract organs. Non-stress plasma GH levels were unchanged at 4 weeks in both sexes but were elevated at 10 and 26 weeks in females and at 19 and 26 weeks in males. Serial samples of tail vein blood were obtained at 4-h intervals for 44 h from MBH-isolated and shamoperated females at 17 weeks postoperatively, and from similar groups of males at 19 weeks. GH levels were elevated in MBH-isolated rats of both sexes during the afternoons and evenings. Only sham-operated females showed evidence of a 24-h rhythmicity in circulating GH levels. The amplitudes of trough to peak excursions were similar in MBH-isolated and control females, but these excursions were reduced in MBH-isolated males. Although opposite effects on linear growth were noted in the two sexes, the resulting growth rates of operated males and females were similar, suggesting that MBH isolation disrupts mechanisms that normally regulate sex-specific growth patterns. Despite the sex difference in growth responses, MBH isolation caused an eventual increase in plasma GH levels in both sexes. Therefore, it is unlikely that the sex difference in growth responses is attributable exclusively to corresponding changes in circulating GH levels. A reduction in levels of circulating gonadal steroids may be an important factor. The elevations in plasma GH levels observed in both sexes suggest that MBH isolation interferes with mechanisms which inhibit GH secretion.

Animals↗
PubMed1976

Extrahypothalamic control of stress-induced inhibition of growth hormone secretion in the rat.

The aim of these experiments was to determine whether the telencephalon is essential for stress-induced suppression of plasma GH levels and, if so, which telencephalic structures are involved. In the first study, the telencephalon was completely removed from adult female rats by suction; intact and sham-operated rats served as controls. At 24 h after surgery, blood samples were collected at the initiation of and 15 min after a 3-min immobilization-blood withdrawal stress procedure and used for determining non-stress and stress plasma levels of GH, respectively. GH was measured by radioimmunoassay. In contrast to the normal stress-induced decrements in GH levels observed in controls, this response was blocked and stress caused a paradoxical increase (P less than 0.01) in GH levels in telencephalon-ablated rats. These results suggested that the telencephalon is essential for stress-induced inhibition of GH secretion. Therefore, the several components of the telencephalon were ablated individually in additional experiments to determine the structure(s) involved. Placement of large, bilateral lesions in the amygdala or complete removal by suction of hippocampus, septum or striatum did not interfere with the normal GH response to stress at 24 h after surgery. However, removal of the preoptic region duplicated the effects of complete telencephalon ablation i.e., the normal stress-induced decrement was not only blocked but also reversed. These findings suggest that the preoptic region is essential for mediating inhibition of GH secretion in response to immobilization-blood withdrawal stress and that other telencephalic structures are not essential for this neuroendocrine response.

Amygdala↗
PubMed1975

Leader esteem for the least preferred co-worker score, training, and effectiveness: an experimental examination.

A laboratory experiment supported Fiedler's Contingency Model analysis of leadership training. The effect of leadership training on group performance was contingent on leadership style, that is, the leader's relation to his least preferred co-worker (LPC). Training improved the performance of high LPC leaders, but was detrimental to the performance of groups with low LPC leaders. High intelligence leaders profited more from training than low intelligence leaders, but low intelligence leaders were more productive overall. Leader LPC times Intelligence interactions indicated that follower satisfaction and interpersonal affect were highest for groups with high LPC-low intelligence leaders or low LPC-high intelligence leaders. Implications for contingency theories of leadership are discussed.

Efficiency↗
PubMed1975

An ultrastructural examination of the role of cell membrane surface coat material during neurulation.

Data from neural crest cultures indicate that cell surface coat material (CSM) is directly involved in cellular migration and events surrounding differentiation. To investigate whether the CSM also has a morphogenetic role, embryos of the amphibian Ambystoma maculatum were examined ultrastructurally throughout the stages of neurulation. Segments of the neural axis were fixed in glutaraldehyde-containing Alcian blue 8GX, which reportedly enhances preservation of CSM, and were postfixed in OsO4 containing 1 percent lanthanum nitrate, which stains the CSM. The medial groove formed by the appearance of the neural ridges contains a large amount of CSM and numerous vesicles coated with lanthanum-positive material. In contrast, the lateral ridge surfaces are covered by a small amount of uniformly distributed CSM and a paucity of vesicles. As the ridges begin to fold there is a progressive increase in the amount of CSM within the presumptive neural tube region. Further convergence of the neural folds is accompanied by an increase of CSM at their leading edges. As the folds approximate each other, lanthanum-positive material physically bridges the gap. However, as the apposing tissue actually abuts to form the neural tube, no CSM is observed in the remaining interspace. The specific distribution and sequential accumulation of cell CSM during the events of neurulation strongly suggest its direct participation in the morphogenetic process.

Ambystoma↗
PubMed1975

Effects of stress on plasma corticosterone and growth hormone levels in rats with median eminence-pituitary islands.

The effects of stress on plasma corticosterone and growth hormone (GH) were determined in adult female rats 24 h after forebrain removal in order to study the anatomical substrate essential for stress-induced alteration of pituitary function. Rats with median eminence-pituitary islands (MEPI) showed significant increments in plasma corticosterone levels 15 min after immobilization-blood withdrawal stress. Rats with basal hypothalamic-pituitary islands (BHPI) showed comparable increments, suggesting that the presence of hypothalamic tissue in addition to median eminence did not enhance the steroid response. A subsequent study demonstrated that MEPI rats are capable of a 2nd response, 6 h after the first. MEPI rats also showed a significant 50% increase in plasma GH levels 15 min after immobilization-blood withdrawal. In a final experiment, MEPI rats showed corticosterone but not GH responses to immobilization applied without blood withdrawal. These data offer further evidence that some stressful stimuli can alter pituitary functions under short-term conditions in the absence of hypothalamic or other forebrain neurons.

Animals↗
PubMed1975

Effects of PCBs, DDT, and mercury compounds upon egg production, hatchability and shell quality in chickens and Japanese quail.

Dietary polychlorinated biphenyls (PCBs), DDT and related compounds, in well controlled experiments, produced no detrimental effects upon egg shell quality in Single Comb White Leghorm chickens or in Japanese quail. PCBs caused some decrease in egg production and a drastic reduction in hatchability in chickens, but not in Japanese quail. Inorganic mercury as HgSO4 or HgCl2, at dietary levels up to 200 p.p.m. of Hg, had only small effects, if any, upon egg production, hatchability, shell quality, morbidity and mortality. However, methyl mercury chloride at levels which provided 10 or 20 mg. of Hg per kg. of diet caused severe effects upon egg weight, egg production, fertility, hatchability, egg shell strength, morbidity and mortality. The results of these experiments demonstrate that the decrease in egg shell quality which has occurred in eggs of White Leghorn hens over the past three decades is not due to contamination of commercial feeds with DDT or its derivatives, or with PCBs. The extent to which environmental contamination with methyl mercury is responsible for decreased egg shell strength in commercial laying hens, and possible synergistic relationships between methyl mercury, DDT, DDE and PCBs in reducing egg production, hatchability and shell strength, remain to be determined.

Adipose Tissue↗
PubMedDate not supplied

Wood-drying condensate from Eastern white pine induced cytotoxicity and genotoxicity in vitro.

Eastern white pine is one of the most important commercial species of wood in the Northeast. Condensates extracted from this wood were tested to detect potential cytotoxicity and genotoxicity in Chinese Hamster Ovary (CHO) cells in the absence of S-9 activation. Cytotoxicity was measured by the Trypan blue exclusion assay, mitotic index (MI) and proliferative rate index (PRI). Genotoxicity was measured by the chromosome aberration (CA) assay and sister chromatid exchange (SCE) analysis. Both cytotoxic and genotoxic effects were observed. Laboratory-generated Eastern white pine condensate reduced the viability of CHO cells. The number of viable cells was roughly inversely proportional to dosage over a range of 91 percent to 58 percent survival in treated groups as compared to 2.4 x 10(5) viable cells (100 percent) in the control. The mitotic index (MI) data also showed an inverse correlation with dosage. The highest scorable dose limited by toxicity was determined to be 1 ml of Eastern white pine condensate in a total of 10 ml of medium. Lastly, a dose response curve was observed using the CA assay and also with the SCE analysis. The present findings support results obtained from Ames testing of Eastern white pine condensate and also corroborate results derived from human peripheral-blood lymphocytes.

Animals↗