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Biomedical subjects

T M Lee

Publications and source records attributed to T M Lee.

At least 109 records · Page 6Linked to original sources
PubMed1995

Seasonal variations in circadian rhythms persist in gonadectomized golden-mantled ground squirrels.

Circadian wheel-running activity was monitored in intact and gonadectomized female and male golden-mantled ground squirrels maintained in a 14L:10D photoperiod at 21 degrees C. Marked advances in phase angle of activity onset and increases in the duration of the daily active phase occurred each year in intact animals coincident with the phase of reproductive activity. Surprisingly, long-term gonadectomized squirrels of both sexes manifested similar seasonal changes in the circadian system. Seasonal circadian variations in locomotor activity are generated by a circannual clock independent from and not influenced by concurrent changes in secretion of gonadal hormones.

Animals↗
PubMed1994

Effect of vomeronasal organ removal on behavioral estrus and mating latency in female meadow voles (Microtus pennsylvanicus).

The vomeronasal organ (VNO) mediates the induction of behavioral estrus in prairie voles by male chemosignals; however, the importance of this system for the initiation of estrus in meadow voles, a species in which spontaneous estrus has been postulated, is unknown. This experiment was designed to investigate the influence of VNO-mediated chemosensory information on behavioral estrus in meadow voles housed in photoperiods simulating summer (long photoperiods; 14L:10D) and winter (short photoperiods; 10L:14D). The VNO was removed from nulliparous female meadow voles, and the percentage of animals mating after removal and the timing of mating onset were assessed. Removal of the organ did not suppress mating or change the timing of mating onset in females housed in short photoperiods. In animals housed in long photoperiods, in contrast, removal of the organ significantly increased the percentage of females mating and the percentage of females mating rapidly after pairing. The results indicate that chemosensory information mediated via the VNO is not necessary for the induction of behavioral estrus in meadow voles and lends support to the hypothesis that meadow voles have a spontaneous estrus. We postulate that polygynous, solitary meadow voles reproduce more effectively with spontaneous estrus than with the induced estrus described for monogamous, group-living prairie voles.

Animals↗
PubMed1994

Luteinizing hormone and prolactin in mated female meadow voles housed in long and short day lengths.

Fertility differs dramatically between female meadow voles (Microtus pennsylvanicus) housed in long (LD; 14 h light/day) and short (SD; 10 h light/day) day lengths. All mated LD females ovulate, and 75-100% produce litters. In contrast, 40% of SD females that mate only after long contact with a male do not ovulate, and fertility for SD females is much lower (30-40% produce litters overall). Because copulation causes the surge in LH required for ovulation and the increase in prolactin (PRL) needed to maintain corpora lutea, we hypothesized that SD females might have lower ovulation rates and litter production because of inadequate hormonal responses. Serum LH was measured 24 h before, and 30, 60, 90, 120, and 180 min after, mating. Prolactin was measured before, and 24 and 48 h after, copulation. LD and SD females that ovulated demonstrated a sharp increase in LH levels at 30 and 60 min post mating, but LH in non-ovulating females was approximately 50% lower than that of ovulating females at 30 and 60 min post mating. PRL in LD females was double baseline levels at 24 and 48 h after mating. PRL in SD females increased at 24 h, but declined to pre-mating levels by 48 h post mating. These data suggest that reduced fertility in short day lengths in female voles may be related to two separate problems: 1) The rise in LH following copulation is insufficient in some females to cause ovulation. 2) PRL may not remain elevated long enough to support functional corpora lutea in some females that ovulate.

Animals↗
PubMed1994

The effect of occupational therapy education on students' perceived attitudes toward persons with disabilities.

OBJECTIVES: The effect of occupational therapy education on students' perceived attitudes toward persons with disabilities was studied. METHOD: The perceived attitudes of 144 occupational therapy students toward persons with disabilities were measured before (retrospective pretest) and after (posttest) the students attended formal professional education at the University of Alberta. RESULTS: Posttest scores were significantly higher than the retrospective pretest scores, indicating that students' attitudes became more positive after they commenced formal professional education. The posttest scores of students at various levels of education, however, did not show any significant difference. CONCLUSION: On the basis of these observations, a positive but nonlinear relationship between occupational therapy education and attitudes toward persons with disabilities was postulated.

Attitude↗
PubMed1994

Tricholin, a new antifungal agent from Trichoderma viride, and its action in biological control of Rhizoctonia solani.

Tricholin, a ribosome-inactivating protein isolated from the culture broth of Trichoderma viride, has been shown to exert fungicidal effects on Rhizoctonia solani through a multi-hit kinetic interaction. Tricholin causes a parallel cessation of growth, uptake of amino acids, and protein biosynthesis. The in vivo mode of action of tricholin on protein synthesis and cell growth appears to be attributed to the diminishing of the polysome formation in R. solani through damage to large ribosomal subunits. These results concur with previous data and prove that tricholin is an effective inhibitor of protein synthesis. The efficacy of tricholin as an antibiotic agent was estimated to have a duration of approximately 42 hours.

Antifungal Agents↗
PubMed1993

The shear strength and the failure mode of plasma-sprayed hydroxyapatite coating to bone: the effect of coating thickness.

Plasma-sprayed hydroxyapatite coated (HAC) 50 and 200 microns thick on Ti-6Al-4V cylinders was transcortically implanted in the femora of canines to evaluate in detail the effect of coating thickness on the pushout shear strength and failure mode examined under scanning electron microscope after the periods of 4, 6, 8, and 12 weeks. The HAC coating exhibited higher shear strength at 50 microns than at 200 microns. Its failure mode was conclusively at or near the HAC-bone interface, and the slight attack of body fluid had not degraded the implant to the extent that failure occurred at the HAC-Ti alloy interface after 12 weeks of observation. For 200 microns-HAC, failure was found at the HAC-bond interface, inside the HAC lamellar splat layer and at the HAC-Ti alloy substrate interface, depending on the period of implantation. It was also deduced that the variation of failure mode of 200 microns-HAC with time could not be accounted for by the attack of body fluid alone; the degradation must be a synergetic adverse result of residual stress in the HAC and the attack of body fluid.

Analysis of Variance↗
PubMed1993

The sensitivity of magnetic resonance image signals of a rat brain to changes in the cerebral venous blood oxygenation.

The sensitivity of magnetic resonance image signals of the brain to the change in the cerebral blood oxygenation was measured in gradient echo images of rat brains at a field strength of 7 T. The sensitivity depended on the blood vessel volume relative to the tissue volume within the image voxel, and signal intensities in the cortical area were well correlated with the change in the venous blood de-oxygenation level at the sagittal sinus. Tissue signals in the image (15 ms echo time) showed a sensitivity of 10-20% change for the full range of deoxygenation level from 0-100%. From these observations and image simulations, the extent of the signal response to some neuro-stimulation which induces an increase in regional cerebral blood flow has been estimated for 4 T field strength.

Animals↗
PubMed1993

Female meadow voles have a preferred mating pattern predicted by photoperiod, which influences fertility.

In a previous study, Meek and Lee found that female meadow voles mated within three distinct time periods after pairing with a male, and fertility was influenced by the time of mating and photoperiod. In the present studies, we tested the hypothesis that different patterns of mating would correlate with high and low fertility. We found two very different patterns of mating were correlated with high fertility. Females housed in long daylengths (long day; 14 h light/day) and mating within 48 h of pairing with a male, received few mounts, intromissions, and intromissions per ejaculatory series, with very short interintromission intervals. All long-day females utilizing this mating pattern ovulated, and 86-100% produced litters. We suggest this pattern of mating is associated with spontaneous estrus. In contrast to long-day females mating within 48 h, females housed in short daylengths (short day; 10 h light/day) and mating between 14-48 h after pairing with a male, received significantly more short mounts and intromissions, with longer interintromission intervals. These short day females all ovulated and 86% produced litters. We suggest that this pattern of mating is associated with an induced estrus. Short-day females that did not exhibit this pattern of mating (66%) produced far fewer litters. We discuss two mechanisms by which fertility may be inhibited in most short-day females.

Animals↗
PubMed1993

Development of meadow voles is influenced postnatally by maternal photoperiodic history.

The importance of maternal photoperiodic history during lactation on the postnatal development of meadow vole pups was tested by cross-fostering pups on the day of birth between photorefractory females (housed for 26 wk in a 10:14-h light-dark cycle before mating) and photosensitive females (housed for 2 wk in a 10:14-h light-dark cycle before mating). Control pups were cross-fostered to females with the same photoperiodic history as the gestational dam. Somatic growth and food intake of cross-fostered pups were influenced by the photoperiod of the postnatal lactating dam. Pre- and postnatal maternal photoperiodic history interacted with the sex of the offspring to influence reproductive development. Pelage development was determined exclusively by the prenatal maternal photoperiodic history. The impact of a postnatal maternal influence on pup development of photoperiod-sensitive traits is discussed.

Animals↗
PubMed1993

Prediction of fertility by mating latency and photoperiod in nulliparous and primiparous meadow voles (Microtus pennsylvanicus).

Mating behavior and litter production of female meadow voles (Microtus pennsylvanicus) housed in long (14 h light: 10 h dark; long day; LD) or short (10 h light: 14 h dark; short day; SD) photoperiods were monitored to determine whether the reduced birthrate of SD females resulted from a lack of copulation. All females mated, but fewer SD females gave birth. LD and SD females fell into three distinct groups based on mating latency. The rapid onset group (RO) mated between 7 min and 9 h after pairing, the intermediate onset group (IO) mated between 16-44 h and the late onset group (LO) mated after 58-262 h of male contact. Sixty-seven per cent of LD females were assigned to group RO, 27% to IO, and 6% to LO. In contrast, 30% of SD females were assigned to group RO, 35% to IO and 35% to LO. Fertility was predicted by mating latency. Sixty-nine per cent of RO, 93% of IO and 33% of LO animals gave birth. In a further experiment, a small-mouthed cup was added to the environment to serve as an escape for females wishing to avoid mating. Although females did not use the cup to escape male approaches, mating occurred in only 66% of SD females, but was observed in all LD females. In a final experiment, mating latency and litter production were recorded in primiparous LD and SD females initially observed in the first experiment. Group LO was eliminated in parous females; all primiparous LD and SD females mated within 48 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Ethylene-Induced Polyamine Accumulation in Rice (Oryza sativa L.) Coleoptiles.

Effects of ethylene on free polyamine biosynthesis in rice (Oryza sativa L. cv Taichung Native 1) coleoptiles were investigated in sealed and aerobic conditions. In sealed conditions, putrescine increased significantly and coincided with ethylene accumulation. Application of ethylene in sealed containers promoted putrescine accumulation over that in sealed controls. This ethylene-enhanced putrescine accumulation was inhibited by the ethylene action inhibitor 2,5-norbornadiene at 4000 muL/L. In aerobic conditions, ethylene and 1-aminocyclopropane-1-carboxylic acid also induced putrescine accumulation. Activity of arginine decarboxylase (EC 4.1.1.19) and S-adenosylmethionine decarboxylase (EC 4.1.1.50) increased on exposure to ethylene in aerobic conditions. Ornithine decarboxylase (EC 4.1.1.17) activity, however, remained unchanged. The ethylene-induced putrescine accumulation was inhibited by 5 x 10(-4)m alpha-difluromethylarginine, but not by 5 x 10(-4)m alpha-difluromethylornithine. Apparently, arginine decarboxylase, not ornithine decarboxylase, mediates the ethylene-induced putrescine accumulation. The increased S-adenosylmethioinine decarboxylase activity, however, did not result in a significant spermidine/spermine accumulation. In ethylene-treated coleoptiles, the accumulation of putrescine paralleled the increase of coleoptile length in both sealed and aerobic conditions. alpha-difluromethylarginine inhibited ethylene induced putrescine accumulation and coleoptile elongation. It seems that putrescine biosynthesis might be involved in the ethylene-induced elongation of rice coleoptiles.

Journal Article↗
PubMed1992

Estradiol phase-shifts circannual rhythms of golden-mantled ground squirrels.

Ovariectomized golden-mantled ground squirrels (Spermophilus lateralis) were implanted with estradiol benzoate (EB)-filled or empty capsules. Body weight was monitored for at least 1 yr before, during, and after hormone treatment. EB treatment of 6-7 mo duration, restricted to the weight-gain phase, decelerated weight gain and delayed attainment of peak weight by 34 days; the period of the circannual rhythm, measured between successive trough weights, was 36 days longer in squirrels treated with estradiol than in untreated animals. EB treatment of 2- to 4-mo duration, restricted to the weight-loss phase, accelerated weight loss, advanced attainment of trough weights by 57 days, and decreased the period of the circannual rhythm by 66 days. Estradiol-induced phase delays and advances were preserved in the year after discontinuation of hormone treatment. These results favor the existence of circannual phase-response curves to hormones and provide a system for pharmacological manipulation of circannual rhythms.

Animals↗
PubMed1991

Suprachiasmatic nucleus and photic entrainment of circannual rhythms in ground squirrels.

The efficacy of photoperiod as a zeitgeber for entrainment of circannual body weight and estrous rhythms was tested in female golden-mantled ground squirrels maintained for 3 or more years in either a simulated natural photoperiod (SNP) or a fixed LD 14:10 photoperiod (FP). The role of the retinohypothalamic tract--suprachiasmatic nucleus (RHT-SCN) projection in photic entrainment was assessed in animals that sustained destruction of the SCN (SCNX). Circannual rhythms were lengthened by the SNP as compared to the FP. Mean periods (tau's) for neurologically intact animals in the third year of testing were 49.6 +/- 0.3 weeks and 43.1 +/- 1.2 weeks (p less than 0.001) for the SNP and FP groups, respectively; furthermore, 56% and 7% of animals in these groups had tau's not significantly different from 365 days (p less than 0.005), and within-group variability was lower for SNP than for FP squirrels (p less than 0.01). SCNX squirrels differed from animals with the SCN intact (SCNC), as evidenced by higher within-group variability (p less than 0.001); only 29% of SCNX squirrels had tau's not different from 365 days (p less than 0.03 compared to the SCNC group). The coupling between estrous and body weight rhythms that was evident in SCN-intact SNP and FP squirrels was disrupted in SCNX animals. The RHT-SCN pathway is implicated in entrainment and in maintenance of normal phase relations among the several circannual rhythms. In a second experiment, female squirrels were maintained for 2.5 years in an accelerated SNP that compressed two normal annual photocycles into each calendar year. Of 12 squirrels, 3 had tau's that did not differ significantly from 6 months; 6 had tau's equivalent to 12 months; and 3 had tau's significantly different from both 6 months and 12 months. The data suggest that photoperiod is a major zeitgeber for entrainment of golden-mantled ground squirrels circannual rhythms.

Animals↗
PubMed1990

Prolactin counteracts effects of short day lengths on pelage growth in the meadow vole, Microtus pennsylvanicus.

To test whether growth of the winter coat in short day lengths is contingent on suppression of plasma prolactin (Prl) levels, female meadow voles (Microtus pennsylvanicus) were kept in short day lengths for 12 weeks and were injected daily with saline or Prl; long-day animals were treated with either the dopamine agonist, bromocryptine (bromo), bromo plus Prl, or saline. Prl treatment prevented the growth of the winter coat normally observed after 12 weeks in short day lengths, but bromocryptine did not stimulate pelage growth in long-day voles. Pelage growth in short day lengths appears contingent upon decreased plasma prolactin levels.

Analysis of Variance↗
PubMed1990

Oxygenation-sensitive contrast in magnetic resonance image of rodent brain at high magnetic fields.

At high magnetic fields (7 and 8.4 T), water proton magnetic resonance images of brains of live mice and rats under pentobarbital anesthetization have been measured by a gradient echo pulse sequence with a spatial resolution of 65 x 65-microns pixel size and 700-microns slice thickness. The contrast in these images depicts anatomical details of the brain by numerous dark lines of various sizes. These lines are absent in the image taken by the usual spin echo sequence. They represent the blood vessels in the image slice and appear when the deoxyhemoglobin content in the red cells increases. This contrast is most pronounced in an anoxy brain but not present in a brain with diamagnetic oxy or carbon monoxide hemoglobin. The local field induced by the magnetic susceptibility change in the blood due to the paramagnetic deoxyhemoglobin causes the intra voxel dephasing of the water signals of the blood and the surrounding tissue. This oxygenation-dependent contrast is appreciable in high field images with high spatial resolution.

Animals↗
PubMed1990

Magnetic resonance imaging of blood vessels at high fields: in vivo and in vitro measurements and image simulation.

Unusually high image contrast in vivo magnetic resonance imaging of the brain becomes observable at high magnetic fields when the blood oxygenation level is lowered. The cause of the contrast has been attributed to a magnetic susceptibility effect induced by paramagnetic deoxyhemoglobin in red cells. When the cylinder axis of a blood vessel is not parallel to the main magnetic field, the susceptibility difference produces varying local fields around the blood vessel. In gradient-echo images, not in spin-echo images, these local fields cause intravoxel dephasing of the water signal of the surrounding tissue. This description of the contrast enhancement has been confirmed by a series of in vitro blood sample experiments and image simulations. A predicted contrast change has been demonstrated in brain images of a mouse placed at two different orientations in the magnet. From the simulated images, the dependence of the contrast on the field strength has been estimated.

Animals↗
PubMed1990

Brain magnetic resonance imaging with contrast dependent on blood oxygenation.

Paramagnetic deoxyhemoglobin in venous blood is a naturally occurring contrast agent for magnetic resonance imaging (MRI). By accentuating the effects of this agent through the use of gradient-echo techniques in high fields, we demonstrate in vivo images of brain microvasculature with image contrast reflecting the blood oxygen level. This blood oxygenation level-dependent (BOLD) contrast follows blood oxygen changes induced by anesthetics, by insulin-induced hypoglycemia, and by inhaled gas mixtures that alter metabolic demand or blood flow. The results suggest that BOLD contrast can be used to provide in vivo real-time maps of blood oxygenation in the brain under normal physiological conditions. BOLD contrast adds an additional feature to magnetic resonance imaging and complements other techniques that are attempting to provide positron emission tomography-like measurements related to regional neural activity.

Animals↗