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M J Duncan

Publications and source records attributed to M J Duncan.

At least 55 records · Page 3Linked to original sources
PubMed1990

Cloning and expression of the gene encoding the fructose-1,6-diphosphate-dependent L-(+)-lactate dehydrogenase of Streptococcus mutans.

The fructose-1,6-diphosphate-dependent lactate dehydrogenase from Streptococcus mutans JH1000 was purified by a modification of published methods. The sequence of 27 amino-terminal amino acids was determined, which allowed us to construct a 17-base DNA probe that had 32-fold degeneracy. The probe was used to screen a genomic library in pBR322. Of 18 reactive clones, 1 was found that expressed lactate dehydrogenase (LDH) activity identical to that of S. mutans with regard to dependence on fructose-1,6-diphosphate, thermal inactivation profile, and inhibition by sodium oxamate. Extracts of this clone possessed a protein band that comigrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with purified LDH from JH1000. Compared with controls, the clone was shown to produce elevated amounts of L-(+)-lactic acid during growth in the presence of glucose, thereby indicating that the activity was expressed in vivo. This result was substantiated by demonstrating that the activity could complement a mutation in the fermentative D-(-)-LDH of Escherichia coli. Subcloning showed that the S. mutans LDH subunit is encoded by a 1.2-kilobase gene. Our ability to clone this gene is expected to have great practical significance in the construction of an effector strain for use in the replacement therapy of dental caries.

Amino Acid Sequence↗
PubMed1989

Characteristics and autoradiographic localization of 2-[125I]iodomelatonin binding sites in Djungarian hamster brain.

These studies investigated the characteristics and regional distribution of 2-[125I]iodomelatonin binding in Djungarian hamster brain. The results showed that 2-[125I]iodomelatonin labels two types of binding sites, which resemble the ML-1 and ML-2 melatonin subtypes previously described in other tissues. The 2-[125I]iodomelatonin binding site identified in whole brain membranes has a nanomolar affinity (Kd = 1.48 +/- 0.26 nM) and biochemical and pharmacological characteristics identical to those of the ML-2 site of Syrian hamster whole brain. The 2-[125I]iodomelatonin site in the hypothalamus has a picomolar affinity (Kd = 43.4 +/- 5.1 pM) and resembles the ML-1 site of chicken retina. The localization of 2-[125I]iodomelatonin labeling in autoradiographic studies of the Djungarian hamster brain includes the suprachiasmatic nuclei, the median eminence, the reuniens nucleus, and the paraventricular nucleus of the thalamus.

Animals↗
PubMed1988

Influence of photoperiod and gonadal steroids on hibernation in the European hamster.

Torpor was monitored daily in adult male and female European hamsters (Cricetus cricetus) induced to hibernate by exposure to a cold environment (6 degrees C). The effect of photoperiodic manipulations or administration of exogenous gonadal steroids was examined in gonadectomized or intact hamsters. 1. Gonadal regression occurred in all short day, but only in some long day, cold-exposed hamsters. Entry into hibernation was not observed until reproductive regression had occurred. Thus, gonadal atrophy appears to be a necessary precondition for hibernation. 2. Castrated hamsters in the short day cold condition showed a significantly greater incidence of torpor than those in the long day cold condition. Hence, photoperiod affected torpor independently of its effect on the gonadal cycle. 3. Testosterone, when administered via silastic capsules at near physiological levels, completely inhibited torpor in gonadectomized male and female hamsters hibernating in the short day cold condition. 4. In ovariectomized females, torpor was unaffected by progesterone treatment, but partially inhibited by estradiol. A greater inhibition of torpor was observed when estradiol-primed females were administered both estradiol and progesterone simultaneously. Thus, the effect of both hormones may be functionally comparable to that of the single testicular hormone. 5. Estradiol inhibited torpor to a greater extent in intact and ovariectomized female hamsters hibernating in long days than those in short days, suggesting an effect of photoperiod on responsiveness to estradiol. These results indicate an inverse relationship between the gonadal and hibernation cycles, and a probable role for gonadal steroids to influence the timing of the hibernation season. However, non-gonadal factors must also be involved in controlling hibernation, since photoperiod affected the incidence of torpor in gonadectomized animals and because hamsters were able to terminate hibernation in the absence of gonadal hormones.

Animals↗
PubMed1988

2-[125I]iodomelatonin binding sites in hamster brain membranes: pharmacological characteristics and regional distribution.

Studies in a variety of seasonally breeding mammals have shown that melatonin mediates photoperiodic effects on reproduction. Relatively little is known, however, about the site(s) or mechanisms of action of this hormone for inducing reproductive effects. Although binding sites for [3H]melatonin have been reported previously in bovine, rat, and hamster brain, the pharmacological selectivity of these sites was never demonstrated. In the present study, we have characterized binding sites for a new radioligand, 2-[125I]iodomelatonin, in brains from a photoperiodic species, the Syrian hamster. 2-[125I]Iodomelatonin labels a high affinity binding site in hamster brain membranes. Specific binding of 2-[125I]iodomelatonin is rapid, stable, saturable, and reversible. Saturation studies demonstrated that 2-[125I]iodomelatonin binds to a single class of sites with an affinity constant (Kd) of 3.3 +/- 0.5 nM and a total binding capacity (Bmax) of 110.2 +/- 13.4 fmol/mg protein (n = 4). The Kd value determined from kinetic analysis (3.1 +/- 0.9 nM; n = 5) was very similar to that obtained from saturation experiments. Competition experiments showed that the relative order of potency of a variety of indoles for inhibition of 2-[125I]iodomelatonin binding site to hamster brain membranes was as follows: 6-chloromelatonin greater than or equal to 2-iodomelatonin greater than N-acetylserotonin greater than or equal to 6-methoxymelatonin greater than or equal to melatonin greater than 6-hydroxymelatonin greater than or equal to 6,7-dichloro-2-methylmelatonin greater than 5-methoxytryptophol greater than 5-methoxytryptamine greater than or equal to 5-methoxy-N,N-dimethyltryptamine greater than N-acetyltryptamine greater than serotonin greater than 5-methoxyindole (inactive). Compounds known to act at serotonergic, adrenergic, or dopaminergic receptors were either inactive or relatively ineffective as compared to melatonin. These results suggest that 2-[125I]iodomelatonin is a selective, high affinity probe for identifying melatonin receptor binding sites in rodent brain.

Animals↗
PubMed1986

Developmental appearance of light-dark entrainment in the rat.

Previous studies show that the developing circadian system is entrained by a maternal signal during the prenatal and early postnatal period. The present study investigated the developmental onset of retina-mediated, light-dark entrainment. Juvenile rats were exposed to phase-shifts in the light-dark cycle at different ages and the pineal N-acetyltransferase rhythm was monitored on postnatal day 10. The results show that retina-mediated, light-dark entrainment begins by postnatal day 6 and overrides maternal entrainment by postnatal day 8.

Acetyltransferases↗
PubMed1986

The blood supply of the bone component of the compound osteo-cutaneous radial artery forearm flap--an anatomical study.

This paper reports the results of an investigation into the blood supply of that portion of the distal radius which may be incorporated into the fasciocutaneous radial artery forearm flap. The findings demonstrate that when detached from its medullary blood supply, this segment of bone is supplied predominantly by two fascioperiosteal branches of the radial artery augmented by a musculoperiosteal plexus at the site of attachment of flexor pollicis longus.

Adult↗
PubMed1986

Pineal melatonin rhythms in female Turkish hamsters: effects of photoperiod and hibernation.

Daily rhythms of pineal and serum melatonin content were characterized for adult female Turkish hamsters (Mesocricetus brandti) exposed to long days (16L:8D, 22 degrees C) or after transfer to short days (10L:14D, 22 degrees C). The nocturnal peak of pineal melatonin content was found to be approximately 3 b greater in duration on short than on long days. Changes in levels of serum melatonin closely paralleled those of pineal melatonin. Thus, an effect of photoperiod on synthesis and secretion of pineal melatonin was demonstrated. In a separate experiment, female hamsters were induced to hibernate by exposure to a short-day, cold environment (10L:14D, 6 degrees C). During the 4 to 5-mo hibernation season, Turkish hamsters are known to display 4 to 8-day hours of torpor (body temperature = 7-9 degrees C) alternating with 1 to 3-day intervals of euthermia (body temperature = 35-37 degrees C). Little evidence of nocturnal synthesis or secretion of pineal melatonin was detected in females sampled during torpor. However, animals sampled during the first day after arousal from a torpor bout displayed melatonin rhythms no different in phase or amplitude from those seen in females held at 22 degrees C. Thus, despite the absence of pineal melatonin output during torpor, the pineal gland of hibernating Turkish hamsters produces an appropriately phased, rhythmic melatonin signal during intervals of euthermia.

Aging↗
PubMed1985

Photic influences on the developing mammal.

In adult mammals, the daily light-dark cycle acts via the retinohypothalamic pathway to entrain the circadian clock in the suprachiasmatic nuclei (SCN) and to communicate information about daylength to photoperiodic species. Studies in rats show that during late fetal and early neonatal life, before the retinohypothalamic pathway has innervated the SCN, the maternal circadian system entrains the timing of the developing clock to prevailing lighting conditions. Although the nature of the maternal output signal(s) used to entrain the developing clock has not been elucidated, the maternal SCN are a necessary component of maternal entrainment during both prenatal and postnatal life. Maternal entrainment of the fetal and neonatal clock thus ensures that the developing circadian system is synchronized to the outside world until maturation of the retinohypothalamic pathway permits direct photic entrainment. The maternal circadian system is not only necessary for entrainment of the developing circadian system, but recent studies suggest it may also provide the immature mammal with important photoperiodic information. In the montane vole (Microtus montanus) and the Djungarian hamster (Phodopus sungorus), the prenatal photoperiod affects postnatal photoperiodic responses, and cross-fostering experiments show that this information about daylength is perceived by the fetus. This prenatal information, in conjunction with postnatal perception of photoperiod, allows the developing animal to determine which way the season is changing and to modify the rate of reproductive maturation accordingly.

Aging↗
PubMed1985

Resurfacing weight bearing areas of the heel. The role of the dorsalis pedis innervated free tissue transfer.

Five cases of chronic ulceration following skin graft resurfacing of the weight bearing surface of the heel are presented. All were managed with debridement and coverage with a free innervated dorsalis pedis tissue transfer. The technical refinements that have contributed to the reliability of the flap include careful distal identification of the first dorsal metatarsal artery (FDMA) and division of the dorsalis pedis artery (DPA) under direct vision below the takeoff of the FDMA. Donor site morbidity has been minimized by taking care to preserve the extensor paratenon as a bed for the subsequent skin graft and by immobilization of the donor foot with plaster and bed rest for 10 days. Four of the patients were followed for 2, 4, 4, and 6 years; one was lost to follow-up. All were active with protective sensation in their flaps. No instances of flap breakdown and no significant donor site morbidity were noted. The dorsalis pedis innervated free tissue transfer is recommended as a reliable procedure for resurfacing weight bearing areas of the foot when simpler methods have failed.

Adolescent↗
PubMed1985

Mandibular reconstruction in the radiated patient: the role of osteocutaneous free tissue transfers.

This paper discusses our experience with the second metatarsal and iliac crest osteocutaneous transfers for mandibular reconstruction. The prime indication for this type of reconstruction was for anterior mandibular defects when the patient had been previously resected. Midbody to midbody defects were reconstructed with the metatarsal and larger defects with the iliac crest. In most cases, an osteotomy was done to create a mental angle. The evaluation of speech, oral continence, and swallowing revealed good results in all patients unless lip or tongue resection compromised function. Facial contour was excellent in metatarsal reconstructions. The iliac crest cutaneous flap provided a generous supply of skin for both intraoral reconstruction and external skin coverage but tended to be bulky, particularly when used in the submental area. Thirty three of 36 flaps survived completely. Flap losses were due to anastomosis thrombosis (1), pedicle compression (1), and pedicle destruction during exploration for suspected carotid blowout (1). Ninety three percent of bone junctions developed a solid bony union despite the mandible having had a full therapeutic dose of preoperative radiation. Despite wound infections in 8 patients, and intraoral dehiscence with bone exposure in 12 patients, all but one of these transfers went on to good bony union without infection in the bone graft.

Adolescent↗
PubMed1985

Physiological doses of prolactin stimulate pelage pigmentation in Djungarian hamster.

The Djungarian hamster exhibits a dark agouti pelage during the summer. Under the influence of decreased daylength, this species molts and develops a predominantly white winter coat. After a patch of white fur was plucked from hamsters housed in short photoperiod, chronic infusion of 10 or 20 micrograms ovine prolactin (o-PRL)/day led to the growth of a patch of pigmented fur, thus reversing the effect of the decreased daylength. Circulating o-PRL levels produced by the 10-micrograms/day infusions ranged from 17.9 +/- 4.0 to 35.1 +/- 13.8 (SE) ng/ml and thus approximated the endogenous circulating prolactin levels found in hamsters with the dark summer pelage (6, 9). Infusion of o-PRL stimulated pigmentation of the pelage of castrated as well as intact hamsters, suggesting that the testes do not mediate this effect. Infusion of ovine growth hormone (20 micrograms/day) did not stimulate pigmentation, and infusion of alpha-melanocyte-stimulating hormone (10 micrograms/day) gave inconclusive results.

Animals↗
PubMed1985

Testicular function and pelage color have different critical daylengths in the Djungarian hamster, Phodopus sungorus sungorus.

Testicular function and pelage color are regulated by photoperiod in the Djungarian hamster. To investigate the critical daylengths of these functions, adult male hamsters were exposed to one of four photoperiods: 16 h of light, 8 h of darkness (16L:8D), 14L:10D, 12L:12D, or 10L:14D. 10L:14D and 12L:12D induced the winter molt and testicular regression, in contrast to 14L:10D which induced only the latter response, and 16L:8D which maintained the summer pelage and large testes. Melatonin injections administered 4, 2, or 0 h before lights-off to hamsters exposed to 16L:8D mimicked the effects in hamsters exposed to 10:14D, 12L:12D or 14L:10D, respectively, on pelage color and testicular weight. Based on previous observations, the elevated circulating melatonin levels resulting from these injections were expected to extend the endogenous melatonin peak. Thus, this finding suggests that the duration of circadian melatonin elevation is the critical parameter determining its effect not only on the gonads, but also on the pelage. Since 14L:10D induced testicular regression but not the winter molt, this study also investigated whether circulating FSH levels, known to affect testicular function, and PRL levels, which have been shown to affect pelage color, might be affected differently by 14L:10D. Both FSH and PRL levels were found to be suppressed in 14L:10D hamsters compared to those in 16L:8D hamsters, although the interval between the initial decrease and eventual recovery was less than that in 10L:14D hamsters. Thus, the differential responses of the pelage and gonads to 14L:10D do not appear to be based on selective suppression of FSH in this photoperiod. However, different responses to 14L:10D compared to 10L:14D may be related to the shorter period of suppression of both PRL and FSH by the 14L:10D daylengths.

Animals↗
PubMed1985

Effects of photoperiod, pinealectomy and castration on body weight and daily torpor in Djungarian hamsters (Phodopus sungorus).

During the autumn and winter Djungarian hamsters (Phodopus sungorus) exhibit regression of the gonads, development of a white winter pelage, loss of body weight and daily torpor. These seasonal events are largely regulated by changes in photoperiod. The present experiments were designed to examine the role of the testes and the pineal gland in photoperiodically induced daily torpor and body weight loss. Hamsters displayed a loss of body weight and daily torpor when exposed to a short-day photoperiod in a cold environment, but these phenomena did not occur in hamsters exposed to long days and cold. Testicular regression is probably a precondition for the display of torpor, since daily torpor was almost totally inhibited in hamsters which were exposed to short days and in which testosterone was administered from subcutaneous silicone elastomer implants. Nevertheless, decreased testosterone secretion alone is not a sufficient condition for induction of daily torpor, since torpor was rarely observed in hamsters exposed to long days, even after castration. In addition to decreased testicular activity, the pineal gland is also involved in establishing conditions for torpor. Thus, pinealectomy prevented the display of torpor by castrated hamsters exposed to short days. Body weight changes were also found to be influenced by both testicular hormone and pineal activity. These observations indicate that the pineal gland is involved, as a part of the photoperiodic mechanism, in regulating a variety of physiological events and that some of these actions of the pineal are independent of its extensively described actions on the reproductive axis.

Adaptation, Physiological↗
PubMed1984

Hormonal regulation of the annual pelage color cycle in the Djungarian hamster, Phodopus sungorus. I. Role of the gonads and pituitary.

The Djungarian hamster exhibits an agouti pelage in the summer and a predominantly white pelage in the winter. This pelage color cycle is known to be regulated by the length of the daily photoperiod probably acting through the pineal gland, as is the seasonal cycle of reproductive function with which it is closely correlated ( Figala et al., '73; Hoffmann, ' 78b ). The possibility of a causal relationship between the decline in gonadal hormone secretion and the coat color change occurring in short photoperiod was examined. Gonadectomized and intact male and female hamsters were exposed to either long (16L:8D) or short ( 10L : 14D ) photoperiod for several months. Gonadectomy neither induced the change to the winter pelage color in long photoperiod-housed animals, nor prevented either the change to the winter pelage or the spontaneous return to summer pelage color in short photoperiod-housed animals. Chronic implants of testosterone in castrated males delayed and attenuated the short photoperiod-induced coat color change. Administration of ovine prolactin (100 micrograms/day) stimulated pigmentation in hamsters with the winter pelage, whereas administration of a alpha MSH (30 micrograms/day) was without effect. These results suggest that changes in pelage color may be regulated largely by changes in pituitary prolactin secretion and modified to some extent by changes in gonadal steroid hormone secretion.

Animals↗
PubMed1984

Hormonal regulation of the annual pelage color cycle in the Djungarian hamster, Phodopus sungorus. II. Role of prolactin.

This study investigated whether photoperiod-induced changes in circulating prolactin levels, which have been observed in the Djungarian hamster ( Yellon and Goldman, '83; Duncan and Goldman, ' 83a ), might be involved in seasonal pelage color changes in this species. Injection of ovine prolactin (100 micrograms/day) inhibited the short photoperiod-induced winter molt. This finding indicated that the suppression of endogenous prolactin levels normally occurring in short photoperiod-housed hamsters (Duncan and Goldman, ' 83a ) may induce the winter molt. Suppression of prolactin secretion with bromoergocryptine (200 micrograms/day) strongly inhibited the spring molt, while concomitant treatment with ovine prolactin (100 micrograms/day) overcame this effect of bromoergocryptine. Injection of bromoergocryptine (200 micrograms/day) stimulated the winter molt in castrated hamsters housed in long photoperiod; concomitant injection of prolactin (100 micrograms/day) reversed this effect as well. These findings strongly suggested that an increase in endogenous prolactin levels may be necessary for the development and maintenance of the summer pelage.

Animals↗
PubMed1984

Free cartilage grafts: the role of perichondrium.

Using adult rabbits, free ear cartilage grafts with and without perichondrium were overlapped and sutured to each other and then placed in preformed pseudosheath pockets for 1 to 12 weeks. The specimens were evaluated at various time intervals as to histopathologic changes at the interface and breaking load as a measure of the strength of the healing response. The results obtained strongly suggest that perichondrium responds briskly to repair injury and that the breaking load is greater in the presence of perichondrium and increases with time. It is suggested that perichondrium be included with free cartilage grafts for optimum survival and intercartilaginous healing.

Animals↗