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R T Gemmell

Publications and source records attributed to R T Gemmell.

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

Development of lung, kidney and skin in the brushtail possum, Trichosurus vulpecula.

The thyroid gland is not present at birth in marsupials and thyroid function begins during the latter half of pouch life. The hormonal output of the thyroid gland is important for normal development. In this study the structure of the lung, kidney and skin of the developing possum was examined and the structural development of these three organs was described. The lung of the newborn brushtail possum was functional and continued to develop during pouch life, alveolar formation beginning at day 39 and concluding at day 113 postpartum. The mesonephric kidneys of the newborn possum degenerated and were replaced by the metanephric kidneys, the nephrogenic zone of the metanephric kidney being present from 35 to 96 days postpartum. No new nephrons were formed after day 96. After the completion of nephrogenesis, the kidney increases in size through glomerular and tubular growth. The sequence of steps in the development of the possum skin was identical to that observed in other marsupials. The epidermis of the possum was thickest at 60 microns on about day 28 postpartum and as development proceeded the epidermis gradually decreased in thickness. A sparse number of primordia of hair follicles were observed at day 10 and the possum had a good covering of hair by day 129 postpartum. Correlation between the development of the lung, kidney and skin with the previously published plasma thyroxine concentration in the young possum suggests that thyroxine from the mother and from the young is important in the development of these three organs.

Animals↗
PubMed1995

Effect of changing from a short-day to long-day photoperiod on the breeding season of the brushtail possum (Trichosurus vulpecula).

In Queensland, possums (Trichosurus vulpecula) in the wild and in captivity first give birth during March and April and continue to give birth throughout the year until November. The possum has a gestation length of 17.5 days, gives birth to one young, and lactation continues for approximately 180 days. If the newborn possum is removed during the breeding season, the possum will ovulate approximately 9 days later and give birth approximately 26 days after removal of the pouch young (RPY). Repeated RPY may be used to determine the duration of the breeding season. In this study, the effect on the breeding season of a marked change in photoperiod From a short-day to a long-day was examined by comparing three groups of possums in different photoperiods for 13 months. One group of five female and two mail possums (group A) was housed in a natural photoperiod and a second group (B) was housed in a short-day photoperiod (10 h light: 14 h dark) throughout the study. The third group (C) was housed in a short-day photoperiod until each possum gave birth, the pouch young was removed, and the possum transferred to a long-day photoperiod room (14 h light: 10 h dark) for the remainder of the study. The possums held in a natural photoperiod, group A, gave birth to a total of 27 births in the one breeding season from March to October.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

A comparative study of the corpus luteum.

The corpus luteum (CL) is a transitory organ which has a regulatory role in reproduction. Sharks, amphibians and reptiles have corpora lutea that produce progesterone which influences the rate of embryonic development. The egg-laying monotremes and the two major mammalian groups, eutherian and marsupial, have a CL that secretes progesterone. Most eutherians have allowed for the uterine development of their young by extending the length of the oestrous cycle and the CL or placenta actively secretes progesterone until birth. Gestation in the marsupial does not extend beyond the length of an oestrous cycle and the major part of fetal development takes place in the pouch. Where the extension of the post-luteal phase in the eutherian has allowed for the uterine development of young, the marsupial has extended the pre-luteal phase of the oestrous cycle and has evolved an alternative reproductive strategy, embryonic diapause. The mechanism for the secretion of hormones from the CL has been controversial for many years. Densely-staining secretory granules have been observed in the CL of sharks, marsupials and eutherians. These granules have been reported to contain relaxin, oxytocin or mesotocin, and progesterone. A hypothesis to suit all available data is that all hormones secreted by the CL are transported within such granules. In conclusion, although there are obvious differences in the mode of reproduction in the two main mammalian groups, it is apparent that there is a great deal of similarity in the hormonal control of regression of the CL and parturition.

Amphibians↗
PubMed1995

Halobaculum gomorrense gen. nov., sp. nov., a novel extremely halophilic archaeon from the Dead Sea.

A novel extremely halophilic archaeon was isolated from the Dead Sea. This isolate is rod shaped and, like Halobacterium sodomense, requires a relatively low level of sodium ions for growth and a very high level of magnesium; optimal growth occurs in the presence of 0.6 to 1.0 M Mg2+. The new strain resembles members of the Halobacterium saccharovorum-Halobacterium sodomense-Halobacterium trapanicum group in many physiological properties. However, the polar lipid composition of this organism is characteristic of representatives of the genus Haloferax; a sulfated diglycosyl diether is present, and the glycerol diether analog of phosphatidylglycerosulfate is absent. The G+C content of the DNA is 70 mol%. We found that on the basis of 16S rRNA sequence data our new isolate occupies a position intermediate between the position of the Halobacterium saccharovorum group and the position of the genus Haloferax and is sufficiently different from the previously described members of the Halobacteriaceae to justify classification in a new species and a new genus. We propose the name Halobaculum gomorrense gen. nov., sp. nov. for this organism; the type strain is strain DSM 9297.

Archaea↗
PubMed1995

Comparative aspects of oxytocin-like hormones in marsupials.

Unlike eutherian mammals which secrete only oxytocin (OT), marsupials secrete the typically reptilian mesotocin (MT) and/or OT as their oxytocic peptides. Our laboratories have been conducting research on various aspects of the roles of OT-like peptides in three marsupials, the brushtail possum, the northern brown bandicoot and the tammar wallaby. By providing information on the functions of OT-like peptides in these species we hope to provide some clues as to the evolution of neurohypophysial hormones in marsupials. Brain and peripheral distributions of OT-like peptides have been studied in the possum and bandicoot. As in eutherian mammals, OT-like peptides are distributed throughout the brain and are present in the testis, corpus luteum, prostate and adrenal glands. Studied on the regulation of release of MT into plasma in the possum show that it is regulated by similar mechanisms to OT release in eutherian mammals. OT receptors have been characterized and localized in the possum and the tissue distributions and pharmacological characteristics of the receptor are similar to both the sheep and rat OT receptors. The marsupial OT receptor shows no pharmacological specificity for MT over OT which is reflected in the similar potency of these peptides in eliciting contractions of the uterus of the tammar wallaby in vitro. MT seems to play an important but not essential role in parturition in the tammar. MT concentrations are increased immediately after delivery in the tammar but infusion of an OT antagonist before expected birth delays but does not prevent parturition. The presence of OT receptors in the marsupial mammary gland and the sensitivity of the gland to exogenous OT and stimulation of mesotocinergic neurones demonstrates that these peptides are important for marsupial lactation. Our data suggest that the presence of MT with or without OT in marsupials is a result of a neutral mutation rather than functional evolution.

Animals↗
PubMed1994

Mesotocin and arginine-vasopressin in the corpus luteum of an Australian marsupial, the brushtail possum (Trichosurus vulpecula).

The neuropeptide hormones arginine-vasopressin (AVP) and oxytocin (OT) have been found in the ovarian follicles and corpora lutea (CL) of many eutherian mammals. In ruminants, there is persuasive evidence that luteal OT is involved in luteolysis via stimulation of uterine prostaglandins. However, based on scant evidence, the marsupial ovary has been viewed as being devoid of OT-like and AVP-like peptides. In this study, corpora lutea from the brushtail possum were examined for OT, AVP, and mesotocin (MT) by a combination of reverse phase HPLC, radioimmunoassay, and immunohistochemistry (IHC). Peptides extracted from each of five CL were separated by HPLC and each fraction was assayed for AVP, MT, and OT. Two immunoreactive peaks were found, corresponding to AVP and MT standards. The amount of each peptide was 8.7 +/- 2.22 pmol MT/g (mean +/- SEM) and 5.7 +/- 1.0 pmol AVP/g, respectively. The mean MT/AVP ratio was 1.55 compared to 0.26 for the pituitary. IHC (streptavidin-peroxidase method) of Bouin's-fixed CL showed staining for MT in the cytoplasm of luteal cells which was absent in stromal tissue and nonluteal ovarian tissue. Not all luteal cells were immunopositive and no topographical distribution of stained cells was observed. IHC localization of AVP was not attempted. It was concluded that the CL of the brushtail possum contains low quantities of MT and AVP, which in the case of MT is probably synthesized by the immunochemically staining cells of the CL.

Animals↗
PubMed1994

Structural development in the newborn marsupial, the stripe-faced dunnart, Sminthopsis macroura.

The structure of various sense organs and endocrine glands was examined in the stripe-faced dunnart, Sminthopsis macroura. This marsupial has the shortest gestation known for all mammals, 10.5-11 days. The morphology of the anterior pituitary, adrenal gland, olfactory epithelium, Merkel cells around the mouth and the utricle of the vestibular system of S. macroura was similar to that observed in other newborn marsupials. These structures are thought to be required by the newborn to transfer from the uterus to the pouch. The stage of development of the urinary system, the semicircular canals of the vestibular system, eyes and lungs was slightly different to that of other newborn marsupials. These structures are thought to have secondary importance in allowing the newborn to reach the teat. Although marsupials display variation in gestation length and produce newborn of differing body weights, there is little difference in morphology between various newborn marsupial species.

Animals↗
PubMed1993

Posterior pituitary of the newborn marsupial possum, Trichosurus vulpecula.

The fetal anterior pituitary-adrenal axis is thought to be involved in the initiation of birth in both eutherian and marsupial mammals. Little is known about the structure and function of the posterior pituitary at birth in the marsupial. Immunocytochemistry, high pressure liquid chromatography, and radioimmunoassay were used to identify vasopressin and mesotocin in the posterior pituitary of a newborn marsupial, the brushtail possum, Trichosurus vulpecula. The concentrations of vasopressin and mesotocin in the head of the newborn possum were 0.34 and 0.28 ng, respectively. The concentration of vasopressin was always greater than that of mesotocin, and the amounts of neuropeptides present in the head increased as the possum developed.

Aging↗
PubMed1993

The development of thermoregulation in the marsupial brushtail possum Trichosurus vulpecula.

1. The adult possums showed a circadian rhythm of body temperature with a peak in temperature around midnight and a nadir at noon. 2. The young possum within the pouch displayed a circadian rhythm with the highest temperatures during the day and the lowest in the early evening. 3. Although the body temperature of the young possum exceeded that of the mother occassionally, for the major part of the 24 hr the body temperature of the young was lower than that of the mother. 4. The young possum could maintain a steady body temperature between 140 and 167 days post partum. A circadian rhythm of temperature was observed between 157-190 days post partum. 5. All adipose tissue examined with the light and electron microscope had the morphology of white adipose tissue.

Adipose Tissue↗
PubMed1993

Developmental changes in the erythrocyte metabolism in bandicoot Isoodon macrourus.

Activities of 13 different enzymes were measured in the erythrocytes of juvenile and adult bandicoots, Isoodon macrourus. Seven of these enzymes had significantly (p < 0.05 or less) greater activities in the juveniles compared to the adult animals. The activity of one enzyme--phosphofructokinase--was significantly (p < 0.01) lower in the juveniles. However, the activity of NADH-methaemoglobin reductase (MR) was similar in the two groups of animals. The rates of lactate production using four different substrates (glucose, galactose, inosine and adenosine) were also higher in the juveniles. These results indicate that the erythrocytes of juvenile bandicoots are metabolically more active than those of the adult animals and follow the general pattern of higher metabolic activity in the young red cells in eutherian mammals, with possible exception of NADH-MR activity.

Animals↗
PubMed1993

Effect of photoperiod on the breeding season of the marsupial possum Trichosurus vulpecula.

The production of young by three groups of eight possums, housed in a natural, a short-day (10 h light:14 h dark) and a long-day (14 h light:10 h dark) photoperiod was monitored for 24 months to determine the role of photoperiod on the occurrence and duration of the breeding season. Possums were housed in each of the three light regimens on 22 November. The possum has a gestation duration of 17.5 days. Removal of the newborn young leads to ovulation approximately 9 days later and birth 26 days later. Repeated removal of pouch young was used to determine the duration of the breeding season. Possums in a natural photoperiod showed two breeding seasons for the 2 year observation, from March to October of each year. Over the same 2 year period, there were three breeding periods in possums in short-day and long-day photoperiod. A comparison of the timing of the first breeding season showed that short-day photoperiod brought the breeding season forward by 2 months and long-day photoperiod delayed it by 2.5 months. The total number of months in which births occurred was the same for natural and short-day photoperiod (16 out of 24 months) and less for long-day photoperiod (11 months). Fertility in the three groups was also examined. Within each group, there was no change in fertility with consecutive seasons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Development of the vestibular and auditory system of the northern native cat, Dasyurus hallucatus.

The developing vestibular and auditory system of the native cat Dasyurus hallucatus was examined from birth to day 55 postpartum to determine when the six sensory regions had an adult structure. The utricle, a sensory epithelium with an overlying discrete population of otoliths, was present in the newborn native cat. The saccule, which has a similar structure to the utricle, and the three crista ampullaris of the semicircular canals, were present by day 21 postpartum. The organ of Corti was formed by day 50 and the external ear duct was patent by day 55 postpartum. Hair is first seen on the native cat by day 45 when the young first leave the pouch. They are left in the nest and travel on the back of the lactating mother until about day 80. The eyes open on approximately day 75. Thus, the native cat has fully functional visual, auditory, and vestibular systems when the juvenile leaves the nest.

Age Factors↗
PubMed1992

Brain content and plasma concentrations of arginine vasopressin in an Australian marsupial, the brushtail possum Trichosurus vulpecula.

Arginine vasopressin (AVP) has been identified and quantified in the brain and plasma of the possum using a highly specific radioimmunoassay and high-performance liquid chromatography. Large amounts of AVP were found in the pituitary (16.3 +/- 0.56 micrograms/pituitary, n = 5) and hypothalamus (398 +/- 82.5 ng/hypothalamus), and significant amounts of AVP were also present in the cerebral cortex (26.8 +/- 11.5 ng/cortex). Plasma AVP concentrations were significantly lower (2.2 +/- 0.45 pg/ml, n = 10) during anesthesia compared to concentrations while conscious (4.5 +/- 1.19 pg/ml). Severe hemorrhage markedly increased plasma concentrations to 1091 +/- 225 pg/ml (n = 8). It was concluded that AVP is present in the possum brain, pituitary, and plasma, and that its secretion is stimulated by hypovolemia and inhibited by surgical stress.

Analysis of Variance↗
PubMed1992

Mesotocin and oxytocin in the brain and plasma of an Australian marsupial, the northern brown bandicoot, Isoodon macrourus.

1. Mesotocin (MT) and oxytocin (OT) were measured in the brain and plasma of bandicoots using reverse phase high performance liquid chromatography and specific radioimmunoassays. 2. MT and OT were found in the pituitary (1.25 +/- 0.10 micrograms/MT; 0.725 +/- 0.077 micrograms/OT) and hypothalamus (38.37 +/- 6.46 ng/MT; 19.1 +/- 4.61 ng/OT). Smaller amounts were present in the cerebral cortex. 3. Basal plasma concentrations ranged from 1.5 to 8.1 pg/ml for both peptides (N = 14) and were elevated by stress. 4. It was concluded that both MT and OT are secreted by the bandicoot brain and that stress stimulates secretion.

Animals↗
PubMed1992

The transfer of thyroxine from the mother to the young of the marsupials, the bandicoot (Isoodon macrourus) and the possum (Trichosurus vulpecula).

1. The young of the bandicoot and possum are of similar weight at birth (200-250 mg) but by day 50 post-partum have weights of 100 and 20 g, respectively. The aim of this study was to determine whether the disparate growth rate was associated with a difference in the transfer of thyroxine from mother to young. 2. Radioactive thyroxine was injected intramuscularly into the lactating female and 24 hr later a blood sample was obtained from the mother and the pouch young removed. The amount of radioactive thyroxine remaining in the blood and within the young was determined. 3. The data obtained indicated that milk is a source of thyroid hormones in early pouch life. 4. The hypothesis that greater quantities of thyroxine are transferred in the milk of bandicoots than that of brushtail possums is not supported.

Animals↗
PubMed1992

Development of the urinary system of the marsupial native cat Dasyurus hallucatus.

The development of the mesonephros and metanephros was examined in the marsupial Northern native cat, Dasyurus hallucatus, from birth through to the end of lactation. The mesonephros was present at birth, reached a maximum volume 11 days after birth and had regressed completely by day 30. The metanephros was present on day 2; glomeruli were first seen on day 8, and nephrogenesis continued until day 89 post partum. The newborn native cat is at a very primitive stage of development compared to other marsupials. However, at weaning, like other marsupial species, the native cat has developed a fully morphological and functional urinary system.

Animals↗
PubMed1992

The role of photoperiod on the initiation of the breeding season of the brushtail possum (Trichosurus vulpecula).

The role of photoperiod on the initiation of the breeding season of brushtail possums was investigated in possums housed in three light regimens: a short-day, a natural and a long-day photoperiod. Seven possums were housed in a natural photoperiod. Four possums were transferred to a short-day photoperiod (10 h light, 14 h dark) and eight possums to a long-day photoperiod (14 h light, 10 h dark) on 22 November, when the daylength was 13.34 h. The first rises in plasma progesterone concentrations were observed on 9 January +/- 9 days (n = 4), 11 March +/- 6 days (n = 7) and 6 May +/- 6 days (n = 8), for possums held in short-day, natural or long-day photoperiods respectively. Similarly, births were observed on 12 January and 14 February in the short-day group, from 3 March to 8 May for the natural photoperiod group, and from 5 May to 8 August for the long-day group. These results suggest that photoperiod is important in the timing of the breeding season. However, annual breeding will commence in a nonstimulatory long-day photoperiod. Thus a long-day photoperiod does not prevent breeding activity.

Animals↗