Robert T. Gemmell

Birth in marsupials

Birth is an event that allows the relatively immature marsupial to move from the internal environment of the uterus to the external environment of the pouch. The newborn marsupial passes down from the uterus to the urogenital sinus and then makes its way to the pouch and attaches to the teat at a very early stage of development. From the studies available, there appear to be three methods used by the newborn to move from the uterus to the pouch. In marsupials with a forward pouch such as the red kangaroo, tammar wallaby and the brushtail possum, the mother positions her urogenital sinus below the pouch and the newborn climb upward towards the pouch. The young climb with a swimming motion, moving the head from side-to-side and use the forearms in alternate strokes. In the bandicoot with a backward facing pouch, the mother positions the urogenital sinus above the pouch and the young slither down into the pouch. The young do not have a definite crawl, as seen with the macropodids and possum. The third method of birth has been observed in the marsupials without a definite pouch that have a mammary region that develops as the young grow in size. This type of pouch is observed in the dasyurids. The mother was noted to stand on four legs with her hips raised so that the urogenital sinus was above the pouch and the newborn young crawled downwards from the sinus to the pouch. In all species, birth was completed in 2-4 min.

Physiological changes in brushtail possums, Trichosurus vulpecula, transferred from the wild to captivity

To determine the effect of relocation on the health of possums, the body weights and hormone and immune responses of 11 male and 9 female brushtail possums were monitored following transfer from the environs of Brisbane into an established breeding colony in Brisbane. The possums were monitored weekly for the first 20 weeks of captivity, and their immune responses assessed again 12 months after capture. Over the first 5 weeks of captivity, male possums lost a mean of 8.8% of their original body weight, and females lost 15.3% over the first 6 weeks. Variation between individual possums was evident, and the 11 male possums could be divided into two groups, those that gained weight (number of animals, N = 4) and those that lost weight (N = 7) in captivity. Four males gained weight following capture, and their body weight after 20 weeks of captivity was higher than at capture. The remaining seven males lost weight over the 20 weeks following introduction into captivity, resulting in a lower weight at week 20 than at capture. All of the nine female possums lost weight and were slower to regain weight compared to the males. Plasma cortisol concentrations did not vary greatly over the 20 weeks in male possums, and the mean plasma concentration of cortisol for the 11 male possums was 7.8 ng/ml (number of samples, n = 220). The female possums showed a different pattern. The concentration of cortisol for the nine female possums at week 1 was 34.0 ng/ml, which was significantly higher than 13.3 ng/ml at week 20 (P < 0.016). No significant variation in the mean concentration of plasma thyroxine of 5.7 ng/ml occurred in the 11 male possums over the 20-week period (n = 220). The plasma concentration of thyroxine for the nine female possums was 2.5 ng/ml (n = 54) for the first 6 weeks. At week 6, an increase in the concentration of thyroxine occurred, and a peak concentration of 6.9 ng/ml was reached at week 13. This increase correlated with the females regaining body weight. A low concentration of thyroxine is often associated with stress, thus an increase in the concentration of this hormone, combined with an increase in body weight, may indicate that these females had begun to adjust to their new environment. The seven male possums that lost weight following introduction into captivity displayed a significantly higher concentration of cortisol (9.1 compared with 5.3 ng/ml P < 0.01), and a lower concentration of thyroxine compared to the four males that gained weight following capture (4.7 compared with 7.3 ng/ml, P < 0.005). Over the 20-week period, the total number of white blood cells increased, and the number of neutrophils increased in both males and females. The proliferative response of lymphocytes from male possums to the T-cell mitogen, phytohaemagglutin (PHA) decreased significantly over the 20-week period (P < 0.002). In females an initial decrease in the reactivity of lymphocytes observed over the first 10 weeks was followed by an increase in this response over the remaining 10-week period. Twelve months following capture, the white blood cell parameters of both males and females had returned to similar levels to those of the first 1-5 weeks. The reactivity of lymphocytes from male possums that had been in captivity for 12 months was significantly higher than that of the first 20 weeks of captivity (P < 0.005). Females that had been in captivity for 12 months displayed lymphocyte responses similar to those observed at weeks 16-20. The body weight and hormonal results would suggest that possums undergo a more severe stress response than males immediately following their capture. In contrast, the immune response of males is lower than females and is depressed for a longer period following capture.

Birth in the brushtail possum, Trichosurus vulpecula (Marsupialia : Phalangeridae)

Birth has been observed and described in a number of marsupials. However, the ability of the newborn marsupial to move from the uterus to the pouch and locate the teat is still not fully understood. Birth and the path taken by the newborn from the urogenital sinus to the teat within the pouch were filmed in the brushtail possum, Trichosurus vulpecula. Prior to birth, females began to lick the pouch and urogenital sinus vigorously. The young took approximately 2 min to transfer from the urogenital sinus to the pouch and attached to the teat within 10–15 min. To determine the senses used by the newborn possum to reach the pouch, young were removed from the anaesthetised mothers immediately after birth and placed outside the pouch. From the subsequent observations, the newborn possum instinctively crawled upwards. However, when the newborn was in the vicinity of the pouch, odours emanating from the pouch presumably attracted the young. Thus, the senses of gravity and of olfaction were used by the newborn to reach the teat and probably the sense of touch, via the mechanoreceptor Merkel cells around the mouth, allowed the young to attach to the teat.

Ontogeny of the Immune System of the Brushtail Possum, Trichosurus vulpecula

The numbers and distribution of T and B cells in the thoracic thymus, spleen and intestinal tissue and the proliferation of T lymphocytes were examined during pouch life and in the adult to determine when the developing brushtail possum reaches immunological maturity. CD3‐positive cells were observed in the thoracic thymus at day 2 post‐partum indicating that the thymus produces T lymphocytes at or soon after birth. By day 25 the thymus was fully populated with CD3‐positive T lymphocytes and they were observed in distinct regions of the cortex and medulla. By day 48 post‐partum, B and T lymphocytes were identified in the follicles and parafollicular areas of the spleen. Although the numbers of T and B cells in the spleen increased significantly from day 25 to day 100 post‐partum (P < 0.005), fewer cells were present at day 150 post‐partum than in the adult (P < 0.05). Peyers patches were not observed in the intestines up to day 73 post‐partum. However, both T and B cells were observed in the intestinal lymph nodes. Although the T lymphocytes at weaning showed a proliferative response, the response was not as great as that observed in the adult possum. Thus, the immune system of the possum is not fully developed at weaning but continues its development after pouch life. Anat Rec 256:354–365, 1999.

Effect of lantana on the ultrastructure of the liver of sheep

The caudate lobe of the liver of normal sheep and of sheep poisoned by the plant Lantana camara L. was fixed by perfusion with a mixture of glutaraldehyde and paraformaldehyde. The tissues were prepared and then examined with a transmission electron microscope. It was concluded that ingestion of lantana is followed by closure of bile canaliculi and damage to microvilli and that these changes contribute to the decrease in bile secretion seen during lantana poisoning. A marked increase occurred in the agranular endoplasmic reticulum but the significance of this is not known. It may be related to alterations in the amount of drug metabolizing enzymes or to retention of bile constituents.

The ultrastructure of the lung of two newborn marsupial species, the northern native cat, Dasyurus hallucatus, and the brushtail possum, Trichosurus vulpecula

SummaryThe lungs of newborn northern native cats, Dasyurus hallucatus and newborn brushtail possums, Trichosurus vulpecula were examined by both light and electron microscopy. The native cat has a birth weight of 18 mg after a gestation of about 21 days, whereas the brushtail possum weights 200 mg at birth and has a gestation period of 17.5 days. The lungs of the native cat are two large respiratory sacs, with a respiratory lining of squamous cells and surfactant-secreting cells. The capillaries are located within the connective tissue just below this respiratory epithelium. The visceral covering of the lung is formed by squamous cells. The lungs of the possum are composed of numerous large respiratory sacs which are separated by connective tissue septa in which the capillaries are located. The sacs, as in other species, are lined with squamous cells and surfactant secreting cells. It is proposed that the structure of the lung of the newborn marsupial is related more to the size of the newborn rather than to the length of the gestation period.

Weekly variations in body weight and plasma testosterone concentrations in the captive male possum, Trichosurus vulpecula

The possum is a seasonally breeding marsupial which gives birth in Queensland from March through to September. To ascertain whether this seasonality in breeding is manifest in the male reproductive system, body weight and plasma testosterone concentrations were examined in five possums. Plasma testosterone concentrations fluctuated throughout the year and a seasonal cycle was observed, with a peak in testosterone concentration in March and a nadir in September. Body weights fluctuated in a similar manner. Statistical analysis suggested that the annual plasma testosterone profile correlated well with the rate of change of daylength.

LANTANA POISONING: A CHOLESTATIC DISEASE OF CATTLE AND SHEEP

I. ABSTRACT Lantana poisoning is a hepatotoxic disease of ruminants caused by the ingestion of Lantana camara L. and is characterized by cholestasis. The toxic compounds are the triterpenes lantadene A and lantadene B. The toxins exert their effects on the hepatocytes and the canaliculi appear to be a major site of injury. Within a few hours after ingestion of the plant there is a decrease in canalicular ATPase activity and collapse of canaliculi. Although the secretory function of the hepatocytes is lost, their ability to metabolize compounds is retained to some extent: they are able to conjugate bilirubin. Toxicity is associated with an increase in the agranular endoplasmic reticulum in hepatocytes, but the significance of this change is not clear. Experiments have confirmed that lantana causes gallbladder paralysis but not intestinal paralysis.

Physiological changes in the brushtail possum (Trichosurus vulpecula) following relocation from Armidale to Brisbane, Australia

To determine the effect of relocation on the health of possums the body weights and hormone and immune responses of six male and nine female brushtail possums were monitored for 20 weeks following transfer from the environs of Armidale into enclosures in Brisbane. Over the first 6 weeks of captivity, male possums lost 11.0% of their original body weight and females lost 16.8%. The mean concentrations of plasma cortisol in the male and female possums were 14.5 and 29.4 ng/mL, respectively, and did not change over the 20-week period. Male and female possums displayed a similar pattern of thyroxine secretion over the 20 weeks, with low concentrations up to week seven (2.1 and 2.7 ng/mL, respectively) increasing to 6.9 and 5.8 ng/mL in weeks 7-12 (P < 0.005). This increase in the concentration of thyroxine corresponded with the increase in body weight. The number of white blood cells (WBCs) and the percentage of neutrophils increased from the capture to week 6-10. However, during the last 10 weeks of captivity the number of WBCs and the percentage of neutrophils decreased, indicating recovery of the immune system. This was in accord with the proliferative response of lymphocytes to the T cell mitogen PHA that increased from weeks 11-15 to weeks 16-20 in both male and female possums. The results above suggest that the Armidale possums, like the Brisbane possums, were stressed following their relocation; however, their immune systems were able to gradually recover as they adjusted to their new environment in Brisbane. The death rate of pouch young and of adult female possums after relocation was considerably higher in the Armidale possums compared to Brisbane possums. The mortality rate of Brisbane possums over the first 20 weeks of captivity was 8.3% and 19.6% for male and female possums, respectively, and for Armidale possums 16.6% and 47.1%, respectively. The possums transferred from the environs of Armidale into captivity in Brisbane were under greater stress than possums captured in Brisbane and placed in captivity in Brisbane.

The role of the corpus luteum of lactation in the bandicoot Isoodon macrourus (Marsupialia: Peramelidae)

The concentration of progesterone in the plasma of the bandicoot was determined during pregnancy, during lactation, following removal of the young, and following surgical removal of the corpora lutea of lactation alone or along with the removal of the young. The corpus luteum of pregnancy continued into lactation and secreted progesterone for the first 19 days of lactation. In the later stages of lactation, the corpus luteum, which persisted morphologically until Day 45, was not secretory. Ovulation occurred approximately 20 days after the removal of the pouch young early in lactation. However after removal of both young and corpora lutea ovulation occurred in approximately 10 days. Thus early in lactation, when it is secreting progesterone, the corpus luteum may exert an additional ovulation inhibitory effect over and above that provided by suckling, but at later stages of lactation it is the suckling stimulus which is all important in inhibiting ovulation.