Bren Gannon

Postnatal development of the lung parenchyma in a marsupial: The Tammar wallaby

Marsupials are born at an early stage of development, and lung development from an air‐sac stage to maturity occurs in the air‐breathing environment, the pouch.

The Microvasculature of Rat Salivary Glands

The blood vessels together with the parenchymal components of rat salivary glands were studied by scanning electron microscopy (SEM) after removal of stromal connective tissue by acid hydrolysis plus

Development of the Marsupial Cardiorespiratory System

Fetal development is characterised by two major processes, the differentiation of cells and tissues, and the growth of organs and the body as a whole. In these functions, marsupials differ from eutherian mammals in that the majority of the growth phase occurs in an air-breathing situation, rather than the liquid intrauterine environment of the eutherian fetus. Such differences ultimately relate to the relatively shorter period of gestation versus lactation in marsupials as compared to eutheria and the consequentially smaller mass of the neonate.

Effects of long term denervation on smooth muscle of the chicken expansor secundariorum

SummaryDenervation of the expansor secundariorum muscle of the adult and 2 week chicken, by sectioning the brachial plexus, resulted in an approximate twofold increase in dry weight over 8 weeks. Unlike skeletal muscle, no ultrastructural changes were exhibited by the smooth muscle cells for a period of up to 5 months post denervation. No evidence of hypertrophy of the individual muscle cells was observed, but following colchicine treatment a definite increase in the number of mitotic figures was noted within muscle bundles indicating that the increase in dry weight of the expansor muscle is due to hyperplasia of the smooth muscle cells. The results are discussed in relation to in vitro studies of the interaction of sympathetic nerves with smooth muscle.

Protective effects of the synthetic prostaglandin enprostil on the gastric microvasculature after ethanol injury in the rat

The effect of pretreatment with the synthetic prostaglandin E2 analogue enprostil on ethanol damage to the rat gastric mucosa was studied. Microvascular casts were prepared and studied by scanning electron microscopy. The permeability of mucosal capillaries to fluorescein isothiocyanate-labeled albumin (FITC-albumin) given intravenously was examined by fluorescence microscopy. After administration of ethanol (1 ml absolute ethanol intragastrically) alone, casts showed gross disruption of the normal structure, with large foci of loss of the patency of the capillary network, frequently extending to the level of the submucosal vessels. There was exudation of casting material into the mucosal interstitium and onto the surface of the cast. After administration of FITC-albumin, there was a marked increase in interstitial fluorescence throughout the full thickness of the mucosa. Pretreatment with enprostil (1 microgram/kg intragastrically) prevented most of the damaging effects of ethanol. Increased microvascular permeability to FITC-albumin was noted only in the most superficial layers of the mucosa. These studies characterize the effect of ethanol on the gastric microvasculature and indicate that pretreatment with enprostil restricts this damaging effect to the superficial mucosal microvessels. These studies further suggest that microvascular damage is an early event in ethanol injury, apparently preceding epithelial erosion.

Aquaporin-1 in blood vessels of rat circumventricular organs

Although the water channel protein aquaporin-1 (AQP1) is widely observed outside the rat brain in continuous, but not fenestrated, vascular endothelia, it has not previously been observed in any endothelia within the normal rat brain and only to a limited extent in the human brain. In this immunohistochemical study of rat brain, AQP1 has also been found in microvessel endothelia, probably of the fenestrated type, in all circumventricular organs (except the subcommissural organ and the vascular organ of the lamina terminalis): in the median eminence, pineal, subfornical organ, area postrema and choroid plexus. The majority of microvessels in the median eminence, pineal and choroid plexus, known to be exclusively fenestrated, are shown to be AQP1-immunoreactive. In the subfornical organ and area postrema in which many, but not all, microvessels are fenestrated, not all microvessels are AQP1-immunoreactive. In the AQP1-immunoreactive microvessels, the AQP1 probably facilitates water movement between blood and interstitium as one component of the normal fluxes that occur in these specialised sensory and secretory areas. AQP1-immunoreactive endothelia have also been seen in a small population of blood vessels in the cerebral parenchyma outside the circumventricular organs, similar to other observations in human brain. The proposed development of AQP1 modulators to treat various brain pathologies in which AQP1 plays a deleterious role will necessitate further work to determine the effect of such modulators on the normal function of the circumventricular organs.

Recruiting problem‐based learning (PBL) tutors for a PBL‐based curriculum: the Flinders University experience

To examine the contribution made to problem‐based learning (PBL) by individual teachers and by departments in years 1 and 2 of a new graduate‐entry medical programme (GEMP) with a PBL‐based curriculum.

Morphometric analysis of postnatal lung development in the tammar wallaby: light microscopy.

Postnatal growth of the lung in the tammar wallaby, Macropus eugenii, was investigated using morphometric techniques with light microscopy. Lung volume, parenchymal and non-parenchymal volume densities were measured. Volume densities of parenchymal airspace and tissue and non-parenchymal conducting airways and large blood vessels were determined. Lung volume and all the other parameters that were measured showed a biphasic increase in relation to increase in body mass. All parameters, with the exception of airway volume, increased relatively slowly in relation to increase in mass in the first 70 days after birth, when the pouch young are ectothermic. Between 70 and 180 days, during the period of transition from ectothermy to endothermy, the parameters increased more rapidly, suggesting accelerated lung growth in preparation for the extra metabolic demands associated with the establishment of thermoregulatory control in the pouch young. Specific lung volume in the adult tammar is lower than that of eutherians of equivalent mass, however, the parenchymal volume is relatively high.

An evaluation of the phenomenon of cytoprotection using quantitative histological criteria

The concept of ‘cytoprotection’ is derived from observations that exogenous prostaglandins protect the gastric mucosa against injurious agents at doses insufficient to inhibit acid secretion. Measurements of the extent of cytoprotection generally rely on inspection of the open stomach for assessment of the extent of damage. Recent studies indicate that such macroscopic criteria are inaccurate. This study reports the development of quantitative histological techniques that enable valid studies of cytoprotection. Using a rat model of cytoprotection, injury was induced with 1 ml of absolute ethanol. Cytoprotection was induced with 25 μg prostaglandin E2 (PG) intragastrically 15 or 30 min prior to ethanol exposure. The area of macroscopic damage was measured with a computer‐based digitizer. Semi‐thin plastic sections of eight separate areas of the stomach were examined histologically and the length and depth of damage were measured using the digitizer. Surface area and volume of mucosal damage were calculated from these values. On macroscopic assessment after exposure to ethanol for 15 min, 44.6% of the surface appeared damaged. After pretreatment with PG the extent of ethanol damage appeared to be reduced. On microscopic assessment, however, the extent of damage was much greater with 94.5% of the surface damaged after ethanol alone and 73.7% surface damaged after pretreatment with PG. Thus, macroscopic assessment clearly underestimates the extent of damage. However, these data do indicate that PG protects the surface epithelium from the effects of ethanol. A much clearer demonstration of protection is evident from measurement of the volume of mucosa damaged. After ethanol alone, 31.5% of the mucosal volume was damaged compared with 3.8% when pretreatment by PG was given. When measurements were performed after exposure to ethanol for 30 min, significantly less surface

Morphometric estimate of gas-exchange tissue in the new-born tammar wallaby, Macropus eugenii

The lung of the new-born marsupial is at the terminal air sac stage of development. The maturational status of the lung of new-born tammar wallaby was assessed using established morphometric techniques and the results were compared with data from a morphometric study of the lung of the rat. Volume densities of the parenchyma and non-parenchyma, conducting airways and blood vessels, the relative volumes of airspace and tissue, the thickness and the composition of the septa differed between the two species. In addition the volume of capillaries and the surface area of the effective gas-exchange tissue was greater in the new-born rat than in the new-born tammar pouch young. The lung of the new-born tammar appears to be at an earlier phase of the terminal air sac stage than that of the new-born rat. Lung development up to birth appears to be commensurate to the metabolic needs of the organism at birth.