James O'Shea

EphA/ephrin-A interactions during optic nerve regeneration: restoration of topography and regulation of ephrin-A2 expression

During visual system development, interactions between Eph tyrosine kinase receptors and their ligands, the ephrins, guide retinal ganglion cell (RGC) axons to their topographic targets in the optic tectum. Here we show that Eph/ephrin interactions are also involved in restoring topography during RGC axon regeneration in goldfish. Following optic nerve crush, EphA/ephrin-A interactions were blocked by intracranial injections of recombinant Eph receptor (EphA3-AP) or phospho-inositol phospholipase-C. Topographic errors with multiple inputs to some tectal loci were detected electrophysiologically and increased projections to caudal tectum demonstrated by RT-97 immunohistochemistry. In EphA3-AP-injected fish, ephrin-A2-expressing cells in the retino-recipient tectal layers were reduced in number compared to controls and their distribution was no longer graded. The findings, supported by in vitro studies, implicate EphA/ephrin-A interactions in restoring precise topography and in regulating ephrin-A2 expression during regeneration.

Neural regulation of the pulmonary vasculature in a semi-arboreal snake, Elaphe obsoleta.

SummaryThe innervation of the pulmonary vasculature of the semi-arboreal rat snake,Elaphe obsoleta, was examined with glyoxylic acid-induced catecholamine histochemistry, peptide immunohistochemistry, and in vitro perfusion of the pulmonary vasculature. An adrenergic innervation was present on the pulmonary artery, the smaller pulmonary arteries, the veins draining the lung, and the main pulmonary vein. Vasoactive intestinal polypeptide-like immunoreactive axons were observed on the pulmonary artery and vein, small arteries, and occasionally small veins within the lung parenchyma. A dense plexus of substance P-like immunoreactive (SP-LI) axons was observed on the distal extrinsic pulmonary artery. SP-LI axons were found on the more distal arteries within the lung parenchyma, but not on the veins. The distribution of calcitonin gene-related peptide- and SP-LI axons was similar suggesting that the axons are sensory nerves. In the perfused pulmonary vasculature, vagal stimulation caused a predominant vasoconstriction which was abolished by atropine indicating it was cholinergic in nature. A post-stimulus vasodilatation was abolished by bretylium and propranolol indicating it was adrenergic in nature. The responses to nerve stimulation were located in both the extrinsic and intrinsic pulmonary vasculature. No evidence for non-adrenergic, noncholinergic transmission to the vascular smooth muscle was found. The extensive, functional innervation of the main pulmonary artery, as well as the more distal vasculature within the lung, may reflect adaptation to cardiovascular problems imposed by an elongated body and arboreal habits.

Sperm production and immune function in two Australian bats, Chalinolobus morio and Nyctophilus geoffroyi

One assumption of the immunocompetence handicap hypothesis is that androgens increase the expression of secondary sex characters while concomitantly suppressing immune function. Primary sex function, such as spermatogenesis, may also benefit from immune down-regulation since spermatozoa are not recognised as self by the immune system. Males with greater parasite resistance should therefore be able to experience higher androgens levels with a resultant increase in spermatogenic investment and ejaculate quality, plus greater suppression of the immune system. We investigate this possibility in two species of Australian bat. Testis size was used as a measure of ejaculate investment and quality, and spleen size was used as an indicator of immune function. Significant negative relationships were found between spleen and testis mass in one species and a negative trend was noted in a second. When the overall effect size was calculated, the negative association across both species was statistically significant. Our results are consistent with the immunocompetence handicap hypothesis since males able to withstand greater immune system down-regulation had larger testes.

Social Structure and Patterns of Movement of the Western Pebble-mound Mouse, Pseudomys chapmani, at Marandoo, Western Australia

Mounds of the western pebble-mound mouse, Pseudomys chapmani, are found throughout the species’ Pilbara range in areas with iron-ore deposits of economic significance. Translocation techniques are being examined as a means of minimising the impact of mining on this species. In the absence of detailed information on the biology of Pseudomys chapmani, translocation is inadvisable. To provide such basic information, animal densities, mound demographics and population sizes, and home-range and core-area sizes were obtained by a combination of trapping and radio-tracking. Mounds of Pseudomys chapmani were found to be inhabited by social groups of up to 12 animals. Estimates of home-range size gave mean ( s.e.) values of 14·4 6·7 ha and 4·6 2·7 ha for males and females, respectively; core areas were recorded at 0·93 0·29 ha for males and 0·29 0·16 ha for females. Considerable overlap of home ranges was recorded between individuals from the same and different mounds. Overlap at the core-area level occurred only between individuals from the same mound. The high level of social complexity and mound fidelity indicates that translocations should be directed at the level of the social group rather than at the level of the individual.

Renal vasculature and excretory system of the agamid lizard, Ctenophorus ornatus

The structure and ultrastructure of the vasculature and nephric tubules of the kidney of the Ornate Dragon Lizard, Ctenophorus (=Amphibolurus) ornatus, was investigated by light microscopy and scanning electron microscopy of resin casts. Compared with other agamid lizards, the arterial supply of only two arteries per kidney is small. The number of glomeruli per kidney in C. ornatus, at between 400 and 600, is low by reptilian standards and very low for lizards. The glomeruli are not only comparatively few in number but are also simple in the nature of their capillary configuration. These features are suggestive of a greatly reduced surface area for arterial filtration. In contrast to the small arterial supply, the afferent venous supply, the renal portal system (RPS), is substantial and forms an extensive capillary network throughout the kidneys. No venous shunts were found in the kidneys, suggesting that the venous network is functioning as a true portal system. Valves were not identified within the RPS, implying that neural control of general vascular tone could alter velocity and perhaps the direction of blood flow by changing pressure profiles. The nephroi are comparatively short and display features consistent with the production of urate precipitates as the primary nitrogenous waste product. A close association between the distal tubule (DT) and the glomerular hilus may demonstrate a simple form of a juxtaglomerular apparatus. The finding of aglomerular tubules indicates an important role for tubular secretion. The results of this study indicate that these lizards may have a reduced reliance on filtration for homoiostasis and a greater reliance on tubular secretion.

VEGF-induced choroidal damage in a murine model of retinal neovascularisation

Background/aims: Photoreceptor-specific upregulation of vascular endothelial growth factor (VEGF) in a transgenic mouse model (Kimba) of retinal neovascularisation induces retinal vascular damage which appears similar to that in diabetic retinopathy. Here we have determined whether the choroidal vasculature is also affected in Kimba. Methods: Kimba mice were assessed with fundus fluorescein angiography for mild, moderate or severe retinal vascular leakage prior to preparation of choroidal corrosion casts for quantitative analysis using scanning electron microscopy. VEGF was located immunohistochemically. Results: Choroidal abnormalities included microaneurysms, constriction, shrinkage and dropout in the capillaries and tortuosity and loops in the arteries and veins which were similar to those observed in corrosion casts of the human choroid in diabetes. Similar to human diabetes, choroidal neovascularisation was not observed. The severity of choroidal damage correlated with the extent of retinal vascular leakage. In addition to the expected presence of VEGF in photoreceptors, VEGF was also detected in the pigment epithelium and choroid in the transgenic mice. Conclusion: We show that elevated retinal VEGF levels trigger pathophysiological changes in the choroid. We suggest that therapies to prevent vascular damage in diabetes must target both the retinal and choroidal vasculatures.

Functional Morphology of the Forelimb of Living and Extinct Tree-Kangaroos (Marsupialia: Macropodidae)

Tree‐kangaroos are a unique group of arboreal marsupials that evolved from terrestrial ancestors. The recent discovery of well‐preserved specimens of extinct tree‐kangaroo species (genus Bohra) within Pleistocene cave deposits of south‐central Australia provides a unique opportunity to examine adaptive evolution of tree‐kangaroos. Here, we provide the first detailed description of the functional anatomy of the forelimb, a central component of the locomotor complex, in the extant Dendrolagus lumholtzi, and compare its structure and function with representatives of other extant marsupial families. Several features were interpreted as adaptations for coping with a discontinuous, uneven and three‐dimensional arboreal substrate through enhanced muscular strength and dexterity for propulsion, grasping, and gripping with the forelimbs. The forelimb musculoskeletal anatomy of Dendrolagus differed from terrestrial kangaroos in the following principal ways: a stronger emphasis on the development of muscles groups responsible for adduction, grasping, and gripping; the enlargement of muscles that retract the humerus; and modified shape of the scapula and bony articulations of the forelimb bones to allow improved mobility. Many of these attributes are convergent with other arboreal marsupials. Tree‐kangaroos, however, still retain the characteristic bauplan of their terrestrial ancestors, particularly with regard to skeletal morphology, and the muscular anatomy of the forelimb highlights a basic conservatism within the group. In many instances, the skeletal remains of Bohra have similar features to Dendrolagus that suggest adaptations to an arboreal habit. Despite the irony of their retrieval from deposits of the Nullarbor “Treeless” Plain, forelimb morphology clearly shows that the species of Bohra were well adapted to an arboreal habitat. J. Morphol. 2011.

Temperature sensitivity of cardiac muscarinic receptors in bat atria and ventricle

In contrast to other mammals, muscarinic receptors in the bat ventricle can mediate significant decrease in basal contractile force (greater than 50%), not only at 37 degrees C but also at hibernation temperature (12 degrees C). At frequencies of contraction that approximate in vivo values for 37-12 degrees C, no significant shift in receptor affinity or maximum response to applied acetylcholine was found for either ventricular or atrial muscle. Low temperature does not appear to compromise receptor function in hibernators. The atypical cholinergic innervation of the ventricle may maintain a regulative role during hibernation.

No evidence of sperm conjugate formation in an Australian mouse bearing sperm with three hooks

Sperm conjugation occurs when two or more sperm physically unite for motility or transport through the female reproductive tract. In many muroid rodent species, sperm conjugates have been shown to form by a single, conspicuous apical hook located on the sperm head. These sperm “trains” have been reported to be highly variable in size and, despite all the heads pointing in roughly the same direction, exhibit a relatively disordered arrangement. In some species, sperm “trains” have been shown to enhance sperm swimming speed, and thus have been suggested to be advantageous in sperm competition. Here, we assessed the behavior of sperm in the sandy inland mouse (Pseudomys hermannsburgensis), a muroid rodent that bears sperm with three apical hooks. First, we accrued genetic evidence of multiple paternity within “wild” litters to unequivocally show that sperm competition does occur in this species. Following this we utilized both in vitro and in vivo methodologies to determine whether sandy inland mouse sperm conjugate to form motile trains. Our observations of in vitro preparations of active sperm revealed that sandy inland mouse sperm exhibit rapid, progressive motility as individual cells only. Similarly, histological sections of the reproductive tracts of mated females revealed no in vivo evidence of sperm conjugate formation. We conclude that the unique, three-hooked morphology of the sandy inland mouse sperm does not facilitate the formation of motile conjugates, and discuss our findings in relation to the different hypotheses for the evolution of the muroid rodent hook/s.

Cardiac autonomic innervation of the western pygmy possum (Cercatetus concinnus) and golden bandicoot (Isoodon auratus)

Evidence for a functional ventricular parasympathetic innervation of the mammalian heart between and within taxa remains controversial. We have previously proposed that the presence of a functional parasympathetic innervation of the ventricle was indicative of heterothermy, and is essential for maintaining ventricular stability at low body temperature. However, it is possible that the presence of such an innervation is also representative of the primitive mammalian state. In this study, we aimed to determine whether a functional parasympathetic innervation of the ventricle, that is capable of actively reducing the force of contraction, is present across metatherian mammals. Using in vitro isolated cardiac preparations, we examined evidence for a functional ventricular parasympathetic innervation of the ventricle in two species of metatherian mammal, one heterotherm (Western pygmy possum; Cercatetus concinnus) and one homeotherm (Golden bandicoot; Isoodon auratus), from different families to complement existing data from a heterothermic dasyurid. Both C. concinnus and I. auratus had a potent biphasic response to transmural electrical stimulation in both atrial and ventricular preparations. Both the decrease and increase in the force of contraction in response to stimulation were almost entirely blocked by the cholinergic and adrenergic antagonists, atropine and propranolol, respectively. These observations provide clear evidence for a parasympathetic innervation of the ventricle that is capable of directly influencing the force of contraction across metatherian mammals with different thermoregulatory strategies. While this innervation may facilitate heterothermy, this suggests that the presence of such an innervation pattern is indicative of the primitive mammalian state.