Hierarchical imaging and computational analysis of three-dimensional vascular network architecture in the entire postnatal and adult mouse brain

The formation of new blood vessels and the establishment of vascular networks are crucial during brain development, in the adult healthy brain, as well as in various diseases of the central nervous system. Here, we describe a step-by-step protocol for our recently developed method that enables hierarchical imaging and computational analysis of vascular networks in postnatal and adult mouse brains. The different stages of the procedure include resin-based vascular corrosion casting, scanning electron microscopy, synchrotron radiation and desktop microcomputed tomography imaging, and computational network analysis. Combining these methods enables detailed visualization and quantification of the 3D brain vasculature. Network features such as vascular volume fraction, branch point density, vessel diameter, length, tortuosity and directionality as well as extravascular distance can be obtained at any developmental stage from the early postnatal to the adult brain. This approach can be used to provide a detailed morphological atlas of the entire mouse brain vasculature at both the postnatal and the adult stage of development. Our protocol allows the characterization of brain vascular networks separately for capillaries and noncapillaries. The entire protocol, from mouse perfusion to vessel network analysis, takes ~10 d.

Type I interferon causes thrombotic microangiopathy by a dose-dependent toxic effect on the microvasculature

Many drugs have been reported to cause thrombotic microangiopathy (TMA), yet evidence supporting a direct association is often weak. In particular, TMA has been reported in association with recombinant type I interferon (IFN) therapies, with recent concern regarding the use of IFN in multiple sclerosis patients. However, a causal association has yet to be demonstrated. Here, we adopt a combined clinical and experimental approach to provide evidence of such an association between type I IFN and TMA. We show that the clinical phenotype of cases referred to a national center is uniformly consistent with a direct dose-dependent drug-induced TMA. We then show that dose-dependent microvascular disease is seen in a transgenic mouse model of IFN toxicity. This includes specific microvascular pathological changes seen in patient biopsies and is dependent on transcriptional activation of the IFN response through the type I interferon α/β receptor (IFNAR). Together our clinical and experimental findings provide evidence of a causal link between type I IFN and TMA. As such, recombinant type I IFN therapies should be stopped at the earliest stage in patients who develop this complication, with implications for risk mitigation.

Magnetic resonance angiography and vascular corrosion casting as tools in biomedical research: application to transgenic mice modeling Alzheimer's disease

In vivo imaging technologies are presently receiving considerable attention in the biomedical and pharmaceutical research areas. One of the principal imaging modalities is magnetic resonance imaging (MRI). The multiparametric nature of MRI enables anatomical, functional and even molecular information to be obtained non-invasively from intact organisms at high spatial resolution. Here we describe the use of one MRI modality, namely angiography (MRA), to non-invasively study the arterial vascular architecture of APP23 transgenic mice modeling Alzheimer's disease. Because the spatial resolution of the technique is limited, the in vivo studies are complemented by a powerful analysis of the vasculature using vascular corrosion casting. Both techniques revealed age-dependent blood flow alterations and cerebrovascular abnormalities in these mice. Our experience suggests that MRA complemented by cast analysis are important tools to describe vascular alterations and test new therapy concepts in animal models of AD. Furthermore, being non-invasive, MRA can also be applied to studies in patients suffering from this disease.

Cellular characterization of the peritumoral edema zone in malignant brain tumors

Brain edema is a hallmark of human malignant brain tumors and contributes to the clinical course and outcome of brain tumor patients. The so-called perifocal edema or brain swelling imposes in T2-weighted MR scans as high intensity areas surrounding the bulk tumor mass. The mechanisms of this increased fluid attraction and the cellular composition of the microenvironment are only partially understood. In this study, we focus on imaging perifocal edema in orthotopically implanted gliomas in rodents and correlate perifocal edema with immunohistochemical markers. We identified that areas of perifocal edema not only include the tumor invasion zone, but also are associated with increased glial fibrillary acidic protein (GFAP) and aquaporin-4 expression surrounding the bulk tumor mass. Moreover, a high number of activated microglial cells expressing CD11b and macrophage migration inhibitory factor (MIF) accumulate at the tumor border. Thus, the area of perifocal edema is mainly dominated by reactive changes of vital brain tissue. These data corroborate that perifocal edema identified in T2-weighted MR scans are characterized with alterations in glial cell distribution and marker expression forming an inflammatory tumor microenvironment.

Hemodynamics in the leech: blood flow in two hearts switching between two constriction patterns

Two tubular, segmented hearts propel blood through the closed circulatory system of the medicinal leech and switch every 20-40 beats between two constriction patterns. We showed recently that within one heartbeat cycle, heart segments on one side constrict peristaltically rear-to-front (;peristaltic heart'), followed by nearly synchronous front-to-rear constrictions in the contralateral heart segments (;synchronous heart'). Using optical recordings from intact leeches, we now characterize the hemodynamic properties of the cardiac cycle of individual heart segments in different regions to ask whether the reversal of constrictions affects flow into, out of, and along the hearts. We measured total vessel capacity in corrosion casts and blood volume in individual heart segments of dissected leeches. We show that the peristaltic heart provides the propulsive force for forward and rearward flow and supplies the peripheral circulation through segmental efferent vessels. In comparison, the synchronous heart pumps less blood, most of which enters the segmental circulation. The heart sphincter, located in the posterior section of each heart segment, directs blood flow differently in the two modes. In the peristaltic heart, the sphincter prevents backflow and promotes longitudinal, forward flow while in the synchronous heart the sphincter restricts longitudinal, rearward flow and instead promotes flow into the segmental circulation. Blood is shunted via the contractile latero-dorsal arches from the dorsal intestinal vessel into the peristaltic heart in posterior segments 14 to 18. Switching between the two constriction patterns provides nutrient-rich blood to the vascular beds on both sides.

Polyurethane elastomer: A new material for the visualization of cadaveric blood vessels

A multitude of various materials are available for the visualization of cadaveric vessels, ranging from natural materials like gelatin and latex to synthetic materials like silicone rubber or acrylates. To achieve a detailed overview of the vascular architecture in microvascular studies in experimental flap surgery, the injected material should have low viscosity to assure perfusion of even the smallest vessels. In addition, the material ideally should have either no or only minimal shrinkage, and should harden within a reasonable time, but retain sufficient elasticity and resistance to withstand tearing off the delicate vessels during subsequent dissection or casting. Because none of the available injection materials adequately combines these attributes, we evaluated the polyurethane elastomer "PU4ii" in latissimus dorsi muscles as a new material for the visualization of cadaveric vessels in comparison with the frequently used silicone rubber. The dissection of vessels injected with PU4ii proved easy largely because of its exceptional hardness. Even if not visible before dissection, the completely perfused vessels were easily palpated in the surrounding fat or muscle tissue of the microsurgical latissimus dorsi model. Despite the significantly higher hardness of PU4ii over silicone rubber (98 Sh-A vs. 12 Sh-A), PU4ii proved enough elasticity (20-25 N/mm(2) E modulus) and a high tear resistance (64-68 N/mm vs. 15 N/mm) preventing breakage during dissection even within the smallest vessels. In contrast to silicone rubber (and latex or gelatin), the high corrosion resistance and form stability of PU4ii also allowed building of casts for qualitative examination by scanning electron microscopy and quantitative analysis of the vessel density using micro-computed tomography with accurate 3D representation. In this study we show that PU4ii has physical characteristics that make it a multi-purpose material that allows at the same breath an excellent gross visualization of the architecture of cadaveric blood vessels as well as a detailed evaluation of casts by modern microscopic and or radiologic tools. Thus, the new polyurethane elastomer PU4ii is in many respects superior to the widely used silicone rubber and can be strongly recommended as a visualization material for a comprehensive evaluation of cadaveric blood vessels in microsurgery.

Hierarchical microimaging for multiscale analysis of large vascular networks

There is a wide range of diseases and normal physiological processes that are associated with alterations of the vascular system in organs. Ex vivo imaging of large vascular networks became feasible with recent developments in microcomputed tomography (microCT). Current methods permit to visualize only limited numbers of physically excised regions of interests (ROIs) from larger samples. We developed a method based on modified vascular corrosion casting (VCC), scanning electron microscopy (SEM), and desktop and synchrotron radiation microCT (SRmicroCT) technologies to image vasculature at increasing levels of resolution, also referred to as hierarchical imaging. This novel approach allows nondestructive 3D visualization and quantification of large microvascular networks, while retaining a precise anatomical context for ROIs scanned at very high resolution. Scans of entire mouse brain VCCs were performed at 16-microm resolution with a desktop microCT system. Custom-made navigation software with a ROI selection tool enabled the identification of anatomical brain structures and precise placement of multiple ROIs. These were then scanned at 1.4-microm voxel size using SRmicroCT and a local tomography setup. A framework was developed for fast sample positioning, precise selection of ROIs, and sequential high-throughput scanning of a large numbers of brain VCCs. Despite the use of local tomography, exceptional image quality was achieved with SRmicroCT. This method enables qualitative and quantitative assessment of vasculature at unprecedented resolution and volume with relatively high throughput, opening new possibilities to study vessel architecture and vascular alterations in models of disease.

New polyurethane-based material for vascular corrosion casting with improved physical and imaging characteristics

Vascular corrosion casting has been established as a method to reconstruct the three-dimensional (3D) structure of blood vessels of organs and tissues. After replacing the blood volume with a low viscosity resin, the surrounding tissue is removed to replicate the vascular architecture, typically using scanning electron microscopy (SEM). To date available casting resins have had significant limitations such as lack of viscosity, leading to insufficient perfusion of smallest capillaries in organs and tissues of smaller species, interaction with surrounding tissue or fragility of resulting casts. We have reported here about a new polyurethane-based casting resin (PU4ii) with superior physical and imaging characteristics. Low viscosity, timely polymerization, and minimal shrinking of PU4ii produces high quality casts, including the finest capillaries. These casts are highly elastic while retaining their original structure to facilitate postcasting tissue dissection and pruning of casts. SEM images illustrate the high reproduction quality, including endothelial cell imprints, features that allow one to discern arterial and veinal vessels. For quantitative analysis, casts from PU4ii can be imaged using micro-computed tomography to produce digital 3D reconstructions. The inherent fluorescence of PU4ii is sufficient to reproduce casts with or without tissue using confocal microscopy (CM). Because of the simplified casting procedure, the high reproducibility and the superior reproduction quality, a combination of vascular corrosion casting using PU4ii with advanced imaging technologies has great potential to support the description of vascular defects and drug effects in disease models using mutant mice.

Do spermathecal morphology and inter-mating interval influence paternity in the polyandrous beetle Tribolium castaneum?

Abstract

In polyandrous insects, postcopulatory sexual selection is a pervasive evolutionary force favouring male and female traits that allow control of offspring paternity. Males may influence paternity through adaptations for sperm competition, and females through adaptations facilitating cryptic female choice. Yet, the mechanisms are often complex, involving behaviour, physiology or morphology, and they are difficult to identify. In red flour beetles (Tribolium castaneum), paternity varies widely, and evidence suggests that both male and female traits influence the outcome of sperm competition. To test the role of spermathecal morphology and of sperm storage processes on the outcome of sperm competition, we mated each of 26 virgin females with two males, one of which carrying a phenotypic marker to assign offspring paternity. We manipulated the interval between mating with the first and the second male, to create different conditions of sperm storage (overlapping and non-overlapping) in the female reproductive tract. To investigate the role of sperm storage more closely, we examined the relationship between paternity and spermathecal morphology in a subset of 14 experimental females. In addition, we also characterized variation in spermathecal morphology in three different strains, wildtype, Chicago black and Reindeer. No significant influence of the intermating interval was found on the paternity of the focal male, although the direction of the difference was in the expected direction of higher last male paternity for longer intervals. Moreover, paternity was not significantly associated with spermathecal morphology, although spermathecal volume, complexity, and tubule width varied significantly and substantially among individuals in all investigated strains.

Age-dependent cerebrovascular abnormalities and blood flow disturbances in APP23 mice modeling Alzheimer's disease

Neuropathological changes associated with Alzheimer's disease (AD) such as amyloidplaques, cerebral amyloid angiopathy, and related pathologies are reproduced in APP23 transgenic mice overexpressing amyloid precursor protein (APP) with the Swedish mutation. Magnetic resonance angiography (MRA) was applied to probe, in vivo, the cerebral arterial hemodynamics of these mice. Flow voids were detected at the internal carotid artery of 11-month-old APP23 mice. At the age of 20 months, additional flow disturbances were observed in large arteries at the circle of Willis. Vascular corrosion casts obtained from the same mice revealed that vessel elimination, deformation, or both had taken place at the sites where flow voids were detected by MRA. The detailed three-dimensional architecture of the vasculature visible in the casts assisted the identification of smaller vessels most likely formed as substitution or anastomosis within the circle of Willis. Angiograms and corrosion casts from nontransgenic, age-matched mice manifested no major abnormalities in the cerebrovascular arterial flow pattern. Because no transgene overexpression has been found in the cerebrovasculature of APP23 mice and no deposits of amyloid-beta (Abeta) were observed in large arteries in the region of the circle of Willis, the present results suggest that soluble Abeta may exert deleterious effects on the vasculature. Our findings support the idea that cerebral circulatory abnormalities evolving progressively could contribute to AD pathogenesis. The study also shows the power of MRA to identify changes of vascular function in genetically engineered mice. MRA as a noninvasive technique could be applied to test new therapeutic concepts in animal models of AD and in humans.

Neural mechanisms in insect navigation: polarization compass and odometer

Insect navigation relies on path integration, a procedure by which information about compass bearings pursued and distances travelled are combined to calculate position. Three neural levels of the polarization compass, which uses the polarization of skylight as a reference, have been analyzed in orthopteran insects. A group of dorsally directed, highly specialized ommatidia serve as polarization sensors. Polarization-opponent neurons in the optic lobe condition the polarization signal by removing unreliable and irrelevant components of the celestial stimulus. Neurons found in the central complex of the brain possibly represent elements of the compass output. The odometer for measuring travelling distances in honeybees relies on optic flow experienced during flight, whereas desert ants most probably use proprioreceptive cues.

Detectors for polarized skylight in insects: a survey of ommatidial specializations in the dorsal rim area of the compound eye

Apart from the sun, the polarization pattern of the sky offers insects a reference for visual compass orientation. Using behavioral experiments, it has been shown in a few insect species (field crickets, honey bees, desert ants, and house flies) that the detection of the oscillation plane of polarized skylight is mediated exclusively by a group of specialized ommatidia situated at the dorsal rim of the compound eye (dorsal rim area). The dorsal rim ommatidia of these species share a number physiological properties that make them especially suitable for polarization vision: each ommatidium contains two sets of homochromatic, strongly polarization-sensitive photoreceptors with orthogonally-arranged analyzer orientations. The physiological specialization of the dorsal rim area goes along with characteristic changes in ommatidial structure, providing actual anatomical hallmarks of polarized skylight detection, that are readily detectable in histological sections of compound eyes. The presence of anatomically specialized dorsal rim ommatidia in many other insect species belonging to a wide range of different orders indicates that polarized skylight detection is a common visual function in insects. However, fine-structural disparities in the design of dorsal rim ommatidia of different insect groups indicate that polarization vision arose polyphyletically in the insects.

Internal female reproductive anatomy and genital interactions during copula in the yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae)

Insect genitalia have been extensively studied for taxonomic purposes, but functional anatomy has rarely been examined. We report here on the detailed internal anatomy of the reproductive tract of female yellow dung flies (Scathophaga stercoraria) and the mechanics of copula and sperm transfer. Female dung flies have paired accessory glands, three spermathecae (one singlet and one doublet), each with its own narrow duct, a large muscular bursa copulatrix, which is met by the common oviduct dorso-anteriorly, and paired lateral oviducts and ovaries. The bursa is lined internally with a thick cuticle. During copula and while ejaculating, the male aligns the gonopore with the spermathecal duct entrances to the bursa and pinches the female's abdomen at approximately this point. Sperm packing in the spermathecae appears quite orderly, and structurally the sperm appear typical of many insects. Aedeagus withdrawal appears to remove some bursal sperm. The results are discussed in relation to other Diptera.

Microvillar orientation in the photoreceptors of the ant Cataglyphis bicolor

Polarization sensitivity in arthropod photoreceptors is crucially dependent on the arrangement of the microvilli within the rhabdom. Here, we present an electron-microscopical study in which the degree of microvillar alignment and changes in the cross-sectional areas of the rhabdoms along their length were studied in the compound eye of the desert ant, Cataglyphis bicolor. Serial cross-sections through the retina were taken and the orientation of the microvilli was determined in the photoreceptors of individually identified ommatidia. The reconstructions of microvillar alignment were made in the three anatomically and functionally distinct regions of the Cataglyphis compound eye: the dorsal rim area (DRA), the dorsal area (DA), and the ventral area (VA). The following morphological findings are consistent with polarization sensitivities measured previously by intracellular recordings. (1) The microvilli of the DRA photoreceptors are aligned in parallel along the entire length of the cell from the distal tip of the rhabdom down to its proximal end, near the basement membrane. The microvilli of the retinular cells R1 and R5 are always parallel to each other and perfectly perpendicular, with only minor deviation, to the microvillar orientation of the remaining receptor cells. (2) In the DA and VA regions of the eye, the microvillar tufts of the small receptors R1, R3, R5, R7, and R9 change their direction repetitively every 1-4 micrometer for up to 90 degrees. In contrast, the large receptor cells R2, R4, R6, and R8 maintain their microvillar orientation rigidly. (3) In the DRA ommatidia, the cross-sectional areas of the rhabdomeres do not change along the length of the rhabdom, but substantial changes occur in the DA and VA ommatidia.

Histamine-like immunoreactivity in the visual system and brain of an orthopteran and a hymenopteran insect

The distribution of histamine-like immunoreactivity has been analyzed in the visual system and brain of the cricket Gryllus campestris and of the bee Apis mellifera by using an antiserum against histamine. Specific immunolabeling of the photoreceptors has been found in the compound eyes and ocelli of both examined species. Intense immunostaining can be also detected in the midbrain of these species. The axons of immunoreactive cells innervate almost every area in the protocerebrum. Most of the reactive neurons are typically wide-field neurons with bilateral ramifications that form dense arborizations. Numerous small buttons on the arborizations probably represent pre- and postsynaptic sites. The histamine-like immunoreactive neurons are apparently connected to many postsynaptic neurons. In both bees and crickets, some regions of the nervous system such as the first two optic neuropils and the central body show the same labeling pattern, whereas the mushroom bodies exhibit no immunoreactivity. Nevertheless, several differences in the staining pattern can be seen: the glomeruli of the antennal lobe are invaded by histamine-like immunoreactive fibers in the bee but not in the cricket. Furthermore, an interneuron connects the second and third optic neuropil in the cricket, whereas no histamine-like immunoreactive interneuron is found in the second optic neuropil in the bee. In accord with the work of other authors on the distribution histamine in the insect nervous system, we suggest that histamine is not only a transmitter within the visual system, but also a transmitter or co-transmitter in the insect midbrain.

Specialized ommatidia for polarization vision in the compound eye of cockchafers, Melolontha melolontha (Coleoptera, Scarabaeidae)

The superposition eye of the cockchafer, Melolontha melolontha, exhibits the typical features of many nocturnal and crepuscular scarabaeid beetles: the dioptric apparatus of each ommatidium consists of a thick corneal lens with a strong inner convexity attached to a crystalline cone, that is surrounded by two primary and 9-11 secondary pigment cells. The clear zone contains the unpigmented extensions of the secondary pigment cells, which surround the cell bodies of seven retinula (receptor) cells per ommatidium and a retinular tract formed by them. The seven-lobed fused rhabdoms are composed by the rhabdomeres of the receptor cells 1-7. The rhabdoms are optically separated from each other by a tracheal sheath around the retinulae. The orientation of the microvilli diverges in a fan-like fashion within each rhabdomere. The proximally situated retinula cell 8 does not form a rhabdomere. This standard form of ommatidium stands in contrast to another type of ommatidium found in the dorsal rim area of the eye. The dorsal rim ommatidia are characterized by the following anatomical specializations: (1) The corneal lenses are not clear but contain light-scattering, bubble-like inclusions. (2) The rhabdom length is increased approximately by a factor of two. (3) The rhabdoms have unlobed shapes. (4) Within each rhabdomere the microvilli are parallel to each other. The microvilli of receptor 1 are oriented 90 degrees to those of receptors 2-7. (5) The tracheal sheaths around the retinulae are missing. These findings indicate that the photoreceptors of the dorsal rim area are strongly polarization sensitive and have large visual fields. In the dorsal rim ommatidia of other insects, functionally similar anatomical specializations have been found. In these species, the dorsal rim area of the eye was demonstrated to be the eye region that is responsible for the detection of polarized light. We suggest that the dorsal rim area of the cockchafer eye subserves the same function and that the beetles use the polarization pattern of the sky for orientation during their migrations.

Three-dimensional reconstruction: a tissue embedding method for alignment of serial sections

Three-dimensional (3D) reconstruction from serial sections that are undistorted and true-to-life is only possible when a reference system exists that allows correct matching of the section drawings. This paper describes a simple method for producing reference lines that ensures proper alignment of the drawings. (1) The specimen is embedded in a rectangular form, (2) the sides of the block are painted, and (3) the embedded specimen is sectioned exactly perpendicular to the painted sides of the block. Thus, in each section the paint appears as dark lines which serve as reference lines for matching the sections.

Insect optic lobe neurons identifiable with monoclonal antibodies to GABA

Five monoclonal antibodies against GABA were tested on glutaraldehyde fixed sections of optic lobes of three insect species, blowflies, houseflies and worker bees. The specificity of these antibodies was analyzed in several tests and compared with commercially available anti-GABA antiserum. A very large number of GABA-like immunoreactive neurons innervate all the neuropil regions of these optic lobes. Immunoreactive processes are found in different layers of the neuropils. The immunoreactive neurons are amacrines and columnar or noncolumnar neurons connecting the optic lobe neuropils. In addition some large immunoreactive neurons connect the optic lobes with centers of the brain. Some neuron types could be matched with neurons previously identified with other methods. The connections of a few of these neuron types are partly known from electron microscopy or electrophysiology and a possible role of GABA in certain neural circuits can be discussed.

Mapping and ultrastructure of serotonin-immunoreactive neurons in the optic lobes of three insect species

With antibodies to serotonin (5-HT) we have mapped immunoreactive neurons in the optic lobes of three species, the blowfly Calliphora, the desert ant Cataglyphis, and the worker bee Apis. The main emphasis in this investigation is on a system of 5-HT-positive neurons connecting the most peripheral neuropil of the optic lobes, the lamina, to more central neuropil regions. To aid in electron microscopical identification of these neurons we used immunocytochemistry at the EM-level and Golgi-EM for Calliphora and horseradish peroxidase (HRP) labelling for the other two insects. The immunoreactive terminals in Calliphora and the HRP-labelled ones in the other insects contain large (c. 100 nm) granular vesicles and smaller (c.60 nm) clear vesicles. In Cataglyphis and Apis the profiles with granular vesicles are presynaptic to second order neurons of the lamina, whereas in Calliphora no synaptic contacts were found. In this animal the 5-HT-positive terminals are situated distal to the synaptic layer of the lamina, in a region of retinal photoreceptor axons and perikarya of the lamina monopolar neurons. In Catagylphis and Apis the interactions of the 5-HT-neurons with the laminar neurons might occur through chemical synapses, whereas in Calliphora neuroactive substance could be released non-synaptically from varicosities distal to the synaptic layer. The possible involvement of 5-HT in control of neuronal activity in the optic lobes is discussed.

Retrograde labelling of photoreceptors in different regions of the compound eyes of bees and ants

The geometry of retinal receptor arrays and the projection patterns of photoreceptor axons are unravelled in the compound eyes of bees and ants by backfilling large populations of photoreceptors with horseradish peroxidase or Lucifer yellow. Such retrograde labelling techniques are applied in the insect retina for the first time. They brilliantly label populations of specific receptor types within more than 100 ommatidia. Such preparations are obtained in three distinctly different parts of the eye: (1) the part of the retina that is positioned at the uppermost dorsal margin of the eye and specialized for the detection of polarized skylight; (2) the remainder of the dorsal retina; and (3) the ventral retina. As shown by the large populations of labelled photoreceptors, the retinal receptor arrays differ strikingly between different parts of the eye. Furthermore, there exist similarities as well as marked differences between bees and ants. Former hypotheses concerning the location of photoreceptor terminals in the first and second visual neuropil have all been based on a few individual Golgi-labelled photoreceptors. The results presented in this paper, based on retrograde mass impregnations of selected types of photoreceptors, confirm some of the former hypotheses and reject others. The new findings are important for understanding how insects analyse polarized skylight.

Pore canals in the cornea of a functionally specialized area of the honey bee's compound eye

The fine structure of the cornea in an anatomically and functionally specialized part of the honey bee's compound eye (dorsal rim area) was examined by light microscopy, transmission electron and scanning electron microscopy. Under incident illumination the cornea appears grey and cloudy, leaving only the centers of the corneal lenses clear. This is due to numerous pore canals that penetrate the cornea from the inside, ending a few micron below the outer surface. They consist of (1) a small cylindrical cellular evagination of a pigment cell (proximal), and (2) a rugged-walled, pinetree-shaped extracellular part (distal). The functional significance of these pore canals is discussed. It is concluded that their light scattering properties cause the wide visual fields of the photoreceptor cells measured electrophysiologically in the dorsal rim area, and that this is related to the way this eye region detects polarization in skylight.

Control of ovine lupinosis: experiments on the use of fungicides

Experiments were conducted in 4 successive years to assess whether certain fungicides when applied to lupins would control the disease, ovine lupinosis. Results were variable, ranging from failure of fungicidal sprays to prevent the disease in 1969/70 to partial success in 1970/71. Fumigation with methyl bromide was very effective. It is concluded that none of the fungicides tried could be considered as a practical means of controlling the disease.

Zamia palm (Macrozamia reidlei) poisoning of sheep

Sheep mortalities caused by the ingestion of leaves of the zamia palm (Macrozamia reidlei) were recorded from 6 properties in Western Australia from 1966 to 1971. Deaths occurred in sheep less than 2 years of age and involved from 2 to 9% of the flock. The primary lesion was acute hepatic necrosis, neurological effects were not recorded. The condition was reproduced experimentally when crushed kernel, mascerated leaf or leaf extract was administered by stomach tube.