Recruitment of the male-specific lethal (MSL) dosage compensation complex to an autosomally integrated roX chromatin entry site correlates with an increased expression of an adjacent reporter gene in male Drosophila

Drosophila dosage compensate (equalize X-linked gene products) by doubling the transcription of most X-linked genes in males. The MSL (male-specific lethal) ribonucleoprotein complex consisting of at least five proteins and two non-coding RNAs (roX1 and roX2) is essential for this transcription response. Recently it has been shown that the X-linked roX1 and roX2 genes each contain at least one chromatin entry site for the MSL complex. In this study we show that insertion of either roX1 or roX2 DNA sequences, upstream of an insulated lacZ reporter gene controlled with the constitutive armadillo promoter (arm-lacZ), results in a significant elevation of expression of lacZ in males. However, full compensation, that is a precise doubling of lacZ expression in males relative to females, was only observed in some lines carrying autosomal insertions of either roX1-arm-lacZ or roX2-arm-lacZ transgenes. Furthermore, we found that a 419-base pair fragment of roX1 that contains an MSL binding site was sufficient to cause a modest elevation of expression of lacZ in males, but this response was significantly less than obtained with a full-length roX1 cDNA. This is the first direct demonstration that insertion of an MSL chromatin entry site on an autosome results in elevated expression in males of genes near the entry site.

New methodologies for the preparation of porphodimethenes and their conversion to trans-porphyrins with functionalized naphthyl spacers

The MacDonald [2 + 2]-type condensation of readily available 5-aryl-substituted dipyrromethanes with acenaphthenequinone leads to the trans-syn- and anti-porphodimethenes, which in turn can be converted to the alpha,alpha- and alpha,beta-porphyrin atropisomers, respectively. Treatment of the metalated or unmetalated porphodimethenes with KOH or NaOMe in THF followed by protonation with HCl results in a ring opening of the acenaphthenone and formation of the trans-8-carboxynaphthylporphyrins or their esters (NaOMe) after oxidation. Alternatively, the porphyrin formation can be accomplished by reaction of the porphodimethenes with acids in the presence of water or methanol. Reaction with NaBH(4) in a THF--methanol mixture yields the corresponding dialcohols in nearly quantitative yields. Sixteen different building blocks were prepared in order to evaluate the generality of this new synthetic approach, with Ar = 2,4,6-Me(3)C(6)H(2); 2,6-Cl(2)C(6)H(3); 2,6-F(2)C(6)H(3); 3,4-tBu(2)C(6)H(3); 3,4,5-(MeO)(3)C(6)H(2); 4-BrC(6)H(4); 4-MeC(6)H(4); and 4-MeOOCC(6)H(4) at the meso positions. The synthesized porphodimethenes and porphyrins have been fully characterized, and the X-ray structure analyses of three representative derivatives are presented.

MacDonald [2 + 2]-type condensation with vicinal diketones: synthesis and properties of novel spiro-tricyclic porphodimethenes

[structure: see text] Acid-catalyzed [2 + 2] condensation reactions of polycyclic aromatic vicinal diketones including aceanthrenequinone, phenathrenequinone, and pyrene-4,5-dione with 5-mesityldipyrromethanes are outlined, and this methodology provides a flexible entry to spiro-tricyclic porphodimethenes. The porphodimethene products have been fully characterized, including X-ray structure analyses and fluorescence spectroscopy. In the case of the phenanthrenone-substituted macrocycle, the two spiro-locks can be ring-opened to form a trans-bis(2'-hydroxymethylbiphenyl)-substituted porphyrin.

Translating the psychobiology of post-traumatic stress disorder into clinically useful analogy

Psychological theorizing about post-traumatic stress disorder (PTSD) has developed considerably since early behavioural formulations (Brewin, Dalgleish, & Joseph, 1996; Mowrer, 1960) and there have been parallel developments in biological understanding (Yehuda, 1998). However clinical practice has not been affected by the new psychobiology. It is suggested that it is possible to translate this new understanding into a clinically useful analogy that will help circumvent the difficulties of forming a therapeutic alliance with trauma victims which have been reported (Pitman et al., 1991; Scott & Stradling, 1997).

Age-related alterations of cardiac tissue microstructure and material properties in Fischer 344 rats

The cardiac aging process is accompanied by global mechanical dysfunction that reflects increased myocardial stiffness. Accordingly, age-related changes in microscopic material properties of myocardium were delineated with high-frequency ultrasound (US) (30 to 44 MHz) tissue characterization methods for aging Fischer 344 rats at 6 (adult), 18 (aged), and 24 (senescent) months of age. The excised lateral wall of the left ventricle of rats (n = 10 per group) was insonified with a 50-MHz acoustic microscope for determination of integrated backscatter, backscatter coefficient and attenuation coefficient. Histological and biochemical analyses for collagen content and cardiac myocyte diameter were performed. Collagen concentration increased progressively with age, with the greatest increments occurring from 6 to 18 months (38.0 +/- 6.3 to 53.0 +/- 7.1 mg/g dry wt), and leveling off at 24 months (60.0 +/- 7.4 mg/g dry wt). Tissue microscopic material properties also changed progressively from 6 to 24 months of age, as determined by US methods: integrated backscatter increased (-44.7 +/- 1.8 vs. -40.8 +/- 1.9 dB, p < 0.05), attenuation increased (47.1 +/- 5.9 to 65.3 +/- 7.8 dB/cm, p < 0.05), and the backscatter coefficient increased (0.73 +/- 0.16 x 10(-5) to 3.76 +/- 1.6 x 10(-5) cm(-1), p < 0.05), from 6 to 24 months of age in each case. Age-related alterations in indices of cardiac microscopic material properties were closely correlated with the changes in cardiac microstructure. Ultrasonic tissue characterization may prove to be a sensitive tool to monitor changes in the cardiac microstructure, such as increased collagen deposition, that occur within age-related diastolic dysfunction.

Investigating the structural and electronic properties of nitrile hydratase model iron(III) complexes using projected unrestricted Hartree-Fock (PUHF) calculations

Important structural and mechanistic details concerning the non-heme, low-spin Fe(III) center in nitrile hydratase (NHase) remain poorly understood. We now report projection unrestricted Hartree-Fock (PUHF) calculations on the spin preferences of a series of inorganic complexes in which Fe(III) is coordinated by a mixed set of N/S ligands. Given that many of these compounds have been prepared as models of the NHase metal center, this study has allowed us to evaluate this computational approach as a tool for future calculations on the electronic structure of the NHase Fe(III) center itself. When used in combination with the INDO/S semiempirical model, the PUHF method correctly predicts the experimentally observed spin state for 12 of the 13 Fe(III)-containing complexes studied here. The one compound for which there is disagreement between our theoretical calculations and experimental observation exhibits temperature-dependent spin behavior. In this case, the failure of the PUHF-INDO/S approach may be associated with differences between the structure of the Fe(III) complex present under the conditions used to measure the spin preference and that observed by X-ray crystallography. A preliminary analysis of the role of the N/S ligands and coordination geometry in defining the Fe(III) spin preferences in these complexes has also been undertaken by computing the electronic properties of the lowest energy Fe(III) spin states. While any detailed interpretation of our results is constrained both by the limited set of well-characterized Fe(III) complexes used in this study and by the complicated dependence of Fe(III) spin preference upon metal-ligand interactions and coordination geometry, these PUHF-INDO/S calculations support the hypothesis that the deprotonated amide nitrogens coordinating the metal stabilize the low-spin Fe(III) ground state seen in NHase. Strong evidence that the sulfur ligands exclusively define the Fe(III) spin state preference by forming metal-ligand bonds with significant covalent character is not provided by these computational studies. This might, however, reflect limitations in modeling these systems at the INDO/S level of theory.

Time evolution of enhanced ultrasonic reflection using a fibrin-targeted nanoparticulate contrast agent

Complex molecular signaling heralds the early stages of pathologies such as angiogenesis, inflammation, unstable atherosclerotic plaques, and areas of remote thrombi. In previous studies, acoustic enhancement of blood clot morphology was demonstrated with the use of a nongaseous, fibrin-targeted acoustic nanoparticle emulsion delivered to areas of thrombosis both in vitro and in vivo. In this study, a system was designed and constructed that allows visualization of the evolution of acoustic contrast enhancement. To evaluate the system, two targets were examined: avidin-complexed nitrocellulose membrane and human plasma clots. The time evolution of enhancement was visualized in 10-min increments for 1 h. A monotonic increase was observed in ultrasonic reflection enhancement from specially treated nitrocellulose membranes for targeted emulsions containing perfluorooctylbromide (1.30+/-0.3 dB) and for perfluorooctane (2.64+/-0.5 dB) within the first 60 min of imaging. In comparison, the inherently nonechogenic plasma clots showed a substantial increase of 12.0+/-0.9 dB when targeted with a perfluoro-octane emulsion. This study demonstrates the concept of molecular imaging and provides the first quantifiable time-evolution report of the binding of a site-targeted ultrasonic contrast agent. Moreover, with the incorporation of specific drug treatments into the nanoparticulate contrast agent, ultrasonic molecular imaging may yield reliable detection and quantification of nascent pathologies and facilitate targeted drug therapy.

High-resolution MRI characterization of human thrombus using a novel fibrin-targeted paramagnetic nanoparticle contrast agent

In this study, the sensitivity of a novel fibrin-targeted contrast agent for fibrin detection was defined in vitro on human thrombus. The contrast agent was a lipid-encapsulated perfluorocarbon nanoparticle with numerous Gd-DTPA complexes incorporated into the outer surface. After binding to fibrin clots, scanning electron microscopy of treated clots revealed dense accumulation of nanoparticles on the clot surfaces. Fibrin clots with sizes ranging from 0.5-7.0 mm were imaged at 4.7 T with or without treatment with the targeted contrast agent. Regardless of sizes, untreated clots were not detectable by T(1)-weighted MRI, while targeted contrast agent dramatically improved the detectability of all clots. Decreases in T(1) and T(2) relaxation times (20-40%) were measured relative to the surrounding media and the control clots. These results suggest the potential for sensitive and specific detection of microthrombi that form on the intimal surfaces of unstable atherosclerotic plaque.

The biodegradation of surfactants in the environment

The possible contamination of the environment by surfactants arising from the widespread use of detergent formulations has been reviewed. Two of the major surfactants in current use are the linear alkylbenzene sulphonates (LAS) and the alkyl phenol ethoxylates (APE). These pass into the sewage treatment plants where they are partially aerobically degraded and partially adsorbed to sewage sludge that is applied to land. The biodegradation of these and a range of other surfactants both in wastewater treatment plants and after discharge into natural waters and application to land resulting in sewage sludge amended soils has been considered. Although the application of sewage sludge to soil can result in surfactant levels generally in a range 0 to 3 mg kg(-1), in the aerobic soil environment a surfactant can undergo further degradation so that the risk to the biota in soil is very small, with margins of safety that are often at least 100. In the case of APE, while the surfactants themselves show little toxicity their breakdown products, principally nonyl and octyl phenols adsorb readily to suspended solids and are known to exhibit oestrogen-like properties, possibly linked to a decreasing male sperm count and carcinogenic effects. While there is little serious risk to the environment from commonly used anionic surfactants, cationic surfactants are known to be much more toxic and at present there is a lack of data on the degradation of cationics and their fate in the environment.

A repressible female-specific lethal genetic system for making transgenic insect strains suitable for a sterile-release program

We have developed a tetracycline-repressible female-specific lethal genetic system in the vinegar fly Drosophila melanogaster. One component of the system is the tetracycline-controlled transactivator gene under the control of the fat body and female-specific transcription enhancer from the yolk protein 1 gene. The other component consists of the proapoptotic gene hid under the control of a tetracycline-responsive element. Males and females of a strain carrying both components are viable on medium supplemented with tetracycline, but only males survive on normal medium. A strain with such properties would be ideal for a sterile-insect release program, which is most effective when only males are released in the field.

In vivo molecular imaging of stretch-induced tissue factor in carotid arteries with ligand-targeted nanoparticles

Molecular imaging permits tissues to be functionally characterized by identification of specific cell-surface receptors with targeted contrast agents. In our study, a ligand-targeted acoustic nanoparticle system was used to identify the angioplasty-induced expression of tissue factor by smooth muscle cells within the tunica media. Pig carotid arteries were overstretched bilaterally with balloon catheters, treated with a tissue factor-targeted or a control nanoparticle system, and imaged with intravascular ultrasound (20 MHz) before and after treatment. Carotid wall acoustic reflectivities were unaffected by overstretch injury. Tissue factor-targeted nanoemulsion bound and increased the echogenicity of smooth muscle cells expressing tissue factor within the tunica media. The targeted emulsion increased the arterial wall gray scale (99.4+/-14.5; P<.05) relative to pretreatment (41.8+/-11.1, P<0.05) and the control gray scale (pre-emulsion: 49.3+/-9.5; post-emulsion: 43.7+/-6.4; P<.05). The area of acoustic enhancement appeared to coincide with expression of induced tissue factor in the tunica media confirmed by immunohistochemistry. We have demonstrated that this novel nanoemulsion can infiltrate into arterial walls after balloon injury and localize the expression of overstretch-induced tissue factor within pig carotid arteries. Molecular imaging and quantification of complex, biochemical change, such as tissue factor expression after angioplasty, may prove to be a prognostically important predictor of subsequent restenosis.

Delineation of the extracellular determinants of ultrasonic scattering from elastic arteries

Elastic arteries consist of three primary components: elastin fibers, extracellular collagen matrix and smooth muscle cells. However, the relative contribution of elastin and collagen fibers to overall ultrasonic scattering from an intact arterial wall is poorly understood. To define the principal source of extracellular scattering from the medial layer of elastic arteries, canine ascending aortas (n = 10) were excised, fixed and sectioned for insonification. Subsequently, aortic specimens were restudied after treatment to dissolve all tissue components except extracellular collagen matrix (n = 5) and elastin fibers (n = 5). Histological staining revealed very few elastin fibers and sparse intact collagen in collagen-isolated and elastin-isolated tissues, respectively. Integrated backscatter, attenuation and backscatter coefficients differentiated these two treated tissues. The backscatter coefficient for elastin-isolated tissue demonstrated a fivefold increase over collagen-isolated tissue, suggesting that elastin fibers represent a primary scattering component within elastic arteries, and the collagen fibers may provide a secondary component of scattering.

Development of an insulated reporter system to search for cis-acting DNA sequences required for dosage compensation in Drosophila

Dosage compensation (equalization of X-linked gene products) occurs in Drosophila melanogaster by a two-fold transcriptional increase of X-linked gene expression in the male. The cis-acting X-linked DNA sequences required for dosage compensation (called DCREs) remain elusive, despite numerous attempts to identify them. We have developed an insulated reporter system to minimise problems previously encountered with identifying these elements. The system consists of the constitutive autosomal armadillo promoter fused to the lacZ reporter gene (called arm-lacZ) which was flanked by SCS insulator elements to block potential repressive effects of an autosomal chromatin environment. Seven X-linked DNA fragments, totaling 62.7 kb, were each inserted between the SCS element and the armadillo promoter. If an X-linked fragment contains a DCRE, then transgenic males carrying an autosomal insert of the construct should produce twice the beta-galactosidase activity of females. However, in all cases, males and females expressed the same level of lacZ. Thus, it's likely that none of the X-linked fragments contained a DCRE, suggesting these elements may be rarer than previously thought. The insulated reporter system was also used to test the hypothesis that some genes may be dosage compensated due to repression by Sex lethal (Sxl) in females. A fragment from the runt gene containing three Sxl binding sites was inserted into the 3' untranslated region of arm-lacZ. Transgenic males carrying an autosomal insert of the construct had on average 1.31-1.46 times the level of beta-galactosidase than females, suggesting that some genes could be compensated, at least partially, by Sxl repression in females.

Molecular imaging of stretch-induced tissue factor expression in carotid arteries with intravascular ultrasound

RATIONALE AND OBJECTIVES

Molecular imaging with targeted contrast agents enables tissues to be distinguished by detecting specific cell-surface receptors. In the present study, a ligand-targeted acoustic nanoparticle system is used to identify angioplasty-induced expression of tissue factor by smooth muscle cells within carotid arteries.

METHODS

Pig carotid arteries were overstretched with balloon catheters, treated with tissue factor-targeted or a control nanoparticle system, and imaged with intravascular ultrasound before and after treatment.

RESULTS

Tissue factor-targeted emulsions bound and increased the echogenicity and gray-scale levels of overstretched smooth muscle cells within the tunica media, versus no change in contralateral control arteries. Expression of stretch-induced tissue factor in carotid artery media was confirmed by immunohistochemistry.

CONCLUSIONS

The potential for abnormal thrombogenicity of balloon-injured arteries, as reflected by smooth muscle expression of tissue factor, was imaged using a novel, targeted, nanoparticulate ultrasonic contrast agent.

Alkali salts of C3-symmetric, linked aryloxides: selective binding of substrates with metal aggregates

The lithium, sodium, and potassium salts of tris(3,5-dialkyl-2-hydroxyphenyl)methanes (tert-butyl, tert-pentyl, methyl) have been prepared by reaction of the triarylmethane with n-butyllithium, sodium hydride, and potassium hydride, respectively. These compounds are all hexanuclear aggregates composed of two triarylmethane units. Whereas the lithium salt is compact and cannot bind oxygen-donor solvent molecules, the sodium and potassium systems have vacant coordination sites that can interact with solvents. For the sodium compounds, the solvent can be subsequently removed, and the resulting coordinatively unsaturated compounds have been shown to selectively bind oxygen-donor substrates (ethers, aldehydes, and ketones) of suitable size and shape. The paper reports the synthesis and characterization of these novel compounds, including thirteen crystal structures of the salts and their adducts.

High-frequency ultrasound for quantitative characterization of myocardial edema

Myocardial edema has been associated with impaired ventricular compliance and diastolic filling. To determine the sensitivity of high-frequency (40 MHz) ultrasound to myocardial edema, we employed a model in which myocardial edema was induced by immersion of tissue in isotonic saline. The effect of freezing tissue on edema formation was also evaluated. Rat hearts were arrested at end-diastole and insonified fresh within 15 min of excision (n = 5) or following being frozen for 24 h and thawed (n = 4). Measurements of attenuation, backscatter, tissue thickness and speed of sound were performed at baseline and hourly for 4 h, and compared with direct measurements of myocardial edema. Fresh tissue demonstrated a greater propensity for the development of edema than frozen tissue. Integrated backscatter increased in both tissues, whereas the magnitude and slope of attenuation decreased as edema evolved. We conclude that high-frequency ultrasound sensitively detects myocardial edema, and we propose that the extension of these methods to clinical frequencies may prove useful for monitoring and treatment of cardiac edematous disease states.

Effect of grafted polyethylene glycol (PEG) on the size, encapsulation efficiency and permeability of vesicles

Liposomes have been prepared by the vesicle extrusion method (VETs) from mixtures of dipalmitoylphosphatidylcholine (DPPC), phosphatidylinositol (PI) and dipalmitoylphosphatidylethanolamine with covalently linked poly(ethylene glycol) molecular mass 5000 and 2000 (DPPE-PEG 5000 and DPPE-PEG 2000) covering a range of 0-7.5 mole%. The encapsulation of D-glucose has been studied and found to be markedly dependent on the mole% DPPE-PEG. The permeability of the liposomes to D-glucose has been measured both as a function of temperature and liposome composition. The permeability coefficients for D-glucose increase with mole% DPPE-PEG 5000 and with temperature over the range 25-50 degrees C. The activation energies for glucose permeability range from 90 to 23 kJ mol(-1). The decrease in activation energy with increasing temperature is attributed to an increasing number of bilayer defects as the liposome content of PEG-grafted lipid is increased. The dependence of D-glucose encapsulation as a function of PEG-grafted lipid content is discussed in terms of the conformation of the PEG molecules on the inner surface of the bilayer. For liposomes containing DPPE-PEG 5000 the relative percentage encapsulation of glucose, assuming that the PEG surface layer excludes glucose, is comparable to that predicted from the mushroom and brush conformational models.

MSL1 plays a central role in assembly of the MSL complex, essential for dosage compensation in Drosophila

In male Drosophila, histone H4 acetylated at Lys16 is enriched on the X chromosome, and most X-linked genes are transcribed at a higher rate than in females (thus achieving dosage compensation). Five proteins, collectively called the MSLs, are required for dosage compensation and male viability. Here we show that one of these proteins, MSL1, interacts with three others, MSL2, MSL3 and MOF. The latter is a putative histone acetyl transferase. Overexpression of either the N- or C-terminal domain of MSL1 has dominant-negative effects, i.e. causes male-specific lethality. The lethality due to expression of the N-terminal domain is reduced if msl2 is co-overexpressed. MSL2 co-purifies over a FLAG affinity column with the tagged region of MSL1, and both MSL3 and MOF co-purify with the FLAG-tagged MSL1 C-terminal domain. Furthermore, the MSL1 C-terminal domain binds specifically to a GST-MOF fusion protein and co-immunoprecipitates with HA-tagged MSL3. The MSL1 C-terminal domain shows similarity to a region of mouse CBP, a transcription co-activator. We conclude that a main role of MSL1 is to serve as the backbone for assembly of the MSL complex.

The extracellular matrix is an important source of ultrasound backscatter from myocardium

Ultrasound tissue characterization with measurement of backscatter has been employed in numerous experimental and clinical studies of cardiac pathology, yet the cellular components responsible for scattering from cardiac tissues have not been unequivocally identified. This laboratory has proposed a mathematical model for myocardial backscatter that postulates the fibrous extracellular matrix (ECM) as a significant determinant of backscatter. To demonstrate the importance of ECM, this group sought to determine whether measurements of backscatter from the isolated ECM could reproduce the known directional dependence, or anisotropy of backscatter, from intact cardiac tissues in vitro. Segments of left ventricular free wall from ten formalin fixed porcine hearts were insonified at 50 MHz, traversing the heart wall from endo- to epicardium to measure the anisotropy of myocardial backscatter, defined as the difference between peak (perpendicular to fibers) and trough (parallel to fibers) backscatter amplitude. The tissue segments were then treated with 10% NaOH to dissolve all of the cellular components, leaving only the intact ECM. Scanning electron micrographs (SEM) were obtained of tissue sections to reveal complete digestion of the cellular elements. The dimensions of the residual voids resulting from cell digestion were approximately the diameter of the intact myocytes (10-30 microm). These samples were reinsonified after seven days of treatment to compare the anisotropy of integrated backscatter. The magnitude of anisotropy of backscatter changed from 15.4 +/- 0.8 to 12.6 +/- 1.1dB for intact as compared with digested specimens. Because digestion of the myocardium leaves only extracellular sources of ultrasonic scattering, and because the isolated ECM exhibits similar ultrasonic anisotropy as does the intact myocardium, it is concluded that there is a direct association between the ECM and the anisotropy of backscatter within intact tissue. Thus, it is suggested that ultrasonic tissue characterization represents a potentially clinically applicable method for delineating the structure and function of the ECM.

High-frequency ultrasound detection of the temporal evolution of protein cross linking in myocardial tissue

The progressive increase in stiffening of the myocardium associated with the aging process and abetted by comorbid conditions such as diabetes may be linked to an excessive number of collagen cross links within the myocardial extra-cellular matrix. To determine whether ultrasound can delineate changes in the physical properties of heart tissue undergoing cross linking, the authors employed a model in which increased cross linking was induced by treating rat myocardial tissue with specific chemical fixatives. Rat hearts (n=5 each group) were arrested at end-diastole, insonified (30 to 50 MHz) fresh within a few minutes of excision in a phosphate buffered solution, placed in a fixative (10% formalin or 2.5% glutaraldehyde) and insonified at 30-minute intervals thereafter for 24 hours. Ultrasonic attenuation increased in tissues cross linked with formalin (maximal change: 27.2+/-3.4 dB/cm) and glutaraldehyde (maximal change: 40.2+/-5.6 dB/cm) over a 24-hour period. The frequency dependence of the attenuation coefficient increased as a function of the extent of collagen cross links in formalin (maximal change: 0.8+/-0.3 dB/cm-MHz) and glutaraldehyde (maximal change: 0.9+/-0.6 dB/cm-MHz). This study represents the first time that the precise time course of myocardial protein cross linking in situ has been characterized by using real time monitoring, and the physiologic effect has been delineated on microscopic material properties.

In vitro characterization of a novel, tissue-targeted ultrasonic contrast system with acoustic microscopy

Targeted ultrasonic contrast systems are designed to enhance the reflectivity of selected tissues in vivo [Lanza et al., Circulation 94, 3334 (1996)]. In particular, these agents hold promise for the minimally invasive diagnosis and treatment of a wide array of pathologies, most notably tumors, thromboses, and inflamed tissues. In the present study, acoustic microscopy was used to assess the efficacy of a novel, perfluorocarbon based contrast agent to enhance the inherent acoustic reflectivity of biological and synthetic substrates. Data from these experiments were used to postulate a simple model describing the observed enhancements. Frequency averaged reflectivity (30-55 MHz) was shown to increase 7.0 +/- 1.1 dB for nitrocellulose membranes with targeted contrast. Enhancements of 36.0 +/- 2.3 dB and 8.5 +/- 0.9 dB for plasma and whole blood clots, respectively, were measured between 20 and 35 MHz. A proposed acoustic transmission line model predicted the targeted contrast system would increase the acoustic reflectivity of the nitrocellulose membrane, whole blood clot, and fibrin plasma clot by 2.6, 8.0, and 31.8 dB, respectively. These predictions were in reasonable agreement with the experimental results of this paper. In conclusion, acoustic microscopy provides a rapid and sensitive approach for in vitro chracterization, development, and testing of mathematical models of targeted contrast systems. Given the current demand for targeted contrast systems for medical diagnostic and therapeutic use, the use of acoustic microscopy may provide a useful tool in the development of these agents.

The carriage of Pasteurella haemolytica in sheep and its transfer between ewes and lambs in relation to mastitis

The possible presence of Pasteurella haemolytica in the mouth of lambs and on the skin of the teats of ewes was investigated. The organism was found in the mouth of ewes and lambs and, soon after lambing, on the teat skin of ewes. It was not isolated from the teat skin of pregnant ewes 1-14 days before lambing or from the teat skin one week after the lambs had been weaned. The transfer of P. haemolytica to the teat skin is undoubtedly mediated by the lamb. There is ample opportunity for the teat orifice to be exposed to P. haemolytica during the suckling period and it is known that only a few colony-forming units of virulent organisms are required to initiate mastitis.