PYY3-36 infused systemically or directly into the VTA attenuates fentanyl seeking in male rats

More effective treatments for fentanyl use disorder are urgently needed. An emerging literature indicates that glucagon-like peptide-1 receptor (GLP-1R) agonists attenuate voluntary opioid taking and seeking in rodents. However, GLP-1R agonists produce adverse malaise-like effects that may limit patient compliance. Recently, we developed a dual agonist of GLP-1Rs and neuropeptide Y2 receptors (Y2Rs) that attenuates fentanyl taking and seeking at doses that do not produce malaise-like effects in opioid-experienced rats. Whether activating Y2Rs alone is sufficient to reduce opioid taking and seeking, however, is not known. Here, we investigated the efficacy of the Y2R ligand PYY3-36 to reduce fentanyl self-administration and the reinstatement of fentanyl-seeking behavior, a model of relapse in humans. Male rats were allowed to self-administer fentanyl (2.5 μg/kg, i.v.) for 21 days on a fixed-ratio 5 (FR5) schedule of reinforcement. Rats were then pretreated with vehicle or PYY3-36 (50 μg/kg s.c.; 0.1 and 1.0 μg/100 nL intra-VTA) prior to fentanyl self-administration test sessions. There were no effects of systemic or intra-VTA PYY3-36 on intravenous fentanyl self-administration. Opioid taking was then extinguished. Prior to subsequent reinstatement test sessions, rats were pretreated with vehicle or PYY3-36 (50 μg/kg s.c.; 0.1 and 1.0 μg/100 nL intra-VTA). Both systemic and intra-VTA administration of PYY3-36 attenuated fentanyl reinstatement in male rats at doses that did not affect food intake or produce adverse malaise-like effects. These findings indicate that Y2R agonism alone is sufficient to decrease fentanyl-seeking behavior during abstinence in opioid-experienced rats and further support strategies aimed at targeting Y2Rs for treating opioid use disorders.

ECM-transmitted shear stress induces apoptotic cell extrusion in early breast gland development

Epithelial cells of human breast glands are exposed to various mechanical ECM stresses that regulate tissue development and homeostasis. Mechanoadaptation of breast gland tissue to ECM-transmitted shear stress remained poorly investigated due to the lack of valid experimental approaches. Therefore, we created a magnetic shear strain device that enabled, for the first time, to analyze the instant shear strain response of human breast gland cells. MCF10A-derived breast acini with basement membranes (BM) of defined maturation state and basoapical polarization were used to resemble breast gland morphogenesis in vitro. The novel biophysical tool was used to apply cyclic shear strain with defined amplitudes (≤15%, 0.2 Hz) over 22 h on living spheroids embedded in an ultrasoft matrix (<60 Pa). We demonstrated that breast spheroids gain resistance to shear strain, which increased with BM maturation and basoapical polarization. Most intriguingly, poorly developed spheroids were prone to cyclic strain-induced extrusion of apoptotic cells from the spheroid body. In contrast, matured spheroids were insensitive to this mechanoresponse—indicating changing mechanosensing or mechanotransduction mechanisms during breast tissue morphogenesis. Together, we introduced a versatile tool to study cyclic shear stress responses of 3D cell culture models. It can be used to strain, in principle, all kinds of cell clusters, even those that grow only in ultrasoft hydrogels. We believe that this approach opens new doors to gain new insights into dynamic shear strain-induced mechanobiological regulation circuits between cells and their ECM.

Intrinsic cell rheology drives junction maturation

A fundamental property of higher eukaryotes that underpins their evolutionary success is stable cell-cell cohesion. Yet, how intrinsic cell rheology and stiffness contributes to junction stabilization and maturation is poorly understood. We demonstrate that localized modulation of cell rheology governs the transition of a slack, undulated cell-cell contact (weak adhesion) to a mature, straight junction (optimal adhesion). Cell pairs confined on different geometries have heterogeneous elasticity maps and control their own intrinsic rheology co-ordinately. More compliant cell pairs grown on circles have slack contacts, while stiffer triangular cell pairs favour straight junctions with flanking contractile thin bundles. Counter-intuitively, straighter cell-cell contacts have reduced receptor density and less dynamic junctional actin, suggesting an unusual adaptive mechano-response to stabilize cell-cell adhesion. Our modelling informs that slack junctions arise from failure of circular cell pairs to increase their own intrinsic stiffness and resist the pressures from the neighbouring cell. The inability to form a straight junction can be reversed by increasing mechanical stress artificially on stiffer substrates. Our data inform on the minimal intrinsic rheology to generate a mature junction and provide a springboard towards understanding elements governing tissue-level mechanics.

Mechanical strength of specific bonds acting isolated or in pairs: a case study on engineered proteins

The dynamic strength of multiple specific bonds exposed to external mechanical force is of significant interest for the understanding of biological adhesion. Exploiting the well-established FLAG tag technology, we engineered model proteins exhibiting no, one, or two identical binding sites for a monoclonal antibody. Bonds between these engineered proteins and the antibody were studied with dynamic force spectroscopy. On single bonds between a FLAG-tag and the antibody, we observed two regimes corresponding to two different activated complexes, that is, two intermediate states along the reaction path for bond breakage. Dynamic force spectroscopy on double bonds showed the same two regimes. The actual yield forces of double bonds slightly exceeded those of single bonds. A simplified kinetic model with analytical solutions was developed and used to interpret the measured spectra.

Tube width fluctuations in F-actin solutions

We determine the statistics of the local tube width in F-actin solutions, beyond the usually reported mean value. Our experimental observations are explained by a segment fluid theory based on the binary collision approximation. In this systematic generalization of the standard mean-field approach, effective polymer segments interact via a potential representing the topological constraints. The analytically predicted universal tube width distribution with a stretched tail is in good agreement with the data.

The contribution of chevon from Africa to global meat production

Africa's goat population increased by 75% between 1980 and 2005 and constitutes 30% of the world goat population. Although Africa produces about 20% of the world's chevon, its share of world chevon market has been declining. Exports from Africa represent less than 5% of the total world trade. Most goats are raised by smallholder farmers for subsistence and trading in informal markets. The world renowned Boer, Kalahari Red and Savanna goats are meat breeds that were developed in South Africa. Information on most African goat breeds is scanty, but there seems to be large variations in the breed characteristics, which suggests a potential for selective breeding for more and meat breeds. Recommendations for enhancing goat production in Africa include, prioritizing research and technology transfer on meat goat production, development of more chevon breeds, devising methods to enhance the quality of African chevon through pre- and post-harvest interventions, and improved support from government institutions and policy.

Theoretical analysis of single-molecule force spectroscopy experiments: heterogeneity of chemical bonds

We show that the standard theoretical framework in single-molecule force spectroscopy has to be extended to consistently describe the experimental findings. The basic amendment is to take into account heterogeneity of the chemical bonds via random variations of the force-dependent dissociation rates. This results in a very good agreement between theory and rupture data from several different experiments.

Ellipsometric microscopy: developments towards biophysics

Ellipsometric microscopy is a novel technique that combines the merits of ellipsometry and light microscopy, i.e. it allows noninvasive, label-free measurements of thin film thickness and refractive index at high lateral resolution. Ellipsometric microscopy has been successfully applied to silicon-air interfaces. However, typical biological systems require immersion in an aqueous buffer. Thus the authors have adapted the instrument for the observation of the interface between glass and water. In particular, the comparatively small differences in refractive indices between substrate and ambient media proved to be a challenge for instrument design. The first experiments with this new instrument are presented.

Dynamic force spectroscopy to probe adhesion strength of living cells

We studied the mechanical strength of the adhesion of living cells to model membranes. The latter contained a RGD lipopeptide which is a high affinity binding site for a cell adhesion molecule (integrin alpha(V)beta(3)). Cells adhered specifically to the vesicles. We used micropipette aspiration for breaking this adhesion with well defined forces. Systematic variation of the rate of force application revealed pronounced kinetic effects. The dependence of the detachment forces on the loading rate was well described by a power law (exponent approximately 0.4), in agreement with recent theoretical work.

Shape instability of a biomembrane driven by a local softening of the underlying actin cortex

We present a theory showing that local shape instabilities of composite biological membranes, consisting of a lipid bilayer and an underlying actin cortex, can be triggered by a local softening of the membrane-associated cytoskeleton. A membrane containing such cortical defects can form blisters or invaginations, depending on external conditions. The theoretical predictions agree with observations provided by two sets of experiments: (i) microscopic observations of shape changes of giant vesicles with underlying shells of a thin actin network show the formation of local blisters and (ii) micropipet aspiration experiments of Dictyostelium discoideum cells in which we observed the formation of blisters in the aspirated cell part. In the latter experiments, the existence of a hole in the underlying cortex is confirmed by observation of the entrance of cell organelles into the blister. Our model may also be applied to the formation of lobopodia, fast-growing cell protrusions that play an important role in the locomotion and spreading of biological cells.

A micromechanic study of cell polarity and plasma membrane cell body coupling in Dictyostelium

We used micropipettes to aspirate leading and trailing edges of wild-type and mutant cells of Dictyostelium discoideum. Mutants were lacking either myosin II or talin, or both proteins simultaneously. Talin is a plasma membrane-associated protein important for the coupling between membrane and actin cortex, whereas myosin II is a cytoplasmic motor protein essential for the locomotion of Dictyostelium cells. Aspiration into the pipette occurred above a threshold pressure only. For all cells containing talin this threshold was significantly lower at the leading edge of an advancing cell as compared to its rear end, whereas we found no such difference in cells lacking talin. Wild-type and talin-deficient cells were able to retract from the pipette against an applied suction pressure. In these cells, retraction was preceded by an accumulation of myosin II in the tip of the aspirated cell lobe. Mutants lacking myosin II could not retract, even if the suction pressures were removed after aspiration. We interpreted the initial instability and the subsequent plastic deformation of the cell surface during aspiration in terms of a fracture between the cell plasma membrane and the cell body, which may involve destruction of part of the cortex. Models are presented that characterize the coupling strength between membrane and cell body by a surface energy sigma. We find sigma approximately 0.6(1.6) mJ/m(2) at the leading (trailing) edge of wild-type cells.

Desmin filaments studied by quasi-elastic light scattering

We studied polymers of desmin, a muscle-specific type III intermediate filament protein, using quasi-elastic light scattering. Desmin was purified from chicken gizzard. Polymerization was induced either by 2 mM MgCl(2) or 150 mM NaCl. The polymer solutions were in the semidilute regime. We concluded that the persistence length of the filaments is between 0.1 and 1 microm. In all cases, we found a hydrodynamic diameter of desmin filaments of 16-18 nm. The filament dynamics exhibits a characteristic frequency in the sense that correlation functions measured on one sample but at different scattering vectors collapse onto a single master curve when time is normalized by the experimentally determined initial decay rate.

Energy landscapes of receptor-ligand bonds explored with dynamic force spectroscopy

Atomic force microscopy (AFM) has been used to measure the strength of bonds between biological receptor molecules and their ligands. But for weak noncovalent bonds, a dynamic spectrum of bond strengths is predicted as the loading rate is altered, with the measured strength being governed by the prominent barriers traversed in the energy landscape along the force-driven bond-dissociation pathway. In other words, the pioneering early AFM measurements represent only a single point in a continuous spectrum of bond strengths, because theory predicts that these will depend on the rate at which the load is applied. Here we report the strength spectra for the bonds between streptavidin (or avidin) and biotins-the prototype of receptor-ligand interactions used in earlier AFM studies, and which have been modelled by molecular dynamics. We have probed bond formation over six orders of magnitude in loading rate, and find that the bond survival time diminished from about 1 min to 0.001 s with increasing loading rate over this range. The bond strength, meanwhile, increased from about 5 pN to 170 pN. Thus, although they are among the strongest noncovalent linkages in biology (affinity of 10(13) to 10(15) M(-1)), these bonds in fact appear strong or weak depending on how fast they are loaded. We are also able to relate the activation barriers derived from our strength spectra to the shape of the energy landscape derived from simulations of the biotin-avidin complex.

Micropipet-based pico force transducer: in depth analysis and experimental verification

Measurements of forces in the piconewton range are very important for the study of molecular adhesion and mechanics. Recently, a micropipet-based force transducer for this type of experiment was presented (E. Evans, K. Ritchie, and R. Merkel, 1995, Biophys. J., 68:2580-2587). In the present article we give a detailed mechanical analysis of this transducer, including nonlinear effects. An analytical expression for the transducer stiffness at small elongations is given. Using magnetic tweezers (F. Ziemann, J. Rädler, and E. Sackmann, 1994, Biophys. J., 66:2210-2216), we were able to determine the force displacement relation of this transducer experimentally. Forces from approximately 10 pN to 500 pN were applied. Theoretical predictions and experimental results coincide remarkably well.

Diffusion measurement of fluorescence-labeled amphiphilic molecules with a standard fluorescence microscope

The lateral diffusion of fluorescence-labeled amphiphilic tracer molecules dissolved within a two-dimensional matrix of lipids was measured by continuous illumination of an elongated rectangular region. The resulting spatial concentration profile of unbleached tracer molecules was observed with a standard epifluorescence microscope and analyzed with digital image-processing techniques. These concentration profiles are governed by the mobility of the tracers, their rate of photolysis, and the geometry of the illuminated area. For the case of a long and narrow illuminated stripe, a mathematical analysis of the process is given. After prolonged exposure, the concentration profile can be approximated by a simple analytical function. This fact was used to measure the quotient of the rate of photolysis, and the diffusion constant of the fluorescent probe. With an additional measurement of the rate of photolysis, the mobility of the tracer was determined. As prototype experiments we studied the temperature dependence of the lateral diffusion of N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-dipalmitoylphosphatidyl++ + ethanolamine in glass-supported bilayers of L-alpha-dimyristoylphosphatidylcholine. Because of its simple experimental setup, this technique represents a very useful method of determining the lateral diffusion of fluorescence-labeled membrane molecules.

Sensitive force technique to probe molecular adhesion and structural linkages at biological interfaces

Adhesion and cytoskeletal structure are intimately related in biological cell function. Even with the vast amount of biological and biochemical data that exist, little is known at the molecular level about physical mechanisms involved in attachments between cells or about consequences of adhesion on the material structure. To expose physical actions at soft biological interfaces, we have combined an ultrasensitive transducer and reflection interference microscopy to image submicroscopic displacements of probe contact with a test surface under minuscule forces. The transducer is a cell-size membrane capsule pressurized by micropipette suction where displacement normal to the membrane under tension is proportional to the applied force. Pressure control of the tension tunes the sensitivity in operation over four orders of magnitude through a range of force from 0.01 pN up to the strength of covalent bonds (approximately 1000 pN)! As the surface probe, a microscopic bead is biochemically glued to the transducer with a densely-bound ligand that is indifferent to the test surface. Movements of the probe under applied force are resolved down to an accuracy of approximately 5 nm from the interference fringe pattern created by light reflected from the bead. With this arrangement, we show that local mechanical compliance of a cell surface can be measured at a displacement resolution set by structural fluctuations. When desired, a second ligand is bound sparsely to the probe for focal adhesion to specific receptors in the test surface. We demonstrate that monitoring fluctuations in probe position at low transducer stiffness enhances detection of molecular adhesion and activation of cytoskeletal structure. Subsequent loading of an attachment tests mechanical response of the receptor-substrate linkage throughout the force-driven process of detachment.

Intersecting polymers in lipid bilayers: cliques, static order parameters and lateral diffusion

We have modelled a macrolipid polymer composed of lipid molecules (monomers) embedded in a lipid bilayer or monolayer and polymerized via their polar groups. Because of fluctuations perpendicular to the plane of the bilayer, the polar region occupied by the polymer chain possesses sufficient space so that the polymer might exhibit 'self-intersection' if its conformational state is projected onto the plane of the bilayer/monolayer. We represent the plane of the bilayer/monolayer by a triangular lattice. Each site can be occupied by a monomer or be empty (and thus occupied by one of the unpolymerizable lipids which make up the bilayer/monolayer). A macrolipid is represented by a sequence of N monomers connected by N-1 bonds. Bonds may be either short (connecting nearest neighbour monomers) or long (between second neighbour monomers), in accord with the average properties of the spacers between the polymerized lipids. We have carried out computer simulation of this system using the Carmesin-Kremer bond stretching algorithm. Although no two monomers can occupy the same site, bonds may cross each other. We analyzed the dependence of <R2> and <R2G> approximately N2vc and <Nsc> + <Nmc> approximately N2 sigma c, where Nsc and Nmc are the number of bond-crossings in the same macrolipid ('self-crossing') or in two different macrolipids ('mutual-crossing'). For single macrolipids, we confirmed that vc = 3/4 and have found that sigma c approximately 0.52, which we consider supports that sigma c = 1/2. For the dense case with monomer concentration, c = 0.72, we found that vc = 1/2 and that sigma c approximately 0.52 supports that sigma c = 1/2. In the semi-dilute regime (c = 0.2) we found crossover behaviour, although sigma c = 1/2. The total number of bond crossings thus scale like N, independent of concentration. We studied the connectivity of the system by calculating the weight averaged cluster, or 'clique', size. Cliques are defined as being composed of all macrolipids which exhibit at least one crossing bond with one other member of the clique. We found that while the average clique contains about two macrolipids at low concentrations, the clique size approaches the maximum possible value at high concentrations if the macrolipids are sufficiently long. In the latter case a transition appears to occur as the macrolipid length increases. This transition occurs at length = 40 when c = 0.72. These observations should have experimental consequences for the viscoelastic properties of the system.(ABSTRACT TRUNCATED AT 400 WORDS)

Adipocyte size and number in dietary obesity resistant and susceptible rats

Fat depot cellularity was assessed in overfed dietary obesity resistant S 5B/Pl (S) and susceptible Osborne-Mendel (OM) rats. Cell number and lipid per cell were determined for three fat depots in both 24- and 105-day-old rats. Between these two ages, fat cell number doubled in inguinal fat depots of S rats fed high- or low-fat diets and OM rats fed a low-fat diet, but quadrupled in OM rats fed a high-fat diet. The size of adipocytes in this depot was influenced by strain but not by diet. Compared to normal weight S rats, 24-day-old overfed S rats had twice as many adipocytes in the perirenal-retroperitoneal fat depot. Overfed OM rats had 3 times perirenal-retroperitoneal fat depot. Overfed OM rats had 3 times as many. In OM rats fed the high-fat diet, there was a 16-fold increase in adipocyte number between 24 and 105 days of age. Overfeeding caused a slight increase in perirenal-retroperitoneal adipocyte size in 24-day-old rats but had little influence on cell size in 105-day-old rats.