MORPHOLOGICAL CHANGES AND THE REQUIREMENTS FOR MACROMOLECULE SYNTHESIS DURING EXCYSTMENT OF ACANTHAMOEBA CASTELLANII

Light and phase-contrast microscopic observations of excystment in Acanthamoeba castellanii have been used to classify cells in excysting populations as free trophozoites, or mature, activated, or preemergent cysts. These categories have been used to describe the kinetics of excystment. A pH of 7 and a temperature of 30°C have been found to be optimal for the activation of mature cysts. Both activation and emergence are inhibited by cycloheximide and actinomycin D, but neither process is much affected by hydroxyurea. Cell-free extracts of high molecular weight components of cyst cytoplasm can support protein synthesis in vitro, although less efficiently than similar extracts from trophozoites. Evidence indicates that some of the functional RNA in the cyst extracts is synthesized before excystment.     

The dependency of fetal left ventricular biomechanics function on myocardium helix angle configuration

The helix angle configuration of the myocardium is understood to contribute to the heart function, as finite element (FE) modeling of postnatal hearts showed that altered configurations affected cardiac function and biomechanics. However, similar investigations have not been done on the fetal heart. To address this, we performed image-based FE simulations of fetal left ventricles (LV) over a range of helix angle configurations, assuming a linear variation of helix angles from epicardium to endocardium. Results showed that helix angles have substantial influence on peak myofiber stress, cardiac stroke work, myocardial deformational burden, and spatial variability of myocardial strain. A good match between LV myocardial strains from FE simulations to those measured from 4D fetal echo images could only be obtained if the transmural variation of helix angle was generally between 110 and 130°, suggesting that this was the physiological range. Experimentally discovered helix angle configurations from the literature were found to produce high peak myofiber stress, high cardiac stroke work, and a low myocardial deformational burden, but did not coincide with configurations that would optimize these characteristics. This may suggest that the fetal development of myocyte orientations depends concurrently on several factors rather than a single factor. We further found that the shape, rather than the size of the LV, determined the manner at which helix angles influenced these characteristics, as this influence changed significantly when the LV shape was varied, but not when a heart was scaled from fetal to adult size while retaining the same shape. This may suggest that biomechanical optimality would be affected during diseases that altered the geometric shape of the LV.

     

Sperm quality of Colossoma macropomum after room‐temperature and cold storage

The objective of this study was to evaluate the effects of cold and room‐temperature storage on the quality of Colossoma macropomum sperm. The experiment was carried out in December (end of Spring), in Nova Mutum‐MT, Brazil, involving nine C. macropomum males (4 years old; 6.4 ± 1.5 kg average weight). The fish were selected and transferred to masonry tanks (4 m³) in a laboratory (water renewal rate: 10 L/s; average water temperature: 28°C). Subsequently, reproduction was induced using 2.5 mg of crude carp pituitary extract/kg and the semen was harvested 240 degree hours after hormonal induction. The following sperm characteristics were analyzed every 5 hr using Image J/casa software: total motility (MOT), curvilinear velocity (VCL), average path velocity (VAP), straight‐line velocity (VSL), straightness of sperm path (STR), wobble (WOB), progressive motility (PROG), beat cross frequency (BCF) and total number of spermatozoa (NSPZ). A fresh sample of semen from each animal was kept at room temperature (25.3 ± 1.2°C). For analysis of cooled semen, syringes were kept in cooling boxes at an average temperature of 16.9 ± 2.1°C. The reduction (p < 0.05) of MOT in semen kept at room temperature occurred at 10 hr (13.95%); in cooled semen, however, MOT declined at 15 hr (76.87%). At 15 hr, there was practically no MOT in the semen kept at room temperature (0.20%), whereas in the cooled semen this situation was observed only at 35 hr (2.91%) The MOT of cooled sperm was higher (p < 0.05) at all times (except zero time), compared with the semen maintained at room temperature. At 15 hr, the cooled spermatozoa showed higher (p < 0.05) VCL (142.18 μm/s) and BCF (29.72 Hz) than those maintained at room temperature (VCL: 51.18 μm/s; BCF: 19.57 Hz). After 15 hr, only the cooled sperm showed quality. In conclusion, semen cooling allows for extending the viability of C. macropomum spermatozoa from 5 to 10 hr without compromising their quality in most characteristics. At 15 and 25 hr of cooling, sperm viability is still observed, though with decreased quality.     

Heat-Induced Whey Protein Gels: Effects of pH and the Addition of Sodium Caseinate

The effects of pH (6.7 or 5.8), protein concentration and the heat treatment conditions (70 or 90 °C) on the physical properties of heat-induced milk protein gels were studied using uniaxial compression, scanning electron microscopy, differential scanning calorimetry, and water-holding capacity measurements. The systems were formed from whey protein isolate (10–15% w/v) with (5% w/v) or without the addition of caseinate. The reduction in pH from 6.7 to 5.8 increased the denaturation temperature of the whey proteins, which directly affected the gel structure and mechanical properties. Due to this increase in the denaturation temperature of the β-lactoglobulin and α-lactalbumin, a heat treatment of 70 °C/30 min did not provide sufficient protein unfolding to form self-supporting gels. However, the presence of 5% (w/v) sodium caseinate decreased the whey protein thermo stability and was essential for the formation of self-supporting gels at pH 6.7 with heat treatment at 70 °C/30 min. The gels formed at pH 6.7 showed a fine-stranded structure, with great rigidity and deformability as compared to those formed at pH 5.8. The latter had a particulate structure and exuded water, which did not occur with the gels formed at pH 6.7. The addition of sodium caseinate led to less porous networks with increased gel deformability and strength but decreased water exudation. The same tendencies were observed with increasing whey protein concentration.     

Motor learning by observing

Learning complex motor behaviors like riding a bicycle or swinging a golf club is based on acquiring neural representations of the mechanical requirements of movement (e.g., coordinating muscle forces to control the club). Here we provide evidence that mechanisms matching observation and action facilitate motor learning. Subjects who observed a video depicting another person learning to reach in a novel mechanical environment (imposed by a robot arm) performed better when later tested in the same environment than subjects who observed similar movements but no learning; moreover, subjects who observed learning of a different environment performed worse. We show that this effect is not based on conscious strategies but instead depends on the implicit engagement of neural systems for movement planning and control.     

Maternal protein malnutrition does not impair insulin secretion from pancreatic islets of offspring after transplantation into diabetic rats

Pancreatic islets from adult rats whose mothers were protein restricted during lactation undersecrete insulin. The current work analyzes whether this secretory dysfunction can be improved when the pancreatic islets are grafted into hyperglycemic diabetic rats. Two groups of rats were used: the adult offspring from dams that received a low protein diet (4%) during the initial 2/3 of lactation (LP) and, as a control, the adult offspring from dams that consumed a normal protein diet (23%) during the entire period of lactation (NP). Islets from NP- and LP-rats were transplanted into diabetic recipient rats, which were generated by streptozotocin treatment. The islets were transplanted via the portal vein under anesthesia. The fed blood glucose levels were monitored during the 4 days post-transplantation. Transplanted islets from LP-rats (T LP) decreased the fed glucose levels of diabetic rats 34% (21.37 ± 0.24 mM, p<0.05); however, the levels still remained 2-fold higher than those of the sham-operated controls (6.88 ± 0.39 mM, p<0.05). Grafts with NP-islets (T NP) produced the same effect as the LP-islets in diabetic rats. The high fasting blood glucose levels of diabetic rats were improved by the transplantations. Islet grafts from both rat groups recovered 50% of the retroperitoneal fat mass of the diabetic rats (0.55 ± 0.08 g/100 g of body weight for T NP and 0.56 ± 0.07 g/100 g of body weight for T LP, p<0.05). Because pancreatic islets from both the NP- and LP-rats were able to regulate fasting blood glucose concentrations in hyperglycemic rats, we propose that the altered function of pancreatic islets from LP-rats is not permanent.