Thrombin causes subsecond changes in protein phosphorylation of platelets

We have developed a general quenched-flow approach to study platelet function as early as 0.3 seconds after stimulation. Phosphorylation of 20- and 40-kd proteins has been analyzed during the first five seconds of platelet response to thrombin from 0.1 to 5.0 U/mL and compared with the progress of aggregation and serotonin secretion. The onset time for aggregation and phosphorylation of both proteins was less than one second, although with lowest (less than 0.5 U/mL) thrombin levels, a lag of up to 0.6 seconds occurred before 40K phosphorylation increased. The thrombin sensitivity of aggregation and 20K phosphorylation was approximately twice that of 40K phosphorylation, with Ka values of 0.51 and 0.53 v 1.10 U/mL, respectively. External calcium was necessary for maximal 20K phosphorylation, since EDTA inhibited this by 30%. The 40K phosphorylation was not affected by EDTA. Platelet activation by thrombin thus induced biochemical changes well before one second. The quenched-flow approach may help to reveal relationships between phospholipase activation, calcium fluxes, and protein phosphorylation during these early periods of platelet function.     

Aromatase-knockout mouse carrying an estrogen-inducible enhanced green fluorescent protein gene facilitates detection of estrogen actions in vivo

Aromatase is an enzyme that converts androgen to estrogen in the gonads and also at extragonadal sites, including the brain. In this study we developed a transgenic mouse that carries an enhanced green fluorescent protein (EGFP) gene inducible by estrogen through an estrogen response element to facilitate detection of estrogen actions in vivo. The expression of EGFP in aromatase-deficient (Ar(-/-)) female mice was significantly suppressed at the pituitary gland, ovary, uterus, and gonadal fat pad and was induced by dietary 17beta-estradiol to wild-type (Ar(+/+)) levels or higher. These results demonstrate that the expression of the EGFP gene is tissue selective and estrogen dependent in vivo. Employing this transgenic mouse, we examined whether estrogen synthesis in the extragonadal sites is necessary for reproduction in female mice. When ovaries of Ar(-/-) mice were replaced with Ar(+/+) ovaries, a significant induction of EGFP expression in the pituitary gland and uterus was observed. Histological examinations showed the presence of antral follicles in the replaced ovaries, indicating that the transplants are functional in Ar(-/-) mice. After crossing with males, three of 10 Ar(-/-)females with Ar(+/+) ovaries became pregnant and fed their pups. Collectively, these observations indicate that estrogen synthesis in the ovary is sufficient for supporting female reproduction, and that infertility of Ar(-/-) females is primarily due to a defect in estrogen synthesis in the ovary.     

Calorie restriction promotes remyelination in a Cuprizone-Induced demyelination mouse model of multiple sclerosis

Metabolic Brain Disease - Over the past few decades several attempts have been made to introduce a potential and promising therapy for Multiple sclerosis (MS). Calorie restriction (CR) is a dietary...     

Experimental Investigation on the Structural Performance of Single Span Hollow Core Slab under Successive Impact Loading

In Lebanon and many other countries where structures are vulnerable to impact loads caused by accidental rock falls due to landslides, specifically bridges with hollow core slab, it is mandatory to develop safe and efficient design procedures to design such types of structures to withstand extreme cases of loading. The structural response of concrete members subjected to low velocity high falling weight raised the interest of researchers in the previous years. The effect of impact due to landslide falling rocks on reinforced concrete (RC) slabs has been investigated by many researchers, while very few studied the effect of impact loading on pre-stressed structures, noting that a recent study was conducted at Beirut Arab University which compared the dynamic behavior of reinforced concrete and post-tensioned slabs under impact loading from a 605 kg impactor freely dropped from a height of 20 m. Hollow core slabs are widely used in bridges and precast structures. Thus, studying their behavior due to such hazards becomes inevitable. This study focuses on these types of slabs. For a better understanding of the behavior, a full scale experimental program consists of testing a single span hollow core slab. The specimen has 6000 mm × 1200 mm × 200 mm dimensions with a 100 mm cast in a place topping slab. Successive free fall drops cases from 14 m height will be investigated on the prescribed slab having a span of 6000 m. This series of impacts will be held by hitting the single span hollow core slab at three different locations: center, edge, and near the support. The data from the testing program were used to assess the structural response in terms of experimental observations, maximum impact and inertia forces, structural damage/failure: type and pattern, acceleration response, and structural design recommendations. This research showed that the hollow core slab has a different dynamic behavior compared to the post tensioned and reinforced concrete slabs mentioned in the literature review section.