A simple model of the photosynthetic unit has been constructed and used for simulated Förster-type energy migration, fluorescence and intersystem crossing, in order to gain insight into the conditions that influence both the form and the lifetime of the fluorescence decay in vivo. The model consists of a two-dimensional random lattice with one central trap. The simulation was done by means of repetitive Monte Carlo-type computations. The results obtained show that the form of the decay curve changes from exponential to non-exponential, as the chlorophyll concentration (molecules/nm2) is increased. The fluorescence lifetimes (tau 1/e) were also found to decrease substantially with only slight increases inc concentration. At a concentration comparable to that of chlorophyll in the chloroplast, both the form of the fluorescence decay and the lifetime are in fair agreement with experiment in vivo. The reasons for non-exponentially of the decay as well as the properties of energy migration are discussed. Preliminary work involving the dependence of trapping rate on donor concentration is also presented.

Computers↗

PubMedDate not supplied

Influences of adenosine on the fetus and newborn.

Few signaling molecules have the potential to influence the developing mammal as the nucleoside adenosine. In contrast to most neurotransmitters, adenosine is released by all cells and is present in all tissues. The adenosinergic system is therefore not dependent on the presence of mature synaptic structures or an intact autonomic nervous system for its release. However, similar to other signaling molecules, adenosine levels are dynamically regulated and increase with increased tissue activity, hypoxia, or stress. Local adenosine concentrations thus provide a "humoral barometer" of acute changes in cellular physiology. The receptors that transduce adenosine action include A1, A2a, A2b, and A3 adenosine receptors. These receptors differ in their affinities for adenosine and in patterns of tissues expression. During development A1 adenosine receptors (A1ARs) are especially important, and A1ARs are among the earliest receptors expressed in the embryonic brain and heart. In the developing heart, the adenosinergic system is the dominant regulator of fetal cardiac function and A1AR activation inhibits cardiac cell division leading to cardiac hypoplasia. In the forming central nervous system, A1AR activation potently inhibits the development of axons and can lead to leukomalacia. These recent data suggest that adenosine is an important modulator of mammalian development.

Adenosine↗

PubMedDate not supplied

Imaging of plantaris muscle rupture.

Rupture of plantaris muscle is demonstrated in two patients, one with magnetic resonance imaging (MRI) and one with ultrasound. This entity, thought to be clinically common, has never before been demonstrated at surgery or with imaging. Anatomic and physiologic aspects of the diagnosis that enable radiologists to make the diagnosis, once familiar with the entity, are discussed.

Adult↗

PubMedDate not supplied

Wavy pelvis sign in CT of multiple hereditary osteochondromatosis.

We report three patients with multiple hereditary osteochondromatosis with pelvic CT findings indicating the presence of multiple small osteochondromata. Despite normal appearance of plain radiography in these cases, a characteristic wavy appearance of pelvic brim, which has not been described to date, was clearly shown in all three cases. The finding of wavy pelvis may indicate that pelvic osteochondromata are not as rare as indicated by plain radiographic studies and that malignant degeneration in pelvic osteochondromata may be related to their high incidence. One of these patients had an intracapsular hip joint loose body, originating from femoral neck osteochondroma. This complication is previously unreported.

Adult↗

PubMedDate not supplied

Wee care: reaching teenage mothers and changing their lives.

Explore the source record for details and available documents.

Adolescent↗

PubMedDate not supplied

Development of a nude mouse model of ras-mediated neoplasia using WR21 cells from a transgenic mouse salivary tumor.

A novel cell line (WR21) was derived from a salivary tumor in a male wap-ras transgenic mouse. Salivary tumors in wap-ras transgenic mice are extremely aggressive and express high levels of oncogenic ras protein from the activated, human Ha-ras transgene. WR21 cells also expressed high levels of oncogenic ras protein in vitro and in vivo. They gave rise to aggressive, highly anaplastic solid tumors when injected subcutaneously into athymic nude mice and approximately 90% of the mice had lung metastases by the fifth week of tumor growth. WR21 tumors were inhibited by cyclophosphamide, 5-fluorouracil, adriamycin, mitomycin C and actinomycin D, but not methotrexate. Our results suggest that the WR21/nude mice model will be useful for testing the efficacy of drug therapies against ras-mediated neoplasias.

Animals↗