Population synchronized

The bacterial culture converts a portion of the supplied nutrient into vegetative cells, spores, crystalline protein toxin, soluble toxins, exoenzymes, and metabolic excretion products by the time of complete sporulation of the population. Although synchronous growth is not necessary, nearly simultaneous sporulation of the entire population is desired in order to obtain a uniform product. Depending on the manner of recovery of active material for the product, it will contain the insolubles including bacterial spores, crystals, cellular debris, and residual medium ingredients plus any soluble materials which may be carried with the fluid constituents. Diluents, vehicles, stickers, and chemical protectants, as the individual formulation procedure may dictate, are then added to the harvested fermentation products. The materials are used experimentally and commercially as dusts, wettable powders, and sprayable liquid formulations. Thus, a... 

Regardless of the underlying etiology, all seizures involve a sudden electrical disturbance of the cerebral cortex. A population of neurons fires rapidly and repetitively for seconds to minutes. Cortical electrical discharges become excessively rapid, rhythmic, and synchronous. This phenomenon is presumably related to an excess of excitatory neurotransmitter action, a failure of inhibitory neurotransmitter action, or a combination of the two. In the individual patient, however, it is usually impossible to identify which neurochemical factors are responsible. 

The term seizure denotes a fleeting change of behavior caused by the disordered, synchronous and rhythmic firing of populations of neurons 629... 

By the early 1960s it was clear that simple experiments on P uptake were inadequate to distinguish different species of RNA in mixed populations of cells at different stages of the cell cycle. The future for labeling experiments with 32P in cell biology was to lie mainly with synchronized cells and for studies on nucleic acids, with molecular biological techniques. 

For a mutation that occurs at the very edge of the total population wave, 0, the transport speed is equal to the speed of propagation front, v = c the two waves, of the total population and of the mutation, are synchronized. 

The question of how glycolytic oscillations synchronize in a population of yeast cells is of great current interest [51]. It has long been known that the oscillations disappear in a yeast suspension when the cell density decreases below a critical value. Acetaldehyde appears to act as synchronizing factor in such suspensions [52], and the way it allows cells to synchronize is being... 

P. Richard, B. M. Bakker, B. Teusink, K. Van Dam, H. V. Westerhoff, Acetaldehyde mediates the synchronization of sustained glycolytic oscillations in populations of yeast cells. Eur. 

The olfactory system of the male is extremely sensitive to 17,20jSP. The fish respond to a concentration of 5 x 10 ° mol/1. This amount(3 x 10 molecules) is released by a 90 mm female fish into 1 liter water. The females are also very sensitive to 17,20/3P. It may stimulate ovulation. Of 47 vitellogenic females 13 ovulated when 17,20/3P was added to the water, while only 1 of 43 did so in untreated water (Dulka etal, 1987). Both sexes probably release 17,20/3P. Ecologically, this bisexual pheromone is thought to synchronize milt production with ovulation and thus coordinate spawning in local populations (Dulka etal, 1987 Sorensen and Stacey, 1990). 

These same authors also report a dose-dependent increase in the apoptotic rate after the administration of gemcitabine (33), which they believe correlates with the elimination of the more radioresistant S phase population of cells and redistribution of the remaining cells into more radiosensitive compartments of the cell cycle. They also report in another study that reoxygenation of the resistant hypoxic fraction of tumor cells is also a mechanism for the action of gemcitabine (34). Therefore, elimination of these S phase tumor cells may aid the radiation response by not only causing cell cycle synchronization but also by leading to reoxygenation of hypoxic cells. 

This classification of anticancer drugs has inherent limitations. For instance, it may be difficult to generalize about the phase specificity of a particular drug, since this may vary among cell types. Several techniques are available to synchronize cell populations in such a way that most cells will be in the same phase of the cell cycle. After synchronization, one can treat cells in each phase and determine their relative sensitivity to drugs throughout the cell cycle. 

In a population of animal cells undergoing synchronous division, some CDK activities show striking oscillations (Fig. 12-43). These oscillations are the result of four mechanisms for regulating CDK activity phosphorylation or dephosphorylation of the CDK, controlled degradation of the cyclin subunit, periodic synthesis of CDKs and cyclins, and the action of specific CDK-inhibiting proteins. 

A note of caution must be inserted at this point. It appears, at first sight, that there is a meaning that can be attached to the absolute phase of the field and to the phases of the molecular expectation values. However, it must be remembered that the phase of the molecular quantity is induced by the radiation field prior to the present time. Therefore all phases must be related to the phase of a previous pulse that synchronizes the molecular clock with the field clock. With this synchronization it is possible to understand how quantum mechanical interference between events induced in the past propagates and can be used to control energy and/or population transfer at a later time. 

Figure 12.6 Plasmid nuclear localization must precede gene expression. Synchronized TC7 cells were cytoplasmically microinjected with 1000 copies of GFP-expressing plasmids (Dean et al., 1999b). After microinjection, the cells were scored for GFP expression as a function of time. The injected plasmids expressed GFP from the CMV immediate early promoter/enhancer and either contained (open circles) or lacked (closed circles) the SV40 enhancer downstream of the GFP gene. The dotted line represents the time of cell division in this population. As can be seen, plasmids without the SV40 enhancer failed to localize to the nucleus and gave no GFP expression, while plasmids containing the sequence began to express gene product within several hours of cytoplasmic injection.

We have found that using mature females as embryo donors is a key deviation from standard transgenic mouse production practices. The mature females typically produce fewer oocytes compared to pre-pubescent females, but the oocytes that are released tend to yield more developmentally synchronized populations of zygotes as well as zygotes of similar quality and injectibility. ... 

As evidenced by Figure 10.15, some asynchronous motion does exist for this sample within the 2990 cm"1 band. The intensity of this behavior is an order of magnitude less than the synchronous motion, as noted by the scales of the maximum contour levels in both plots. This asynchronous data suggests that the two populations of C-H bonds (those on the backbone carbons, and those associated with the methyl groups) do not precisely orient in phase with one another. Since these data were collected at a frequency above the mechanical glass transition, this could be a manifestation of the appearance of glassy modes of re-... 

During a cycle of an oscillation a number of PNs spike in synchrony (Laurent and Davidowitz, 1994 Wehr and Laurent, 1996). Other neurons may spike as well but are not phase locked to any cycles. The population of neurons acting in synchrony is dependent on the stimulus identity. Thus, a different odor evokes synchronous activity in another (but often overlapping) subset of PNs. 

The results of simulations indicate that, when the circadian delivery of 5-FU peaks at 4 a.m., differential effects of the drug on a population of healthy cells and on a population of tumor cells may be observed depending on whether the two cell populations are entrained or not by the circadian clock [33]. Another source of differential effect pertains to the degree of variability, given that, as previously noted, synchronization of the cells minimizes cytotoxic damage when the circadian 5-FU modulated delivery pattern peaks at 4 a.m. The results are markedly different when the circadian pattern of 5-FU delivery peaks at 4 p.m. [33]. Then the cytotoxic effect of the drug on the two populations is the inverse as that predicted for the circadian pattern peaking at 4 a.m. The effect of variability therefore depends on the circadian pattern of 5-FU delivery and on the possibility of entrainment of the cell cycle by the circadian clock. 

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