Resistant population

Powell, W.R., Bright, S., and Bello, S.M. (2000). Developmental and tissue-specific expression of AHRl, AHR2, and ARNT2 in dioxin-sensitive and -resistant populations of the marine fish—Fundulus heteroclitus. Toxicological Sciences 57, 229-239. 

Tricyclic antidepressants can be used with caution by experienced clinicians in treatment-resistant populations. 

A field trial was conducted using 0.005% bromethalin bait against a resistant population of house mice in a poultry house. Resistance had been verified by using the standard WHO laboratory procedure. About two-thirds of the mice tested were resistant to warfarin. Control was achieved under extremely difficult conditions (i.e., extremely large population with an abundant food supply in a complex physical environment). 

Thus, although few controlled studies have been performed in well-characterized treatment-resistant populations, further studies using these techniques would prove useful in determining the role of these interventions in the treatment of refractory major depressive disorder. 

Using the knowledge of the development of resistance to synthetic chemicals, one can predict that an organism encountering a new inhibitory NP in its food source, or in its environment, will evolve a capacity to adapt to the new chemical. By behavioural choices, or by chance circumstances, some individuals in the population will not be exposed to a lethal dose of the NP and the descendants of those individuals will eventually form resistant populations. 

Another issue is subjects who volunteer for an advertised study. Undoubtedly, some will have the true disorder, but others, although responding to an advertisement, may only minimally meet symptom criteria and may not have spontaneously sought help otherwise. This situation is particularly apparent when the disorder approximates normal emotions or problems. Some symptomatic volunteers may include newly recognized classic cases, whereas patients referred to a tertiary referral center may be an atypical, treatment-resistant population. 

At one time, TCAs were thought to be more effective than the MAOIs, but recent investigation has found these two classes equally effective ( 184). The poorer showing in some of the earlier studies was the result of subtherapeutic doses of MAOIs administered to treatment-resistant populations (e.g., psychotic depressions, which are... 

The question is not whether there may be in vitro evidence but whether residue levels, singly or in combination, can select for resistant populations in vivo experiments. Under in vivo conditions, an antimicrobial residue that is stable to cooking processes would have to move through the stomach and the intestine, would then be metabolized during the passage or would be absorbed and excreted. A portion of it will not occur in the colon, the site of this specific action. Only a small portion of the ingested dose will reach the colon and remain there for a certain time, since many conditions have an influence upon the final concentration at the site of action in the colon. 

Observed differences between strains of rats and mice, as described below, may be the result of gene polymorphisms. In cases involving insecticide selection pressure, resistant populations may arise as a result of direct mutations of insecticide-metabolizing enzymes and/or insecticide target sites that are passed on to succeeding generations. 

Moss, S.R. and G.W. Cussans (1991). The development of herbicide-resistant populations of Alopecurus myosuroides (black-grass) in England, pp. 45-55. In Caseley, J.C., G.W. Cussans, and R.K. Atkin, eds., Herbicide Resistance in Weeds and Crops. Oxford, UK Butterworth-Heinemann. 

Gaeddert et al. (1997) found that cross-resistance of the ALS-resistant Palmer amaranth biotype occurred among 16 postemergence ALS herbicides evaluated. Sprague et al. (1995) found that two suspected resistant populations of Palmer amaranth and common waterhemp were resistant to imazethapyr and cross-resistant to the sulfonylureas, chlorimuron and thifensulfuron, at 10 times higher than labeled rates. 

Anderson et al. (1995, 1998a, b) reported that a primisulfuron-resistant shattercane biotype found after 3 years of consecutive treatments was cross-resistant at all rates of primisulfuron, nicosulfuron, and imazethapyr. Lee et al. (1999) found that when shattercane from three resistant accessions were intercrossed, all the F2 populations were resistant to primisulfuron, indicating that the ALS-resistant alleles in the three accessions were at the same locus, or possibly linked loci. When the accessions were crossed with the wild type, comparisons between the F1 susceptible, and resistant populations showed that primisulfuron resistance was expressed as a dominant, partially dominant, and additive trait. 

We are learning from experience and research that there are problems in crop production from repeated use of herbicides without mixing partners, or without alternating the use of herbicides with different modes of action. Not only do the resistant weeds become problems, but they lead to additional applications of the herbicides, adding further expense and further pressure to the development of resistant populations. 

Bader, B.M., M.S. DeFelice, J.S. Dilbeck, and C.S. Holman (1995). Effect of ALS herbicide programs on common waterhemp and shattercane resistant populations. Proc. North Cent. Weed Sci. Soc., 50 131-132. 

Depending on the nature of the drug and on the method of evaluation, the measurement of a recovery period could result in underestimation or overestimation of any lethal effect on cells. It is important that the recovery period is not very long, since cell death could be masked by a resistant population growth. 

Figure 6.6 Within- and between-population variation in desiccation resistance (A) and cuticular lipid quantity (B) as a function of body melanization in northern and southern Indian populations of Zaprionus indianus and Drosophila melanogaster. In both species, populations from drier (northern) habitats are more desiccation resistant. The desiccation-resistant population of D. melanogaster is melanic, whereas desiccation resistance in Z. indianus is correlated with higher amounts of surface lipids. From Parkash et al. (2008a) reproduced with permission.

The relatively low development of resistance is also reflected in the low MPC [245], which defines the threshold concentration of anti-infectives sufficient for preventing the development of resistant populations. For clinical use, the MPC must be below the serum concentration or the concentration in the infected tissue. This requirement is met by the 8-methoxy quinolones moxifloxacin and gati-floxacin [246]. Tests carried out on l-cyclopropyl-7-piperazinyl-quinolones showed... 

Tolyporphyrin A from the microalga Tolypothrix nodosa reverses multidrug resistance in a Vinblastine-resistant population of human ovarian adenocarcinoma cells. In a synthesis of Tolyporphin A, four 0-benzyl groups were cleaved from the C-glycoside rings of 150.1 [Scheme 4.150] using zinc chloride and ethane-... 

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