4-Epidoxycycline: an alternative to doxycycline to control gene expression in conditional mouse models

Since the pioneering work by Gossen and Bujard in 1992 demonstrating the usefulness of the Escherichia coli derived tet resistance operon for regulating gene expression a large collection of doxycycline-controlled transgenic mice has been established. Gene switching in eukaryotic tissue culture cells or mice requires administration of tetracycline, anhydrotetracycline or doxycycline to efficiently inactivate the transactivator protein tTA (TET-OFF system) or alternatively to activate the reverse transactivator protein rtTA (TET-ON system). However, the antibiotic activity of doxycycline can create an imbalance of the intestinal flora, resulting in diarrhoea and in a smaller number of animals in colitis. Previous studies reported that 4-epidoxycycline (4-ED), a hepatic metabolite of doxycycline, does not function as an antibiotic in mice. This gave us the idea that 4-ED might be useful for controlling gene expression in mice without the unwanted antibiotic side effect. To study the applicability of 4-ED for control of gene expression we used cell lines expressing the oncogene HER2 under control of tTA (TET-OFF) as well as rtTA (TET-ON). 4-ED and doxycycline were similarly efficient in switching on or -off HER2 expression. In vivo we used a conditional mouse model that allows switching off HER2 in tumor tissue. We show that (i) doxycycline, 7.5mg/ml in drinking water (used as a positive control), (ii) 4-ED, 7.5mg/ml in drinking water, (iii) 4-ED, 10mg/kg body weight, s.c., and (iv) anhydrotetracycline, 10mg/kg, s.c. (used as a second positive control), were similarly efficient. Using mice with tumor volumes of 1.6cm(3) all four schedules led to a tumor remission of more than 95% within 7 days. In conclusion, 4-ED is similarly efficient as doxycycline to control gene expression in vitro and in mice. Since 4-ED lacks the antibiotic activity of doxycycline it may help to avoid adverse side effects and selection of resistant bacteria.

Dopamine-antagonistic, anticholinergic, and GABAergic effects on declarative and procedural memory functions

Declarative and procedural memory functions are related to dissociable neuroanatomic substrates. In the present study differential effects of pharmacologically induced changes in dopaminergic, GABAergic, and cholinergic activity in the brain on declarative (object and face recognition, immediate and delayed word recall) and procedural memory processes (compensatory tracking) were investigated. In a double-blind design, either 3 mg of haloperidol, 11 mg of midazolam, 1 mg of scopolamine, or placebo were administered to 80 healthy volunteers randomly assigned to one of the four drug conditions. Although all three drugs produced a detrimental effect on immediate and delayed word recall, recall performance was substantially more impaired by the benzodiazepine midazolam than by either haloperidol or scopolamine. While recognition of faces was affected by neither of the drugs, performance on object recognition was significantly decreased by midazolam as compared to placebo. Procedural learning was markedly impaired by all drugs but, again, the observed effect was most pronounced with midazolam. Additional analyses of measures of subjective activation, cortical arousal, and psychomotor performance argued against the assumption that the observed memory-impairing effects were secondary to drug-induced sedation. The overall pattern of results revealed that memory processes are much more susceptible to changes in GABAergic than in dopaminergic or cholinergic neurotransmitter activity. Furthermore, the present findings point to the conclusion that the modulating effects of dopaminergic, GABAergic, and cholinergic neurotransmitter systems on declarative and procedural memory functions are less specific than suggested by neuropsychological studies in patients.

Plain radiography with a rare-earth screen: comparison with calcium tungstate screen

Plain radiographic examinations were performed on 388 patients (adult and pediatric) using either a calcium tungstate or rare-earth screen. Radiographs were compared for overall image quality, mottle, contrast, density, and detail. The rare-earth screen produced radiographs with significantly more mottle than did the standard screen. However, this was almost never of diagnostic importance. A small but significant decrease in overall image quality also was found with the rare-earth screen. This was the result of minor differences between the grading of optimal and good. A major advantage of rare-earth screens is a 50% or more reduction in radiation exposure. The results here show that rare-earth screens may be used in plain radiographic examinations without a clinically important decrease in image quality.