Measurement of the quality factor of a new low-frequency differential accelerometer for testing the equivalence principle.

A cryogenic differential accelerometer has been developed to test the weak equivalence principle to a few parts in 10(15) within the framework of the general relativity accuracy test in an Einstein elevator experiment. The prototype sensor was designed to identify, address, and solve the major issues associated with various aspects of the experiment. This paper illustrates the measurements conducted on this prototype sensor to attain a high quality factor (Q ∼ 10(5)) at low frequencies (<20 Hz). Such a value is necessary for reducing the Brownian noise to match the target acceleration noise of 10(-14) g/√Hz, hence providing the desired experimental accuracy.

Co-operation of the 5' and 3' untranslated regions of ornithine decarboxylase mRNA and inhibitory role of its 3' untranslated region in regulating the translational efficiency of hybrid RNA species via cellular factor.

The 5' untranslated region (UTR) has an inhibitory role in the translatability of ornithine decarboxylase (ODC) mRNA and of hybrid mRNA species, whereas the ODC 3' UTR causes a partial release of this inhibition. We designed experiments to explore whether the co-operation between ODC 5' UTR and 3' UTR in the translational regulation is due to a direct interaction of those sequences or whether it is mediated by their interaction with cellular factor(s). We stably transfected Chinese hamster ovary (CHO)-K1 cells and transiently transfected COS-1 cells with expression vectors carrying different chimaeric DNAs having the luciferase (LUC) coding sequence as reporter gene, the ODC 5' UTR or the ODC 3' UTR, or both, in the appropriate positions. We compared the results obtained by assaying the LUC activities of both transfected cell lines with each chimaeric DNA with those observed by translating the hybrid RNAs in a translation system in vitro. When the ODC 3' UTR was present, we observed a partial release of the translation inhibition owing to the ODC 5' UTR only in vivo. The releasing effect was restored in vitro by the addition of cytoplasmic extracts from wild-type CHO-K1 or COS-1 cells, prepared 2 and 8 h after their release from serum starvation. We also observed a partial inhibition of the translatability of the hybrid RNA owing to the presence of the ODC 3' UTR itself; the translational efficiency could be rescued by cell extract from 8 h serum-stimulated cells. The co-operation between the ODC-UTRs might be mediated by factors expressed by cells during particular phases of the cell cycle. Excess copies of the ODC-UTRs, expressed in trans, could compete in binding limited amounts of such regulatory factors and remove them from interaction with the endogenous ODC mRNA. This phenomenon should be reflected by modifications of the kinetics of ODC and/or LUC activities during serum stimulation. The overexpression of the ODC 3' UTR determined an increase in both endogenous ODC activity and LUC activity. Moreover, in the transfectants expressing the hybrid RNA species bearing the ODC 3' UTR the basal ODC activity is higher than that observed in control cells. We suggest that excess copies of the ODC 3' UTR mis-regulate the endogenous ODC translatability, probably by tying up regulatory molecules expressed by cells in limited amounts and sequestering them from the ODC mRNA species they should interact with.

Enhanced levels of biochemical markers for cobalamin deficiency in totally gastrectomized rats: uncoupling of the enhancement from the severity of spongy vacuolation in spinal cord.

The totally gastrectomized (TGX) rat is a new experimental model for studying the pathogenesis of cobalamin (Cbl)-deficient myelopathy, i.e., subacute combined degeneration, total gastrectomy (TG) serving as a surgical paradigm of human pernicious anemia. We determined the serum levels of some biochemical indicators of Cbl deficiency in TGX rats at 2 to 10 months after TG. Methylmalonic acid (MMA) rose within 2 months and progressively increased thereafter until the end of the investigation period. 2-Methylcitric acid (MCA) rose significantly by 6 months and showed a further increment 4 months later. Homocysteine was only clearly elevated much later than the serum MMA, i.e., 10 months after the operation. The concentrations of MMA, MCA, and cystathionine were increased in kidney, liver, and spinal cord (SC) of TGX rats at 10 months. Chronic treatment of TGX rats with Cbl greatly decreased the serum levels of all the metabolic indicators of Cbl deficiency. Chronic peroral administration of the antibiotic lincomycin to TGX rats in an attempt to suppress the enteric flora markedly decreased serum MMA levels. Only Cbl, however, given either for the first 2 months after TG or for the third and fourth postoperative months (i.e., after SC abnormalities had already appeared) significantly decreased the severity of spongy vacuolation in SC white matter, although not completely preventing or repairing the neuropathological damage. Therefore, neither the early impairment in TGX rats of the Cbl-dependent methylmalonyl-coenzyme A mutase reaction nor the more delayed impairment of the Cbl-dependent methionine synthase step, as reflected by changes in serum metabolite levels, seems to be causally related to the TG-induced spongy vacuolation in SC white matter.

Different patterns of expression of ornithine decarboxylase mRNAs in rat liver after acute administration of hepatocarcinogens.

In the present study, we have evaluated the induction of ornithine decarboxylase (ODC) activity in rat liver after acute in vivo administration of different hepatocarcinogens, and correlated the ODC activity peaks with the accumulation of the three ODC-related mRNA species in rat liver at different times after the intraperitoneal injection of different hepatocarcinogens. ODC activity peaked 16 h after 2-acetylaminofluorene (2-AAF) treatment, while accumulation of the three ODC-mRNAs, starting 4 h after the injection, was maximal 6 h later. Thioacetamide (TAA) administration caused a single peak of ODC activity 20 h after treatment, while there had been the maximum increases of the three ODC-mRNAs 4-h earlier. The first ODC activity peak occurred 20 h after treatment with 3'-methyl-4-(dimethylamino)azobenzene (MDAB), at the same time that accumulation of the ODC-mRNAs was maximum. There was no increase in ODC-mRNA accumulation at 28 h or 36 h after MDAB treatment, the time at which ODC activity once again peaked. All the ODC-related transcripts accumulated after MDAB treatment, although to different degrees. The 1.7 kilobase (kb) transcript accumulated the most after 2-AAF treatment. After TAA treatment, the 2.2 kb mRNA was the most abundantly expressed. In neonatal liver, in which ODC activity is physiologically high, the 1.7 kb mRNA is expressed more abundantly than the other two ODC-related transcripts. These results demonstrate that the peak of ODC enzyme activity does not always correspond in time with the peak of ODC-mRNA accumulation; that different hepatocarcinogens induce different patterns of accumulation of the ODC-related transcripts; and that the minor ODC-related transcript (1.7 kb) in rat liver seems to be expressed not only constitutively but is also inducible.

Subacute combined degeneration in the spinal cords of totally gastrectomized rats. Ornithine decarboxylase induction, cobalamin status, and astroglial reaction.

BACKGROUND: The totally gastrectomized (TGX) rat is a new experimental model with which to produce widespread spongy vacuolation in spinal cord (SC) white matter, strongly reminiscent of that observed in subacute combined degeneration (SCD) of human SC. EXPERIMENTAL DESIGN: We did in long-term experiments combined biochemical and histologic studies on SCs from both TGX-rats and rats fed a cobalamin-deficient (Cbl-D) diet. We also investigated the effects of single in vivo administration of some neurotrophic growth factors on the activity of L-ornithine decarboxylase (ODC) (the key-point in the polyamine biosynthetic pathway) in rat SC. RESULTS: Biochemically, ODC activity was still induced 3 and 6 months after total gastrectomy (TG), while it did not change significantly even after 9 months of feeding a Cbl-D diet. Both TG and feeding the Cbl-D diet greatly decreased the cobalamin level in both serum and SC, although these decreases occurred more slowly in rats fed a Cbl-D diet. Nerve growth factor did not induce ODC in either Cbl-D myeloneuropathy; epidermal growth factor induced ODC in both Cbl-D myeloneuropathies. Basic fibroblast growth factor induced SC ODC only in TGX-rats. Histologically, spongy vacuolation was still widespread 3 and 6 months after TG, while it was spotty even after 9 months of feeding a Cbl-D diet. There was massively increased staining of astrocytes positive for glial fibrillary acidic protein, mainly in the gray matter, in both Cbl-D myeloneuropathies. Finally, repeated in vivo injections of cobalamin to TGX rats only partially reduced ODC induction, the severity of spongy vacuolation, and the increase in glial fibrillary acidic protein-positive astrocytes. CONCLUSIONS: These results suggest: (a) ODC induction is a persistent and inherent feature in the TG-induced SCD of rat SC; (b) an increase in glial fibrillary acidic protein positive astrocytes in rat SC is not mandatorily connected with an increase in polyamine biosynthesis; (c) a mere deficiency of Cbl seems to be not the only key-point in the pathogenesis of the ODC induction and of the SCD-like lesions, both brought about in rat SC by TG.

Subacute combined degeneration and induction of ornithine decarboxylase in spinal cords of totally gastrectomized rats.

Totally gastrectomized rats have been used to induce a spongy demyelination in the white matter of the spinal cord (SC) which is strongly reminiscent of that observed in subacute combined degeneration of human SC. Totally gastrectomized rats are deprived of intrinsic factor and thereafter become deficient in cobalamin. Morphologically, the spongy demyelination of the white matter of the rat SC, was evident 2 months after total gastrectomy. Biochemically, we investigated the hypothesis that polyamine biosynthesis might be deranged in the rat SC with experimental subacute combined degeneration, since polyamines are well known to be bound to myelin in the mammalian central nervous system. We measured the levels of both the polyamine biosynthetic decarboxylases, L-ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase, the key points in the polyamine biosynthetic pathway, in these SC. There was a sharp increase in ODC activity in SC 2 months after total gastrectomy, without significant changes in S-adenosyl-L-methionine decarboxylase activity. The increase in ODC activity seems to be organ-specific and was not due to a proliferation of neuroglial cells. Interestingly enough, the same morphologic and biochemical features found in SC of 2-month-totally-gastrectomized rats were present also in SC of newborn rats, which indeed showed incomplete myelination, vacuolated appearance, and an ODC activity level higher than that of adult SC. Therefore, total gastrectomy seems to induce a type of regression in the SC of totally gastrectomized rats toward neonatal life, at least in terms of the degree of myelination and of ODC activity level. Biochemically, no changes in ODC activity were observed in SC of rats fed a cobalamin-deficient diet for 3 months. Morphologically, only a proliferation of neuroglial cells with a moderate demyelination was observed in SC of these rats maintained on a cobalamin-deficient diet for 3 months.

Polyamine biosynthetic decarboxylases in muscles of rats with different experimental myopathies.

The activities of the two polyamine biosynthetic decarboxylases (PBD), L-ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase (SAMD), have been measured in quadriceps femoris of rats killed at different times after the induction of calciphylaxis- or serotonin(5-HT)-induced myopathy. Decreases in both PBD levels were observed at early times after both myotoxic treatments. Subsequent progressive increases in both enzyme levels were observed to nearly control values by 4 days after 5-HT administration. In the 5-HT-treated rats, the effects on the myocardial PBD activities were different from those in skeletal muscle, with no effect on ODC but much on SAMD, when rats were killed shortly after 5-HT injection. These results demonstrate that the time-course of the changes in PBD activities in quadriceps femoris mirrors quite well the successive occurrence of degenerative and regenerative processes during the calciphylaxis-induced myopathy and the 5-HT-induced myopathy; it is 5-HT that is mainly responsible for the decreases in PBD levels observed in both experimental myopathies, since dihydrotachysterol alone was without any effect on PBD activity levels and 5-HT alone was effective; myocardial ODC reacts more slowly to 5-HT than quadriceps femoris ODC.