dCTP misincorporation in a Chinese hamster mutator phenotype: the role of GGA genetic context

Clone CSA7 is a CHEF18 hamster cell line that shows an increasedintracellular accumulation of dCTP. To localize the mutationsthat accumulate spontaneously in a functional gene of such amutator phenotype, independent CSA7 mutants of the hypoxanthine–guaninephosphoribosyl transferase (hprt) gene were isolated and screenedby a polymerase chain reaction–single strand conformationpolymorphism technique. Sixty-two percent of mutants produceddetectable changes of the strand migration profile and the mutationswere preferentially localized in the exons 3 (31%) and 6 (62%).The sequencing of such exons revealed that the rate of C baseincorporation was the major mutation pathway and that the Abase of a GGA sequence was the preferential site of misincorporation. ³To whom correspondence should be addressed     

Desensitization of AMPA Receptors Limits the Amplitude of EPSPs and the Excitability of Motoneurons of the Rat Isolated Spinal Cord

Intracellular recording was used to study the effect of cyclothiazide, a selective blocker of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor desensitization, on lumbar motoneurons of the rat isolated spinal cord. Cyclothiazide (25 μM) enhanced the responses to AMPA in a tetrodotoxin-insensitive fashion, without affecting those produced by N -methyl-D-aspartate or γ-aminobutyric acid. Excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation were strongly potentiated in amplitude while paired-pulse depression (produced by applying pairs of pulses at 2 s interval) of the EPSP was decreased. In the presence of cyclothiazide the frequency of spontaneous synaptic events was greatly increased and network-driven bursting activity developed with eventual loss of electrical excitability. The present results suggest that pharmacological block of AMPA receptor desensitization led to strong excitation of motoneurons and indicate a physiological role of desensitization in protecting these nerve cells from overactivity.     

An evaluation of Tourette Syndrome and medication use in Canada

Self-report data were gathered from a national sample of over 200 Canadian Tourette Syndrome (TS) patients. Information regarding symptom severity both on and off medication was gathered along with an analysis of different medications in use, and patient ratings of effectiveness of those medications. Patients also rated their own mental health. Results indicated that approximately 60% of TS patients take some form of medication for relief from their symptoms. Of these, over 80% reported that symptoms are less severe when medicated. The most commonly prescribed medications in order of popularity are haloperidol, pimozide, clonidine and benztropine mesylate (Cogentin). Patient ratings of effectiveness of these medications places haloperidol first, pimozide second and clonidine third although all were found to be "somewhat" to "very" effective. Of those TS patients on medications, 50% rated their own mental health as good to excellent and 50% rated it as fair to poor.     

The potential role of lonidamine (LND) in the treatment of malignant glioma

Summary Up-to-date unsatisfactory results obtained in multimodality treatments of malignant glioma have prompted the research of new therapeutic modalities with unconventional modes of action. Lonidamine (LND) is a drug which reduces aerobic glycolytic activity in both human and experimental tumors. This effect mainly depends on the inhibition of mitochondrially-bound hexokinase (HK) which is present in large amounts in malignant cells. A Phase II study was conducted on patients with recurrent glioma; 12 patients were admitted to the study. Clinical side effects were moderate, necessitating a reduction of the dosage in only 1 case. The objective results were evaluated according to the indications of Levin. 2 responders and 3 cases of stable disease were observed out of 10 evaluable patients. The potential value of this new drug is discussed.     

Increased circulating interleukin-7 levels in HIV-1-infected women

Sex-based differences in CD4 T-cell (CD4) counts are well recognized, but the basis for these differences has not been identified. Conceivably, homeostatic factors may play a role in this process by regulating T-cell maintenance and repletion. Interleukin (IL)-7 is essential for normal T-cell production and homeostasis. We hypothesized that differences in IL-7 might contribute to sex-based differences in CD4 counts. Circulating IL-7 levels were analyzed in 299 HIV-1-infected women and men. Regression analysis estimated that IL-7 levels were 40% higher in women than in men (P = 0.0032) after controlling for CD4 count, age, and race. Given the important role of IL-7 in T-cell development and homeostasis, these findings suggest that higher IL-7 levels may contribute to higher CD4 counts in women.     

Detecting danger--or just another odorant? Olfactory sensitivity for the fox odor component 2,4,5-trimethylthiazoline in four species of mammals

2,4,5-trimethylthiazoline (TMT) is a volatile component of the anal gland secretion of the red fox and elicits behavioral and physiological fear responses in the rat. Using instrumental conditioning paradigms, we determined olfactory detection thresholds for TMT in three rats, a natural prey species of the red fox, and compared their performance to that of three squirrel monkeys, three spider monkeys and four pigtail macaques, all non-prey species of the red fox. We found that the rats were able to discriminate concentrations between 0.04 and 0.10 ppt (parts per trillion) of TMT from the odorless solvent which is by far the lowest olfactory detection threshold for an odorant reported in rats so far. In contrast, the spider monkeys needed 0.14-1.38 ppb (parts per billion), the pigtail macaques 0.41-4.07 ppb, and the squirrel monkeys 4.07-13.80 ppb to detect TMT which does not rank among the lowest olfactory thresholds reported for these three primate species. Thus, these results support the assumption that the behavioral relevance of an odorant may be an important determinant of a species' olfactory sensitivity.     

Adsorption of serum fetuin to hydroxylapatite does not contribute to osteoblast phenotype modifications

Osteoblasts exhibit enhanced differentiation and altered gene profiles when cultured on hydroxyapatite (HA) compared to plastic surfaces. To begin determining mechanisms for this response, we used proteomics to identify proteins predominantly found in osteoblasts on HA but not plastic surfaces. Two-dimensional gel electrophoresis and Western analyses indicate that fetuin is abundant in extracts from HA, but not plastic surfaces. Incubation of HA and plastic surfaces with cell culture medium (containing 10% serum) under cell-free conditions shows that fetuin is predominantly derived from the culture medium serum and readily adsorbs to the HA surface. However, we did detect low levels of fetuin B mRNA in osteoblasts. Serum albumin, actin-beta, apolipoprotein-AI, and vimentin also adsorbed to HA. To determine the role of fetuin in the HA-induced osteoblast phenotype changes, osteoblasts were seeded onto fetuin-coated or uncoated HA under serum-free conditions. Osteoblast morphology was similar on both HA surfaces, suggesting that HA alone (without adsorbed serum proteins) is sufficient for cell attachment and spreading. Similarly, genes previously reported to be modulated by HA (glvr-1, DMP-1, osteoglycin, and proliferin 3) were modulated even in the absence of fetuin or other serum proteins. These data show that HA surface can be enriched selectively with fetuin from serum; however, neither fetuin or other serum proteins are required to mediate HA-induced osteoblast attachment, spreading, or changes in expression of genes examined. This finding suggests that factors intrinsic to HA are required for the response.     

Analysis of aberrant somatic hypermutation (SHM) in non-Hodgkin's lymphomas of patients with chronic HCV infection

Hepatitis C virus (HCV) and aberrant somatic hypermutation (SHM) have each been suggested to contribute to the development of B-cell non-Hodgkin's lymphoma (NHL). The incidence of PIM-1, PAX-5, RhoH/TTF, and c-MYC mutations in tumour biopsy specimens from 32 HCV-infected B-cell NHL patients was analysed to determine whether the extent of aberrant SHM among these patients differed from that previously reported for HCV-negative B-cell NHL patients. Mutation of PIM-1, PAX-5, RhoH/TTF, and c-MYC was detected in 4 (13%), 5 (16%), 4 (13%), and 4 (13%) of 32 samples, respectively. In HCV-positive B-cell NHL patients, the frequency of aberrant SHM was lower than that already found in HCV-negative B-cell NHL patients. This indicates that, unlike B-cell lymphomas from HCV-negative patients, aberrant SHM may not contribute significantly to malignant transformation in HCV-associated B-cell lymphomas.     

Homeostasis and the age-associated defect of CD4 T cells

Survival and homeostatic division of naive CD4 T cells is regulated by the cellular and non-cellular milieu and together these processes ensure that a population of naive CD4 T cells persists into old age. However, the naive CD4 T cells from aged animals show reduced IL-2 production, proliferation, helper function and effector generation and memory function. We explore here whether the age-related defects in naive CD4 T cells are due to the aged environment from which they come or to intrinsic defects that are caused by homeostasis and their long lifespan.