Baseline frequency of sister-chromatid exchanges (SCE) in newborn lymphocytes and its relationship to in vivo aging in humans

Heparinised cord blood from newborns and peripheral venous blood from three other age groups of individuals (1-75 years) have been cultured in vitro to obtain baseline frequencies of SCE and to see if the frequency of baseline SCE in vitro varies as a function of aging in vivo. The results demonstrate an age-dependent variation in the frequency of SCEs. Although the SCE frequency was lowest (5.10/cell) in 1-5-year-old infants, a significantly higher (P less than 0.001) frequency (8.97/cell) was observed in the cord blood of newborns. In old age, the level of SCE also increased. The plausible reason(s) for such observations is discussed.     

Metabolic relevance of selenium in the insectCorcyra cephalonica

Requirement, uptake, and subcellular distribution of Na₂ ⁷⁵SeO₃ in the larvae of the insectC. cephalonica was investigated. That Se is well tolerated byC. cephalonica upto an added level of 2 ppm in the diet is suggested by the observed increase in body weight, total protein, and succinate dehydrogenase levels. Significant increases in the State 3 respiration ensued with Se supplementation up to 2 ppm in the mitochondrial oxidation of D-glycerol 1-phosphate, succinate and NADH, along with concomitant unaltered State 4 respiration, leading to enhanced RCR values. Maximal uptake of⁷⁵Se was registered in the larvae maintained on basal diet when subjected to short-term exposure to 0.5 ppm⁷⁵Se level. When exposure level was further increased up to 20 ppm, the observed decrease in the uptake of⁷⁵Se suggested that Se status of larvae itself controlled the tissue uptake. Subcellular distribution pattern revealed maximal incorporation of⁷⁵Se (cpm/g tissue) in the supernatant fraction, whereas, maximal specific⁷⁵Se activity (cpm/mg protein) was associated with the mitochondrial fraction. Autoradiography of the soluble fractions indicated the presence of single selenoprotein in the larval group with short term 2 ppm⁷⁵Se exposure. Inherent Se controls both the extent and the nature of distribution of mitochondrial⁷⁵Se incorporation. Uptake of⁴⁵Ca by the insect mitochondria was enhanced by dietary Se up to 2 ppm but was unaffected by addition ofin vitro ⁷⁵Se in the medium. A more fundamental role for Se in the mitochondrial energy metabolism emerges from these studies.     

Cell-bound cholinesterase inTrichoderma harzianum

Cell-bound cholinesterase enzyme activity is reported for the first time in the mycelium ofTrichoderma harzianum. This enzyme hydrolyzes both the acetylcholine and the butyryl thiocholine esters. TheK _m andV _max for choline ester are 0.69 mM and 1.0 nmol acid released min^–1 g^–1 protein. However, the thiocholine ester has aK _m value of 2.2 mM andV _max value of 3.33 nmol product formed min.^–1 g^–1 protein. The enzyme is inhibited by eserine, a true classical cholinesterase inhibitor.     

Protein sequences as random fractals

The analysis of primary sequences from a protein sequence data base suggests that the sequences can be considered as examples of constrained random fractals. Fractal dimensions of the positional distributions of the 20 residues along the chain have been calculated. These fractal dimensions can be used as indices of intrinsic preferences of various residues.     

Improved ethanol tolerance and production in strains of Clostridium thermocellum

Two Clostridium thermocellum strains were improved for ethanol tolerance, to 5% (v/v), by gradual adaptation and mutation. The best mutant gave an ethanol yield of 0.37 g/g substrate, with a growth yield 1.5 times more than its parent. Accumulation of acids and reducing sugars by the mutant strain with 5% (v/v) ethanol was lower than that of the parent strain with 1.5% (v/v) ethanol.     

Traveling Waves and the Processing of Weakly Tuned Inputs in a Cortical Network Module

Recent studies have shown that local cortical feedback can havean important effect on the response of neurons in primary visualcortex to the orientation of visual stimuli. In this work, westudy the role of the cortical feedback in shaping thespatiotemporal patterns of activity in cortex. Two questionsare addressed: one, what are the limitations on the ability ofcortical neurons to lock their activity to rotatingoriented stimuli within a single receptive field? Two, can thelocal architecture of visual cortex lead to the generation ofspontaneous traveling pulses of activity? We study theseissues analytically by a population-dynamic model of ahypercolumn in visual cortex. The order parameter thatdescribes the macroscopic behavior of the network is thetime-dependent population vector of the network. We firststudy the network dynamics under the influence of a weakly tunedinput that slowly rotates within the receptive field. We showthat if the cortical interactions have strong spatialmodulation, the network generates a sharply tuned activityprofile that propagates across the hypercolumn in a path thatis completely locked to the stimulus rotation. The resultantrotating population vector maintains a constant angular lagrelative to the stimulus, the magnitude of which grows with thestimulus rotation frequency. Beyond a critical frequency thepopulation vector does not lock to the stimulus but executes aquasi-periodic motion with an average frequency that is smallerthan that of the stimulus. In the second part we consider thestable intrinsic state of the cortex under the influence of isotropic stimulation. We show that if the local inhibitoryfeedback is sufficiently strong, the network does not settleinto a stationary state but develops spontaneous travelingpulses of activity. Unlike recent models of wave propagation incortical networks, the connectivity pattern in our model isspatially symmetric, hence the direction of propagation ofthese waves is arbitrary. The interaction of these waves withan external-oriented stimulus is studied. It is shown that thesystem can lock to a weakly tuned rotating stimulus if thestimulus frequency is close to the frequency of the intrinsic wave.     

Effects of a highly purified antiserum to FSH on testicular function in immature rats

Effects of highly purified antiserum (AS) to follicle stimulating hormone (FSH) on testicular function was studied in immature rats. Treatment with FSHAS for 10 days, from 25-34, decreased weights of the testis (p .001) and increased weights of the epididymis (p .05). Numbers of the cell types in the seminiferous epithelium, particularly Type A spermatogonia pachytene spermatocytes and spermatids, were markedly reduced, possibly due to: 1) decreased division of the initial stem cells, 2) impairment of division of Type B spermatogonia and their transformation to pachytene spermatocytes, and 3) desquamation and degeneration of pachytene spermatocytes and spermatids. FSHAS also affected the sertoli cell function which was reflected in the decreased binding of androgens to supernatant fraction of the testis and epididymides. Treatment with luteinizing hormone-AS for 5 days did not affect testicular function but the binding of androgens to the supernatants of the caput and cauda epididymides and ventral prostate was significantly reduced (p .001). These data indicate that FSH is necessary for the maintenance of the cellular integrity of the seminiferous epithelium during the completion of the 1st wave of spermatogenesis.     

Studies on follicular growth in the immature rat and hamster: Effect of a single injection of gonadotropin or estrogen on the rate of3H-thymidine incorporation into ovarian DNAin vitro

Initiation of follicular growth by specific hormonal stimuli in ovaries of immature rats and hamsters was studied by determining the rate of incorporation of³H-thymidine into ovarian DNAin vitro. Incorporation was considered as an index of DNA synthesis and cell multiplication. A single injection of pregnant mare serum gonadotropin could thus maximally stimulate by 18 hr³H-thymidine incorporation into DNA of the ovary of immature hamsters. Neutralization of pregnant mare serum gonadotropin by an antiserum to ovine follicle stimulating hormone only during the initial 8–10 hr and not later could inhibit the increase in³H-thymidine incorporationin vitro observed at 18 hr, suggesting that the continued presence of gonadotropin stimulus was not necessary for this response. The other indices of follicular growth monitored such as ovarian weight, serum estradiol and uterine weight showed discernible increase at periods only after the above initial event. A single injection of estrogen (diethyl stilbesterol or estradiol-l7β) could similarly cause 18 hr later, a stimulation in the rate of incorporation of³H-thymidine into DNAin vitro in ovaries of immature rats. The presence of endogenous gonadotropins, however, was obligatory for observing this response to estrogen. Evidence in support of the above was two-fold: (i) administration of antiserum to follicle stimulating hormone or luteinizing hormone along with estrogen completely inhibited the increase in³H-thymidine incorporation into ovarian DNAin vitro; (ii) a radioimmunological measurement revealed following estrogen treatment, the presence of a higher concentration of endogenous follicle stimulating hormone in the ovary. Finally, administration of varying doses of ovine follicle stimulating hormone along with a constant dose of estrogen to immature rats produced a dose-dependent increment in the incorporation of³H-thymidine into ovarian DNAin vitro. These observations suggested the potentiality of this system for developing a sensitive bioassay for follicle stimulating hormone.