A simple integrative electrophysiological model of bursting GnRH neurons

In this paper a modular model of the GnRH neuron is presented. For the aim of simplicity, the currents corresponding to fast time scales and action potential generation are described by an impulsive system, while the slower currents and calcium dynamics are described by usual ordinary differential equations (ODEs). The model is able to reproduce the depolarizing afterpotentials, afterhyperpolarization, periodic bursting behavior and the corresponding calcium transients observed in the case of GnRH neurons.     

Generation of altered transcripts by retroviral insertion within the c-myb gene in two murine monocytic leukemias

Two murine monocytic leukemia cell lines, WEHI-265 and WEHI-274, were found to carry a rearranged c-myb gene. The rearrangements are due to insertion of a deleted Moloney murine leukemia virus (Mo-MLV) provirus in the 5' region of the c-myb gene and thus are similar to rearrangements in the ABPL tumors (G. L. C. Shen-Ong, M. Potter, J. F. Mushinski, S. Lavu, and E. P. Reddy, Science 226:1077-1080, 1984). In each cell line, the retroviral insertion has induced high levels of two aberrant RNA species, which, as in the ABPL tumors (G. L. C. Shen-Ong, H. C. Morse, M. Potter, and J. F. Mushinski, Mol. Cell. Biol. 6:380-392, 1986), contain both viral (Mo-MLV) and cellular (myb) sequences. Both species lack the sequences encoding the amino terminus of the c-myb protein and thus could encode a protein which, like the v-myb gene products (and the predicted ABPL myb proteins), is truncated at the amino terminus. We have found that the larger (5.3 kilobase [kb]) and more abundant of the tumor-specific myb RNAs was predominantly nuclear, while the smaller species (3.9 kb) was cytoplasmic. Furthermore, our data imply that the 3.9-kb RNA was derived from the 5.3-kb RNA by an additional splice which utilized a cryptic splice acceptor site within the viral gag sequences. On the basis of subcellular distribution and predicted translational potential, we conclude that the 3.9-kb RNA is probably the mRNA which encodes a truncated myb protein. We also show that, due to different insertion points in W265 and W274, the W274 myb RNAs contained sequences from a c-myb exon upstream of the exons represented in the W265 (and ABPL) RNAs. The significance of our findings with regard to transformation by myb in these tumors is discussed.     

Comparative studies of somatostatin-14 and some of its fragments on passive avoidance behavior, open field activity and on barrel rotation phenomenon in rats

Behavioral effects of somatostatin-14, and some of its fragments [somatostatin(3–8), somatostatin(9–14), somatostatin(7–10)] after intracerebroventricular (ICV) administration have been investigated in male rats. In a passive avoidance learning test, somatostatin-14 (0.6 nM) given immediately after the learning session increased the avoidance latency at 24 hr after the injection, when compared to a somatostatin(3–8) (0.6 nM)-treated group. However, compared to a saline-treated group, the peptides did not significantly influence the avoidance latency. Somatostatin-14 administered in higher dose (6.0 nM) decreased the avoidance latency compared to the saline-treated group, while its fragments did not influence it. In an open field behavioral test, immediately after the 24-hr passive avoidance test, 6 nM of somatostatin-14 decreased the rearing activity, while the fragments did not influence this behavior. Somatostatin-14 produced barrel rotation in a dose-related manner, but after the injection of a high dose of the peptide (12 nM) all of the animals died in cardiorespiratory failure (apnea, pulmonary oedema). The fragments did not produce barrel rotation.     

The cryptoendolithic microbial environment in the Ross Desert of Antarctica: Light in the photosynthetically active region

The vertical zonation of the Antarctic cryptoendolithic community appears to form in response to the light regime in the habitat. However, because of the structure of the habitat, the light regime is difficult to study directly. Therefore, a mathematical model of the light regime was constructed, which was used to estimate the total photon flux in different zones of the community. Maximum fluxes range from about 150m photons m^–2 s^–1 at the upper boundary of the community to about 0.1m photons m^–2 s^–1. Estimates of the annual productivity in the community indicate that the lowest zone of the community is light limited, with the maximal annual carbon uptake equivalent to less than the carbon content of one algal (Hemichloris) cell.     

Detection of a single-copy gene on plant chromosomes by in situ hybridization

Summary DNA recombinant technology, combined with improvements in hybridization efficiency and quality of chromosome spreads, has made the method of in situ hybridization a reliable tool for gene mapping used by mammalian cytogeneticists to complement other methods. By appropriate alterations of the method, we demonstrate that detection of unique genes can be achieved along plant chromosomes despite some inherent disadvantages of the plant material. Using genomic subclones homologous to 6.6 kb of the single-copy chalcone synthase gene in parsley, we report the first example of chromosomal detection and localization of a unique endogenous gene in plants.     

Selenium in the blood of patients with colorectal cancer and neoplastic polyp.

Samples of whole blood were obtained from 51 patients with newly diagnosed colorectal cancer as well as from 76 patients with neoplastic colorectal polyp, and from 30 healthy blood bank donors. Selenium was determined by the fluorimetric method. Significantly decreased selenium concentrations of blood samples from patients with colorectal cancer and villous adenoma were found. There was not any correlation between the blood selenium levels of patients with adenomatous polyp and the severity of dysplasia in removed polyps. The lowest mean selenium level in patients with villous adenoma indicates that selenium deficiency may be an important factor in the development of colorectal cancer arising from villous adenomas.     

The mechanism of the search for homology promoted by recA protein. Facilitated diffusion within nucleoprotein networks

recA protein promotes the homologous pairing of single strands with duplex DNA by polymerizing on the single strands to make presynaptic nucleoprotein filaments which are polyvalent with respect to duplex DNA and which consequently form large networks or coaggregates when duplex DNA is added. Previous work has shown that efficient homologous pairing occurs within these networks. In the experiments described here, we observed that the length of the duplex DNA determined the stability of coaggregates, their steady state level, and the yield of joint molecules. Correspondingly, heterologous duplex DNA when preincubated with presynaptic filaments excluded subsequently added homologous duplex DNA from coaggregates and inhibited homologous pairing; the extents of exclusion and inhibition were determined by the length of the heterologous duplex DNA. On the other hand, long heterologous duplex DNA when added together with short homologous duplex DNA was capable of stimulating the absorption of the homologous molecules into coaggregates and increasing the rate of homologous pairing. In reactions involving short duplex molecules, polyamines exerted comparable effects on coaggregation and homologous pairing. We conclude that coaggregates are instrumental in homologous pairing, that they constitute distinct domains that are responsible for the processive or first order character of the pairing reaction, and that they act by concentrating DNA and facilitating diffusion.     

Papovaviral sialoadenitis in athymic nude rats

A wasting disease was found in 32 athymic nude rats. The rats had parotid sialoadenitis with intranuclear inclusion bodies in ductal and acinar epithelial cells. Other common lesions included bronchitis, bronchiolitis and secondary bacterial pneumonia. Less commonly, rhinitis and Harderian adenitis were seen. Intranuclear inclusions were also seen in bronchial epithelium of 1 rat, Harderian gland acini of 1 rat and laryngeal glands of 2 rats. Viral particles, averaging 45 nm in diameter, sometimes in crystalline arrays, were found in the nucleus of parotid epithelial cells. By the use of the avidin-biotin-peroxidase complex (ABC) immunoperoxidase technique, antibodies to disrupted SV40 virus (the group specific antigen of the polyomavirus (miopapovavirus) genus of the papovavirus family) reacted with intranuclear inclusions and cytoplasm of parotid epithelium and inclusions in lung and Harderian gland. The viral antigen did not cross react with antibodies to mouse polyoma, mouse K or disrupted bovine papilloma viruses.