Distribution of the olfactory fiber input into the olfactory tubercle of the in vitro isolated guinea pig brain

The olfactory tubercle (OT) is a cortical component of the olfactory system involved in reward mechanisms of drug abuse. This region covers an extensive part of the rostral ventral cerebrum and is relatively poorly studied. The intrinsic network interactions evoked by olfactory input are analyzed in the OT of the in vitro isolated guinea pig brain by means of field potential analysis and optical imaging of voltage-sensitive signals. Stimulation of the lateral olfactory tract induces a monosynaptic response that progressively decreases in amplitude from lateral to medial. The monosynaptic input induces a disynaptic response that is proportionally larger in the medial portion of the OT. Direct stimulation of the piriform cortex and subsequent lesion of this pathway showed the existence of an associative disynaptic projection from the anterior part of the piriform cortex to the lateral part of the OT that integrates with the component mediated by the local intra-OT collaterals. Optical and electrophysiological recordings of the signals evoked by stimulation of the olfactory tract during arterial perfusion with the voltage-sensitive dye di-2-ANEPEQ confirmed the pattern of distribution of the mono and disynaptic responses in the OT. Finally, current source density analysis of laminar profiles recorded with 16-channel silicon probes confirmed that the monosynaptic and disynaptic potentials localize in the most superficial and the deep portions of the plexiform layer I, as suggested by previous reports. This study sets the standard for further analysis of the modulation of network properties in this largely unexplored brain region.     

The cell cycle: accelerators, brakes, and checkpoints

PROLIFERATIVE CUES TRIGGER a complex series of molecular signaling events in cells. Early in the cell cycle, cells are faced with an important decision that affects their fate. They either initiate a round of replication or they withdraw from cell division. Passage through the restriction point, or "point of no return," marks cellular commitment to a new round of division. Genetic mutations that predispose individuals to tumorigenesis often affect pathways that influence cellular proliferation. Many of the mutated genes give rise to molecules that are no longer able to appropriately regulate the mammalian cell cycle; the end result is neoplasia. In this review, the critical elements that permit cell cycle progression and the positive and negative regulators that affect the process are reviewed.     

The role of interleukin-5 in manifestation of bronchial hyperreactivity (an experimental study)

Mechanography was used to study contractile reaction of airway smooth muscles in experimental bronchial asthma in intact guinea-pigs and those incubated with IL-5. Development of experimental bronchial asthma (BA) in the animals leads to enhancement of contractile reactions of bronchial smooth muscles in response to histamine action. The exposure to IL-5 of the preparations of bronchial smooth muscles increases histamine-mediated bronchial contractility. This may explain the phenomenon of IL-5-mediated bronchial hyperreactivity in the absence of eosinophilic damage to the tissues. Expression of mRNA of IL-5 receptor alpha-chain suggests that development of IL-5-mediated hypersensitivity of bronchial smooth muscles occurs due to the presence of a relevant IL-5 receptor on their surface.     

Automated in vitro screening of teratogens

We present a new in vitro assay for screening of potential teratogens, based on staining of cultured mouse fibroblastoid L929 cells for the determination of number of live and dead cells and of cell morphology, employing automatic video recording, followed by detection of the stained specimen and calculation of endpoint values by the use of a computerized microscope workstation. Ten different parameters were combined empirically into a single index describing general alterations in cell morphology, and, subsequently, measurements of alterations in morphology and proliferation were combined to produce a single empirical index aimed at predicting teratogenic potency. The assay was employed in two different laboratories on 10 coded compounds; 7 compounds that have demonstrated in vivo teratogenic potentials: valproic acid (VPA), pentyl-4-yn-VPA, retinoic acid (RA), 13-cis-RA, AM580, thalidomide, and alpha-EM12 and 3 compounds for which no teratogenic potential has been demonstrated: isobutyl-4-yn-VPA, phytanic acid, and beta-EM12. Within each of the three groups of compounds the nonteratogens generally caused smaller alterations in cell morphology than the teratogens, although the effects of thalidomide and related compounds generally were minor or insignificant. The data support the hypothesis that cell morphology and proliferation in combination with other endpoints may be employed for in vitro screenings of potential teratogens, although studies of additional compounds are needed in order to establish the general validity of the procedure.     

Expression of p57(KIP2) potently blocks the growth of human astrocytomas and induces cell senescence

Astrocytic tumors frequently exhibit defects in the expression or activity of proteins that control cell-cycle progression. Inhibition of kinase activity associated with cyclin/cyclin-dependent kinase co-complexes by cyclin-dependent kinase inhibitors is an important mechanism by which the effects of growth signals are down-regulated. We undertook the present study to determine the role of p57(KIP2) (p57) in human astrocytomas. We demonstrate here that whereas p57 is expressed in fetal brain tissue, specimens of astrocytomas of varying grade and permanent astrocytoma cell lines do not express p57, and do not contain mutations of the p57 gene by multiplex-heteroduplex analysis. However, the inducible expression of p57 in three well-characterized human astrocytoma cell lines (U343 MG-A, U87 MG, and U373 MG) using the tetracycline repressor system leads to a potent proliferative block in G(1) as determined by growth curve and flow cytometric analyses. After the induction of p57, retinoblastoma protein, p107, and E2F-1 levels diminish, and retinoblastoma protein is shifted to a hypophosphorylated form. Morphologically, p57-induced astrocytoma cells became large and flat with an expanded cytoplasm. The inducible expression of p57 leads to the accumulation of senescence-associated beta-galactosidase marker within all astrocytoma cell lines such that approximately 75% of cells were positive at 1 week after induction. Induction of p57 in U373 astrocytoma cells generated a small population of cells ( approximately 15%) that were nonviable, contained discrete nuclear fragments on Hoechst 33258 staining, and demonstrated ultrastructural features characteristic of apoptosis. Examination of bax and poly-(ADP ribose) polymerase levels showed no change in bax, but decreased expression of poly-(ADP ribose) polymerase after p57 induction in all astrocytoma cell lines. These data demonstrate that the proliferative block imposed by p57 on human astrocytoma cells results in changes in the expression of a number of cell cycle regulatory factors, cell morphology, and a strong stimulus to cell senescence.     

Influence of Alkaline Earth Metals on Structure Formation and Magnesium Alloy Properties

The main aim of this work is to improve the structure and properties of the magnesium alloy ML5 by modifying it with alkaline earth metals (ALM). The separate and joint influence of calcium and barium on the macrostructure and microstructure of the alloy of Mg-Al-Zn system was investigated. The qualitative and quantitative estimation of the structural components was carried out. Alkali earth metals were included in complex intermetallic phases and serve as additional crystallization centers. Modification of magnesium alloys with alkaline earth metals is established in an amount of 0.05 to 0.1 wt. % increased the bulk percentage of intermetallic phases by ~1.5 times, shifting them towards smaller size groups while simultaneously forming spherical intermetallic phases located in the grain centre and serving as additional crystallization centers. In this case, grain size reduction and significant refinement of the alloy structural components were provided. The dependency of the separate and joint influence of alkali earth metals on the castings complex of properties of the magnesium alloy has been established. Thus, a separate modification of the ML5 alloy provided the maximum level of its strength and ductility with the addition of 0.1% Ca or Ba. The modification of the complex (0.1% Ca + 0.1% Ba) of the magnesium alloy decreased the dimensions of its structural components 1.5 times and increased the strength of the alloy by 20%, the ductility by 2 times and the long-term heat resistance 1.5 times due to the formation of the intermetallic phases of the complex composition. Linear dependences were obtained that describe the influence of the characteristics of the structural components of the modified magnesium alloy on its mechanical properties. The developed technology for modifying cast magnesium alloys with alkaline earth elements provides an improvement in casting quality and allows the reliability and durability of responsible casting operation.