Transgenic animals as a tool for studying the effect of the c-myc proto-oncogene on cardiac development

Transgenic animals provide a model system to elucidate the role of specific proteins in development. This model is now being used increasingly in the cardiovascular system to study cardiac growth and differentiation. During cardiac myocyte development a transition occurs from hyperplastic to hypertrophic growth. In the heart the switch from myocyte proliferation to terminal differentiation is synchronous with a decrease in c-myc mRNA abundance. To determine whether c-myc functions to regulate myocyte proliferation and/or differentiation, we examined the in vivo effect of increasing c-myc expression during fetal development and of preventing the decrease in c-myc mRNA expression that normally occurs during myocyte development. The model system used was a strain of transgenic mice exhibiting constitutive expression of c-myc mRNA in cardiac myocytes throughout development. Increased c-myc mRNA expression is associated with both atrial and ventricular enlargement in the transgenic mice. This increase in cardiac mass is secondary to myocyte hyperplasia, with the transgenic hearts containing greater than twice as many myocytes as nontransgenic hearts. The results of this study indicate that constitutive expression of c-myc mRNA in the heart during development results in enhanced hyperplastic growth, and suggest a regulatory role for the c-myc protooncogene in cardiac myogenesis.     

Ophiostoma novo-ulmi sp. nov., causative agent of current Dutch elm disease pandemics

The aggressive subgroup of the Dutch elm disease pathogen Ophiostoma ulmi (Buism.) Nannf. syn. Ceratocystis ulmi (Buism.) Moreau is named as a new species, O. novo-ulmi, and is thereby separated from the old non-aggressive subgroup, which is retained as O. ulmi. O. novo-ulmi differs from O. ulmi in colony morphology, growth rate, optimum temperature for growth, perithecial neck length, pathogenicity to elm, bark colonising ability, cerato-ulmin protein production, synnemetal and protoperithecial production, mating type frequency, protein and isozyme polymorphisms, mitochondrial DNA and nuclear DNA polymorphisms, and mitochondrial DNA size. In addition, a strong unidirectional fertility barrier operates between the two species, while their hybrids show remarkable variation, poor fitness, and many are infertile. These aspects are summarised. New information on perithecial dimensions is presented. O. ulmi is redefined and a neotype designated. The status of the Eurasian and North American races of O. novo-ulmi is currently under investigation.Abbreviations EAN Eurasian race - NAN North American race     

Morphometric investigations of the colon mucosa in chronicTrypanosoma cruzi infected rats

The objective of this investigation was to study the morphometry of the epithelial mucosa in the chronic phase ofT. cruzi infection. Nine young female Wistar rats were inoculated withT. cruzi. Ten months after inoculation the animals were sacrificed and the proximal colon was collected for morphometric measurements of the thickness of the muscle layers, the number of neurons in the myenteric plexus, the crypt cell population (CCP), crypt cell production per crypt (CCPC) and turnover time (TT) of the epithelium. There was no muscle layer hypertrophy but there was significant denervation in the group inoculated withT. cruzi, which also showed hyperplasia of the epithelium. The data suggest that denervation of the myenteric plexus did not induce hypertrophy of the propria muscle layer itself but altered the morphometry of the colonic epithelium inT. crwzi-infected animals, with increased development of CCP and TT. It is possible that this epithelial hyperplasia, as a consequence of a longer crypt cell TT, increased the absorption and secretion activities of the colon, which in turn may participate in the genesis of the enteromegalies observed in the chronic phase of Chagas’ Disease.     

Effect of ferric nitrilotriacetate on rostral mesencephalic cells

After murine fetal cells from the rostral mesencephalic tegmentum were isolated, prepared, and cultured; neuronal and glial cells in primary mixed cell cultures were exposed to ferric nitrilotriacetate (Fe-NTA) at varying concentrations. Studies were performed at 23 days in culture after 14 day exposure to Fe-NTA. In addition to morphologic studies, biochemical assays including specific [³H]flunitrazepam (FLU) binding, clonazepam (CLO)-displaceable [³H]-FLU binding, Ro5-4864-displaceable [³H]-FLU binding, [³H]dopamine (DA) uptake, [³H]haloperidol (HAL) binding, [³H]spiperone (SP) binding, glutamine synthetase activity (GS), and protein determinations were performed. The data demonstrate that chelated ferric iron has an adverse effect on these cells. The data also demonstrate that increasing concentrations of Fe-NTA resulted in massive neuronal dropout leaving the culture population virtually all glial; however, the specific binding of [³H]HAL and [³H]SP increased. There was a concomitant decrease in both glutamine synthetase activity and overall protein content. The mechanism of enhancement in the presence of Fe-NTA of [³H]HAL and [³H]SP binding is unknown and may be unique, but may be related to the known increase in D₂ receptor ligand affinity in the presence of other multivalent cations (Ca²⁺ and Mg²⁺).     

颈动脉内注入腺苷对呼吸,血压和肾交感神经活动的影响

在33只麻醉家兔,观察了颈动脉内注入腺苷所诱发的平均动脉压、心率,呼吸和肾交感神经活动的变化。结果如下:(1)颈动脉内注入腺苷后,平均动脉压呈剂量依赖性下降;呼吸加快,深度变化不明显,剪断窦神经后注入腺苷,仍引起平均动脉压下降,而呼吸变化消失。(2)隔离的颈动脉窦灌流液内加入腺苷后,平均动脉压下降,心率减慢;颈动脉体(CB)失活后反应消失。(3)将腺苷灌注到颈动脉窦区后,平均动脉压下降,肾交感神经传出放电活动增加,CB 失活或剪断窦神经后,反应消失。由此提示:腺苷可作为兴奋 CB 的一种物质,引起平均动脉压降低,心率减慢,呼吸加强和肾交感神经放电活动增加。     

Recombinant Trypanosoma cruzi antigens and Chagas' disease diagnosis: analysis of a workshop

Abstract A workshop organized by the Ibero-American Project of Biotechnology evaluated the diagnostic potential of several cloned Trypanosoma cruzi recombinant antigens for Chagas' disease serodiagnosis. A set of recombinants, Antigen 2, Antigen 13, SAPA, H49, A13, JL5, JL7, JL8, JL9, and RA1 provided by three different South American laboratories were probed with a panel of 236 South American serum samples. Antigens JL7, H49, Antigen 2, and A13 scored as the best diagnostic recombinant reagents. The results suggested that the main advantage of using cloned peptides for chronic Chagas' disease diagnosis resided in their highly specific immunoreactive properties.     

The effect of geochemical factors on prevalences of dental diseases for prehistoric inhabitants of the state of Missouri

In previous epidemiological studies, it has been suggested that geochemical factors besides fluoride may affect the prevalences of dental diseases. Our objective in this study was to determine whether the prevalences of periodontal diseases, coronal caries, and root caries for prehistoric inhabitants vary between geochemical regions of the state of Missouri. Burial sites were located on unique maps that depict geochemical variation among regions of the state. Data on dental caries and alveolar bone loss were gathered from 179 of the best preserved skeletal remains of the Late Woodland (A.D. 400-900) and Mississippian (A.D. 900-1700) periods. Mean caries scores and proportions of individuals with caries were calculated for these geochemical regions. Average alveolar bone loss was regressed on age for the individuals of these regions. Significant differences in caries and bone loss were found between several regions. These differences cannot be adequately explained by fluoride concentrations or by diet. It is suggested that geochemical factors, in addition to fluoride, may have affected the prevalences of dental diseases.     

The membrane potential modulates the ATP-dependent Ca pump of cardiac sarcolemma

The effect of membrane potential on the activity of the ATP-dependent Ca²⁺ pump of isolated canine ventricular sarcolemmal vesicles were investigated. The membrane potential was controlled by the intravesicular and extravesicular concentration of K⁺, and the initial rates of Ca²⁺ uptake both in the presence and the absence of valinomycin were determined. The rate of Ca²⁺ uptake was stimulated by a inside-negative potential induced in the presence of valinomycin. The valinomycin-dependent stimulation was enhanced by the addition of K⁺ channel blocker, tetraethylammonium ion or Ba²⁺. The electrogenicity of cardiac sarcolemmal ATP-dependent Ca²⁺ pump is suggested from the increase of Ca²⁺ uptake by negative potential induced by valinomycin.     

Quantitative gap junction alterations in mammalian heart cells quickly frozen or chemically fixed after electrical uncoupling

Summary The gap junction morphology was quantified in freeze-fracture replicas prepared from rat auricles that had been either quickly frozen at 6 K or chemically fixed by glutaraldehyde, in a state of normal cell-to-cell conduction or in a state of electrical uncoupling. The general appearance of the gap junctions was similar after both preparative procedures. A quantitative analysis of three gap junctional dimensions provided the following measurements in the quickly frozen conducting auricles (mean±sd): (a) P-face particles' diameter 8.27±0.74 nm (n =5709), (b) P-face particles' center-to-center distance 10.78±2.12 nm (n=4800), and (c) E-face pits' distance 9.99±2.19 nm (n=1600). Corresponding values obtained from chemically fixed tissues were decreased by about 3% for the particle's diameter and about 5% for the particles' and pits' distances. Electrical uncoupling by the action of either 1 mM 2–4-dinitrophenol (DNP), or 3.5 mMn-Heptan-1-ol (heptanol), induced a decrease of the particle's diameter, which amounted to –0.69±0.01 nm (mean ±se) in the quickly frozen preparations and –0.71±0.01 nm in the chemically fixed ones. The particles' distance was decreased by –0.96±0.04 nm in the quickly frozen samples and by –0.90 ±0.03 nm in the chemically fixed ones and the E-face pits' distance was similarly reduced. All differences were statistically significant (P<0.001 for all dimensions). Electrical recoupling after the heptanol effect promoted a return of these gap junctional dimensions towards normal values, which was about 50% complete within 20 min. It is concluded that very similar morphological alterations of the gap junctional structure are induced in the mammalian heart by different treatments promoting electrical uncoupling and that these conformational changes appear independently of the preparative procedure. The suggestion that the observed decrease of the particles' diameter is genuinely related to the closing mechanism of the unit cell-to-cell channel set in thei centers is thus confirmed.