Does bradycardia or hypertension enhance gas transfer in rainbow trout (Oncorhynchus mykiss)?

Experiments were conducted to test the hypothesis that branchial gas transfer is enhanced in rainbow trout during hypoxia or hypercarbia by bradycardia and systemic vasoconstriction. Gas transfer was indirectly assessed by continuous monitoring of arterial blood gases, PaO2 and PaCO2. Cardiac frequency was maximally decreased by 34.9+/-4.3 and 8.6+/-3.2 bpm in hypoxic and hypercarbic fish, respectively. Pre-treating fish with atropine (1micromol kg(-1)) attenuated or abolished the bradycardia during hypoxia and hypercarbia, respectively. However, there were no significant differences in the arterial blood gases between the control and atropinized fish. Dorsal aortic blood pressure was increased maximally by 11.3+/-2.8 and 17.7+/-2.0mm Hg in the hypoxic and hypercarbic fish. Pre-treatment of fish with prazosin (2.4micromol kg(-1)) prevented these increases in blood pressure. Blood gases were unaltered by prazosin treatment in the hypercarbic fish. However, in the hypoxic fish, gas transfer appeared to be impaired by prazosin on the basis of lowered PaO2 (by approximately 35 mm Hg compared to control fish) and increased PaCO2 (by approximately 0.3mm Hg). Because the normal hyperventilatory response to hypoxia was prevented by prazosin, it is possible that the impairment of gas transfer was related to inadequate ventilation rather than to any differences in the pressor response. The present results provide no evidence that gas transfer in rainbow trout is enhanced by bradycardia nor do they reveal any obvious benefit associated with the increases in blood pressure that accompany hypoxia and hypercarbia.     

Hepatitis B surface antigen and its subtypes in an institution for the mentally retarded.

The prevalence of hepatitis B surface antigen (HBsAg) in 155 patients with Down''s syndrome (DS) and 209 with other types of mental retardation (OMR) at Huronia Regional Centre, Orillia, Ontario was 34.8 and 5.3%, respectively. There was no significant difference in prevalence between males and females in either group of patients. In 75 matched pairs (DS-OMR) the HBsAg prevalence was 45% in DS and 8.3% in OMR males; in females 40% of those with DS were HBsAg-positive, whereas all the OMR residents were negative. The prevalence of HBsAg in both DS and OMR groups was higher in those admitted in early childhood and in those who had resided in the institution for more than 10 years. In all 54 HBsAg-positive DS patients the antigen subtype was ad. Among the 11 HBsAg-positive OMR patients the subtype was ad in 10 cases and ay in 1.     

Dicistronic Gene Expression in Developing Zebrafish

Internal ribosome entry sites (IRESs) allow ribosomal access to messenger RNA without a requirement for cap recognition and subsequent scanning to an initiator AUG. Hence, IRESs have been adapted into dicistronic vectors for the expression of more than one gene from a single mRNA. Dicistronic vectors have been used for many applications in mammalian tissue culture and transgenesis. However, whether the IRESs from mammalian viruses function without temporal or spatial restrictions in nonmammalian organisms like zebra fish (Danio rerio) is unknown. Therefore, we have examined the expression capabilities of the encephalomyocarditis virus (EMCV) IRES during zebrafish embryogenesis. We determined that the EMCV IRES was sufficient to permit detectable expression of several second cistron reporters during zebrafish embryogenesis, including luciferase and green fluorescent protein. This suggests that our dicistronic vectors are suitable for general use in any vertebrate system, from fish to humans. Received March 26, 1999; accepted June 14, 1999.     

A novel trans-complementation assay suggests full mammalian oocyte activation is coordinately initiated by multiple, submembrane sperm components

To initiate normal embryonic development, an egg must receive a signal to become activated at fertilization. We here report that the ability of demembranated sperm heads to activate is abolished after incubation over the range 20-44 degreesC and is sensitive to reducing agents. On the basis of this observation, we have developed a microinjection-based, trans-complementation assay in order to dissect the heat-inactivated sperm-borne oocyte-activating factor(s) (SOAF). We demonstrate that the failure of heat-inactivated sperm heads to activate an egg is rescued by coinjection with dithiothreitol-solubilized SOAF from demembranated sperm heads. The solubilized SOAF (SOAFs) is trypsin sensitive and is liberated from demembranated heads in a temperature-dependent manner that inversely correlates with the ability of sperm heads to activate. This argues that SOAFs is a proteinaceous molecular species required to initiate activation. Injection of oocytes with mouse or hamster sperm cytosolic factors, but not SOAFs alone, induced resumption of meiosis, further suggesting that these cytosolic factors and SOAF are distinct. Collectively, these data strongly suggest that full mammalian oocyte activation is initiated by the coordinated action of one or more heat-sensitive protein constituents of the perinuclear matrix and at least one heat-stable submembrane component.