Effect of Group vs. Single Housing on Phenotypic Variance in C57BL/6J Mice

Objective: To determine if group housing affects the variance of body composition parameters in a highly inbred mouse strain. Research Methods and Procedures: Thirty 3‐week‐old male C57BL/6J mice were obtained from the Jackson Laboratory. Fifteen mice were housed individually, and 15 mice were housed in groups of 5/cage. Animals were fed ad libitum and maintained in the same room under a 12:12‐hour light/dark photoperiod at 22 °C for 9 weeks. Animals were killed, and fat mass, soft‐lean tissue mass, bone mineral density (BMD), and bone mineral content (BMC) were determined by DXA. At necropsy, weights of the paired epididymal fat pads, paired retroperitoneal fat pads, right inguinal fat pad, liver, kidneys, paired testes, and seminal vesicles were obtained. Results: Relative to mice housed singly, group‐housed mice showed significantly greater variance in percentage of body fat, testes weight, and BMC. Group‐housed mice tended to show greater variance in liver weights and BMD. Mice housed singly were smaller, had less soft‐lean tissue mass and BMC, and lower BMD when compared with group‐housed mice. Discussion: These results suggest that with respect to body composition parameters, mice housed singly are more similar to one another than are group‐housed mice, most likely because of a reduction in environmental (predominately behavioral/social) effects. Thus, mice housed singly may be more representative of genotypic effects on body composition than group‐housed mice. Whether other inbred strains of mice show similar responses to housing condition is unknown.     

Neurobiology: Paper alert

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in neurobiology.     

Tissue tropism of swine influenza viruses and reassortants in ex vivo cultures of the human respiratory tract and conjunctiva

The 2009 pandemic influenza H1N1 (H1N1pdm) virus was generated by reassortment of swine influenza viruses of different lineages. This was the first influenza pandemic to emerge in over 4 decades and the first to occur after the realization that influenza pandemics arise from influenza viruses of animals. In order to understand the biological determinants of pandemic emergence, it is relevant to compare the tropism of different lineages of swine influenza viruses and reassortants derived from them with that of 2009 pandemic H1N1 (H1N1pdm) and seasonal influenza H1N1 viruses in ex vivo cultures of the human nasopharynx, bronchus, alveoli, and conjunctiva. We hypothesized that virus which can transmit efficiently between humans replicated well in the human upper airways. As previously reported, H1N1pdm and seasonal H1N1 viruses replicated efficiently in the nasopharyngeal, bronchial, and alveolar epithelium. In contrast, representative viruses from the classical swine (CS) (H1N1) lineage could not infect human respiratory epithelium; Eurasian avian-like swine (EA) (H1N1) viruses only infected alveolar epithelium and North American triple-reassortant (TRIG) viruses only infected the bronchial epithelium albeit inefficiently. Interestingly, a naturally occurring triple-reassortant swine virus, A/SW/HK/915/04 (H1N2), with a matrix gene segment of EA swine derivation (i.e., differing from H1N1pdm only in lacking a neuraminidase [NA] gene of EA derivation) readily infected and replicated in human nasopharyngeal and bronchial epithelia but not in the lung. A recombinant sw915 with the NA from H1N1pdm retained its tropism for the bronchus and acquired additional replication competence for alveolar epithelium. In contrast to H1N1pdm, none of the swine viruses tested nor seasonal H1N1 had tropism in human conjunctiva. Recombinant viruses generated by swapping the surface proteins (hemagglutinin and NA) of H1N1pdm and seasonal H1N1 virus demonstrated that these two gene segments together are key determinants of conjunctival tropism. Overall, these findings suggest that ex vivo cultures of the human respiratory tract provide a useful biological model for assessing the human health risk of swine influenza viruses.     

A finite difference model of O2 transport in aortic valve cusps: importance of intrinsic microcirculation

Recent studies have reported the presence of a microcirculation within the tissue of aortic valves. To test the hypothesis that this vascular bed is needed to satisfy the oxygen demands of the cusp tissue, a two-dimensional (2D) finite difference model of oxygen diffusion was developed. The in vivo environment was modeled for vascular and avascular cusps using thickness data from precise radiographic measurements of fresh porcine valves, and O2 diffusivity (DO2) and O2 consumption (VO2) values from experimental data. The location and density of the cusp vasculature were determined by the model to prevent oxygen levels from falling to zero. Validation of the model was performed by simulation of the experimental measurements of cusp DO2 and VO2. For a test cusp with uniform thickness, the model returned simulated DO2 and VO2 measurements within 1.43% and 0.18% difference of the true parameter values, respectively. For native cusps, the simulated DO2 measurements were sensitive to thickness variations (-38 to +21% difference), whereas the VO2 measurements were minimally affected (8% difference). An improved DO2 measurement technique was found to reduce these errors to <5% and is recommended for analysis of experimental data. In the avascular case, the model predicted large regions of hypoxic tissue, whereas in the vascular case, the model predicted vessel locations and densities similar to what was experimentally observed in porcine cusps. Overall, the in vivo model developed in this study confirmed the need for an intrinsic microcirculation in the thicker basal regions of aortic cusps.     

Construction and preliminary immunobiological characterization of a novel, non-reverting, intranasal live attenuated whooping cough vaccine candidate

We describe the construction and immunobiological properties of a novel whooping cough vaccine candidate, in which the aroQ gene, encoding 3-dehydroquinase, was deleted by insertional inactivation using the kanamycin resistance gene cassette and allelic exchange using a Bordetella suicide vector. The aroQ B. pertussis mutant required supplementation of media to grow but failed to grow on an unsupplemented medium. The aroQ B. pertussis mutant was undetectable in the trachea and lungs of mice at days 6 and 12 post-infection, respectively. Antigen-specific antibody isotypes IgG1 and IgG2a, were produced, and cell-mediated immunity [CMI], using interleukin-2 and interferon-gamma as indirect indicators, was induced in mice vaccinated with the aroQ B. pertussis vaccine candidate, which were substantially enhanced upon second exposure to virulent B. pertussis. Interleukin- 12 was also produced in the aroQ B. pertussis-vaccinated mice. On the other hand, neither IgG2a nor CMI-indicator cytokines were produced in DTaP-vaccinated mice, although the CMI-indicator cytokines became detectable post-challenge with virulent B. pertussis. Intranasal immunization with one dose of the aroQ B. pertussis mutant protected vaccinated mice against an intranasal challenge infection, with no pathogen being detected in the lungs of immunized mice by day 7 post-challenge. B. pertussis aroQ thus constitutes a safe, non-reverting, metabolite-deficient vaccine candidate that induces both humoral and cellmediated immune responses with potential for use as a single-dose vaccine in adolescents and adults, in the first instance, with a view to disrupting the transmission cycle of whooping cough to infants and the community.