Peter K Benson

Adeno-associated virus (AAV) is a single-stranded DNA parvovirus that causes no currently known pathology in humans. Despite the fact that this virus is of increasing interest to molecular medicine as a vector for gene delivery, relatively little is known about the cellular mechanisms controlling infection. In this study, we have examined endocytic and intracellular trafficking of AAV-2 using fluorescent (Cy3)-conjugated viral particles and molecular techniques. Our results demonstrate that internalization of heparan sulfate proteoglycan-bound AAV-2 requires alphaVbeta5 integrin and activation of the small GTP-binding protein Rac1. Following endocytosis, activation of a phosphatidylinositol-3 (PI3) kinase pathway was necessary to initiate intracellular movement of AAV-2 to the nucleus via both microfilaments and microtubules. Inhibition of Rac1 using a dominant N17Rac1 mutant led to a decrease in AAV-2-mediated PI3 kinase activation, indicating that Rac1 may act proximal to PI3 kinase during AAV-2 infection. In summary, our results indicate that alphaVbeta5 integrin-mediated endocytosis of AAV-2 occurs through a Rac1 and PI3 kinase activation cascade, which directs viral movement along the cytoskeletal network to the nucleus.

To determine factors that influence the occurrence of congenital cytomegalovirus (CMV) infection, the authors surveyed prospectively 8,254 infants born in eastern Iowa between October 1989 and June 1994. The authors conducted a case-control study to identify maternal risk factors, matching each CMV-infected infant with three uninfected infants according to hospital and date of birth. CMV strains were compared by using the polymerase chain reaction (PCR) to identify common sources of infection. Of the 7,229 infants cultured successfully for CMV, 35 (0.48%) were congenitally infected. Mothers of CMV-infected infants were more likely to be single (odds ratio (OR) = 3.05, p = 0.016), to work in sales (OR = 4.93, p = 0.008), or to be students (OR = 5.01, p = 0.017). Conversely, women who worked in health-care professions were less likely to have a congenitally infected infant (OR = 0.14, p = 0.049). PCR analysis indicated 27 distinct strains of CMV, but two groups of infants (two infants per group) excreted strains with indistinguishable molecular patterns. One of these pairs of infants had older siblings who attended the same child-care center during their mothers' pregnancies. The authors concluded that demographic and occupational factors influenced the risk of giving birth to an infant with congenital CMV infection. Many distinct CMV strains were identified, suggesting that major point source outbreaks had not occurred. Nonetheless, point source acquisition of CMV from child-care environments did account for some cases of congenital CMV infection in eastern Iowa.

Neural correlates of temporal resolution in the central auditory system are currently under intense investigation. The gap detection paradigm offers a simple, yet important, test of temporal acuity because changes in behavioral gap thresholds have been correlated with deficits in complex stimulus processing, such as speech perception. In gap detection studies, silent gaps are typically shaped by rapid (< 1.0 ms) rise/fall (R/F) times, i.e., rapid decreases and increases in sound intensity. However, in nature, the envelopes surrounding silent periods can vary significantly in R/F time. Therefore, we investigated whether changes in the R/F time surrounding the silent gap affect neural processing by inferior collicular (IC) neurons. Gap R/F times were varied between 0.5 and 16 ms and the discharge pattern, response rate, and first spike latency of IC neurons were measured for gap widths up to 100 ms. Neurons were classified into phasic or tonic discharge patterns based on peri-stimulus time histograms elicited to 100 ms noise carriers. The results indicate that (1) minimal gap thresholds increased with R/F time regardless of response type, (2) first spike latency variance increased systematically with R/F time for units which had small first spike standard deviations at short R/F times, and (3) the response rate of some units (called 'gap-tuned') changed as a function of both R/F time and gap width. Gap-tuned units responded strongly to a particular gap width only when the envelope of the gap was shaped by a particular R/F time. For gap-tuned units, increases in R/F time shifted the tuning to larger gap widths and also broadened the response profile. These results show that temporal acuity of neurons in the IC, as measured by the gap detection paradigm, is sensitive to the envelope surrounding gaps embedded in noise carriers.