The purpose of this study was to investigate the effect of altered local temperature on soleus H-reflex and compound muscle action potential (M wave) in young and older women. H-reflex and M wave responses were elicited in 10 young (22.3 +/- 3.3 years) and 10 older (72.5 +/- 3.2 years) women at three muscle temperatures: control (34.2 +/- 0.3 degrees C), cold (31.3+/-0.5 degrees C) and warm (37.1 +/- 0.2 degrees C). H-reflex output, expressed as the ratio between maximal H-reflex and maximal M wave (H(max)/M(max)), was lower in the older, compared with the younger, group, regardless of temperature. In control temperature conditions, for example, the H(max)/M(max) ratio was 36.8 +/- 24% in the young and 25.4 +/- 20% in the older (P<0.05). Warming had no effect on the H-reflex output in either group, whilst cooling increased H-reflex output only in the younger group (+28%). In both groups, cooling increased (+5.3%), and warming decreased (-5.5%) the H-reflex latency. This study confirms that older individuals experience a reduced ability to modulate the reflex output in response to a perturbation. In a cold environment, for example, the lack of facilitation in the reflex output, along with a delayed reflex response could be critical to an older individual in responding to postural perturbations thus potentially compromising both static and dynamic balance.

No abstract

A cytopathic human immunodeficiency virus type 1 (HIV-1) isolate containing multiple virus genotypes was molecularly cloned, and the biological activity of six randomly selected clones was assessed by transfection into human lymphoid or glial cell lines. Five infectious clones of HIV-1, termed N1T-A through-E, were isolated in this manner. Clones N1T-A,-B,-C, and-E could be distinguished by restriction endonuclease mapping, whereas clones N1T-B and-D had identical maps with the enzymes used. Each clone exhibited a distinct host cell range as well as markedly different infection kinetics and cytopathogenic properties when tested in human cell lines of T-lymphocytic, monocytic, and astrocytic origin. In particular, infection with HIV-1 clone N1T-E was characterized by slow kinetics and lack of significant cytopathic effects in acutely and chronically infected cells. Clone N1T-A, similar to the parental isolate NIT, exhibited a wide host cell range, fast kinetics of infection, and high cytopathogenicity. These data indicate that HIV-infected individuals may carry multiple HIV-1 genotypes with distinct cytopathogenic potential and cell tropism. Analysis of virus isolates must take into account the contribution, or masking, of individual virus clones.

Visual information is used for postural stabilization in humans. However, little is known about how eye movements prevalent in everyday life interact with the postural control system in older individuals. Therefore, the present study assessed the effects of stationary gaze fixations, smooth pursuits, and saccadic eye movements, with combinations of absent, fixed and oscillating large-field visual backgrounds to generate different forms of retinal flow, on postural control in healthy young and older females. Participants were presented with computer generated visual stimuli, whilst postural sway and gaze fixations were simultaneously assessed with a force platform and eye tracking equipment, respectively. The results showed that fixed backgrounds and stationary gaze fixations attenuated postural sway. In contrast, oscillating backgrounds and smooth pursuits increased postural sway. There were no differences regarding saccades. There were also no differences in postural sway or gaze errors between age groups in any visual condition. The stabilizing effect of the fixed visual stimuli show how retinal flow and extraocular factors guide postural adjustments. The destabilizing effect of oscillating visual backgrounds and smooth pursuits may be related to more challenging conditions for determining body shifts from retinal flow, and more complex extraocular signals, respectively. Because the older participants matched the young group's performance in all conditions, decreases of posture and gaze control during stance may not be a direct consequence of healthy aging. Further research examining extraocular and retinal mechanisms of balance control and the effects of eye movements, during locomotion, is needed to better inform fall prevention interventions.

The nature of the interaction between human immunodeficiency virus (HIV) and human cells of astrocytic origin was studied in vitro with cultured glial cells and intact HIV or infectious molecular clones of the virus. Infection of glial cells with intact HIV was characterized by low-level expression of viral transcripts as detected by Northern blotting and in situ hybridization (<10 copies of HIV RNA per cell), transient virus replication, absence of viral antigens detectable by immunofluorescence, and complete lack of cytopathic effects. However, the HIV-infected glial cells persistently expressed HIV tatlll gene activity as detected by a chloramphenicol acetyltransferase assay, and HIV transcripts could be detected by in situ hybridization in 20 to 30% of cells up to 4 months after infection, suggesting that the lack of cytopathicity in HIV-exposed cells was not due to transient viral infection. To evaluate whether increased expression and replication of HIV in glial cells would have any effect on cell growth and viability, we established HIV-positive glial cell lines by cotransfection of cells * Corresponding author. MATERIALS AND METHODS Cells and viruses. Human glial cell lines U-251MG (H80) (4) and U-373MG (38) were obtained from D. D. Bigner and the American Type Culture Collection (Rockville, Md.), 3774 on September 28, 2020 by guest http://jvi.asm.org/ Downloaded from INFECTION OF HUMAN GLIAL CELLS BY HIV AND HIV CLONES 3775 respectively, and were cultivated in Dulbecco modified Eagle medium supplemented with 10% fetal bovine serum. The CD4-positive T-cell line CEM (16) was received from L. Montagnier, and the HIV lysis-resistant subclone of CEM, CR10, was established in our laboratory (6). The suspension cultures were maintained in RPMI 1640 medium supplemented with 5% fetal bovine serum. The NiT isolate of HIV (32) was propagated in CEM or CR10 cells. Glial cells were infected with cell-free, virus-containing supernatants as described previously (11). Plasmids. Plasmid pSV2neo (37) was obtained from Bethesda Research Laboratories (Gaithersburg, Md.). The murine glial fibrillary acidic protein (GFAP) cDNA (28) was donated by M. Shelanski and subcloned into the plasmid pGEM4 (Promega Biotec, Inc., Madison, Wis.) to allow the synthesis of both sense-and antisense-orientation RNAs. The HIV TAT region probe, pTBtat, was prepared similarly with the 0.7-kilobase (kb) EcoRI-KpnI fragment of HIV NiT proviral DNA (32). The infectious HIV DNA clone pNlT-E2 was prepared as described elsewhere (K. Sakai, S. Dewhurst, C. Meier, and D. J. Volsky, submitted for publication). The nearly full-length HIV DNA probe used for Southern blot analysis was prepared as an 8.9-kb Sacl-Sacl fragment from the HIV N1G-G clone (32). Plasmid X-TAT was donated by S. Rhode, and plasmid RSV CAT (20) was obtained from the American Type Culture Collection. Chemicals and radiochemicals. Photobiotin was purchased from Bresa Ltd. (Adelaide, South Australia). Fluorochromeconjugated or native streptavidin and RNases A and Ti were purchased from ...