Modulation of mechanosensory responses by motoneurons that regulate skin surface topology in the leech

Central regulation of somatosensory signals has been extensively studied, but little is known about their regulation in the periphery. Given the widespread exposure of the skin sensory terminals to the environment, it is of interest to explore how somatosensory sensitivity is affected by changes in properties of the skin. In the leech, the annuli that subdivide the skin can be erected under the control of the annulus erector (AE) motoneurons. To analyze whether this surface change influences mechanosensory sensitivity, we studied the responses of low threshold mechanosensory T cells to mechanical stimulation of the skin as AE motoneurons were activated. In segments of the body wall connected to the corresponding ganglion and submerged in an aqueous environment, T cells responded to localized bubbling on the skin and to water flow parallel to its surface. Excitation of AE motoneurons diminished these responses in a way that depended on the motoneuron firing frequency. Video recordings established that the range of AE firing frequencies that produced effective annulus erection coincided with that influencing T cell responses. In isolated ganglia, AE firing had no effect on T cell excitability, suggesting that annulus erection diminished T cell responsiveness to mechanical input. Counteracting this effect, mechanosensory inputs inhibited AE motoneurons. However, because depolarization of AE cells caused a decrease in their input resistance, the more active the motoneuron, the less sensitive it became to inhibitory signals. Thus when brought to fire, AE motoneurons would stay "committed" to a high activity level, and this would limit sensory responsiveness to incoming mechanical signals.     

4E-binding protein phosphorylation and eukaryotic initiation factor-4E release are required for airway smooth muscle hypertrophy

The molecular mechanisms of airway smooth muscle hypertrophy, a feature of severe asthma, are poorly understood. We previously established a conditionally immortalized human bronchial smooth muscle cell line with a temperature-sensitive SV40 large T antigen. Temperature shift and loss of large T cause G1-phase cell cycle arrest that is accompanied by increased airway smooth muscle cell size. In the present study, we hypothesized that phosphorylation of eukaryotic initiation factor-4E (eIF4E)-binding protein (4E-BP), which subsequently releases eIF4E and initiates cap-dependent mRNA translation, was required for airway smooth muscle hypertrophy. Treatment of cells with chemical inhibitors of PI 3-kinase and mammalian target of rapamycin blocked protein synthesis and cell growth while decreasing the phosphorylation of 4E-BP and increasing the binding of 4E-BP to eIF4E, consistent with the notion that 4E-BP1 phosphorylation and eIF4E function are required for hypertrophy. To test this directly, we infected cells with a retrovirus encoding a phosphorylation site mutant of 4E-BP1 (AA-4E-BP-1) that dominantly inhibits eIF4E. Upon temperature shift, cells infected with AA-4E-BP-1, but not empty vector, failed to undergo hypertrophic growth. We conclude that phosphorylation of 4E-BP, eIF4E release, and cap-dependent protein synthesis are required for hypertrophy of human airway smooth muscle cells.     

Behavior of the bone-titanium interface after push-in testing: a morphological study

Fourteen titanium dental implants (Tioblast) were implanted singly in the proximal tibia of New Zealand rabbits for 120 days. A bone defect was surgically produced and filled with Bio-Oss around six of these implants. After the animals were sacrificed and their organs harvested, bone segments were fixed and methacrylate embedded after the push-in test had been performed. Microradiography was performed on longitudinal sections of the implants, whereas scanning electron microscope analysis was performed on the remaining embedded half-implants using secondary electrons only. The results showed that the implants were apically and coronally surrounded by bone, whether Bio-Oss was used or not. Fractures were evident through the newly formed bone and between the pre-existing and newly formed bone. Some fracture lines propagated through the bone and stopped at the implant surface without continuing along the bone-titanium interface. Detachment between the implant and the bone occurred at the coronal extremity of the implants and along its cervical region. These results highlight the fact that the bone-titanium interface has a high resistance to loading. It exhibited greater resistance than the newly formed bone and seems to behave in a manner similar to the cement lines of osteons.     

Invasion profiles of Brazilian field isolates of Plasmodium falciparum: phenotypic and genotypic analyses

The invasion of red blood cells (RBCs) by Plasmodium falciparum is dependent on multiple molecular interactions between erythrocyte receptors and parasite ligands. Invasion studies using culture-adapted parasite strains have indicated significant receptor heterogeneity. It is not known whether this heterogeneity reflects the parasite invasion arsenal in the field. We have studied the invasion phenotypes of 14 distinct field isolates from the Legal Amazon areas of Brazil by using erythrocyte invasion assays to investigate invasion into normal, enzyme-treated, and clinical-mutant RBCs. Analysis of these isolates revealed four distinct invasion profiles. Using En(a-) cells to get an unequivocal estimate of the use of glycophorin A (GPA) as a receptor, we found that the 175-kDa erythrocyte-binding antigen (EBA-175)/GPA pathway was used by a minority of the parasite isolates studied. Although polymorphism of region II domains at specific amino acid positions in both EBA-140 and EBA-181 was found in these field isolates, this did not correlate with invasion profiles and thus receptor selectivity. These studies have further confirmed the existence of a significant diversity of invasion pathways in nature and suggest that additional parasite ligands will have to be targeted to devise global vaccines that will work in the field.     

First isolation of Cryptococcus neoformans var. gattii, serotype C, from the environment in Colombia.

The natural habitat of Cryptococcus neoformans var. gattii, serotype B in the environment was established by Australian investigators who demonstrated its association with species of Eucalyptus. The aim of the present study was to search for the habitat of this variety in a city of Colombia, where clinical cases due to this variety occur with great frequency. For a period of 5 months detritus, vegetable material and air samples in and around 68 almond trees (Terminalia catappa) located in the city were studied. C. neoformans var. gattii serotype C was the only variety isolated from two of the 68 trees sampled. These trees were positive for 4 of the 5 months during which they were studied. From the first positive sample kept under refrigeration, it was possible to isolate the fungus up to 3 months later. This is the first report of the isolation of serotype C from the environment. More studies are required in order to establish the ecological significance of this finding.     

Effect of age and preexisting antibody on serum antibody response of infants and children to the F and G glycoproteins during respiratory syncytial virus infection.

The serum antibody response of 50 infants and children infected with respiratory syncytial virus (RSV) was determined by a glycoprotein-specific enzyme-linked immunosorbent assay, and the effects of age and preexisting antibody titer at the time of RSV infection on response to the G and F glycoproteins of RSV were examined. The immune response to the G and F glycoproteins was assessed with anti-human immunoglobulin A to permit measurement of the response of young infants in the presence of maternally derived immunoglobulin G. The findings suggested that age primarily affects the response to the F glycoprotein and that preexisting antibody titer affects the response to the G glycoprotein.     

Coxsackievirus-mediated hyperglycemia is enhanced by reinfection and this occurs independent of T cells

The induction of autoimmunity by viruses has been hypothesized to occur by a number of mechanisms. Coxsackievirus B4 (CB4) induces hyperglycemia in SJL mice resembling diabetes in humans. While virus is effectively cleared within 2 weeks, hyperglycemia does not appear until about 8-12 weeks postinfection at a time when replicative virus is no longer detectable. In SJL mice, reinfection with CB4 enhanced the development of hyperglycemia. As predicted, the immune system responded more rapidly to the second infection and virus was cleared more swiftly. However, while infiltrating T cells were found within the pancreas, depletion of the CD4 T cell population prior to secondary infection or use of CD8 knock-out mice had no effect on the development of virus-mediated hyperglycemia. In conclusion, enhanced hyperglycemia induced by CB4 occurs independent of the T cell response.