A practical vibration isolation workstation for electrophysiology

Vibration control is a major concern in electrophysiological research, particularly during intracellular recording where movements of only a few micrometers may disrupt the cell membrane. The workstation described here is based on the concept of a table nested within a second table. The inner table supports a vibration-isolated surface while the outer table provides protection and a bench-top for equipment. The work surface is supported on squash balls in order to avoid the substantial cost of passive commercial isolators. The properties of the squash ball isolators were found to be similar to a set commercial isolators when compared with respect to impulse response, compliance and transmissibility. The table has been successfully used for both intra- and extracellular recording over a 3-year period. Work efficiency was enhanced by the close proximity of the bench-top and isolated work surface, while perimeter protection helped maintain stable recordings.     

Longitudinal Dynamic Loading of a Steel Pole Transmission Line

Model test results have demonstrated that it is possible to simulate a number of dynamic loading conditions on a scale model of an actual transmission line system, taking into account a large number of variables, and producing results having direct interpretation at full scale. The method appears to be particularly useful in identifying any potential "trouble areas" in an existing design such as the use of horizontal struts on light angle structures, and/or adequacy of fatigue strength under galloping conditions. A sample of the principal findings of this investigation are: 1) A method for rapidly calculating the flexibility (stiffness) of steel pole transmission structures has been developed. The method relies on computer print-out data supplied by pole manufactures at the time of bid evaluation. 2) Results of broken static wire tests show that structure flexibility reduces both the dynamic load and the residual load below the load calculated for a rigid structure. 3) The maximum loads occur for broken static wire on the most flexible structure, and for ice unload of static wire on the most stiff structure. The latter result is subject to the further restraint of a horizontal strut at a light angle. 4) Unexpectedly high loads were found on the stiffer structure with long insulators (including the horizontal strut) for galloping conductor and galloping static wire tests.     

The effects of magnetic quenching on glassy barium ferrite

Barium ferrite (BaFe₁₂O₁₉) prepared by solution evaporation techniques from ethylene glycol/citric acid or ethylene glycol/pyridine-1-oxide solutions is initially obtained in a glassy form. Although visual observations on samples heated to 1250° C showed that transparency was maintained in thin sections, X-ray powder diffraction studies showed the development of ordered regions of BaFe₁₂O₁₉. Prolonged heating at 1250° C resulted in a loss of visual transparency. Samples of partially amorphous material cooled rapidly in a weak magnetic field were found to have a magnetization considerably higher than samples cooled in the absence of a field. Samples rendered polycrystalline by heating for extended periods at 1250° C showed a lower magnetization on magnetic quenching.     

Photo-neuroendocrine control of seasonal cycles in body weight, pelage growth and reproduction: lessons from the HPD sheep model

Two experiments are reported in which the relationship between the orientation of the typical contour of a lamella in relation to the observer, and the ability of the observer to learn the correct position and orientation of sets of lamellae in three-dimensional arrays, was examined. For lamellae presented with their typical contour in a plane other than the observer's frontoparallel plane, the results of both experiments indicated that participants encoded lamellae in such a way that their typical contour appeared to be closer to the observer's frontoparallel plane than the respective stimulus. The relationship of the present findings to previous results on children's drawings and to the concept of the picture plane are considered.     

Transgenic expression of the endothelin-B receptor prevents congenital intestinal aganglionosis in a rat model of Hirschsprung disease

The spotting lethal rat, a naturally occurring rodent model of Hirschsprung disease, carries a deletion in the endothelin-B receptor (EDNRB) gene that abrogates expression of functional EDNRB receptors. Rats homozygous for this mutation (sl) exhibit coat color spotting and congenital intestinal aganglionosis. These deficits result from failure of the neural crest-derived epidermal melanoblasts and enteric nervous system (ENS) precursors to completely colonize the skin and intestine, respectively. We demonstrate that during normal rat development, the EDNRB mRNA expression pattern is consistent with expression by ENS precursors throughout gut colonization. We used the human dopamine-beta-hydroxylase (DbetaH) promoter to direct transgenic expression of EDNRB to colonizing ENS precursors in the sl/sl rat. The DbetaH-EDNRB transgene compensates for deficient endogenous EDNRB in these rats and prevents the intestinal defect. The transgene has no effect on coat color spotting, indicating the critical time for EDNRB expression in enteric nervous system development begins after separation of the melanocyte lineage from the ENS lineage and their common precursor. The transgene dosage affects both the incidence and severity of the congenital intestinal defect, suggesting dosage-dependent events downstream of EDNRB activation in ENS development.     

Colonization of living skin equivalents by Malassezia furfur

In previous studies, we withdrew thyroid hormones by thyroidectomy before, at, or after the onset of photostimulation and showed that male American tree sparrows (Spizella arborea) are programmed for seasonal reproduction and postnuptial molt by or before Week 3 on long days. In this corollary study, we withdrew long days before or after the control circuits had been programmed. After 1 day to 4 wk on long days, groups of thyroid-intact males were returned to short days until Week 7, when they were moved to constant light and evaluated for photosensitivity or photorefractoriness and postnuptial molt. Long-day controls held 7 wk on long days showed robust testicular growth through Week 6 and then spontaneous testicular regression. Testes of short-day controls and of males photostimulated for 1 day remained small. In all other groups, photostimulation induced testicular growth, which gave way to regression during exposure to short days. Long-day controls tested photorefractory at Week 7 and initiated molt by Week 10. All other groups tested photosensitive and did not molt. Our demonstration that long days are required for expression of seasonal reproduction and postnuptial molt in thyroid-intact male tree sparrows previously programmed for these events suggests that long days create a milieu that is permissive for expression.     

Immunocytochemical study of retinal diode laser photocoagulation in the rat

AIM: To determine the nature of the cellular infiltrate, alterations in cell adhesion molecules, and MHC II antigen expression in the rat retina following diode laser retinal photocoagulation. METHOD: 20 normal Lister rats underwent diode laser photocoagulation of the retina. Frozen sections from eyes enucleated at 0, 1, 5, 13, and 33 days post laser were examined for T cells (R7.3), CD4 T cells (W3/25), activated CD4 T cells (OX-40), CD8 T cells (OX-8), B cells (OX-33), and macrophages (OX-42), MHC II antigen (OX-6), and E-Selectin-1, VCAM-1, and ICAM-1. RESULTS: Retinal diode laser photocoagulation stimulated a wound healing response in the outer retina and choroid. The cellular infiltrate included macrophages and activated CD4 T cells at 13 and 33 days post laser. Glial cells in the inner plexiform and inner nuclear layers expressed MHC II antigen at 24 hours only. ICAM-1 antigen was induced in RPE cells and in Muller cells in the inner retina at all time intervals post laser and intense staining for ICAM-1 was present around intraretinal migrated cells at 13 and 33 days post laser. VCAM-1 antigen expression was induced in the choroidal vascular endothelium and RPE at 13 and 33 days after laser as was E-Selectin-1 antigen expression which was also evident focally at the external limiting membrane in association with migrated cells adjacent to the burn. CONCLUSIONS: These results suggest that alterations in cell adhesion molecules may regulate the migration and activation of retinal pigment epithelium, macrophages and CD4 T cells at the outer blood-retinal barrier and choroid following diode laser photocoagulation of the normal Lister rat retina.     

The high-affinity sulphonylurea receptor regulates KATP channels in nerve terminals of the rat motor cortex

The coexpression of sulphonylurea binding sites and ATP-sensitive K+(KATP) channels was examined in the rat motor cortex, an area of the CNS exhibiting a high density of sulphonylurea binding. These channels were not detected on neuronal cell bodies, but sulphonylurea-sensitive KATP channels and charybdotoxin-sensitive, large-conductance calcium-activated K+ BKCa channels were detected by patch clamping of fused nerve terminals from the motor cortex. Subcellular fractionation revealed that high-affinity sulphonylurea binding sites were enriched in the nerve terminal fraction, whereas glibenclamide increased calcium-independent glutamate efflux from isolated nerve terminals. It is concluded that neuronal sulphonylurea receptors and KATP channels are functionally linked in the motor cortex and that they are both selectively expressed in nerve terminals, where the KATP channel may serve to limit glutamate release under conditions of metabolic stress.