Spatial learning by rats across visually disconnected environments

Two spatial tasks were designed to test specific properties of spatial representation in rats. In the first task, rats were trained to locate an escape hole at a fixed position in a visually homogeneous arena. This arena was connected with a periphery where a full view of the room environment existed. Therefore, rats were dependent on their memory trace of the previous position in the periphery to discriminate a position within the central region. Under these experimental conditions, the test animals showed a significant discrimination of the training position without a specific local view. In the second task, rats were trained in a radial maze consisting of tunnels that were transparent at their distal ends only. Because the central part of the maze was non-transparent, rats had to plan and execute appropriate trajectories without specific visual feedback from the environment. This situation was intended to encourage the reliance on prospective memory of the non-visited arms in selecting the following move. Our results show that acquisition performance was only slightly decreased compared to that shown in a completely transparent maze and considerably higher than in a translucent maze or in darkness. These two series of experiments indicate (1) that rats can learn about the relative position of different places with no common visual panorama, and (2) that they are able to plan and execute a sequence of visits to several places without direct visual feed-back about their relative position.     

Humoral immunity and regulation of intrapulmonary growth of Legionella pneumophila in the immunocompetent host

The potential role of humoral immunity in regulating intrapulmonary growth of Legionella pneumophila in the immunocompetent host was investigated using a murine model of Legionnaires' disease. Intratracheal inoculation of A/J mice with a virulent strain of L. pneumophila (10(6) bacteria per mouse) resulted in the recruitment of B lymphocytes into the lung and the development of anti-L. pneumophila Ab. Opsonization of L. pneumophila in vitro with anti-L. pneumophila-specific mAb resulted in a significant decrease in intrapulmonary growth of the bacteria at 24 to 72 h postinfection. Transmission electron microscopic analysis of lung tissue from L. pneumophila- infected mice demonstrated that while there was no significant difference between phagocytosis of the unopsonized and opsonized L. pneumophila by alveolar macrophages at 24 h postinfection, phagocytosis of opsonized bacteria by alveolar mononuclear phagocytic cells was significantly enhanced at 48 h postinfection. Depletion of A/J mice of complement before intratracheal inoculation of opsonized L. pneumophila (10(6) bacteria per mouse) did not significantly alter intrapulmonary growth of L. pneumophila. These results suggest that anti-L. pneumophila Ab, produced during replicative L. pneumophila lung infections, may regulate intrapulmonary growth of L. pneumophila in the immunocompetent host by decreasing the viability of extracellular L. pneumophila and by enhancing phagocytosis of the bacteria by alveolar mononuclear phagocytic cells by a complement-independent mechanism.     

Kidney in Galloway-Mowat syndrome: clinical spectrum with description of pathology

The Galloway-Mowat syndrome, a rare inherited disorder, is characterized by congenital microcephaly with hypotonia and developmental delay, often hiatus hernia, and nephrotic syndrome manifested in infancy or in early childhood. The glomerular lesion has been poorly characterized in the few previous reports of this syndrome. We studied three siblings with microcephaly and nephrotic syndrome occurring during the first two weeks of life. Hematuria, glycosuria and renal failure were also present. Renal biopsy and postmortem specimens of two patients were studied. Glomerular structure was disorganized; capillary lumina were of varying calibers, capillary walls were adherent to one another, and mesangial zones were poorly demarcated. Glomerular basement membrane ultrastructure was markedly altered. The normal trilaminar structure was obscured or replaced by flocculent material; furthermore, 6 to 8 nm fibrils of unknown nature permeated the space between endothelial and epithelial cells. Non-glomerular basement membranes were unaltered in appearance. This syndrome apparently represents, in part, a new disorder of glomerular basement membrane formation and function.     

Analysis of the interaction of water with the manganese cluster of photosystem II using isotopically labeled water

The association of water with the Mn of the water oxidizing complex was investigated using H2(17)O- and 2H2O-reconstituted lyophilized photosystem II particles. The pulsed electron paramagnetic resonance (EPR) technique of electron spin echo envelope modulation (ESEEM) was used to investigate the interaction of the magnetic 2H and 17O nuclei with the paramagnetic S2 state of the Mn complex and other photosystem II components. ESEEM offers a much more specific and sensitive detection of this type of interaction than continuous wave (CW) EPR. Unlike earlier reports using CW EPR, these experiments did not detect any interaction of water with the multiline EPR signal from the S2 state of the Mn complex. No signals indicating specific interaction of either H or O with the multiline signal were detected. Signals due to 2H and 17O were detected only at the Larmour frequency, indicating nonspecific "distant ENDOR" effects. A weak interaction with 17O was detected both in S1, when the Mn is EPR silent, and in S2, but only on the high-field side of g = 2. This interaction may be with the Rieske iron-sulfur center in the cytochrome b6f complex. The results were the same whether the multiline signal was generated by 200 K illumination of dark-frozen samples, or by room temperature illumination in the presence of the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Illumination at room temperature in the presence of an electron acceptor to allow multiple turnovers of the system with cycling of the S states did not result in the appearance of any new interactions. These results appear to exclude close (less than 6 A) binding of water to the Mn center giving rise to the multiline signal, and also to exclude mechanisms in which water oxidation involves the breaking and re-formation of the mu-oxo bridges of the Mn complex. They cannot, however, exclude models in which water binding to the manganese complex and direct oxidation by the manganese complex occur in the higher S states, or are catalyzed by one bis(mu-oxo) Mn dimer while oxidizing equivalents are accumulated in the S2 state by a second bis(mu-oxo) Mn dimer.     

Conditioning-related protection from acoustic injury: effects of chronic deefferentation and sham surgery

The inner ear can be made less vulnerable to acoustic injury by a "conditioning" treatment involving exposure to a moderate-level acoustic stimulus before the acoustic overexposure. The present study was designed to explore the role of the olivocochlear (OC) system in this "protection." Guinea pigs were divided into a number of groups: some (trauma-only) were exposed to a traumatic noise for 4 h at 109 dB SPL; others (condition/trauma) were conditioned by daily exposure to the same noise at 85 dB SPL before the traumatic exposure. In OC-intact animals, the condition/trauma group showed significantly less permanent threshold shift (PTS) than the trauma-only group as measured via compound action potentials and distortion-product otoacoustic emissions (DPOAEs). Other animals with identical noise-exposure regimens underwent deefferentation surgery before the start of conditioning: the OC bundle (OCB) was cut in the brain stem, either at the midline (cutting the crossed OCB to both ears) or at the sulcus limitans (cutting all OC fibers to 1 side). Lesion success was quantified by measuring OC fascicles to the outer hair cell region in each ear. The results from the surgical groups showed that total loss of the OCB significantly increased the noise-induced PTS, whereas loss of the COCB only did not; that the conditioning exposure in deefferented animals increased, rather than decreased, the PTS from the traumatic exposure; and that animals undergoing sham surgery (brain stem cuts that failed to transect the OCB) appeared protected whether or not they received the conditioning noise exposure. The latter result suggests that conditioning-related protection may arise from a generalized stress response, which can be elicited by noise exposure, brain surgery, or a variety of other means. The former results make an OC role in the conditioning process, per se, difficult to assess, given the large effects of OC activity on general acoustic vulnerability.     

Electron microscopy of the lesions produced in the human dura mater by Quincke beveled and Whitacre needles

INTRODUCTION: Comparisons of Quincke needles and non traumatic "pencil point" needles in recent years have reported lower rates of post dural puncture headache using the later type. Our new understanding of the morphology of the human dura mater motivated us to study dural lesions caused by the Whitacre 25 G and Quincke 26 G needles, using scanning electron microscopy with the aim of determining whether there is an anatomic basis for the different outcomes. METHOD: The dura mater from three fresh cadavers of individuals aged 65, 70 and 72 years were punctured 40 times at an angle of 90 degrees each time. The Whitacre 25 G needle was used for 20 punctures and the Quincke 26 G needle was used for the other 20. Half the punctures were performed with the bevel in the parallel alignment and the other half with the bevel perpendicular to the spinal column. Fifteen min after causing the punctures, specimens were fixed in solutions of glutaraldehyde phosphate buffer and dehydrated in acetone. After critical point removal of the acetone, after the specimens were treated with carbon and metallized with gold. The lesions were examined externally and internally and expressed as the ratio of area of lesion to diameter of the needle that had caused them. RESULTS: Whitacre needle: each lesion consisted in the superimposition of multiple damaged layers that started to close individually. After 15 min the outermost layers were 90% closed and the innermost ones had closed entirely. Layers in the arachnoid surface of the dura mater had closed from 86 to 88%, while deeper layers in the thick part had closed 97 to 98%. Quincke needle: lesions were V-shaped or half-moon shaped, much like the opening formed by a can opener, on both the external and internal surfaces. Alignment of the bevel of the needle parallel to the spinal column did not lead to a different shape of puncture. After 15 min the lesions had closed 94 to 95% on the epidural surface and 95 to 96% on the arachnoid side, a difference attributable to the retraction of the arachnoid layers over the spinal column. CONCLUSION: Non traumatic beveled dural needles, termed "pencil point needles", only partially separate dural fibers, and lesions caused by these needles develop in a more complex way. The Quincke 26G needle produced a puncture that is morphologically different from that caused by the Whitacre 25G needle, although lesions produced by both types close more than 94% after 15 min. We believe the size of the lesion caused by these needles does not explain the difference in post dural puncture headache due to loss of spinal fluid.     

Update on physical state of bile

Because of recent assertions by a group of investigators that structures called "lamellae" instead of mixed micelles are present in human bile, the nature of biliary cholesterol solubilization and transport ("carriage") has again become a matter of dispute. "Lamellae" are rod- or tubular- shaped banded images observed when biles are negatively stained and dehydrated during electron microscopy; they are believed to be composed principally of biliary phospholipid (which is mostly lecithin) and cholesterol. It is well known that when mixed together in aqueous systems, lecithin and cholesterol, which are otherwise insoluble amphiphilic lipids, swell to form stacked or multilamellar liquid crystals that have regular periodicity because of the bilayer arrangement of the molecules. Provided super-micellar concentrations of cholesterol are present, multilamellar vesicles occur spontaneously in concentrated model biles, and are a frequent occurrence in human gallbladder biles that are beginning to nucleate cholesterol crystals. When multilamellar vesicles are negatively stained and dehydrated, they produce "lamellae" images by electron microscopy. Coincidentally, images of "lamellae" are also produced when purely micellar bile, either model or native is treated similarly. In this review we show that these images are an artifact. This artifact is produced by the dehydration process itself and is due to a phase change i.e. a change in molecular packing which is predicted by the appropriate phase diagram. As a consequence, a dehydrated "lamellae" phase results and the overall effect is an electron microscopic image that is identical to those produced by multilamellar vesicles in supersaturated or lithogenic biles.(ABSTRACT TRUNCATED AT 250 WORDS)