Relative contributions of burst and tonic responses to the receptive field properties of lateral geniculate neurons in the cat.

1. In an anesthetized, paralyzed in vivo preparation, we recorded extracellular responses of 61 geniculate neurons (2 W, 25 X, 33 Y, and 1 mixed) to drifting sine-wave gratings of various spatial frequency, temporal frequency, and contrast. Our goal was to study the differential contributions to these visual responses of bursting caused by voltage dependent, low-threshold (LT) Ca2+ spikes and of purely tonic responses unrelated to LT spikes. Cells responding with LT spikes are said to be in the burst firing mode and those responding in a purely tonic fashion to be in the relay or tonic firing mode. We separated the total visual response into LT burst and tonic components by use of the empirical criteria set forth in our intracellular study described in the previous paper (Lu et al. 1992). A response component was considered to be an LT burst if its action potentials displayed interspike intervals < or = 4 ms and if the first spike in the burst episode occurred after a silent period of > or = 100 ms (or > or = 50 ms when the neuron responds to visual stimuli at temporal rates > or = 8 Hz). All other activity is considered to be part of the tonic response. 2. In addition to LT bursts, we recognized another type of burst response, the high-threshold (HT) burst. These also have clusters of action potentials with interspike intervals < or = 4 ms. However, HT bursts, unlike LT bursts, lack a preburst silent period. HT bursts are part of the tonic response component and merely reflect the gradual decrease in interspike intervals that occurs as the cell becomes more depolarized and thus more responsive. Thus interspike interval is a necessary but insufficient criterion to identify LT bursts. 3. Visually evoked LT bursts were recorded among W, X, and Y cells. When evoked, LT bursts occurred in phase with drifting sine-wave grating stimuli at a rate never exceeding one per stimulus cycle. In response to individual cycles of the visual stimulus, LT bursts could comprise the total response, a tonic component could comprise the total response, or an LT burst and tonic component could be mixed. When a stimulus evoked a mixture of LT bursts and tonic response components, LT bursts were always the first response. 4. Of the 61 cells tested with grating stimuli, 47 exhibited LT bursts and 14 did not. Those that did exhibited varying amounts of burstiness.(ABSTRACT TRUNCATED AT 400 WORDS)     

Monocyte/macrophage activation by normal bacteria and bacterial products: implications for altered epithelial function in Crohn's disease

Intestinal immune cells are less reactive than those in the peripheral blood; however, such cells from patients with Crohn's disease may be more responsive to bacterial products. Our study examined if nonpathogenic bacteria or lipopolysaccharide (LPS), can affect epithelial function in the presence of monocytes/macrophages. Lamina propria mononuclear cells (LPMCs) and peripheral blood monocytes (PBMs) were obtained from patients with Crohn's disease and control patients. Filter-grown T84 epithelial monolayers were co-cultured with nonactivated or LPS-activated LPMCs or PBMs for 48 hours. Epithelial secretory [baseline short-circuit current (Isc) and DeltaIsc to forskolin] and barrier (transepithelial electrical resistance) parameters were measured in Ussing chambers. LPS-activated PBMs from both controls and patients with Crohn's disease significantly increased Isc ( approximately 300%) and reduced transepithelial electrical resistance ( approximately 40%). Epithelial function was not altered after co-culture with control LPMCs +/- LPS. However, LPMCs from patients with Crohn's disease spontaneously secreted tumor necrosis factor-alpha, and induced epithelial changes similar to those produced by LPS-activated PBMs. Co-culture with control Escherichia coli and PBMs induced comparable changes in epithelial physiology, which were abrogated by anti-tumor necrosis factor-alpha antibody. We conclude that LPMCs of patients with Crohn's disease are spontaneously activated, possibly by gram-negative luminal bacteria, and can directly cause significant alterations in epithelial ion transport and barrier functions.     

Outer membranes are competitive inhibitors of Escherichia coli O157:H7 adherence to epithelial cells.

Escherichia coli of serotype O157:H7 are Vero cytotoxin-producing enteric pathogens that have been associated recently with sporadic cases and outbreaks of hemorrhagic colitis and with the hemolytic-uremic syndrome. Adherence of many enteropathogenic bacteria to mucosal surfaces is a critical step in the pathogenesis of diarrheal disease. We showed previously that adherence of E. coli O157:H7 strain CL-56 to epithelial cells in vitro is inhibited by outer membranes. In this study we examined whether outer membranes from a series of E. coli O157:H7 strains mediated competitive inhibition of bacterial binding to epithelial cells grown in tissue culture. We also determined which constituents of the outer membrane mediated inhibition of CL-56 adherence. Binding of six O157:H7 strains to HEp-2 cells was determined by quantitating the number of adherent bacteria in the presence and absence of outer membranes which were extracted from each strain with N-lauroyl sarcosinate (1.7%, wt/vol). After separation of outer membranes by gel electrophoresis, four bands (94, 40, 36, and 30 kDa) were collected by electroelution. Immune sera were raised in rabbits to each of the four eluted bands. Outer membrane extracts from each of the six O157:H7 strains inhibited binding of homologous organisms to the HEp-2 cells. At dilutions which did not cause bacterial agglutination, antiserum raised against the 94-kDa outer membrane protein showed maximal inhibition of bacterial adherence (17.0 +/- 7.3% adherence of control levels). Growth of bacteria in iron-depleted broth did not affect their binding to HEp-2 cells, suggesting that iron-regulated outer membranes were not involved. Fluid accumulation in ileal ligated loops of rabbits in response to E. coli O157:H7 challenge was diminished following both parenteral immunization with outer membranes extracted from the homologous strain and coincubation of organisms with immune serum which contained antibodies to outer membrane extracts. These data indicate that outer membranes are competitive inhibitors of E. coli O157:H7 adherence. Specific constituents of the outer membrane may function as bacterial attachment factors (i.e., adhesins) for E. coli O157:H7 adherence to epithelial cell surfaces.     

Effects of membrane voltage on receptive field properties of lateral geniculate neurons in the cat: contributions of the low-threshold Ca2+ conductance.

1. Thalamic relay cells, including those of the lateral geniculate nucleus, display a low-threshold spike (LT spike), which is a large depolarization due to an increased Ca2+ conductance. Typically riding the crest of each LT spike is a burst of from two to seven action potentials, which we refer to as the LT burst. The LT spike is voltage dependent, because if the cell's resting membrane potential is more depolarized than roughly -60 mV, the LT spike is inactivated, but if more hyperpolarized, the spike is deinactivated and can be activated by a depolarization, such as from an afferent excitatory postsynaptic potential (EPSP). Thalamic relay cells thus display two response modes: a relay or tonic mode, when the cell is depolarized and LT spikes are inactivated, leading to tonic firing of action potentials; and a burst mode, when the cell is hyperpolarized and tends to respond with LT spikes and their associated bursts of action potentials. 2. We were interested in the contribution of the LT spike on the transmission of visually evoked signals through geniculate relay cells to visual cortex. We recorded intracellularly from geniculate cells in an anesthetized, paralyzed, in vivo cat preparation to study the effects of membrane voltage, and thus the presence or absence of LT spikes, on responses to drifting sine-wave gratings. We monitored the visually evoked responses of 14 geniculate neurons (6 X, 7 Y, and 1 unclassified) at different membrane potentials at which LT spikes were inactivated or deinactivated. 3. Changing membrane voltage during visual stimulation switched the response mode of every cell between the relay and burst modes. In the burst mode, LT spikes occurred in phase with the visual stimulus and not at rhythmic intervals uncorrelated to visual stimuli. To any given stimulus cycle, the cell responded usually with an LT burst or a tonic response, and rarely was more than one LT burst evoked by a stimulus cycle. Occasionally a single cycle evoked both an LT burst and tonic response, but always the LT burst occurred first. 4. The spatial tuning characteristics of the cells did not differ dramatically as a function of membrane potential, because the tuning of the LT bursts was quite similar to that of the tonic response component. Although we did not obtain complete temporal tuning properties, we did note that hyperpolarized cells responded reliably with LT bursts at several temporal frequencies. 5. A consistent difference was seen between the LT burst and tonic response components in terms of response linearity.(ABSTRACT TRUNCATED AT 400 WORDS)     

Enhanced mitochondrial degradation of yeast cytochrome c with amphipathic structures

The dispensable N-terminus of iso-1-cytochrome c (iso-1) in the yeast Saccharomyces cerevisiae was replaced by 11 different amphipathic structures. Rapid degradation of the corresponding iso-1 occurred, with the degree of degradation increasing with the amphipathic moments; and this amphipathic-dependent degradation was designated ADD. ADD occurred with the holo-forms in the mitochondria but not as the apo-forms in the cytosol. The extreme mutant type degraded with a half-life of approximately 12 min, whereas the normal iso-1 was stable over hours. ADD was influenced by the ⁺/^– state and by numerous chromosomal genes. Most importantly, ADD appeared to be specifically suppressed to various extents by deletions of any of the YME1, AFG3, or RCA1 genes encoding membrane-associated mitochondrial proteases, probably because the amphipathic structures caused a stronger association with the mitochondrial inner membrane and its associated proteases. The use of ADD assisted in the differentiation of substrates of different mitochondrial degradation pathways.     

Fulminant disseminated Varicella Zoster virus infection without skin involvement.

BACKGROUND: Varicella Zoster virus (VZV) infection is potentially very serious in bone marrow transplant recipients, and may manifest as a disseminated visceral infection. This condition is generally accompanied by a vesicular rash. OBJECTIVES: We review here a case of fulminant fatal disseminated VZV infection, not accompanied by skin involvement, and the laboratory approaches currently available to diagnose this disease. STUDY DESIGN: Post mortem tissue samples were subjected to histopathological examination, and tested for herpesviruses by electron microscopy and PCR. RESULTS: Intranuclear inclusions were noted by histological examination in the lungs, liver, kidneys and bone marrow. Particles with a herpesvirus morphology were visualized in liver tissue. VZV DNA was detected in liver and bone marrow by PCR followed by sequencing of the amplicons. Viremia was documented by retrospective testing of the serum by PCR. CONCLUSIONS: A disseminated VZV infection which proved rapidly fatal was demonstrated in a case without skin manifestations. This rare presentation of VZV infection is potentially underdiagnosed. Testing for VZV viremia by PCR can at the very least suggest the diagnosis although whether plasma-associated viremia is truly pathognomonic of visceral disseminated infection remains to be established.     

Transvaginal sonographic assessment of cervical length changes during triplet gestation

The current study aimed to evaluate the contribution of transvaginal sonography (TVS) for monitoring cervical changes during the second half of triplet gestation. Forty-five pregnant women with triplets pregnancies were prospectively scanned by TVS from approximately 26 weeks gestation and were longitudinally followed-up until delivery. Based on a receiver-operating curve it was found that a cervical length of 25 mm is the most accurate parameter (94% sensitivity and 45% specificity) for predicting premature delivery < or =33 gestational weeks. Thus, a single cervical length measurement of < or =25 mm at 26 weeks gestation correlated well with premature delivery at < or =33 weeks (chi(2); P = 0.002). Using the linear regression model, a mathematical equation [(Week of delivery = 27.4 + 1.6 x cervical length; R(2) = 0.46; P = 0.01)] for predicting the gestational age of delivery (dependent variable) was determined based on mid-gestation cervical measurements (predictors). In parturient women with triplet gestation, TVS assessment of the uterine cervix offers insight into the cervical status and provides valuable information for prenatal care. This includes both monitoring the cervical changes throughout third trimester as well as predicting the likelihood of premature delivery.     

Cellular effects of deep brain stimulation: model-based analysis of activation and inhibition

Deep brain stimulation (DBS) is an effective therapy for medically refractory movement disorders. However, fundamental questions remain about the effects of DBS on neurons surrounding the electrode. Experimental studies have produced apparently contradictory results showing suppression of activity in the stimulated nucleus, but increased inputs to projection nuclei. We hypothesized that cell body firing does not accurately reflect the efferent output of neurons stimulated with high-frequency extracellular pulses, and that this decoupling of somatic and axonal activity explains the paradoxical experimental results. We studied stimulation using the combination of a finite-element model of the clinical DBS electrode and a multicompartment cable model of a thalamocortical (TC) relay neuron. Both the electric potentials generated by the electrode and a distribution of excitatory and inhibitory trans-synaptic inputs induced by stimulation of presynaptic terminals were applied to the TC relay neuron. The response of the neuron to DBS was primarily dependent on the position and orientation of the axon with respect to the electrode and the stimulation parameters. Stimulation subthreshold for direct activation of TC relay neurons caused suppression of intrinsic firing (tonic or burst) activity during the stimulus train mediated by activation of presynaptic terminals. Suprathreshold stimulation caused suppression of intrinsic firing in the soma, but generated efferent output at the stimulus frequency in the axon. This independence of firing in the cell body and axon resolves the apparently contradictory experimental results on the effects of DBS. In turn, the results of this study support the hypothesis of stimulation-induced modulation of pathological network activity as a therapeutic mechanism of DBS.     

Surface tension of animal cartilage as it relates to friction in joints

Measurements of the surface tension of articular cartilage and friction experiments were carried out to provide further evidence in support of a new theory regarding the mechanism of friction in joints. To determine the surface tension of cartilage, contact angle measurements were used in conjunction with the equation of state for interfacial tensions. The advancing contact angle between saline drops and articular cartilage was found to be 100°±5°, indicating a highly hydrophobic surface. The corresponding surface tension value was calculated to be 22.5 ergs/cm². Friction of cartilage against hydrophobic surfaces is shown to be lower than the friction of cartilage against hydrophilic surfaces. All these results further support the theory that lubrication by nonwetting drops occurs in joints and may be responsible for the exceptional friction characteristics of the joints.