Variation in GABA mini amplitude is the consequence of variation in transmitter concentration

Miniature postsynaptic currents (minis) in cultured retinal amacrine cells, as in other central neurons, show large variations in amplitude. To understand the origin of this variability, we have exploited a novel form of synapse in which pre- and postsynaptic receptors sample the same quantum of transmitter. At these synapses, mini amplitudes measured simultaneously in the 2 cells show a strong correlation, accounting for, on average, more than half of the variance in amplitude. Two pieces of evidence support the conclusion that variations in the amount of transmitter in different quanta underlie this correlation. First, diazepam, which enhances GABA binding, increases mini amplitude, implying therefore that transmitter concentration is not saturating. Second, we show that amplitude distributions from all cells, even those with a small number of release sites, have the same shape, implying that most or all variance is intrinsic to each release site.

Signal clipping by the rod output synapse

The properties of synapses between retinal neurons make an essential contribution to early visual processing. Light produces a graded hyperpolarization in photoreceptors, up to 25 mV in amplitude, and it is conventionally assumed that all of this response range is available for coding visual information. We report here, however, that the rod output synapse rectifies strongly, so that only potential changes within 5 mV of the rod dark potential are transmitted effectively to postsynaptic horizontal cells. This finding is consistent with the voltage-dependence of the calcium current presumed to control neurotransmitter release from rods. It suggests functional roles for the strong electrical coupling of adjacent rods and the weak electrical coupling of adjacent rods and cones. The existence of photoreceptor coupling resolves the apparent paradox that rods have a 25 mV response range, while signals greater than 5 mV in amplitude are clipped during synaptic transmission. We predict that the strengths of rod-rod and rod-cone coupling are quantitatively linked to the relationship between the rod response range and the synapse operating range.

Control of transmitter release from retinal amacrine cells by Ca2+ influx and efflux

Cultured retinal amacrine cells show quantal GABAergic synaptic transmission. Voltage clamping pre- and post-synaptic cells of an isolated pair has allowed us to examine the entry and removal of Ca2+ at synaptic terminals. Brief presynaptic Ca2+ currents elicit an initial postsynaptic current that probably reflects the roughly synchronous exocytosis of docked vesicles. Prolonged Ca2+ currents elicit an additional second phase of release whose time course can greatly exceed that of the presynaptic voltage step. The time course of this second phase reflects a sustained increase in cytosolic Ca2+ and is matched closely by the activity of the presynaptic Na-Ca exchanger, as revealed by an exchange current. Eliminating the activity of the exchanger by removal of external Na+ prolongs this second phase of transmission greatly. Because transmitter release at these synapses outlasts Ca+ channel opening, Na-Ca exchange plays a significant role in shaping transmission.

The effects of dark rearing on the development of the visual cortex of the rat

The effects of dark rearing on the development of the visual cortex has been studied in Wistar rats, as have the effects of subsequent light exposure on recovery. Five groups of animals were used: (1) light exposed until 30-40 days post partum (dpp) (2) dark reared until 30-40 ddp (3) dark reared until 80-120 dpp (4) dark reared to 21 dpp, then light exposed until 40 dpp (5) light exposed to 21 dpp and then dark reared until 40 dpp. Golgi-Cox impregnations of layer IV stellate cell dendritic fields were analysed and total neuronal and glial counts were also done within layer IV of the primary visual cortex. Normal visual stellate cell dendritic fields were radially organised, with the highest dendritic density being recorded below the soma. In short term visually deprived animals and in the exposed only for 21 dpp and then reared in light until 40 dpp the radial distribution of dendrites was maintained but the peak density shifted to above the soma. In all other experimental groups this abnormal polarisation was still present but not as marked. Measurement of branching indices suggested that these field changes resulted from increased branching and growth in the superficial domain and not from the reorientation of dendrites. Differential glial counts revealed a significantly higher number of microglia in dark reared animals than in controls. Neuronal numbers were not affected.

The kinetics of quantal transmitter release from retinal amacrine cells

Exocytosis of transmitter at most synapses is a very fast process triggered by the entry of Ca2+ during an action potential. A reasonable expectation is that the fast step of exocytosis is followed by slow steps readying another vesicle for exocytosis but the identity and kinetics of these steps are presently unclear. By voltage clamping both pre- and postsynaptic neurons in an isolated pair of retinal amacrine cells, we have measured evoked synaptic currents and responses to single vesicles of transmitter (minis). From these currents, we have computed the rate of exocytosis during a sustained presynaptic depolarization. We show here that for these cells, release is consistent with a scheme of "fire and reload." Large Ca2+ influx causes the rapid release of a small number of vesicles, typically approximately 10 per presynaptic neuron, likely corresponding to those vesicles already docked. After this spike of exocytosis whose peak is 150 quanta per release site per s, continued Ca2+ influx sustains release at only 22 quanta per release site per s, probably rate-limited by the docking of fresh vesicles.

Effects of ethanol on postnatal cell acquisition in the rat cerebellum

Cell generation and cell survival were investigated in the cerebellum of young rats exposed to 10% v/v ethanol in drinking water throughout gestation and lactation. At 12 days postpartum, cell cycle parameters in the external granular layer showed no significant change from control values, and the cell acquisition rate was unaffected. However, the external granular layer appeared thicker in ethanol-treated than in control 12-day-old animals, and a significant increase in cell death in the internal granular layer was observed. It is suggested that the effect of ethanol on the developing cerebellum may involve reduction of granule cell number consequent to increased granule cell death, and possibly retarded migration from the proliferating precursor cell pool.

A study of alcohol effects on the brain during gestation and lactation

Pregnant Wistar rats were maintained on a diet of food pellets and a 10% (v/v) solution of ethanol in water during pregnancy and up to 21 days postpartum. Control groups were given food pellets and water ad libitum. The consumption of food and liquid was monitored throughout this period, so that daily food- and ethanol-derived caloric intake, daily liquid intake, and dose of alcohol ingested could be determined. The body weights and whole brain weights of ethanol-exposed offspring did not differ significantly from controls at any time from birth up to 21 days postpartum. However, cerebellar weights were significantly reduced in 21-day-old ethanol-exposed offspring. Areal analysis of the cerebellar vermis showed a 9% reduction in 21-day-old ethanol-exposed offspring compared with controls. Although there were no differences in total vermal area between control and treated rats at 12 days, ethanol-exposed offspring had a significantly more extensive external granular layer. In midgestation, pregnant females registered peak alcohol levels of 118 mg/100 ml blood 1 hr prior to the end of the dark cycle, while during lactation peak levels of 135 mg/100 ml blood were obtained. Neonate alcohol levels peaked slightly later and reached much lower values (44 mg/100 ml blood) during the lactation period. Ingested alcohol intake and blood alcohol levels fall within the range associated in man with the fetal alcohol syndrome, and it is suggested that the experimental regime described is a useful method for investigating the effects of alcohol on the developing nervous system.

Tau-dependent suppression of adult neurogenesis in the stressed hippocampus

Stress, a well-known sculptor of brain plasticity, is shown to suppress hippocampal neurogenesis in the adult brain; yet, the underlying cellular mechanisms are poorly investigated. Previous studies have shown that chronic stress triggers hyperphosphorylation and accumulation of the cytoskeletal protein Tau, a process that may impair the cytoskeleton-regulating role(s) of this protein with impact on neuronal function. Here, we analyzed the role of Tau on stress-driven suppression of neurogenesis in the adult dentate gyrus (DG) using animals lacking Tau (Tau-knockout; Tau-KO) and wild-type (WT) littermates. Unlike WTs, Tau-KO animals exposed to chronic stress did not exhibit reduction in DG proliferating cells, neuroblasts and newborn neurons; however, newborn astrocytes were similarly decreased in both Tau-KO and WT mice. In addition, chronic stress reduced phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR)/glycogen synthase kinase-3β (GSK3β)/β-catenin signaling, known to regulate cell survival and proliferation, in the DG of WT, but not Tau-KO, animals. These data establish Tau as a critical regulator of the cellular cascades underlying stress deficits on hippocampal neurogenesis in the adult brain.

Are some minis multiquantal?

The amplitude distribution of miniature postsynaptic currents (minis) in many central neurons has a large variance and positive skew, but the sources of this variance and skew are unresolved. Recently it has been proposed that spontaneous Ca2+ influx into a presynaptic bouton with multiple release sites could cause spontaneous multiquantal minis by synchronizing release at all sites in the bouton, accounting for both the large variance and skew of the mini distribution. We tested this hypothesis by evoking minis with internally perfused, buffered Ca2+ and the secretagogue alpha-latrotoxin, both in the absence of external Ca2+. With these manipulations, the synchronized release model predicts that the mini distribution should collapse to a Gaussian distribution with a reduced coefficient of variation. Contrary to this expectation, we find that mini amplitude distributions under these conditions retain a large variance and positive skew and are indistinguishable from amplitude distributions of depolarization-evoked minis, strongly suggesting that minis are uniquantal.

The effect of ethanol on the cellular composition of the cerebellum

Pregnant Wistar rats were fed on a diet of food pellets and a 10% (v/v) solution of ethanol in water during pregnancy and up to 21 days postnatally. Control groups were given food pellets and water ad libitum. Areal analysis of the cerebellum of neonates showed a significant reduction of 9.7% to 12.4% in three selected lobules of the mid-sagittal vermis. Although there were no significant decreases in the linear frequency and absolute number of Purkinje cells, all three lobules showed a small percentage decrease in the length of Purkinje cell layer. The total number of granule cells was significantly reduced in all three lobules, and the ratio of granule cells to Purkinje cells was reduced by between 8.6% and 13.6%, although not significantly. The pyknotic index in the external granular layer (but not in the internal granular layer) and significantly increased at 21 days, while mitotic activity was unchanged. The extent of the diminution in the cell number of the internal granular layer suggests that besides increased cell death there may be a disturbance of cell proliferation kinetics in the precursor pool of the external granular layer. Although it is known that high blood levels can cause death of Purkinje cells, the moderate alcohol blood levels attained in this study were insufficient to do so.

Evaluation of characteristics of Pediococcus spp. to be used as a vaginal probiotic

AIMS

The aim of our research was to select, identify and characterize an isolate of lactic acid bacteria to be considered as a vaginal probiotic.

METHODS AND RESULTS

Thirty-five isolates of Pediococcus spp. showed bacteriocinogenic activity against Listeria monocytogenes and the ability to survive in simulated vaginal fluid (SVF) at pH 4.2. One isolate of Pediococcus spp. was selected and characterized to evaluate its safety before the use as vaginal probiotic. Pediococcus pentosaceus SB83 did not show the presence of virulence factors such as the production of gelatinase, lipase and DNase, haemolytic activity, nor the presence of virulence genes (genes esp, agg, gelE, efaAfm, efaAfs, cylA, cylB and cylM). Pediococcus pentosaceus SB83 was considered sensitive to chloramphenicol, gentamicin, streptomycin, kanamycin, erythromycin and ampicillin. This strain was considered resistant to tetracycline and vancomycin. Pediococcus pentosaceus SB83 was a biofilm producer at different pH values (4.2, 5.5 and 6.5) in SVF and in de Man, Rogosa and Sharpe medium.

CONCLUSIONS

The in vitro results provide a basis for the use of P. pentosaceus SB83 as a vaginal probiotic, to prevent colonization by L. monocytogenes in pregnant women.

SIGNIFICANCE AND IMPACT OF STUDY

The application of vaginal probiotics could have the potential for preventing vaginal infections and consequently reduce abortion and neonatal infections.

Behaviour of Listeria monocytogenes isolates through gastro-intestinal tract passage simulation, before and after two sub-lethal stresses

The effects of previous exposure to sub-lethal acidic and osmotic stresses on the survival of Listeria monocytogenes during exposure to gastro-intestinal (GI) tract simulation, was investigated. Six L. monocytogenes strains isolated from cheeses were selected and exposed to high salt concentrations or acidic conditions and their viability compared in quick and slow digestions. The results demonstrated that (i) all isolates were more sensitive to the exposure to acidic than to osmotic sub-lethal conditions (ii) significant differences (p < 0.05) between the two types of digestion were observed; in slow digestion, the log reduction was higher for all the tested isolates (iii) all isolates were inhibited in the presence of bile salts for both types of digestion (iv) differences between quick and slow digestion were not observed (p > 0.05) after exposure to either osmotic or acidic stress (v) a higher cellular inactivation (p < 0.001) was observed during the passage through the GI tract simulation after exposure to osmotic than to acidic stresses and (vi) neither osmotic nor acidic sub-lethal stresses conferred resistance to simulated GI tract conditions.

Structure of the receptive fields of bipolar cells in the salamander retina

1. The receptive-field structure of bipolar cells in the salamander retina has been examined using isolated retinae from dark-adapted eyes. 2. Receptive-field mapping was carried out with a 25-microns diam spot of light whose wavelength and intensity was intended to stimulate rods rather than cones. 3. Both hyperpolarizing and depolarizing bipolar cells showed receptive fields having a single central point of maximum sensitivity from which sensitivity declined radially. Antagonistic surrounds could not be demonstrated using a small spot of light. 4. The diameter of receptive fields was found to vary between 374 and 662 micron, consistent with a single bipolar cell being effectively connected to 323-1,275 rods. 5. Lucifer yellow injections of bipolar cells revealed dendritic arbors whose greatest dimensions varied between 43 and 70 microns, consistent with a direct synaptic connection of between 10 and 24 rods to each bipolar cell. 6. We rule out signal spread within the rod network, extensive lateral ramification of rod process, nonlinearity of synaptic transmission, and light scatter, as possible explanations of large bipolar cell receptive fields. It seems likely, instead, that signals are extensively shared between bipolar cells.

The effects of glycine and GABA on isolated horizontal cells from the salamander retina

1. Horizontal cells, identified by their morphology, were isolated from the salamander retina and examined in whole cell patch clamp. 2. All cells showed large outward currents activating positive to about -50 mV, and a minority of cells showed fast, tetrodotoxin-suppressible Na+ currents. Slow inward currents that might shape the light responses were never observed. 3. All cells showed conductance increases to both gamma-aminobutyric acid (GABA) and glycine that were completely blocked by bicuculline and strychnine, respectively. No cross-blocking by these antagonists was observed. Partial replacements of Cl- with large, impermeant anions indicated that both GABA- and glycine-evoked currents were carried by Cl- ions. 4. Responses to both GABA and glycine desensitized strongly with time constants of approximately 2 s. 5. Responses to glutamate were not enhanced by glycine. Similarly, responses to GABA were not enhanced by glutamate. 6. GABA-mediated synaptic interactions between horizontal cells may account for the changes in the kinetics of horizontal cell light responses seen when glycine is applied to the intact retina.

Women's narratives in primary care medical encounters

OBJECTIVE

This study asked how women's narratives of social and emotional problems are dealt with in primary care encounters. Our conceptual work extended perspectives from narrative analysis to focus on elements of ideology, social control, underlying structure, and features of discourse that appear marginal to medicine's technical tasks.

METHOD

Based on a critical review of both quantitative and qualitative techniques in research on patient-doctor communication, we developed an interpretive method with criteria to guide sampling, transcription, interpretation, and presentation of findings. We applied the method to encounters which were selected randomly from a data base derived from a stratified random sample of 336 audiotaped encounters involving patients and primary care internists.

FINDINGS

As shown by illustrative encounters, women's narratives in primary care often express emotional troubles related to gender roles. Medical discourse in these encounters tends to marginalize contextual issues that contribute to women's distress. Such discourse conveys acceptance of reproductive commitments, medical management of psychic distress, and lack of criticism regarding social problems that affect women.

CONCLUSIONS

Narrative analysis clarifies the medical processing of women's emotional problems that derive in large part from the social context of medicine. Women patients and medical practitioners often deal with these issues in primary care encounters rather than in psychiatric settings. These findings suggest directions for improving the discourse of primary care encounters.

Angiomatoid fibrous histiocytoma of the arm treated by radiotherapy for local recurrence--case report

The Angiomatoid Fibrous Histiocytoma is a rare tumor of soft tissues, which occurs mainly in children and young adults, with low malignancy grade. It has the capacity of local recurrence, but rarely metastizes. It is frequently difficult to differentiate this from vascular tumors, namely hemangioendotheliomas and angiosarcomas, or simply organized hematomas. The authors present a case of a patient with an angiomatoid fibrous histiocytoma of the arm, treated with radiotherapy after three postsurgical recurrences.

Neurotensin induces calcium oscillations in cultured amacrine cells

The peptide, neurotensin, is found in a class of amacrine cells synapsing chiefly with other amacrine cells in the chicken retina (Li & Lam, 1990; Watt et al., 1991). To investigate the possible effects of neurotensin, we have used Ca2+ imaging to measure cytosolic Ca2+ concentrations in cultured chick amacrine cells. Following a delay of about 2 min, neurotensin (300 nM) induced oscillations in Ca2+ concentration that typically had a period of 2 min and peak values of about 300 nM when averaged over the cell body. The phospholipase C inhibitors U-73, 112 and 4'-bromophenacyl bromide terminated oscillations induced by neurotensin but the protein kinase inhibitors H7 and staurosporine did not inhibit oscillations, increasing their frequency instead. In the absence of external Ca2+, neurotensin induced only a single Ca2+ transient, much briefer than when external Ca2+ was present. Together these results suggest that neurotensin activates phospholipase C, thereby producing IP3 that triggers Ca2+ release from an internal store. Although this released Ca2+ contributes to periodic Ca2+ peaks, the majority of cytosolic Ca2+, even in the first peak, comes from Ca2+ influx across the plasmalemma.

Pediococcus pentosaceus SB83 as a potential probiotic incorporated in a liquid system for vaginal delivery

Pediococcus pentosaceus SB83 is a bacteriocinogenic culture having potential use as a vaginal probiotic. The objective of this study was to evaluate the behaviour of P. pentosaceus SB83 incorporated in a liquid system for eventually formulating a gel for vaginal delivery. The vaginal probiotic incorporated into glycerol was able to survive in simulated vaginal fluid at normal vaginal pH (4.2) and at pH of vaginal infections (5.5 and 6.5). The probiotic can be stored at 4 °C for a longer period of time than at room temperature, however, after 13 weeks of storage at low temperature, there was a total loss of viable cells. The probiotic strain incorporated into glycerol showed bacteriocinogenic activity in simulated vaginal fluid, although the antimicrobial activity against Listeria monocytogenes declined during storage. This study showed the behaviour of P. pentosaceus SB83 in glycerol and in simulated vaginal fluid. However, it is necessary to optimise the formulation to produce an actively probiotic vaginal gel.

Dual effect of glycine on horizontal cells of the tiger salamander retina

1. The effects of glycine on horizontal cells have been examined by microelectrode recording from superfused retinas isolated from the salamander. 2. Low concentrations of glycine (less than 50 microM) hyperpolarized horizontal cells and increased the magnitude of their light responses. Millimolar concentrations produced the opposite effect of depolarizing these cells and reducing their light response amplitudes. 3. In the presence of Co2+ and Mg2+ at concentrations sufficient to suppress the light response, millimolar glycine still exerted a depolarizing effect on horizontal cells, implying that this effect was largely a direct one on horizontal cell membranes. 4. Although both the rod and the cone contributions to horizontal cell light responses were reduced by millimolar glycine, rod input was reduced more, suggesting that millimolar glycine may also exert a presynaptic effect. 5. Strychnine (10 microns) antagonized the effects of millimolar glycine and, in the absence of exogenously applied glycine, caused horizontal cells to hyperpolarize and their light responses to increase in amplitude. This result implies that, in darkness, glycine is tonically released onto horizontal cells and maintains them in a state of partial depolarization. 6. The low-concentration effect of glycine was accompanied by an increased membrane resistance and receptive field size but no change in the balance of rod and cone input. 7. Low concentrations of glycine were often seen to cause a speeding of light responses, whereas high concentrations sometimes caused a slowing of response kinetics. Response kinetics were found to correlate with horizontal cell dark membrane potential so that, positive to -30 mV, depolarization slowed responses whereas kinetics at more negative values were largely independent of voltage.

[Microbiological examination of non-pasteurized ice creams]

Realizou-se exame microbiológico em 24 amostras de sorvetes não pasteurizados, todos preparados de maneira não industrial e à base de leite (creme, nata, chocolate), fabricados por 12 sorveterias diferentes da cidade de Araraquara, SP. Colheram-se duas amostras de cada sorveteria com intervalo de 15 dias entre as colheitas. Realizaram-se as seguintes provas: contagem de bactérias aeróbicas ou facultativas mesófilas e psicrófilas e de Staphylococcus aureus; determinação do Número Mais Provável (NMP) de coliformes totais e fecais e da presença de Salmonella. As técnicas utilizadas foram aquelas convencionalmente usadas para tais determinações. Não foi encontrada Salmonella em nenhuma das amostras e de cerca de 16,6% delas isolou-se Staphylococcus aureus. Em proporções variáveis verificou-se a presença de microrgarnismos deteriorantes e daqueles indicadores de poluição de origem fecal.

Evaluation of a new IOL scleral fixation technique without capsular support

PURPOSE

The purpose of this study was to compare a new intraocular lens (IOL) scleral fixation technique (scleral incision) with the scleral flap surgical technique as regards to efficacy, surgical complications, advantages, disadvantages, and surgery costs in cases with no capsular support.

MATERIAL AND METHODS

This was a retrospective study conducted on thirty patients (30 eyes), ten of whom were aphakic, eleven had traumatic cataract, seven had post-phacoemulsification complications, and two had lens luxation. The patients were divided into two groups (I - scleral incision technique and II - scleral flap technique) of fifteen patients each, during a study period lasting eighteen months. The great majority of the procedures were performed under general anesthesia and by the same surgeon. Statistical analysis was done using SPSS. The numerical variables were compared using the t test and the categorical ones using the Fisher exact test. We performed multifactorial analysis to build a model that could predict and compare the complications associated with each technique. An explicative model was built using logistic regression.

RESULTS

We observed a threefold higher rate of complications associated with the scleral flap technique when compared to the scleral incision technique. This difference was particularly relevant as regards the occurrence of free scleral flap and hyphema. No statistically significant differences were observed regarding vitreous hemorrhage, choroidal hemorrhage, retinal detachment, difficulty in the external pulling of the Prolene suture, breaking of the Prolene suture, and anterior chamber collapse. We found a significant association between intraoperative complications and the technique used (higher number of complications with the scleral flap) and also with some systemic diseases (patients with hypertension had more intraoperative complications). The number of late complications resulting from the scleral flap technique was much higher than those observed with the scleral incision technique; however, the number of the cases we studied is insufficient to reach statistical significance.

CONCLUSION

The duration of the procedure using the IOL scleral incision technique is significantly lower than using the scleral flap technique. Intraoperative complications were significantly associated with the technique used: more frequent with scleral flap. Late complications were mainly associated with systemic and previous ocular diseases.

Synthesis of (3) H, (2) H4 and (14) C-SCH 417690 (Vicriviroc)

Vicriviroc or SCH 417690 is a potent and selective antagonist of the CCR5 receptor. CCR5 receptor antagonists have the potential for the treatment of HIV infections. Four distinct isotopically labelled forms of SCH 417690 were synthesized. Low specific activity [(3) H]SCH 417690 was prepared for a preliminary absorption, distribution, metabolism and excretion evaluation of the compound and [(14) C]SCH 417690 for more definitive absorption, distribution, metabolism and excretion work, including an absorption, metabolism and excretion study in man. In addition, high specific activity [(3) H]SCH 417690 was prepared for CCR5 receptor binding work and [(2) H4 ]SCH 417690 was prepared as an internal standard for a liquid chromatography-mass spectrometry bioanalytical method. The paper discusses the synthesis of four isotopically labelled forms of SCH 417690.