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G Neves

Publications and source records attributed to G Neves.

10 recordsLinked to original sources
PubMed2001

Calcium influx selects the fast mode of endocytosis in the synaptic terminal of retinal bipolar cells.

To investigate the regulation of endocytosis by Ca(2+), we have made capacitance measurements in the synaptic terminal of depolarizing bipolar cells from the retina of goldfish. After a brief depolarization, all of the excess membrane was retrieved rapidly (tau approximately 1 s). But when the rise in free [Ca(2+)] was reduced by the introduction of Ca(2+) buffers [1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate (BAPTA) or EGTA], a large fraction of the membrane was retrieved by a second, slower mechanism (tau > or = 10 s). The block of fast endocytosis by EGTA could be overcome by increasing the amplitude of the Ca(2+) current, demonstrating that Ca(2+) influx was the trigger for fast endocytosis. These manipulations of the Ca(2+) signal altered the relative proportions of fast and slow endocytosis but did not modulate the rate constants of these processes. A brief stimulus that triggered fast endocytosis did not generate a significant rise in the spatially averaged [Ca(2+)], indicating that Ca(2+) regulated endocytosis through an action close to the active zone. The slow mode of retrieval occurred at the resting [Ca(2+)]. These results demonstrate that Ca(2+) influx couples fast endocytosis and exocytosis at this synapse.

Buffers↗
PubMed2001

The actions of barium and strontium on exocytosis and endocytosis in the synaptic terminal of goldfish bipolar cells.

1. We investigated the properties of Ca2+-sensitive steps in the cycling of synaptic vesicles by comparing the actions of Ca2+, Ba2+ and Sr2+ in the synaptic terminal of depolarizing bipolar cells isolated from the retina of goldfish. FM1-43 fluorescence and capacitance measurements demonstrated that exocytosis, endocytosis and vesicle mobilization were maintained when external Ca2+ was replaced by either Ba2+ or Sr2+. 2. The rapidly releasable pool of vesicles (RRP) was equivalent to 1.5 % of the membrane surface area when measured in the presence of 2.5 mM Ca2+, but only 0.4 % in 2.5 mM Sr2+. The relative sizes of the RRP in Ca2+, Sr2+ and Ba2+ were 1.0, 0.28 and 0.1, respectively. We conclude that a smaller proportion of docked vesicles are available for fast exocytosis triggered by the influx of Sr2+ or Ba2+ compared to Ca2+. 3. The slow phase of exocytosis was not altered when Ca2+ was replaced by Ba2+, but it was accelerated 1.6-fold in Sr2+. The peak concentrations of Ca2+, Sr2+ and Ba2+ (measured using Mag-fura-5) were approximately 4, approximately 14 and approximately 60 microM, respectively. The order of efficiency for the stimulation of slow exocytosis was Ca2+ approximately Sr2+ > Ba2+. 4. Exocytosis was prolonged after the influx of Sr2+ and Ba2+. Sr2+ was cleared from the synaptic terminal with the same time constant as Ca2+ (1.3 s), but Ba2+ was cleared 10-100 times more slowly. Although Ba(2+) stimulates the slow release of a large number of vesicles, it did so less efficiently than Ca2+ or Sr2+. 5. The recovery of the membrane capacitance was equally rapid in Sr2+ and Ca2+, demonstrating that the fast mode of endocytosis could be triggered by either cation.

Animals↗
PubMed2000

Screening for the antidepressant activity of some species of Hypericum from South Brazil.

The crude methanol extracts of three species of the genus Hypericum (H. brasiliense, H. caprifoliatum and H. myrianthum) native to South Brazil were evaluated for the antidepressant activity according to the forced swimming test, a classical animal model for antidepressant drug screening. Among the species studied, only H. caprifoliatum showed activity. Thus, this plant was fractionated with solvents in increasing polarity (petroleum ether; petroleum ether: chloroform (1:1); chloroform and methanol). The petroleum ether fraction was the only one which demonstrated antidepressant activity at a dose of 270 mg/kg/day (i.p.). The chemical analyses showed that this fraction is rich in phenolic compounds, mainly of the phloroglucinol type.

Analysis of Variance↗
PubMed2000

R. Daudt, G. L. Von poser, G. Neves and S. M. K. Rates, 'Screening for the antidepressant activity of some species of hypericum from south Brazil'. Phytotherapy research14(5) 2000, 344-346

The original article to which this Erratum refers was published in Phytotherapy Research 14(5) 2000, 344-346. Following the publication of this paper in the August 2000 issue of Phytotherapy Research (14(5):344-346), it has come to our attention that there is a misleading statement regarding conclusions cited from the work of Butterweck et al. 1998. The discussion in the recent PTR paper states that those authors are 'in favour of the hypothesis that the antidepressant activity is due to the hypericin only'. We wish to make it clear that this is not the case, and the Butterweck paper actually concludes that 'both naphthodianthrones must be considered as active constituents of the crude extract of H. perforatum. However, previous studies indicate that the other consitutuents of the crude drug also have activity'. The authors apologize for this error and are happy to correct it.

Journal Article↗
PubMed2000

Psychopharmacological screening of Pfaffia glomerata Spreng. (Amarathanceae) in rodents.

The alcoholic extract of Pfaffia glomerata roots (100, 500, 1000 mg/kg, intraperitoneally (i.p.), and 500, 1000, 1500 mg/kg, per os) was studied in several behavioral animal models for the evaluation of central activity: open field, barbiturate sleeping time, pentilenotetrazole (PTZ)-induced convulsions, elevated plus-maze, step-down inhibitory avoidance and forced swimming test. The acute treatment (500 mg/kg, i.p.) interfered with the open-field habituation, decreased sleep latency and increased barbiturate-induced sleeping time, protected partially the animals of PTZ-induced convulsions, decreased the memory retention in step-down inhibitory avoidance, and did not have an important effect in the elevated plus-maze test and forced swimming test. The same extract at 1000 mg/kg per os did not cause any effect in barbiturate sleeping time and pentilenotetrazole-induced convulsions models. Thus, the effect on the memory was deeper evaluated in the step-down inhibitory avoidance task. When administered by intraperitoneal route, the extract showed a dose-dependent effect causing full amnesia at 1000 mg/kg. On the other hand, when it was given by oral route at 500, 1000 and 1500 mg/kg, no influence on the memory retention was observed. These results suggest that the alcoholic extract of P. glomerata roots presents different effects depending on the route of administration: by i.p route, it seems to be a central nervous system depressant agent; by oral route, it seems to be ineffective, at least in the tested doses.

Administration, Oral↗
PubMed1999

The retina.

Explore the source record for details and available documents.

Animals↗
PubMed1999

The kinetics of exocytosis and endocytosis in the synaptic terminal of goldfish retinal bipolar cells.

1. The kinetics of exocytosis and endocytosis were studied in the giant synaptic terminal of depolarizing bipolar cells from the goldfish retina. Two techniques were applied: capacitance measurements of changes in membrane surface area, and fluorescence measurements of exocytosis using the membrane dye FM1-43. 2. Three phases of exocytosis occurred during maintained depolarization to 0 mV. The first component was complete within about 10 ms and involved a pool of 1200-1800 vesicles (with a total membrane area equivalent to about 1.6 % of the surface of the terminal). The second component of exocytosis involved the release of about 4400 vesicles over 1 s. The third component of exocytosis was stimulated continuously at a rate of about 1000 vesicles s-1. 3. After short depolarizations (< 200 ms), neither the FM1-43 signal nor the capacitance signal continued to rise, indicating that exocytosis stopped rapidly after closure of Ca2+ channels. The fall in capacitance could therefore be used to monitor endocytosis independently of exocytosis. The capacitance measured after brief stimuli began to fall immediately, recovering to the pre-stimulus baseline with a rate constant of 0.8 s-1. 4. The amount of exocytosis measured using the capacitance and FM1-43 techniques was similar during the first 200 ms of depolarization, suggesting that the most rapidly released vesicles could be detected by either method. 5. After a few seconds of continuous stimulation, the net increase in membrane surface area reached a plateau at about 5 %, even though continuous exocytosis occurred at a rate of 0.9 % s-1. Under these conditions of balanced exocytosis and endocytosis, the rate constant of endocytosis was about 0.2 s-1. The average rate of endocytosis during maintained depolarization was therefore considerably slower than the rate observed after a brief stimulus. 6. After longer depolarizations (> 500 ms), both the capacitance and FM1-43 signals continued to rise for periods of seconds after closure of Ca2+ channels. The continuation of exocytosis was correlated with a persistent increase in [Ca2+]i in the synaptic terminal, as indicated by the activation of a Ca2+-dependent conductance and measurements of [Ca2+]i using the fluorescent indicator furaptra. 7. The delayed fall in membrane capacitance after longer depolarizations occurred along a double exponential time course indicating the existence of two endocytic processes: fast endocytosis, with a rate constant of 0.8 s-1, and slow endocytosis, with a rate constant of 0.1 s-1. 8. Increasing the duration of depolarization caused an increase in the fraction of membrane recovered by slow endocytosis. After a 100 ms stimulus, all the membrane was recycled by fast endocytosis, but after a 5 s depolarization, about 50 % of the membrane was recycled by slow endocytosis. 9. These results demonstrate the existence of fast and slow endocytic mechanisms at a synapse and support the idea that prolonged stimulation leads to an increase in the amount of membrane retrieved by the slower route. The rise in cytoplasmic Ca2+ that occurred during longer depolarizations was correlated with stimulation of continuous exocytosis and inhibition of fast endocytosis. The results also confirm that transient and continuous components of exocytosis coexist in the synaptic terminal of depolarizing bipolar cells.

Algorithms↗
PubMed1987

Juvenile Parkinsonism: clinical and metabolic characteristics.

Twenty one patients with idiopathic Parkinsonism beginning before the age of 40 years were investigated. The mean duration of the disease was 19 years. There was a good and sustained response to levodopa. Only four patients reached stages IV and V (Hoehn and Yahr). Intolerance to levodopa was observed in the more advanced stages of the disease. In the series the familial incidence of Parkinsonism (2 cases) and essential tremor (3 cases) was very low. Thyroid disorder, diabetes mellitus or macrocytic anaemia was not found in any of the cases.

Adult↗
PubMedDate not supplied

Visual processing: the devil is in the details.

Ganglion cells convey information from the retina back to the brain. Recent experiments have examined how ganglion cell receptive fields are assembled from many incoming signals.

Animals↗