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D F Ventura

Publications and source records attributed to D F Ventura.

18 recordsLinked to original sources
PubMed2006

Losses of immunoreactive parvalbumin amacrine and immunoreactive alphaprotein kinase C bipolar cells caused by methylmercury chloride intoxication in the retina of the tropical fish Hoplias malabaricus.

To quantify the effects of methylmercury (MeHg) on amacrine and on ON-bipolar cells in the retina, experiments were performed in MeHg-exposed groups of adult trahiras (Hoplias malabaricus) at two dose levels (2 and 6 microg/g, ip). The retinas of test and control groups were processed by mouse anti-parvalbumin and rabbit anti-alphaprotein kinase C (alphaPKC) immunocytochemistry. Morphology and soma location in the inner nuclear layer were used to identify immunoreactive parvalbumin (PV-IR) and alphaPKC (alphaPKC-IR) in wholemount preparations. Cell density, topography and isodensity maps were estimated using confocal images. PV-IR was detected in amacrine cells in the inner nuclear layer and in displaced amacrine cells from the ganglion cell layer, and alphaPKC-IR was detected in ON-bipolar cells. The MeHg-treated group (6 microg/g) showed significant reduction of the ON-bipolar alphaPKC-IR cell density (mean density = 1306 +/- 393 cells/mm2) compared to control (1886 +/- 892 cells/mm2; P < 0.001). The mean densities found for amacrine PV-IR cells in MeHg-treated retinas were 1040 +/- 56 cells/mm2 (2 microg/g) and 845 +/- 82 cells/mm2 (6 microg/g), also lower than control (1312 +/- 31 cells/mm2; P < 0.05), differently from the data observed in displaced PV-IR amacrine cells. These results show that MeHg changed the PV-IR amacrine cell density in a dose-dependent way, and reduced the density of alphaKC-IR bipolar cells at the dose of 6 microg/g. Further studies are needed to identify the physiological impact of these findings on visual function.

Amacrine Cells↗
PubMed2006

Effects of mercury intoxication on the response of horizontal cells of the retina of thraira fish (Hoplias malabaricus).

Methyl mercury (MeHg) is highly neurotoxic, affecting visual function in addition to other central nervous system functions. The effect of mercury intoxication on the amplitude of horizontal cell responses to light was studied in the retina of the fish Hoplias malabaricus. Intracellular responses were recorded from horizontal cells of fish previously intoxicated with MeHg by intraperitoneal injection (IP group) or by trophic exposure (T group). Only one retina per fish was used. The doses of MeHg chloride administered to the IP group were 0.01, 0.05, 0.1, 1.0, 2.0, and 6.0 mg/kg. The amplitudes of the horizontal cell responses were lower than control in individuals exposed to 0.01 (N = 4 retinas), 0.05 (N = 2 retinas) and 0.1 mg/kg (N = 1 retina), whereas no responses were recorded in the 1.0, 2.0, and 6.0 mg/kg groups. T group individuals were fed young specimens of Astyanax sp previously injected with MeHg corresponding to 0.75 (N = 1 retina), 0.075 (N = 8 retinas) or 0.0075 (N = 4 retinas) mg/kg fish body weight. After 14 doses, one every 5 days, the amplitude of the horizontal cell response was higher than control in individuals exposed to 0.075 and 0.0075 mg/kg, and lower in individuals exposed to 0.75 mg/kg. We conclude that intoxication with MeHg affects the electrophysiological response of the horizontal cells in the retina, either reducing or increasing its amplitude compared to control, and that these effects are related to the dose and/or to the mode of administration.

Animals↗
PubMed2004

Contrast sensitivity threshold measured by sweep-visual evoked potential in term and preterm infants at 3 and 10 months of age.

Although healthy preterm infants frequently seem to be more attentive to visual stimuli and to fix on them longer than full-term infants, no difference in visual acuity has been reported compared to term infants. We evaluated the contrast sensitivity (CS) function of term (N = 5) and healthy preterm (N = 11) infants at 3 and 10 months of life using sweep-visual evoked potentials. Two spatial frequencies were studied: low (0.2 cycles per degrees, cpd) and medium (4.0 cpd). The mean contrast sensitivity (expressed in percentage of contrast) of the preterm infants at 3 months was 55.4 for the low spatial frequency (0.2 cpd) and 43.4 for the medium spatial frequency (4.0 cpd). At 10 months the low spatial CS was 52.7 and the medium spatial CS was 9.9. The results for the term infants at 3 months were 55.1 for the low spatial frequency and 34.5 for the medium spatial frequency. At 10 months the equivalent values were 54.3 and 14.4, respectively. No difference was found using the Mann-Whitney rank sum T-test between term and preterm infants for the low frequency at 3 or 10 months or for the medium spatial frequency at 3 or 10 months. The development of CS for the medium spatial frequency was equally fast for term and preterm infants. As also observed for visual acuity, CS was equivalent among term and preterm infants, suggesting that visual experience does not modify the development of the primary visual pathway. An earlier development of synapses in higher cortical visual areas of preterm infants could explain the better use of visual information observed behaviorally in these infants.

Contrast Sensitivity↗
PubMed2001

Ultraviolet colour opponency in the turtle retina.

We have examined the functional architecture of the turtle Pseudemys scripta elegans retina with respect to colour processing, extending spectral stimulation into the ultraviolet, which has not been studied previously in the inner retina. We addressed two questions. (i) Is it possible to deduce the ultraviolet cone spectral sensitivity function through horizontal cell responses? (ii) Is there evidence for tetrachromatic neural mechanisms, i.e. UV/S response opponency? Using a constant response methodology we have isolated the ultraviolet cone input into the S/LM horizontal cell type and described it in fine detail. Monophasic (luminosity), biphasic L/M (red-green) and triphasic S/LM (yellow-blue) horizontal cells responded strongly to ultraviolet light. The blue-adapted spectral sensitivity function of a S/LM cell peaked in the ultraviolet and could be fitted to a porphyropsin cone template with a peak at 372 nm. In the inner retina eight different combinations of spectral opponency were found in the centre of the receptive field of ganglion cells. Among amacrine cells the only types found were UVSM-L+ and its reverse. One amacrine and four ganglion cells were also opponent in the receptive field surround. UV/S opponency, seen in three different types of ganglion cell, provides a neural basis for discrimination of ultraviolet colours. In conclusion, the results strongly suggest that there is an ultraviolet channel and a neural basis for tetrachromacy in the turtle retina.

Animals↗
PubMed1997

Electrophysiological measurements of spectral sensitivities: a review.

Spectral sensitivities of visual systems are specified as the reciprocals of the intensities of light (quantum fluxes) needed at each wavelength to elicit the same criterion amplitude of responses. The review primarily considers the methods that have been developed for electrophysiological determinations of criterion amplitudes of slow-wave responses from single retinal cells. Traditional flash methods can require tedious dark adaptations and may yield erroneous spectral sensitivity curves which are not seen in such modifications as ramp methods. Linear response methods involve interferometry, while constant response methods involve manual or automatic adjustments of continuous illumination to keep response amplitudes constant during spectral scans. In DC or AC computerized constant response methods, feedback to determine intensities at each wavelength is derived from the response amplitudes themselves. Although all but traditional flash methods have greater or lesser abilities to provide on-line determinations of spectral sensitivities, computerized constant response methods are the most satisfactory due to flexibility, speed and maintenance of a constant adaptation level.

Color Perception↗
PubMed1996

An AC constant-response method for electrophysiological measurements of spectral sensitivity functions.

A number of methods have been used in the past to measure spectral sensitivity (S(lambda)) functions of electric responses in the visual system. We present here a microcomputer based, AC, constant-response method for automatic on-line measurement of S(lambda) in cells with or without a sustained tonic response. It is based on feedback adjustment of light intensity to obtain constant peak-to-peak amplitudes of response to a flickering stimulus as the spectrum is scanned between 300 and 700 nm in 4 nm steps. It combines the advantages of: (1) on-line presentation of S(lambda) curves; (2) constant light adaptation; (3) sampling of many points; and (4) fast data collection time. The system can be applied to sensitivity or threshold (e.g., S(lambda), dark adaptation, receptive field) measurements of any electrically recorded visual response.

Animals↗
PubMed1995

Large sample population age norms for visual acuities obtained with Vistech-Teller Acuity Cards.

PURPOSE: To determine population age norms in the first three years of life for binocular and monocular grating visual acuity (VA) obtained with Vistech-Teller Acuity Cards (TAC). METHODS: TAC was used to estimate grating acuity in 646 healthy infants and children born at due date +/- 2 weeks, all of whom underwent ophthalmologic and orthoptic evaluation. The sample consisted of 20 age groups from 0 to 36 months. Sixty-nine percent of the children attended day care centers in the city of São Paulo. The sample was composed of white (63.0%), mulatto (25.2%), African-Brazilian (11.0%), and Asian (0.8%) infants and children, most of whom (97%) were from low-income families. Tests were conducted by eight highly trained testers, six of whom were orthoptists. RESULTS: Binocular and monocular norms for grating VA are presented in terms of tolerance limits for 90% of the population with 95% probability. The range of tolerance limits is approximately 2.5 octaves at most ages. There were no statistical differences among scores obtained by the different testers. There were no differences in VA due to race, sex, and first or second eye tested. The results on binocular (99.3%) and monocular (96.2%) testability and on mean test duration (13 minutes for one binocular and two monocular measurements) confirm the clinical applicability of TAC. CONCLUSIONS: The binocular and monocular grating VA norms obtained in this large-sample study are different from the preliminary norms published with the TAC. Results from this and other studies (see Mayer et al, page 671, this issue) strongly point to a need for redefinition of the preliminary VA norms.

Aging↗
PubMed1992

The spectral input systems of hymenopteran insects and their receptor-based colour vision.

Spectral sensitivity functions S(lambda) of single photoreceptor cells in 43 different hymenopteran species were measured intracellularly with the fast spectral scan method. The distribution of maximal sensitivity values (lambda max) shows 3 major peaks at 340 nm, 430 nm and 535 nm and a small peak at 600 nm. Predictions about the colour vision systems of the different hymenopteran species are derived from the spectral sensitivities by application of a receptor model of colour vision and a model of two colour opponent channels. Most of the species have a trichromatic colour vision system. Although the S(lambda) functions are quite similar, the predicted colour discriminability curves differ in their relative height of best discriminability in the UV-blue or blue-green area of the spectrum, indicating that relatively small differences in the S(lambda) functions may have considerable effects on colour discriminability. Four of the hymenopteran insects tested contain an additional R-receptor with maximal sensitivity around 600 nm. The R-receptor of the solitary bee Callonychium petuniae is based on a pigment (P596) with a long lambda max, whereas in the sawfly Tenthredo campestris the G-receptor appears to act as filter to a pigment (P570), shifting its lambda max value to a longer wavelength and narrowing its bandwidth. Evolutionary and life history constraints (e.g. phylogenetic relatedness, social or solitary life, general or specialized feeding behaviour) appear to have no effect on the S(lambda) functions. The only effect is found in UV receptors, for which lambda max values at longer wavelengths are found in bees flying predominantly within the forest.

Animals↗
PubMed1989

Comparative study of temporal summation and response form in hymenopteran photoreceptors.

1. Temporal summation was measured in green-sensitive photoreceptors of seven hymenopteran species with various life styles: three bees, Melipona quadrifasciata quadrifasciata, Trigona spinnipes and Bombus morio; one wasp, Polistes canadensis; and three ants, Pseudomyrmex phyllophilus, Camponotus rufipes, and Atta sexdens rubropilosa. In all species approximate agreement with Bloch's law was confirmed. 2. Critical durations (tc), which varied from 10 ms (Pseudomyrmex) to 46 ms (Atta), are discussed in relation to the life styles of the species and to the mechanisms causing the differences. 3. The direct measures of critical duration obtained are compared to estimates made by convolution or integration of impulse responses measured here in one species and from published data. Linear convolution of typical impulse responses is shown to result in significant departures from Bloch's law, a fact that seems to have been overlooked in the literature. 4. The method used to measure temporal summation involved recording responses to 300-ms stimuli at various intensities; the form of these responses varied greatly from species to species. Possible causes of these variations are discussed.

Animals↗
PubMed1989

Morphological changes in the ommatidia of an ant in the day and night states.

Morphological changes in dioptric structures, in the position of screening pigments and in the microvillar arrangement of the rhabdom were observed in Atta sexdens ant ommatidia exposed to different light/dark schedules. During the day there was a funneling of the crystalline cone and the pigments were close to the rhabdom. At night the crystalline cone became thicker and shorter than in the day state and the pigments moved away from the rhabdom. Endogenous control for these changes was demonstrated in ants kept in continuous darkness. A small but significant contribution of extraocular brain structures to the modulation of pigment position was also demonstrated.

Animals↗
PubMed1988

Cardioselectivity of cetamolol compared with atenolol and nadolol.

The selectivity of the beta-adrenoceptor blockade produced by single oral doses of cetamolol, atenolol, and nadolol was compared in normal male subjects. Study 1 established the dose at which each drug provides equivalent beta-1 blockade. Beta-1 blockade was estimated using the degree of inhibition of the increased heart rate (HR) response to graded exercise. Cetamolol (30 mg), atenolol (100 mg), and nadolol (80 mg) all attenuated the HR response to a comparable extent. This result established that the dose ratio of cetamolol:atenolol:nadolol of 1.00:3.33:2.67 provides equipotent beta-1 blockade. This ratio of doses was used in Studies 2 and 3 to evaluate the antagonism of beta-2-mediated responses to titrated doses of intravenous isoproterenol (ISO) by low and high doses of each drug. Beta-2 blockade was assessed using the attenuation of ISO-induced reductions in diastolic blood pressure (DBP) in Study 2 and ISO-induced increases in specific airway conductance (sGAW) in Study 3. For within drug comparisons, antagonism of the HR increase induced by ISO (a response mediated by both beta-1 and beta-2 receptors) was also examined. Treatments included cetamolol (15 and 60 mg), atenolol (50 and 200 mg), and nadolol (40 and 160 mg in Study 2; 40 mg only in Study 3). All drugs tested suppressed the HR, DBP, and sGAW responses to ISO, and this blockade was dose dependent. Cetamolol and nadolol produced approximately equipotent beta-1 blockade, whereas cetamolol at both doses produced a less potent beta-2 blockade. Atenolol antagonized ISO effects on all parameters less than either cetamolol or nadolol. Quantitative cardioselectivity indices revealed that cetamolol 60 mg was the most cardioselective and nadolol 40 mg the least. Data from the three studies demonstrate that cetamolol is cardioselective relative to nadolol and that, in contrast to atenolol, cardioselectivity appears to increase at the higher dose.

Acetamides↗
PubMed1987

Temporal summation and critical duration in bee photoreceptors: a comparison of measurement methods.

Temporal summation of visual stimuli by single retinular cells in the compound eye of the bee Melipona quadrifasciata were measured by three different methods. Critical duration was best defined by interpolating intensity-duration response functions. Measurement of responses to two types of equal-energy stimuli gave more precise evaluation of the degree of summation below the critical duration; single pulses produced an unexpected deviation from Bloch's Law.

Animals↗
PubMed1987

Marking and recording of monopolar cells in the bee lamina.

Monopolar cells in the lamina ganglionaris of the honeybee, Apis mellifera, were marked individually for the first time and intracellular recordings made. The electrophysiological responses were mainly hyperpolarizing with peaks and descending plateaux; one specific cell gave depolarizing responses, sustained in UV, and phasic at other wavelengths. Spectral sensitivity curves obtained by the spectral scanning method showed maximum sensitivity at 520 nm. Three morphological cell types were encountered, all of which differ considerably from those described by Ribi (1).

Animals↗
PubMed1982

Effects of sodium barbitone on learning and memory-storage of an appetitive and an aversive task.

In order to test the effects of sodium barbitone on the acquisition and retention of an appetitively and an aversively reinforced behavior, mice were trained in a spatial discrimination Y-maze task. Learning was observed in both situations, with acquisition unimpaired by the drug. Sodium barbitone did, however, affect retention of both tasks in all groups treated with the drug before training. Results are discussed in light of the various modes of action of this drug, i.e., as an inhibitor of protein synthesis, as a blocker of catecholamine biosynthesis, with regard to its effects on paradoxical sleep and on gamma-amino-butyric acid (GABA).

Animals↗
PubMed1981

Role of histamine in regulating pulmonary vascular tone and reactivity.

The profile of histamine responsiveness of the pulmonary circulation and the role of endogenous histamine in regulating pulmonary vascular tone and reactivity were studied using the isolated perfused feline pulmonary circulation. Repetitive cumulative dose-response curves demonstrated a progressive decline in the response of the pulmonary circulation to histamine. The present studies also demonstrated elaboration of histamine by the perfused feline lung, and showed that decreasing this elaboration by mast-cell stabilization with cromolyn sodium (disodium cromoglycate, DSCG) had no significant effect on pulmonary vascular tone but resulted in greater lobar vasoconstriction to infused histamine. In contrast, DSCG had no significant effect on the pulmonary pressor response to serotonin, norepinephrine, hypoxia, and hypercapnia. These data suggest that 1) pulmonary; vascular tachyphylaxis occurs with exogenously infused histamine; 2) the withdrawal of endogenous histamine results in greater pulmonary vasoconstriction to exogenously infused histamine; an 3) the histamine release, which was prevented by DSCG, has no role in mediating pulmonary hypoxic or hypercapnic vasoconstriction in the cat.

Aminophylline↗
PubMedDate not supplied

Tetrachromatic input to turtle horizontal cells.

Recent physiological experiments support behavioral and morphological evidence for a fourth type of cone in the turtle retina, maximally sensitive in the ultraviolet (UV). This cone type has not yet been included in the models proposed for connectivity between cones and horizontal cells. In this study, we examined the inputs of UV, S, M, and L cones to horizontal cells. We used the high-resolution Dynamic Constant Response Method to measure the spectral sensitivity of horizontal cells without background light and after adaptation to UV, blue (B), green (G), and red (R) light. We concluded the following: (1) Tetrachromatic input to a Y/B horizontal cell was identified. The spectral-sensitivity curves of the cell in three of the adaptation conditions were well represented by L-, M-, and S-cone functions. Adaptation to blue light revealed a peak at 372 nm, the same wavelength location as that determined behaviorally in the turtle. A porphyropsin template could be closely fitted to the sensitivity band in that region, strong evidence for input from a UV cone. (2) The spectral-sensitivity functions of R/G horizontal cells were well represented by the L- and M-cone functions. There was no indication of UV- or S-cone inputs into these cells. (3) The spectral sensitivities of the monophasic horizontal cells were dominated by the L cone. However, the shape of the spectral-sensitivity function depended on the background wavelength, indicating secondary M-cone input. Connectivity models of the outer retina that predict input from all cone types are supported by the finding of tetrachromatic input into Y/B horizontal cells. In contrast, we did not find tetrachromatic input to R/G and monophasic horizontal cells. Chromatic adaptation revealed the spectral-sensitivity function of the turtle UV cone peaking at 372 nm.

Adaptation, Ocular↗
PubMedDate not supplied

UV responses in the retina of the turtle.

To study processing of UV stimuli in the retina of the turtle, Trachemys dorbignii, we recorded intracellular responses to spectral light from 89 cells: 54 horizontal (47 monophasic, five (R/G) biphasic and two (Y/B) triphasic), 14 bipolar, 12 amacrine, and nine ganglion cells. Spectral sensitivities were measured with monochromatic flashes or with the dynamic constant response method in dark or chromatic adapted states. Stray light and second-order harmonics were also measured. (1) All cells responded to UV stimuli, although none had maximum sensitivity in the UV. (2) Most horizontal, bipolar, and amacrine cells had red-peaked spectral sensitivities. (3) Red adaptation of all monophasic horizontal cells indicated a single red input, except one that had additional peaks in the blue and UV. (4) Responses of biphasic and triphasic horizontal cells to UV light were always hyperpolarizing. Opposition between hyperpolarizing and depolarizing responses at long wavelengths indicates that UV responses were not due to the beta band of red receptors. (5) An unstained spectrally opponent bipolar cell hyperpolarized in the center to green light and antagonistically depolarized in the surround to UV, blue, and green flashes, but hyperpolarized to red. (6) All dark-adapted amacrine cells were red-peaked monophasic cells, but red adaptation broadened their spectral-sensitivity curves or displaced their peaks. An A15, an A18, and an A24 wide-field amacrine cell were stained. (7) A G15 bistratified ganglion cell is shown here for the first time to be spectrally opponent. This UVB/RG cell depolarized to UV and blue and hyperpolarized to red and green. It differs from previously reported turtle ganglion cells in being color opponent in the entire field, not only in the surround, and in showing spatial opponency.

Animals↗