RESUMEN

OBJECTIVE: The aim of the study was to assess the geometric characteristics of rat pial microcirculation and describe the vessel bifurcation patterns by 'connectivity matrix'. METHODS: Male Wistar rats were used to visualize pial microcirculation by a fluorescent microscopy technique through an open cranial window, using fluorescein isothiocyanate bound to dextran (molecular weight 70 kDa). The arteriolar network was mapped by stop-frame images. Diameters and lengths of arterioles were measured with a computer-assisted method. Pial arterioles were classified according to a centripetal ordering scheme (Strahler method modified according to diameter) from the smallest order 1 to the largest order 5 arterioles in the preparation. A distinction between arteriolar segments and elements was used to express the series-parallel features of the pial arteriolar networks. A connectivity matrix was used to describe the connection of blood vessels from one order to another. RESULTS: The arterioles were assigned 5 orders of branching by Strahler's ordering scheme, from order 1 (diameter: 16.0 +/- 2.5 microm) to order 5 (62 +/- 5.0 microm). Order 1 arterioles gave origin to capillaries, assigned order 0. The diameter, length and branching of the 5 arteriolar orders grew as a geometric sequence with the order number in accordance with Horton's law. The segments/elements ratio was the highest in order 4 and 3 arterioles, indicating the greatest asymmetry of ramifications. Finally, the branching vessels in the networks were described in details by the connectivity matrix. Fractal dimensions of arteriolar length and diameter were 1.75 and 1.78, respectively. CONCLUSIONS: The geometric characteristics of rat pial microcirculation indicate that distribution of vessels is fractal. The connectivity matrix allowed us to describe the number of daughter vessels spreading from parent vessels. This ordering scheme may be useful to describe vessel function, according to diameter, length and branching.

Asunto(s)

Arterias Cerebrales/anatomía & histología , Animales , Arteriolas/anatomía & histología , Dextranos , Fluoresceína-5-Isotiocianato/análogos & derivados , Colorantes Fluorescentes , Fractales , Masculino , Microscopía Fluorescente/métodos , Modelos Cardiovasculares , Ratas , Ratas Wistar

RESUMEN

OBJECTIVE: The aim of the study was to assess the rat pial microvessel alterations due to transient bilateral common carotid artery occlusion (BCCAO) and to investigate the mechanism of 10% hypertonic glycerol neuroprotection. Our suggestion was that 10% glycerol solution infusion could dilate pial arterioles through nitric oxide release and/or stimulation of ATP-sensitive potassium (K(ATP)) channels. Therefore, we studied the effects of hypertonic glycerol after inhibition of nitric oxide synthase, with N(G)-nitro-L-arginine-methyl ester or N(G)-nitro-L-arginine, or K(ATP) channels with glibenclamide. METHODS: Pial microcirculation of male Wistar rats was visualized by a fluorescent microscopy technique through an open cranial window, using fluorescein isothiocyanate bound to dextran (molecular weight 70 kDa). BCCAO was induced for 30 min and reperfusion lasted 60 min. The arterioles were classified according to the Strahler ordering scheme. Permeability increase was quantified by normalized grey levels (NGL). Leucocytes were stained with rhodamine 6G. Perfused capillary length and capillary red blood cell (RBC) velocity were measured by computer-assisted methods. RESULTS: The arterioles were assigned 5 orders of branchings, from order 1 (diameter 16.0 +/- 2.5 microm) to order 5 (62.0 +/- 5.0 microm). BCCAO caused inhomogenous changes in diameter of arterioles and leakage of fluorescent dextran, that was further enhanced by reperfusion (0.45 +/- 0.05 NGL, p < 0.01). Adhesion of leukocytes to venules was marked and capillary perfusion was reduced by 39.2 +/- 6.0% of baseline as well as capillary RBC velocity. 10% glycerol solution caused an increase in diameter of all arterioles within 25 +/- 2 min of administration (by 20 +/- 5% in order 4, 25 +/- 4% in order 3 and 18 +/- 3% in order 2; p < 0.01). Leakage (0.19 +/- 0.03 NGL, p < 0.01), leukocyte adhesion (2.0 +/- 1.0/100 microm of venular length, p < 0.01) and capillary occlusion (reduction by 13.0 +/- 5.5% of baseline) were prevented compared with controls. Capillary RBC velocity increased compared with controls. N(G)-nitro-L-arginine-methyl ester or N(G)-nitro-L-arginine infused prior to glycerol caused vasoconstriction and reduced the protective effects of hypertonic glycerol on permeability increase. The number of adherent leukocytes and perfused capillary length decreased, while capillary RBC velocity was higher than baseline. Glibenclamide prior to 10% glycerol solution blunted glycerol-induced vasodilatation, but did not affect protection by hypertonic glycerol on blood-brain barrier disruption, leukocyte adhesion and capillary perfusion, preserving high capillary RBC velocity. Papaverine (20 mg/kg body weight) induced an increase in arteriolar diameter, enhancing interstitial edema; adhesion of leukocytes was marked as well as capillary occlusion, while capillary RBC velocity increased. CONCLUSIONS: 10% glycerol solution was able to prevent microvascular alterations due to BCCAO protecting cerebral tissue. The effects appear to be due to hyperosmolality causing stimulation of K(ATP) channels, increase in vessel wall shear stress and release of nitric oxide.

Asunto(s)

Estenosis Carotídea/tratamiento farmacológico , Circulación Cerebrovascular/efectos de los fármacos , Glicerol/farmacología , Fármacos Neuroprotectores/farmacología , Piamadre/irrigación sanguínea , Vasodilatación/efectos de los fármacos , Vasodilatadores/farmacología , Animales , Velocidad del Flujo Sanguíneo/efectos de los fármacos , Permeabilidad Capilar/efectos de los fármacos , Arteria Carótida Común/cirugía , Estenosis Carotídea/metabolismo , Estenosis Carotídea/patología , Estenosis Carotídea/fisiopatología , Adhesión Celular/efectos de los fármacos , Quimiotaxis de Leucocito/efectos de los fármacos , Modelos Animales de Enfermedad , Gliburida/farmacología , Glicerol/administración & dosificación , Soluciones Hipertónicas , Infusiones Intravenosas , Canales KATP/efectos de los fármacos , Canales KATP/metabolismo , Ligadura , Masculino , Microcirculación/efectos de los fármacos , Microcirculación/fisiopatología , Microscopía Fluorescente , NG-Nitroarginina Metil Éster/farmacología , Fármacos Neuroprotectores/administración & dosificación , Óxido Nítrico/metabolismo , Óxido Nítrico Sintasa/antagonistas & inhibidores , Óxido Nítrico Sintasa/metabolismo , Nitroarginina/farmacología , Papaverina/farmacología , Piamadre/metabolismo , Bloqueadores de los Canales de Potasio/farmacología , Ratas , Ratas Wistar , Flujo Sanguíneo Regional/efectos de los fármacos , Vasodilatadores/administración & dosificación

RESUMEN

OBJECTIVE: The effects of insulin (0.18 nM-0.18 microM) on reduced capillary perfusion, microvascular permeability increase and leukocyte adhesion induced by ischemia-reperfusion injury were investigated in the hamster cheek pouch microcirculation. To gain insight into the insulin's mechanism of action, the effects of its higher concentration (0.18 microM) were investigated after inhibition of tyrosine kinase (TK), nitric oxide synthase (NOS), protein kinase C (PKC), phosphatidylinositol 3-kinase and K+(ATP) channels, alone or in combination. Two concentrations for each inhibitor were used. METHODS: Microcirculation was visualized by fluorescence microscopy. Perfused capillary length, microvascular permeability, leukocyte adhesion to venular walls, vessel diameter and capillary red blood cell velocity were assessed by computer-assisted methods. Measurements were made at baseline (B), after 30 min of ischemia (I), and after 30 min of reperfusion (R). RESULTS: In control animals, perfused capillary length decreased by 63 +/- 5% of baseline at R. Microvascular permeability increased at I and R, while leukocyte adhesion was most pronounced in V1 postcapillary venules at R. Insulin dose-dependently preserved capillary perfusion at R (-28 +/- 6 and -15 +/- 6% of baseline), but was unable to prevent the increase in permeability at I (0.25 +/- 0.05 and 0.29 +/- 0.06 Normalized Grey Levels, NGL) and R (0.49 +/- 0.10 and 0.53 +/- 0.09 NGL), according to the concentrations. Adhesion of leukocytes was observed mostly in V3 venules at R (9 +/- 2 and 10 +/- 2/100 microm venular length, with the lower and higher concentration, respectively). Nitric oxide synthase inhibition by N(G)-nitro-L-arginine-methyl ester prior to insulin did not affect capillary perfusion at R (-18 +/- 3% of baseline with higher concentration), but prevented permeability increase (0.20 +/- 0.04 NGL, according to higher concentration) and reduced leukocyte adhesion in V3 venules at R (1.5 +/- 1.0/100 microm of venular length, with higher concentration). Blockade of K+(ATP) channels by glibenclamide prior to insulin decreased perfused capillary length at R (-58 +/- 6% of baseline with higher concentration), attenuated leakage at R (0.30 +/- 0.04 NGL, according to higher concentration) and caused leukocyte adhesion mainly in V1 venules at R (9.0 +/- 1.5/100 microm of venular length, with higher concentration). Inhibition of either TK, PKC or phosphatidylinositol 3-kinase did not affect microvascular responses to insulin. Simultaneous inhibition of TK and NOS did not increase protection. CONCLUSIONS: Insulin prevents ischemia-reperfusion injury by promoting capillary perfusion through an apparent activation of K+(ATP) channels and increase in nitric oxide release.

Asunto(s)

Insulina/farmacología , Mucosa Bucal/irrigación sanguínea , Daño por Reperfusión/prevención & control , Alcaloides , Androstadienos/farmacología , Animales , Benzofenantridinas , Benzoquinonas , Permeabilidad Capilar/efectos de los fármacos , Mejilla , Cricetinae , Gliburida/farmacología , Lactamas Macrocíclicas , Masculino , Mesocricetus , Microcirculación/efectos de los fármacos , NG-Nitroarginina Metil Éster/farmacología , Fenantridinas/farmacología , Canales de Potasio/fisiología , Proteína Quinasa C/antagonistas & inhibidores , Proteína Quinasa C/fisiología , Quinonas/farmacología , Rifabutina/análogos & derivados , Wortmanina

RESUMEN

The aim of the present study was to assess the effects of topically applied triiodothyronine (T(3)) and thyroxine (T(4)) on the arterioles of hamster cheek pouch microcirculation in vivo. Microvessels were visualized using a fluorescent microscopy technique. Topical application of T(3) (3.08, 30.8, 61.5, 307, 615, and 6,150 nM/l) consistently induced dose-dependent dilation of arterioles within 2.0 +/- 0.5 min of administration. The application of T(4) (150, 257, 514, and 5,140 nM/l) caused different dose-dependent effects: dilation at the three lower doses within 16 +/- 2 min and rhythmic diameter changes at the highest dose. Aging of hamsters did not alter the arteriolar responses to T(3) and T(4). T(3)-induced dilation was countered by the inhibition of nitric oxide synthase with N(G)-nitro-L-arginine-methyl ester or N(G)-nitro-L-arginine. Iopanoic acid (IPA), which inhibits types I and II 5'-deiodinase, abolished the dilation elicited by 514 nM T(4) but did not affect T(3)-dependent dilation. 6-Propyl-2-thiouracil (PTU), which inhibits type I 5'-deiodinase only, did not affect the dilation induced by T(4). IPA and PTU did not impair arteriolar dilation induced by acetylcholine or sodium nitroprusside. These results indicate that T(3) induces arteriolar dilation, likely through nitric oxide release. The local conversion of T(4) to T(3) appears to be crucial for the dilation induced by T(4).

Asunto(s)

Boca/irrigación sanguínea , Flujo Sanguíneo Regional/efectos de los fármacos , Tiroxina/farmacología , Triyodotironina/farmacología , Animales , Antimetabolitos/farmacología , Arteriolas/efectos de los fármacos , Medios de Contraste/farmacología , Cricetinae , Inhibidores Enzimáticos/farmacología , Ácido Yopanoico/farmacología , Masculino , Mesocricetus , NG-Nitroarginina Metil Éster/farmacología , Óxido Nítrico Sintasa/antagonistas & inhibidores , Nitroarginina/farmacología , Propiltiouracilo/farmacología

RESUMEN

AIMS/HYPOTHESIS: The aim of this study was to verify whether retinal photoreceptors, like other tissues, are subject to oxidative stress during diabetes. METHODS: Oxidative stress was monitored by the oxidation of preloaded dehydrorhodamine 123 into fluorescent rhodamine 123, during a period of intense illumination of isolated rod retinal receptor cells. These were obtained from 22 Syrian hamsters injected with streptozotocin (50 mg/kg body weight., intraperitoneal route) 90 days before the study began. Eleven hamsters were treated daily with melatonin (0.4 mg/kg body wt., per os), an antioxidant synthesized within photoreceptors. Isolated photoreceptors were bathed on the stage of a Leitz Orthoplan microscope, where the fluorescent lamp also served as the light stimulus (485 nm). Fluorescence irradiance was measured by photometry and stored in a personal computer for further analysis. RESULTS: The light-induced oxidant production greatly decreased and was also delayed in the streptozotocin-injected hamsters compared with the control hamsters matched for age. Similar effects were obtained in control photoreceptors after 40 min incubation with 2-2'-azobis (2-amidinopropane) dihydrochloride, a potent lipoperoxidation inducer. The effect of melatonin was to partially restore the light-induced fluorescence response. CONCLUSION/INTERPRETATION: The depression of the light-induced oxidative response in diabetic photoreceptors could be ascribed to a hyperglycaemia-induced background of oxidative stress whereby the light-oxidizable substrate is actually lowered. Melatonin induces a larger fluorescence response during illumination, probably as a consequence of its antioxidant effect during diabetes, which would provide more oxidizable lipids.

Asunto(s)

Diabetes Mellitus Experimental/fisiopatología , Estrés Oxidativo , Células Fotorreceptoras de Vertebrados/fisiología , Amidinas/farmacología , Animales , Antioxidantes/farmacología , Glucemia/metabolismo , Peso Corporal , Colesterol/sangre , Cricetinae , Colorantes Fluorescentes , Cinética , Luz , Peroxidación de Lípido , Melatonina/farmacología , Mesocricetus , Oxidantes/farmacología , Estrés Oxidativo/efectos de los fármacos , Estrés Oxidativo/efectos de la radiación , Células Fotorreceptoras de Vertebrados/efectos de los fármacos , Triglicéridos/sangre

RESUMEN

Systemic hypoxia (8%, 11% and 15% oxygen gas mixture inspiration) has been shown to increase the frequency of arteriolar rhythmic diameter changes in hamster skeletal muscle microcirculation. The effects of phentolamine on vasomotion frequency during systemic hypoxia were studied in Syrian hamsters implanted with a plastic chamber in the dorsum skin. Phentolamine (50 microg/100 g body wt.) was injected intravenously before the 20-min exposure to 11% oxygen gas mixture. The microvessels were studied with a fluorescent microscopy technique, using fluorescein isothiocyanate bound to dextran (mol. wt. 150,000) as a tracer. Vessel diameters were measured with a shearing method. Fourier transform and autoregressive modeling were used to assess the time variant features of diameter changes. Under baseline conditions, the arterioles were characterized by rhythmic diameter changes with fundamental frequency related to vessel size. The terminal branchings were dominated by order 3 vessel activity (frequency: 0.08-0.16 Hz) spreading downstream to all daughter arterioles. Systemic hypoxia caused an increase in vasomotion frequency of order 3 arterioles up to 0.3-0.5 Hz (average: 0.40 +/- 0.06 Hz) and a significant decrease in mean diameter (-28 +/- 5%). Phentolamine completely suppressed the rhythmic changes in diameter of order 3 arterioles that dilated significantly (+ 30 +/- 4%). Therefore, the effects of systemic hypoxia on arteriolar vasomotion appear to be triggered by an increase in sympathetic nervous discharge that induces a rise in frequency up to 0.3-0.5 Hz.

Asunto(s)

Antihipertensivos/farmacología , Hipoxia/fisiopatología , Músculo Esquelético/irrigación sanguínea , Fentolamina/farmacología , Sistema Nervioso Simpático/efectos de los fármacos , Vasoconstricción/efectos de los fármacos , Animales , Presión Sanguínea/efectos de los fármacos , Cricetinae , Hipoxia/tratamiento farmacológico , Masculino , Mesocricetus , Microcirculación/efectos de los fármacos , Piel/irrigación sanguínea , Sistema Nervioso Simpático/fisiología

RESUMEN

The relationship between oxidative stress and Bcl-2 expression was investigated in two different experimental models of oxidative stress. Acute oxidative stress was assessed by measuring, with fluorescence microscopy and cytofluorimetry, the increase in fluorescence of the oxidation-sensitive probe dihydrorhodamine 123, both in retinal rod receptor cells exposed to bright light (0.32 mW/cm(2) for 15 minutes) and in human endothelial cells treated with the immunosuppressant cyclosporin A (200 microM for 21 h). In both cell types, acute oxidative stress reduced Bcl-2 expression and also caused a significant increase in the level of nucleosomes. Interestingly, chronic treatment with clinical concentrations of cyclosporin A (0.5-2.5 microM for 8 days) led to a significant increase in Bcl-2 expression, while nucleosomes were similar to control level. This suggests that up-regulation of Bcl-2 protein by low levels of oxidants may represent a critical factor in cellular adaptation to drug toxicity.

Asunto(s)

Endotelio Vascular/metabolismo , Neuronas/metabolismo , Estrés Oxidativo , Proteínas Proto-Oncogénicas c-bcl-2/metabolismo , Endotelio Vascular/citología , Ensayo de Inmunoadsorción Enzimática , Humanos , Microscopía Fluorescente , Neuronas/citología , Células Fotorreceptoras Retinianas Bastones/citología , Células Fotorreceptoras Retinianas Bastones/metabolismo , Espectrometría de Fluorescencia , Sustancias Reactivas al Ácido Tiobarbitúrico/metabolismo , Regulación hacia Arriba

RESUMEN

Dark-adapted, single photoreceptors isolated from the frog retina produce reactive oxygen species (ROS) after about 1 min of illumination with saturating light that we verified by their oxidation of preloaded dihydrorhodamine 123 (DHR) into the fluorescent rhodamine 123 (RHO). In this preparation we tested the antioxidant effects of vitamin E and of melatonin. Melatonin at picomolar and low nanomolar concentrations was determined to be 100 times more potent in inhibiting the light-induced oxidative processes than was vitamin E. On the contrary, both compounds exerted potent prooxidant effects at micromolar concentrations that is above the physiological levels of melatonin. This provides evidence that physiological concentrations of melatonin in a living cell may exert protective actions against a natural oxidant stimulus (light). This helps to define the functional role of endogenous melatonin in photoreceptors, which by their physiological characteristics, are among the marked producers of ROS in the organism.

Asunto(s)

Antioxidantes/farmacología , Melatonina/farmacología , Células Fotorreceptoras de Vertebrados/efectos de los fármacos , Animales , Anuros , Relación Dosis-Respuesta a Droga , Fenclonina/farmacología , Fluorescencia , Colorantes Fluorescentes , Indoles/metabolismo , Cinética , Luz , Melatonina/antagonistas & inhibidores , Melatonina/fisiología , Mitocondrias/efectos de los fármacos , Mitocondrias/metabolismo , Estimulación Luminosa , Células Fotorreceptoras de Vertebrados/metabolismo , Especies Reactivas de Oxígeno/metabolismo , Retina/citología , Retina/efectos de los fármacos , Rodamina 123 , Rodaminas , Vitamina E/farmacología

RESUMEN

We here report the activity of the neurohormone melatonin (MLT) as a scavenger of free radicals in two different experimental models: (a) linoleic acid peroxidation initiated by different free radical-generating systems and (b) a multilamellar vesicle system composed of dilinoleoylphosphatidylcholine. In system (a) linoleic acid peroxidation, induced by either the water-soluble initiator 2,2'-azobis (2-amidinopropane) dihydrochloride (ABAP) or Fe2+-EDTA addition to 2.6 mM linoleic acid dispersed in SDS-phosphate buffer, was evaluated as the formation of conjugated dienes, measured spectrophotometrically at 236 nm. MLT did not reduce the rate of peroxidation induced by ABAP, but did reduce, in a concentration-dependent fashion, the rate of the reaction activated by Fe2+-EDTA. In system (b) multilamellar vesicles were used as the substrate for lipid peroxidation, initiated by Fe2+-EDTA and determined by means of malonaldehyde (MDA) and 4-hydroxyalkenal (4-HDA) content. MLT was found to be slightly more effective in system (b) than in the dispersed linoleic acid system (see a). These results show that MLT inhibits lipid damage induced by oxygen free radicals. However, MLT is only about one one-hundredth as effective an antioxidant as vitamin E in the micelles system.

Asunto(s)

Antioxidantes/farmacología , Peroxidación de Lípido/efectos de los fármacos , Melatonina/farmacología , Especies Reactivas de Oxígeno , Amidinas/farmacología , Ácido Edético , Malondialdehído/metabolismo , Oxidantes/farmacología

RESUMEN

The results from recent experiments on the cellular physiology of the trout pineal photoreceptors are briefly reviewed. The arguments are mainly concerned with pineal phototransduction. These studies have stimulated further research on melatonin, a molecule produced in pineal as well as in retinal photoreceptors. A discussion follows on our actual research object, that is a study of the influences of endogenous melatonin upon retinal receptor cells activities.

Asunto(s)

Antioxidantes/metabolismo , Calcio/fisiología , Ritmo Circadiano/fisiología , Potenciales Evocados Visuales/fisiología , Melatonina/fisiología , Células Fotorreceptoras/fisiología , Glándula Pineal/fisiología , Animales , Humanos , Glándula Pineal/citología , Estudios Prospectivos

RESUMEN

Experiments were conducted to verify whether the neurohormone melatonin influences the membrane conductance of photoreceptors isolated from the frog retina. It has been found that 20 microM melatonin decreases membrane conductances both in the linear and non linear ranges by <0.4 nS. These actions are estimated to produce in dark adapted photoreceptors an increase of the response to a dim light induced change of the dark current of about 21%, i.e. from 1.3 to 1.62 mV/pA.

Asunto(s)

Melatonina/fisiología , Potenciales de la Membrana/fisiología , Células Fotorreceptoras/fisiología , Animales , Anuros

RESUMEN

OBJECTIVE: We used the hamster cheek pouch microcirculation to investigate the effects of melatonin (ME) on ischemia reperfusion (I-R) injury by in vivo microscopy. ME is a hormone produced by the pineal gland and is the most powerful and effective hydroxyl radical scavenger detected to date in vitro. The second aim was to determine the scavenger effect of ME in cheek pouch microcirculation when topically applying an oxygen-derived free radical generating system. METHODS: Ischemia was induced by clamping the cheek pouch for 30 min followed by 30 min of reperfusion. We quantified the increase in permeability, the perfused capillary length and leukocyte adhesion by computerized methods. Microcirculation was also exposed to a hypoxanthine-xanthine oxidase (H-X) system. RESULTS: In control hamsters I-R was associated with increased permeability, increased number of leukocytes sticking to venules, and decreased perfused capillary length. Treatment with ME completely inhibited microvascular edema formation and reduced the number of leukocytes sticking to venules after reperfusion. Moreover, ME prevented the marked decrease in perfused capillary length, preserving microvascular perfusion. ME topically applied reduced significantly the permeability increase due to H-X exposure. CONCLUSIONS: The beneficial effect of ME may be related to its antioxidant properties. These protect the endothelial barrier integrity as well as preserve microvascular blood perfusion by dysfunctions after I-R.

Asunto(s)

Melatonina/uso terapéutico , Microcirculación/efectos de los fármacos , Daño por Reperfusión/prevención & control , Animales , Permeabilidad Capilar/efectos de los fármacos , Adhesión Celular/efectos de los fármacos , Mejilla , Cricetinae , Leucocitos/efectos de los fármacos , Masculino , Mesocricetus , Microcirculación/patología , Daño por Reperfusión/patología

RESUMEN

Intracellular recordings from 103 photoreceptors in the excised pineal body of adult trouts were obtained by using single electrode current- and voltage-clamp techniques. The photoresponses to brief flashes showed the same polarity but a slower time course than those previously recorded from retinal photoreceptors of lower vertebrates. Pineal photoreceptors showed spectral sensitivity peaks at about 495 and 521 nm and absolute sensitivity comparable to retinal cone cells of the same species. The photoreceptor membrane conductance, measured under voltage clamp during moderate illumination was about 10% lower than in the dark, and the extrapolated reversal potential of the response was at 60 mV above the dark membrane potential. The addition of 3-isobutyl-1-methylxanthine (IBMX) to the perfusate was followed by a receptor depolarization in the dark and by a slow-down of the response kinetic. Pineal receptor cells produce constant amplitude responses during steady illumination, without displaying the delayed slow depolarization typically associated with light adaptation of retinal photoreceptors. Photoresponses to brief flashes superimposed on a steady illumination are decreased in amplitude by an amount directly related to the background intensity. Increase of the background intensity leads to threshold increments without significant changes of the saturation intensity, resulting in a gradual compression of the cell dynamic range. These results were discussed relative to light adaptation in retinal photoreceptors. The conclusion can be drawn that the response properties of pineal photoreceptors during steady illumination are part of an unknown, self-regulating mechanism to lock the rate of metabolism and secretion of indolamines to the absolute level of diurnal light.

Asunto(s)

Células Fotorreceptoras/fisiología , Glándula Pineal/fisiología , Trucha/fisiología , 1-Metil-3-Isobutilxantina/farmacología , Animales , Adaptación a la Oscuridad , Electrofisiología , Potenciales de la Membrana/fisiología , Hidrolasas Diéster Fosfóricas/metabolismo , Estimulación Luminosa , Células Fotorreceptoras/enzimología , Glándula Pineal/efectos de los fármacos , Umbral Sensorial

RESUMEN

Intracellular recordings were obtained from pineal photoreceptors of the trout Salmo irideus. Illumination produced graded hyperpolarizing responses whose time course resembled that of retinal cones in lower vertebrates. Current-voltage relations were derived by using a voltage-clamp technique in the dark and during illumination. Membrane resistance values obtained in the dark were about 550 M omega, and they increased during illumination. The extrapolated reversal potential of the photocurrent is about 55 mV above the dark membrane potential, indicating that an ionic mechanism similar to that in retinal photoreceptors may be involved.

Asunto(s)

Membrana Celular/fisiología , Células Fotorreceptoras/fisiología , Glándula Pineal/fisiología , Salmonidae/fisiología , Trucha/fisiología , Animales , Conductividad Eléctrica , Potenciales de la Membrana

RESUMEN

Double cones of tench and goldfish retina are characterized by extensive subsurface cisternae underlying the plasma membranes at the appositional area between the principal and accessory cone. Such a membrane system is absent in double cones of turtle and salamander retina. Measurements on both transverse and longitudinal sections gave a total appositional area of about 75 square microns, the subsurface cisterna in each element of the double cone being around 8-10% smaller due to multiple fenestrations at the level of the paraboloid. No gap junctions joining the inner segments of tench and goldfish double cones were detected, while gap junctions could be observed at the level of the ellipsoid and paraboloid of turtle double cones. The possible role of the subsurface cisternae in functional interactions between double cone elements is discussed.

Asunto(s)

Células Fotorreceptoras/ultraestructura , Animales , Peces , Carpa Dorada , Microscopía Electrónica , Especificidad de la Especie , Tortugas , Urodelos

RESUMEN

Intracellular recording were obtained from isolated single and double cone cells of the tench retina. Photoresponses show features characteristic of other species and behave linearly with very dim illumination. The cells spectral sensitivity matches their pigment absorption spectrum measured by previous authors. The principal and accessory members of double cones show a maximal sensitivity peak at about 644 and 547 nm, respectively. In addition, each of the two action spectra shows a secondary inflection at the peak wavelength of the adjacent member, suggesting functional coupling between the two members of double cones.

Asunto(s)

Peces/fisiología , Células Fotorreceptoras/fisiología , Animales , Conductividad Eléctrica , Técnicas In Vitro , Microscopía Electrónica , Células Fotorreceptoras/citología , Células Fotorreceptoras/ultraestructura

RESUMEN

Analyses of the photoresponses and morphologies of ganglion cells in the turtle retina suggests that these cells are of two types: type A ganglion cells receive predominantly bipolar inputs, while type B ganglion cells receive a mixture of inputs from bipolar and amacrine cells. According to these classification criteria, ganglion cells may reflect either activities of the outer or of the inner plexiform layer, respectively. To corroborate the validity of this classification a number of basic properties of ganglion cells were analysed. It was found that double colour opponency was characteristic of type A cells and directional selectivity was performed only by type B cells. In addition, the absolute sensitivity and the firing rate of type A cells were significantly higher than those of type B cells.

Asunto(s)

Retina/fisiología , Células Ganglionares de la Retina/fisiología , Tortugas/fisiología , Animales , Color , Electrofisiología , Potenciales Evocados Visuales , Técnicas In Vitro , Estimulación Luminosa , Células Ganglionares de la Retina/citología , Tortugas/anatomía & histología

RESUMEN

Ganglion cells in the turtle retina respond to increments of saturating illumination of the receptive field centre by progressively decreasing the number of spikes of the responses, perhaps as a result of membrane inactivation. Intracellular recording indicates that a simultaneous illumination of the receptive field surround greatly facilitates the "suprasaturated" central responses, while the expected centre-surround antagonism is still present between photoresponses below saturation. It is suggested that both pre- and post-synaptic mechanisms provide the ganglion cells with the unique possibility, among other retinal cells, to shift their full dynamic range across more than 3 log units of illumination intensity.

Asunto(s)

Retina/fisiología , Células Ganglionares de la Retina/fisiología , Potenciales de Acción , Adaptación Ocular , Animales , Técnicas In Vitro , Potenciales de la Membrana , Estimulación Luminosa , Tortugas

RESUMEN

The structure of electrophysiologically identified bipolar, amacrine and ganglion cells has been studied in the turtle retina. The distribution of these cells processes within the inner plexiform layer (i.p.l.) was evident after intracellular injection of horseradish peroxidase (HRP) or Procion yellow. The observations indicated that ganglion cells may be subdivided into two groups, on the basis of their organization of inputs. Type A ganglion cells receive only bipolar cells inputs, and Type B ganglion cells receive an additional input from amacrine cells. Each of the two groups of ganglion cells performs specific visual functions, like color discrimination or directional sensitivity.

Asunto(s)

Retina/fisiología , Células Ganglionares de la Retina/fisiología , Tortugas/fisiología , Animales , Electrofisiología , Vías Nerviosas , Retina/citología , Retina/ultraestructura , Células Ganglionares de la Retina/ultraestructura

RESUMEN

Intracellular recordings were obtained from amacrine cells afterwards identified morphologically by horseradish peroxidase injection. There is a correlation between the time course of the photoresponses and the distribution of the cell processes across the inner plexiform layer (i.p.l.). Cells producing the shortest duration, transient 'on-off' photoresponses branched in a single, narrow stratum of the i.p.l. (3-7 microns across). Transient photoresponses with a longer time course were recorded from cells branching in a thicker stratum of i.p.l. (up to 20 microns), or from bistratified cells. Amacrine cells producing sustained centre-on or centre-off photoresponses were radially diffused across the whole i.p.l.; therefore this type of photoresponse need not be associated with a specific cellular stratification within the i.p.l. It is concluded that the two main functional types of amacrine cell, i.e. transient on-off and sustained centre-on and centre-off, are subject to different structural organization of inputs than are the homologous physiological types of ganglion cells in this species, in the cat and in the carp. In a summary diagram the observed characteristics of the photoresponses are tentatively explained in terms of a non-homogeneous distribution of bipolar synaptic inputs along amacrine cell processes.

Asunto(s)

Retina/fisiología , Visión Ocular , Animales , Peroxidasa de Rábano Silvestre , Luz , Potenciales de la Membrana , Retina/citología , Tortugas