Biomedical subjects

F S Werblin

Publications and source records attributed to F S Werblin.

14 recordsLinked to original sources

PubMed1991

Amacrine cells in the tiger salamander retina: morphology, physiology, and neurotransmitter identification.

Amacrine cells of the vertebrate retina comprise multiple neurochemical types. Yet details of their electrophysiological and morphology properties as they relate to neurotransmitter content are limited. This issue of relating light responsiveness, dendritic projection, and neurotransmitter content has been addressed in the retinal slice preparation of the tiger salamander. Amacrine cells were whole-cell clamped and stained with Lucifer yellow (LY), then processed to determine their immunoreactivity (IR) to GABA, glycine, dopamine or tyrosine hydroxylase (TOH), and glucagon antisera. Widefield, ON-OFF amacrine cells were glycine-IR. The processes of these cells extended laterally in the inner plexiform layer (IPL) from 250-600 microns. They were either multistratified in the IPL or monostratified near the IPL midline. Three multistratified ON-OFF narrowfield glycine-IR cells also were found. Four types of ON amacrine cells were found to be GABA-IR; all types had their processes concentrated in the proximal IPL (sublamina b). Type I cells were narrowfield (approximately 100 microns) with a compact projection. Type II cells were widefield (220-300 microns) with a sparse projection. Type III cells had an asymmetrical projection and varicose processes. Type IV cells were pyriform and monostratified in sublamina b. One narrowfield ON-OFF amacrine cell, with processes broadly distributed in the middle of the IPL, was GABA-IR. This cell appeared similar to an ON-OFF cell that was glycine-IR and may comprise a type in which GABA and glycine colocalize. Another class of amacrine cell, with processes forming a major plexus along the distal border of the IPL and a lesser plexus in the proximal IPL, produced slow responses at light ON and OFF; these cells were dopamine/TOH-IR. A narrowfield class of transient ON-OFF amacrine cell, with processes ramifying throughout both sublaminae a and b of the IPL, were glucagon-IR; these cells appeared to be dye-coupled at the soma. We have shown that, with respect to GABA, glycine, dopamine, and glucagon, salamander amacrine cells fall into rather discrete groups on the basis of ramification patterns in the IPL and responses to photic stimulation. The physiological, structural, and neurochemical diversity of amacrine cells is indicative of multiple and complex roles in retinal processing.

Ambystoma↗

PubMed1990

Time course of the membrane current underlying sensory transduction in salamander olfactory receptor neurones.

1. Odour elicited currents in freshly isolated olfactory receptor neurones were analysed using the whole-cell patch-clamp technique. Brief pulses (35-50 ms) and steps (100 ms-5 s) of odour solution were delivered by pressure ejection from a nearby micropipette. 2. Pulses of odour solution directed at the cell induced an inward depolarizing current of 50-750 pA leading to the generation of action potentials. The I-V relation for this current was linear over the range -60-(+)20 mV and showed a reversal potential of +5 mV. The magnitude of the current increased with stimulus strength, for a given pulse duration, over approximately one decade of concentration change. 3. Pulses of odour solution focally delivered to the cilia elicited a large response, but those directed toward the soma did not. Conversely pulses of K+ solution at the cilia failed to evoke any response while those directed at the dendrite and soma elicited an inward clamp current. This provides direct evidence that odour sensitivity is localized mainly to the cilia and possibly the distal dendrite. 4. The odour elicited current activated with a long latency of 150-600 ms after the odour solution arrived at the cell. This latency, as well as the time-to-peak and the rise half-time, were relatively independent of stimulus concentration, changing less than 25% over the entire concentration range of stimulus sensitivity. These observations are consistent with the participation of a second messenger system in olfactory transduction. 5. For brief stimulus pulses less than 100 ms, the stimulus diffused away before the odour response current reached its peak value, so that the peak and decay of the odour response occurred in the absence of significant odour stimulus. The time course of the current decay was fitted by a single exponential with a time constant that was concentration dependent, varying from 0.8 to 1.3 s. 6. For longer steps of stimulus presentation, up to 1 s, the magnitude of the response current became a function of the duration of the pulse as well as the stimulus concentration, indicating that the transduction process involved an integrating step. This is consistent with the idea that the odour elicited current is the result of the summation of many smaller unitary events. From responses to weak stimulation an integration period of 700-1000 ms was calculated. 7. During prolonged steps of maintained stimulus presentation (greater than 5 s) the odour elicited current was transient.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1990

The spatial distribution of excitatory and inhibitory inputs to ganglion cell dendrites in the tiger salamander retina.

In response to focal stimuli, ganglion cell dendrites receive excitation over a relatively narrow extent of the inner plexiform layer (IPL). This excitation is embedded in 2 wider lateral inhibitory regions. Here we estimate the lateral dimensions of the inhibitory regions. Ganglion cells were whole-cell patch-clamped and dendrites were identified and located in retinal slices using Lucifer yellow in the pipettes. The spatial distribution of ganglion cell dendritic sensitivity was measured with puffs of transmitter substances applied at different distances along the dendrites. All ganglion cell dendrites were sensitive to glutamate, GABA, and glycine across their full extent. The responses to puffs decreased with lateral distance from the soma and were well fit by Gaussians. The responses to puffs of potassium showed a similar decrement with distance. Since potassium channels are probably uniformly distributed along the dendrites, the similarity in profiles suggests that receptor density is also uniform along the dendrites. The spatial distribution of responses of ganglion cells to excitatory and inhibitory synaptic inputs was measured by depolarizing local populations of bipolar terminals (and subsequently local populations of amacrine cells) with transretinal current (TRC). TRC-stimulating electrodes were displaced laterally, with respect to the ganglion cell soma, to generate response profiles. We estimated the dimensions of the inhibitory and excitatory signals received by the ganglion cells by removing the contributions of their dendrites, the stimulus, and other interneurons from the response profiles. The excitatory signal extended less than 100 microns, the approximate dimensions of the ganglion cell dendrites, and corresponds roughly to the width of the bipolar inputs. The GABAergic signal extended, on average, 253 microns and glycinergic signal extended, on average, 315 microns. These inhibitory signal dimensions correspond to the width of classes of amacrine cell processes measured in other studies.

Animals↗

PubMed1987

Gated currents in isolated olfactory receptor neurons of the larval tiger salamander.

The electrical properties of enzymatically isolated olfactory receptor cells were studied with whole-cell patch clamp. Voltage-dependent currents could be separated into three ionic components: a transient inward sodium current, a sustained inward calcium current, and an outward potassium current. Three components of the outward current could be identified by their gating and kinetics: a calcium-dependent potassium current [IK(Ca)], a voltage-dependent potassium current [IK(V)], and a transient potassium current (Ia). Typical resting potentials were near -54 mV, and typical input resistance was 3-6 G omega. Thus, only 3 pA of injected current was required to depolarize the cell to spike threshold near -45 mV. The response to a current step consisted of either a single spike regardless of stimulus strength, or a train of less than 8 spikes, decrementing in amplitude and frequency over approximately equal to 250 msec. Thus, the receptor response cannot be finely graded with stimulus intensity.

Animals↗

PubMed1979

Synaptic inputs to the ganglion cells in the tiger salamander retina.

The postsynaptic potentials (PSPs) that form the ganglion cell light response were isolated by polarizing the cell membrane with extrinsic currents while stimulating at either the center or surround of the cell's receptive field. The time-course and receptive field properties of the PSPs were correlated with those of the bipolar and amacrine cells. The tiger salamander retina contains four main types of ganglion cell: "on" center, "off" center, "on-off", and a "hybrid" cell that responds transiently to center, but sustainedly, to surround illumination. The results lead to these inferences. The on-ganglion cell receives excitatory synpatic input from the on bipolars and that synapse is "silent" in the dark. The off-ganglion cell receives excitatory synaptic input from the off bipolars with this synapse tonically active in the dark. The on-off and hybrid ganglion cells receive a transient excitatory input with narrow receptive field, not simply correlated with the activity of any presynaptic cell. All cell types receive a broad field transient inhibitory input, which apparently originates in the transient amacrine cells. Thus, most, but not all, ganglion cell responses can be explained in terms of synaptic inputs from bipolar and amacrine cells, integrated at the ganglion cell membrane.

Animals↗

PubMed1979

Time- and voltage-dependent ionic components of the rod response.

1. The electrical properties of individual rods, physically isolated from the rod network, were measured in terms of the time course of response and voltage-current relations derived from current steps. Properties were measured in normal and altered bathing media designed to reveal the ionic basis for the time and voltage dependent properties of the rod response. 2. In normal media the rod membrane was strongly outward-rectifying with slope resistance near 100 M omega when hyperpolarized, but near 10 M omega when depolarized from a typical ambient level near 35 mV. The membrane become inward rectifying for hyperpolarizations beyond -95 mV, with slope resistance near 70 M omega. 3. The normal hyperpolarizing overshoot associated with the rod response was strongly potential dependent: the overshoot in response to a current step disappeared when the membrane was first depolarized or hyperpolarized by more than about 10 mV from the -35 mV ambient potential level. The decay from overshoot elicited either by current or light, could be approximated with a first order time constant of about 150 msec. 4. In the absence of sodium the peak-plateau sequence remained intact. Membrane resistance increased during transition to the plateau. The plateau became more hyperpolarized than the early phase during responses beyond -75 mV. These results indicate a time- and voltage-dependent conductance other than sodium contributes to the peak-plateau response, probably potassium. 5. Outward rectification was greatly reduced in the presence of 15 mM-TEA, suggesting that it is mediated by potassium activation. 6. Inward rectification, and the associated transients near -95 mV were eliminated in the presence of 2 mM-caesium, suggesting that potassium conductance contributes to the time and voltage dependent inward rectification.

Animals↗

PubMed1978

The response properties of the steady antagonistic surround in the mudpuppy retina.

1. The graded response of bipolar and ganglion cells to test flashes at the receptive field centre, spans only a limited portion of the test intensity domain: more than 90% of the graded response range can be elicited by test flashes differing by less than 100 to 1. 2. In the presence of steady illumination of the receptive field surround, the absolute levels of log test intensities required to elicit 90% of the graded response are increased (reset), but the relation in (1) still applies. 3. Each point in the receptive field surround, when illuminated, contributes to the resetting of the required centre test flash intensities by a weighing that decreases exponentially with distance from the centre. The space constant is 0.25 mm. 4. When the receptive field surround is fully covered with illumination, the centre test flash intensities required to elicit 90% of the response range must be increased by about tenfold for each tenfold increase in surround intensity over a surround intensity domain of about 1000 to 1. 5. The absolute levels of surround and required centre test intensities are inter-related: when the receptive field surround is fully covered, a test flash with intensity equal to that of the surround elicits a half-maximal response. Thus, in the presence of a full field background, the bipolar potential is held near its half-maximum response potential. 6. The graded resetting of the required centre test flash intensities is well correlated with the graded increase in horizontal cell response as the surround intensity and area are varied. It is inferred that units with response and receptive field properties like those of the horizontal cells, when driven by surround illumination, act as interneurones to reset the relationship between required test flash intensity and response in bipolar and ganglion cells.

Action Potentials↗

PubMed1978

The properties of surround antagonism elicited by spinning windmill patterns in the mudpuppy retina.

1. A truncated spinning windmill pattern, illuminating only the receptive field surround, shown previously to activate amacrine cells, was used to elicit activity at the inner plexiform layer and to reduce the response of ganglion cells to test flashes at the receptive field centre. 2. The spinning windmill pattern reduced the ganglion cell response over its entire graded range by a fixed amount, and reduced the domain of test intensities required for graded activity. 3. The windmill effect was graded for windmill intensities over a domain of about 1000 to 1. The effect was constant for windmill velocities from about 0.05 to 0.5 rev/sec, and diminished beyond these velocities. 4. The windmill effect varied with windmill area as though each retinal point contributed to the reduction of ganglion cell response with a weighting which fell exponentially from the receptive field centre. The space constant was 0.35 mm. 5. The graded reduction in ganglion cell response was closely correlated with the graded increase in amacrine cell activity when the windmill intensity, area, and velocity were varied. It is inferred that amacrine cells, activated by the windmill, act to reduce the response range of the ganglion cells, primarily through a feed-forward pathway.

Action Potentials↗

PubMed1978

Synaptic transmission to the horizontal cells in the retina of the larval tiger salamander.

1. The receptive field diameter for most horizontal cells far exceeds the lateral spread of processes for any cell. Therefore horizontal cells probably receive synaptic input from neighbours as well as from the photoreceptors. The electrical effects of these two synaptic inputs were studied. 2. We have characterized the electrical properties of the horizontal cell inputs by determining the current-voltage curves in dark and light. These curves were compared with those obtained in the presence of Co2+ or Mg2 was nearly identical to the curve in the light. 4. The putative transmitter substances glutamate, aspartate and GABA depolarized the cells by increasing conductance. Current-voltage curves measured in the presence of these substances intersected the dark and light curves at +50 mV, the same level at which the dark and light curves intersect. 5. The light response of cells uith broad receptive fields, between 1.0 and 2.0 mm, showed little or no change in conductance associated with the light response. The input resistance was near 20 Momega, and the current-voltage curves intersected at an extrapolated potential level near 200 mV. 6. In the presence of ACh, electrical properties of the broad field cells reverted to those of the narrow field cells: the receptive field was reduced to 0.5 mm, the imput resistance increased, and the current-voltage curves intersected near +50 mV. Thus ACh appeared to interrupt synaptic input from neighbouring horizontal cells. 7. The results confirm the suggestion that horizontal cells receive a tonic excitatory input from the photoreceptors which is decreased by light. They show that horizontal cells receive an additional input from their neighbours, not associated with a measurable conductance change. The input from neighbours is selectively interrupted by ACh, but the nature of this synapse and of the cholinergic action is not known.

Acetylcholine↗

PubMed1978

Transmission along and between rods in the tiger salamander retina.

1. The electrical pathways that couple the rods and that link the outer segments of the rods to the coupled network, were evaluated. Two separate micro-electrodes were inserted into the inner or outer segments of the same or neighbouring rods under visual control. Current was passed through one electrode, and the resulting potential recorded with the other. 2. The input resistance, measured at the inner or outer segment in a rod in the network, is strongly outward rectifying. It is typically near 40 Momega when the membrane is hyperpolarized 10 mV or more by extrinsic current, less than 10 Momega when the membrane is depolarized by 5 mV or more, and near 30 Momega at the no-current level. 3. When current is injected into the outer segment, the response in the inner segment is nearly identical with that at the outer segment, suggesting that the resistance coupling the segments is not high relative to the input resistance of the rod in the network. 4. Under voltage clamp the light response current for a rod in the network is of constant magnitude for potential levels between -80 and -20 mV. This suggests that there is little or no measurable light elicited conductance change associated with the response, possibly a consequence of coupling between rods. 5. The rod response increases with increasing diameter of a concentric test flash up to about 200 micron, or about 16 rod diameters. 6. When current is injected into one rod, the response in its immediate neighbours is between a quarter and one tenth that recorded in the injected rod for all potential levels in the injected rod. 7. The membrane time constant, measured in a rod in the network, is proportional to the voltage-dependent input resistance at 0.16 msec/Momega. With assumptions about the geometry of the rod network this represents a membrane capacitance of 1.5 muF/cm2. 8. The data can be approximated by a network model of square array. The model predicts that: the outer segment contributes less than half the current for the total rod response, the membrane resistance of an individual rod is greater than twice the measured input resistance for the rod in the network, near 60 Momega, and the coupling resistance for each arm of the network is about 4 times the individual rod resistance, near 240 Momega.

Animals↗

PubMed1978

Light, voltage, and time-dependent components of the rod response.

Individual rods were physically isolated from the retina. Since these rods are isopotential and uncoupled from the network, measurements of light- and voltage-dependent changes in resistance at the rod membrane can be obtained. The studies show that the reversal potential for the light response is near 0 mV. The hyperpolarizing overshoot at the onset of the response persists even when the rod is hyperpolzrized with current, suggesting that the overshoot is a voltage-rather than light-dependent event. In the absence of sodium in the bathing medium, the overshoot reverses polarity near--75 mV and is associated with an increase in resistance, suggesting that it is mediated by a voltage-dependent inactivation of potassium. Strong outward rectification is blocked by TEA; inward rectification is blocked by cesium, suggesting two other voltage-dependent changes in potassium conductance. Under voltage clamp a region of negative resistance appears at the dark potential level when the rod has been previously depolarized. The possible mechanisms for negative resistance are discussed.

Animals↗

PubMed1977

Regenerative amacrine cell depolarization and formation of on-off ganglion cell response.

1. Recordings from amacrine and ganglion cells in the mudpuppy retina suggest mechanisms whereby the relatively slow, sustained light responses measured in bipolar cells are converted to rapid, brief, transient activity in the on-off ganglion cells. 2. Double-barrel electrodes were used to control the membrane potential under voltage clamp. The clamp revealed synaptic currents, but eliminated the otherwise obvious spike activity elicited by steps of illumination in both amacrine and ganglion cells, suggesting that the spikes are initiated near the somata. 3. The synaptic current in the on-off ganglion cells was biphasic: a brief inward (depolarizing) membrane current preceded a transient outward (hyperpolarizing) membrane current by about 20 msec. Each component could be isolated by polarizing the membrane to a level near the reversal potential for the other. Each was apparently due to a transient conductance increase of sawtooth shape with a 40 msec time to peak and a decay longer than 400 msec. 4. Synaptic membrane current in amacrine cells was monophasic and inward (depolarizing) of similar sawtooth shape at all potential levels. It was apparently mediated by a conductance increase to ions with a reversal potential more positive than the dark level. 5. When amacrine cells were depolarized in the dark under voltage clamp, a large transient inward membrane current with threshold within 4 mV of the dark level was generated. This regenerative event is capable of boosting a small, 4 mV e.p.s.p. to more than 30 mV in a few milliseconds, thereby generating the leading edge of a rapid sawtooth response. 6. The results suggest that the rapid transient on-off activity in ganglion cells is mediated by opposing sawtooth shaped synaptic currents with different latencies. It is inferred that each of these antagonistic imputs is generated by a regenerative depolarization in amacrine cells which then form synaptic inputs to the ganglion cells.

Action Potentials↗

PubMed1975

Regenerative hyperpolarization in rods.

1. The electrical properties of the rods in Necturus maculosus were studied at the cell body and the outer segments in dark and light under current and voltage clamp with a pair of intracellular electrodes separated by about 1 mum. 2. The membrane resistance in the dark was voltage- and time-dependent both for the cell body and the outer segment. Slight depolarizations in the cell body reduced the slope resistance from 60 to 10 M omega with a time constant of about 1 sec. Polarization in either direction, at the outer segment, when greater than about 20 mV, reduced the slope resistance from 60 to 30 M omega. The dark potential in the cell body was typically -30 to -35 m V; at the outer segment it was typically only -10 to -15 mV. 3. The light-elicited voltage response in both the cell body and the outer segment was largest with the membrane near the dark potential level. In both regions, the response was reduced when the membrane was polarized in either direction. 4. Under voltage-clamp conditions, a reversal potential for the light response near + 10 mV was measured at the outer segment. At the cell body no reversal potential for the light response was measured; there the clamping current required during the light response was almost of the same magnitude at all potential levels. 5. When the membrane at the cell body was hyperpolarized in the dark under voltage clamp, a transient outward current, typically about one-half the magnitude of the initial inward clamping current was required to maintain the membrane at the clamped potential level. This outward current transient was associated with a decrease in membrane resistance with similar time course. The transient outward current reversed and became inward when the membrane was clamped to potentials more negative than -80 mV. Thus, the transient outward current appears to involve a transient activation initiated by hyperpolarization. I is regenerative in that it is initiated by hyperpolarization and tends to further hyperpolarize the membrane. 6. The reversal potential for the light response was measured at the outer segment but not at the cell body. The regenerative hyperpolarization was measured at the cell body but not at the outer segment. Thus, the outer segment and cell body appear to have different electrical properties: a light-elicited resistance increase at the outer segment causes a potential-dependent transient decrease at the inner rod. 7. An electrical model of the rod, based upon estimates of the membrane resistances and membrane e.m.f.s. in the dark, was derived from the data. This model predicts the appropriate response potentials at outer segment and cell body when perturbed by the measured light-elicited resistance increase at the outer segment. An estimate of membrane current in dark, of 0-2 mA, is also derived from the model.

Animals↗

PubMed1975

Anomalous rectification in horizontal cells.

1. The electrical properties of horizontal cells in the mudpuppy in light and dark were measured with a pair of micropipettes separated by about 1 mum with low coupling resistance so that no bridge circuitry was required. 2. All horizontal cells studied showed significant anomalous rectification: the current-voltage characteristic for about 60 per cent of the cells studied had a slope resistance of about 20-30 M omega at the dark potential level; the slope resistance increased by about 15% for each 10 mV depolarization and decreased by about 15% for each 10 mV hyperpolarization. The remaining 40% of the horizontal cells showed a higher input resistance at corresponding potential levels but had similar rectifying properties. 3. The increase in resistance with depolrization developed with a time course of about 1/2 sec when steady steps of outward current were passed across the membrane, but the time course for resistance decrease with hyperpolarization was much shorter for steady inward current steps. In about half the horizontal cells there was a transient decrease in resistance lasting about 100 msec immediately following the outward current steps superimposed upon the slower sustained resistance increase. 4. The normal 20-30 mV hyperpolarizing light response was associated with little or no change in input resistance. However, if the membrane potential was held at the dark potential level with extrinsic current, thereby eliminating the potential-dependent resistance change, a light-elicited resistance increase of about 10 M omega was measured. 5. The time-dependent change in membrane resistance elicited by polarizing steps of current obscured the reversal potential for the response. However, when the reversal potential was measured at short times following polarization of the membrane, before the time-dependent resistance change developed, it was estimated at between +15 and +50 m V. 6. The results suggest that the horizontal cell response is mediated by a light-elicited resistance increase at the synaptic membrane which is obscured by a potential- and time-dependent resistance decrease at another part of the membrane.

Animals↗