Biomedical subjects

R M Glantz

Publications and source records attributed to R M Glantz.

At least 19 recordsLinked to original sources

PubMed2001

Polarization analysis in the crayfish visual system.

It is proposed that polarization sensitivity at the most peripheral stages of the crayfish visual system (lamina ganglionaris and medulla externa) is used to enhance contrast and thus may contribute to motion detection in low contrast environments. The four classes of visual interneurons that exhibit polarization sensitivity (lamina monopolar cells, tangential cells, sustaining fibers and dimming fibers) are not sensitive exclusively to polarized light but also respond to unpolarized contrast stimuli. Furthermore, many of these cells and the sustaining fibers in particular exhibit a greater differential e-vector responsiveness to a changing e-vector than to e-vector variations among steady-state stimuli. While all four cell types respond modestly to light flashes at an e-vector of 90 degrees to the preferred orientation, the dynamic response to a changing e-vector is small or absent at this orientation. Because the sustaining fibers exhibit polarization sensitivity, and they provide afferent input to a subset of optomotor neurons, the latter were also tested for polarization sensitivity. The optomotor neurons involved in compensatory reflexes for body pitch were differentially sensitive to the e-vector angle of a flash of light, with maximum responses for e-vectors near the vertical. The motor neurons also exhibited a maximum response near the vertical e-vector to a continuously rotating polarizer. Two scenarios are described in which the sensitivity to a changing e-vector can produce motion responses in the absence of intensity contrast.

Animals↗

PubMed2000

Tachykinin-related peptide and GABA-mediated presynaptic inhibition of crayfish photoreceptors.

Off-axis illumination elicits lateral inhibition at the primary visual synapse in crustacea and insects. The evidence suggests that the inhibitory action is presynaptic (i.e., on the photoreceptor terminal) and that the amacrine neurons of the lamina ganglionaris (the first synaptic layer) may be part of the inhibitory pathway. The neurotransmitters and the synaptic mechanisms are unknown. We show by immunocytochemistry that GABA and a tachykinin-related peptide (TRP) are localized in the amacrine neurons of the crayfish lamina ganglionaris. Indirect evidence suggests that GABA and TRP may be colocalized in these neurons. The extensive processes of the amacrine neurons occupy lamina layers containing the terminals of photoreceptors. Application of exogenous GABA and TRP to photoreceptor terminals produces a short-latency, dose-dependent hyperpolarization with a decay time constant on the order of a few seconds. TRP also exhibits actions that evolve over several minutes. These include a reduction of the receptor potential (and the light-elicited current) by approximately 40% and potentiation of the action of GABA by approximately 100%. The mechanisms of TRP action in crayfish are not known, but a plausible pathway is a TRP-dependent elevation of intracellular Ca(2+) that reduces photoreceptor sensitivity in arthropods. Although the mechanisms are not established, the results indicate that in crayfish photoreceptors TRP displays actions on two time scales and can exert profound modulatory control over cell function.

Animals↗

PubMed1998

Directionality and inhibition in crayfish tangential cells.

The purpose of this study was to characterize the inhibitory mechanism(s) associated with directionally selective motion detection (DS) in nonspiking tangential cells of crayfish optic lobe. The experiments employed intracellular recording of synaptic potentials elicited with sinewave gratings and pharmacological techniques. Previous studies established that tangential cells are subject to bicuculline-sensitive GABA-mediated inhibition. In this study DS was reduced by 90% by bicuculline. The reduction in DS was accompanied by a substantial increase in the response to null-direction motion. Bicuculline also altered the response to pulses of illumination. The magnitude and time course of inhibition were derived from the time varying difference between the control light response and that elicited during bicuculline perfusion. Both the inhibitory delay (relative to excitation) and the inhibitory amplitude are close to the expectations of a linear model of DS. The inhibition is not prolonged with respect to excitation but its risetime is approximately 2.5 times longer. The result implies a longer time constant in the inhibitory pathway relative to that in the excitatory pathway and places limits on the frequency response of inhibition and DS. The velocity-dependence of DS is related to the time course of inhibition. The stimulus drift velocity eliciting maximum directionality is inversely proportional to the inhibitory delay. Bicuculline did not influence orientation selectivity. It is concluded that the quantitative features of bicuculline-sensitive, GABA-mediated inhibition are consistent with a linear model of DS.

Animals↗

PubMed1998

Two-channel polarization analyzer in the sustaining fiber-dimming fiber ensemble of crayfish visual system.

Polarization sensitivity (PS) was examined in two classes of neurons, sustaining fibers and dimming fibers, in the medulla externa (second optic neuropile) of the crayfish, Pacifasticus leniusculus. Visual responses were recorded intracellularly and extracellularly. The influence of e-vector orientation (theta) was probed in steady-state responses, with brief flashes and with a rotating polarizer. The results indicate that the entire sustaining fiber population appears to be maximally sensitive to vertically polarized light. Although the evidence is less complete for dimming fibers, they appear to be maximally inhibited by vertically polarized light and excited by horizontally polarized light. Thus the sustaining fibers and dimming fibers form a two-channel polarization analyzer that captures the main features of the polarization system established in photoreceptors and lamina monopolar cells. The available evidence suggests that this two-channel system has the same characteristics across most or all of the retinula. Lateral inhibition in sustaining fibers is differentially sensitive to theta. Inhibition is substantial at theta = 90 degrees (horizontal) and essentially absent at theta = 0 degrees. The details of the sustaining fiber polarization response closely follow features established in more peripheral neurons, including the magnitude of PS, enhanced responsiveness to a changing e-vector, and modest directionality to a changing e-vector in approximately 40% of the cells.

Animals↗

PubMed1996

Polarization sensitivity in the crayfish optic lobe: peripheral contributions to opponency and directionally selective motion detection.

1. Polarization sensitivity (PS) was examined in nonspiking interneurons, tangential cells, of the crayfish optic lobe. Stationary PS profiles were measured with pulses of illumination at fixed intensity and varied evector orientation (theta). Dynamic polarization responsiveness was examined with a rotating polarizer. The dynamic response was assessed with variations in rotation velocity and direction and for variations in intensity. 2. Eighty percent of the cells tested were polarization sensitive. These were divided into two types. Type I cells exhibited PS magnitudes comparable with those of photoreceptors and lamina monopolar cells in the same species. Most type I cells exhibited a directionally selective response to a rotating polarizer. 3. Type II cells exhibited PS magnitudes substantially higher than those observed in lamina neurons. These cells also revealed evidence for a polarization opponency mechanism. 4. The results are interpreted in terms of a general hypothesis for polarization feature detection, on the basis of four principles. 1) Most or all tangential cells are subject to inhibition. 2) The inhibitory pathway is polarization sensitive. 3) If the theta producing the maximum response at fixed stimulus intensity (theta max) of the inhibitory input is similar to theta max - 90 degrees of the excitatory input, then the inhibition forms the basis of a polarization opponency mechanism. 4) If theta max of the inhibitory input is similar but not identical to theta max of the excitatory input, then the inhibitory input provides a basis for directionally selective polarization vision.

Animals↗

PubMed1995

Directionally selective motion detection in the sustaining fibers of the crayfish optic nerve: linear and nonlinear mechanisms.

1. Directional selectivity of crayfish sustaining fibers was examined with drifting sine wave gratings and with intracellular and extracellular recordings. Directionality was measured for variations in stimulus contrast, spatial frequency, and temporal frequency. 2. Sustaining fibers exhibit directional selectivity in the magnitude of the compound postsynaptic potential (PSP), the impulse frequency modulation response, and the mean firing rate. The mean synaptic potential is insensitive to direction. The directionality of the mean impulse rate appears to arise by rectification in the voltage-to-impulse transduction. 3. The preferred directions of three identified sustaining fibers are similar to those of head-down optomotor neurons to which these sustaining fibers project. 4. The modulatory response, elicited by gratings drifting in the preferred direction, increased linearly with contrast until saturation (typically at a contrast of 0.5), where maximum directional selectivity obtains. 5. The magnitude of the directional response is a band-pass function of spatial and temporal frequency and exhibits reversal of directionality (i.e., aliasing) at high spatial and temporal frequencies. The results imply a spatial sampling interval of 4.5 degrees and a temperature-dependent inhibitory delay of 40-90 ms. The PSP modulation response shares several features with that of neighboring tangential (Tan1) neurons. 6. A qualitative model is proposed for the transformation of a phase-sensitive, linear directional response to a phase-insensitive and nonlinear time-averaged response, based on the functional connections from Tan1 neurons to sustaining fibers to optomotor neurons. The model includes a threshold rectification, a synaptic band-pass filter, and differences in temporal phase among converging modulatory signals.

Animals↗

PubMed1994

The spatiotemporal transfer function of crayfish lamina monopolar neurons.

1. The graded, synaptic potentials of first-order visual interneurons (lamina monopolar cells) were examined with intracellular recordings. The spatiotemporal properties were characterized with drifting sine wave gratings and annuli. 2. Annulus-elicited inhibition is maximal for annulus-test pulse intervals of approximately 140 ms and declines exponentially. The inhibition declines with increasing annular internal radii (ri). 3. Grating responses were examined with respect to spatial and temporal frequency. The gratings elicit sinusoidal signals that are approximately linear with contrast. 4. Variations in spatial frequency produce response functions with a low-pass or modest band-pass characteristic, which are described by a difference of Gaussians sensitivity profile. The central Gaussian approximates the sensitivity profile of photoreceptors. The inhibitory Gaussian is similar to the inhibitory field estimated with annulus pulses. The peak of the inhibitory Gaussian is approximately 18% of the peak excitatory Gaussian. 5. Variations in temporal frequency generally produce transfer functions with a band-pass characteristic and a peak at 1.0 Hz. These data were described by a difference of exponentials function convolved with a low-pass filter that approximates the photoreceptor response. The inhibitory time course estimated from these data was similar to that of the annulus measurements. 6. The spatiotemporal properties of lateral inhibition are consistent with inhibitory action by the lamina amacrine neurons. The proposed model is spatiotemporally inseparable and nonrecurrent. 7. Eleven of 20 monopolar cells tested exhibited a strong orientation preference with a bias to the vertical. Photoreceptors exhibit little or no orientation preference.

Animals↗

PubMed1994

Directional selectivity in a nonspiking interneuron of the crayfish optic lobe: evaluation of a linear model.

1. Intracellular recordings, sine wave gratings, and paired flashes were used to characterize the directional selectivity (DS) of the peripheral neurons of the crayfish visual pathway. DS was observed in nonspiking tangential (Tan1) neurons of the distal medulla externa and it is expressed by the amplitude of the modulated synaptic potential elicited with drifting gratings. 2. The directional mechanism was characterized by variations in the grating contrast, spatial frequency, and temporal frequency. DS is both contrast and velocity dependent. 3. The velocity dependence of DS for fixed stimulus contrast can be described by a linear model including a delay and subtractive compare operation. This mechanism operates over the entire useful range of spatial and temporal frequencies. 4. The parameters of the linear model can be estimated from the spatiotemporal structure of the Tan1 cell receptive field. The receptive field exhibits a spatially asymmetric inhibitory subfield that is offset from the excitatory subfield by 3-5 degrees (1-2 ommatidia). The inhibition is delayed relative to excitation by 50-100 ms. 5. The contrast dependence of DS reflects an apparent nonlinearity in the mechanism that determines the null response amplitude. The preferred response magnitude is approximately linear with variations in contrast. 6. The nonlinearity observed in the null direction can in principle be attributed to either a tonic excitation at 0 contrast or a threshold for inhibition. There is evidence for both processes in the Tan1 cell visual response.

Acetylcholine↗

PubMed1991

An arthropod NMDA receptor.

Identified crayfish visual interneurons respond to illumination with a compound EPSP of up to 40 mV. L-glutamate, quisqualate, and kainate mimic the depolarizing action of the natural transmitter. In reduced Mg2+, N-methyl-D-aspartate (NMDA) elicits a depolarization with a reversal potential (Erev) = -60 mV. Erev is independent of extracellular calcium but shifts to +4 mV if potassium conductances are blocked by intracellular CS+. The results suggest that NMDA may gate more than one class of ionic channel. The NMDA-elicited response is enhanced and prolonged by glycine, and kynurenate competitively blocks the action of glycine. The NMDA antagonist, D-AP7, selectively blocks the NMDA response while enhancing the EPSP. The actions of NMDA are consistent with a role in the neural mechanisms of visual adaptation. This is the first description of an NMDA receptor in an invertebrate.

2-Amino-5-phosphonovalerate↗

PubMed1991

Motion detection and adaptation in crayfish photoreceptors. A spatiotemporal analysis of linear movement sensitivity.

Impulse and sine wave responses of crayfish photoreceptors were examined to establish the limits and the parameters of linear behavior. These receptors exhibit simple low pass behavior which is well described by the transfer function of a linear resistor-capacitor cascade of three to five stages, each with the same time constant (tau). Additionally, variations in mean light intensity modify tau twofold and the contrast sensitivity by fourfold. The angular sensitivity profile is Gaussian and the acceptance angle (phi) increases 3.2-fold with dark adaptation. The responses to moving stripes of positive and negative contrast were measured over a 100-fold velocity range. The amplitude, phase, and waveform of these responses were predicted from the convolution of the receptor's impulse response and angular sensitivity profile. A theoretical calculation based on the convolution of a linear impulse response and a Gaussian sensitivity profile indicates that the sensitivity to variations in stimulus velocity is determined by the ratio phi/tau. These two parameters are sufficient to predict the velocity of the half-maximal response over a wide range of ambient illumination levels. Because phi and tau vary in parallel during light adaptation, it is inferred that many arthropods can maintain approximately constant velocity sensitivity during large shifts in mean illumination and receptor time constant. The results are discussed relative to other arthropod and vertebrate receptors and the strategies that have evolved for movement detection in varying ambient illumination.

Adaptation, Ocular↗

PubMed1990

A neuronal nicotinic acetylcholine receptor in crayfish neurons.

In warm-blooded vertebrates, neuronal nicotinic acetylcholine receptors (nAChRs) are distinguished from muscle endplate receptors by their ligand affinities and sensitivity to several toxins. In the crayfish optic lobe, synaptic and acetylcholine (ACh)-elicited responses are blocked by toxins (F-toxin and neosurugatoxin) selective for neuronal nAChRs and are insensitive to the alpha-neurotoxins selective for endplate nAChRs.

Acetylcholine↗

PubMed1989

Acetylcholine and GABA mediate opposing actions on neuronal chloride channels in crayfish.

A central principle of neural integration is that excitatory and inhibitory neurotransmitters effect the opening of distinct classes of membrane ionic channels and that integration consists of the summation of the opposing ionic currents on the postsynaptic membrane. In tangential cells of crayfish optic lobes, a hyperpolarizing, biphasic synaptic potential is produced by the concurrent action of acetylcholine and gamma aminobutyric acid (GABA). Acetylcholine hyperpolarizes the cell and increases chlorine conductance. GABA depolarizes the cell by closing some of the same chloride channels. Therefore, in this case integration is achieved by the antagonistic actions of two transmitters on the same ionic channel.

Acetylcholine↗

PubMed1989

Acetylcholine in the crayfish optic lobe: concentration profile and cellular localization.

The crayfish optic lobe contains high levels of acetylcholine (ACh) and choline as measured with a chemiluminescent assay in small fragments of optic lobe tissue. The highest concentrations were found in the medulla externa and medulla interna (second and third optic neuromeres), which have ACh concentrations of 270 pmol/mg tissue. This concentration is about 16 times that measured in the photoreceptors and lamina ganglionaris (the first optic neuromere). Immunocytochemistry (based upon antisera to choline-glutaryl-BSA) revealed low levels of ACh-like reactivity in the lamina ganglionaris associated with the terminal arbors of centrifugal and/or tangential neurons. The most intense ACh-like reactivity was observed in monopolar neurons of the medulla externa and medulla interna. One monopolar neuron/medullary column (or about 2500 neurons/medullary neuropile) exhibited reactivity and an estimated cytoplasmic concentration of 8.1 mM.

Acetylcholine↗

PubMed1989

Cholinergic synapses and the organization of contrast detection in the crayfish optic lobe.

The actions of acetylcholine (ACh) were examined on 4 classes of multicolumnar interneurons whose dendrites lie in close proximity to the putative cholinergic transmedullary neurons described in the companion report. ACh-elicited responses in each cell type resemble visually elicited synaptic events and persist following synaptic blockade with 20 mM CoCl2. Tangential cells exhibit a hyperpolarizing response to ACh that resembles the visual response in reversal potential and dependence on extracellular chloride. The visual response is potentiated by the anticholinesterase, neostigmine (0.1 mM). Visual and carbachol-elicited responses are blocked by nicotinic ganglionic antagonists (e.g., 10(-6) M pempidine) that are 10-100 times more potent than D-tubocurarine. Medullary amacrine cells exhibit depolarizing responses to ACh (10(-6) M) and light with similar reversal potentials. The visual response is potentiated by neostigmine. Dimming fibers respond to light and ACh with a hyperpolarization that inhibits the maintained discharge. The sustaining fiber response to ACh reflects both direct responses and indirectly elicited synaptic actions. The direct action is a hyperpolarization possibly related to the visual "off-response." It is associated with an increased conductance and a reversal potential negative to the dark potential. The off-response is abolished by curare and pempidine and potentiated by neostigmine. ACh appears to orchestrate several aspects of the dual-channel contrast detection system of the optic lobe. The actions of ACh on tangential cells, amacrine cells, and dimming fibers are all consistent with the effects of a spatially localized increment in light intensity and a corresponding local release of ACh in the retinotopic columnar array.

Acetylcholine↗

PubMed1988

Immunocytochemical studies of the distribution of acetylcholine in the crayfish brain.

A number of studies indicate that acetylcholine is an important transmitter in most crustacean primary afferents and in at least several central pathways. Little is known, however, regarding the structure or distribution of cholinergic pathways in the central nervous system. The recent introduction of antibodies to choline-protein conjugates provides a potentially powerful means for localizing putative cholinergic neurons and pathways in the nervous system. Acetylcholine was localized with immunocytochemical procedures in the axons and terminals of cephalic primary afferents and in interneurons of the crayfish brain. The most intensely reactive loci were the primary sensory neuropiles, which contain the terminals of the statocyst afferents (parolfactory lobes) and antennal afferents (antennal lobe). These results are generally in accord with previous findings based upon choline uptake and enzyme assay in lobster cephalic nerves. We also found evidence consistent with the presence of acetylcholine in the globular interneurons of the accessory lobe and in descending interneurons which originate in the dorsal medial and anterior clusters of the protocerebrum. The axons of several neurons in the circumesophageal connective (descending interneurons and primary afferents) are also reactive to the choline antibody.

Acetylcholine↗

PubMed1988

Interval coding and band-pass filtering at oculomotor synapses in crayfish.

1. Crayfish exhibit steady-state compensatory eyestalk rotations in response to rotations of the organism or the visual surround. For stimuli in the vertical planes (pitch or roll) the visual reflexes are mediated by identified visual interneurons [sustaining fibers (SFs)], which synapse on identified oculomotor neurons (Mns) (18). 2. The optimal visual stimulus is broad-field intense illumination (simulated skylight) distributed over the dorsal half of the cornea. These stimuli are also optimal for eliciting a regular pacing discharge in SFs with dorsal receptive fields (17). Since a unique discharge pattern is associated with the reflex stimulus, we proposed that the pacing discharge interval encodes the stimulus condition and is optimal for driving the motoneuron discharge. 3. The cross-correlation of SF and Mn impulse trains exhibit large peaks (or troughs) at short latencies associated with strong excitatory (or inhibitory) interactions and "secondary effects" at longer delays associated with the periodicity of the Mn impulse train. The secondary peaks and troughs indicate delayed periods of elevated or depressed Mn excitability synchronized to the reference train (SF) events. From the structure of the cross-correlograms and the motoneuron autocorrelograms we predicted that the spike-to-spike synaptic throughput should be differentially sensitive to the various classes of SF interspike intervals. 4. The hypotheses were tested with logical-correlation functions that directly measure the relative synaptic efficacy of several classes of SF intervals during a continuous train at constant mean rate. The results indicate that the SF-to-Mn excitatory synapse is maximally driven by SF impulses separated by approximately 85 ms. These events are about 2.5 times as effective as the impulses associated with short intervals (less than 20 ms) and 1.4 times as effective as the spikes of long intervals (250 ms). The optimal interval in the various preparations is highly to correlated to the period of the Mn discharge and the SF modal interspike interval. Inhibitory synapses are also differentially sensitive to the SF interspike intervals, but they exhibit summation rather than depression in response to short interspike intervals. 5. These results are generally consistent with previously formulated relationships (39), which govern the synaptic modulation of pacemakers and may apply to any synaptic interaction in which the postsynaptic neuron exhibits a regular discharge. 6. Combinations of long and short intervals with the same mean rate as the optimal interval are not as effective in driving the SF-to-Mn synapse.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

The functional organization of the crayfish lamina ganglionaris. I. Nonspiking monopolar cells.

The light responses of the second order lamina monopolar neurons were examined in the crayfish compound eye. Single cartridge monopolar neurons (M1-M4) exhibited nonspiking hyperpolarizing light responses; for M1, M3 and M4 the transient 'on' response operated over the same intensity range as the receptor, 3.5 log units. M2 operated in a much narrower intensity range (1.5 log unit). The 'on' responses were associated with a 19% increase in conductance. The hyperpolarizing 'on' response can be reversed at 18 mV below the resting membrane potential. The half-angular sensitivity width of monopolar cells (in partially dark-adapted eyes) is 15 degrees X 8 degrees (horizontal by vertical). Off axis stimuli elicit attenuated hyperpolarizing responses associated with a diminished conductance increase or depolarizing responses associated with a net decrease in conductance. The latter result is consistent with the presynaptic inhibition of a 'back-ground' transmitter release which normally persists in the dark. Lateral inhibition is elicited from the area immediately surrounding the excitatory field, and it is associated with diminished transient responses and an accelerated decay of the response. Inhibitory stimuli decrease the conductance change associated with the hyperpolarizing response. The surround stimuli can also elicit depolarizing 'off' responses with reversal potentials positive to the membrane resting potential. It is concluded that the rapidly repolarizing monopolar cell response is modulated by both pre- and postsynaptic inhibitory mechanisms. A compartment model indicates that signal attenuation along a 500 microns length of monopolar cell axon is 22-34%. Simulation of steady-state signal transmission suggests that passive (decremental) conduction is sufficient to convey 66 to 78% of the monopolar cell signal from lamina to medulla. The current-voltage relation in current clamp is linear over the physiological operating range, and there is no evidence for rectification. Hyperpolarization of single monopolar cells (M1-M4) provides a polysynaptic excitatory signal to the medullary sustaining fibers.

Animals↗

PubMed1987

The functional organization of the crayfish lamina ganglionaris. II. Large-field spiking and nonspiking cells.

The functional properties of the multicolumnar interneurons of the crayfish lamina ganglionaris were examined by intracellular recording and the cell structures were revealed with the aid of Lucifer yellow or horseradish peroxidase iontophoresis. The multicolumnar monopolar cell M5 responds to a light pulse with a depolarizing compound EPSP and a burst of action potentials. Both the EPSP amplitude and the spike rate decay toward a lower level plateau in less than 200 ms after light onset. M5 is subject to surround inhibition, which is associated with a compound IPSP and net hyperpolarization of the membrane potential. Direct depolarization of M5 may provide a weak excitatory drive to medullary sustaining fibers (SF). Tangenital-cell type 1 (Tan1) has a broad expanse of neurites in the lamina (covering 10 to 15 cartridges) and a much narrower projection in the medulla (1 to 3 cartridges). The response to a light pulse has a long latency consistent with a polysynaptic receptor to Tan1 pathway. The response consists of a nearly rectangular hyperpolarization. Light 'off' elicits a depolarization and a burst of impulses. The polarity of the 'on' response can be reversed by hyperpolarizing the membrane by 23 mV. The receptive field is broad and the intensity-response function exceeds 4 log units. Direct hyperpolarization of Tan1 provides a strong excitatory signal to medullary SFs both in the dark and in the presence of illumination. We propose that Tan1 provides the principal steady-state excitatory drive to the SFs. Tangential-cell type 2 (Tan2) is distinguished from Tan1 by the extent and shape of the lamina process, which is a vertically oriented neurite spanning most of the lamina in a single plane. Functionally, Tan2 is similar in most respects to Tan1, but the response latency is much shorter, comparable to that of monopolar cells. T-cells may exhibit spontaneous impulse activity in the dark which is inhibited by a short latency hyperpolarizing light response. The receptive field, which is about 2 X larger than that of the columnar monopolar cells, is correlated with a small but multicolumnar dendritic arbor in the lamina. Since T-cells are aminergic, it is possible that the amines are normally released in the dark. A single amacrine cell was fully characterized. It exhibited a short latency hyperpolarizing response to light onset and a strong depolarizing 'off' response.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗