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

121

SUMMARY1. Effects of L-glutamate and its analogues on membrane potentials of solitary horizontal cells were studied by intracellular recording. L-glutamate depolarized these cells at micromolar concentrations (> 10,sM), while D-glutamate and L-a-amino adipic acid produced slight depolarizations only at millimolar concentrations. Neither L-nor D-aspartate, even at millimolar doses, produced any change in solitary horizontal-cell resting potential.2. Solitary horizontal-cell responses to L-glutamate did not desensitize detectably. Responses to pairs of brief, ionophoretic pulses of L-glutamate were nearly equal in amplitude at inter-pulse intervals as short as 50 ms. Responses to maintained applications of low doses of L-glutamate did not decline for as long as 2 min.3. Depolarizing responses were produced by ionophoretic applications of Lglutamate near cell somata as well as dendrites. The mean sensitivity was 1t4 + 1-5 mV/nC with a maximum of 5-1 mV/nC. 4. Depolarizing responses to L-glutamate reversed in polarity at membrane potentials between 0 and -20 mV, were accompanied by a decrease in membrane slope resistance, and were suppressed by replacement of extracellular sodium ions with choline.5. These results demonstrate that chemosensitivity of retinal horizontal cells to acidic amino acids persists after dissociation protocols, and in several respects resembles that found in horizontal cells in situ. These findings are consistent with the notion that retinal horizontal cells receive a synaptic input involving L-glutamate or a similar substance.

Section: Reversal Potential Of Solitary Horizontal-cell Responses To supporting

confidence: 64%

Responses of solitary retinal horizontal cells from Carassius auratus to L‐glutamate and related amino acids.

Ishida

Kaneko

Tachibana

1984

121

“…The calculated final concentrations (mM) of the major constituents were: NaCl, 104; KC1, 2-1; CaC12, 3-6; Na2HPO4, 0-5; MgCl2, 0-4; MgSO4, 0-3; glucose, 5; HEPES, 5; pH adjusted to 7-6. The osmolarity of this solution (223 m-osmole/kg, measured with a vapour pressure osmometer) is 5 % higher than that of the solution used conventionally for the salamander retina (Marshall & Werblin, 1978). This medium was found to give much healthier, longer-lasting preparations, and significantly increased the success rate of the experiments.…”

Section: Solutionsmentioning

confidence: 85%

Behaviour of the rod network in the tiger salamander retina mediated by membrane properties of individual rods

Attwell

Wilson

1980

180

175

SUMMARY1. The spread of electrical signals between rods in the salamander retina was examined by passing current into one rod and recording the voltage responses in nearby rods. Rod network behaviour, measured in this way, was simulated from data on rod membrane properties gathered in voltage-clamp experiments on single isolated rods.2. The network voltage responses to square current pulses became smaller, more transient, and had a longer time-to-peak, for rods further away from the site of current injection. Depolarizing currents produced smaller responses than hyperpolarizing currents of the same magnitude.3. Neighbouring rods and cones were coupled less strongly than neighbouring rods. 4. The response of the rod network to current injection was unaffected by 2 mMaspartate-, which eliminates transmission from receptors to horizontal cells.5. The input resistance of single isolated rods, measured at the resting potential, varied between 100 and 680 MQ. The lower values were probably due to damage by the micro-electrodes. Electrical coupling was found to be very strong between the rod inner and outer segments. 6. A strong 'instantaneous' outward rectification seen in isolated rods at potentials positive to -35 mV was reduced, but not abolished, by 15 mM-TEA.7. In normal solution, isolated rods exhibited a voltage-and time-dependent current, IA, whose kinetics were approximated by a single first-order gating variable, and whose activation curve spanned the range between -40 and -80 mV. The time constant for the current varied with voltage and was 60-200 msec between -140 and -40 mV.8. A reversal potential for IA could not be found between -140 and -40 mV in normal solution, and the fully activated current, IA, was approximately voltageindependent, with a magnitude of , 0*1 nA over this potential range. 9. By several criteria, IA behaved as a single inward current activated by hyperpolarization. Pharmacological studies suggest, however, that it is the sum of at least two currents with very similar kinetics.10. Most isolated rods exhibited a very slow (T , 3 see) increase in net outward

“…Coupling to cones was not studied here. The coupling was not affected when the retina was bathed in Ringer containing 2 mM-CoCl2, sufficient to block synaptic transmission to the horizontal cells (Marshall & Werblin, 1978). This suggests that rods are coupled electrotonically.…”

Section: Electrical Properties Of Isolated Rodsmentioning

confidence: 92%

“…The eyecup experiments were done with a conventional optical stimulator described previously (Werblin, 1975;Marshall & Werblin, 1978). Half-maximal responses were elicited from a tungsten source delivering 0-3 /sW/cm2, as measured with the photometric filter of a United Detector Technology Model 40A Optometer.…”

Section: Light Stimulationmentioning

confidence: 99%

Transmission along and between rods in the tiger salamander retina.

Werblin¹

1978

Self Cite

269

172

SUMMARY1. 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 MD when the membrane is hyperpolarized 10 mV or more by extrinsic current, less than 10 MQ when the membrane is depolarized by 5mV or more, and near 30MQ 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.