ELECTROPHYSIOLOGY AND PHARMACOLOGY OF A LOCAL CIRCUIT FEEDBACK SYSTEM IN NEURONS OF THE OCELLAR RETINA.
Item
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Title
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ELECTROPHYSIOLOGY AND PHARMACOLOGY OF A LOCAL CIRCUIT FEEDBACK SYSTEM IN NEURONS OF THE OCELLAR RETINA.
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Identifier
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AAI8222983
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identifier
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8222983
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Creator
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STONE, SUSAN LIPSKY.
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Contributor
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Richard L. Chappell
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Date
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1982
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Animal Physiology
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Abstract
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Intracellular electrophysiological and pharmacological studies of photoreceptor and L-neuron (second order neuron) responses in the dragonfly ocellar retina suggest the hyperpolarizing OFF transient in the receptor reflects synaptic feedback from L-neuron dendrites onto receptor terminals. The receptor OFF response was normally observed when recording more proximally, closer to the nuclear and synaptic regions but was not seen when recording more distally, closer to the rhabdomeric end of the cell. Both the hyperpolarizing OFF response in the receptor and the depolarizing OFF response in the L-neuron are apparently generated in the ocellar plexiform layer because they were not eliminated when the L-neuron processes were isolated from the brain by severing the ocellar nerve. Direct evidence for synaptic feedback onto receptor terminals is provided by antidromic stimulation experiments, in which a normal-appearing OFF transient was recorded intracellularly from the dark-adapted receptor in response to the application of brief hyperpolarizing current pulses to the ocellar nerve, and pharmacological studies in which the responses of ocellar retinal neurons (in intact and cut nerve preparations) were modified by various drugs known to interfere with synaptic transmission. Cholinergic agonists mimicked some effects of light on the receptor and L-neuron response, curare reduced or blocked the receptor OFF response and eliminated all activity in the L-neuron, and picrotoxin increased the magnitude of the OFF response in both types of ocellar neurons. These findings are consistent with a sign-conserving feedback model and support the view that the receptor transmitter may be acetylcholine and the feedback (L-neuron) transmitter could be GABA. In addition, some of the results suggest that lateral synaptic interactions between photoreceptors and L-neuron dendrites may also contribute to the observed changes in the waveform of ocellar retinal responses.;Spontaneous fluctuations in dark potential were commonly observed in intact nerve preparations following exposure to drugs, and in cut nerve preparations untreated with drugs. In photoreceptors, the dark potential appeared to fluctuate between two distinct dark equilibrium levels. Such spontaneous dark oscillatory behavior may represent disruption of the dark equilibrium of a local circuit feedback loop whose stability is perturbed by pharmacological manipulation or by isolating L-neuron processes from the brain.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Biology
