The Journal of General Physiology, Vol 67, 417-431, Copyright © 1976 by The Rockefeller University Press
Putative synaptic mechanisms of inhibition in Limulus lateral eye
AR Adolph
Serotonin (5-HT) perfusion of a thin section of Limulus lateral eye
hyperpolarizes retinular and eccentric cell membrane potential, and blocks
spike action potentials fired by the eccenteric cell. The indoleamine does
not directly affect retinular cell receptor potential or eccenteric cell
generator potential in response to light stimuli. LSD perfusion blocks both
this inhibitory action of 5-HT and light- evoked, synaptically mediated,
lateral inhibition. Iontophoretic application of 5-HT to the synaptic
neuropil produces shorter latency and duration and larger amplitude of
inhibition than does the perfusion technique. This inhibition is dose
dependent; the accompanying inhibitory postsynaptic potential (IPSP)
appears to have an equilibrium potential more hyperpolarized than normal
resting potential levels of ca. -50 mV. IPSP amplitude is sensitive to
extracellular potassium ion concentration: it increases with decreased
[K+]0 and decreases with increased [K+]0. LSD blocks the inhibition
produced by iontophoretic application of 5-HT. Interaction between
light-evoked, natural synaptic transmitter-mediated IPSP's and 5-HT IPSP's
suggests a common postsynaptic receptor or
transmitter-receptor-permeability change mechanism.
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