The Journal of Neuroscience, September 1, 2001, 21(17):6957-6966
Transfer of Visual Motion Information via Graded Synapses
Operates Linearly in the Natural Activity Range
Rafael
Kurtz,
Anne-Kathrin
Warzecha, and
Martin
Egelhaaf
Lehrstuhl für Neurobiologie, Fakultät für
Biologie, Universität Bielefeld, Postfach 10 01 31, D-33501
Bielefeld, Germany
Synaptic transmission between a graded potential neuron and a
spiking neuron was investigated in vivo using sensory
stimulation instead of artificial excitation of the presynaptic neuron.
During visual motion stimulation, individual presynaptic and
postsynaptic neurons in the brain of the fly were
electrophysiologically recorded together with concentration changes of
presynaptic calcium
(
[Ca2+]pre).
Preferred-direction motion leads to depolarization of the presynaptic
neuron. It also produces pronounced increases in
[Ca2+]pre and the postsynaptic spike
rate. Motion in the opposite direction was associated with
hyperpolarization of the presynaptic cell but only a weak reduction in
[Ca2+]pre and the postsynaptic spike
rate. Apart from this rectification, the relationships between
presynaptic depolarizations,
[Ca2+]pre, and postsynaptic
spike rates are, on average, linear over the entire range of activity
levels that can be elicited by sensory stimulation. Thus, the
inevitably limited range in which the gain of overall synaptic signal
transfer is constant appears to be adjusted to sensory input strengths.
Key words:
calcium cooperativity; fly; graded synapse; insect; lobula plate; motion vision; presynaptic calcium; synaptic gain; synaptic transmission; tangential cell
Copyright © 2001 Society for Neuroscience 0270-6474/01/21176957-10$05.00/0