The Journal of Neuroscience, September 15, 2000, 20(18):7122-7130
Short-Term Synaptic Plasticity Contributes to the Temporal
Filtering of Electrosensory Information
Eric S.
Fortune and
Gary J.
Rose
Department of Biology, University of Utah, Salt Lake City, Utah
84112-0840
Short-term synaptic depression and facilitation often are elicited
by different temporal patterns of activity. Short-term plasticity may
contribute, therefore, to temporal filtering by impeding synaptic
transmission for some temporal patterns of activity and facilitating
transmission for other patterns. We examined this hypothesis by
investigating whether short-term plasticity contributes to the temporal
filtering properties of midbrain electrosensory neurons. Postsynaptic
potentials were recorded in response to sensory stimuli and to direct
stimulation of afferents, in vivo. Stimulating afferents
with pairs of pulses at a rate of 20 pairs/sec ["tetanus (20 Hz)"] induced PSP depression. This PSP depression was similar
to that observed for electrosensory stimuli of the same temporal
frequency. Analysis of PSPs elicited by a pair of pulses that preceded
versus followed the tetanus revealed that PSP depression was caused by
synaptic depression, not by a loss of facilitation. Behavioral studies
indicate that fish can detect slow changes in signal amplitude (slow
AM) in backgrounds of fast fluctuations. Correspondingly, midbrain
neurons respond well to slow AM even in the presence of fast AM. In
many neurons, facilitation enhanced responses to trains (8-10 pulses;
100 Hz) that represented activity patterns elicited by slow AM, despite
induction of synaptic depression by a tetanus (20 Hz). The interplay
between synaptic depression and facilitation, therefore, can act as a
filter of temporal information. Some neurons that showed little
facilitation nonetheless responded to low temporal-frequency
information after induction of depression by fast information; this
likely results from the convergence of inputs with different temporal
filtering properties.
Key words:
whole-cell patch; sensory processing; synaptic
depression; facilitation; jamming avoidance response; in
vivo; midbrain; intracellular
Copyright © 2000 Society for Neuroscience 0270-6474/00/20187122-09$05.00/0
