In Vitro Plasticity of the Direct Feedback Pathway in the Electrosensory
System of Apteronotus leptorhynchus
Daliang Wang and Leonard Maler
Department of Cellular and Molecular Medecine, University of Ottawa
Ottawa, Ontario, Canada
APStracts 4:0104N, 1997.
ABSTRACT
1. We have used field and intracellular recording from pyramidal cells in an
in vitro preparation of the electrosensory lateral line lobe (ELL) of
Apteronotus leptorhynchus to investigate synaptic plasticity of a direct
feedback pathway: the stratum fibrosum (StF).
2. Tetanic stimulation of the StF enhanced the StF-evoked synaptic response by
145% in field and the EPSP 190% in intracellular recordings. Maximal
enhancement occurred at 5 s and lasted for about 120 seconds. Tetanic
frequencies of 100-300 Hz produced enhancement; lower or higher frequencies
failed to produce statistically significant changes in EPSP amplitude. Rates
of 100-200 Hz occur in vivo in the cells of origin of the StF, suggesting that
this form of plasticity may be operative under natural conditions.
3. We could not elicit either long term potentiation or depression by any
stimulation protocol of the StF; in the case of long term potentiation this
held even when excitatory transmission was enhanced by application of
bicuculline, a GABAA antagonist.
4. When tetanic stimulation of the StF was paired with hyperpolarization of
pyramidal cells, subsequent StF-evoked EPSPs were increased by 146% (5 minutes
post-tetanus); this anti-Hebbian synaptic enhancement lasted for about 10
minutes. Neither tetanic stimulation alone, hyperpolarization alone or tetanic
stimulation paired with pyramidal cell depolarization altered StF-evoked EPSP
amplitudes on this time scale. Anti-Hebbian synaptic enhancement was not
blocked by the NMDA receptor antagonist APV.
5. The in vitro demonstration of anti-Hebbian plasticity at StF synapses
replicates similar in vivo results. Anti-Hebbian synaptic plasticity of the
StF may be responsible in part for the ability of gymnotiform fish to reject
redundant electrosensory signals.
Received 16 June 1997; accepted in final form 19 June 1997.
APS Manuscript Number J278-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 July 1997