Long-Term Plasticity at Excitatory Synapses on Aspinous Interneurons in
Area CA1 Lacks Synaptic Specificity.
A.I. Cowan, C. Stricker, L.J. Reece and S.J. Redman.
Division of Neuroscience, John Curtin School of Medical Research Australian
National University, Canberra, A.C.T. 0200, Australia.
APStracts 4:0256N, 1997.
ABSTRACT
The synaptic specificity of LTP was examined at synapses formed on aspinous
dendrites of interneurons whose somata were located in the pyramidal cell
layer of hippocampal area CA1. Intracellular recordings from slices prepared
from rats were used to monitor excitatory post-synaptic potentials (EPSPs)
elicited by extracellular stimulation in stratum radiatum. Two synaptic inputs
were evoked at 0.5 Hz by stimulating axons adjacent to stratum pyramidale and
stratum lacunosum moleculare. After obtaining baseline recordings (ò 10 min),
one of the EPSPs was conditioned. The protocol involved tetanic stimulation,
sometimes combined with somatic depolarization. Low frequency stimulation of
the two pathways was then resumed and EPSPs were recorded for at least 30
minutes. We observed both homosynaptic and heterosynaptic changes in synaptic
strength. Long-term potentiation (LTP) and depression (LTD) were seen in both
pathways and all possible combinations of changes in the two EPSPs were
observed, including heterosynaptic LTP associated with either homosynaptic LTP
or LTD. Intracellular BAPTA (10 mM) abolished alterations in synaptic
strength. When axons in stratum radiatum synapse onto a spiny pyramidal cell,
synaptic specificity of LTP is preserved. However, the results obtained from
aspinous interneurons show that synaptic specificity of LTP is lost. These
results are consistent with the hypothesis that spines provide post-synaptic
mechanism(s) for conferring specificity to LTP.
Received 3 March 1997; accepted in final form 11 September 1997.
APS Manuscript Number J186-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997