| LeDoux Lab 2005 SfN Abstracts |
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| INHIBITON PROVIDES A MECHANISM FOR MODULATING SYNAPTIC PLASTICITY IN THE LATERAL AMYGDALA | |
| S.Rosis*; A.D.Reyes; J.E.LeDoux | |
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Modifications of synaptic efficacy are postulated to
underlie formation of aversive memories in the lateral amygdala (LA).
Specifically, projections from the auditory thalamus to the LA are
thought to be strengthened, via long-term potentiation (LTP), when
an auditory conditioned stimulus (CS) is paired with an aversive unconditioned
stimulus (US). Experiments in vitro have found that LTP in LA is most
readily induced when the inhibitory transmitter GABA is blocked, suggesting
that under natural conditions inhibition must be suppressed for plasticity
to occur. We find that inhibition does not occlude LTP but rather
narrows the range of conditions under which it is induced. Whole-cell
current-clamp recordings were obtained from projection neurons in
the dorsal portion of the LA. Coronal slices were prepared from male
Sprague-Dawley rats. Bipolar stimulating electrode was placed to stimulate
fibers originating, in part, from the auditory thalamus. US input
was mimicked with postsynaptic spikes evoked by injecting a step of
current (500ms) to the soma. Three different current intensities were
used, chosen to span the full range of firing of the neuron. CS input
was mimicked by stimulating thalamic afferents with 15 pulses at 30
Hz. To explore the role of inhibition in LA plasticity, LTP was induced
with 10 pairings (10 sec apart) of thalamic stimulation and one of
the three postsynaptic current injections in the presence and absence
of picrotoxin (50 M),
a selective GABAA antagonist. In the absence of picrotoxin,
the amount of LTP depended on the magnitude of the depolarizing current
step and the number of postsynaptic spikes evoked during induction,
with maximal LTP occurring at the highest firing rate. The specificity
was eliminated in the presence of picrotoxin: LTP was induced maximally,
independent of both postsynaptic depolarization magnitude and firing
rate. Functionally, inhibition may act to ensure that learning in
the LA occurs only under specific conditions, thereby minimizing spurious
changes in synaptic strength.Support Contributed By: MH070150 MH46516 & MH58911 |
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| Program No. 415.4 Poster presentation:Monday, Nov. 14, 11:00 AM - 12:00 PM Location: HH27 |
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