The lateral amygdala (LA) contains cells that form associations
between an auditory conditional stimulus (CS) and a foot-shock unconditional
stimulus (US) during fear conditioning. Extracellular recordings
have shown selective auditory responses in LA, but it is unclear
how any frequency specificity is manifest at the synaptic level
in LA neurons. We investigated this issue in urethane-anesthetized
rats that were restrained in a stereotaxic frame via hollow ear-bars.
Tones of 5 distinct frequencies between 1-17 kHz were delivered
through the earbars while we recorded intracellularly from LA neurons
using K-acetate-filled quartz micropipettes. Most recorded neurons
showed a distinct preference to a particular auditory stimulus frequency
measured by amplitude and slope of the elicited EPSP. However, several
cells responded to a broader range of acoustic frequencies. In a
subset of the recorded cells we paired one frequency with a depolarizing
pulse (0.5 - 3.0 nA; 70 ms; 20-100 trials) delivered through the
recording electrode (the tone and depolarization served as CS and
US, respectively). Following pairing, the EPSPs elicited by a single
frequency tone were enhanced, relative to those elicited by auditory
stimuli not paired with depolarization. These data are in agreement
with extracellular studies showing relative auditory specificity
of LA neurons. Moreover, the results suggest that conditioning of
LA cells takes place when auditory presynaptic inputs co-occur with
postsynaptic depolarization, such as might result from pairing with
a natural US.
Supported by: MH46516
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