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