| ROLE OF AMYGDALA IN CONDITIONED VERSUS UNCONDITIONED
RESPONDING TO AVERSIVE STIMULI |
| H.T. Blair*; F. Sotres-Bayon; M.A.P. Marta; J.E.
LeDoux |
| Ctr Neural Sci, NYU, New York, NY, USA |
|
Rats were fear conditioned by
pairing conditioned (CS; noise) and unconditioned (US; shock) stimuli.
Conditioned responding was assessed by freezing to the CS, and unconditioned
responding by US-evoked motor activity. The amygdala was inactivated
by bilateral infusion of muscimol (0.125mg/0.5mL). Muscimol prior
to training blocked freezing to the CS when rats were later tested
drug free, and muscimol prior to testing blocked freezing when rats
had been trained drug free, indicating that amygdala activity was
necessary for acquisition and expression of conditioned freezing.
Muscimol prior to training attenuated the motor response to the US,
suggesting that amygdala activity was involved in some aspect of US
processing. To investigate whether the US response depended on synaptic
plasticity, ifenprodil (1.0mg/0.5mL) was infused to block amygdala
plasticity. Ifenprodil prior to training blocked freezing to the CS
when rats were tested drug free, but ifenprodil prior to testing did
not block CS freezing when rats had been trained drug free, indicating
that amygdala plasticity was necessary for acquisition but not expression
of conditioned freezing. Ifenprodil prior to training did not affect
the US response, indicating amygdala plasticity was not needed for
US processing. The amydala is important for attaching reinforcement
value to stimuli, so inactivation of amygdala may reduce shock responses
by diminishing aversiveness of shock. Amygdala plasticity is involved
in storage of CS-US associations, so blocking plasticity in amygdala
may prevent the CS from acquiring aversive reinforcement value during
conditioning, without affecting reinforcement properties of the US.
Supported by: MH12341 to HTB; MH38774 to JEL
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