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Role of amygdala in conditioned versus unconditioned responding to aversive stimuli



Role of amygdala in conditioned versus unconditioned responding to aversive stimuli



Society for Neuroscience Abstract Viewer & Itinerary Planner : Abstract No 85 11



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.

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