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The Journal of Neuroscience, May 15, 2001, 21(10):3619-3627
Neurotoxic Lesions of the Lateral Nucleus of the Amygdala
Decrease Conditioned Fear But Not Unconditioned Fear of a Predator
Odor: Comparison with Electrolytic Lesions
Karin J.
Wallace and
Jeffrey B.
Rosen
Department of Psychology and Neuroscience Program, University of
Delaware, Newark, Delaware 19716
Considerable evidence suggests that the lateral (LA) and basal (BA)
nuclei of the amygdala are sites of plasticity and storage of emotional
memory. Recent arguments, however, have seriously challenged this view,
suggesting that the effects of amygdala lesions are attributable
to interference with performance of fear behavior and not learning and
memory. One way to address this controversy is to measure the same
behavioral response during both conditioned and unconditioned fear.
This is done in the present study by measuring fear-related freezing
behavior after electrolytic and neurotoxic lesions of the LA or LA/BA
nuclei in rats in a contextual fear conditioning paradigm and
unconditioned fear to a predator odor. Electrolytic LA lesions
attenuated post-shock freezing, retention test freezing, and freezing
to the predator odor trimethylthiazoline (TMT). In contrast,
excitotoxic NMDA lesions of the LA had no effect on post-shock freezing
but significantly attenuated retention test freezing. Furthermore,
excitotoxic LA lesions did not diminish freezing to TMT. Larger
excitotoxic lesions that included the BA significantly reduced freezing
in both the post-shock and retention tests but did not appreciably
decrease freezing to TMT. The results suggest that the LA is important for memory of learned fear but not for generation of freezing behavior.
In addition, the BA plays a role in freezing in conditioned fear
situations but not in unconditioned fear. The studies suggest that the
LA and BA play different roles in fear conditioning, but neither of
them has a significant role in unconditioned freezing to a predator odor.
Key words:
fear conditioning; context conditioning; amygdala; basolateral nucleus of the amygdala; lateral nucleus of the amygdala; basal nucleus of the amygdala; unconditioned fear; fox odor; freezing
Copyright © 2001 Society for Neuroscience 0270-6474/01/21103619-09$05.00/0
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