Auditory fear conditioning and conditioned stress raise NO(3) level in the Amygdala.
BACKGROUND
The conditioned fear response is considered to be acquired by experimental animals when tone information is combined with that of an electrical foot shock (unconditioned stimulus) in the amygdala. Nitric oxide biosynthesized in the brain is reportedly involved in several kinds of learning.


METHODS
In this study, we continuously monitored the NO(3)(-) level, as a marker of nitric oxide production, in the amygdala starting before the application of tone and electrical foot shock stimuli together (conditioned group) or the tone stimulus alone (control group) on day 1, until after the tone information was given (both groups) on day 2, using the in vivo microdialysis method.


RESULTS
The NO(3)(-) level of the conditioned group was increased on both day 1 and day 2, while that of the control group was not elevated on either day. Freezing behavior was observed in the conditioned but not the control rats.


CONCLUSIONS
Although the sources of NO(3)(-) remain uncertain, these results suggest that nitric oxide is associated with auditory fear conditioning and the response to a conditioned stimulus.
Sato
Taku
T
Department of Psychiatry, Kitasato University School of Medicine, Sagamihara, Japan.
Suzuki
Eiji
E
Yokoyama
Masamoto
M
Watanabe
Shigeru
S
Miyaoka
Hitoshi
H