The 3-second auditory conditioned stimulus is a more effective stressor than the 20-second auditory conditioned stimulus in male rats.
Using fear-conditioning model, we have used a 3-s auditory conditioned stimulus (CS) as a stressor and observed fear and stress responses during a specific experimental period regardless of the presence or absence of the CS. Because the CS was extremely short compared with the experimental period, we observed responses primarily in the absence of the CS. In contrast, most studies in the literature have analyzed responses in the presence of the CS. Therefore, the characteristics of fear and stress responses in the absence of the CS remain to be clarified. To clarify this, we compared the characteristics of fear and stress responses elicited by a 3-s auditory CS with those observed during a 20-s auditory CS. The basolateral complex of the amygdala (BLA), but not the bed nucleus of the stria terminalis (BNST), participated in the fear response elicited by the 3-s CS, whereas both the BLA and BNST were involved in the response observed during the 20-s CS. Additional analyses revealed that the BNST participated in the fear response during the 20-s CS when the CS was paired with a 0.75-mA, but not with a 0.9-mA, foot shock, and to the contextual CS. In addition, the fear response elicited by the 3-s CS was more resistant to extinction than that during the 20-s CS. Finally, the 3-s CS produced more intense freezing and corticosterone secretion than the 20-s CS. On the basis of these characteristics, we conclude that the 3-s auditory CS is a more effective stressor than the 20-s auditory CS. Our findings also suggest that foot shock intensity is an additional determinant in the type of fear response induced by the CS.
Laboratory of Veterinary Ethology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. Electronic address: akiyo@mail.ecc.u-tokyo.ac.jp.
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Kiyokawa
Laboratory of Veterinary Ethology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
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Mikami
Laboratory of Veterinary Ethology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
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Mikamura
Laboratory of Veterinary Ethology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
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Ishii
Laboratory of Veterinary Ethology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
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Takeuchi
Laboratory of Veterinary Ethology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
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Mori
D000161:Acoustic Stimulation; D000679:Amygdala / Q000187:drug effects / Q000502:physiology; D000818:Animals; D003214:Conditioning, Classical / Q000502:physiology*; D005239:Fear / Q000502:physiology*; D007051:Ibotenic Acid; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012686:Septal Nuclei / Q000187:drug effects / Q000502:physiology; D013315:Stress, Psychological / Q000503:physiopathology*; D013997:Time Factors
D007051:Ibotenic Acid
CS duration; auditory fear conditioning; bed nucleus of the stria terminalis; corticosterone; foot shock intensity; sustained fear response