HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 289/3/R784    most recent 00018.2005v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by El-Wazir, Y. M. Articles by Randall, D. C. Search for Related Content PubMed PubMed Citation Articles by El-Wazir, Y. M. Articles by Randall, D. C.

NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Differential acquisition of specific components of a classically conditioned arterial blood pressure response in rat

¹Department of Physiology, Faculty of Medicine, Suez Canal University, Ismailia, Egypt; and ²Department of Physiology, College of Medicine, and ³Center for Biomedical Engineering, University of Kentucky, Lexington, Kentucky

Submitted 11 January 2005 ; accepted in final form 26 April 2005

Presenting a 15-s pulsed tone, the conditional stimulus (CS⁺), followed by 0.5-s tail shock, to a well-trained rat causes a sudden, but transient, pressor response (C₁). Blood pressure (BP) then drops before increasing again (C₂). A steady tone of the same frequency never followed by a shock (a discriminative stimulus, or CS^–) evokes a C₁ but not a C₂ response. Experiment 1 tested the hypothesis that this BP response pattern does not depend on the nature of the tone (i.e., pulsed vs. steady) used for CS⁺ and CS^–. The tones were reversed from the traditional paradigm, above, in nine rats. The C₁ BP increase for a steady-tone CS⁺ (+4.8 ± 1.9 mmHg, mean change ± SE) and a pulsed CS^– (+2.9 ± 1.3 mmHg) did not differ. Conversely, C₂ showed a clear discrimination (CS⁺: +5.1 ± 1.2 mmHg, CS^–: +0 .7 ± 0.8 mmHg; P < 0.05). Experiment 2 tested the hypothesis that the C₁ and C₂ BP responses first appear at different times during training. On training day 1, five 15-s pulsed tones (CS⁺) were presented to each of 18 rats; the last tone was followed by a tail shock. Likewise, five steady CS^– tones never followed by shock were given. Training continued for 2 more days, with each CS⁺ followed by shock. At the end of day 2, CS⁺ evoked a C₁ BP response (+3.9 ± 0.9 mmHg) but no C₂ (+0.6 ± 0.4 mmHg, not significant vs. pretone). By the end of day 3, CS⁺ evoked a significant (vs. baseline) C₁ (+7.3 ± 1.4 mmHg) and C₂ (+3.3 ± 0.8 mmHg). Conversely, although CS^– evoked a C₁ response (3.5 ± 1.3 mmHg), there was no C₂ (+0.7 ± 0.5 mmHg; not significant). We conclude that 1) C₁ and C₂ are acquired at different rates, 2) early in training C₁ is an orienting response evoked by both tones, and 3) C₂ is only acquired as an animal learns to associate the CS⁺ tone with shock. This suggests that C₁ and C₂ are controlled by different processes in the brain.

Pavlovian conditioning; orienting response; habituation; learning