Spontaneous recovery, time course, and circadian influence on habituation of the cardiovascular responses to repeated re
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NEUROSCIENCE
Spontaneous recovery, time course, and circadian influence on habituation of the cardiovascular responses to repeated restraint stress in rats Carlos E. Santos 1,2 & Ricardo Benini 1,2 & Carlos C. Crestani 1,2 Received: 31 March 2020 / Revised: 30 July 2020 / Accepted: 14 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We investigated the spontaneous recovery, time course, and the influence of the time of day on the habituation of the cardiovascular responses with repeated exposure to restraint stress in male rats. Habituation of the corticosterone response to repeated restraint stress was also evaluated. The circulating corticosterone response decreased during both the stress and recovery periods of the tenth session of restraint. Habituation of the cardiovascular responses was identified as a faster return to baseline values of the heart rate (HR) and blood pressure (BP) during the recovery period of the tenth session of restraint. Habituation of the HR and BP was still observed after 10 days of discontinuation of the repeated exposure to restraint stress. However, spontaneous recovery of habituated responses was observed 20 days after the final restraint stress session. Time course analysis revealed decreased HR response during the recovery period of the third restraint session, without further reduction on the fifth, seventh, and tenth sessions. Decreased BP response was identified on the third and fifth sessions, whereas reduced tail skin temperature response was observed only on the fifth and seventh sessions. Regarding the time of day, habituation of the tachycardiac response was identified at the tenth session when repeated restraint stress was performed in the morning and night periods, but not in the afternoon. These findings provided evidence of spontaneous recovery of the habituation of cardiovascular responses to repeated restraint stress. Moreover, cardiovascular habituation was dependent on the number of trials and time of day. Keywords Adaptation . Blood pressure . Heart rate . Circadian rhythm . Long term . Time of day
Introduction Physiological responses evoked during acute exposure to aversive events constitute prominent adaptive mechanisms in the short term [9, 15, 38]. However, frequent occurrence of these responses owing to repeated exposure to aversive threats might leads to morphological dysfunctions and Carlos E. Santos and Ricardo Benini contributed equally to this work. * Carlos C. Crestani [email protected] 1
Department of Drugs and Pharmaceutics, Laboratory of Pharmacology, School of Pharmaceutical Sciences, São Paulo State University (UNESP), Rodovia Araraquara KM 01 (Campus Universitário), Araraquara, SP 14800-903, Brazil
2
Joint UFSCar-UNESP Graduate Program in Physiological Sciences, São Carlos, SP, Brazil
pathologies [11, 15, 20, 28]. In this sense, a decrease in stress-evoked responses is frequently observed during repeated exposure to the same non-life threatening aversive stimulus (i.e., homotypic stressor) [19, 20, 27,
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