title: Proven cardiac changes during death-feigning (tonic immobility) in rabbits (Oryctolagus cuniculus).
abstract: Tonic immobility (TI) is a response to fear or threat by remaining motionless, principally when attacked by predators from which there is no possibility of escape. Thus, here we demonstrate a way of easily reproducing this phenomenon in a laboratory setting and characterize the cardiac electromechanical alterations during TI. We observed a significant decrease in heart rate (HR) and changes of rhythm in electrocardiogram during TI in rabbits. Echocardiogram showed a significant increase in the left ventricle chamber diameter during systole and a consequent decrease in fractional shortening and ejection fraction, in addition to the HR and rhythm changes. There was also a significant decrease in aortic and pulmonary artery blood flow. Diastolic functional changes included a significant decrease of the peak atrial contraction velocity (A peak) and consequent increase in the ratio of peak early diastolic velocity to A peak and increased isovolumetric relaxation time. We were able to prove that TI changes the cardiac function considerably. Although the "fight-or-flight" response is the most common response to fear, which is characterized by the action of sympathetic nervous system with tachycardia and increased physical activity, TI is an alternative anti-predator behavior causing cardiac changes opposite to the "fight-or-flight" phenomenon.
authors: Department of Veterinary Medicine, Federal University of Paraná, Rua dos Funcionários, 1540, Curitiba, PR, 80035-050, Brazil, amaliaturner@uol.com.br.
authors: Amália Turner
authors: AT
authors: Giannico
authors: Leandro
authors: L
authors: Lima
authors: Rogério Ribas
authors: RR
authors: Lange
authors: Tilde Rodrigues
authors: TR
authors: Froes
authors: Fabiano
authors: F
authors: Montiani-Ferreira
mesh_terms: D000818:Animals; D001011:Aorta / Q000502:physiology; D003971:Diastole / Q000502:physiology; D004562:Electrocardiography; D005239:Fear / Q000502:physiology; D005260:Female; D046352:Freezing Reaction, Cataleptic / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006352:Heart Ventricles; D008297:Male; D011651:Pulmonary Artery / Q000502:physiology; D011817:Rabbits; D012039:Regional Blood Flow; D013599:Systole / Q000502:physiology; D013997:Time Factors