Cardiovascular regulation in Squamates: validation of the decerebrated rattlesnake model for studies on regulatory processes of the cardiovascular system

Abstract

The Autonomic Nervous System (ANS) is responsible for the integration of several systemic functions in order to maintain of homeostasis at rest to support a diversity of biological challenges, in preparation for cyclic events, or for coordination of adjustments to face specific physiological states. The effort to evaluate autonomic functions and/or the functional role of specific adjustments often relates to a great instrumental challenge and deals with the impact of animal stress - by animal handling and procedures development -, or autonomic attenuation by anesthesia. Decerebrated animals have its cortex and thalamus removed and, after anesthetic recovery, the animal remains with a big part of its physiological operational functions, allowing monitoring and study without, however, any processing related to pain or conscious awareness. Such kind of preparation has been used to deepen investigations in several areas of zoology, physiology and health. Such preparations can provide access to a large number of information that could not otherwise be obtained, allowing significant advances in several areas with the use of a reduced number of animals. With this project, we suggest to validate and adjust a decerebrated rattlesnake model to be able to access several regulatory mechanisms. With that model, it will be possible to acquire and combine multiple cardiorespiratory, metabolic and temperature data and so, we will be able to address complex questions about the autonomic regulation of physiological processes. The present proposal is the initial movement for a long-term investigation plan on autonomic function and cardiorespiratory and vascular adjustments. In this initial project, we aimed to analyze the feasibility of the decerebration procedure on rattlesnakes and also to test a series of autonomic reflexes to determine the impact of this model. So, the snakes will be descerebrated to account for two experimental groups (anesthetized and non-anesthetized decerebrated snakes) that will have cardiovascular parameters: fH; HRV; blood pressure (systemic and pulmonary - S-P), stroke volume (S-P), resistance (S-P), baroreflex gain, central and superficial temperature, among other factors analyzed in relation to stimuli that would trigger autonomic reflexes for cardiovascular adjustments: head lift, tail lift, skin heating, blood pressure by drugs stimulation and chemoreceptors stimulation. We will work with the hypotheses that the use of anesthetized animals reduces the effectiveness of investigations that depend on the ANS integrity; and that the decerebrated rattlesnake model can provide (in terms of responsiveness and magnitude) the parameters analyzed. We judge that the model, since its viability was demonstrated, will be of extreme relevance for autonomic, cardiovascular and respiratory studies in reptiles and vertebrates. The possibility of access and analyze multiple data will also provide us the reduction of the number of used animals. (AU)