Microvascular anatomy and physiology laboratory class using the Australian cane toad

Abstract

The microvasculature is a key part of the cardiovascular system and teaching microvascular structure and function is a key part of any cardiovascular science course. The Australian cane toad Bufo marinus / Rhinella marina is an economical and widely available species within Australia which can be used to demonstrate basic principles of blood flow and microvascular anatomy and physiology in an in vivo setting. In the laboratory class, cane toads of either gender (approx. 120 g) are anesthetized by immersion in 0.3 % ethyl 3‐aminobenzoate methanesulfonate (MS‐222) for 15 min and for the duration of the class (about 2 hr) swabs soaked in MS‐222 are placed on the skin. Level of anaesthesia is regularly assessed by the corneal reflex. At the end of the class toads are euthanized by cardiac removal (UNSW ACEC approval #19/67B). The surgical procedure involves a small incision in the upper abdomen, through which a lung, the bladder and the mesentery may be exteriorized and the microvasculature examined under a microscope equipped with a camera for video streaming to high definition monitors. The class is designed to demonstrate principles delivered in lectures and allow students to integrate knowledge of these principles into microvascular homeostasis and adaptation to interventions. Microvascular features which can be clearly demonstrated include microvascular anatomy and structural adaptations in different tissues, including the lung (pulmonary microcirculation), urinary bladder and mesentery. Observable physiological phenomena include blood flow velocity and its’ effect blood cell behaviour, axial streaming, plasma skimming, leukocyte rolling and adhesion, vasoconstriction and the response of the mesenteric microvasculature to haemorrhage. Student learning is assessed through pre‐ and post‐class exercises completed on‐line. The pre‐class exercise includes demonstrative videos and a brief quiz. This is intended to ensure students have read and understood the laboratory class notes, along with some basic vascular science, prior to the class, avoiding time‐wasting. The post‐class exercise includes video material recorded during the class accompanied by a quiz aimed at testing the students’ understanding of the observations made; for example, the physiological advantage of unique microvascular anatomy in certain tissues, or the mechanism underlying capillary swelling and hemodilution during haemorrhage. The videos can be edited into a package and used to deliver the class in an on‐line format if required. Thus, the cane toad preparation allows key aspects of microvascular anatomy, physiology, pharmacology and rheology to be demonstrated and taught in a clear and compelling fashion.