Research

Development and Evolution of Respiratory Rhythm Generation:
The main project in my laboratory focuses on the development and regulation of respiratory rhythm generation, particularly in anuran amphibians. My laboratory uses an in vitro brainstem preparation from bullfrogs (Lithobates catesbeiana) to investigate how respiratory rhythm is generated and regulated during development. The in vitro brainstem model is particularly useful for examining the control of respiratory rhythm at the cellular and network level. A unique feature of this model is that the all of the developmental stages, from tadpole to adult, can be examined under identical experimental conditions. Observed changes in respiratory motor behavior can, therefore, be ascribed to development rather than from technical considerations. No other respiratory developmental model has this particular feature. Because anuran amphibians make a transition from water to land during metamorphosis, studying the mechanisms of respiratory rhythm generation might also provide insight into the evolution of central respiratory mechanisms. The results my students and I have obtained using this model indicate there are significant changes in the regulation of respiratory rhythm generation and that many of these changes take place at the onset of metamorphosis. Future plans in this area of research are to locate specific neuroanatomical brainstem areas that contribute to rhythm generation, record and characterize neurons from these anatomical locations, examine the role of pacemaker and network contributions to rhythm generation, examine the role of oxygen-sensing mechanisms in the respiratory response to hypoxia, and examine the role of intracellular calcium as a neuroprotective signaling mechanism in anoxia.

Regulation of Lymph Movement in Anuran Amphibians:
A second ongoing project in my laboratory, in collaboration with Drs. Stan Hillman (Portland State Univ.), Bob Drewes (California Academy of Sciences) and Phil Withers (Univ. of Western Australia), examines the regulation of lymph movement in frogs and toads. Anuran amphibians produce lymph at extraordinary rates – approximately ten times that of mammals; yet, very little is known about how amphibians maintain cardiovascular homeostasis. Previous work suggested that the paired, contractile lymph hearts are responsible for the movement of lymph. Our work has generated an entirely new hypothesis for lymph movement: 1) pressure differences that are created by compartmentalization of hind limb spaces into lymph sacs that differ in compliance in order to move lymph horizontally, 2) negative and positive pressure differences created by contraction of skeletal muscles to move lymph vertically, 3) lung ventilation creating pressure differentials in anterior lymph sacs that help move lymph vertically.