Carl L. Reiber

Professor and Associate Dean, College of Sciences

Ph.D. University of Massachusetts, Amherst (1992)

Comparative Physiology

carl.reiber@unlv.edu

My research activities focus on physiological and ontogenetic plasticity of cardiac development and regulation. This paradigm encompasses the idea that animals develop the physiological regulatory machinery necessary (within genotype) to meet the immediate metabolic demands placed on the system during a defined life or developmental stage. The general goals of my research are to establish a more thorough understanding of the physiological and ontogenetic mechanisms that allow the heart and circulatory system to provide an appropriate blood supply to meet the demands of a stressful environment. This research is based on a comparative approach, using animals that best demonstrate relevant physiological functions, which has also led to cross-taxonomic comparisons allowing for a better understanding of evolutionary and environmental relationships. Over the past few years we have moved from questions based on the physiological mechanisms of cardiac and respiratory regulation to more integrated approaches ranging from systems level to cellular and molecular mechanisms. This slight shift in direction has been “question” driven and will allow our laboratory to investigate mechanistic issues as new questions evolve.

Overview

The crustacean heart consists of a single muscular chamber that is suspended within the pericardial sinus. During cardiac contraction, hemolymph is ejected through multiple arterial outlets, each artery supplying a defined region of the animal. An artery branches laterally three to four times before terminating in tissue sinuses where exchange takes place. Hemolymph then flows through a series of larger sinuses, passes through the gills and finally back to the heart. Control of hemolymph circulation may be imposed at any number of points along the circuit. The primary control mechanisms appear to be the force and rate of cardiac contraction and the tonus of the cardioarterial valves located at the entrance to each artery.

Heart beat of the grass shrimp (Palaemonetes pugio)

The heart and the cardioarterial valves respond to neurohormones such as proctolin, CCAP, serotonin and dopamine. Injection of neurohormones results in alteration of force and rate of cardiac contraction as well as modulation of arterial outflow via contraction of the valves. These regulatory pathways are established sequentially during embryonic development. The ontogenetic timing of this can determine if an embryo or larvae is able to meet the demands placed upon the developing organism both physiologically and environmentally. Changes to this developmental sequence in response to changing physiological demands or environmental conditions can potentially have long term effects on adult physiology. The ontogenetic timing of key regulatory pathways and physiological function of the cardiovascular system may allow crustaceans to exploit such diverse environments as anoxic burrows, warm estuary waters and terrestrial habitats.

As the crustacean cardiovascular system shows itself to be complex and highly regulation, many questions are being asked. Some of the more basic questions deal with fundamental hemodynamic issues during development (pressure-flow relationships), neurohormonal regulation by the cardiac ganglion and pericardial organs, receptor-ligand interactions and intracellular transaction mechanisms. The technical advances seen in the field of physiology, coupled with advances in biochemistry, molecular biology and computer systems has led to an explosion in research in these areas.

Selected Publications

• Burggren, W.W. and C.L. Reiber. 2006. Evolution of Cardiovascular Systems. In the William Aird edited The Endothelium: A Comprehensive Reference. Cambridge University Press.
• Harper, S.L. and C.L. Reiber. 2006. Cardiac development in crayfish: ontogeny of cardiac physiology and aerobic metabolism in the red swamp crayfish Procambarus clarkii. Journal of Comparative Physiology B (online).
• New Directions in Physiological Ontogeny. 2005. Ed. Burggren, Warburton, Reiber, Spicer and Pelster. Cambridge Press
• Guadagnoli, J.A., Braun, A.M., Roberts, S.P. and C.L. Reiber. 2005. Environmental hypoxia influences hemoglobin subunit composition in the branchiopod crustacean Triops longicaudatus. Journal of Experimental Biology. 208: 3543-3551.
• Reiber, C.L. and S.P. Roberts. 2005. Ontogeny of physiological regulatory mechanisms: Fitting into the environment Introduction to the Symposium. Comparative Biochemistry and Physiology, Part A. 141: 359-361.
• Guadagnoli, J.A., Jones, L.A. and C.L. Reiber. 2005. The influence of reproductive state on cardiac parameters and hypoxia tolerance in the Grass Shrimp, Palaemonetes pugio. Functional Ecology. 19: 976-981.

additional publications...