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Home  Web of Dowds John Dowd, Ph.D. |
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Written by Steven Dowd
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John Dowd, Ph.D. Postdoctoral Fellow, Research Associate, Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL
Since entering graduate school Ive been studying the general question of how do organisms orient towards (or away from) appropriate stimuli in the environment. My training has been in neurobiology, and the organisms I studied were mostly insects. How does an insect orient towards a potential mate or away from a predator? |
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Now, the organism I study is E. coli, but the behavior Im interested in is still orientation. How is a unicellular organism able to orient towards food and away from toxic substances?
The swimming behavior of E.coli (and other bacteria) is a "random walk" -- the bacterium swims in a straight line, but occasionally stops and heads off in a new random direction. These changes in direction are called tumbles. When the bacterium encounters some attractive substance (such as simple amino acids), it tumbles less frequently. As a result of this change in tumble frequency, E. coli will tend to follow a chemical gradient, i.e. they will tend to swim towards areas where theres more food. This behavior is known as chemotaxis.
Using a computerized motion-analysis system, we can track the swimming behavior of single bacteria over time. When the cells are exposed to an abrupt increase in attractant levels, we can measure a clear change in the cells tumble frequency and speed of swimming.
In animals, the translation of sensory input to motor output (or stimulus to response) is mediated by the nervous system. In E.coli, this translation is mediated by a protein cascade. A great deal is known about these Che(motactic) proteins. A series of mutations have been made in the Che proteins, and these mutations result in predictable changes in the chemotactic behavior of the bacteria.
PROFESSIONAL STATUS
Research Associate
Department of Biological Sciences
University of Illinois at Chicago, Chicago, IL
EDUCATION
1970-1974 St. Peters College, Jersey City, New Jersey
B.A. in Psychology, 1974
1974-1978 Colorado State University, Fort Collins, Colorado
Graduate Student in Physiological Psychology
1986-1992 University of Illinois at Chicago, Chicago, Illinois
Ph.D. in Neurobiology, 1992
1992-1994 Cornell University, Ithaca, New York
Research Associate in Department of Neurobiology and Behavior
PUBLICATIONS
Dowd, JP and Matsumura, P (1997) The use of flash photolysis for a high- resolution temporal and spatial analysis of bacterial chemotactic behavior: CheZ is not always necessary for chemotaxis. Molec. Microbiol., ,25, 295-302.
Ye, S, Dowd, JP, and Comer, CM (1995) A motion tracking system for simultaneous recording of rapid locomotion and neural activity from an insect. J. Neurosci. Meth., 60, 199, 210.
Comer, CM and Dowd, JP (1992) Multisensory processing for movement: Antennal and cercal mediation of escape turning in the cockroach. Biological Neural Networks in Invertebrates: Neurethology and Robotics Beer, R, Ritzmann, R, and McKenna, T (eds). Academic Press.
Comer, CM, Dowd, JP, and Stubblefield, GT (1988) Escape responses following elimination of the giant interneuron pathway in the cockroach, Periplaneta americana. Brain Res. 445, 370-375.
Dowd, JP and Comer, CM (1988) The neural basis of orienting behavior: A computational approach to the escape turn of the cockroach. Biol. Cybern. 60, 37-48.
Smith, SR, Dowd, JP, Wheeler, BC, and Comer, CM (1988) Analysis of multi-unit data from a neural ensemble controlling directed movement. IEEE Conf. Engr. Med. Biol. 10, 1171-1172.
Comer, CM and Dowd, JP (1987) Escape turning behavior of the cockroach. Changes in directionality induced by unilateral lesions of the abdominal nervous system. J. Comp. Physiol. 160, 571-583.
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