Daniel K. Hartline
Area 1: Integrative mechanisms in simple neural networks
We are pursuing a broad quantitative approach to the study of integration in neural networks, involving areas of quantitative neurophysiology, biophysics, pharmacology, computer science and mathematical modeling. In this we are utilizing simple invertebrate material to provide tractable model systems in which to evolve predictive theories of network operation. The overall goal is to be able to accurately account for the observed output of a network given any input. The approach is to make quantitative measurements of cellular and synaptic properties of individually reidentifiable neurons. The measurements are incorporated into physiologically accurate models of the networks. Comparison between model predictions and physiological observations expose gaps in our understanding, help determine new directions for investigation and provide new insights into the design and functioning of the systems. (See personal web pages linked above for more information).
The particular system we are using for studies on network mechanisms, the stomatogastric ganglion of decapod crustaceans, is at the same time being used as a model for how nervous systems generate repetitive coordinated motor patterns, such as those controlling walking, swimming, flying, breathing and heart beat in other animals. Some years ago we found special active cellular properties, that we termed ěplateau potentials,î which underlie production of rhythmic stomatogastric motor activity. Plateau properties have since been implicated in pattern production in a great variety of other organisms including mammals. We work on the biophysical basis of these plateau potentials and on their modulatory regulation by specific inputs from the central nervous system, as well as by hormones. In addition (in a collaboration at the University of Washington) we have been investigating the role of spatial distribution of cellular mechanisms over branching neuritic trees and the involvement of non-spike synaptic interactions in producing coordinated motor patterns. Specific project areas include:
* Cellular properties that promote endogenous production of nerve impulse bursts,
* Modulatory regulation of these properties,
* The involvement of non-spiking synaptic interactions in producing coordinated motor patterns (collaboration with Dr. Katherine Graubard of the University of Washington).
* The computational properties of cellular mechanisms distributed over branching dendritic trees (collaboration with Dr. Katherine Graubard of the University of Washington)
* The nature and correctability of space-clamp errors in voltage clamp experiments on neurons with attached processes (collaboration with Dr. Ann Castelfranco).
Area 2: Neuroecology of zooplankton sensory systems
(in collaboration with Dr. Petra Lenz)
In this work, we are examining the relation between physiological and morphological properties of a zooplankter's sensory systems and the animal's ecology. The sensory systems reflect unusual adaptations to pelagic life when compared to similar systems in benthic and nektonic forms. Particular modifications of these sensory properties may reflect differences in ecology among phyletic groups.
Of particular recent interest have been mechanisms involved in predator-evasion behavior in calanoid copepods including:
* Detection thresholds, behavioral and physiological, for small hydrodynamic disturbances
* Physiological characterization of giant antennal mechanoreceptors
* Characterization, distribution, development and ecological significance of myelination in copepod nervous systems
* Escape reactions of free-swimming copepods to hydrodynamic and photic stimuli, most recently in younger developmental stages as well as adults (collaboration with Dr. Edward Buskey, of the University of Texas at Austin)
* We are also collaborating with Dr. Barbara Beltz, of Wellesley College, on localization of neurotransmitters and peptides in reidentifiable neurons of the copepod nervous system.
Castelfranco, A.M. and Hartline, D.K. (2002) "Simulations of space-clamp errors in estimating parameters of voltage-gated conductances localized at different electrotonic distances" Neurocomputing 44-46: 75-80
Hartline, D.K. and Castelfranco, A.M. (2003) "Simulations of voltage clamping poorly space-clamped voltage-dependent conductances in a uniform cylindrical neurite" J. comput. Neurosci. 14: 253-269
Castelfranco, A.M. and Hartline, D.K. (2004) Corrections for space-clamp errors in measured parameters of voltage-dependent conductances in a cylindrical neurite Biol. Cybern. 90: 280-290
Buskey, E.J., Lenz, P.H. and Hartline, D.K. (2002) Escape behavior of planktonic copepods to hydrodynamic disturbances: High speed video analysis Mar. Ecol. Progr. Ser. 235: 135-146
Buskey, E.J. and Hartline, D.K. (2003) High speed video analysis of the escape responses of the copepod Acartia tonsa to shadows. Biol. Bull. 204: 28-37.
Lenz, P.H., Hower, A.E. and Hartline, D.K. (2004) Force production during pereiopod power strokes in Calanus finmarchicus J. mar. Systems 49: 133-144
Lenz, P.H., Hower, A.E. and Hartline, D.K. (2005). Temperature compensation in the escape response of a marine copepod, Calanus finmarchicus (Crustacea). Biol. Bull. 209: 75-85.