Research Areas: Cellular and Systems Neurobiology

My research focuses on reticulospinal neurons--nerve cells that project from the hindbrain (or brainstem) to the spinal cord. In fishes, this group of neurons is quite important because it is the major route by which the brain communicates to the spinal cord and thereby controls locomotor behaviors. Surprisingly little is known, however, about the functions of reticulospinal neurons. We are studying these nerve cells in larval zebrafish because they are relatively few in number (approximately 102 in total) and because they are accessible to optical recording techniques. So far, we have discovered that neural activity in one particular group of reticulospinal neurons is segmentally organized and that a segmental code is used to control the direction of the fishes' escape behavior. We are now exploring the involvement of segmental codes in the generation of other behaviors such as navigational or turning behaviors. Eventually one would like to understand the functioning of the mammalian hindbrain. But until the larval zebrafish hindbrain, with its 102 reticulospinal neurons, is understood, the mammalian hindbrain, with its billions of neurons, may remain an intractable problem.

In this project, I have been using fluorescent calcium indicators and laser-scanning confocal microscopy to investigate the nervous system over a broad range of scales. At one extreme we can visualize subcellular events such as the distribution of calcium signals in the dendrites and nucleus of a nerve cell. At an intermediate level, the responses of single cells or populations of nerve cells can be imaged. At the "coarsest" level of imaging, we can record the behavior of the whole animal. For such behavioral studies, we first photo-ablate (or kill) specific nerve cells using the confocal laser. Then, using a high-speed camera, we make detailed measurements of the behavioral deficit. Overall, it should be possible with this set of techniques to directly link subcellular or molecular events to the functioning of neural circuits and ultimately to changes in the behavior of the animal.

• Hill SA, Liu X-P, Borla MA, Jose JV and O’Malley DM (2005) Neurokinematic modeling of complex swimming patterns of the larval zebrafish. in press in Neurocomputing.
  
• O’Malley DM, Sankrithi NS, Borla MA, Parker S, Banden S, Gahtan E and Detrich HW (2004) Optical Physiology and Locomotor Behaviors of Wild-Type and Nacre Zebrafish. in The Zebrafish: Cellular and Molecular Biology, Detrich HW, Westerfield M and Zon LI, eds., Academic Press, San Diego, CA.
  
• O’Malley DM, Zhou Q and Gahtan E (2003) Probing Neural Circuits in the Zebrafish: A Suite of Optical Techniques. Methods, 30:49-63.
  
• Gahtan E and O’Malley DM (2003) Visually-guided injection of identified reticulospinal neurons in zebra-fish: a survey of spinal arborization patterns. Journal of Comparative Neurology, 459:186-200.
  
• Borla MA, Palecek B, Budick SA and O’Malley DM. (2002) Prey capture by larval zebrafish: evidence for fine axial motor control. Brain Behavior & Evolution, 60:207-229.
  
• Gahtan E, Sankrithi N, Campos JB and O’Malley DM (2002) Evidence for a widespread brainstem escape network in larval zebrafish. Journal of Neurophysiology, 87:608-614.
  
• Gahtan E and O’Malley DM (2001) Rapid lesioning of large numbers of identified vertebrate neurons: applications in zebrafish. Journal of Neuroscience Methods, 108:97-110.
  
• Budick SA and O’Malley DM (2000) Locomotive repertoire of the larval zebrafish: swimming, turning and prey capture. Journal of Experimental Biology, 203:2565-2579.