Brian Mulloney
1155 Life Sciences Addition
530.752.1110
bcmulloney (at) ucdavis (dot) edu
Colleagues in Mulloney's lab this year: Wendy M. Hall, Patricia Harness
Recent graduate student: Carolyn M. Sherff, Ph.D. (now NRSA postdoctoral fellow, UC Irvine)
B.S., Zoology and Chemistry, McGill University , 1963
M.A., Zoology, University of California, Berkeley , 1967
Ph.D., Zoology, University of California, Berkeley , 1969
Neurobiology, neuroethology, and education of graduate students and postdoctoral students for careers in biological research.
I am interested in how an animal's nervous system produces the overt behaviors that we observe. My research concentrates on how the central nervous system of arthropods, particularly crayfish, works. The behaviors of these animals are complex, but their nervous systems have a structural elegance that makes the challenge of understanding these behaviors in cellular terms achievable. In answering questions about the neural basis of behaviors in these animals, we also provide probable explanations of complex behaviors in other animals, including vertebrates.
Some time ago, we began to analyze the central mechanisms that cause the swimmerets of crayfish to produce coordinated cycles of power-strokes and return-strokes whenever the animal swims forward. We demonstrated that each limb has its own module of neurons that can operate independently. This means that the normal coordination of movements of different limbs is imposed on these modules by a separate circuit of coordinating interneurons, and that we can study the organization of a module and of the coordinating circuit as separate problems.
My strategy is to combine electrophysiological experiments with computational analysis of the hypotheses these experiments generate. We have identified a small set of nonspiking local interneurons that are key components of each module. We have developed a minimal cellular model of the organization of a module, and are starting to test it experimentally. We have also described three types of intersegmental coordinating interneurons that are necessary and sufficient for normal intersegmental coordination, and described how these interneurons respond to changes in excitation of the system. We have developed a cellular model of the circuit formed by these interneurons. This model has dynamics similar to the dynamics of the real system, and that predicts the connections these interneurons make within their target modules.
In a series of experimental tests of the assumptions and predictions of these models, we have described the structures of the axons of these coordinating interneurons as they pass through neighboring ganglia, and identified a new type of commissural interneuron in each ganglion. These commissural interneurons receive monosynaptic connections from coordinating interneurons, and relay this information to one of the modules in their home ganglion. These commissural interneurons are non-spiking. Using this system, we will describe in cellular detail how information from one module is converted to an impulse train in the coordinating axons, and then reconverted in the commissural neurons to a graded signal that can alter the activity of the target module in such a way that the two modules maintain a constant intersegmental difference in phase.
Positions open: There are openings in my group for both a postdoctoral fellow and a graduate student. These positions are funded by grants from NSF and NIH. The postdoctoral fellow should have experience with microelectrode recording and an interest in circuit dynamics. Potential fellows should contact me directly: bcmulloney@ucdavis.edu .
The student position will be filled by a student who has been admitted to the UCDavis Neuroscience Doctoral Program ( http://neuroscience.ucdavis.edu/grad/ ), Animal Behavior Program (http://www.dbs.ucdavis.edu/gradgroups/ab/ ), or Physiology Program ( http://biosci.ucdavis.edu/ggc/pgg/ ).
Mulloney, B. and W.M. Hall (2003) Local commissural interneurons integrate information from intersegmental coordinating interneurons. J. Comp. Neurol. 466: 366-376.
Mulloney, B. (2003) During fictive locomotion, graded synaptic currents drive bursts of impulses in swimmeret motor neurons. J. Neurosci. 23: 5953-5962.
Jones, S.R., B. Mulloney, T.J. Kaper and N. Kopell (2003) Coordination of cellular pattern-generating circuits that control limb movements: the sources of stable differences in intersegmental phases. J.Neurosci. 23: 3457-3468.
Mulloney, B., T. Naranzogt and W.M. Hall (2003) Architectonics of crayfish ganglia. Micros. Res. Tech. 60: 253-265.
Naranzogt, T., W.M. Hall, and B. Mulloney (2001) Limb movments during locomotion: Tests of a model of an intersegmental coordinating circuit. J. Neurosci. 21: 7859-7869.
Nakagawa, H. and B. Mulloney (2001) Local specification of relative strengths of synapses between different abdominal stretch-receptor axons and their common target neurons. J.Neurosci. 21:1645-1655.
Mulloney, B. and W.M. Hall (2000) Functional organization of crayfish abdominal ganglia: III. Swimmeret motor neurons. J. Comp. Neurol. 419: 233-243.
Namba H., B. Mulloney (1999) Coordination of limb movements: Three types of intersegmental interneurons in the swimmeret system, and their responses to changes in excitation. J Neurophysiol. 81: 2437-2450.
Skinner, F.K. and B. Mulloney (1998) New advances in understanding intersegmental coordination in invertebrates and vertebrates. Curr. Op. Neurobiol. 8:725-732.
Mulloney, B., H. Namba, F.K. Skinner and W.M. Hall (1998) Intersegmental coordination of swimmeret movements: mathematical models and interneurons. In: Neuronal mechanisms for generating locomotor activity (Kiehn, O et al., eds) Ann NY Acad Sci. 860:266-280.
Skinner, F.K. and B. Mulloney (1998) Intersegmental coordination of limb movements during locomotion: mathematical models predict circuits that drive swimmeret beating. J. Neurosci. 18: 38331-3842.
Mulloney, B., H. Namba, H.-J. Agricola and W.M. Hall (1997) Modulation of force during locomotion: differential action of Crustacean Cardioactive Peptide on power-stroke and return-stroke motor neurons. J Neurosci 17:6872-6883.
Skinner, F.K., N. Kopell and B. Mulloney (1997) Mathematical models of the crayfish swimmeret system. In: Computational Neuroscience: Trends in Research, 1997 (Bower JH ed), pp 839-843. New York: Plenum.
Mulloney, B. (1997) A test of the excitability-gradient hypothesis in the swimmeret system of crayfish. J. Neurosci. 17:1860-1868.
Skinner, F.K., N. Kopell, B. Mulloney (1997) How does the crayfish swimmeret system work? Insights from nearest neighbor coupled oscillator models. J. Comput. Neurosci. 4:151-160.
Sherff, C.M., B. Mulloney (1997) Passive properties of swimmeret motor neurons. J. Neurophysiol. 78:92-102.
Sherff, C.M. and B. Mulloney (1996) Tests of the motor neuron model of the local pattern-generating circuits in the swimmeret system. J. Neurosci. 16:2839-2859.
Braun, G. and B. Mulloney (1995) Coordination in the crayfish swimmeret system: Differential excitation causes changes in intersegmental phase J. Neurophysiol. 73:880-885.
Acevedo, L.D., W.M. Hall and B. Mulloney (1994) Proctolin and excitation of the crayfish swimmeret system. J. Comp. Neurol. 375:612-627.
Murchison, D., Chrachri, A. and B. Mulloney (1993) A separate local pattern-generating circuit controls the movements of each swimmeret in crayfish. J. Neurophysiol. 70:2620-2631.
Braun, G. and B. Mulloney (1993) Cholinergic modulation of the swimmeret motor system in crayfish. J. Neurophysiol. 70:2391-2398.
Mulloney, B., D. Murchison and A. Chrachri (1993) Modular organization of pattern-generating circuits in a segmental motor system: the swimmerets of crayfish. Semin. Neurosci. 5(1):49-58.
Center for Neuroscience