Neurobiology and Anatomy Department at The University of Texas Medical School at Houston
Department of Neurobiology and Anatomy
The Department ofNeurobiology

Douglas A. Baxter, Ph.D.

Professor, Research
Tel: 713.500.5565
E-mail: douglas.baxter@uth.tmc.edu


Cellular And Network Processes Underlying Behavior And Behavioral Plasticity

Douglas A. Baxter, Ph.D. - Associate Professor, ResearchA set of fundamental issues in neuroscience concerns the neural mechanisms underlying behavior and behavioral plasticity (e.g., learning). It is generally believed that the ability of the nervous system to generate behaviors arises from the organization of neurons into circuits and that the functional capabilities of these circuits emerge from the interactions among the intrinsic biophysical properties of individual neurons, the pattern of synaptic connections among these neurons and the physiological properties of the synaptic connections. To adapt to an ever changing environment, the performance of these neural circuits must be modified, either by feedback occurring during the behavior or by previous experience.

Our laboratory uses two approaches, one computational and the other experimental, to investigate how neural circuits are organized, what principles underlie their function, and the consequences of sensory inputs and of modulatory influences.

Empirical studies utilize the marine mollusc Aplysia, which has a relatively simple nervous system with large, identifiable neurons that are accessible for detailed anatomical, biophysical and biochemical analyses. Computational studies utilize a program entitled "Simulator for Neural Networks and Action Potentials (SNNAP)", which is a general-purpose tool for the rapid development and simulation of realistic models of neurons and neural networks. Currently, we are examining two neural circuits, one mediating a defensive withdrawal reflex and another mediating feeding behaviors. Such analyses of relatively simple neural circuits can contribute substantially to an understanding of basic principles that underlie functions of more complex neural systems.

Learning And Cognition
A: Neural circuit mediating the tail/siphon withdrawal reflex. B: Intracellular recordings of an action potential in a sensory neuron (SN) and the resulting excitatory postsynaptic potential in PI-4. C: Computer simulation of the synaptic connection between SN and PI-4.
Selected Reading

Baxter, DA, Bittner, GD, Brown, TH. (1985) Quantal mechanism of long-term synaptic potentiation. Proc. Natl. Acad. Sci. USA, 82:5978-5982.

Baxter, DA, Byrne, JH. (1989) Serotonergic modulation of two potassium currents in the pleural sensory neurons of Aplysia. J. Neurophysiol., 62:665-679.

Byrne, JH, Baxter, DA, Buonomano, DV, Raymond, JL. (1990). Neuronal and network determinants of simple and higher-order features of associative learning: Experimental and modeling approaches. Cold Spring Harbor Symp. Quant. Biol., 55:175-186.

Bittner, GD, Baxter, DA. (1991) Synaptic plasticity at crayfish neuromuscular junctions: Facilitation and augmentation. Synapse, 7:235-243.

White, JA, Ziv, I, Cleary, LJ, Baxter, DA and Byrne, JH. (1993) The role of interneurons in controlling the tail-withdrawal reflex in Aplysia: A network model. J. Neurophysiol., 70:1777-1786.

Ziv, I, Baxter, DA and Byrne, JH. (1994) Simulator for neural networks and action potentials: Description and application. J. Neurophysiol., 71:294-308.

Nargeot, R, Baxter, DA and Byrne, JH. (1997) Contingent-dependent enhancement of rhythmic motor patterns: an in vitro analog of operant conditioning. J. Neurosci., 17:8093-8105.

Baxter, DA, Canavier CC, Clark, JW, Byrne, JH. (1999) Computational model of the serotonergic modulation of sensory neurons in Aplysia. J. Neurophysiol., 82:2914-2935.

Smolen, P, Baxter, DA, and Byrne, JH. (2000) Mathematical modeling of gene networks. Neuron, 26:567-580.

Lechner, HA, Baxter, DA, Byrne, JH. (2000) Classical conditioning of feeding in Aplysia: II. Neurophysiological correlates. J. Neurosci., 20:3377-3386.

Susswein, AJ, Hurwitz, I, Thorne, R, Byrne, JH, Baxter, DA. (2002) Mechanisms underlying fictive feeding in Aplysia: Coupling between a large neuron with plateau potentials and a spiking neuron. J. Neurophysiol., 87:2307-2323.

Nargeot, R, Baxter, DA, Byrne, JH. (2002) Correlation between activity in neuron B52 and two features of fictive feeding in Aplysia. Neurosci. Lett., 328: 85-88.

Smolen, P, Baxter, DA, Byrne, JH. (2002) A reduced model clarifies the role of feedback loops and time delays in the Drosophila circadian oscillator. Biophy. J., 83: 2349-2359.

Brembs, B, Lorenzetti, FD, Reyes, F, Baxter, DA, Byrne, JH. (2002) Operant reward learning in Aplysia: Neuronal correlates and mechanisms. Science, 296: 1706-1709.

Antzoulatos, E, Clearly, LJ, Eskin, A, Baxter, DA, Byrne, JH. (2003) Desensitization of postsynaptic glutamate receptors contributes to high-frequency homosynaptic depression of Aplysia sensorimotor synapses. Learn. Mem.

Baxter, DA, Canavier, CC, Byrne, JH. (2003) Dynamical properties of excitable membranes. In: Byrne, JH and Roberts, J. (Eds.), From Molecules to Networks: An Introduction to Cellular and Molecular Neuroscience (pp. 161-196). New York, Academic Press.

Cai, Y, Baxter, DA, Crow, T. (2003) Computational study of enhanced excitability in Hermissenda: Membrane conductances modulated by 5-HT. J. Comput. Neurosci., 15: 105-121.

Flynn, M, Cai, Y, Baxter, DA, Crow, T. (2003) A computational study of the role of spike broadening in synaptic facilitation of Hermissenda. J. Comput. Neurosci., 15: 29-41.

Hayes, RD, Byrne, JH, Baxter, DA. (2003) Neurosimulation: Tools and resources. In: Arbib, M.A. (Ed.), The Handbook of Brain Theory and Neural Networks, Second Edition (pp. 776-780). Cambridge, MIT Press.

Luo, C, Clark, JW, Canavier, CC, Baxter, DA, Byrne, JH. (2003) Multimodal behavior in a four neuron ring circuit: mode switching. IEEE Trans. Biomed.Eng.

Phares, GA, Antzoulatos, EG, Baxter, DA, Byrne, JH. (2003) Burst-induced synaptic depression and its modulation contribute to information transfer at Aplysia sensorimotor synapses: empirical and computational analyses. J. Neurosci.

Steffen, M, Seay, C, Amini, B, Cai, Y, Feigenspan, A, Baxter, DA, Marshak, DW. (2003) Spontaneous activity of dopaminergic retinal neurons. Biophy. J.

Search PubMed for additional articles.