Assistant Professor
Member, CISAB
Member, Program in Neuroscience

Ph.D., University of Washington, 1996

Program Affiliation: Evolution, Ecology and Behavior

Research Groups Affiliation: Behavior

Phone: 812/856-0109
Fax: 812/855-6705
Email Troy

Smith Lab website

How does the nervous system control species-typical behavior and how do hormones influence neural physiology to modify behavior?   Our laboratory addresses these questions by studying the neuroendocrine control of sexually dimorphic communication behavior in weakly electric fish.

Weakly electric fish

Electric organs evolved independently in at least six lineages of fish.   Although a few electric fish species produce strong discharges used in defense or to stun prey (e.g. electric eels), most electric fish species produce weak electric organ discharges (EODs) that they use to locate objects in their environment and to communicate with each other.

Because the frequency and waveform of the EOD varies both across species and between the sexes, electric fish can use their electrical signals to communicate their species, sex, and breeding status to other fish.   Sex differences in EOD signals are regulated by androgens and/or estrogens.

The neural circuit that controls the EOD contains of only a few types of neurons, and the activity of these neurons is directly related to the frequency of the EOD signal.   This simplicity allows us to study the mechanisms of a sexually dimorphic behavior from cellular to organismal levels of analysis.

Current research in our laboratory focuses on five main questions:

1. How does the nervous system control rhythmic behavior? We use electrophysiological techniques to study how neurons in the brainstem and spinal cord generate the command signal for the precise, high frequency rhythm of the EOD.
2. How do hormones modify the nervous system to produce sex differences in behavior?   By studying the differences between males and females in the structure and function of neurons that control the EOD, we seek to understand how hormone actions on single neurons and neural circuits influence sexual dimorphism in the behavioral output of those circuits.
3. How has the nervous system evolved to produce species diversity in behavior?   We are interested in neurophysiological differences between species of fish that produce low frequency discharges (<100 Hz) and species that produce high frequency discharges (>1000 Hz).   These studies will contribute to our understanding of how neuronal physiology evolved to produce species diversity in rhythmic behavior.
4. What mechanisms underlie species diversity in sexual dimorphism of behavior?   EOD frequency is higher in females than males in some species, but lower in females than males in other species.   We are interested in the physiological and evolutionary mechanisms that underlie reversals in the direction of sexual dimorphism across species.
5. What mechanisms cause species and sex differences in more complex electrocommunication signals? Electric fish modulate the frequency and amplitude of their electrical signals to produce more complex communication signals called "chirps."  We are studying the neural and hormonal mechanisms that contribute to species and sex differences in chirping behavior.

We use a wide range of techniques to address these questions: behavioral analysis; manipulation and measurement of hormone levels; neuroanatomy; pharmacology; and electrophysiology.

Turner, C.R., Derylo, M., de Santana, C.D., Alves-Gomes, J.A., and Smith, G.T. 2007. Phylogenetic comparative analysis of electric communication signals in ghost knifefishes (Gymnotiformes: Apteronotidae). Journal of Experimental Biology  210:4104-4122.

Kolodziejski, J.A., Sanford, S., and Smith, G.T. 2007. Signal frequency affects chirping differently in two closely-related species of electric fish. Journal of Experimental Biology 210:2501-2510.

Telgkamp, P., Combs, N., and Smith, G.T. 2007. Serotonin in a diencephalic nucleus controlling communication in an electric fish: Sexual dimorphism and relationship to indicators of dominance. Developmental Neurobiology 67:339-354.

Zhou, M. and Smith, G.T. 2006. Structure and sexual dimorphism of the electrocommunication signals of the weakly electric fish Adontosternarchus devenanzii. Journal of Experimental Biology 209:4809-4818.

Smith, G.T., Unguez, G.A., and Weber, C. 2006. Distribution of Kv1-like potassium channels in the electromotor and electrosensory systems of a weakly electric fish. Journal of Neurobiology 66:1011-1031. (cover article)

Smith, G.T. 2006. Pharmacological characterization of ionic currents that regulate high-frequency spontaneous activity of electromotor neurons in the weakly electric fish Apteronotus leptorhynchus. Journal of Neurobiology 66:1-18.

Kolodziejski, J.A., Nelson, B.S., and Smith, G.T. 2005. Sex and species differences in neuromodulatory input to a premotor nucleus: a comparative study of substance P and communication behavior in weakly electric fish. Journal of Neurobiology 62:299-315.

Smith, G.T., Allen, A.R., Gammie, S.C., and Oestreich, J. 2005. Immunohistochemistry for L-citrulline reveals nitric oxide production in nitric oxide synthase-expressing neurons in the electromotor and electrosensory systems of the weakly electric fish, Apteronotus leptorhynchus.  Brain Behavior and Evolution 65:1-13.

Zakon, H. H. and Smith, G. T. 2002.  Weakly electric fish:  behavior, neurobiology, and neuroendocrinology.  In: Hormones, Brain, and Behavior (eds. Pfaff, D., Arnold, A., Etgen, A., Fahrbach, S., Moss, R., and Rubin, R.) New York: Academic Press. vol. 2, pp. 349-374.

Smith, G.T. and Zakon, H.H.  2000.  Pharmacological characterization of ionic currents that regulate the firing frequency of the medullary pacemaker nucleus neurons in a weakly electric fish.  Journal of Neurobiology 42: 270-286.