My laboratory studies how ion channels, hormones, and behavior interact in a vertebrate communication system.  We pursue this goal in a unique and powerful model organism, weakly electric fish.  These fish image their world and communicate by generating electric fields in the surrounding water and detecting minute distortions of their electric fields.  The electric fields are generated by the discharge of a specialized electric organ, and each electric organ discharge (EOD) is produced by the simultaneous action potentials of specialized cells within the electric organ, known as electrocytes.

Electric fish are specialists in both the modulation and precise regulation of action potential waveform, making them ideal model organisms for exploring the biochemical and biophysical control of excitable membrane physiology where real-time changes in ion channel activity have direct and immediate effects on behavior.   Sex steroids organize sexual dimorphism and shape plasticity in the electrocyte action potentials, and peptide hormones regulate rapid changes in the ionic currents that shape the electrocyte action potential, producing rapid modulations of EOD waveform in in response to circadian cues and immediate social conditions. Our work focuses on investigating the cellular and ionic mechanisms of EOD generation and plasticity, the regulation of electrocyte ion currents by steroid and peptide hormones, as well as the behavioral consequences of EOD waveform modulations.

To learn more about this research, visit Dr. Markham's research web page. and Dr. Markham's personal web page.

• Saenz DE, Gu T, Ban Y, Winemiller KO, Markham MR (2021) Derived loss of signal complexity and plasticity in a genus of weakly electric fish. Journal of Experimental Biology 224(12). DOI: 10.1242/jeb.242400 
  
• Markham MR (2019) Biophysical Basis of Electric Signal Diversity. In: Electroreception: Fundamental Insights from Comparative Approaches (Carlson BA, Sisneros JA, Popper AN, Fay RR, eds), pp 125-161. Springer International Publishing.
• Swapna I, Ghezzi A, York JM, Markham MR, Halling DB, Lu Y, Gallant JR, Zakon HH (2018) Electrostatic tuning of a potassium channel in electric fish. Currremt Biology, 28, 2094-2102.
• Joos B, Markham MR, Lewis JE, Morris CE (2018) A model for studying the energetics of sustained high frequency firing. PLoS One 13:e0196508.
• Markham MR, Ban Y, McCauley AG, Maltby, R (2016). Energetics of Sensing and Communication in Electric Fish: A Blessing and a Curse in the Anthropocene? Integrative and Comparative Biology. 56, 889-900.
• Ban Y, Smith BE, Markham MR (2015). A highly-polarized excitable cell separates sodium channels from sodium-activated potassium channels by more than a millimeter. Journal of Neurophysiology, 114, 520-530. 
• Sinnett PM, Markham MR (2015) Food restriction reduces and leptin increases the amplitude of an active sensory and communication signal in a weakly electric fish. Hormones and Behavior, 71, 31-40.
• Markham MR, Zakon HH (2014) Ionic Mechanisms of microsecond-scale spike timing in single cells. The Journal of Neuroscience 34: 6668-6678.
• Lewis, J. E., Gilmour, K. M., Moorhead, M. J., Perry, S. F., & Markham, M. R. (2014). Action potential energetics at the organismal level reveal a trade-off in efficiency at high firing rates. The Journal of Neuroscience, 34(1), 197-201..
• Markham, M. R., & Stoddard, P. K. (2013). Cellular mechanisms of developmental and sex differences in the rapid hormonal modulation of a social communication signal. Hormones and Behavior, 63(4), 586-597.
• Markham, M. R., Kaczmarek, L. K., & Zakon, H. H. (2013). A sodium-activated potassium channel supports high-frequency firing and reduces energetic costs during rapid modulations of action potential amplitude. Journal of Neurophysiology, 109(7), 1713-1723.