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The Journal of Neuroscience, March 29, 2006, 26(13):3412-3422; doi:10.1523/JNEUROSCI.5274-05.2006

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Cellular/Molecular
Participation of Sodium Currents in Burst Generation and Control of Membrane Excitability in Mesencephalic Trigeminal Neurons

Akifumi Enomoto,^1,2 Juliette M. Han,¹ Chie-Fang Hsiao,¹ Nanping Wu,¹ and Scott H. Chandler¹

¹Department of Physiological Science, University of California at Los Angeles, Los Angeles, California 90095, and ²First Department of Oral Maxillofacial Surgery, Graduate School of Dentistry, Osaka University, Osaka 565-0871, Japan

Correspondence should be addressed to Dr. Scott H. Chandler, Department of Physiological Science, University of California at Los Angeles, 2859 Slichter Hall, Los Angeles, CA 90095. Email: schandler{at}physci.ucla.edu

Subthreshold sodium currents are important in sculpting neuronal discharge and have been implicated in production and/or maintenance of subthreshold membrane oscillations and burst generation in mesencephalic trigeminal neurons (Mes V). Moreover, recent data suggest that, in some CNS neurons, resurgent sodium currents contribute to production of high-frequency burst discharge. In the present study, we sought to determine more directly the participation of these currents during Mes V electrogenesis using the action potential-clamp method. In postnatal day 8–14 rats, the whole-cell patch-clamp method was used to record sodium currents by subtraction in response to application of TTX in voltage-clamp mode using the action potential waveform as the command protocol. We found that TTX-sensitive sodium current is the main inward current flowing during the interspike interval, compared with the h-current (I_h) and calcium currents. Furthermore, in addition to the transient sodium current that flows during the upstroke of action potential, we show that resurgent sodium current flows at the peak of afterhyperpolarization and persistent sodium current flows in the middle of the interspike interval to drive high-frequency firing. Additionally, transient, resurgent, and persistent sodium current components showed voltage- and time-dependent slow inactivation, suggesting that slow inactivation of these currents can contribute to burst termination. The data suggest an important role for these components of the sodium current in Mes V neuron electrogenesis.

Key words: subthreshold oscillations; resurgent sodium current; persistent sodium current; interspike interval; slow inactivation; oral–motor activity

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Received Dec. 9, 2005; revised Feb. 8, 2006; accepted Feb. 9, 2006.

Correspondence should be addressed to Dr. Scott H. Chandler, Department of Physiological Science, University of California at Los Angeles, 2859 Slichter Hall, Los Angeles, CA 90095. Email: schandler{at}physci.ucla.edu

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