Physiological and Theoretical Analysis of K+ Currents Controlling Discharge in Neonatal Rat Mesencephalic Trigeminal Neurons

• Published in: Journal of neurophysiology 1997-02, Vol.77 (2), p.537-553
• Main Authors: Negro, Christopher A. Del, Chandler, Scott H
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn - physiology; Mesencephalon - physiology; Neurons - physiology; Patch-Clamp Techniques; Potassium Channels - physiology; Rats; Trigeminal Nerve - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.1997.77.2.537

Christopher A. Del Negro and Scott H. Chandler Department of Physiological Science, University of California at Los Angeles, Los Angeles, California 90095-1568 Del Negro, Christopher A. and Scott H. Chandler. Physiological and theoretical analysis of K + currents controlling discharge in neonatal rat mesencephalic trigeminal neurons. J. Neurophysiol. 77: 537-553, 1997. Whole cell voltage- and current-clamp recordings were obtained from mesencephalic trigeminal sensory (Mes 5) neurons identified visually in thin brain stem slices of neonatal rats with the use of infrared video microscopy. These cells exhibited accommodation in spike discharge responses to depolarizing current injection protocols whose duration differed as a function of holding potential ( 50 vs. 65 mV). Several spikes were elicited before the membrane response accommodated from 50 mV, whereas from 65 mV only single action potentials were evoked. In response to similar protocols, application of the K + channel blocker 4-aminopyridine (4-AP) (50 µM to 2 mM) caused sustained repetitive spiking whereas tetraethylammonium (TEA) (10-30 mM) did not cause repetitive spiking. In voltage clamp, 4-AP application (100 µM) revealed a sustained outward current ( I 4-AP ) that was active between 60 and 30 mV. I 4-AP was responsible for suppressing sustained repetitive spiking behavior, producing accommodation under normal circumstances. TEA application in voltage clamp revealed a sustained outward current evoked positive to 40 mV. Two transient outward currents (TOCs) were identified by prepulse protocols typically used to characterizeA-type currents: a 4-AP-insensitive fast TOC, and a slow TOC( I TOC-S ) sensitive to 4-AP (>500 µM). A Ca 2+ -dependent outward current that activated positive to 30 mV was also characterized. A mathematical model of a Mes 5 neuron was assembled from our voltage-clamp records to simulate the dynamic interaction of outward currents during membrane excitation. We conclude that in Mes 5 neurons, the 4-AP-sensitive currents I TOC-S and I 4-AP determine the duration of spike trains. In particular, the noninactivating I 4-AP determines whether cells exhibit sustained repetitive discharge or accommodate in response to depolarizing current. Neurotransmitter modulation of this current or modulation of the resting membrane potential could modify the output properties of Mes 5 neurons, and therefore the properties of these currents must be incorporated into our current understanding of