J Neurophysiol (March 1, 2003). 10.1152/jn.00850.2002
Submitted on Submitted 24 September 2002; accepted in final form 14 November 2002

Development of Inward Rectification and Control of Membrane Excitability in Mesencephalic V Neurons

 ¹Department of Physiological Science and the Brain Research Institute, Los Angeles, California 90095;  ²1st Department of Oral and Maxillofacial Surgery, Graduate School of Dentistry, Osaka University, Osaka 565-0871, Japan; and  ³Department of Biokinesiology, University of Southern California, Los Angeles, California 90089

Tanaka, Susumu, Nanping Wu, Chie-Fang Hsaio, Jack Turman Jr., and Scott H. Chandler. Development of Inward Rectification and Control of Membrane Excitability in Mesencephalic V Neurons. J. Neurophysiol. 89: 1288-1298, 2003. The present study was performed to assess the postnatal development and functional roles of inward rectifying currents in rat mesencephalic trigeminal (Mes V) neurons, which are involved in the genesis and control of oral-motor activities. Whole cell voltage-clamp recordings obtained from Mes V neurons in brain stem slices identified fast (I_KIR) and slow (I_h) inward rectifying currents, which were specifically blocked by BaCl₂ (300-500 µM) or 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyrimidinium chloride (ZD 7288, 10 µM), respectively. The whole cell current density for these channels increased between postnatal days 2 to 12 (P2-P12), and the time courses for I_h activation and deactivation were each well described by two time constants. Application of ZD 7288 produced membrane hyperpolarization in the majority of cells and prolonged afterhyperpolarization repolarization. Additionally, in the presence of ZD 7288, spike frequency was decreased and adaptation was more pronounced. Interestingly, these neurons exhibited a voltage-dependent membrane resonance (<10 Hz) that was prominent around resting potential and more negative to rest and was blocked by ZD 7288. These results suggest that I_h contributes to stabilizing resting membrane potential and controlling cell excitability. The presence of I_h imparts the neuron with the unique property of low-frequency membrane resonance; the ability to discriminate between synaptic inputs based on frequency content.