演題番号 : P3-h06
齋藤 康彦 / Yasuhiko Saito:1 柳川 右千夫 / Yuchio Yanagawa:1
1:群馬大院・医・遺伝発達行動学 / Dept Genetic and Behavioral Neuroscience, Gunma Univ Grad Sch of Medicine
The prepositus hypoglossi nucleus (PHN) is a brainstem structure involved in an oculomotor neural integrator, in which transient signals proportional to eye/head velocity are converted into sustained signals proportional to eye position. Our previous whole-cell voltage-clamp recordings in rat slice preparations demonstrated that application of high frequency stimulation (100 Hz, 20 pulses) to the vicinity of a recorded PHN neuron induced an increase in the frequency of EPSCs, which lasted for several seconds. The sustained EPSC responses are reduced by 1-naphthyl acetyl spermine (50 μM), a blocker of Ca2+-permeable AMPA (CP-AMPA) receptors. These findings suggest that sustained EPSC responses induced in the PHN are attributed to activation of CP-AMPA receptors. In the present study, we verified whether PHN neurons express CP-AMPA receptors by the analyses of current responses to iontophoretic application of kainate that is a non-desensitizing agonist of AMPA receptors. Of 88 PHN neurons recorded, more than half (53/88) exhibited inward rectifying current-voltage (I-V) relationship, which is characteristic of CP-AMPA receptors. Furthermore, to clarify whether Ca2+ permeability of PHN neurons exhibiting inward rectifying I-V relationship of kainate responses is higher, we examined the reversal potential of the responses in the Na+-free, high Ca2+ (20 mM) solution. The reversal potentials of neurons exhibiting inward rectifying I-V relationship were higher than those of neurons exhibiting outward rectifying I-V relationship. Estimation of the relative permeability coefficients of Ca2+ based on the reversal potentials confirmed that Ca2+ permeability was higher in AMPA receptors exhibiting inward rectifying I-V relationship than those exhibiting outward rectifying I-V relationship. All these results indicate that there are a substantial number of PHN neurons expressing CP-AMPA receptors, which play a key role in generation of sustained EPSC responses.