| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2005: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
GABArgic neurons in the substantia nigra pars reticulata (SNr) exhibit spontaneous firing activity among highest in the brain. Continuous supply of oxygen and glucose is essential to ensure such neuronal activity. Indeed, we have shown that the SNr neurons exert a crtical role in sensing hypoxic conditions and suppressing hypoxia-induced propagation of generalized seizure via opening of ATP-sensitive potassium channels (K_<ATP>). Moreover, SNr neurons exhibited, in acute slice preparations, glucose-sensitivity, an increase of firing when extracellular glucose concentration is lowered, through K_<ATP> channel-independent mechanisms. However, it was unclear if the glucose sensitivity is an intrinsic property of the SNr neurons or is produced by cell-to-cell interactions such as synaptic transmissions. In the present study, we aimed to clarify this using acutely dissociated SNr neurons with perforated patch clamp techniques (Yamada K et al., the 84th Annual Meeting of the Physiological So
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ciety of Japan). 1.Most acutely dissociated SNr GABAergic neurons (10/14;〜70%) showed significant depolarization (5.7±2.4 mV for 4 mM glucose;31C) when extracellular glucose concentration was lowered from 10 mM to 4-8 mM in a concentration-dependent manner, suggesting that the resting potentials of SNr neurons can be regulated by extracellular glucose concentration. 2.Similarly to in the slice, acutely disscoiated SNr neurons responded to lowering glucose by either an increase, an increase followed by a decrease, no change, and a decrease, indicating that intrinsic property of SNr neurons contributes to the glucose sensitivity. 3.Upon lowering glucose, although a portion of acutely dissociated SNr neurons showed repeated abrupt increases in firing rate as in the slice, an individual increase did not persist long (such as for minutes ; termed as multiminute oscillation) compared to the slice preparation. Rather, the firing pattern consisted of discreate sets of short duration (0.5-1 sec) bursts of high frequency firing, wherease SNr neurons in the slice showed tonic firing of over 100 Hz for 10-20 sec with no burst when SNr neurons were extracellularly recorded, suggesting that cell-to-cell interaction and/or intact morphology may be important for the low glucose-induced stable increase of firing. The multiminute oscillation in the slice was inhibited by Low Ca (high Mg), suggesting that synaptic transmissions are required for the persistent increase in the high-frequency firing. The oscillation was not affected by blockade of GABA_A, GABA_B, non-NMDA, and NMDA receptors. We are currently investigating candidate transmitters. 4.To elucidate the physiological role of the glucose sensitivity of SNr neurons, we are developing glucose-sensing electrodes by a new approach. Optical imaging using a fluorescent glucose derivative 2-NBDG (Yamada K et al., Nature protocol,2007) is also appliled to understand the role of cell-to-cell interaction in the glucose sensitivity in the SNr. Less
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