Abstract
Midbrain substantia nigra pars reticulata (SNr) consists mostly of GABAergic neurons, of which spontaneous firing rate is among highest in the brain, suggesting that demand for energy source such as oxygen and glucose is very high. Indeed, severe hypoxia suppresses the firing rate of SNr GABAergic neurons both in slice and acutely dissociated conditions. We have shown that ATP-sensitive potassium (KATP) channels exert a critical role in the hypoxic response of these neurons. On the other hand, when the extracellular glucose concentration was moderately lowered, the firing rate of most SNr neurons was increased in a KATP channel-independent manner, and some exhibit periodical, abrupt increases in the firing rate (up to 120Hz) in slice (multiminutes oscillation). Although molecular mechanisms underlying the glucose-sensitive responses remain unknown, no such oscillation was detected when neurons were dissociated, suggesting that interaction between multiple cellular components is important. Actually, the oscillation was blocked by low extracellular Ca2+ in slice, although it was not affected by blockade of EAA- and GABA-mediated transmissions. In the present study, we provide electrophysiological and anatomical data suggesting that glycine participates in the glucose sensitivity of the SNr GABAergic neurons both in juvenile and adult stages. [J Physiol Sci. 2008;58 Suppl:S82]
