Abstract
The midbrain nucleus substantia nigra pars reticulata (SNr) consists mainly of GABAergic projection neurons. These SNr GABAergic neurons exhibit the highest spontaneous activity in the brain, suggesting their very high demand for energy substrates such as oxygen and glucose. SNr neurons are extremely sensitive to hypoxia, ceasing firing upon opening of their ATP-sensitive potassium (KATP) channels, well before the hypoxia-induced general self-defense reactions in other neuron types. Unexpectedly, approximately two thirds of SNr GABAergic neurons showed increased spontaneous activity as the extracellular glucose concentration was lowered from 10 to 4-6 mM in acute slice, indicating that SNr contains glucose-sensitive neurons. In addition, a small proportion of SNr neurons exhibited multiple, abrupt increses in firing rate with periods ranging in minutes. At 1-3 mM glucose, the firing rate ceased after a rapid increase. No significant change in firing was observed by increasing the glucose from 10 to 20 mM. These responses were independent of the KATP channels, and persisted under blockade of GABAA, NMDA, and non-NMDA receptors, suggesting a postsynaptic mechanism. Thus, the altered activity of the SNr, a major output neucleus of the basal ganglia, itself might signal the metabolic state of the brain to its target nuclei. [Jpn J Physiol 55 Suppl:S59 (2005)]
