Multiminute oscillations in mouse substantia nigra pars reticulata neurons in vitro

Abstract

In acute slice of substantia nigra pars reticulata (SNr), a small proportion (6.6%) of GABAergic neurons exhibited abrupt increases in spontaneous firing rate from baseline frequency (∼40 Hz) to peak (>100 Hz) with periods ranging in minutes when GABA A receptors were blocked by 20 μM bicuculline. The combination of GABA B, non-NMDA, and NMDA blockers, SCH50911 (10 μM), 6,7-dinitro-quinoxaline-2,3-dione (20 μM), and dl-2-amino-5-phosphonovalerate (50 μM), respectively, did not affect the incidence or properties of these multiminute oscillations, indicating that disinhibition induced by blockade of GABA A receptors is crucial in their generation. Incidence of oscillatory activity was increased to 16% by elevation of the K + concentration to 8 mM from basal level (6.24 mM). The SNr neurons exhibiting oscillatory activity with the addition of bicuculline had shown irregular fluctuations in basal firing rate, while the non-oscillatory neurons had shown a more regular baseline firing pattern. This is the first in vitro report of oscillations in firing rate of multiminute range in basal ganglia.