Multiminute oscillations in mouse substantia nigra pars reticulata neurons in vitro

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 ( approximately 40 Hz) to peak (>100 Hz) with periods ranging in minutes when GABA(A) receptors were blocked by 20 microM bicuculline. The combination of GABA(B), non-NMDA, and NMDA blockers, SCH50911 (10 microM), 6,7-dinitro-quinoxaline-2,3-dione (20 microM), and DL-2-amino-5-phosphonovalerate (50 microM), 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.