Spontaneous apamin-sensitive hyperpolarizations in dopaminergic neurons ofneonatal rats

Intracellular recordings from substantia nigra slices revealed the existenc e of spontaneous hyperpolarizations (amplitude 2-8 mV, duration 100-400 ms) at -60 mV in most dopaminergic neurons of neonatal (9-15 days) but not adu lt rats. These events were blocked by apamin (300 nM) and bicuculline metho chloride (100-300 mu M), which blocks apamin-sensitive currents. They were unaffected by the selective gamma-aminobutyric acid-A (GABA,) antagonists S R95531 (100 mu M) and picrotoxin (30-50 mu M), the GABA, antagonist CGP3534 8 (300 mu M), the D2 antagonist haloperidol ( 1 mu M), and the metabotropic antagonist MCPG (1 mM). The hyperpolarizations were strongly attenuated or abolished when recording electrodes contained 200 mM 1,2-bis (2-aminopheno xy) ethane-N,N,N',N'-tetraacetic acid. They were resistant to tetrodotoxin in the majority of the cells. They had some voltage dependency and were in some cases transiently potentiated when cells were briefly depolarized by c urrent injection. We conclude that dopaminergic neurons have developmentall y regulated physiological properties. These spontaneous hyperpolarizations might affect the firing rate of these cells, which was found to be lower in neonates than in adults.