SPONTANEOUS BURSTING ACTIVITY OF DOPAMINERGIC NEURONS IN MIDBRAIN SLICES FROM IMMATURE RATS: ROLE OF N-METHYL-d-ASPARTATE RECEPTORS
1997
Abstract Dopamine neurons in midbrain coronal slices from adult rats (40–70 days old) discharged only in pacemaker-like mode. Irregular or bursting mode was never observed. In contrast, dopamine neurons in slices from immature rats (15–21 days old) exhibited not only pacemaker-like firing (53.4% of neurons), but also irregular and bursting patterns (28.3 and 18.3%, respectively). Glutamate and kainate increased the firing rate but failed to induce bursts in dopamine neurons from either adult or immature rats. N -Methyl- d -aspartate augmented the firing rate in all neurons from adult rats and produced a modest increase of bursts in only three out of 18 cells. In slices from immature rats, N -methyl- d -aspartate activated the discharge rate in all neurons and also induced bursts in 37 and 53% of pacemaker and irregular neurons, respectively, and increased the occurrence of spikes in bursts in 76% of spontaneously bursting neurons. The selective N -methyl- d -aspartate receptor antagonist (±)2-amino,5-phosphonopentanoic acid prevented N -methyl- d -aspartate-induced changes and also reduced spontaneous bursts, suggesting that bursting discharge is mediated by N -methyl- d -aspartate receptor activation. While pacemaker neurons from immature and from adult rats exhibited the same sensitivity to N -methyl- d -aspartate-induced stimulation of firing rate, spontaneously bursting neurons were more sensitive than pacemaker neurons from either immature or adult rats. The present study indicates that spontaneous bursting, dependent on N -methyl- d -aspartate receptor activation, is present, and may be induced, in dopamine neurons in slices from immature rats. Its absence from cells in slices from adult rats may reflect a reduced sensitivity of N -methyl- d -aspartate receptors on dopamine or the loss of the N -methyl- d -aspartate-activated burst generator.
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