SPONTANEOUS BURSTING ACTIVITY OF DOPAMINERGIC-NEURONS IN MIDBRAIN SLICES FROM IMMATURE RATS - ROLE OF N-METHYL-D-ASPARTATE RECEPTORS

Dopamine neurons in midbrain coronal slices from adult rats (40-70 day s old) discharged only in pacemaker-like mode. Irregular or bursting m ode was never observed. In contrast, dopamine neurons in slices from i mmature rats (15-21 days old) exhibited not only pacemaker-like firing (53.4% of neurons), but also irregular and bursting patterns (28.3 an d 18.3%, respectively). Glutamate and kainate increased the firing rat e 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 on ly three out of 18 cells. In slices from immature rats, N-methyl-D-asp artate activated the discharge rate in all neurons and also induced bu rsts in 37 and 53% of pacemaker and irregular neurons, respectively, a nd increased the occurrence of spikes in bursts in 76% of spontaneousl y bursting neurons. The selective N-methyl-D-aspartate receptor antago nist (+/-)2-amino,5-phosphonopentanoic acid prevented N-methyl-D-aspar tate-induced changes and also reduced spontaneous bursts, suggesting t hat bursting discharge is mediated by N-methyl-D-aspartate receptor ac tivation. While pacemaker neurons from immature and from adult rats ex hibited the same sensitivity to N-methyl-D-aspartate-induced stimulati on 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-as partate receptor activation, is present, and may be induced, in dopami ne neurons in slices from immature rats. Its absence from cells in sli ces from adult rats may reflect a reduced sensitivity of N-methyl-D-as partate receptors on dopamine or the loss of the N-methyl-D-aspartate- activated burst generator. (C) 1997 IBRO. Published by Elsevier Scienc e Ltd.