G. Mereu et al., SPONTANEOUS BURSTING ACTIVITY OF DOPAMINERGIC-NEURONS IN MIDBRAIN SLICES FROM IMMATURE RATS - ROLE OF N-METHYL-D-ASPARTATE RECEPTORS, Neuroscience, 77(4), 1997, pp. 1029-1036
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.