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 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.
Mereu
G
G
Department of Experimental Biology, B. Loddo, University of Cagliari, Italy.
Lilliu
V
V
Casula
A
A
Vargiu
P F
PF
Diana
M
M
Musa
A
A
Gessa
G L
GL
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D004298:Dopamine / Q000502:physiology*; D004594:Electrophysiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D007608:Kainic Acid / Q000494:pharmacology; D008297:Male; D008636:Mesencephalon / Q000737:chemistry / Q000166:cytology*; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000737:chemistry / Q000502:physiology*; D010507:Periodicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*
D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016202:N-Methylaspartate; D015763:2-Amino-5-phosphonovalerate; D007608:Kainic Acid; D004298:Dopamine