Excitatory tonus is required for the survival of granule cell precursors during postnatal development within the cerebellum.
In addition to protective effects within the adult central nervous system (CNS), in vivo application of N-methyl-d-aspartate inhibitors such as (+) MK-801 have been shown to induce neurodegeneration in neonatal rats over a specific developmental period. We have systematically mapped the nature and extent of MK-801-induced neurodegeneration throughout the neonatal murine brain in order to genetically dissect the mechanism of these effects. Highest levels of MK-801-induced neurodegeneration are seen in the cerebellar external germinal layer; while mature neurons of the internal granule layer are unaffected by MK-801 treatment. Examination of external germinal layer neurons by electron microscopy, terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) and bromodeoxyuridine (BrdU) labeling, and caspase-3 activation demonstrate that these neurons die through the process of programmed cell death soon after they exit from the cell cycle. Significantly, ablation of caspase-3 activity completely inhibited the MK-801-induced (and developmental) programmed cell death of external germinal layer neurons. Similar to caspase-3, inactivation of muscarinic acetylcholine receptors in vivo using scopolamine inhibited MK-801-induced programmed cell death. By contrast, the GABAergic agonist diazepam, either alone or in combination with MK-801, enhanced programmed cell death within external germinal layer neurons. These data demonstrate that, in vivo, cerebellar granule neurons undergo a dramatic change in intracellular signaling in response to molecules present in the local cellular milieu during their first 24 h following exit from the cell cycle.
Kanungo
A K
AK
Department of Pharmaceutical Sciences, University of Toronto, Toronto, Ontario, Canada M5S 3M2.
Liadis
N
N
Robertson
J
J
Woo
M
M
Henderson
J T
JT
D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001973:Bromodeoxyuridine / Q000378:metabolism; D053148:Caspase 3 / Q000172:deficiency / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D002531:Cerebellum / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development*; D018680:Cholinergic Antagonists / Q000494:pharmacology; D003975:Diazepam / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018757:GABA Modulators / Q000494:pharmacology; D020287:In Situ Nick-End Labeling / Q000379:methods; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission / Q000379:methods; D009410:Nerve Degeneration / Q000139:chemically induced / Q000235:genetics / Q000473:pathology; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D012601:Scopolamine / Q000494:pharmacology; D013234:Stem Cells / Q000187:drug effects / Q000502:physiology*
D018680:Cholinergic Antagonists; D018691:Excitatory Amino Acid Antagonists; D018757:GABA Modulators; D016291:Dizocilpine Maleate; D012601:Scopolamine; D053148:Caspase 3; D001973:Bromodeoxyuridine; D003975:Diazepam