Volume 16, Number 19,
Issue of October 1, 1996
pp. 6134-6145
Copyright ©1996 Society for Neuroscience
Neuron Death in the Substantia Nigra of Weaver Mouse Occurs Late
in Development and Is Not Apoptotic
Received May 30, 1996; revised July 11, 1996; accepted July 15, 1996.
Tinmarlar F. Oo1,
Richard Blazeski2,
Susan M. W. Harrison3,
Claire Henchcliffe1,
Carol A. Mason2,
Suzanne K. Roffler-Tarlov3, and
Robert E. Burke1
1 Department of Neurology, and
2 Departments of Pathology, and Anatomy and Cell Biology,
Center for Neurobiology and Behavior, College of Physicians and
Surgeons, Columbia University, New York, New York 10032, and
3 Departments of Neuroscience, and Anatomy and Cell
Biology, Tufts University, Boston, Massachusetts 02111
Weaver is a spontaneous mutation in mice
characterized by the postnatal loss of external granule cells in the
cerebellum and dopaminergic neurons of the midbrain, especially in the
substantia nigra. We have shown previously that natural cell death with
the morphology of apoptosis occurs in the substantia nigra of normal
rodents during postnatal development. We therefore sought to determine
whether the loss of dopaminergic neurons in homozygous weaver mice
occurs during the period of natural cell death in the substantia nigra
and whether it has the morphology of apoptosis. We have found, using a
silver stain technique, that although apoptotic cell death does occur
early postnatally in homozygous weaver substantia nigra, it also does
so with equal magnitude in wild-type and heterozygous weaver
littermates. Unique to homozygous weavers is the occurrence of
degenerating neurons in the nigra that are not apoptotic. These
degenerating neurons are observed at postnatal day 7, and they are most
abundant on postnatal days 24-25. The nonapoptotic nature of this cell
death is confirmed by negative in situ end labeling of
nuclear DNA fragmentation and by ultrastructural analysis.
Ultrastructural studies reveal irregular chromatin aggregates in the
nucleus, as well as marked cytoplasmic changes, including the formation
of vacuoles and distinctive stacks of dilated cisternae of endoplasmic
reticulum. We interpret these changes as indicative of either a variant
morphology of programmed cell death or a pathological degenerative
process mediated by an as yet unknown mechanism related to the recently
described mutation in the GIRK2 potassium channel.
Key words:
weaver;
apoptosis;
programmed cell death;
substantia
nigra;
potassium channel;
development;
ultrastructure