The Journal of Neuroscience, August 1, 1998, 18(15):5614-5629
Induction of Interleukin-1 Associated with Compensatory
Dopaminergic Sprouting in the Denervated Striatum of Young Mice: Model
of Aging and Neurodegenerative Disease
Angela
Ho and
Mariann
Blum
Fishberg Research Center for Neurobiology, Mount Sinai School of
Medicine, New York, New York 10029
Young mice challenged with the neurotoxin
1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which selectively
destroys the substantia nigra dopaminergic neurons in the midbrain,
exhibit spontaneous recovery of dopaminergic nerve terminals. However, such recovery becomes attenuated with age. Here we report that newly
sprouted fibers originate from spared dopaminergic neurons in the
ventral tegmental area. We found that interleukin-1 (IL-1), an immune
response-generated cytokine that can enhance dopaminergic sprouting
when exogenously applied, increased dramatically in the denervated
striatum of young mice (2 months) compared with middle-aged mice (8 months) after MPTP treatment. Young mice displayed a maximal 500%
induction of IL-1
synthesis that remained elevated for
several weeks in the dorsal and ventral striatum, whereas middle-aged
mice exhibited a modest 135% induction exclusively in the dorsal
striatum for a week. IL-1
immunoreactivity was localized in
GFAP-immunoreactive hypertrophied astrocytes and neurons within the
denervated striatum of young mice. However, no induction of IL-1
mRNA was seen in the midbrain in either age group despite glial
activation. Because we have reported that IL-1 can regulate
astroglia-derived dopaminergic neurotrophic factors, it was surprising
that no changes were observed in acidic and basic fibroblast growth
factor or glial cell line-derived neurotrophic factor mRNA levels
associated with MPTP-induced plasticity of dopaminergic neurons in the
striatum of young mice. Interestingly, we found that dopaminergic
neurons express IL-1 receptors, thus suggesting that IL-1
could
directly act as a target-derived dopaminergic neurotrophic factor to
initiate or enhance the sprouting of dopaminergic axonal terminals.
These findings strongly suggest that IL-1
could play an important
role in MPTP-induced plasticity of dopaminergic neurons.
Key words:
IL-1; compensatory sprouting; dopaminergic neurons; growth factors; MPTP; Parkinson's disease; aging
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