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The Journal of Neuroscience, May 1, 2000, 20(9):3085-3094
Activation of Group II Metabotropic Glutamate Receptors Inhibits
Synaptic Excitation of the Substantia Nigra Pars Reticulata
Stefania Risso
Bradley1,
Michael J.
Marino1,
Marion
Wittmann3,
Susan T.
Rouse1,
Hazar
Awad1,
Allan I.
Levey2, and
P. Jeffrey
Conn1
Departments of 1 Pharmacology and
2 Neurology, Emory University, Atlanta, Georgia 30322, and
3 Tierphysiologie, University of Tuebingen, D-72076
Tuebingen, Germany
Loss of nigrostriatal dopaminergic neurons in Parkinson's disease
(PD) leads to increased activity of glutamatergic neurons in the
subthalamic nucleus (STN). Recent studies reveal that the resultant
increase in STN-induced excitation of basal ganglia output nuclei is
responsible for the disabling motor impairment characteristic of PD. On
the basis of this, it is possible that any manipulation that reduces
activity at excitatory STN synapses onto basal ganglia output nuclei
could be useful in the treatment of PD. We now report that group II
metabotropic glutamate receptors (mGluRs) are presynaptically localized
on STN terminals and that activation of these receptors inhibits
excitatory transmission at STN synapses. In agreement with the
hypothesis that this could provide a therapeutic benefit in PD, a
selective agonist of group II mGluRs induces a dramatic reversal of
catalepsy in a rat model of PD. These results raise the exciting
possibility that selective agonists of group II mGluRs could provide an
entirely new approach to the treatment of PD. These novel therapeutic
agents would provide a noninvasive pharmacological treatment that does
not involve the manipulation of dopaminergic systems, thus avoiding the
problems associated with current therapies.
Key words:
substantia nigra pars reticulata; subthalamic nucleus; group II metabotropic glutamate receptors; Parkinson's disease; catalepsy; presynaptic inhibition
Copyright © 2000 Society for Neuroscience 0270-6474/00/2093085-10$05.00/0
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