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Volume 17, Number 9,
Issue of May 1, 1997
pp. 3168-3177
Copyright ©1997 Society for Neuroscience
PET Measurement of Dopamine D2 Receptor-Mediated
Changes in Striatopallidal Function
Received Jan. 6, 1997; accepted Feb. 11, 1997.
Kevin J. Black1, 2,
Mokhtar H. Gado1, and
Joel
S. Perlmutter1
1 Departments of Radiology, Neurology and
Neurological Surgery, and 2 Psychiatry, Washington
University School of Medicine, St. Louis, Missouri 63130
This study was designed to validate an in vivo
measurement of the functional sensitivity of basal ganglia neuronal
circuits containing dopamine D2 receptors. We hypothesized
that a D2 agonist would decrease striatopallidal neuronal
activity, and hence regional cerebral blood flow (rCBF) over the axon
terminals in the globus pallidus. Quantitative pallidal blood flow was
measured using positron emission tomography (PET) with bolus injections
of H215O and arterial sampling in six baboons
before and after intravenous administration of the selective
D2 agonist U91356a. We also tested whether the response to
U91356a was modified by previous acute administration of various
antagonists. Another baboon had serial measurements of blood flow under
identical conditions, but received no dopaminergic drugs. In all
animals that received U91356a, pallidal flow decreased in a
dose-related manner. Global CBF had a similar response, but the decline
in pallidal flow was greater in magnitude and remained significant
after accounting for the global effect. A D2 antagonist,
but not antagonists of D1, serotonin-2, or peripheral D2 receptors, prevented this decrease. This work
demonstrates and validates an in vivo measure of the
sensitivity of D2-mediated basal ganglia pathways. It also
supports the hypothesis that activation of the indirect striatopallidal
pathway, previously demonstrated using nonselective D2-like
agonists, can be mediated specifically by D2 receptors. We
speculate that the U91356a-PET technique may prove useful in detecting
functional abnormalities of D2-mediated dopaminergic
function in diseases such as parkinsonism, dystonia, Tourette syndrome,
or schizophrenia.
Key words:
globus pallidus;
dopamine
D2 receptor;
positron emission tomography;
pharmacological activation;
baboon;
U91356a
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