Journal of Neuroscience, Vol 15, 7105-7120, Copyright © 1995 by Society for Neuroscience
Cholinergic, GABAergic, and glutamate-enriched inputs from the mesopontine tegmentum to the subthalamic nucleus in the rat
MD Bevan and JP Bolam
MRC Anatomical Neuropharmacology Unit, Department of Pharmacology, Oxford, United Kingdom.
In order to clarify the origin and to examine the neurochemistry and
synaptology of the projection from the mesopontine tegmentum (MTg) to the
subthalamic nucleus (STN), rats received discrete deposits of anterograde
tracers in different regions of the MTg. Anterogradely labeled fibers were
examined in the light and electron microscopes. The distribution of GABA or
glutamate immunoreactivity was examined by post- embedding
immunocytochemistry. The anterograde tracing demonstrated that the
projection to the STN arises from at least three divisions of the MTg: the
area defined by the cholinergic neurons of the pedunculopontine region
(PPN-Ch 5), the more medial and largely noncholinergic midbrain
extrapyramidal area (MEA) and to a lesser extent the laterodorsal tegmental
nucleus (LDTg). Post-embedding immunocytochemistry revealed that there are
GABA-immunopositive and immunonegative components to this projection and at
least a proportion of the GABA-immunonegative component is enriched in
glutamate immunoreactivity. The similarity of the morphology, trajectory
and synaptology of the anterogradely labeled fibers and the choline
acetyltransferase (ChAT)-immunopositive fibers supports the proposal that
at least part of the projection is cholinergic. The terminals anterogradely
labeled from the MTg and the ChAT-immunoreactive terminals form
asymmetrical synapses with the dendrites and spines of subthalamic neurons.
Both anterogradely labeled and ChAT-positive terminals make convergent
synaptic contacts with GABA-immunoreactive terminals that form symmetrical
synaptic contacts and are probably derived from the globus pallidus. Taken
together these findings imply that the MTg sends cholinergic, GABAergic and
glutamatergic projections to the STN where at least one of the functional
roles is to modulate the indirect pathway of information flow through the
basal ganglia that is carried via the pallidosubthalamic projection.
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