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Abstract

The characterization of the functional interactions between the metabotropic glutamate receptors (mGluR) and the dopaminergic (DR) receptors in the corticostriatal projections may provide a possible interpretation of synaptic events in the basal ganglia. It has been suggested that presynaptic D2-type receptor located on glutamatergic corticostriatal neurons regulates the release of glutamate. In a first approach we have studied the cellular distribution of the D4R and the mGluRs in cerebral cortex and striatum employing immunocytochemistry. D4R positive neurons were particularly numerous in medial prefrontal cortex mainly occupying layers II and III. An even distribution was found on small round-shaped neurons in the striatum. Group I mGluR1alpha-like immunoreactivity (mGluR1alpha-LI) was found in medial and deep layers of the cerebral cortex while group III mGluR4a labeled more superficial layers; group II mGluR2/3 signal was intense on fine fibers with a punctate appearance. In the striatum, mGluR1alpha and mGluR2/3 stained mainly fibers while mGluR4a labeled round shaped cell bodies. After lateral ventricular injection of colchicine, an axonal transport and firing activity blocker, D4R labeling significantly increased in cerebral cortex and decreased in the striatum. mGluR1alpha and mGluR4a signal decreased in cerebral cortex and only mGluR4a signal decreased in the striatum. These results support previous reports indicating a presynaptic localization of D4R in the striatum. In contrast, striatal mGluR1alpha appears to be a postsynaptic receptor probably synthesized in situ. Our results do not support the hypothesis of a colocalization of D4 receptor and one or more of the metabotropic glutamatergic receptors studied here.

Pramipexole Reduces zif-268 mRNA Expression in Brain Structures involved in the Generation of Harmaline-Induced Tremor

“…Moreover, a recent study has demonstrated that striatal perfusion of pramipexole reduced optogenetically-induced glutamate release from the corticostriatal terminals in vivo which was counteracted also by L745-870 [37]. The latter result suggested a contribution of presynaptic D4 receptors localized on corticostriatal terminals [38] in the above effect of pramipexole [37]. Since glutamate is an important factor activating zif-268 expression in the brain (for Refs.…”

“…Anatomical localization of dopamine D4 receptors might support this assumption. These receptors are abundant in pyramidal and non-pyramidal neurons of the cerebral cortex, especially in its frontal regions, which provide glutamatergic projections not only to the striatum [38,39] but to the IO, as well [40,41]. Therefore, the presence of D4 receptors on terminals of the cortico-olivary projection is possible.…”