title: Shifts in striatal responsivity evoked by chronic stimulation of dopamine and glutamate systems.
abstract: Dopamine and glutamate are key neurotransmitters in cortico-basal ganglia loops affecting motor and cognitive function. To examine functional convergence of dopamine and glutamate neurotransmitter systems in the basal ganglia, we evaluated the long-term effects of chronic stimulation of each of these systems on striatal responses to stimulation of the other. First we exposed rats to chronic intermittent cocaine and used early-gene assays to test the responsivity of the striatum to subsequent acute motor cortex stimulation by application of the GABA(A) (gamma-aminobutyric acid alpha subunit) receptor antagonist, picrotoxin. Reciprocally, we studied the effects of chronic intermittent motor cortex stimulation on the capacity for subsequent acute dopaminergic treatments to induce early-gene activation in the striatum. Prior treatment with chronic intermittent cocaine induced motor sensitization and significantly potentiated the striatal expression of Fos-family early genes in response to stimulation of the motor cortex. Contrary to this, chronic intermittent stimulation of the motor cortex down-regulated cocaine-induced gene expression in the striatum, but enhanced striatal gene expression induced by a full D1 receptor agonist (SKF 81297) and did not change the early-gene response elicited by a D2 receptor antagonist (haloperidol). These findings suggests that repeated dopaminergic stimulation produces long-term enhancement of corticostriatal signalling from the motor cortex, amplifying cortically evoked modulation of the basal ganglia. By contrast, persistent stimulation of the motor cortex inhibits cocaine-stimulated signalling in the striatum, but not signalling mediated by individual dopamine receptor sites, suggesting that chronic cortical hyperexcitability produces long-term impairment of dopaminergic activity and compensation at the receptor level. These findings prompt a model of the basal ganglia function as being regulated by opposing homeostatic dopamine-glutamate neurotransmitter interactions. The model provides a framework for analysing the neurological alterations associated with disorders of the basal ganglia and their treatment with pharmacotherapies affecting dopamine and glutamate neurotransmitter systems.
authors.affiliation: Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, 45 Carleton Street, Cambridge, MA 02139, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Canales
authors.forename: C
authors.initials: C
authors.lastname: Capper-Loup
authors.forename: D
authors.initials: D
authors.lastname: Hu
authors.forename: E S
authors.initials: ES
authors.lastname: Choe
authors.forename: U
authors.initials: U
authors.lastname: Upadhyay
authors.forename: A M
authors.initials: AM
authors.lastname: Graybiel
mesh_terms: D000818:Animals; D003042:Cocaine / Q000008:administration & dosage; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D004298:Dopamine / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D010852:Picrotoxin / Q000008:administration & dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000378:metabolism; D017470:Receptors, Glutamate / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013239:Stereotyped Behavior / Q000187:drug effects / Q000502:physiology
chemical_list: D003042:Cocaine; D004298:Dopamine; D018698:Glutamic Acid; D010852:Picrotoxin; D017447:Receptors, Dopamine D1; D017470:Receptors, Glutamate