Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1) controls activation of extracellular signal-regulated kinase (ERK) signaling in the striatum and long-term behavioral responses to cocaine.
BACKGROUND
Ras-extracellular signal-regulated kinase (Ras-ERK) signaling is central to the molecular machinery underlying cognitive functions. In the striatum, ERK1/2 kinases are co-activated by glutamate and dopamine D1/5 receptors, but the mechanisms providing such signaling integration are still unknown. The Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1), a neuronal specific activator of Ras-ERK signaling, is a likely candidate for coupling these neurotransmitter signals to ERK kinases in the striatonigral medium spiny neurons (MSN) and for modulating behavioral responses to drug abuse such as cocaine.


METHODS
We used genetically modified mouse mutants for Ras-GRF1 as a source of primary MSN cultures and organotypic slices, to perform both immunoblot and immunofluorescence studies in response to glutamate and dopamine receptor agonists. Mice were also subjected to behavioral and immunohistochemical investigations upon treatment with cocaine.


RESULTS
Phosphorylation of ERK1/2 in response to glutamate, dopamine D1 agonist, or both stimuli simultaneously is impaired in Ras-GRF1-deficient striatal cells and organotypic slices of the striatonigral MSN compartment. Consistently, behavioral responses to cocaine are also affected in mice deficient for Ras-GRF1 or overexpressing it. Both locomotor sensitization and conditioned place preference are significantly attenuated in Ras-GRF1-deficient mice, whereas a robust facilitation is observed in overexpressing transgenic animals. Finally, we found corresponding changes in ERK1/2 activation and in accumulation of FosB/DeltaFosB, a well-characterized marker for long-term responses to cocaine, in MSN from these animals.


CONCLUSIONS
These results strongly implicate Ras-GRF1 in the integration of the two main neurotransmitter inputs to the striatum and in the maladaptive modulation of striatal networks in response to cocaine.
Fasano
Stefania
S
Institute of Experimental Neurology, Division of Neuroscience, San Raffaele Foundation and University, Milano, Italy.
D'Antoni
Angela
A
Orban
Paul C
PC
Valjent
Emmanuel
E
Putignano
Elena
E
Vara
Hugo
H
Pizzorusso
Tommaso
T
Giustetto
Maurizio
M
Yoon
Bongjune
B
Soloway
Paul
P
Maldonado
Rafael
R
Caboche
Jocelyne
J
Brambilla
Riccardo
R
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology*; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D003042:Cocaine / Q000008:administration & dosage / Q000494:pharmacology*; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009434:Neural Pathways / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017447:Receptors, Dopamine D1 / Q000819:agonists; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D020666:ras-GRF1 / Q000235:genetics* / Q000502:physiology*
D018690:Excitatory Amino Acid Agonists; D017447:Receptors, Dopamine D1; D020666:ras-GRF1; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D003042:Cocaine