L-type Ca2+ channels mediate adaptation of extracellular signal-regulated kinase 1/2 phosphorylation in the ventral tegmental area after chronic amphetamine treatment.
L-type Ca2+ channels (LTCCs) play an important role in chronic psychostimulant-induced behaviors. However, the Ca2+ second messenger pathways activated by LTCCs after acute and recurrent psychostimulant administration that contribute to drug-induced molecular adaptations are poorly understood. Using a chronic amphetamine treatment paradigm in rats, we have examined the role of LTCCs in activating the mitogen-activated protein (MAP) kinase pathway in the ventral tegmental area (VTA), a primary target for the reinforcing properties of psychostimulants. Using immunoblot and immunohistochemical analyses, we find that in chronic saline-treated rats a challenge injection of amphetamine increases phosphorylation of MAP [extracellular signal-regulated kinase 1/2 (ERK1/2)] kinase in the VTA that is independent of LTCCs. However, in chronic amphetamine-treated rats there is no increase in amphetamine-mediated ERK1/2 phosphorylation unless LTCCs are blocked, in which case there is robust phosphorylation in VTA dopamine neurons. Examination of the expression of phosphatases reveals an increase in calcineurin [protein phosphatase 2B (PP2B)] and MAP kinase phosphatase-1 (MKP-1) in the VTA. Using in situ hybridization histochemistry and immunoblot analyses, we further examined the mRNA and protein expression of the LTCC subtypes Ca(v)1.2 and Ca(v)1.3 in VTA dopamine neurons in drug-naive animals and in rats after chronic amphetamine treatment. We found an increase in Ca(v)1.2 mRNA and protein levels, with no change in Ca(v)1.3. Together, our results suggest that one aspect of LTCC-induced changes in second messenger pathways after chronic amphetamine exposure involves activation of the MAP kinase phosphatase pathway by upregulation of Ca(v)1.2 in VTA dopaminergic neurons.
NMR Center, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA. rajadhan@helix.mgh.harvard.edu
Anjali
A
Rajadhyaksha
Isabelle
I
Husson
Shirish S
SS
Satpute
Karsten D
KD
Küppenbender
J Q
JQ
Ren
Rejean M
RM
Guerriero
David G
DG
Standaert
Barry E
BE
Kosofsky
D000661:Amphetamine / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D015151:Immunoblotting; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000096:biosynthesis; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D017557:Ventral Tegmental Area / Q000187:drug effects* / Q000378:metabolism
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D000697:Central Nervous System Stimulants; D012333:RNA, Messenger; D000661:Amphetamine; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1