Abstract
Cocaine-amphetamine-regulated transcript (CART), a neuropeptide involved in the brain's reward/reinforcement circuit, modulates the effects of psychostimulants, including cocaine. The CART gene has been characterized, and binding sites for multiple transcription factors have been identified within the promoter region, including the cAMP-response element, which serves as a binding site for cAMP-response element-binding protein (CREB). CART expression appears to be regulated via cAMP/protein kinase A (PKA)/CREB-mediated signaling in cell culture. Therefore, the goal of these studies was to examine the involvement of cAMP/PKA/CREB-mediated signaling in CART mRNA and peptide expression in vivo in the rat nucleus accumbens. Intra-accumbal injections of forskolin, an adenylyl cyclase activator, stimulated the phosphorylation of CREB and increased both CART mRNA and peptide levels, an effect attenuated by inhibition of PKA with H89 [N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinoline-sulfonamide hydrochloride] and adenosine-3′,5′-cyclic monophosphorothioate, Rp-isomer (Rp-cAMPS). In addition, Rp-cAMPS alone decreased CART mRNA compared with saline-injected controls, suggesting that CART expression may be tonically regulated by PKA. Under certain conditions, cocaine increases CART mRNA levels; thus, we examined the effects of cocaine on forskolin-induced CART mRNA expression in the rat nucleus accumbens. Cocaine plus forskolin significantly increased CART mRNA over either of the drugs administered independently, suggesting that under conditions of heightened cAMP signaling, cocaine may impact CART gene expression. These results suggest that CART expression in vivo in the rat nucleus accumbens is regulated by adenylyl cyclase and cAMP/PKA-mediating signaling and, likely, through the activation of CREB.
Footnotes
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This work was supported by National Institutes of Health/NIDA Grants DA10732 and DA15162.
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doi:10.1124/jpet.105.096123.
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ABBREVIATIONS: CART, cocaine-amphetamine-regulated transcript; NAc, nucleus accumbens; DA, dopamine; CREB, cAMP-response element-binding protein; CRE, cAMP-response element; PKA, protein kinase A; AC, adenylyl cyclase; pCREB, phospho-cAMP-response element-binding protein; NIDA, National Institute on Drug Abuse; INAF, 7-deacetyl-7-[O-(N-methylpiperazino)-g-butyryl]-,dihydrochloride; H89, N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinoline-sulfonamide hydrochloride; Rp-cAMPS, adenosine-3′,5′-cyclic monophosphorothioate, Rp-isomer; SSC, standard saline citrate; OD, optical density; ANOVA, analysis of variance; PPD, preprodynorphin; HCL, hydrochloric acid.
- Received September 28, 2005.
- Accepted November 30, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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