The role of CART in the reward/reinforcing properties of psychostimulants

CART (85-102)-inhibition of psychostimulant-induced hyperlocomotion: importance of cyclization

Synthetic derivative of C-terminal fragment of CART (55-102) with reduced thiol groups, [Abu(86,94)]CART (85-102)(red), given together with amphetamine (5 mg/kg, s.c.) or cocaine (15 mg/kg, s.c.), reversed hyperlocomotion induced by these drugs at a dose of 0.1 microg but not at a higher dose. In the cerebral cortex homogenate, [Abu(86,94)]CART (85-102)(red) was nonspecifically cleaved from N- and C-termini. This peptide contains two chemically blocked Cys residues, and two others in reduced form. Concomitant with cleavage, rapid cyclization occurred. The newly formed cyclic peptides were stable. The cyclic peptide [Abu(86,94)]CART (85-102)(ox) failed to inhibit amphetamine- and cocaine-induced locomotor activity. The ability to inhibit the locomotor-stimulant activity of amphetamine was retained in [Abu(86,88,94,101)]CART (85-102), in which all Cys were replaced with 2-aminobutyric acid to prevent their pairing. Disulfide bridge formation may be an interesting mechanism that prevents proteolysis of [Abu(86,94)]CART (85-102)(red) and terminates its ability to reverse amphetamine-induced hyperlocomotion.

Role of cocaine- and amphetamine-regulated transcript in estradiol-mediated neuroprotection

Estrogen reduces brain injury after experimental cerebral ischemia in part through a genomic mechanism of action. Using DNA microarrays, we analyzed the genomic response of the brain to estradiol, and we identified a transcript, cocaine- and amphetamine-regulated transcript (CART), that is highly induced in the cerebral cortex by estradiol under ischemic conditions. Using in vitro and in vivo models of neural injury, we confirmed and characterized CART mRNA and protein up-regulation by estradiol in surviving neurons, and we demonstrated that i.v. administration of a rat CART peptide is protective against ischemic brain injury in vivo. We further demonstrated binding of cAMP response element (CRE)-binding protein to a CART promoter CRE site in ischemic brain and rapid activation by CART of ERK in primary cultured cortical neurons. The findings suggest that CART is an important player in estrogen-mediated neuroprotection and a potential therapeutic agent for stroke and other neurodegenerative diseases.