CART mRNA expression in rat monkey and human brain: relevance to cocaine abuse

The neuropeptide CART (cocaine and amphetamine regulated transcript) is suggested to be regulated by psychostimulant administration. We review here the localization of CART mRNA expression in the human brain and its possible relevance to human cocaine abuse. Except for strong hypothalamic expression, the CART transcript is predominately expressed in target regions of the mesocorticolimbic dopamine system, such as the nucleus accumbens shell, amygdala complex, extended amygdala and orbitofrontal, enthorhinal and piriform cortices. The discrete limbic localization strongly implies involvement in reward and reinforcement behaviors. We therefore examined CART mRNA expression in both Sprague Dawley rats and Rhesus monkeys that had self-administered cocaine. Cocaine self-administration in the rat (1.5 mg/kg/inj, on a fixed ratio 1 schedule of reinforcement for 1 week) and monkey (0.03 or 0.3 mg/kg/inj on a fixed 3 min interval schedule of reinforcement for 5 or 100 days) did not alter transcript levels in CART expressing nucleus accumbens (monkey not studied), amygdala nuclei or cortical areas. However, in the monkey sublenticular extended amygdala, low dose cocaine self-administration resulted in increased CART transcript levels after both 5 and 100 days of self-administration, whereas no difference was found after high dose self-administration. In conclusion, we found no substantial alterations CART mRNA expression during cocaine self-administration, but this neuropeptide has the anatomical and functional potential to modulate brain areas relevant for cocaine abuse. Further studies are needed to evaluate the involvement of CART in other components of the cocaine abuse cycle.