Cocaine and cocaine expectancy increase growth hormone, ghrelin, GLP-1, IGF-1, adiponectin, and corticosterone while decreasing leptin, insulin, GIP, and prolactin.

The dopamine system-essential for mood and movement-can be activated in two ways: by excitatory inputs that cause burst firing and stamp-in learning or by slow excitatory or inhibitory inputs-like leptin, insulin, ghrelin, or corticosterone-that decrease or increase single-spike (pacemaker) firing rate and that modulate motivation. In the present study we monitored blood samples taken prior to and during intravenous cocaine or saline self-administration in rats. During cocaine-taking, growth hormone and acetylated ghrelin increased 10-fold; glucagon-like peptide-1 (GLP-1) doubled; non-acetylated ghrelin, insulin-like growth factor-1 (IGF-1), and corticosterone increased by 50% and adiponectin increased by 17%. In the same blood samples, leptin, insulin, gastric inhibitory polypeptide (GIP), and prolactin decreased by 40-70%. On the first day of testing under extinction conditions-where the animals earned unexpected saline instead of cocaine-5-fold increases were seen for growth hormone and acetylated ghrelin and equal changes-in amplitude and latency-were seen in each of the other cases except for IGF-1 (which increased at a slower rate). Single-spike firing affects the tonic activation level of the dopamine system, involving very different controls than those that drive burst firing; thus, the present data suggest interesting new targets for medications that might be used in the early stages of drug abstinence.