ACTH self-administration in rats.
The ability of rats to learn a lever pressing response reinforced by a contingent intravenous delivery of ACTH 1--24 and 4--10, was investigated. About 60% of the rats tested learned to press the lever for the two analogues that were infused at a rate of 2.08 microgram per second via a chronically implanted intrajugular catheter. Most of the animals exhibited sustained daily self-injections of 250 to 375 microgram of ACTH 1--24 and more variable amounts of ACTH 4--10. Comparisons with the self-administration of saline and altered responses following a change in the concentration of ACTH 1--24 solution indicated a positively reinforcing effect for the neuropeptide. The self-administration of the ACTH 4--10 analogue demonstrates that this reinforcing property of ACTH is not due to its adrenal stimulating activity. Brain targets possibly involved in the self-administration of ACTH are discussed.