Addictive agents and intracranial stimulation (ICS): Pressing for ICS before and after self-administration of sweetened morphine solutions

Abstract

Rats, fixed with chronically indwelling electrodes for intracranial stimulation (ICS) of the lateral hypothalamic area, pressed a lever for the ICS. They were then given 15 days of opportunity to consume a sweetened morphine solution. They increased their intake of the solution to a mean of 61 mg/kg/day of morphine by the 15th day. During the initial days of 37 days of abstinence, they showed pronounced withdrawal symptoms. Subsequently, they were given another opportunity to consume and they relapsed into taking large quantities of morphine. After another 10 days of abstinence, rats were tested for pressing for ICS before and after 3 h of opportunity to consume sweetened morphine solution (mean morphine consumption = 28 mg/kg/session). The rats pressed reliably more after taking the morphine solution than before taking it and more than on days when they only consumed the sweetened solution without morphine. Consequently, it was concluded that pressing for ICS was accelerated after self-administration of morphine by previously addicted rats.