CONCURRENT SELF-ADMINISTRATION OF ETHANOL AND AN ALTERNATIVE NONDRUG REINFORCER IN MONKEYS - EFFECTS OF INCOME (SESSION LENGTH) ON DEMAND FOR DRUG

Eight rhesus monkeys (Macaca mulata) were trained to self-administer o rally delivered ethanol (8%) and saccharin (0.03 or 0.3% wt/vol) or wa ter under concurrent fixed-ratio (FR) schedules. The FR requirement fo r saccharin was fixed at 32, while the FR for ethanol was varied (4, 8 , 16, 32, 64 and 128) in a nonsystematic order to assess demand for dr ug. Demand was defined as consumption plotted as a function of price ( FR). Income was defined as the duration of access to available resourc es. Income was varied by allowing access to the concurrently available liquids 20, 60 or 180 min per day. Order of testing was counterbalanc ed across monkeys. Saccharin deliveries were much higher than ethanol deliveries under the 180-min income condition; however, they were lowe r than ethanol deliveries when income was reduced to 20 min and the et hanol FR was 4, 8 or 16. Thus, when the price of drug was relatively l ow, consumption of drug exceeded that of the nondrug reinforcer, and t hat relationship was reversed as income decreased. Saccharin deliverie s sustained a proportionally greater reduction due to decreased income compared to ethanol deliveries. As income decreased from 180 to 20 mi n, saccharin deliveries were reduced by an average of 79.1% (across et hanol FR conditions) while ethanol deliveries were reduced by an avera ge of 41.2 and 40.8% when concurrent saccharin or water were available , respectively; thus, drug self-administration was more resistant to i ncome changes than saccharin. The demand for ethanol was shifted downw ard in a parallel fashion as income decreased. As ethanol cost (FR) in creased, there were proportionately greater decreases in ethanol intak e when saccharin was concurrently available compared to when water was available. There was a 35-50% reduction in ethanol deliveries due to concurrent saccharin (versus water) at FR 4, compared to a 55-75% redu ction at FR 128. Cost of ethanol (FR), income level and the availabili ty of a nondrug reinforcer are all variables that modify ethanol-reinf orced behavior, and income alters the relative preference for a drug v ersus nondrug reinforcer.