Reduction of drug self-administration by an alternative non-drug reinforcer in rhesus monkeys: magnitude and temporal effects.
BACKGROUND
Recent studies have shown that non-drug alternative reinforcers reduce drug self-administration. A goal of the present study was to explore factors such as magnitude of the alternative reinforcer and inter-session access to the alternative to identify conditions that lead to optimal reductions in drug intake.


OBJECTIVE
To evaluate the effects of increasing the volume/delivery (v/d) of saccharin on oral phencyclidine (PCP) self-administration in rhesus monkeys given continuous access to PCP and saccharin during daily sessions using a behavioral economic analysis. The effects of availability of a saccharin solution during the inter-session period on session PCP consumption in drug-experienced monkeys was also investigated.


METHODS
Subjects had access to PCP (0.25 mg/ml) and either water or saccharin (0.03%) from two drinking spouts under concurrent and independent fixed-ratio (FR) schedules during daily 3-h sessions. The FR requirements for both available liquids were simultaneously increased (FR4-64). The v/d of saccharin or water was increased (from 0.3 ml to 1.2 ml), while the v/d of PCP remained constant (0.6 ml). In a second experiment, subjects had access to water or saccharin and water during the inter-session period (17.5 h) under an FR1 schedule. PCP and water were available during daily 3-h sessions under concurrent FR schedules. The FR for both liquids was increased (FR16-128).


RESULTS
PCP intake was reduced at all FRs and magnitude conditions when saccharin (versus water) was concurrently available. Varying the v/d of saccharin only had a modest effect on the extent to which PCP intake was decreased at the higher FR values. Inter-session saccharin availability (versus water) reduced session PCP intake and the magnitude of this effect was also greater at the higher FR values.


CONCLUSIONS
The magnitude of the saccharin delivery had an effect on PCP consumption at higher FRs, suggesting that economic factors such as high drug cost (FR) and low cost (responses/ml) of the alternative reinforcer (saccharin) interact to produce a maximum suppression of drug intake. Between-session availability of saccharin also effectively reduced drug intake, and it had a greater effect on the maintenance levels of drug self-administration when the unit price of drug was high.
Campbell
U C
UC
Department of Psychiatry, University of Minnesota Medical School, Minneapolis 55455, USA.
Carroll
M E
ME
D000284:Administration, Oral; D000818:Animals; D003216:Conditioning, Operant; D006213:Hallucinogens / Q000008:administration & dosage / Q000494:pharmacology*; D008253:Macaca mulatta; D008297:Male; D010622:Phencyclidine / Q000008:administration & dosage / Q000494:pharmacology*; D012055:Reinforcement Schedule; D012054:Reinforcement, Psychology; D012439:Saccharin / Q000494:pharmacology; D012646:Self Administration; D013997:Time Factors
D006213:Hallucinogens; D012439:Saccharin; D010622:Phencyclidine