Caffeine increases the motivation to obtain non-drug reinforcers in rats

Abstract

BACKGROUND Caffeine is widely considered to be a reinforcer in humans, but this effect is difficult to measure in non-human animals. We hypothesized that caffeine may have dual reinforcing effects comparable to nicotine - limited primary reinforcing effects, but potent reinforcement enhancing effects. The present studies tested this hypothesis by investigating the effect of caffeine on responding for non-drug rewards. METHODS In two experiments, rats were shaped to respond on a progressive ratio (PR) schedule for sucrose solution (20% w/v; Experiment 1) or a fixed ratio 2 (FR2) schedule for a moderately reinforcing visual stimulus (VS; Experiment 2). Pretreatment with various doses of caffeine (0–50 mg/kg, intraperitoneal injection) were administered prior to tests over successive week days (M-F). In Experiment 1, acute administration of low-moderate caffeine doses (6.25–25 mg/kg) increased responding for sucrose under the PR schedule. This effect of caffeine declined over the initial 15 test days. In Experiment 2, only acute pretreatment with 12.5 mg/kg caffeine increased responding for the visual stimulus and complete tolerance to this effect of caffeine was observed over the 15 days of testing. In follow up tests we found that abstinence periods of 4 and 8 days resulted in incomplete recovery of the enhancing effects of caffeine. CONCLUSION The findings suggest that caffeine enhances the reinforcing effects of non-drug stimuli, but that the pharmacological profile of these effects may differ from other psychomotor stimulants.

Influence of reinforcer magnitude and nicotine amount on smoking's acute reinforcement enhancing effects

“…Studies should continue examining potential mechanisms, such as relating changes in brain activation due to acute nicotine to its reinforcement enhancing effects (e.g., Klinkenberg et al 2013; Paterson, 2009; Wise, 1998). Finally, reinforcement enhancing effects of other drugs of abuse warrant study as they may very well be similar to those observed here with nicotine via smoking (e.g., Lloyd et al, 2012; Sheppard et al, 2012). …”

Sex differences in attenuation of nicotine reinstatement after individual and combined treatments of progesterone and varenicline

“…This hypothesis is supported by findings showing that caffeine produced nicotine-like discriminative stimulus effects in a substitution task [63]. The interaction between caffeine, nicotine and nicotine-associated cues on relapse to nicotine use is important to our understanding of factors that maintain nicotine and tobacco use in humans; however, further exploration is needed the given conditioned reinforcement-enhancement effects of both drugs and the high rate of NIC and CAF co-use [62,64]. …”

Potential sex differences in the pattern of sensory reinforcers enhanced by nicotine.

“…Cousins, Stamat, & deWit, 2001). Finally, although we confirmed overnight smoking abstinence and ad lib exposure prior to sessions, we did not biochemically assess other potential recent drug use, which could possibly affect responding for rewards (e.g., Sheppard et al 2012). …”