Reward and reinforcement produced by drinking sucrose: two processes that may depend on different neurotransmitters

The capacity of sucrose drinking to produce conditioned place preference (CPP) and the effects of dopamine and opioid receptor blockade on acquisition of this preference and on sucrose consumption were evaluated. The establishment of place preference would reflect the reinforcing consequences of drinking, while the amount of sucrose solution consumed would illustrate its rewarding properties. Male Wistar rats were allowed to drink an 18% sucrose solution. No deprivation was used. Drinking produced place preference, and this was blocked with cis(z)-flupentixol, 0.5 mg/kg. Naloxone, 16 mg/kg, not only blocked place preference, but also reduced sucrose consumption. In fact, animals consumed amounts similar to those consumed by rats given plain water. Lower doses of naloxone, 1 and 4 mg/kg, also decreased sucrose consumption, but 1 mg/kg did not block place preference. As the dopamine antagonist did not affect consumption at a dose that inhibited conditioned place preference, it is suggested that dopamine is critical for the establishment of reinforcement produced by sucrose. Opioids seem to be more important for the rewarding effect because naloxone reduces drinking even at a dose that does not affect place preference.