Reward without dopamine

Area of Science:

• Neuroscience
• Behavioral Science
• Pharmacology

Background:

• Dopamine (DA) is widely implicated in reward processing.
• Natural rewards like food and sexual interaction activate dopaminergic systems.
• Sweet tastes are a well-characterized natural reward.

Purpose of the Study:

• To test the hypothesis that dopamine (DA) is necessary for reward.
• To investigate the role of DA in the reward processes associated with sweet tastes.

Main Methods:

• Experiments were conducted using mice genetically engineered to lack dopamine production (DD mice).
• Sucrose preference was assessed using a computerized lickometer to measure responses to rewarding stimuli.
• Behavioral analyses included licking rate, bout size, total licks, and initiation frequency.

Main Results:

• DD mice demonstrated a clear preference for sucrose over water and also preferred saccharin.
• Licking rate, bout size, and bout length were significantly higher in DD mice consuming sweets compared to controls.
• Despite preference, DD mice initiated licking less frequently and had fewer total licks, suggesting a goal-directed behavior deficit.
• Juvenile DD mice showed robust sucrose preference even before experiencing food in the presence of DA.

Conclusions:

• Dopamine (DA) is not required for mice to find the sweet tastes of sucrose or saccharin rewarding.
• The study refutes the necessity of DA for reward processes manifested by sucrose preference.
• DD mice exhibit deficits in goal-directed behavior not specific to reward.