Involvement of dopamine and opioids in the motivation to eat: influence of palatability, homeostatic state, and behavioral paradigms.
BACKGROUND
Motivation for food depends on several variables including food palatability, the homeostatic state of the organism, and the nature of the behavior required to obtain the reward. However, few studies to date have tried to evaluate motivation for food considering all these variables at the same time. Since dopamine and opioids have been deeply involved in the regulation of feeding, it is of interest to investigate their role considering all the mentioned variables.


OBJECTIVE
In this study, we evaluated the involvement of dopamine and endogenous opioids on food consumption and food motivation using behavioral paradigms that differ in the motor requirement to gain access to the reward, when food palatability and homeostatic state were taken into account.


METHODS
Pellets differentiated on palatability were offered to sated and restricted rats in consummatory tests and in different behavioral paradigms measuring motivational state, but requiring different motor outputs (runway and an operant progressive ratio 3 task). Peripheral injections of naloxone or flupenthixol were administered when these tasks were learned and stable.


RESULTS
Naloxone decreased food intake when pellets were palatable, while flupenthixol was without any effect. When considering motivation, naloxone decreased performances in both the runway and progressive ratio tests while flupenthixol was only effective in the progressive ratio test.


CONCLUSIONS
Impairing the opioid neurotransmission diminishes motivation to obtain food, possibly through a decrease in the perceived palatability of the food reward. The dopaminergic system appears to be more involved in the modulation of motivation to obtain food in a cost/benefit-related manner.
Barbano
M Flavia
MF
Group Neuropsychopharmacologie de l'addiction, Centre National de Recherche Scientifique, Unité Mixte de Recherche 5227, Universités Bordeaux 2 et Bordeaux 1, 146, rue Léo Saignat - BP 31, 33076 Bordeaux Cedex, France. fbarbano@iib.unsam.edu.ar
Le Saux
Maryvonne
M
Cador
Martine
M
D000818:Animals; D004298:Dopamine / Q000378:metabolism / Q000502:physiology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004435:Eating / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology*; D005475:Flupenthixol / Q000494:pharmacology; D005518:Food Preferences / Q000502:physiology; D006706:Homeostasis / Q000502:physiology*; D008297:Male; D009042:Motivation; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000502:physiology*
D018492:Dopamine Antagonists; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D009270:Naloxone; D005475:Flupenthixol; D004298:Dopamine