Drinking, but not feeding, is opiate-sensitive in hamsters

Area of Science:

• Neuroscience
• Behavioral Pharmacology
• Comparative Physiology

Background:

• Endogenous opioids play a role in regulating consummatory behaviors.
• Naltrexone (NTX) is a long-lasting opiate antagonist used to study these roles.
• Species differences in opioid system involvement are not fully understood.

Purpose of the Study:

• To investigate the effects of naltrexone (NTX) on feeding and drinking behaviors in male golden hamsters and rats.
• To explore potential species-specific differences in the involvement of endogenous opioids in consummatory behaviors.

Main Methods:

• Administration of naltrexone (NTX) at various doses to hamsters and rats.
• Assessment of food and water intake following NTX administration.
• Evaluation of feeding responses to insulin, food deprivation, and 2-deoxy-D-glucose (2-DG).
• Assessment of drinking responses to water deprivation and hypertonic saline injection.
• Administration of dexamethasone (DEX) to assess its effects on hamster intake.

Main Results:

• Naltrexone (NTX) significantly decreased 24-hour food and water intake in rats, but not in hamsters.
• Hamsters showed a minimal night-to-day feeding ratio compared to rats.
• Naltrexone (NTX) attenuated hamster drinking induced by water deprivation or hypertonic saline.
• Dexamethasone (DEX) had no effect on daily hamster intake, unlike in rats.

Conclusions:

• Hamsters appear to lack an opiate-sensitive feeding system, unlike rats.
• Stimulated drinking behavior in hamsters is mediated by an opiate-sensitive mechanism.
• Significant species differences exist in the role of endogenous opioids in regulating consummatory behaviors.