title: Effects of taste stimulation on beta-endorphin levels in rat cerebrospinal fluid and plasma.
abstract: Opioids are suggested to be involved in generation of palatability and facilitation of consumption of food and fluid. We measured the level of an endogenous opioid, beta-endorphin, in the cerebrospinal fluid (CSF) and plasma after free drinking of water and taste solutions in Wistar rats. When the water-deprived animals were allowed to drink 10 mL of water, the level of beta-endorphin increased significantly 60 and 90 min after the start of drinking in both samples. beta-Endorphin in the CSF increased most after ingestion of 0.5 M sucrose and 0.005 M saccharin followed by 0.1 M NaCl, 0.1 mM quinine and water. An intragastric infusion of 7 mL of water did not change the beta-endorphin level. Essentially the same results were obtained for plasma samples except that NaCl and quinine solutions did not increase beta-endorphin levels. Sucrose became ineffective in releasing beta-endorphin in both samples after the establishment of conditioned taste aversions to this taste stimulus. These results suggest that the release of beta-endorphin is positively correlated with the palatability of taste stimuli, and that CSF beta-endorphin also reflects the reinforcement of fluid intake in thirsty animals.
authors.affiliation: Department of Behavioral Physiology, Faculty of Human Sciences, Osaka University, 565-0871, Osaka, Japan. yamamoto@hus.osaka-u.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Yamamoto
authors.forename: N
authors.initials: N
authors.lastname: Sako
authors.forename: S
authors.initials: S
authors.lastname: Maeda
mesh_terms: D000818:Animals; D003216:Conditioning, Operant / Q000502:physiology; D007441:Intubation, Gastrointestinal; D008297:Male; D009475:Neurons, Afferent / Q000502:physiology; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D013649:Taste / Q000502:physiology*; D013997:Time Factors; D001615:beta-Endorphin / Q000097:blood / Q000134:cerebrospinal fluid / Q000378:metabolism*
chemical_list: D001615:beta-Endorphin