Yamamoto T, Sako N, Maeda S. Effects of taste stimulation on beta-endorphin levels in rat cerebrospinal fluid and plasma.
Physiol Behav 2000;
69:345-50. [PMID:
10869601 DOI:
10.1016/s0031-9384(99)00252-8]
[Citation(s) in RCA: 73] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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.
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