Leptin modulates behavioral responses to sweet substances by influencing peripheral taste structures.
Leptin is a hormone that regulates body weight homeostasis mainly via the hypothalamic functional leptin receptor Ob-Rb. Recently, we proposed that the taste organ is a new peripheral target for leptin. Leptin selectively inhibits mouse taste cell responses to sweet substances and thereby may act as a sweet taste modulator. The present study further investigated leptin action on the taste system by examining expression of Ob-Rb in taste cells and behavioral responses to sweet substances in leptin-deficient ob/ob, and Ob-Rb-deficient db/db mice and their normal litter mates. RT-PCR analysis showed that Ob-Rb was expressed in taste cells in all strains tested. The db/db mice, however, had a RT-PCR product containing an abnormal db insertion that leads to an impaired shorter intracellular domain. In situ hybridization analysis showed that the hybridization signals for normal Ob-Rb mRNA were detected in taste cells in lean and ob/ob mice but not in db/db mice. Two different behavioral tests, one using sweet-bitter mixtures as taste stimuli and the other a conditioned taste aversion paradigm, demonstrated that responses to sucrose and saccharin were significantly decreased after ip injection of leptin in ob/ob and normal littermates, but not in db/db mice. These results suggest that leptin suppresses behavioral responses to sweet substances through its action on Ob-Rb in taste cells. Such taste modulation by leptin may be involved in regulation for food intake.
Section of Oral Neuroscience, Graduate School of Dental Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Noriatsu
N
Shigemura
Rie
R
Ohta
Yuko
Y
Kusakabe
Hirohito
H
Miura
Akihiro
A
Hino
Kiyoshi
K
Koyano
Kiyohito
K
Nakashima
Yuzo
Y
Ninomiya
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D003920:Diabetes Mellitus; D005260:Female; D015870:Gene Expression; D017403:In Situ Hybridization; D020738:Leptin / Q000172:deficiency / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008820:Mice, Obese; D012333:RNA, Messenger / Q000032:analysis; D011956:Receptors, Cell Surface / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D054411:Receptors, Leptin; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012439:Saccharin; D013395:Sucrose; D013649:Taste / Q000187:drug effects*; D013650:Taste Buds / Q000737:chemistry*
D020738:Leptin; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; C515447:leptin receptor, mouse; D013395:Sucrose; D012439:Saccharin