Abstract
Leptin, released from adipose tissue, is known to inhibit obesity by regulating food intake. Our recent studies have revealed taste nerve fibers in the mouth which respond to long-chain fatty acids. In this study, we investigated the effect of leptin on taste responses, particularly on the responses to fatty acid (oleic acid) and sweet substances (sucrose) in fatty and normal Wistar rats. The nerve activities were recorded from the whole nerve bundle or pauci-fiber bundles of the pharyngeal branch of the glossopharyngeal nerve (GP nerve) and the chorda tympani nerve (CT nerve). Oleic acid was applied to the pharyngolaryngeal region and sucrose was applied to the anterior part of the tongue. Oleic acid elicited vigorous discharges in the pharyngeal branch of the GP nerve in both fatty and normal Wistar rats. After intravenous administration of leptin (10 ng/ml, 3 ml/kg), the response to oleic acid was gradually decreased in normal rats, whereas the response in fatty rats was not changed. The response to sucrose in the CT nerve was also decreased by leptin in normal rats, but it was not changed in fatty rats. These results are the first findings indicating the existence of a leptin-suppression-system on the taste response to fatty acids and sweet substances in normal Wistar rats, and suggesting that such systems are lacking in fatty Wistar rats. [Jpn J Physiol 54 Suppl:S176 (2004)]
