Different effects of brain leptin, insulin, or glucose during fasting on thyroid hormone control and hunger neurons in the brain's feeding center

Continuous administration of 30 mU/d insulin or 648 microg/d glucose did not prevent fasting-induced suppression of TRH mRNA levels.

• Leptin infusion reduced fasting-induced increases in neuropeptide Y and agouti-related protein mRNA in the hypothalamic arcuate nucleus.
• Leptin increased proopiomelanocortin and cocaine and amphetamine-regulated transcript mRNA levels during fasting.
• Fasting led to decreased pro-TRH mRNA levels in the paraventricular nucleus and reduced circulating thyroid hormone levels.
• Insulin increased proopiomelanocortin mRNA and both insulin and glucose decreased neuropeptide Y mRNA, but did not affect TRH mRNA or thyroid hormone levels.
• Insulin and glucose may not be essential for the hypothalamic-pituitary-thyroid regulatory system during fasting.

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