Leptin immunoreactivity in the central nervous system in normal and diabetic rats.

An anti-leptin polyclonal antiserum was used to detect leptin-immunoreactivity (-ir) in the central nervous system in rats. Leptin-ir was found in perikaryon and processes of neurons in the hypothalamus, including the paraventricular nucleus, and in several regions in the brainstem, including the nucleus of the solitary tract. In streptozotocin-treated diabetic rats, leptin-ir was dramatically attenuated only in the hypothalamus, and was restored by insulin treatment. Our findings that removal or restoration of systemic insulin regulates hypothalamic leptin-ir suggests that the leptin-ir observed in the brain is sensitive to peripheral hormone status. The presence of insulin-regulated leptin in the hypothalamus reveals a new avenue of research on the central actions of leptin in regulating energy balance and metabolism.