This study investigates the effects of leptin on food intake and energy balance in normal rats, focusing on its action in the hypothalamus. Leptin, a hormone produced by fat cells, is known to regulate body weight and food intake by acting in the hypothalamus. The study used intracerebroventricular (icv) administration of leptin in Long-Evans rats to determine its effects on food intake and hypothalamic neuropeptide gene expression. Leptin administration significantly reduced food intake in rats, with a 50% reduction at 1 hour and 42% at 4 hours compared to vehicle-treated controls. The study also examined the effects of leptin on the expression of neuropeptide Y (NPY) and corticotrophin-releasing hormone (CRH) in the hypothalamus. Leptin decreased NPY mRNA levels in the arcuate nucleus by 24% and increased CRH mRNA levels in the paraventricular nucleus by 38%, suggesting that leptin alters the expression of key neuropeptide genes in the hypothalamus. The study also examined the expression of the leptin receptor gene in the brain. Leptin receptor mRNA was densely concentrated in the arcuate nucleus, with lower levels present in other brain areas involved in energy balance. These findings suggest that leptin acts in the hypothalamus by altering the expression of key neuropeptide genes, which may be involved in the hypothalamic response to fasting. The study also examined the effects of leptin in fasted rats and found that leptin administration increased hypothalamic CRH mRNA levels and decreased NPY mRNA levels, leading to an attenuated feeding response. These results support the hypothesis that leptin acts directly on hypothalamic neurons to induce changes in neuropeptide gene expression. The study concludes that leptin acts in the hypothalamus to regulate food intake and energy balance by altering the expression of key neuropeptide genes. These findings suggest that leptin plays a role in the hypothalamic response to fasting and may be an important component of the body's response to energy depletion.This study investigates the effects of leptin on food intake and energy balance in normal rats, focusing on its action in the hypothalamus. Leptin, a hormone produced by fat cells, is known to regulate body weight and food intake by acting in the hypothalamus. The study used intracerebroventricular (icv) administration of leptin in Long-Evans rats to determine its effects on food intake and hypothalamic neuropeptide gene expression. Leptin administration significantly reduced food intake in rats, with a 50% reduction at 1 hour and 42% at 4 hours compared to vehicle-treated controls. The study also examined the effects of leptin on the expression of neuropeptide Y (NPY) and corticotrophin-releasing hormone (CRH) in the hypothalamus. Leptin decreased NPY mRNA levels in the arcuate nucleus by 24% and increased CRH mRNA levels in the paraventricular nucleus by 38%, suggesting that leptin alters the expression of key neuropeptide genes in the hypothalamus. The study also examined the expression of the leptin receptor gene in the brain. Leptin receptor mRNA was densely concentrated in the arcuate nucleus, with lower levels present in other brain areas involved in energy balance. These findings suggest that leptin acts in the hypothalamus by altering the expression of key neuropeptide genes, which may be involved in the hypothalamic response to fasting. The study also examined the effects of leptin in fasted rats and found that leptin administration increased hypothalamic CRH mRNA levels and decreased NPY mRNA levels, leading to an attenuated feeding response. These results support the hypothesis that leptin acts directly on hypothalamic neurons to induce changes in neuropeptide gene expression. The study concludes that leptin acts in the hypothalamus to regulate food intake and energy balance by altering the expression of key neuropeptide genes. These findings suggest that leptin plays a role in the hypothalamic response to fasting and may be an important component of the body's response to energy depletion.