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Increased body weight gain during the juvenile period leads to early maturation of the reproductive neuroendocrine system and accelerates age at puberty. Although the mechanisms and pathways involved in this process are unclear, leptin and leptin-sensitive cells in the central nervous system may play critical roles. Leptin inhibits the expression of neuropeptide Y (NPY), an orexigenic peptide implicated in mediating the inhibitory effects of undernutrition on GnRH release. Leptin is also involved in regulating neural plasticity of hypothalamic pathways that control feed intake. In an earlier study, we observed that heifers fed to gain weight at a high rate during the juvenile period had elevated circulating concentrations of leptin and reduced NPY expression in the arcuate nucleus. In this study, we hypothesized that those nutritional regimens that accelerate the onset of puberty in heifers lead to diminished NPY …