Neuropeptide-Y (NPY) is a 36-amino acid Cterminally amidated peptide found within the hypothalamus that can potently stimulate carbohydrate feeding. Moreover, the hypothalamic content of NPY can be modulated by peripheral metabolic status. To further evaluate the regulation of NPY synthesis in states of altered metabolic homeostasis, we measured the hypothalamic content of prepro-NPY mRNA in streptozocin (STZ)-diabetic, STZ-diabetic insulin-replaced, and control rats by both nuclease protection and in situ hybridization analyses. Adult male Sprague-Dawley rats received a single injection of STZ (100 mg/kg, ip) or citric acid (control). Beginning 72 h later one group of STZ-treated animals received daily injections of insulin (4 U Ultralente/day). All animals were killed 17-19 days after STZ or control treatment. STZ-treated animals were hyperglycernic and showed growth failure compared to control rats. Glycemic control was restored by insulin replacement, as was partial growth. Nuclease protection analysis revealed an approximately 3- to 4-fold increase in prepro-NPY mRNA levels in the samples from STZ-treated rats vs. control. This increase was returned to control values by insulin replacement. In situ hybridization analysis revealed the STZ-induced increase in hypothalamic prepro-NPY mRNA was detectable in the arcuate nucleus at levels that were in agreement with the nuclease protection results, but that NPY expression in other brain regions appeared to be either unaffected or decreased after STZ treatment. These data suggest that hypothalamic NPY expression is modulated by peripheral metabolic status and provide further explanation for the hyperphagia accompanying STZ-induced diabetes.