Neuropeptide Y (NPY), synthesized in the arcuate nucleus of the hypothalamus, is one of the most potent orexigenic neuropeptides in the brain. The NPY neurons project to other hypothalamic nuclei, such as paraventricular nucleus (PVN), and it is reported that NPY contents in the PVN, but not NPY mRNA levels in the arcuate nucleus, decreased rapidly after food consumption. While many signals reflecting energy balance in the periphery are integrated at the NPY neurons, insulin has been implicated as one of the key regulators for NPY neurons. In the present study, we first examined whether there exist dynamic changes in NPY gene transcription in the arcuate nucleus in association with food intake in rats which had access to food only 4 h a day. To detect possible changes in NPY gene transcription, we measured the expression levels of NPY heteronuclear (hn) RNA, a sensitive indicator of gene transcription, with intronic in situ hybridization. Our data showed that NPY hnRNA levels in the arcuate nucleus decreased rapidly after food consumption. We next examined whether postprandial increases in insulin release might contribute to the rapid downregulation of NPY gene transcription. To do so, insulin-deficient rats by streptozotocin injection were subjected to the same paradigm. Our data showed that NPY hnRNA levels also decreased rapidly after food consumption, suggesting that the postprandial increase in insulin release is not a prerequisite for the rapid downregulation of NPY gene transcription in the arcuate nucleus.
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