Leptin directly suppresses the activity of orexigenic neurons in the hypothalamic arcuate nucleus (ARC). We examined c-Fos-like immunoreactivity (CFLIR) as a marker of ARC neuronal activity indb/dbmice devoid of the signaling form of the leptin receptor (LRb) ands/smice that express LRbS1138[which is defective for STAT3 (signal transducer and activator of transcription) signaling]. Bothdb/dbands/sanimals are hyperphagic and obese. This analysis revealed that CFLIR in agouti related peptide-expressing orexigenic ARC neurons is basally elevated indb/dbbut nots/smice. Consistent with these observations, electrophysiologic evaluation of a small number of neurons ins/sanimals suggested that leptin appropriately suppresses the frequency of IPSCs on ARC proopiomelanocortin (POMC) neurons that are mediated by the release of GABA from orexigenic ARC neurons. CFLIR in POMC neurons ofs/smice was also increased compared withdb/dbanimals. Thus, these data suggest that, although LRb→STAT3 signaling is crucial for the regulation of feeding, it is not required for the acute or chronic regulation of orexigenic ARC neurons, and the activation of STAT3-mediated transcription by leptin is not required for the appropriate development of leptin responsiveness in these neurons.