SFN Poster of the Year 2009

Awarded by ATS at Society for Neuroscience (SFN) Chicago, IL • October 17-21, 2009

374.5/EE116 Leptin-saporin injection into the arcuate nucleus lesions NPY/AGRP and POMC neurons and produces hyperphagia, obesity and changes in diurnal feeding patterns in rats
A-J Li, Q Wang, T T Dinh, S Ritter
featuring IT-28 NPY-SAP; IT-47 Leptin-SAP (Poster; Monday, Oct. 19, 8:00 am – 9:00 am)

Leptin-saporin (Lep-SAP), a conjugate of leptin with a ribosomal inactivating toxin, saporin (Advanced Targeting Systems), is a novel toxin designed to destroy leptin receptor-expressing cells selectively in vitro. However, its lesioning properties in vivo are currently unknown. Here, we injected Lep-SAP into the arcuate nucleus (Arc), to examine its effects on feeding behavior and on leptin receptor-expressing NPY/AGRP and POMC neurons in this area. Immunohistochemical studies showed unilateral injection of Lep-SAP into the Arc dramatically reduced numbers of NPY-Y1- and α-MSH- positive neurons compared to the contralateral side injected with SAP control. Real-time PCR revealed only 11-21% of Agrp and Pomc expression remaining in the Arc after Lep-SAP injection into this region. Rats injected bilaterally with Lep-SAP were unresponsive to central leptin administration and showed dramatic increases in feeding, body weight and light-phase feeding, compared pre-injection baseline. Two weeks after injection, total daily feeding was increased by 75%, light phase feeding by 359% and dark phase feeding by 33%. Control SAP injections did not produce these changes. Clock gene expression in homogenates of whole hypothalamus and liver were quantified at ZT 5-7. Bmal1 expression in hypothalamus and liver of Lep-SAP rats was decreased, while hepatic Per1 expression was increased compared to control. Results demonstrate that Lep-SAP effectively lesions Arc leptin receptor-expressing NPY/AGRP and POMC neurons in vivo, and that rats with this lesion are hyperphagic and obese, possibly due to enhanced hunger drive, lack of responsiveness to leptin and/or changes in circadian control of feeding behavior.