When as little as five micrograms of Neuropeptide Y (NPY) are infused into the third ventricle of a rat, that rat will eat five times more than a normal amount of food over the subsequent two hours. An effective technique to confirm that leptin specifically acts upon NPY-containing neurons to depress feeding is to infuse the hypothalamus with a NPY linked to saporin. Rats treated with NPY-SAP become completely insensitive to the feeding-restraining effects of leptin because they lack NPY receptor-containing neurons in the arcuate nucleus. Results indicate that NPY-SAP binds to and has a higher binding affinity than NPY for the NPY receptor (Figure).1,2
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