Virus-assisted mapping of neural inputs to a feeding center in the hypothalamus

We report the development of a pseudorabies virus that can be used for retr ograde tracing from selected neurons. This virus encodes a green fluorescen t protein marker and replicates only in neurons that express the Cre recomb inase and in neurons in synaptic contact with the originally infected cells . The virus was injected into the arcuate nucleus of mice that express Cre only in those neurons that express neuropeptide Y or the leptin receptor. S ectioning of the brains revealed that these neurons receive inputs from neu rons in other regions of the hypothalamus, as well as the amygdala, cortex, and other brain regions. These data suggest that higher cortical centers m odulate leptin signaling in the hypothalamus. This method of neural tracing may prove useful in studies of other complex neural circuits.