CCK and viral infectious disease: To identify upstream CCKergic inputs to the PVN and visualize the range of viral infection, we injected a mixture of retrograde viral tracer (AAV2-Retro-DIO-EYFP, hereafter referred to as AAV2-Retro) and CTB 555 into the PVN of knock-in mice expressing Cre recombinase at the CCK Locus (Cck-ires-cre, referred to as Cck-cre hereafter; Figure 1A).