SYP and infection: To this end, we labeled the synaptic terminals of c-MafEX neurons with the fusion protein synaptophysin-mCherry while spinoparabrachial neurons (and potentially fibers of passage46) were labeled from the (contra-)lateral parabrachial nucleus (LPb) using a rAAV2-retro-CAG-eGFP, a serotype that was specifically developed for improved axon terminal infection and retrograde transduction47 (Figure 7J).