To decipher neural circuits underlying brain functions, viral tracers are widely applied to map input and output connectivity of neuronal populations. Despite the successful application of retrograde transsynaptic viruses for identifying presynaptic neurons of transduced neurons, analogous anterograde transsynaptic tools for tagging postsynaptically targeted neurons remain under development. Here, we discovered that adeno-associated viruses (AAV1 and AAV9) exhibit anterograde transsynaptic spread properties. AAV1-Cre from transduced presynaptic neurons effectively and specifically drives Cre-dependent transgene expression in selected postsynaptic neuronal targets, thus allowing axonal tracing and functional manipulations of the latter input-defined neuronal population. Its application in superior colliculus (SC) reveals that SC neuron subpopulations receiving corticocollicular projections from auditory and visual cortex specifically drive flight and freezing, two different types of defense behavior, respectively. Together with an intersectional approach, AAV-mediated anterograde transsynaptic tagging can categorize neurons by their inputs and molecular identity, and allow forward screening of distinct functional neural pathways embedded in complex brain circuits. •AAV1 and AAV9 exhibit anterograde transsynaptic spread properties•AAV1-Cre can transsynaptically tag input-defined postsynaptic neurons•Corticocollicular input-defined SC neurons mediate different defense behaviors•With an intersectional approach, the tagging can be postsynaptic cell-type specific Zingg et al. revealed anterograde transsynaptic spread properties of adeno-associated viruses. This novel viral application is useful for tracing and manipulating neural circuits in a postsynaptic cell-type- and input-specific manner, thus facilitating dissection of neural circuits underlying different behaviors.