Collateral sprouting from sensory and motor axons into an end to side attached nerve segment

A nerve segment, sutured end-to-side (ETS) to an intact rat sciatic nerve, becomes invaded by regenerating axons. The origin of these fibres is controversial: it is debated whether or not they represent collateral sprouts from intact axons. Here we demonstrate by double retrograde tracing, using one tracer for the ETS attached segment and another for the sciatic nerve proper double-labelled sensory neurons in 67% of the rats receiving an ETS segments. Double-labelled motor neurons were observed in 11% of the rats. The results show that a nerve segment attached ETS to an intact nerve can induce collateral sprouting of both sensory and motor axons although the extent of such branching may vary with the experimental conditions.