Regeneration and plasticity of neuronal connections in the leech

Although most studies have analysed regeneration at the cell-population level, in many species, including mammals, individual neurons can regenerate selective connections. In order to examine the specificity of regeneration at the level of connections between single neurons attention has turned to invertebrates with their simpler, experimentally more accessible nervous systems. The medicinal leech, once an indispensable part of the medical armoury, possesses a nervous system which has proved particularly useful for studies on recovery from nerve injury. Not only can individual regenerating neurons and their targets be identified in this animal, but it is also possible to manipulate various cellular elements of the system and directly test what stimulates axons to grow and regenerate connections.