Cellular and molecular approaches to neural repair in the medicinal leech

Investigation of repair processes and the effects of damage in the leech has the advantage that it is possible to work with single neurons, and that leech neurons can regenerate. The effects of surface topology on neuronal outgrowth in culture were investigated using patterned substrates produced by photolithography. On grooved substrates with a depth, width and separation of 2 microns, the processes of cultured neurons showed significant alignment. In studies on regeneration, different mechanosensory neurons were shown to respond differently to lesions of their axons. High threshold units (N cells) respond by sprouting of additional processes from the axon hillock region within the CNS, whereas low threshold cells respond with a sprouting only at the lesion site in the nerve root and not within the CNS. Sprouted processes are retained for over a year. When a neuron of a particular modality is killed, cells of the same modality (but not the other) expand their receptive fields to cover the denervated skin. Single channel patch clamp recording experiments have been initiated on damaged neurons. Experiments are in progress to clone genes whose expression is regulated after peripheral nerve injury.