CONTACT BETWEEN IDENTIFIED LEECH NEURONS IN CULTURE PREVENTS RETRACTION OF NEURITES FOLLOWING ELECTRICAL-ACTIVITY

Neurites of individual leech neurones in culture retract in response t o electrical stimulation or K+ depolarisation. The aim of these experi ments was to assess whether retraction of neurites is prevented by the establishment of cell-cell contacts. Retzius and anterior pagoda (AP) cells were isolated from leech ganglia and plated either as single ce lls or in pairs. A profusion of well-developed neurites was observed a fter 5-9 days in culture on laminin-rich leech extracellular matrix ex tract. Brief trains of action potentials in single cells caused neurit es to retract reversibly hy approximately 26 % of their average length , confirming and extending earlier results. In contrast, retraction af ter stimulation was significantly decreased in cultures of paired cell s that had formed synapses or contacts between their processes. Even f ree neurites that had not made contact failed to retract; many neurite s continued to elongate during and after electrical stimulation. These results indicate that the retraction of neurites induced by electrica l stimulation is prevented by the establishment of intercellular conta cts. By stabilising the neurites of neurones contacting potential targ et cells, the search for additional targets and the strengthening of c onnections that are being made can continue in the presence of electri cal activity.