CELL-SURFACE CONTACT MEDIATES NEURONAL RECOGNITION AND SYNAPSE FORMATION BETWEEN 2 IDENTIFIED LEECH NEURONS

An early event in the formation of the serotonergic synapse by the Ret zius (R) onto the pressure-sensitive (P) neurons of the leech is the e limination of an extrasynaptic response to transmitter from sites of c ontact on the postsynaptic cell. This event during synapse formation i s cell-specific in that it is elicited in vitro by contact with the pr esynaptic R cell but not with other neurons. In the study reported her e, we investigated the nature of this interaction between R and P neur ons. The loss of the extrasynaptic response of the P cell was elicited by contact with R cells fixed in a mild paraformaldehyde solution, bu t not by R cells treated with the proteolytic enzyme trypsin prior to fixation. As well, a variety of lectins were assayed for their ability to interfere with synapse formation. The transmitter responses of P c ells plated on lectin-coated substrates were unaffected. However, expo sure of the R cell to the lectin wheat germ agglutinin (WGA), but not to other lectins, prior to pairing prevented the loss of the extrasyna ptic response in contacted P cells and blocked the formation of the R- P synapse in culture. We conclude that recognition by the P cell of th e R cell during synapse formation may be mediated by an R cell-specifi c surface protein which binds wheat germ agglutinin. (C) 1991 John Wil ey & Sons, Inc.