Journal of Neuroscience, Vol 9, 2502-2508, Copyright © 1989 by Society for Neuroscience
Contact-mediated loss of the nonsynaptic response to transmitter during reinnervation of an identified leech neuron in culture
P Drapeau, E Melinyshyn and S Sanchez-Armass
McGill University Centre for Research in Neuroscience, Montreal, Quebec, Canada.
We have examined the modification of responses to transmitter during the
reformation of a specific synapse by identified leech neurons in culture.
Single pressure-sensitive mechanosensory (P) neurons in culture and the
soma of this cell in vivo have 2 conductances that are activated by
application of 5-HT: a Cl conductance and a monovalent cation conductance
(gCations); synaptic release of 5-HT by a serotoninergic Retzius cell in
vivo and in culture activates only the Cl conductance and not gCations in
the P cell. We have characterized the loss of gCations in P cells by
manipulating the culture conditions. When 5-HT was applied from a pipette,
innervated P cells and P cells paired with Retzius cells that had not
formed synapses had a gCations that was markedly reduced compared with
gCations in the single P cell. When 5-HT was included in the culture medium
in which single P cells were grown, gCations was not reduced. When
Retzius-P cell pairs were treated with reserpine, which was shown to
deplete the presynaptic neuron of 5-HT, gCations in the P cell was as low
as in untreated pairs. Pairing aldehyde-fixed Retzius cells with untreated
P cells also resulted in the loss of gCations. The Retzius cell had both
types of receptors, but synapse formation did not affect gCations in the
presynaptic neuron. The results demonstrate that the loss of the
nonsynaptic response of the P cell to transmitter is due to contact between
the neurons rather than to the release of transmitter or trophic
factors.(ABSTRACT TRUNCATED AT 250 WORDS)