Journal of Neuroscience, Vol 4, 228-233, Copyright © 1984 by Society for Neuroscience
Chemical and electrotonic connections between Aplysia neurons in primary culture
R Bodmer, D Dagan and IB Levitan
Dissociated Aplysia neurons will regenerate neurites and form functional
connections in primary cell cultures. The specificity of intercellular
connectivity in these cultures was investigated by coculturing
neurosecretory bag cells with neurons dissociated from the buccal ganglion.
It was found that bag-bag and buccal-buccal electrotonic synapses form with
high frequency, consistent with previous findings in pure bag and buccal
cultures. There is specificity in the formation of these connections, since
no bag-buccal electrotonic synapses were observed. Chemical interactions,
on the other hand, are present between bag and buccal neurons. In a
buccal-bag pair, injection of sufficient depolarizing current into the
buccal cell to elicit a train of action potentials leads to a slow
hyperpolarizing response in the bag cell. The bag cell hyperpolarization is
accompanied by an increase in the cell's input conductance. This connection
appears to be unidirectional, produces a voltage shift in the bag cell
which is opposite in sign to that in the buccal cell, and is blocked by the
removal of Ca2+ from the extracellular medium, indicating that it is
mediated by a chemical neurotransmitter. The selective formation of
electrotonic synapses in these mixed bag-buccal cultures, together with the
presence of chemically mediated interactions, make this system particularly
useful for investigating the establishment of intercellular connectivity.