Selective formation and modulation of electrical synapses between cultured Aplysia neurons.

When dissociated neurons from the mollusc, Aplysia californica, are placed in primary cell culture, they form electrical synapses in a specific, yet alterable, manner. Pairs of neurons from the same ganglion ("homoganglionic" pairs) form electrical synapses with high coupling coefficients. This is due to relatively high macroscopic junctional conductance as determined directly by voltage clamping both neurons of each pair. By contrast, synapses between pairs of neurons from different ganglia ("heteroganglionic" pairs) exhibit lower coupling coefficients as a result of lower macroscopic junctional conductance. Both types of junction are nonrectifying, not gated by voltage, and resistant to uncoupling by octanol and heptanol. This dichotomy of synaptic efficacy is altered upon exposure of the neurons to the lectin, conacanavalin A (Con A). Acute treatment of heteroganglionic cell pairs with Con A increases their junctional conductance to the higher level characteristic of homoganglionic pairs within several hours. However, the higher junctional conductance of homoganglionic pairs is not modulated by Con A. The results presented here suggest that synaptic specificity among these regenerating neurons may be mediated at least in part by ganglion-specific cell-recognition molecules. Furthermore, these molecules may be, or may be linked to, lectin receptors that regulate gap junction channels.