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Electrical synapses are formed by two unrelated gap junction protein families, the primordial innexins (invertebrates) or the connexins (vertebrates). Although molecularly different, innexin- and connexin-based electrical synapses are strikingly similar in their membrane topology. However, it remains unclear if this similarity extends also to more sophisticated functions such as long-term potentiation which is only known in connexin-based synapses. Here we show that this capacity is not unique to connexin-based synapses. Using a method that allowed us to quantitatively measure gap-junction conductance we provide the first and unequivocal evidence of long-term potentiation in an innexin-based electrical synapse. Our findings suggest that long-term potentiation is a property that has likely existed already in ancestral gap junctions. They therefore could provide a highly potent system to dissect shared molecular mechanisms of electrical synapse plasticity.

Finding compounds that affect neuronal function is central for the development of probes or potential therapeutic agents. We have devised an efficacious approach that allows the “unbiased” screening for biological activity of compounds in vivo against molecular targets on various types of neurons with cholinergic, glutamatergic or electrical synapses and muscles. For this, we use the Giant Fiber System, which is a simple neuronal circuit that mediates the escape response in the fly. The giant fiber cell bodies and dendrites are localized in the brain and each extends a single axon into the second thoracic neuromere, where it makes a mixed electrical (GAP junctions) and chemical (ACh neurotransmitter) synapse on the tergo trochanteral motorneuron, which further innervates the jump muscle. The GF also connects to a peripheral synapsing interneuron (PSI), which makes a cholinergic synapse onto the dorsal longitudinal motorneurons (DLM). Both the TTM and the DLM neuromuscular junctions are using glutamate as the neurotransmitter. Here, we show that we are able to routinely screen components of the venom of cone snails by injecting then into the fly while continuing the recordings from GF circuit allowing us to instantly determine whether a compound has an effect on neurons or muscles of this neuronal circuit. Components of the venom of cone snails have been shown to elicit a wide range of physiological effects and are well-established neuronal probes or drug-lead candidates. The use of the tiny drosophila (a model organism) to evaluate the activity of conotoxins represents an efficacious in vivo assay that can be expanded to evaluate other compounds.

Summary Some electrical synapses rectify — they pass current preferentially in one direction. A new study argues that rectifying junctions result when the two sides of the junction contribute hemichannels with different properties to the gap junction.

The morphology of the amphibian papilla in the bullfrog has been studied with light and electron microscopy. The hair cells in the amphibian papilla are equipped with sensory hairs, one of which is a kinocilium. The orientation of the kinocilium varies in a complicated way along the sensory epithelium. At their basal ends, the hair cells are contacted by two types of nerve endings, morphologically identified as afferent‐ and efferent‐type terminals. Efferent‐type endings are more abundant in the broader anterior portion of the sensory epithelium than in the posterior portion. In the middle portion, tight junctions have been found between axons within the epithelium. In some cases, one of these axons could be traced to an afferent‐nerve ending. Tight junctions between neurons have been shown in a number of other systems to represent electrical synapses that transmit impulses with short delay.