Electrical coupling of mechanoreceptor afferents in the crayfish: a possible mechanism for enhancement of sensory signal transmission.

1. Central electrical coupling between primary afferent axons was investigated in an in vitro preparation of the crayfish thoracic locomotor system by using intracellular recordings. 2. Intracellular injection of the dye Lucifer yellow in single afferents resulted in staining of one to three additional afferents through dye-coupling. Three-dimensional confocal imaging of dye-coupled axons revealed a large zone of close apposition that may correspond to the gap junction site. 3. A depolarization preceding the spike in one sensory terminal was shown to facilitate the excitatory postsynaptic potential occurring in postsynaptic motoneurons. Further, a spike in one afferent axon can depolarize other, electrically coupled, axons above spike threshold, resulting in an increased number of active afferents. 4. The electrical coupling occurred between sensory afferents of similar function. It may therefore serve to facilitate sensory signal transmission from functionally homologous afferents onto postsynaptic target neurons.