Basic NeuroscienceA novel, highly sensitive method for assessing gap junctional coupling

•Serotonin has significant advantages over neurobiotin as an indicator of gap junctional intercellular communication.•Serotonin is more sensitive than neurobiotin in microinjection studies.•Serotonin loading can be accomplished in a non-invasive manner by transfection with cDNA encoding a transporter.

To assess gap junctional intercellular communication we have developed a tracer-based methodology which is both highly sensitive and potentially adaptable for in vivo measurements. We found that injection of serotonin revealed significantly more intercellular communication than that injection of the most permeant synthetic tracer currently in use, neurobiotin. Furthermore, mechanical tracer loading steps can be replaced by transfection with human serotonin transporter and the inclusion of serotonin in the medium. Tracer and transporter are detected using immunocytochemical techniques and the presence of cells that are tracer-positive but transporter-negative indicates junctional communication. Tracer loading in vivo using transgenesis, electroporation or viral transduction to direct expression of transporter should be more easily accomplished than with mechanical loading methods.