Formation of Neuromuscular Junctions and Synthesis of Sensory Neuropeptides in the Co-cultures of Dorsal Root Ganglion and Cardiac Myocytes

Aim The interactions between primary sensory neurons and cardiac myocytes are still unclear. In the present study, the co-culture model of dorsal root ganglion (DRG) explant and cardiac myocytes was used to characterize the morphological relationship between primary sensory nerve endings and cardiac myocytes and to investigate whether cardiac myocytes could induce substance P (SP) and calcitonin gene-related peptide (CGRP) synthesis in DRG neurons and release from DRG neurons in the neuromuscular co-cultures. Methods The formation of neuromuscular junctions was observed with scanning electron microscopy (SEM). SP and CGRP expression were detected by immunocytochemistry. Basal SP and CGRP release and capsaicin-evoked SP and CGRP release were analyzed by radioimmunoassay (RIA). Results In this study, neuromuscular junctions were observed in the co-cultures of DRG explant and cardiac myocytes. SP-immunoreactive (IR) and CGRP-IR neurons were detected in both neuromuscular co-cultures and DRG explant cultures, but the number of SP-IR and CGRP-IR neurons migrating from DRG explant was significantly increased in neuromuscular co-cultures. Capsaicin-evoked SP and CGRP release but not basal SP and CGRP release in neuromuscular co-cultures increased significantly as compared with that in the cultures of DRG explant alone. Conclusions The results implicated that the morphological relationship between sensory nerve terminal and cardiac myocyte is much more close in vitro than it is in vivo. Cardiac myocytes may induce sensory neuropeptide synthesis and capsaicin-evoked neuropeptide release in neuromuscular co-cultures. Further experiment needs to be performed about the significance of neuropeptide synthesis and capsaicin-evoked neuropeptide release induced by target cardiac myocytes. Zhen Liu and Huaxiang Liu contributed equally to this article.