Longitudinal directional movement of Alcian blue in Gephyrocharax Melanocheir fish: Revealing interstitial flow and related structure

Abstract

BackgroundObserving interstitial fluid (ISF) is very difficult because interstitial structure collapses and ISF disappears after tissue fixation. Additionally, ISF is colorless, and interstitial flow is weak in vivo. In order to view the interstitial flow, special dye and animal model was chosen to explore the movement characteristic of interstitial flow and related structure. MethodsThe Gephyrocharax Melanocheir (GM) fish, a special animal with translucent body, were placed into 0.03 g/L tricain solution for anesthesia. 20–25 µL Alcian blue (AB) solution which can stain acid mucopolysaccharide immobilized by the collagen net in connective tissue was injected into each fish at a single point with a rate of 2 µL/min via a micro-injection pump. The process of infusion and the movement of the AB in fish were record by a digital camera. The (fresh) frozen sections of AB tracks tissue were performed to observe the morphological feature. ResultsSeveral blue tracks were observed which were formed by longitudinal directional movements of AB solution. For back lateral track, the velocity and length of the movements were significantly fast and longer on the direction toward head than that toward tail (P < 0.01). For lateral middle track, the result was opposite, namely toward tail (P < 0.01). This phenomenon indicated an inherent ISF flow according to Darcy's law. Morphological study showed these tracks were just in septa composed by connective tissue. The stained blue septa formed various shapes as interstitial space for ISF flow and connected with one another like a net. The finding can help us to understand the essence of meridian in traditional Chinese medicine (TCM). ConclusionsThe dynamic asymmetry of the AB tracks revealed interstitial flow in the GM fish body. It implied an inherent interstitial flow along particular pathway formed by septa which may be a key to understand the nature and value of meridians and collaterals in health care.