Detection of Mitotic Neuroblasts Provides Additional Evidence of Steady-State Neurogenesis in the Adult Small Intestinal Myenteric Plexus.

Abstract

Maintenance of normal structure of the enteric nervous system (ENS), which regulates key gastrointestinal functions, requires robust homeostatic mechanisms, since by virtue of its location within the gut wall, the ENS is subject to constant mechanical, chemical, and biological stressors. Using transgenic and thymidine analog-based experiments, we previously discovered that neuronal turnover-where continual neurogenesis offsets ongoing neuronal loss at steady state-represents one such mechanism. Although other studies confirmed that neuronal death continues into adulthood in the myenteric plexus of the ENS, the complicated nature of thymidine analog presents challenges in substantiating the occurrence of adult neurogenesis. Therefore, it is vital to employ alternative, well-recognized techniques to substantiate the existence of adult enteric neurogenesis in the healthy gut. Here, by using established methods of assessing nuclear DNA content and detecting known mitotic marker phosphor-histone H3 (pH3) in Hu⁺ adult ENS cells, we show that ∼10% of adult small intestinal myenteric Hu⁺ cells in mice and ∼20% of adult human small intestinal myenteric Hu⁺ cells show evidence of mitosis and hence are cycling neuroblasts. We observe that proportions of Hu⁺ cycling neuroblasts in the adult murine ENS neither vary with ganglionic size nor do they differ significantly between two intestinal regions, duodenum and ileum, or between sexes. Confocal microscopy provides further evidence of cytokinesis in Hu⁺ cells. The presence of a significant population of cycling neuroblasts in adult ENS provides further evidence of steady-state neurogenesis in the adult ENS.