Myenteric Dogiel Ii Neurons Express Nerve Growth Factor

We have generated lines of transgenic mice that express enhanced green fluorescent protein (EGFP) under the control of the murine nerve growth factor (NGF) promoter. These mice afford us unique temporal and spatial insight into those cellular populations that display NGF promoter activity from early mammalian embryogenesis to adulthood. These mice also offer us the opportunity to assess those cells that express NGF promoter activity in response to injury and/or disease. We have made particular note of a population of EGFP‐positive cells in the colon of these transgenic mice. In adult animals, these EGFP‐positive neurons can be unequivocally identified as a population residing within the myenteric plexus. These neurons have large smooth cell bodies, with two or three axonal processes that give rise to a dense plexus of fibers within the enteric ganglia (these axonal plexuses are also visualized by EGFP). Based on these anatomical features, we have speculated that these EGFP‐positive neurons are primary afferent (or Dogiel type II) neurons. Preliminary assessments of the neurochemical features of these EGFP‐positive neurons reveal that most express the calcium‐binding protein calretinin. We will present additional data regarding the localization of other biomarkers for Dogiel type II neurons, including calcitonin gene‐related peptide. We will also show how these EGFP‐positive cells react to chemically‐induced colitis in adult mice. These data provide strong evidence that primary afferent neurons of the murine colon are a hitherto unexpected source of NGF in the normal and inflamed bowel. This work was supported by the Canadian Institutes of Health Research.