The response of the murine sensory nervous system to augmented levels of colonic nerve growth factor
Armitage, Michael Norman
MetadataShow full item record
The primary goal of this research is to understand the response of the tyrosine receptor kinase A (trkA)-expressing cells of the myenteric plexus, and dorsal root ganglia (DRG) to augmented levels of nerve growth factor (NGF) within the descending colon. Using lines of transgenic mice that express enhanced green fluorescent protein (EGFP) under the control of the NGF promoter, we found a subpopulation of adendritic EGFP+ neurons in the myenteric plexus. These colonic EGFP+ neurons display positive immunostaining for calretinin but not nitric oxide synthase 1, (NOS1), two biomarkers of mouse myenteric neurons. Induction of colonic inflammation confirms local increases in NGF mRNA/protein levels, which coincide with heightened detection of EGFP by myenteric neurons. Though NOS1+ myenteric neurons display positive immunostaining for trkA (the receptor required for NGF binding/signalling), transgenic overexpression of NGF by smooth muscle cells in the colon does not alter the survival, somal size, or axonal density of trkA-expressing NOS1+ myenteric neurons. Mice lacking functional p75NTR (the second receptor required for NGF binding) exhibit significantly less axonal damage among NOS1+ myenteric neurons, in response to chemically induced colonic inflammation. Likewise, trkA-expressing sympathetic axons that innervate the myenteric ganglia display less damage in the absence of p75NTR. Immunostaining of the lumbar DRG of mice with DSS-induced colitis for ionized calcium-binding adapter molecule 1 (Iba1) shows reactivity of Iba1+, macrophage-like cells. Using two-dimensional polyacrylamide gel electrophoresis (2DPAGE) coupled with Matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) several increases in protein expression were found in the lumbar DRG of mice with DSS-induced colitis.