Expression of gap junctions bearing connexin-43 subunits and glial fibrillary acidic protein in the rat dorsal root ganglia following hind paw incision

Abstract

INTRODUCTIONPostoperative pain is a common form of acute pain. Pain from a surgical incision occurs at rest and is exacerbated by coughing, ambulation, and change of dressing. 1 Incisional pain in rodents allows assessment of the mechanisms responsible for increased mechanical sensitivity following a surgical incision and also to investigate novel treatments for postoperative pain. Thus, there are two types of postoperative pain, which include the evoked and non-evoked variety.Non-evoked pain is short lasting, moderate and is the ongoing pain at rest in the patients, which is easier to treat and better relieved by analgesic agents. Evoked pain is intense, long lasting and related to coughing, ambulation, and other related activities.2 The dorsal root ganglia (DRG) play an important role in the transmission ABSTRACT Background: Dorsal root ganglion (DRG) neurons mediate the transmission of sensation from the periphery. DRG neurons are pseudounipolar in nature and enveloped by the satellite glial cells (SC). Satellite glial cells have been reported to influence neuronal excitability via gap junctions. Postoperative pain causes induction of various neurotransmitters such as connexin-43 and glial fibrillary acidic protein (GFAP), in the satellite cells surrounding neuronal cell bodies Objective: To study the expression of connexin-43 and Glial fibrillary acidic protein after hind paw incision. Methods: Male adult Sprague-Dawley rats (n=12) were used. Rats were randomly divided into two groups. Group I (n=6) and Group II (n=6) for immunohistochemical study with glial fibrillary acidic protein (GFAP) and connexin-43 (Cx-43) respectively. In this study, rats were subjected to noxious stimuli on the right hind paw under general anesthesia. Dorsal root ganglia of both sides (L4 spinal nerves) were isolated after transcardiac fixation with 4% paraformaldehyde. The ganglia from the non-incised side were taken as the control group. Results: Unipolar neurons in the DRG were surrounded by satellite cells. The satellite cells were positive for GFAP, which showed increased expression on the surgical side after noxious stimuli. Cx-43 immunostaining also showed an increased expression in the periphery of neuronal cell bodies of surgical side representing the location of gap junctions and hyperexcitability of neurons. Conclusions: Small to medium sized neurons carry pain sensation from the periphery to the central nervous system. Increased gap junctions were noted in small neurons and satellite cells after surgery. Gap junctions might contribute to increased excitability of small neurons in postoperative pain.