Neuroanatomische und elektrophysiologische Grundlagen von Rückenschmerzen: Untersuchungen an Ratten

Role of nerve growth factor in pain

Nerve growth factor (NGF) was first identified as a substance that is essential for the development of nociceptive primary neurons and later found to have a role in inflammatory hyperalgesia in adults. Involvement of NGF in conditions with no apparent inflammatory signs has also been demonstrated. In this review we look at the hyperalgesic effects of exogenously injected NGF into different tissues, both human and animal, with special emphasis on the time course of these effects. The roles of NGF in inflammatory and neuropathic conditions as well as cancer pain are then reviewed. The role of NGF in delayed onset muscle soreness is described in more detail than its other roles based on the authors' recent observations. Acute effects are considered to be peripherally mediated, and accordingly, sensitization of nociceptors by NGF to heat and mechanical stimulation has been reported. Changes in the conductive properties of axons have also been reported. The intracellular mechanisms so far proposed for heat sensitization are direct phosphorylation and membrane trafficking of TRPV1 by TrkA. Little investigation has been done on the mechanism of mechanical sensitization, and it is still unclear whether mechanisms similar to those for heat sensitization work in mechanical sensitization. Long-lasting sensitizing effects are mediated both by changed expression of neuropeptides and ion channels (Na channels, ASIC, TRPV1) in primary afferents and by spinal NMDA receptors. Therapeutic perspectives are briefly discussed at the end of the chapter.

[Understand, investigate and diagnose pain in the musculoskeletal system]

Most patients who attend orthopedic trauma surgery practices present with pain of the musculoskeletal system which can significantly affect the quality of life. For most patients the reason for the pain is quite obvious and can be easily addressed; however, for other patients the mechanism responsible for the pain remains unclear. In these patients it is mandatory to have well founded knowledge about the origin of the pain, possible pathways of pain sensitization and chronification in order to ask the right questions during (pain) anamnesis and to perform an adequate clinical functional examination. This is the foundation to offer an effective treatment to patients or when necessary to initiate further diagnostic investigations in order to avoid pain chronification or to direct patients to a multimodal interdisciplinary approach when the pain is already chronic.

Neuroanatomical pathway of nociception originating in a low back muscle (multifidus) in the rat

The neural mechanisms of low back pain (LBP) are still enigmatic. Presently, low back muscles are being discussed as an important source of LBP. Here, the neuroanatomical pathway of the nociceptive information from the caudal multifidus muscle (MF) was studied. True blue was injected into the MF at the level L5 to visualize the dorsal root ganglion (DRG) cells that supply this muscle. The distribution of the stained cells had a maximum in the DRG L3, not in L5. Injection of 5% formalin into the MF at levels L4 and L5 induced a significant increase in the number of c-Fos-immunoreactive (-ir) nuclei in the dorsal horn in many lumbar segments. Cells expressing c-Fos were particularly numerous in the most lateral part of the ipsilateral laminae I-II. The number of c-Fos-ir nuclei in the dorsal horn of segment L3 was significantly higher than that in segment L5. To visualize supraspinal projections, fluorogold (FG) was injected into the contralateral ventrolateral periaqueductal gray (vlPAG) 6 days prior to formalin or saline injection into the MF. The number of double-labeled dorsal horn neurons (FG-positive plus c-Fos-ir) in all lumbar segments was significantly higher in the formalin group than in the saline group. These results show that (1) the origin of the sensory supply of the MF is shifted two segments cranially relative to the location of the muscle, (2) the spinal cells processing nociceptive input from the caudal MF are widely distributed, and (3) the vlPAG is a supraspinal center of nociception from the MF.