[Chronic pain : Perception, reward and neural processing]

Many chronic pain syndromes are characterized by enhanced perception of painful stimuli as well as alterations in cortical processing in sensory and motor regions. In this review article the alterations in muscle pain and neuropathic pain are described. Alterations in patients with fibromyalgia and chronic back pain are described as examples for musculoskeletal pain and also in patients with phantom limb pain after amputation and complex regional pain syndrome as examples for neuropathic pain. In addition to altered pain perception, cumulative evidence on alterations in the processing of reward and the underlying mechanisms in chronic pain has been described. A description is given of what is known on how pain and reward interact and affect each other. The relevance of such interactions for chronic pain is discussed. The implications of these findings for therapeutic approaches are delineated with respect to sensorimotor training and behavioral therapy, focusing on the effectiveness of these approaches, mechanisms and future developments. In particular, we discuss operant behavioral therapy in patients with chronic back pain and fibromyalgia as well as prosthesis training in patients with phantom limb pain and discrimination, mirror and imaginary training in patients with phantom limb pain and complex regional pain syndrome. With respect to the processing of reward, the focus of the discussion is on the role of reward and associated learning in pain therapy.

[Phantom limb pain. Psychological treatment strategies]

Similar to other pain syndromes phantom limb pain is characterized by learning and memory processes that maintain the pain and increase maladaptive plastic changes of the brain: therefore, psychological interventions that change maladaptive memory processes are useful. In addition to traditional psychological interventions, such as pain management training and biofeedback, more recent developments that involve sensory discrimination training, mirror treatment, graded motor imagery, prosthesis training and training in virtual reality are interesting. These interventions not only reduce phantom limb pain but also reverse the associated maladaptive brain changes.

Limitations of pharmacotherapy: behavioral approaches to chronic pain

Pharmacotherapy is most appropriate in acute pain, whereas in chronic pain states behavioral approaches or a combination of behavioral treatment and pharmacotherapy is more appropriate. In this chapter we first describe the role of learning and memory as well as other psychological factors in the development of chronic pain and emphasize that chronic pain must viewed as the result of a learning process with resulting central neuroplastic changes. We then describe operant behavioral and cognitive-behavioral treatments as well as biofeedback and relaxation techniques and present innovative treatment procedures aimed at altering central pain memories. We complete the section with a discussion of combined behavioral and pharmacological approaches and an interdisciplinary view.

[Phantom limb pain: aspects of neuroplasticity and intervention]

Phantom-limb pain is a common sequel of amputation, occurring in up to 80 % of the amputee population. It must be differentiated from non-painful phantom phenomena, residual-limb pain, and non-painful residual-limb phenomena. A comprehensive model of phantom-limb pain is presented that assigns a major role to pain occurring before the amputation and to central as well as peripheral changes related to it. Special emphasis is put on the role of cortical reorganization in the development of phantom limb pain. Finally, new approaches to the prevention and treatment of phantom limb pain are presented that have a positive influence on phantom limb pain by preventing or reversing cortical reorganization.

Methotrexate resistance conferred by transplantation of drug-resistant transgenic marrow cells fractionated bycounterflow elutriation

Introduction of genes conferring drug resistance into hematopoietic cells may allow for improved chemotherapy by protection of normally drug-sensitive cells from the toxic side-effects of antitumor agents. We recently reported that transplantation of murine marrow transgenic for drug-resistant dihydrofolate reductase (DHFR) protected mice from lethal doses of methotrexate (MTX), demonstrating the feasibility of imparting drug resistance to recipients of marrow expressing drug-resistant DHFR activity. In order to optimize this strategy it is necessary to identify the hematopoietic cell populations which mediate drug resistance. For this purpose, we separated committed progenitor populations from primitive hematopoietic cells in DHFR transgenic marrow by counterflow elutriation (CE). As expected, supplementation with a fraction containing committed progenitors afforded protection from MTX-induced aplasia observed early after transplantion in animals administered MTX. In contrast, supplementation with a fraction containing primitive hematopoietic cells depleted of committed progenitors failed to provide immediate protection from early aplasia, but instead contributed to drug resistance 4 to 5 weeks after transplantation. The presence of primitive hematopoietic progenitors in both fractions was evident from Southern hybridization analysis for donor transgenic cells 2 months post-transplant. We conclude that protection from aplasia associated with MTX administration immediately after transplantation requires expression of drug-resistant DHFR activity in more differentiated, committed hematopoietic cells, while primitive DHFR transgenic progenitors contribute to long-term drug resistance. These results help to define the appropriate target cells for improved chemotherapy by protection of hematopoietic cells through the introduction of new genes conferring drug resistance.