[The messengers from peripheral nervous system to central nervous system: involvement of neurotrophins and cytokines in the mechanisms of acupuncture].

Neurotrophic factors and cytokines are involved in the regulation of neuronal survival, axonal myelination, and synaptic plasticity in both central nervous system (CNS) and peripheral nervous system (PNS). The members of the neurotrophic factor family include nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5). These molecules bind to two types of receptors: (1) tyrosine kinase receptors (TrkA, TrkB, TrkC) and 2) common neurotrophin receptor (p 75 NTR). The internalization and retrograde axonal transport of neurotrophin receptors are important for their signal transduction supporting neuronal survival, synaptic plasticity, and axonal myelination. In addition, a growing body of data suggests that neurotrophins are involved in the pathophysiologicl courses of inflammatory pain, neurodegenerative disease, and psychiatric diseases. Cytokines, including IL-1, IL-2, IL-6, and TNF-alpha,are important mediators of the immune response and play a key role in the diseases by acting on inflammatory immune cells, neuronal cells, muscle cells, and vessel cells. Interestingly, some cytokines (e.g. TNF-alpha, IL-2, TGF-beta) are also able to regulate synaptic plasticity and affect CNS functions. The neurotrophins and cytokines release in response to various stimuli, such as electronic stimulation, or inflammation. This crosstalk from PNS to CNS is involved in the pathophysiology of many human diseases and may contribute to the effects of acupuncture. Based on our knowledge to neurotrophins and cytokines, we proposed the neurotrophin/cytokine hypothesis for the mechanism of acupuncture. This hypothesis may initiate the discussion on the possible roles of neurotrophins/cytokines in the therapeutic effects of acupuncture and shed light to the discovery of mechanism of acupuncture in the treatment of devastating diseases.