Normal Distribution and Plasticity of Serotonin Receptors after Spinal Cord Injury and Their Impacts on Motor Outputs

Following spinal cord injury (SCI) a series of anatomical and functional plastic changes occur in the spinal cord, including reorganization of the spinal neuronal network, alteration of properties of interneurons and motoneurons as well as up- or down-regulation of different neurotransmitter receptors. In mammalian spinal cord, one of the important neurotransmitters, serotonin (5-HT), plays an essential role in modulating sensory, motor and autonomic functions. Following SCI, especially complete spinal cord lesion, the descending supply of 5-HT is lost. As a consequence different 5-HT receptors undergo variant degrees of plastic changes.In this chapter I have systematically reviewed the distribution of different 5-HT receptors in the spinal cord and their plastic changes following SCI where applicable. In addition, the plastic changes of 5-HT supplying system in reaction to SCI have also been reviewed. These results indicate that 5-HT receptors are important factors not only for modulation of normal motor function, their plastic changes are also critical for motor functional recovery and, quite often, for the development of certain pathological states after SCI. Pharmacological and/or genetic intervention of selected 5-HT receptors and/or intrinsic 5-HT producing system in the spinal cord may pave new ways for the restoration of motor functions after SCI