Modulation and short-term plasticity of disynaptic reciprocal Ia inhibition

Transmission in the disynaptic reciprocal Ia inhibitory pathway has not been investigated in detail in humans with chronic incomplete spinal cord injury (SCI). We have investigated whether short-term changes can be induced in the transmission of reciprocal Ia inhibition in both individuals with chronic incomplete SCI and healthy subjects.; In chapter II we describe the extent to which sitting and standing influences the strength of reciprocal Ia inhibition between ankle flexor and extensor muscles in individuals with chronic incomplete SCI (n = 10) and in healthy subjects (n = 15).; In chapter III we describe the extent to which sitting and standing influences the amplitude of motor evoked responses in tibialis anterior (TA) and presynaptic inhibition from ankle flexor to extensor in individuals with chronic incomplete SCI (n = 10) and in healthy subjects (n = 15).; In chapter IV we describe how different forms of sensory input and a combination of sensory and cortical inputs affect the strength of reciprocal Ia inhibition in intact humans (n = 20).; In chapter V we describe how repetitive sensory stimulation affects the strength of reciprocal Ia inhibition in individuals with incomplete SCI (n = 14) and healthy subjects (n = 5). Patterned nerve stimulation (as described above), or vibration over the tibialis anterior tendon were delivered. This study showed that tendon vibration increased reciprocal inhibition that lasted for 5 min in individuals with chronic incomplete SCI, whereas vibration did not modify the strength of reciprocal inhibition in healthy subjects.; In summary, our results provide evidence that transmission in reciprocal Ia inhibitory pathway is decreased or absent after chronic incomplete SCI. This deficit can be temporarily modified with the use of repetitive sensory stimulation. The pattern of sensory nerve stimulation is critical in increasing reciprocal inhibition in healthy subjects. However, after SCI vibration of the TA tendon was critical for increasing reciprocal Ia inhibition between ankle flexor and extensor muscles. We suggest that the nature, pattern and strength of the sensory input, should be considered in future rehabilitation studies that examine whether reciprocal Ia inhibition can be modulated effectively during functional behaviors. (Abstract shortened by UMI.)...