Peripheral inflammation undermines the plasticity of the isolated spinal cord.

Abstract

Peripheral capsaicin treatment induces molecular changes that sensitize the responses of nociceptive neurons in the spinal dorsal horn. The current studies demonstrate that capsaicin also undermines the adaptive plasticity of the spinal cord, rendering the system incapable of learning a simple instrumental task. In these studies, male rats are transected at the second thoracic vertebra and are tested 24 to 48 hours later. During testing, subjects receive shock to one hindleg when it is extended (controllable stimulation). Rats quickly learn to maintain the leg in a flexed position. Rats that have been injected with capsaicin (1% or 3%) in the hindpaw fail to learn, even when tested on the leg contralateral to the injection. This learning deficit lasts at least 24 hours. Interestingly, training with controllable electrical stimulation prior to capsaicin administration protects the spinal cord against the maladaptive effects. Rats pretrained with controllable stimulation do not display a learning deficit or tactile allodynia. Moreover, controllable stimulation, combined with naltrexone, reverses the capsaicin-induced deficit. These data suggest that peripheral inflammation, accompanying spinal cord injuries, might have an adverse effect on recovery.

Pain and motor processing in the human cerebellum

“…25,75 However, associative motor learning in the context of pain-eliciting voluntary movements is not well understood. Animal models show pain-related deficits in motor learning, 23,29 and human studies show that pain can inhibit, 10,37 or facilitate, 16 or not affect motor learning, 31 but these studies do not provide insights into the role that cerebellar circuits play in pain-related adaptive or maladaptive changes in motor learning. The current findings may benefit patients in the future by identifying specific cerebellar targets for interventions such as noninvasive brain stimulation to modulate pain-eliciting movements during rehabilitation.…”

Pain and motor control: From the laboratory to rehabilitation

“…This was argued to be due to changes in cortical excitability in presence of pain (Le Pera et al, 2001). Although it is possible that pain may affect learning processes and animal studies indicate compromised capacity for learning due to pain-induced changes at the spinal cord (Hook et al, 2008), inspection of data from the study of Boudreau et al (2007) suggest that failure of adaptation could be secondary to modified performance of the training task during pain. If quality of movement is maintained, the training-induced changes are unaffected by pain .…”

Temporal regularity determines the impact of electrical stimulation on tactile reactivity and response to capsaicin in spinally transected rats

“…Treatments that induce inflammation, EMR, and central sensitization (e.g. peripheral capsaicin or carrageenan) impair this learning (Ferguson et al, 2006; Hook et al, 2008). Interestingly, variable intermittent shock at an intensity that activates C-fibers also impairs instrumental learning and this effect lasts at least 24 hr (Crown et al, 2002; Baumbauer et al, 2008).…”