Central Plasticity of Cutaneous Afferents Is Associated with Nociceptive Hyperreflexia after Spinal Cord Injury in Rats

Choosing the optimal target area for repeated transcranial magnetic stimulation in treating neuropathic pain in spinal cord injury patients: a comparative analysis

Objective

The specific target area of repeated transcranial magnetic stimulation (rTMS) in treating neuropathic pain resulting from spinal cord injury (SCI-NP) remains uncertain.

Methods

Thirty-four participants with SCI-NP were allocated into three groups, namely, the motor cortex (M1, A) group, the left dorsolateral prefrontal cortex (LDLPFC, B) group, and the control (sham stimulation, C) group. The intervention was administered totally 10 times. Outcome measures assessed pre-(T0) and post-(T1)intervention, including Numerical Rating scale (NRS), anxiety (SAS), depression (SDS), sleep quality (PSQI), brief pain inventory (BPI), and impression of change.

Results

All outcomes in groups A and B significantly changed after intervention (p < 0.05), and the delta value (T1-T0) also significantly changed than group C (p < 0.05). The delta value of SDS in the group B was better than the group A, and the change of pain degree in the group B was moderately correlated with the change in PSQI (r = 0.575, p < 0.05). Both patients in the groups A and B showed significant impression of change about their received therapy (p < 0.05).

Conclusion

Both targets are effective, but LDLPFC is more effective in reducing depression in SCI-NP. Healthcare providers might select the suitable area according to the specific attributes of their patients.

Broad opioid antagonism amplifies disruption of locomotor function following therapy-like hindlimb stretching in spinal cord injured rats

STUDY DESIGN

Preclinical pilot study.

OBJECTIVES

To test the hypothesis that spinal opioidergic circuitry contributes to muscle stretch-induced locomotor deficits.

SETTING

Kentucky Spinal Cord Injury Research Center, Louisville, KY, USA.

METHODS

A pilot study with eight female Sprague-Dawley rats that received 25 g-cm T10 contusion injuries and recovered for 5 weeks. Rats were divided into two groups with one group receiving subcutaneous injections of naltrexone dissolved in saline (15 mg/kg) or an equal volume of saline. Each group received a daily 24-minute stretching protocol during weeks 6, 8, and 11 post-injury. Locomotor function was assessed throughout using the BBB Open Field Locomotor Scale.

RESULTS

Consistent with previous findings, stretching reduced locomotor function in both naltrexone and saline groups. However, the loss of locomotor function appeared earlier in the naltrexone group. Animals in both groups had a similar rate of recovery following the termination of stretching. Interestingly, the administration of naltrexone did not influence acute thermal cutaneous nociceptive responses as measured by a tail-flick assay but caused a significant increase in spasticity following stretch.

CONCLUSIONS

The results of this study suggest that the endogenous opioid system plays a role in modulating the negative impact of muscle stretch on spinal cord motor circuitry that is vulnerable due to loss of descending input. The observed actions of the broad-spectrum opioid antagonist naltrexone imply that pharmaceuticals targeting the endogenous opioid system post-SCI may have unintended consequences.

Assessment of the cutaneous trunci muscle reflex in neurologically abnormal cats

OBJECTIVES

The aim of this study was to evaluate the presence of the cutaneous trunci reflex (CTR) in a population of neurologically abnormal cats in regard to age, body condition score (BCS), sex, breed, evidence of traumatic injury, pain, known metabolic disease, mentation, neurolocalization and diagnostic classification.

METHODS

A retrospective medical record review was performed to identify cats with a history of neurologic disease undergoing a complete neurologic assessment between 24 September 2012 and 20 March 2019. CTR outcome (present, absent), signalment, evidence of traumatic injury, pain, known metabolic disease, mentation, neurolocalization and diagnostic classification were recorded.

RESULTS

A total of 182 cats were identified. The CTR was present in 118 cats (64.8%) and absent in 64 cats (35.2%). Statistical analysis revealed no association between CTR outcome and age, BCS, sex, breed, evidence of traumatic injury, non-spinal pain, known metabolic disease, mentation, neurolocalization or diagnostic classification. A significant association was found between spinal pain and CTR outcome (P = 0.037).

CONCLUSIONS AND RELEVANCE

These findings suggest that elicitation of the CTR in the cat can be unreliable. Further prospective controlled studies are warranted to determine whether continued inclusion of the CTR in feline neurologic examinations is justified. Consideration of the reliability of the CTR is indicated, particularly in the context of fractious or anxious patients for which only a limited window for examination may be present.

Direct evidence for decreased presynaptic inhibition evoked by PBSt group I muscle afferents after chronic SCI and recovery with step-training in rats

KEY POINTS

Presynaptic inhibition is modulated by supraspinal centres and primary afferents in order to filter sensory information, adjust spinal reflex excitability, and ensure smooth movement. After spinal cord injury (SCI), the supraspinal control of primary afferent depolarization (PAD) interneurons is disengaged, suggesting an increased role for sensory afferents. While increased H-reflex excitability in spastic individuals indicates a possible decrease in presynaptic inhibition, it remains unclear whether a decrease in sensory-evoked PAD contributes to this effect. We investigated whether the PAD evoked by hindlimb afferents contributes to the change in presynaptic inhibition of the H-reflex in a decerebrated rat preparation. We found that chronic SCI decreases presynaptic inhibition of the plantar H-reflex through a reduction in PAD evoked by posterior biceps-semitendinosus (PBSt) muscle group I afferents. We further found that step-training restored presynaptic inhibition of the plantar H-reflex evoked by PBSt, suggesting the presence of activity-dependent plasticity of PAD pathways activated by flexor muscle group I afferents.

ABSTRACT

Spinal cord injury (SCI) results in the disruption of supraspinal control of spinal networks and an increase in the relative influence of afferent feedback to sublesional neural networks, both of which contribute to enhancing spinal reflex excitability. Hyperreflexia occurs in ∼75% of individuals with a chronic SCI and critically hinders functional recovery and quality of life. It is suggested that it results from an increase in motoneuronal excitability and a decrease in presynaptic and postsynaptic inhibitory mechanisms. In contrast, locomotor training decreases hyperreflexia by restoring presynaptic inhibition. Primary afferent depolarization (PAD) is a powerful presynaptic inhibitory mechanism that selectively gates primary afferent transmission to spinal neurons to adjust reflex excitability and ensure smooth movement. However, the effect of chronic SCI and step-training on the reorganization of presynaptic inhibition evoked by hindlimb afferents, and the contribution of PAD has never been demonstrated. The objective of this study is to directly measure changes in presynaptic inhibition through dorsal root potentials (DRPs) and its association with plantar H-reflex inhibition. We provide direct evidence that H-reflex hyperexcitability is associated with a decrease in transmission of PAD pathways activated by posterior biceps-semitendinosus (PBSt) afferents after chronic SCI. More precisely, we illustrate that the pattern of inhibition evoked by PBSt group I muscle afferents onto both L4-DRPs and plantar H-reflexes evoked by the distal tibial nerve is impaired after chronic SCI. These changes are not observed in step-trained animals, suggesting a role for activity-dependent plasticity to regulate PAD pathways activated by flexor muscle group I afferents.