Evaluation of the effects of specific opioid receptor agonists in a rodent model of spinal cord injury.

OBJECTIVE: The current study aimed to evaluate the contribution(s) of specific opioid receptor systems to the analgesic and detrimental effects of morphine, observed after spinal cord injury in prior studies. STUDY DESIGN: We used specific opioid receptor agonists to assess the effects of µ- (DAMGO), δ- (DPDPE) and κ- (GR89696) opioid receptor activation on locomotor (Basso, Beattie and Bresnahan scale, tapered beam and ladder tests) and sensory (girdle, tactile and tail-flick tests) recovery in a rodent contusion model (T12). We also tested the contribution of non-classic opioid binding using [+]- morphine. METHODS: First, a dose-response curve for analgesic efficacy was generated for each opioid agonist. Baseline locomotor and sensory reactivity was assessed 24 h after injury. Subjects were then treated with an intrathecal dose of a specific agonist and re-tested after 30 min. To evaluate the effects on recovery, subjects were treated with a single dose of an agonist and both locomotor and sensory function were monitored for 21 days. RESULTS: All agonists for the classic opioid receptors, but not the [+]- morphine enantiomer, produced antinociception at a concentration equivalent to a dose of morphine previously shown to produce strong analgesic effects (0.32 µmol). DAMGO and [+]- morphine did not affect long-term recovery. GR89696, however, significantly undermined the recovery of locomotor function at all doses tested. CONCLUSIONS: On the basis of these data, we hypothesize that the analgesic efficacy of morphine is primarily mediated by binding to the classic µ-opioid receptor. Conversely, the adverse effects of morphine may be linked to activation of the κ-opioid receptor. Ultimately, elucidating the molecular mechanisms underlying the effects of morphine is imperative to develop safe and effective pharmacological interventions in a clinical setting. SETTING: USA. SPONSORSHIP: Grant DA31197 to MA Hook and the NIDA Drug Supply Program.

Exercise therapy and recovery after SCI: evidence that shows early intervention improves recovery of function.

STUDY DESIGN: This was designed as an experimental study. OBJECTIVES: Locomotor training is one of the most effective strategies currently available for facilitating recovery of function after an incomplete spinal cord injury (SCI). However, there is still controversy regarding the timing of treatment initiation for maximal recovery benefits. To address this issue, the present study compares the effects of exercise initiated in the acute and secondary phase of SCI. SETTING: Texas A&M University, College Station, TX, USA. METHODS: Rats received a moderate spinal contusion injury and began an exercise program 1 (D1-EX) or 8 days (D8-EX) later. They were individually placed into transparent exercise balls for 60 min per day, for 14 consecutive days. Control rats were placed in exercise balls that were rendered immobile. Motor and sensory recovery was assessed for 28 days after injury. RESULTS: The D1-EX rats recovered significantly more locomotor function (BBB scale) than controls and D8-EX rats. Moreover, analyses revealed that rats in the D8-EX group had significantly lower tactile reactivity thresholds compared with control and D1-EX rats, and symptoms of allodynia were not reversed by exercise. Rats in the D8-EX group also had significantly larger areas of damage across spinal sections caudal to the injury center compared with the D1-EX group. CONCLUSION: These results indicate that implementing an exercise regimen in the acute phase of SCI maximizes the potential for recovery of function.

Monitoring recovery after injury: procedures for deriving the optimal test window.

Researchers studying the impact of treatments designed to facilitate recovery after neural injury face competing demands. On the one hand, because treatment effects often emerge slowly over days, and because researchers seek evidence of stable long-term effects, it is common practice to observe experimental subjects for many weeks after treatment. On the other hand, the cost of performing studies and the need to evaluate a multitude of alternative treatment procedures requires optimal efficiency, pushing researchers towards shorter test procedures. With these issues in mind, researchers have appeared to derive a test window based on previously published methodologies and inspection of their recovery curves, with testing terminated after the recovery curve reaches asymptote (approaches a slope of 0). An alternative procedure is introduced here that evaluates the stability of the data set over time. Using correlational techniques, researchers can determine whether (1) testing should be continued for additional days; or (2) equivalent statistical power can be achieved in fewer days. This provides a rational decision rule to help researchers balance competing demands. Applying these techniques to a procedure that evaluates the impact of acute treatments on recovery from spinal cord injury, it is shown that equal statistical power can be achieved in half the time, greatly increasing the efficiency with which alternative treatments can be evaluated.

Development of hand preferences in marmosets (Callithrix jacchus) and effects of aging.

The authors investigated the development of unimanual hand use and hand preferences during feeding in 15 marmosets (Callithrix jacchus), ages birth to 51-70 months. Bimanual hand use was common at 1-2 months, but by 5-8 months unimanual holding had developed and so had significant hand preferences. Half of the marmosets preferred to pick up and take food to the mouth with the left hand, and half preferred the right hand. Individuals maintained the same hand preference at all ages examined. Significant relationships were also found between the postures adopted during feeding and the direction of hand preferences displayed by juvenile marmosets. There was a positive correlation between increased suspension and increased left-hand preference, and a negative correlation between increased feeding in a tripedal posture and increased left-hand preference. These results are discussed in terms of motor development and hemispheric specialization.

Intermittent noxious stimulation following spinal cord contusion injury impairs locomotor recovery and reduces spinal brain-derived neurotrophic factor-tropomyosin-receptor kinase signaling in adult rats.

Intermittent nociceptive stimulation following a complete transection or contused spinal cord injury (SCI) has been shown to exert several short- and long-lasting negative consequences. These include maladaptive spinal plasticity, enhanced mechanical allodynia, and impaired functional recovery of locomotor and bladder functions. The neurotrophin, brain-derived neurotrophic factor (BDNF) has been shown to play an important role in adaptive plasticity and also to restore functions following SCI. This suggests that the negative behavioral effects of shock are most likely related to corresponding changes in BDNF spinal levels. In this study, we investigated the cellular effects of nociceptive stimulation in contused adult rats focusing on BDNF, its receptor, tropomyosin-receptor kinase (TrkB), and the subsequent downstream signaling system. The goal was to determine whether the behavioral effect of stimulation is associated with concomitant cellular changes induced during the initial post-injury period. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting were used to assess changes in the mRNA and/or protein levels of BDNF, TrkB, and the downstream signaling proteins calcium-calmodulin kinase II (CaMKII) and extracellular related kinase 1/2 (ERK1/2) at 1 h, 24 h, and 7 days following administration of intermittent noxious shock to the tail of contused subjects. In addition, recovery of locomotor function (Basso, Beattie, and Bresnahan [BBB] score) was assessed daily for the first week after injury. The results showed that, although nociceptive stimulation failed to induce any changes in gene expression at 1 h, it significantly reduced the expression of BDNF, TrkB, ERK2, and CaMKII at 24 h. In general, changes in gene expression were spatially localized to the dorsal spinal cord. In addition, locomotor recovery was impaired by shock. Evidence is also provided suggesting that shock engages a neuronal circuitry without having any negative effects on neuronal survival at 24 h. These results suggest that nociceptive activity following SCI decreases BDNF and TrkB levels, which may significantly contribute to diminished functional recovery.

MicroRNA dysregulation following spinal cord contusion: implications for neural plasticity and repair.

Spinal cord injury (SCI) is medically and socioeconomically debilitating. Currently, there is a paucity of effective therapies that promote regeneration at the injury site, and limited understanding of mechanisms that can be utilized to therapeutically manipulate spinal cord plasticity. MicroRNAs (miRNAs) constitute novel targets for therapeutic intervention to promote repair and regeneration. Microarray comparisons of the injury sites of contused and sham rat spinal cords, harvested 4 and 14 days following SCI, showed that 32 miRNAs, including miR124, miR129, and miR1, were significantly down-regulated, whereas SNORD2, a translation-initiation factor, was induced. Additionally, three miRNAs including miR21 were significantly induced, indicating adaptive induction of an anti-apoptotic response in the injured cord. Validation of miRNA expression by qRT-PCR and in situ hybridization assays revealed that the influence of SCI on miRNA expression persists up to 14 days and expands both anteriorly and caudally beyond the lesion site. Specifically, changes in miR129-2 and miR146a expression significantly explained the variability in initial injury severity, suggesting that these specific miRNAs may serve as biomarkers and therapeutic targets for SCI. Moreover, the pattern of miRNA changes coincided spatially and temporally with the appearance of SOX2, nestin, and REST immunoreactivity, suggesting that aberrant expression of these miRNAs may not only reflect the emergence of stem cell niches, but also the reemergence in surviving neurons of a pre-neuronal phenotype. Finally, bioinformatics analysis of validated miRNA-targeted genes indicates that miRNA dysregulation may explain apoptosis susceptibility and aberrant cell cycle associated with a loss of neuronal identity, which underlies the pathogenesis of secondary SCI.

An animal model of functional electrical stimulation: evidence that the central nervous system modulates the consequences of training.

STUDY DESIGN: Review of how spinal neurons can modulate the consequences of functional electrical stimulation (FES) in an animal model. METHODS: Spinal effects of FES are examined in male Sprague-Dawley rats transected at the second thoracic vertebra. The rats are exposed to FES training 24-48 h after surgery. Experimental manipulations of stimulation parameters, combined with physiological and pharmacological procedures, are used to examine the potential role of spinal neurons. RESULTS: The isolated spinal cord is inherently capable of learning the response-outcome relations imposed in FES training contingencies. Adaptive behavioral modifications are observed when an outcome (electrical stimulation) is contingent on a behavioral response. In contrast, a lack of correlation between the response and outcome in training produces a learning deficit in the spinal cord, rendering it incapable of adaptive learning for up to 48 h. The N-methyl-D-aspartic acid receptor appears to mediate both the adaptive plasticity and loss of plasticity, seen in this spinal model. CONCLUSION: The behavioral effects observed with FES therapies are not simply due to the direct (motor) consequences of stimulation elicited by the activation of efferent motor neurons and/or selected muscles. FES training has the capacity to shape inherent spinal circuits and to produce a long-lasting behavioral modification. Further understanding of the spinal mechanisms underlying adaptive behavioral modification will be integral for establishing functional neural connections in a regenerating spinal system.

Leading-limb preferences in marmosets (Callithrix jacchus): walking, leaping and landing.

The leading-limb preferences of 17 common marmosets (Callithrix jacchus) when they initiated and terminated locomotion were determined from video recordings of the subjects walking on, leaping off, and landing on a plexiglas platform. In a majority of sequences, 11 of 17 subjects landed with the right hand and foot contacting the plexiglas substrate before the left hand and foot. Of the 17 subjects, 8 initiated leaping with the right side of the body, whereas only 3 subjects significantly preferred to initiate leaping with the left hand and foot. Leading-limb preferences displayed during landing were positively correlated with those displayed for leaping and walking, although only two subjects displayed significant leading-limb preferences when walking. By contrast, hand preferences for initiating and terminating locomotion were not related to hand preferences for food holding; 16 of 17 marmosets displayed strong and significant hand preferences for food holding, even though many did not show leading-limb preferences for walking, leaping, or landing. These data seem to suggest that the right arm is stronger in marmosets. The right arm is used initially to decelerate the body and absorb the impact of contact with the landing substrate. The tendency for the right arm to be stronger is balanced by a tendency for the left leg to be stronger (providing the force needed for leaping).

Tongue protrusion dystonia: treatment with botulinum toxin.

We report the treatment experience in a series of patients with involuntary tongue protrusion resulting from oromandibular dystonia (OMD) or Meige's syndrome. A retrospective analysis of clinical findings and results of treatment was conducted on patients treated at Vanderbilt University Medical Center between 1989 and 1995. After unsuccessful treatment with conventional oral medications, nine patients having involuntary tongue protrusion resulting from OMD or Meige's syndrome were treated with botulinum toxin type A (BTX-A) injected into the genioglossus muscle at four sites via a submandibular approach. A marked reduction in tongue protrusion was achieved in six patients (67%). Of 35 consecutive injections, 83% were successful at reducing tongue protrusion. Mild dysphagia complicated 14% of the injections. The average dose injected was 34 (+/- 3) units producing a 15 (+/- 2) week average duration of effect. Injection of the genioglossus with BTX-A may prove to be a valid treatment option for involuntary tongue protrusion related to OMD or Meige's syndrome. A double-blind, placebo-controlled trial is needed to better define efficacy and adverse events.