Contribution of the potassium-chloride cotransporter KCC2 to the strength of inhibition in the neonatal rodent spinal cord in vitro

Multi-session transcutaneous spinal cord stimulation prevents chloride homeostasis imbalance and the development of hyperreflexia after spinal cord injury in rat

Spasticity is a complex and multidimensional disorder that impacts nearly 75% of individuals with spinal cord injury (SCI) and currently lacks adequate treatment options. This sensorimotor condition is burdensome as hyperexcitability of reflex pathways result in exacerbated reflex responses, co-contractions of antagonistic muscles, and involuntary movements. Transcutaneous spinal cord stimulation (tSCS) has become a popular tool in the human SCI research field. The likeliness for this intervention to be successful as a noninvasive anti-spastic therapy after SCI is suggested by a mild and transitory improvement in spastic symptoms following a single stimulation session, but it remains to be determined if repeated tSCS over the course of weeks can produce more profound effects. Despite its popularity, the neuroplasticity induced by tSCS also remains widely unexplored, particularly due to the lack of suitable animal models to investigate this intervention. Thus, the basis of this work was to use tSCS over multiple sessions (multi-session tSCS) in a rat model to target spasticity after SCI and identify the long-term physiological improvements and anatomical neuroplasticity occurring in the spinal cord. Here, we show that multi-session tSCS in rats with an incomplete (severe T9 contusion) SCI (1) decreases hyperreflexia, (2) increases the low frequency-dependent modulation of the H-reflex, (3) prevents potassium-chloride cotransporter isoform 2 (KCC2) membrane downregulation in lumbar motoneurons, and (4) generally augments motor output, i.e., EMG amplitude in response to single pulses of tSCS, particularly in extensor muscles. Together, this work displays that multi-session tSCS can target and diminish spasticity after SCI as an alternative to pharmacological interventions and begins to highlight the underlying neuroplasticity contributing to its success in improving functional recovery.

Constitutive KCC2 Cell- and Synapse-Specifically Regulates NMDA Receptor Activity in the Spinal Cord

K+-Cl- cotransporter-2 (KCC2) critically controls neuronal chloride homeostasis and maintains normal synaptic inhibition by GABA and glycine. Nerve injury diminishes synaptic inhibition in the spinal cord via KCC2 impairment. However, how KCC2 regulates nociceptive input to spinal excitatory and inhibitory neurons remains elusive. Here, we show that basal GABA reversal potentials were significantly more depolarized in vesicular GABA transporter (VGAT)-expressing inhibitory neurons than those in vesicular glutamate transporter-2 (VGluT2)-expressing excitatory neurons in spinal cords of male and female mice. Strikingly, inhibiting KCC2 with VU0463271 increased currents elicited by puff NMDA and the NMDAR-mediated frequency of mEPSCs in VGluT2, but not in VGAT, dorsal horn neurons. Notably, VU0463271 had no effect on EPSCs monosynaptically evoked from the dorsal root in VGluT2 neurons. Furthermore, VU0463271 augmented α2δ-1-NMDAR interactions and their protein levels in spinal cord synaptosomes. In Cacna2d1 KO mice, VU0463271 had no effect on puff NMDA currents or the mEPSC frequency in dorsal horn neurons. Disrupting α2δ-1-NMDAR interactions with α2δ-1 C-terminus mimicking peptide diminished VU0463271-induced potentiation in the mEPSC frequency and puff NMDA currents in VGluT2 neurons. Additionally, intrathecal injection of VU0463271 reduced mechanical and thermal thresholds in wild-type mice, but not in Cacna2d1 KO mice. VU0463271-induced pain hypersensitivity in mice was abrogated by co-treatment with the NMDAR antagonist, pregabalin (an α2δ-1 inhibitory ligand), or α2δ-1 C-terminus mimicking peptide. Our findings suggest that KCC2 controls presynaptic and postsynaptic NMDAR activity specifically in excitatory dorsal horn neurons. KCC2 impairment preferentially potentiates nociceptive transmission between spinal excitatory interneurons via α2δ-1-bound NMDARs.Significance statementImpaired function of potassium-chloride cotransporter-2 (KCC2), a key regulator of neuronal inhibition, in the spinal cord plays a major role in neuropathic pain. This study unveils that KCC2 controls spinal nociceptive synaptic strength via NMDA receptors in a cell type- and synapse type-specific manner. KCC2 inhibition preferentially augments presynaptic and postsynaptic NMDA receptor activity in spinal excitatory interneurons via α2δ-1 (previously known as a calcium channel subunit). Importantly, spinal KCC2 impairment triggers pain hypersensitivity through α2δ-1-coupled NMDA receptors. These findings pinpoint the cell and molecular substrates for the reciprocal relationship between spinal synaptic inhibition and excitation in chronic neuropathic pain. Targeting both KCC2 and α2δ-1–NMDA receptor complexes could be an effective strategy in managing neuropathic pain conditions.

Multi-session transcutaneous spinal cord stimulation prevents chloridehomeostasis imbalance and the development of spasticity after spinal cordinjury in rat

Spasticity is a complex and multidimensional disorder that impacts nearly 75% of individuals with spinal cord injury (SCI) and currently lacks adequate treatment options. This sensorimotor condition is burdensome as hyperexcitability of reflex pathways result in exacerbated reflex responses, co-contractions of antagonistic muscles, and involuntary movements. Transcutaneous spinal cord stimulation (tSCS) has become a popular tool in the human SCI research field. The likeliness for this intervention to be successful as a noninvasive anti-spastic therapy after SCI is suggested by a mild and transitory improvement in spastic symptoms following a single stimulation session, but it remains to be determined if repeated tSCS over the course of weeks can produce more profound effects. Despite its popularity, the neuroplasticity induced by tSCS also remains widely unexplored, particularly due to the lack of suitable animal models to investigate this intervention. Thus, the basis of this work was to use tSCS over multiple sessions (multi-session tSCS) in a rat model to target spasticity after SCI and identify the long-term physiological improvements and anatomical neuroplasticity occurring in the spinal cord. Here, we show that multi-session tSCS in rats with an incomplete (severe T9 contusion) SCI (1) decreases hyperreflexia, (2) increases the low frequency-dependent modulation of the H-reflex, (3) prevents potassium-chloride cotransporter isoform 2 (KCC2) membrane downregulation in lumbar motoneurons, and (4) generally augments motor output, i.e., EMG amplitude in response to single pulses of tSCS, particularly in extensor muscles. Together, this work displays that multi-session tSCS can target and diminish spasticity after SCI as an alternative to pharmacological interventions and begins to highlight the underlying neuroplasticity contributing to its success in improving functional recovery.

Bumetanide increases postsynaptic inhibition after chronic SCI and decreases presynaptic inhibition with step-training

Current anti-spastic medication significantly compromises motor recovery after spinal cord injury (SCI), indicating a critical need for alternative interventions. Because a shift in chloride homeostasis decreases spinal inhibition and contributes to hyperreflexia after SCI, we investigated the effect of bumetanide, an FDA-approved sodium-potassium-chloride intruder (NKCC1) antagonist, on presynaptic and postsynaptic inhibition. We compared its effect with step-training as it is known to improve spinal inhibition by restoring chloride homeostasis. In SCI rats, a prolonged bumetanide treatment increased postynaptic inhibition but not presynaptic inhibition of the plantar H-reflex evoked by posterior biceps and semitendinosus (PBSt) group I afferents. By using in vivo intracellular recordings of motoneurons, we further show that a prolonged bumetanide increased postsynaptic inhibition by hyperpolarizing the reversal potential for inhibitory postsynaptic potentials (IPSPs) after SCI. However, in step-trained SCI rats an acute delivery of bumetanide decreased presynaptic inhibition of the H-reflex, but not postsynaptic inhibition. These results suggest that bumetanide might be a viable option to improve postsynaptic inhibition after SCI, but it also decreases the recovery of presynaptic inhibition with step-training. We discuss whether the effects of bumetanide are mediated by NKCC1 or by off-target effects. KEY POINTS: After spinal cord injury (SCI), chloride homeostasis is dysregulated over time in parallel with the decrease in presynaptic inhibition of Ia afferents and postsynaptic inhibition of motoneurons, and the development of spasticity. While step-training counteracts these effects, it cannot always be implemented in the clinic because of comorbidities. An alternative intervention is to use pharmacological strategies to decrease spasticity without hindering the recovery of motor function with step-training. Here we found that, after SCI, a prolonged bumetanide (an FDA-approved antagonist of the sodium-potassium-chloride intruder, NKCC1) treatment increases postsynaptic inhibition of the H-reflex, and it hyperpolarizes the reversal potential for inhibitory postsynaptic potentials in motoneurons. However, in step-trained SCI, an acute delivery of bumetanide decreases presynaptic inhibition of the H-reflex, but not postsynaptic inhibition. Our results suggest that bumetanide has the potential to decrease spastic symptoms related to a decrease in postsynaptic but not presynaptic inhibition after SCI.

Umbilical cord-derived mesenchymal stromal cell therapy to prevent the development of neurodevelopmental disorders related to low birth weight

Low birth weight (LBW) increases the risk of neurodevelopmental disorders (NDDs) such as attention-deficit/hyperactive disorder and autism spectrum disorder, as well as cerebral palsy, for which no prophylactic measure exists. Neuroinflammation in fetuses and neonates plays a major pathogenic role in NDDs. Meanwhile, umbilical cord-derived mesenchymal stromal cells (UC-MSCs) exhibit immunomodulatory properties. Therefore, we hypothesized that systemic administration of UC-MSCs in the early postnatal period may attenuate neuroinflammation and thereby prevent the emergence of NDDs. The LBW pups born to dams subjected to mild intrauterine hypoperfusion exhibited a significantly lesser decrease in the monosynaptic response with increased frequency of stimulation to the spinal cord preparation from postnatal day 4 (P4) to P6, suggesting hyperexcitability, which was improved by intravenous administration of human UC-MSCs (1 × 10⁵ cells) on P1. Three-chamber sociability tests at adolescence revealed that only LBW males exhibited disturbed sociability, which tended to be ameliorated by UC-MSC treatment. Other parameters, including those determined via open-field tests, were not significantly improved by UC-MSC treatment. Serum or cerebrospinal fluid levels of pro-inflammatory cytokines were not elevated in the LBW pups, and UC-MSC treatment did not decrease these levels. In conclusion, although UC-MSC treatment prevents hyperexcitability in LBW pups, beneficial effects for NDDs are marginal.

Body Weight-Supported Treadmill Training Ameliorates Motoneuronal Hyperexcitability by Increasing GAD-65/67 and KCC2 Expression via TrkB Signaling in Rats with Incomplete Spinal Cord Injury

Spasticity is a typical consequence after spinal cord injury (SCI). The critical reasons are reducing the synthesis of Gamma-Aminobutyric Acid (GABA), glycine and potassium chloride co-transporter 2 (KCC2) inside the distal spinal cord. The current work aimed to test whether exercise training could increase the expression of glutamic acid decarboxylase 65/67 (GAD-65/67, the key enzymes in GABA synthesis) and KCC2 in the distal spinal cord via tropomyosin-related kinase B (TrkB) signaling. The experimental rats were randomly assigned to the following five groups: Sham, SCI/phosphate-buffered saline (PBS), SCI-treadmill training (TT)/PBS, SCI/TrkB-IgG, and SCI-TT/TrkB-IgG. After that, the model of T10 contusion SCI was used, then TrkB-IgG was used to prevent TrkB activity at 7 days post-SCI. Body weight-supported treadmill training started on the 8^th day post-SCI for four weeks. The Hmax/Mmax ratio and the rate-dependent depression of H-reflex were used to assess the excitability of spinal motoneuronal networks. Western blotting and Immunohistochemistry techniques were utilized for measuring the expression of GAD-65, GAD-67, and KCC2. The findings revealed that exercise training could reduce motoneuronal excitability and boost GAD-65, GAD-67, and KCC2 production in the distal region of the spinal cord after SCI. The effects of exercise training were decreased after the TrkB signaling was inhibited. The present exploration demonstrated that exercise training increases GAD-65, GAD-67, and KCC2 expression in the spinal cord via TrkB signaling and that this method could also improve rats with motoneuronal hyperexcitability and spasticity induced by incomplete SCI.

Role of Synaptic Inhibition in the Coupling of the Respiratory Rhythms that Underlie Eupnea and Sigh Behaviors

The preBötzinger complex (preBötC) gives rise to two types of breathing behavior under normal physiological conditions: eupnea and sighing. Here, we examine the neural mechanisms that couple their underlying rhythms. We measured breathing in awake intact adult mice and recorded inspiratory rhythms from the preBötC in neonatal mouse brainstem slice preparations. We show previously undocumented variability in the temporal relationship between sigh breaths or bursts and their preceding eupneic breaths or inspiratory bursts. Investigating the synaptic mechanisms for this variability in vitro, we further show that pharmacological blockade of chloride-mediated synaptic inhibition strengthens inspiratory-to-sigh temporal coupling. These findings contrast with previous literature, which suggested glycinergic inhibition linked sigh bursts to their preceding inspiratory bursts with minimal time intervals. Furthermore, we verify that pharmacological disinhibition did not alter the duration of the prolonged interval that follows a sigh burst before resumption of the inspiratory rhythm. These results demonstrate that synaptic inhibition does not enhance coupling between sighs and preceding inspiratory events or contribute to post-sigh apneas. Instead, we conclude that excitatory synaptic mechanisms coordinate inspiratory (eupnea) and sigh rhythms.

Rehabilitation Decreases Spasticity by Restoring Chloride Homeostasis through the Brain-Derived Neurotrophic Factor-KCC2 Pathway after Spinal Cord Injury

Activity-based therapy is routinely integrated in rehabilitation programs to facilitate functional recovery after spinal cord injury (SCI). Among its beneficial effects is a reduction of hyperreflexia and spasticity, which affects ∼75% of the SCI population. Unlike current anti-spastic pharmacological treatments, rehabilitation attenuates spastic symptoms without causing an active depression in spinal excitability, thus avoiding further interference with motor recovery. Understanding how activity-based therapies contribute to decrease spasticity is critical to identifying new pharmacological targets and to optimize rehabilitation programs. It was recently demonstrated that a decrease in the expression of KCC2, a neuronal Cl- extruder, contributes to the development spasticity in SCI rats. Although exercise can decrease spinal hyperexcitability and increase KCC2 expression on lumbar motoneurons after SCI, a causal effect remains to be established. Activity-dependent processes include an increase in brain-derived neurotrophic factor (BDNF) expression. Interestingly, BDNF is a regulator of KCC2 but also a potent modulator of spinal excitability. Therefore, we hypothesized that after SCI, the activity-dependent increase in KCC2 expression: 1) functionally contributes to reduce hyperreflexia, and 2) is regulated by BDNF. SCI rats chronically received VU0240551 (KCC2 blocker) or TrkB-IgG (BDNF scavenger) during the daily rehabilitation sessions and the frequency-dependent depression of the H-reflex, a monitor of hyperreflexia, was recorded 4 weeks post-injury. Our results suggest that the activity-dependent increase in KCC2 functionally contributes to H-reflex recovery and critically depends on BDNF activity. This study provides a new perspective in understanding how exercise impacts hyperreflexia by identifying the biological basis of the recovery of function.

Serotonergic modulation of sacral dorsal root stimulation-induced locomotor output in newborn rat

Descending neuromodulators from the brainstem play a major role in the development and regulation of spinal sensorimotor functions. Here, the contribution of serotonergic signaling in the lumbar spinal cord was investigated in the context of the generation of locomotor activity. Experiments were performed on in vitro spinal cord preparations from newborn rats (0-5 days). Rhythmic locomotor episodes (fictive locomotion) triggered by tonic electrical stimulations (2Hz, 30s) of a single sacral dorsal root were recorded from bilateral flexor-dominated (L2) and extensor-dominated (L5) ventral roots. We found that the activity pattern induced by sacral stimulation evolves over the 5 post-natal (P) day period. Although alternating rhythmic flexor-like motor bursts were expressed at all ages, the locomotor pattern of extensor-like bursting was progressively lost from P1 to P5. At later stages, serotonin (5-HT) and quipazine (5-HT2A receptor agonist) at concentrations sub-threshold for direct locomotor network activation promoted sacral stimulation-induced fictive locomotion. The 5-HT2A receptor antagonist ketanserin could reverse the agonist's action but was ineffective when fictive locomotion was already expressed in the absence of 5-HT (mainly before P2). Although inhibiting 5-HT7 receptors with SB266990 did not affect locomotor pattern organization, activating 5-HT1A receptors with 8-OH-DPAT specifically deteriorated extensor phase motor burst activity. We conclude that during the first 5 post-natal days in rat, serotonergic signaling in the lumbar cord becomes increasingly critical for the expression of fictive locomotion. Our findings therefore further underline the importance of both descending serotonergic and sensory afferent pathways in shaping locomotor activity during postnatal development. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

A Critical Evaluation of Current Concepts in Cerebral Palsy

Spastic cerebral palsy (CP), despite the name, is not consistently identifiable by specific brain lesions. CP animal models focus on risk factors for development of CP, yet few reproduce the diagnostic symptoms. Animal models of CP must advance beyond risk factors to etiologies, including both the brain and spinal cord.

Furosemide Unmasks Inhibitory Dysfunction after Spinal Cord Injury in Humans: Implications for Spasticity

Spasticity after spinal cord injury has considerable quality of life implications, impacts on rehabilitation efforts and necessitates long-term multi-disciplinary pharmacological and non-pharmacological management. The potassium chloride co-transporter (KCC2) plays a central role in intracellular chloride homeostasis and the inhibitory function of mature neurons. Animal studies consistently have demonstrated a downregulation of KCC2 activity after spinal cord transection, causing a shift from the inhibitory action of gamma-aminobutyric acid and glycine to an excitatory effect. Furosemide, a recognized KCC2 antagonist in animals, blocks the formation of inhibitory post-synaptic potentials in spinal motoneurons without affecting excitatory post-synaptic potentials. Based on observations in animals studies, we hypothesized that furosemide may be used to unmask KCC2 downregulation after spinal cord injury in humans, which contributes to reflex hyperexcitability. We have shown previously that furosemide reduces both pre-synaptic and post-synaptic inhibition in healthy subjects without altering monosynaptic excitatory transmission. These findings provide evidence that furosemide may be used in humans to evaluate inhibitory synapses in the spinal cord. In this present study, we show that furosemide fails to modulate both pre- and post-synaptic inhibitions relayed to soleus spinal motor neurons in persons with spinal cord injury. The lack of furosemide effect after spinal cord injury suggests KCC2 dysfunction in humans, resulting in reduced inhibitory synaptic transmission in spinal neurons. Our findings suggest that KCC2 dysfunction may be an important etiological factor in hyperreflexia after spinal cord injury. These observations may pave the way to novel therapeutic strategies against spasticity centered on chloride homeostasis.

Reactivation of Dormant Relay Pathways in Injured Spinal Cord by KCC2 Manipulations

Many human spinal cord injuries are anatomically incomplete but exhibit complete paralysis. It is unknown why spared axons fail to mediate functional recovery in these cases. To investigate this, we undertook a small-molecule screen in mice with staggered bilateral hemisections in which the lumbar spinal cord is deprived of all direct brain-derived innervation, but dormant relay circuits remain. We discovered that a KCC2 agonist restored stepping ability, which could be mimicked by selective expression of KCC2, or hyperpolarizing DREADDs, in the inhibitory interneurons between and around the staggered spinal lesions. Mechanistically, these treatments transformed this injury-induced dysfunctional spinal circuit to a functional state, facilitating the relay of brain-derived commands toward the lumbar spinal cord. Thus, our results identify spinal inhibitory interneurons as a roadblock limiting the integration of descending inputs into relay circuits after injury and suggest KCC2 agonists as promising treatments for promoting functional recovery after spinal cord injury.

Mild Intrauterine Hypoperfusion Leads to Lumbar and Cortical Hyperexcitability, Spasticity, and Muscle Dysfunctions in Rats: Implications for Prematurity

Intrauterine ischemia-hypoxia is detrimental to the developing brain and leads to white matter injury (WMI), encephalopathy of prematurity (EP), and often to cerebral palsy (CP), but the related pathophysiological mechanisms remain unclear. In prior studies, we used mild intrauterine hypoperfusion (MIUH) in rats to successfully reproduce the diversity of clinical signs of EP, and some CP symptoms. Briefly, MIUH led to inflammatory processes, diffuse gray and WMI, minor locomotor deficits, musculoskeletal pathologies, neuroanatomical and functional disorganization of the primary somatosensory and motor cortices, delayed sensorimotor reflexes, spontaneous hyperactivity, deficits in sensory information processing, memory and learning impairments. In the present study, we investigated the early and long-lasting mechanisms of pathophysiology that may be responsible for the various symptoms induced by MIUH. We found early hyperreflexia, spasticity and reduced expression of KCC2 (a chloride cotransporter that regulates chloride homeostasis and cell excitability). Adult MIUH rats exhibited changes in muscle contractile properties and phenotype, enduring hyperreflexia and spasticity, as well as hyperexcitability in the sensorimotor cortex. Taken together, these results show that reduced expression of KCC2, lumbar hyperreflexia, spasticity, altered properties of the soleus muscle, as well as cortical hyperexcitability may likely interplay into a self-perpetuating cycle, leading to the emergence, and persistence of neurodevelopmental disorders (NDD) in EP and CP, such as sensorimotor impairments, and probably hyperactivity, attention, and learning disorders.

Prochlorperazine Increases KCC2 Function and Reduces Spasticity after Spinal Cord Injury

In mature neurons, low intracellular chloride level required for inhibition is maintained by the potassium-chloride cotransporter, KCC2. Impairment of Cl- extrusion after KCC2 dysfunction has been involved in many central nervous system disorders, such as seizures, neuropathic pain, or spasticity, after a spinal cord injury (SCI). This makes KCC2 an appealing drug target for restoring Cl- homeostasis and inhibition in pathological conditions. In the present study, we screen the Prestwick Chemical Library® and identify conventional antipsychotics phenothiazine derivatives as enhancers of KCC2 activity. Among them, prochlorperazine hyperpolarizes the Cl- equilibrium potential in motoneurons of neonatal rats and restores the reciprocal inhibition post-SCI. The compound alleviates spasticity in chronic adult SCI rats with an efficacy equivalent to the antispastic agent, baclofen, and rescues the SCI-induced downregulation of KCC2 in motoneurons below the lesion. These pre-clinical data support prochlorperazine for a new therapeutic indication in the treatment of spasticity post-SCI and neurological disorders involving a KCC2 dysfunction.

Deletion of the Fractalkine Receptor, CX3CR1, Improves Endogenous Repair, Axon Sprouting, and Synaptogenesis after Spinal Cord Injury in Mice

Impaired signaling via CX3CR1, the fractalkine receptor, promotes recovery after traumatic spinal contusion injury in mice, a benefit achieved in part by reducing macrophage-mediated injury at the lesion epicenter. Here, we tested the hypothesis that CX3CR1-dependent changes in microglia and macrophage functions also will enhance neuroplasticity, at and several segments below the injury epicenter. New data show that in the presence of inflammatory stimuli, CX3CR1-deficient (CX3CR1^-/-) microglia and macrophages adopt a reparative phenotype and increase expression of genes that encode neurotrophic and gliogenic proteins. At the lesion epicenter (mid-thoracic spinal cord), the microenvironment created by CX3CR1^-/- microglia/macrophages enhances NG2 cell responses, axon sparing, and sprouting of serotonergic axons. In lumbar spinal cord, inflammatory signaling is reduced in CX3CR1^-/- microglia. This is associated with reduced dendritic pathology and improved axonal and synaptic plasticity on ventral horn motor neurons. Together, these data indicate that CX3CR1, a microglia-specific chemokine receptor, is a novel therapeutic target for enhancing neuroplasticity and recovery after SCI. Interventions that specifically target CX3CR1 could reduce the adverse effects of inflammation and augment activity-dependent plasticity and restoration of function. Indeed, limiting CX3CR1-dependent signaling could improve rehabilitation and spinal learning.SIGNIFICANCE STATEMENT Published data show that genetic deletion of CX3CR1, a microglia-specific chemokine receptor, promotes recovery after traumatic spinal cord injury in mice, a benefit achieved in part by reducing macrophage-mediated injury at the lesion epicenter. Data in the current manuscript indicate that CX3CR1 deletion changes microglia and macrophage function, creating a tissue microenvironment that enhances endogenous repair and indices of neuroplasticity, at and several segments below the injury epicenter. Interventions that specifically target CX3CR1 might be used in the future to reduce the adverse effects of intraspinal inflammation and augment activity-dependent plasticity (e.g., rehabilitation) and restoration of function.

Goji fruit (Lycium barbarum) protects sciatic nerve function against crush injury in a model of diabetic stress

Excess fructose consumption causes changes in functioning of the central and peripheral nervous systems, which increase the vulnerability of peripheral nerves to traumatic injury. The aim of this study was to evaluate the electrophysiological parameters of responses of motoneurons of the spinal cord at high-frequency stimulation of the distal part of the injured sciatic nerve in a model of diabetic stress under action of Lycium barbarum (LB). Male albino rats were given with drinking water with 50% concentration of dietary fructose for 6 weeks. Starting on the 7th week a crush injury of the left sciatic nerve was carried out. Some of the animals received fructose post-injury for 3 weeks and some of the animals received fructose+dry LB fruits for 3 weeks. In the fructose+crush+LВ group a relatively proportional division of tetanic and posttetanic potentiation and depression in responses of ipsilateral and contralateral motoneurons was observed, which would suggest the modulatory role of LB in short-term synaptic plasticity formation. Generally, LB fruit is able to modulate central nervous system reorganization, amplifying positive adaptive changes that improve functional recovery and promote selective target reinnervation in high fructose-diet rats with sciatic nerve crush-injury.

Spinal circuits for motor learning

Studies of motor learning have largely focussed on the cerebellum, and have provided key concepts about neural circuits required. However, other parts of the nervous system are involved in learning, as demonstrated by the capacity to 'train' spinal circuits to produce locomotion following spinal cord injury. While somatosensory feedback is necessary for spinal motor learning, feed forward circuits within the spinal cord must also contribute. In fact, motoneurons themselves could act as comparators that integrate feed forward and feedback inputs, and thus contribute to motor learning. Application of cerebellar-derived principles to spinal circuitry leads to testable predictions of spinal organization required for motor learning.