Spinal Cord Plasticity Research Articles

Towards non-invasive imaging through spinal-cord generated magnetic fields.

Non-invasive imaging of the human spinal cord is a vital tool for understanding the mechanisms underlying its functions in both healthy and pathological conditions. However, non-invasive imaging presents a significant methodological challenge because the spinal cord is difficult to access with conventional neurophysiological approaches, due to its proximity to other organs and muscles, as well as the physiological movements caused by respiration, heartbeats, and cerebrospinal fluid (CSF) flow. Here, we discuss the present state and future directions of spinal cord imaging, with a focus on the estimation of current flow through magnetic field measurements. We discuss existing cryogenic (superconducting) and non-cryogenic (optically-pumped magnetometer-based, OPM) systems, and highlight their strengths and limitations for studying human spinal cord function. While significant challenges remain, particularly in source imaging and interference rejection, magnetic field-based neuroimaging offers a novel avenue for advancing research in various areas. These include sensorimotor processing, cortico-spinal interplay, brain and spinal cord plasticity during learning and recovery from injury, and pain perception. Additionally, this technology holds promise for diagnosing and optimizing the treatment of spinal cord disorders.

Glial progenitor heterogeneity and plasticity in the adult spinal cord.

Glial progenitor heterogeneity and plasticity in the adult spinal cord.

Sustained morphine exposure alters spinal NMDA receptor and astrocyte expression and exacerbates chronic pain behavior in female rats.

Sustained opioid use has long-term negative impacts on future pain experience, particularly in women. This study aimed to investigate the underlying spinal neurobiology of this clinical observation in an experimental model of joint pain. In this study, we tested the hypothesis that sustained opioid treatment exacerbates chronic pain responses and alters spinal cord dorsal horn astrogliosis and the expression of GluN2B-containing N-methyl-d-aspartate receptors in female rats. Subcutaneous morphine (3 mg/kg) or saline was administered twice daily for 1 week before inducing a model of joint knee pain (intra-articular injection of 2 mg of monosodium iodoacetate [MIA]) in adult female Sprague-Dawley rats, with pain-free controls receiving 50 µL of saline. Pain behavior (weight-bearing and mechanical paw withdrawal thresholds) was measured at baseline and at intervals thereafter. Twice-daily morphine/saline treatment was continued for up to 3 weeks after intra-articular injections, and spinal cord tissue was collected for Western blot analyses. Area under the curve analysis of weight-bearing asymmetry confirmed a significant exacerbation of pain behavior in the morphine/MIA group, compared with the saline/MIA group (F(3,18) = 46.3, P < 0.0001), despite comparable joint damage in both groups. Sustained morphine treatment was associated with significant elevations in dorsal horn expression of astrocytic glial fibrillary acidic protein (27 ± 5% increase) and neuronal GluN2B (80 ± 30% increase), but not microglial IBA1, irrespective of the model of joint pain. These data suggest that sustained morphine treatment in female rats drives spinal cord plasticity, including spinal astrogliosis and the expression of GluN2B-containing N-methyl-d-aspartate receptors, priming the dorsal horn to incoming sensory inputs and producing exacerbated pain responses.

The Protein Acetylation after Traumatic Spinal Cord Injury: Mechanisms and Therapeutic Opportunities.

Spinal cord injury (SCI) leads to deficits of various normal functions and is difficult to return to a normal state. Histone and non-histone protein acetylation after SCI is well documented and regulates spinal cord plasticity, axonal growth, and sensory axon regeneration. However, our understanding of protein acetylation after SCI is still limited. In this review, we summarize current research on the role of acetylation of histone and non-histone proteins in regulating neuron growth and axonal regeneration in SCI. Furthermore, we discuss inhibitors and activators targeting acetylation-related enzymes, such as α-tubulin acetyltransferase 1 (αTAT1), histone deacetylase 6 (HDAC6), and sirtuin 2 (SIRT2), to provide promising opportunities for recovery from SCI. In conclusion, a comprehensive understanding of protein acetylation and deacetylation in SCI may contribute to the development of SCI treatment.

Store-operated calcium entry mediates hyperalgesic responses during neuropathy.

Neuropathic pain (NP), resulting from nerve injury, alters neural plasticity in spinal cord and brain via the release of inflammatory mediators. The remodeling of store-operated calcium entry (SOCE) involves the refilling of calcium in the endoplasmic reticulum via STIM1 and Orai1 proteins and is crucial for maintaining neural plasticity and neurotransmitter release. The mechanism underlying SOCE-mediated NP remains largely unknown. In this study, we found SOCE-mediated calcium refilling was significantly higher during neuropathic pain, and the major component Orai1 was specifically co-localized with neuronal markers. Intrathecal injection of SOCE antagonist SKF96365 remarkably alleviated nerve injury- and formalin-induced pain and suppressed c-Fos expression in response to innocuous mechanical stimulation. RNA sequencing revealed that SKF96365 altered the expression of spinal transcription factors, including Fos, Junb, and Socs3, during neuropathic pain. In order to identify the genes critical for SKF96365-induced effects, we performed weighted gene co-expression network analysis (WGCNA) to identify the genes most correlated with paw withdrawal latency phenotypes. Of the 16 modules, MEsalmon module was the most highly correlated with SKF96365 induced effects. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the enriched genes of MEsalmon module were significantly related to Toll-like receptor signaling, steroid biosynthesis, and chemokine signaling, which may mediate the analgesic effect caused by SKF9636 treatment. Additionally, the SOCE antagonist YM-58483 produced similar analgesic effects in nerve injury- and formalin-induced pain. Our results suggest that manipulation of spinal SOCE signaling might be a promising target for pain relief by regulating neurotransmitter production and spinal transcription factor expression.

Altered Spinal Homeostasis and Maladaptive Plasticity in GFAP Null Mice Following Peripheral Nerve Injury

The maladaptive response of the central nervous system (CNS) following nerve injury is primarily linked to the activation of glial cells (reactive gliosis) that produce an inflammatory reaction and a wide cellular morpho-structural and functional/metabolic remodeling. Glial acidic fibrillary protein (GFAP), a major protein constituent of astrocyte intermediate filaments (IFs), is the hallmark of the reactive astrocytes, has pleiotropic functions and is significantly upregulated in the spinal cord after nerve injury. Here, we investigated the specific role of GFAP in glial reaction and maladaptive spinal cord plasticity following sciatic nerve spared nerve injury (SNI) in GFAP KO and wild-type (WT) animals. We evaluated the neuropathic behavior (thermal hyperalgesia, allodynia) and the expression of glial (vimentin, Iba1) and glutamate/GABA system markers (GLAST, GLT1, EAAC1, vGLUT, vGAT, GAD) in lumbar spinal cord sections of KO/WT animals. SNI induced neuropathic behavior in both GFAP KO and WT mice, paralleled by intense microglial reaction (Iba1 expression more pronounced in KO mice), reactive astrocytosis (vimentin increase) and expression remodeling of glial/neuronal glutamate/GABA transporters. In conclusion, it is conceivable that the lack of GFAP could be detrimental to the CNS as it lacks a critical sensor for neuroinflammation and morpho-functional–metabolic rewiring after nerve injury. Understanding the maladaptive morpho-functional changes of glial cells could represent the first step for a new glial-based targeted approach for mechanisms of disease in the CNS.

Plasticity of the Injured Spinal Cord.

Complete spinal cord injury (SCI) leads to permanent motor, sensitive and sensory deficits. In humans, there is currently no therapy to promote recovery and the only available treatments include surgical intervention to prevent further damage and symptomatic relief of pain and infections in the acute and chronic phases, respectively. Basically, the spinal cord is classically viewed as a nonregenerative tissue with limited plasticity. Thereby the establishment of the “glial” scar which appears within the SCI is mainly described as a hermetic barrier for axon regeneration. However, recent discoveries have shed new light on the intrinsic functional plasticity and endogenous recovery potential of the spinal cord. In this review, we will address the different aspects that the spinal cord plasticity can take on. Indeed, different experimental paradigms have demonstrated that axonal regrowth can occur even after complete SCI. Moreover, recent articles have demonstrated too that the “glial” scar is in fact composed of several cellular populations and that each of them exerts specific roles after SCI. These recent discoveries underline the underestimation of the plasticity of the spinal cord at cellular and molecular levels. Finally, we will address the modulation of this endogenous spinal cord plasticity and the perspectives of future therapeutic opportunities which can be offered by modulating the injured spinal cord microenvironment.

Inhibition of plasminogen/plasmin system retrieves endogenous nerve growth factor and adaptive spinal synaptic plasticity following peripheral nerve injury

Dysfunctions of the neuronal-glial crosstalk and/or impaired signaling of neurotrophic factors represent key features of the maladaptive changes in the central nervous system (CNS) in neuroinflammatory as neurodegenerative disorders. Tissue plasminogen activator (tPA)/plasminogen (PA)/plasmin system has been involved in either process of maturation and degradation of nerve growth factor (NGF), highlighting multiple potential targets for new therapeutic strategies.We here investigated the role of intrathecal (i.t.) delivery of neuroserpin (NS), an endogenous inhibitor of plasminogen activators, on neuropathic behavior and maladaptive synaptic plasticity in the rat spinal cord following spared nerve injury (SNI) of the sciatic nerve.We demonstrated that SNI reduced spinal NGF expression, induced spinal reactive gliosis, altering the expression of glial and neuronal glutamate and GABA transporters, reduced glutathione (GSH) levels and is associated to neuropathic behavior. Beside the increase of NGF expression, i.t. NS administration reduced reactive gliosis, restored synaptic homeostasis, GSH levels and reduced neuropathic behavior.Our results hereby highlight the essential role of tPA/PA system in the synaptic homeostasis and mechanisms of maladaptive plasticity, sustaining the beneficial effects of NGF-based approach in neurological disorders.

Comparison of effect of crush or transection peripheral nerve lesion on lumbar spinal cord synaptic plasticity and microglial dynamics.

In an injury to the peripheral nervous system, the spinal cord and brain structure reorganize connections to optimize the function of the remaining parts. Many cell events are triggered in the spinal cord to support changes in the synaptic connections around motoneurons, where old connections are removed, and new ones created. Microglial cells are primitive macrophages that invade the central nervous system in early stages of neurodevelopment and have several functions, such as eliminating synapses. We investigated the synaptic plasticity after different types of peripheral (sciatic) nerve injury (crush or total transection), as well as the behavior of microglial cells for 2 weeks after a peripheral lesion. As expected, sciatic-nerve injury reduced motor performance in mice, but crushed animals regained partial motor control. Because of sciatic-nerve injury, pre-synaptic inputs decreased around the motoneurons in the ventro-lateral horn, while microglial cells increased around these cells. Microglial cells also exhibited altered morphology in both types of peripheral lesion, indicating a similar underlying mechanism of plasticity. To investigate the involvement of microglia in this scenario, microglial activation was modulated by daily administration of minocycline. The minocycline treatment directly affected the microglial response and impacted the synapse rearrangement in the spinal cord. Together, these results demonstrate that microglia cells are involved in synaptic plasticity in the lumbar spinal cord in both nerve-injury scenarios.Summary of statementHere, we demonstrated that acute plasticity in the lumbar spinal cord (LSC) did not differ between crush and transection of peripheral nerve, and that microglial reactivity in the LSC was important after both injury types.

Sciatic nerve-conditioned medium with the addition of Croton blanchetianus Baill essential oil promotes morphological plasticity in spinal cord cultured cells

Spinal cord injury is a devastating condition that leads to significant disabilities. The treatment for this problem is a challenge in neuroscience, and it is necessary to combine different strategies to obtain functional recovery outcomes. There are many herbal natural products, such as Croton blanchetianus Baill (CB) essential oil, a Brazilian semi-arid bush with neuroprotective substances tested in regeneration processes and synaptic plasticity. Thus, this study analyzed the cellular plasticity of spinal cord neurons and glial cells in the presence of sciatic nerve-conditioned medium (SNCM) before the addition of CB essential oil. Cell morphology was assessed over 96 hours, and immunocytochemistry analyses were conducted for GFAP, GAP-43 and NeuN. Photomicrographs were made by scanning electron microscopy (SEM). Morphological analysis showed evident trophic development in the groups that received CB essential oil (P&gt;0.000), immunoreactivity for GFAP, GAP-43 and NeuN and the plasticity of these cells were confirmed by SEM. This pioneer study about the plasticity of spinal cord neurons and glial cells opens new possibilities and techniques with essential oils for cell therapy in the presence of SNCM, which promoted neuroprotective action.

Motor learning adaptations at the spinal cord level are task- and time-dependent: Implications for future investigations and treatment interventions.

Motor learning adaptations at the spinal cord level are task- and time-dependent: Implications for future investigations and treatment interventions.

Neonatal Inflammation Sex‐dependently Impairs Adult, Spinal Microglia

Neonatal inflammation is common and disrupts adult respiratory control, yet the mechanism(s) underlying the impairments are not well understood. Since microglia are key mediators of central inflammation and are important in the lasting effects of neonatal inflammation in non‐respiratory brain regions, we hypothesized lasting dysfunction in microglia underlie impairments in adult respiratory control. Specifically, we hypothesized neonatal inflammation would increase the number of and inflammatory gene expression in adult microglia. Since adult respiratory motor plasticity in the cervical spinal cord is impaired after neonatal inflammation, we analyzed immunomagnetically isolated microglia from the ventral cervical spinal cord. Interestingly, the number of microglia measured by flow cytometry calibrated with counting beads from adults after neonatal inflammation (LPS; 1 mg/kg, i.p.; postnatal day 4) were unchanged in males (LPS: 14,488 ± 4000, n=4; saline: 12,784 ± 4000, n=4, p=0.97) or females (LPS: 14,611 ± 4500, n=4; saline: 9,062 ± 4500, n=5, p=0.79). Additionally, the number of microglia was not significantly different between males and females (p&gt;0.05). Despite no changes in microglia number, we hypothesized microglia function was impaired by neonatal inflammation. Preliminary transcriptomic analysis suggests neonatal inflammation in adult females (n=2) up‐regulated 7 genes and down‐regulated 1 gene, and in adult males (n=3) down‐regulated 1 gene. Gene ontology revealed these differentially expressed genes are associated with inflammatory signaling. While neonatal inflammation has no impact on the number of microglia, it sex‐dependently increases inflammatory‐related gene expression in females with surprisingly few changes in adult males. Thus, adult, female microglia likely contribute to the lasting impairments in respiratory control following neonatal inflammation. Further, the lasting impairments in adult males are likely mediated by a sex‐specific distinct mechanism. Understanding the sex‐specific inflammatory mechanisms impairing respiratory control is crucial to developing treatment strategies to promote breathing during ventilatory control disorders.Support or Funding InformationSupported by NIH HL141249 (AGH)

Motor learning induces time-dependent plasticity that is observable at the spinal cord level.

The spinal cord is an important contributor to motor learning It remains unclear whether short-term spinal cord adaptations are general or task-specific Immediately after task acquisition, neural adaptations were not specific to the trained task (i.e. were general) Twenty-four hours after acquisition, neural adaptations appeared to be task-specific The neural reorganization and generalization of spinal adaptations appears to be time-dependent. Spinal cord plasticity is an important contributor of motor learning in humans, although its mechanisms are still poorly documented. In particular, it remains unclear whether short-term spinal adaptations are general or task-specific. As a marker of neural changes that are observable at spinal level, we measured the Hoffmann reflex (H-reflex) amplitude in the soleus muscle of 18 young healthy human adults before, immediately after (acquisition), and 24 h after (retention) the learning of a skilled task (i.e. one-legged stance on a tilt board). H-reflexes were elicited 46±30ms before touching the tilt board. Additionally, and at the same time points, we measured the H-reflex with the subject sitting at rest and when performing an unskilled and untrained task (i.e. one-legged stance on the floor). After task acquisition, there was a decrease of the H-reflex amplitude measured at rest but not during the skilled or the unskilled task. At retention, there was a decrease of the H-reflex when measured during the skilled task but not during the unskilled task or at rest. Performance increase was not associated with changes in the H-reflex amplitude. After the acquisition of a new skilled task, spinal changes appeared to be general (i.e. observable at rest). However, 24 h after, these changes were task-specific (i.e. observable only during performance of the trained task). These results imply that skill training induces a time-dependent reorganization of the modulation of spinal networks, which possibly reflects a time-dependent optimization of the feedforward motor command.

Stereological study on the numerical plasticity of myelinated fibers and oligodendrocytes in the rat spinal cord with painful diabetic neuropathy

Painful diabetic neuropathy may associate with nerve morphological plasticity in both peripheral and central nervous system. The aim of this study was to determine numerical changes of myelinated fibers in the spinothalamic tract region and oligodendrocytes in the spinal dorsal horn of rats with painful diabetic neuropathy and the effects of metformin on the above changes. Male Sprague–Dawley rats were randomly allocated into the control group (n = 7), the painful diabetic neuropathy group (n = 6) and the painful diabetic neuropathy treated with metformin group (the PDN + M group, n = 7), respectively. Twenty-eight days after medication, numbers of myelinated fibers in the spinothalamic tract and oligodendrocytes in the spinal dorsal horn were estimated by the optical disector (a stereological technique). Compared to the control group, number of myelinated fibers in the spinothalamic tract increased significantly in the painful diabetic neuropathy and PDN + M group, compared to the painful diabetic neuropathy group, number of myelinated fibers decreased in the PDN + M group (P < 0.05). As the oligodendrocyte in the spinal dorsal horn was considered, its number increased significantly in the painful diabetic neuropathy group compared to the control and the PDN + M group (P < 0.05), there was no significant difference between the control and the PDN + M group (P > 0.05). Our results indicate that painful diabetic neuropathy is associated with a serial of morphometric plasticity in the rat spinal cord including the numerical increase of the myelinated fibers in the spinothalamic tract and the oligodendrocytes in the spinal dorsal horn. The analgesic effect of metformin against painful diabetic neuropathy might be related to its adverse effects on the above morphometric plasticity.

DNA methylation and behavioral changes induced by neonatal spinal transection

Although the importance of epigenetic mechanisms in behavioral development has been gaining attention in recent years, research has largely focused on the brain. To our knowledge, no studies to date have investigated epigenetic changes in the developing spinal cord to determine the dynamic manner in which the spinal epigenome may respond to environmental input during behavioral development. Animal studies demonstrate that spinal cord plasticity is heightened during early development, is somewhat preserved following neonatal transection, and that spinal injured animals are responsive to sensory feedback. Because epigenetic alterations have been implicated in brain plasticity and are highly responsive to experience, these alterations are promising candidates for molecular substrates of spinal plasticity as well. Thus, the current study investigated behavioral changes in the development of weight-bearing locomotion and epigenetic modifications in the spinal cord of infant rats following a neonatal low-thoracic spinal transection or sham surgery on postnatal day (P)1. Specifically, global levels of methylation and methylation status of the brain-derived neurotrophic factor (Bdnf) gene, a neurotrophin heavily involved in both CNS and behavioral plasticity, particularly in development, were examined in lumbar tissue harvested on P10 from sham and spinal-transected subjects. Behavioral results demonstrate that compared to shams, spinal-transected subjects exhibit significantly reduced partial-weight bearing hindlimb activity. Molecular data demonstrate group differences in global lumbar methylation levels as well as exon-specific group differences in Bdnf methylation. This study represents an initial step toward understanding the relationship between epigenetic mechanisms and plasticity associated with spinal cord and locomotor development.

Addition of FGF-2 to sciatic nerve-conditioned medium to promote plasticity in spinal cord cultured cells

Addition of FGF-2 to sciatic nerve-conditioned medium to promote plasticity in spinal cord cultured cells

Exploiting cervicolumbar connections enhances short-term spinal cord plasticity induced by rhythmic movement.

Arm cycling causes suppression of soleus (SOL) Hoffmann (H-) reflex that outlasts the activity period. Arm cycling presumably activates propriospinal networks that modulate Ia presynaptic inhibition. Interlimb pathways are thought to relate to the control of quadrupedal locomotion, allowing for smooth, coordinated movement of the arms and legs. We examined whether the number of active limb pairs affects the amount and duration of activity-dependent plasticity of the SOL H-reflex. On separate days, 14 participants completed 4 randomly ordered 30 min experimental sessions: (1) quiet sitting (CTRL); (2) arm cycling (ARM); (3) leg cycling (LEG); and (4) arm and leg cycling (A&L) on an ergometer. SOL H-reflex and M-wave were evoked via electrical stimulation of the tibial nerve. M-wave and H-reflex recruitment curves were recorded, while the participants sat quietly prior to, 10 and 20min into, immediately after, and at 2.5, 5, 7.5, 10, 15, 20, 25, and 30min after each experimental session. Normalized maximal H-reflexes were unchanged in CTRL, but were suppressed by > 30% during the ARM, LEG, and A&L. H-reflex suppression outlasted activity duration for ARM (≤ 2.5 mins), LEG (≤ 5 mins), and A&L (≤ 30 mins). The duration of reflex suppression after A&L was greater than the algebraic summation of ARM and LEG. This non-linear summation suggests that using the arms and legs simultaneously-as in typical locomotor synergies-amplifies networks responsible for the short-term plasticity of lumbar spinal cord excitability. Enhanced activity of spinal networks may have important implications for the implementation of locomotor training for targeted rehabilitation.

Wheel Running Improves Motor Function and Spinal Cord Plasticity in Mice With Genetic Absence of the Corticospinal Tract.

Our previous studies showed that mutant mice with congenital absence of the corticospinal tract (CST) undergo spontaneous remodeling of motor networks to partially compensate for absent CST function. Here, we asked whether voluntary wheel running could further improve locomotor plasticity in CST-deficient mice. Adult mutant mice were randomly allocated to a “runners” group with free access to a wheel, or a “non-runners” group with no access to a wheel. In comparison with non-runners, there was a significant motor improvement including fine movement, grip strength, decreased footslip errors in runners after 8-week training, which was supported by the elevated amplitude of electromyography recording and increased neuromuscular junctions in the biceps. In runners, terminal ramifications of monoaminergic and rubrospinal descending axons were significantly increased in spinal segments after 12 weeks of exercise compared to non-runners. 5-ethynyl-2′-deoxyuridine (EDU) labeling showed that proliferating cells, 90% of which were Olig2-positive oligodendrocyte progenitors, were 4.8-fold more abundant in runners than in non-runners. In 8-week runners, RNAseq analysis of spinal samples identified 404 genes up-regulated and 398 genes down-regulated, and 69 differently expressed genes involved in signal transduction, among which the NF-κB, PI3K-Akt and cyclic AMP (cAMP) signaling were three top pathways. Twelve-week training induced a significant elevation of postsynaptic density protein 95 (PSD95), synaptophysin 38 and myelin basic protein (MBP), but not of brain derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) and insulin like growth factor-1 (IGF-1). Thus, locomotor training activates multiple signaling pathways, contributes to neural plasticity and functional improvement, and might palliate locomotor deficits in patients.

Anti-nerve growth factor monoclonal antibody: a prospective new therapy for canine and feline osteoarthritis.

It can be argued that chronic pain is the most ubiquitous disease process in all of medicine. All animals, should they live long enough, will probably experience it. And of all chronic pain syndromes, osteoarthritis (OA) remains the most predictable cause in both dogs and cats. Indeed, in dogs the pathophysiology of OA is commonly heritable and conformational, meaning that the disease process begins at a very young age and is lifelong, with at least 30 to 40 per cent of dogs affected clinically.1 In cats, the aetiopathophysiology is less certain but equally prevalent clinically, and more than 90 per cent of cats over the age of 12 years have radiographic changes consistent with degenerative joint disease.2,3 It follows that the hunt for novel therapy targets to address chronic pain in general and OA in particular needs to remain robust. One of those targets, nerve growth factor (NGF) and its binding to tropomyosin receptor kinase A (TrkA) receptor, is at the forefront of this hunt. NGF, produced and utilised by many cell types (including epithelium, endothelium, immunoreactive cells and CNS glia), is found in abundance during neonatal and infant development, and gradually downregulates over time.4 However, it upregulates once again with chronic inflammation, among other circumstances, and becomes an integral component of central sensitisation (wind up), spinal cord plasticity and maladaptive pain signalling. This inevitably results in hyperalgesia: lowered thresholds and exaggerated scope, character, duration and field of pain. Therefore, several anti-NGF/TrkA signalling strategies have been investigated for their pain-modifying capabilities and safety. Chief among these …

Synaptophysin and caspase-3 expression on lumbar segments of spinal cord after sensorimotor restriction during early postnatal period and treadmill training.

The purpose of the current study was to investigate whether locomotor stimulation training could have beneficial effects on spinal cord plasticity consequent to sensorimotor restriction (SR). Male Wistar rats were exposed to SR from postnatal day 2 (P2) to P28. Control and experimental rats underwent locomotor stimulation training in a treadmill from P31 to P52. The intensity of the synaptophysin and caspase-3 immunoreaction was determined on ventral horn of spinal cord. The synaptophysin immunoreactivity was lower in the ventral horn of sensorimotor restricted rats compared to controls animals and was accompanied by an increased caspase-3 immunoreactivity. Those alterations were reversed at the end of the training period. Our results suggest that immobility affects the normal developmental process that spinal cord undergoes in early postnatal life influencing both pro-apoptotic and synapse markers. Also, we demonstrated that this phenomenon was reversed by 3 weeks of treadmill training.