Immunohistochemical detection of calcium/calmodulin-dependent protein kinase II in the spinal cord of the rat and monkey with special reference to the corticospinal tract

Calcium/calmodulin-dependent protein kinase II associates with the K+ channel isoform Kv4.3 in adult rat optic nerve

Spikes are said to exhibit "memory" in that they can be altered by spikes that precede them. In retinal ganglion cell axons, for example, rapid spiking can slow the propagation of subsequent spikes. This increases inter-spike interval and, thus, low-pass filters instantaneous spike frequency. Similarly, a K+ ion channel blocker (4-aminopyridine, 4AP) increases the time-to-peak of compound action potentials recorded from optic nerve, and we recently found that reducing autophosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) does too. These results would be expected if CaMKII modulates spike propagation by regulating 4AP-sensitive K+ channels. As steps toward identifying a possible substrate, we test whether (i) 4AP alters optic nerve spike shape in ways consistent with reducing K+ current, (ii) 4AP alters spike propagation consistent with effects of reducing CaMKII activation, (iii) antibodies directed against 4AP-sensitive and CaMKII-regulated K+ channels bind to optic nerve axons, and (iv) optic nerve CaMKII co-immunoprecipitates with 4AP-sensitive K+ channels. We find that, in adult rat optic nerve, (i) 4AP selectively slows spike repolarization, (ii) 4AP slows spike propagation, (iii) immunogen-blockable staining is achieved with anti-Kv4.3 antibodies but not with antibodies directed against Kv1.4 or Kv4.2, and (iv) CaMKII associates with Kv4.3. Kv4.3 may thus be a substrate that underlies activity-dependent spike regulation in adult visual system pathways.

A systematic review of large animal and human studies of stem cell therapeutics for acute adult traumatic spinal cord injury

Background: Traumatic spinal cord injury (TSCI) is a devastating condition and the search for a cure remains one of the most tenacious healthcare challenges to date. Current therapies are limited in their efficacy to restore full neurological function – resulting in lifelong disability and loss of autonomy. Whilst there remains a necessity to refine therapeutic protocols, stem cell (SC) studies have shown promise in the mending and re-establishment of the spinal cord neuroanatomy. Objectives: We conducted a systematic review of functional outcomes in stem cell therapeutics over the last three decades in large animals and humans. Methods: Medline, Embase, Cochrane and SCOPUS databases were searched for potentially pertinent articles from 1990 to 2020. Studies published in English were included if the stem cells were directly injected into the intraspinal, epidural or intrathecal compartments within two weeks of a traumatic mechanism of injury, including acute intervertebral disc prolapse. The participants were either large animals – defined as canine, porcine or non-human primate in-vivo models – or human patients. Results: Nine studies were included in this review. Statistically significant improvements in motor function and deep pain perception were seen at 8 weeks to 6 months post-SC injection compared to controls. Limitations: Functional outcomes are variably measured across studies. Almost all studies used experimentally induced trauma, which may not accurately represent the complexity of human spinal cord injury. Due to the exclusion criteria, there were no non-human primate studies included, yet these animal models are considered a closer anatomical match to humans than other large mammals. No human studies were included. Conclusions and Implications: Autologous and allogeneic stem cells have been trialled for the reconstitution of damaged and lost cells, remyelination of axons and remodelling of the pathophysiological microenvironment within the injured spinal cord, with some promising outcome data. This may translate to more successful future Phase I/II human clinical trials into the use of stem cells after TSCI in adults.

Zonisamide ameliorates progression of cervical spondylotic myelopathy in a rat model

Cervical spondylotic myelopathy (CSM) is caused by chronic compression of the spinal cord and is the most common cause of myelopathy in adults. No drug is currently available to mitigate CSM. Herein, we made a rat model of CSM by epidurally implanting an expanding water-absorbent polymer underneath the laminae compress the spinal cord. The CSM rats exhibited progressive motor impairments recapitulating human CSM. CSM rats had loss of spinal motor neurons, and increased lipid peroxidation in the spinal cord. Zonisamide (ZNS) is clinically used for epilepsy and Parkinson's disease. We previously reported that ZNS protected primary spinal motor neurons against oxidative stress. We thus examined the effects of ZNS on our rat CSM model. CSM rats with daily intragastric administration of 0.5% methylcellulose (n = 11) and ZNS (30 mg/kg/day) in 0.5% methylcellulose (n = 11). Oral administration of ZNS ameliorated the progression of motor impairments, spared the number of spinal motor neurons, and preserved myelination of the pyramidal tracts. In addition, ZNS increased gene expressions of cystine/glutamate exchange transporter (xCT) and metallothionein 2A in the spinal cord in CSM rats, and also in the primary astrocytes. ZNS increased the glutathione (GSH) level in the spinal motor neurons of CSM rats. ZNS potentially ameliorates loss of the spinal motor neurons and demyelination of the pyramidal tracts in patients with CSM.

Non-canonical heterogeneous cellular distribution and co-localization of CaMKIIα and CaMKIIβ in the spinal superficial dorsal horn

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is a key enzyme in long-term plasticity in many neurons, including in the nociceptive circuitry of the spinal dorsal horn. However, although the role of CaMKII heterooligomers in neuronal plasticity is isoform-dependent, the distribution and co-localization of CaMKII isoforms in the dorsal horn have not been comprehensively investigated. Here, quantitative immunofluorescence analysis was used to examine the distribution of the two major neuronal CaMKII isoforms, α and β, in laminae I–III of the rat dorsal horn, with reference to inhibitory interneurons and neuronal populations defined by expression of parvalbumin, calretinin, and calbindin D28k. Unexpectedly, all or nearly all inhibitory and excitatory neurons showed both CaMKIIα and CaMKIIβ immunoreactivity, although at highly variable levels. Lamina III neurons showed less CaMKIIα immunoreactivity than laminae I–II neurons. Whereas CaMKIIα immunoreactivity was found at nearly similar levels in inhibitory and excitatory neurons, CaMKIIβ generally showed considerably lower immunoreactivity in inhibitory neurons. Distinct populations of inhibitory calretinin neurons and excitatory parvalbumin neurons exhibited high CaMKIIα-to-CaMKIIβ immunoreactivity ratios. CaMKIIα and CaMKIIβ immunoreactivity showed positive correlation at GluA2⁺ puncta in pepsin-treated tissue. These results suggest that, unlike the forebrain, the dorsal horn is characterized by similar expression of CaMKIIα in excitatory and inhibitory neurons, whereas CaMKIIβ is less expressed in inhibitory neurons. Moreover, CaMKII isoform expression varies considerably within and between neuronal populations defined by laminar location, calcium-binding protein expression, and transmitter phenotype, suggesting differences in CaMKII function both between and within neuronal populations in the superficial dorsal horn.

Differential expression of CaMKII isoforms and overall kinase activity in rat dorsal root ganglia after injury

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) decodes neuronal activity by translating cytoplasmic Ca(2+) signals into kinase activity that regulates neuronal functions including excitability, gene expression, and synaptic transmission. Four genes lead to developmental and differential expression of CaMKII isoforms (α, β, γ, δ). We determined mRNA levels of these isoforms in the dorsal root ganglia (DRG) of adult rats with and without nerve injury in order to determine if differential expression of CaMKII isoforms may contribute to functional differences that follow injury. DRG neurons express mRNA for all four isoforms, and the relative abundance of CaMKII isoforms was γ>α>β=δ, based on the CT values. Following ligation of the 5th lumbar (L5) spinal nerve (SNL), the β isoform did not change, but mRNA levels of both the γ and α isoforms were reduced in the directly injured L5 neurons, and the α isoform was reduced in L4 neurons, compared to their contemporary controls. In contrast, expression of the δ isoform mRNA increased in L5 neurons. CaMKII protein decreased following nerve injury in both L4 and L5 populations. Total CaMKII activity measured under saturating Ca(2+)/CaM conditions was decreased in both L4 and L5 populations, while autonomous CaMKII activity determined in the absence of Ca(2+) was selectively reduced in axotomized L5 neurons 21days after injury. Thus, loss of CaMKII signaling in sensory neurons after peripheral nerve injury may contribute to neuronal dysfunction and pain.

CaMKIIβ regulates oligodendrocyte maturation and CNS myelination

CNS myelination and the maturation of the myelinating cells of the CNS, namely oligodendrocytes, are thought to be regulated by molecular mechanisms controlling the actin cytoskeleton. However, the exact nature of these mechanisms is currently only poorly understood. Here we assessed the role of calcium/calmodulin-dependent kinase type II (CaMKII), in particular CaMKIIβ, in oligodendrocyte maturation and CNS myelination. Using in vitro culture studies, our data demonstrate that CaMKIIβ is critical for the proper morphological maturation of differentiating oligodendrocytes, an aspect of oligodendrocyte maturation that is mediated to a large extent by changes in the cellular cytoskeleton. Furthermore, our data provide evidence for an actin-cytoskeleton-stabilizing role of CaMKIIβ in differentiating oligodendrocytes. Using Camk2b knock-out and Camk2b(A303R) mutant mice, our data revealed an in vivo functional role of CaMKIIβ in regulating myelin thickness that may be mediated by a non-kinase-catalytic activity. Our data point toward a critical role of CaMKIIβ in regulating oligodendrocyte maturation and CNS myelination via an actin-cytoskeleton-regulatory mechanism.

Effects of early versus late rehabilitative training on manual dexterity after corticospinal tract lesion in macaque monkeys

Dexterous hand movements can be restored with motor rehabilitative training after a lesion of the lateral corticospinal tract (l-CST) in macaque monkeys. To maximize effectiveness, the optimal time to commence such rehabilitative training must be determined. We conducted behavioral analyses and compared the recovery of dexterous hand movements between monkeys in which hand motor training was initiated immediately after the l-CST lesion (early-trained monkeys) and those in which training was initiated 1 mo after the lesion (late-trained monkeys). The performance of dexterous hand movements was evaluated by food retrieval tasks. In early-trained monkeys, performance evaluated by the success rate in a vertical slit task (retrieval of a small piece of food through a narrow vertical slit) recovered to the level of intact monkeys during the first 1–2 mo after the lesion. In late-trained monkeys, the task success rate averaged ∼30% even after 3 mo of rehabilitative training. We also evaluated hand performance with the Klüver board task, in which monkeys retrieved small spherical food pellets from cylindrical wells. Although the success rate of the Klüver board task did not differ between early- and late-trained monkeys, kinematic movement analysis showed that there was a difference between the groups: late-trained monkeys with an improved success rate frequently used alternate movement strategies that were different from those used before the lesion. These results suggest that early rehabilitative training after a spinal cord lesion positively influences subsequent functional recovery.

Human hepatocyte growth factor promotes functional recovery in primates after spinal cord injury

Many therapeutic interventions for spinal cord injury (SCI) using neurotrophic factors have focused on reducing the area damaged by secondary, post-injury degeneration, to promote functional recovery. Hepatocyte growth factor (HGF), which is a potent mitogen for mature hepatocytes and a mediator of the inflammatory responses to tissue injury, was recently highlighted as a potent neurotrophic factor in the central nervous system. We previously reported that introducing exogenous HGF into the injured rodent spinal cord using a herpes simplex virus-1 vector significantly reduces the area of damaged tissue and promotes functional recovery. However, that study did not examine the therapeutic effects of administering HGF after injury, which is the most critical issue for clinical application. To translate this strategy to human treatment, we induced a contusive cervical SCI in the common marmoset, a primate, and then administered recombinant human HGF (rhHGF) intrathecally. Motor function was assessed using an original open field scoring system focusing on manual function, including reach-and-grasp performance and hand placement in walking. The intrathecal rhHGF preserved the corticospinal fibers and myelinated areas, thereby promoting functional recovery. In vivo magnetic resonance imaging showed significant preservation of the intact spinal cord parenchyma. rhHGF-treatment did not give rise to an abnormal outgrowth of calcitonin gene related peptide positive fibers compared to the control group, indicating that this treatment did not induce or exacerbate allodynia. This is the first study to report the efficacy of rhHGF for treating SCI in non-human primates. In addition, this is the first presentation of a novel scale for assessing neurological motor performance in non-human primates after contusive cervical SCI.

Human hepatocyte growth factor promotes functional recovery in primates after spinal cord injury

Many therapeutic interventions for spinal cord injury (SCI) using neurotrophic factors have focused on reducing the area damaged by secondary, post-injury degeneration, to promote functional recovery. Hepatocyte growth factor (HGF), which is a potent mitogen for mature hepatocytes and a mediator of the inflammatory responses to tissue injury, was recently highlighted as a potent neurotrophic factor in the central nervous system. We previously reported that introducing exogenous HGF into the injured rodent spinal cord using a herpes simplex virus-1 vector significantly reduces the area of damaged tissue and promotes functional recovery. However, that study did not examine the therapeutic effects of administering HGF after injury, which is the most critical issue for clinical application. To translate this strategy to human treatment, we induced a contusive cervical SCI in the common marmoset, a primate, and then administered recombinant human HGF (rhHGF) intrathecally. Motor function was assessed using an original open field scoring system focusing on manual function, including reach-and-grasp performance and hand placement in walking. The intrathecal rhHGF preserved the corticospinal fibers and myelinated areas, thereby promoting functional recovery. In vivo magnetic resonance imaging showed significant preservation of the intact spinal cord parenchyma. rhHGF-treatment did not give rise to an abnormal outgrowth of calcitonin gene related peptide positive fibers compared to the control group, indicating that this treatment did not induce or exacerbate allodynia. This is the first study to report the efficacy of rhHGF for treating SCI in non-human primates. In addition, this is the first presentation of a novel scale for assessing neurological motor performance in non-human primates after contusive cervical SCI.

Transplanted L1 expressing radial glia and astrocytes enhance recovery after spinal cord injury

A major obstacle for the transplantation of neural stem cells (NSCs) into the lesioned spinal cord is their predominant astrocytic differentiation after transplantation. We took advantage of this predominant astrocytic differentiation of NSCs and expressed the paradigmatic beneficial neural cell adhesion molecule L1 in radial glial cells and reactive and nonreactive astrocytes as novel cellular vehicles to express L1 under the control of the promoter for the human glial fibrillary acidic protein (GFAP-L1 NSCs). Behavioral analysis and electrophysiological H-reflex recordings revealed that mice transplanted with GFAP-L1 NSCs showed enhanced locomotor recovery in comparison to mice injected with wild type (WT) NSCs or control mice injected with phosphate-buffered saline (PBS). This functional recovery was further accelerated in mice transplanted with L1-expressing radial glial cells that had been immunoisolated from GFAP-L1 NSCs (GFAP-L1-i cells). Morphological analysis revealed that mice grafted with GFAP-L1 NSCs exhibited increased neuronal differentiation and migration of transplanted cells, as well as increased soma size and cholinergic synaptic coverage of host motoneurons and increased numbers of endogenous catecholaminergic nerve fibers caudal to the lesion site. These findings show that L1-expressing astrocytes and radial glial cells isolated from GFAP-L1 NSC cultures represent a novel strategy for improving functional recovery after spinal cord injury, encouraging the use of the human GFAP promoter to target beneficial transgene expression in transplanted stem cells.

Early exercise in spinal cord injured rats induces allodynia through TrkB signaling

Rehabilitation is important for the functional recovery of patients with spinal cord injury. However, neurological events associated with rehabilitation remain unclear. Herein, we investigated neuronal regeneration and exercise following spinal cord injury, and found that assisted stepping exercise of spinal cord injured rats in the inflammatory phase causes allodynia. Sprague-Dawley rats with thoracic spinal cord contusion injury were subjected to assisted stepping exercise 7 days following injury. Exercise promoted microscopic recovery of corticospinal tract neurons, but the paw withdrawal threshold decreased and C-fibers had aberrantly sprouted, suggesting a potential cause of the allodynia. Tropomyosin-related kinase B (TrkB) receptor for brain-derived neurotrophic factor (BDNF) was expressed on aberrantly sprouted C-fibers. Blocking of BDNF-TrkB signaling markedly suppressed aberrant sprouting and decreased the paw withdrawal threshold. Thus, early rehabilitation for spinal cord injury may cause allodynia with aberrant sprouting of C-fibers through BDNF-TrkB signaling.

In vivo tracing of neural tracts in the intact and injured spinal cord of marmosets by diffusion tensor tractography

In spinal cord injury, axonal disruption results in motor and sensory function impairment. The evaluation of axonal fibers is essential to assess the severity of injury and efficacy of any treatment protocol, but conventional methods such as tracer injection in brain parenchyma are highly invasive and require histological evaluation, precluding clinical applications. Previous advances in magnetic resonance imaging technology have led to the development of diffusion tensor tractography (DTT) as a potential modality to perform in vivo tracing of axonal fibers. The properties and clinical applications of DTT in the brain have been reported, but technical difficulties have limited DTT studies of the spinal cord. In this study, we report the effective use of DTT to visualize both intact and surgically disrupted spinal long tracts in adult common marmosets. To verify the feasibility of spinal cord DTT, we first performed DTT of postmortem marmosets. DTT clearly illustrated spinal projections such as the corticospinal tract and afferent fibers in control animals, and depicted the severed long tracts in the injured animals. Histology of the spinal cords in both control and injured groups were consistent with DTT findings, verifying the accuracy of DTT. We also conducted DTT in live marmosets and demonstrated that DTT can be performed in live animals to reveal in vivo nerve fiber tracing images, providing an essential tool to evaluate axonal conditions in the injured spinal cord. Taken together, these findings demonstrate the feasibility of applying DTT to preclinical and clinical studies of spinal cord injury.

Molecular Mechanism of Learning and Memory Based on the Research for Ca2+/Calmodulin-dependent Protein Kinase II

In the central nervous system (CNS), the synapse is a specialized junctional complex by which axons and dendrites emerging from different neuron intercommunicates. Changes in the efficiency of synaptic transmission are important for a number of aspects of neural function. Much has been learned about the activity-dependent synaptic modifications that are thought to underlie memory storage, but the mechanism by which these modifications are stored remains unclear. Thus, it is important to find and characterize "memory molecules," and "memory apparatus or memory forming apparatus." A good candidate for the storage mechanism is Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II). CaM kinase II is one of the most prominent protein kinases, present in essentially every tissue but most concentrated in the brain. Neuronal CaM kinase II regulates important neuronal functions, including neurotransmitter synthesis, neurotransmitter release, modulation of ion channel activity, cellular transport, cell morphology and neurite extension, synaptic plasticity, learning and memory, and gene expression. Studies concerning this kinase open a door of the molecular basis of nerve function, especially learning and memory, and indicate one direction for the studies in the field of neuroscience. This review presents molecular structure, properties and functions of CaM kinase II, as a major component of neuron, which are mainly developed in our laboratory.

Phosphorylation of neuronal nitric oxide synthase at Ser847 in the nucleus intermediolateralis after spinal cord injury in mice

We previously demonstrated that Ca2+/calmodulin (CaM)-dependent protein kinase IIalpha (CaM-KIIalpha) can phosphorylate neuronal nitric oxide synthase (nNOS) at Ser847 and attenuate NOS activity in neuronal cells. In the present study we focused on chronological alteration in levels and cellular location of nNOS, phosphorylated (p)-Ser847-nNOS (NP847), CaM-KII and p-Thr286-CaM-KIIalpha following spinal cord injury (SCI) in mice. Western blot analysis showed nNOS to be significantly phosphorylated at Ser847 from 3 h after SCI, peaking at 24 h and gradually decreasing thereafter, and CaM-KII to be colocalized with nNOS after SCI. Immunohistochemical analysis revealed that SCI causes an increase in both NP847 and p-Thr286-CaM-KIIalpha in the nucleus intermediolateralis. These findings suggest that SCI induces p-Thr286-CaM-KIIalpha, which phosphorylates the nNOS at Ser847 in the nucleus intermediolateralis where NO is thought to play a role as a neurotransmitter in autonomic preganglionic neurons. Thus, the NP847 signaling pathway might be involved in the autonomic failure which occurs immediately after SCI.

Neuronal Ca2+/calmodulin-dependent protein kinase II--discovery, progress in a quarter of a century, and perspective: implication for learning and memory

Much has been learned about the activity-dependent synaptic modifications that are thought to underlie memory storage, but the mechanism by which these modifications are stored remains unclear. A good candidate for the storage mechanism is Ca2+/calmodulin-dependent protein kinase II (CaM kinase II). CaM kinase II is one of the most prominent protein kinases, present in essentially every tissue but most concentrated in brain. Although it has been about a quarter of a century since the finding, CaM kinase II has been of the major interest in the region of brain science. It plays a multifunctional role in many intracellular events, and the expression of the enzyme is carefully regulated in brain regions and during brain development. Neuronal CaM kinase II regulates important neuronal functions, including neurotransmitter synthesis, neurotransmitter release, modulation of ion channel activity, cellular transport, cell morphology and neurite extension, synaptic plasticity, learning and memory, and gene expression. Studies concerning this kinase have provided insight into the molecular basis of nerve functions, especially learning and memory, and indicate one direction for studies in the field of neuroscience. This review presents the molecular structure, properties and functions of CaM kinase II, as a major component of neurons, based mainly developed on findings made in our laboratory.

Transgenic labeling of the corticospinal tract for monitoring axonal responses to spinal cord injury

The rodent corticospinal tract (CST) has been used extensively to investigate regeneration and remodeling of central axons after injury. CST axons are currently visualized after injection of tracer dye, which is invasive, incomplete and prone to variation, and often does not show functionally crucial but numerically minor tract components. Here, we characterize transgenic mice in which CST fibers are specifically and completely labeled by yellow fluorescent protein (YFP). Using these CST-YFP mice, we show that minor CST components are responsible for most monosynaptic contacts onto motoneurons. Lesions of the main dorsal CST lead to extension of new collaterals, some of them originating from large, heavily myelinated axons within the minor dorsolateral and ventral CST components. Some of these new collaterals form additional direct synapses onto motoneurons. We propose that CST-YFP mice will be useful for evaluating strategies designed to maximize such remodeling and to promote regeneration.

Different basal levels of CaMKII phosphorylated at Thr286/287 at nociceptive and low-threshold primary afferent synapses

Postsynaptic autophosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) at Thr286/287 is crucial for the induction of long-term potentiation at many glutamatergic synapses, and has also been implicated in the persistence of synaptic potentiation. However, the availability of CaMKII phosphorylated at Thr286/287 at individual glutamatergic synapses in vivo is unclear. We used post-embedding immunogold labelling to quantitatively analyse the ultrastructural localization of CaMKII phosphorylated at Thr286/287 (pCaMKII) at synapses formed by presumed nociceptive and low-threshold mechanosensitive primary afferent nerve endings in laminae I-IV of rat spinal cord. Immunogold labelling was enriched in the postsynaptic densities of such synapses, consistent with observations in pre-embedding immunoperoxidase-stained dorsal horn. Presynaptic axoplasm also exhibited sparse immunogold labelling, in peptidergic terminals partly associated with dense core vesicles. Analysis of single or serial pCaMKII-immunolabelled sections indicated that the large majority of synapses formed either by presumed peptidergic or non-peptidergic nociceptive primary afferent terminals in laminae I-II of the spinal cord, or by presumed low-threshold mechanosensitive primary afferent terminals in laminae IIi-IV, contained pCaMKII in their postsynaptic density. However, the postsynaptic levels of pCaMKII immunolabelling at low-threshold primary afferent synapses were only approximately 50% of those at nociceptive synapses. These results suggest that constitutively autophosphorylated CaMKII in the postsynaptic density is a common characteristic of glutamatergic synapses, thus potentially contributing to maintenance of synaptic efficacy. Furthermore, pCaMKII appears to be differentially regulated between high- and low-threshold primary afferent synapses, possibly reflecting different susceptibility to synaptic plasticity between these afferent pathways.

Establishment of graded spinal cord injury model in a nonhuman primate: the common marmoset

Most previous studies on spinal cord injury (SCI) have used rodent models. Direct extrapolation of the results obtained in rodents to clinical cases is difficult, however, because of neurofunctional and anatomic differences between rodents and primates. In the present study, the development of histopathologic changes and functional deficits were assessed quantitatively after mild, moderate, and severe spinal cord contusive injuries in common marmosets. Contusive SCI was induced by dropping one of three different weights (15, 17, or 20 g) at the C5 level from a height of 50 mm. Serial magnetic resonance images showed significant differences in the intramedullary T1 low signal and T2 high signal areas among the three groups. Quantitative histologic analyses revealed that the number of motor neurons, the myelinated areas, and the amounts of corticospinal tract fibers decreased significantly as the injury increased in severity. Motor functions were evaluated using the following tests: original behavioral scoring scale, measurements of spontaneous motor activity, bar grip test, and cage-climbing test. Significant differences in all test results were observed among the three groups. Spontaneous motor activities at 10 weeks after injury were closely correlated with the residual myelinated area at the lesion epicenter. The establishment of a reliable nonhuman primate model for SCI with objective functional evaluation methods should become an essential tool for future SCI treatment studies. Quantitative behavioral and histopathologic analyses enabled three distinct grades of injury severity (15-g, 17-g, and 20-g groups) to be characterized with heavier weights producing more serious injuries, and relatively constant behavioral and histopathologic outcomes.

The contribution of autophosphorylated alpha-calcium-calmodulin kinase II to injury-induced persistent pain

Increases in neuronal activity in response to tissue or nerve injury can lead to prolonged functional changes in the spinal cord resulting in an enhancement/sensitization of nociceptive processing. To assess the contribution of alpha-calcium-calmodulin kinase II (alpha-CaMKII) to injury-induced inflammation and pain, we evaluated nociceptive responses in mice that carry a point mutation in the alpha-CaMKII gene at position 286 (threonine to alanine). The mutated protein is unable to autophosphorylate and thus cannot function independently of calcium and calmodulin. Responses to acute noxious stimuli did not differ between alpha-CaMKII T286A mutant and wild type mice. However, the ongoing pain produced by formalin injury was significantly reduced in the mutant mice, as was formalin-evoked spinal Fos-immunoreactivity. In contrast, the decreased mechanical and thermal thresholds associated with nerve injury, Complete Freund's Adjuvant-induced inflammation or formalin-evoked tissue injury were manifest equally in wild-type and mutant mice. Double-labeling immunofluorescence studies revealed that in the mouse alpha-CaMKII is expressed in the superficial dorsal horn as well as in a population of small diameter primary afferent neurons. In summary, our results suggest that alpha-CaMKII, perhaps secondary to an N-methyl-D-aspartate-mediated calcium increase in postsynaptic dorsal horn nociresponsive neurons, is a critical contributor to the spontaneous/ongoing component of tissue-injury evoked persistent pain.

Transplantation of human neural stem cells for spinal cord injury in primates

Recent studies have shown that delayed transplantation of neural stem/progenitor cells (NSPCs) into the injured spinal cord can promote functional recovery in adult rats. Preclinical studies using nonhuman primates, however, are necessary before NSPCs can be used in clinical trials to treat human patients with spinal cord injury (SCI). Cervical contusion SCIs were induced in 10 adult common marmosets using a stereotaxic device. Nine days after injury, in vitro-expanded human NSPCs were transplanted into the spinal cord of five randomly selected animals, and the other sham-operated control animals received culture medium alone. Motor functions were evaluated through measurements of bar grip power and spontaneous motor activity, and temporal changes in the intramedullary signals were monitored by magnetic resonance imaging. Eight weeks after transplantation, all animals were sacrificed. Histologic analysis revealed that the grafted human NSPCs survived and differentiated into neurons, astrocytes, and oligodendrocytes, and that the cavities were smaller than those in sham-operated control animals. The bar grip power and the spontaneous motor activity of the transplanted animals were significantly higher than those of sham-operated control animals. These findings show that NSPC transplantation was effective for SCI in primates and suggest that human NSPC transplantation could be a feasible treatment for human SCI.

Functional repair of the corticospinal tract by delayed transplantation of olfactory ensheathing cells in adult rats

Adult rats were trained to use their forepaws to retrieve a piece of food. Destruction of the dorsal corticospinal tract on one side at the level of the first cervical segment abolished the use of the ipsilateral forepaw for retrieval for at least 6 months after operation. Where a variable amount of the corticospinal tract was spared, there was a proportionate persistence of retrieval. In lesioned rats that had shown no retrieval for 8 weeks after operation, a suspension of olfactory ensheathing cells was injected into the lesion site. Starting between 1 and 3 weeks after transplantation, all rats with transplants bridging the lesion site resumed retrieval by the ipsilateral forepaw. Biotin dextran anterograde tracing shows regenerating corticospinal axons crossing the bridge, traveling caudally for approximately 10 mm in the distal part of the corticospinal tract and forming terminal arborizations in the spinal gray matter. Functional recovery can occur when only approximately 1% of the corticospinal tract axons are present.

The netrin 1 receptors Unc5h3 and Dcc are necessary at multiple choice points for the guidance of corticospinal tract axons

Migrating axons require the correct presentation of guidance molecules, often at multiple choice points, to find their target. Netrin 1, a bifunctional cue involved in both attracting and repelling axons, is involved in many cell migration and axon pathfinding processes in the CNS. The netrin 1 receptor DCC and its Caenorhabditis elegans homolog UNC-40 have been implicated in directing the guidance of axons toward netrin sources, whereas the C. elegans UNC-6 receptor, UNC-5 is necessary for migrations away from UNC-6. However, a role of vertebrate UNC-5 homologs in axonal migration has not been demonstrated. We demonstrate that the Unc5h3 gene product, shown previously to regulate cerebellar granule cell migrations, also controls the guidance of the corticospinal tract, the major tract responsible for coordination of limb movements. Furthermore, we show that corticospinal tract fibers respond differently to loss of UNC5H3. In addition, we observe corticospinal tract defects in mice homozygous for a spontaneous mutation that truncates the Dcc transcript. Postnatal day 0 netrin 1 mutant mice also demonstrate corticospinal tract abnormalities. Last, interactions between the Dcc and Unc5h3 mutations were observed in gene dosage experiments. This is the first evidence of an involvement in axon guidance for any member of the vertebrate unc-5 family and confirms that both the cellular and axonal guidance functions of C. elegans unc-5 have been conserved in vertebrates.

Alginate, a bioresorbable material derived from brown seaweed, enhances elongation of amputated axons of spinal cord in infant rats

Freeze-dried alginate sponge crosslinked with covalent bonds was developed in our laboratory and has been demonstrated to enhance peripheral nerve regeneration. In this study, we examined spinal cord repair using alginate sponge in infant rats. On postnatal day 8-12, the spinal cord was transversely resected at Th7-Th8 to produce a 2-mm gap. The gap was filled with alginate sponge in the alginate group. For the control group, the gap was left empty. In the alginate group, the recovery of evoked electromyogram and sensory-evoked potentials 6 weeks after surgery indicated that elongation of axons could establish electrophysiologically functional projections through the gap. A histological study revealed that myelinated and unmyelinated axons, surrounded by a perineurial-like structure, had elongated across the gap. An immunohistochemical examination revealed that elongation of astrocytic processes and/or migration of astrocytes into the alginate sponge was induced, whereas astrocyte gliosis was reduced at the interface between the implanted alginate and the host spinal cord, compared with the control group. However, a horseradish peroxidase tracing study revealed ascending and descending fibers had also elongated into the gap and reentered the other stump of the transected spinal cord beyond the gap. These results suggest that alginate might provide a permissive microenvironment for elongation of spinal cord axons.

Neuronal plasticity and signal transduction in nociceptive neurons: implications for the initiation and maintenance of pathological pain

Pathological pain, consisting of tissue injury-induced inflammatory and nerve injury-induced neuropathic pain, is an expression of neuronal plasticity. One component of this is that the afferent input generated by injury and intense noxious stimuli triggers an increased excitability of nociceptive neurons in the spinal cord. This central sensitization is an activity-dependent functional plasticity that results from activation of different intracellular kinase cascades leading to the phosphorylation of key membrane receptors and channels, increasing synaptic efficacy. Central sensitization is both induced and maintained in a transcription-independent manner. Several different intracellular signal transduction cascades converge on MAPK (mitogen-activated protein kinase), activation of which appears to be a master switch or gate for the regulation of central sensitization. In addition to posttranslational regulation, the MAPK pathway may also regulate long-term pain hypersensitivity, via transcriptional regulation of key gene products. Pharmacological intervention targeted specifically at the signal transduction pathways in nociceptive neurons may provide, therefore, new therapeutic opportunities for pathological pain.

Immunohistochemical study of the distribution of Ca(2+)/calmodulin-dependent protein kinase phosphatase in the rat central nervous system

Distribution of Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaM-K Pase) which dephosphorylate multifunctional Ca(2+)/calmodulin-dependent protein kinases (CaM-kinases) in the rat brain and spinal cord were examined immunohistochemically by using an antibody against this enzyme. CaM-K Pase was localized only in the cytoplasm as has been investigated in PC 12 cells, and was never observed in the nucleus. Immunostainability varied from cell group to cell group. Mitral cells in the olfactory bulb, pyramidal neurons in the fifth layer of the cerebral cortex, hippocampal and striatal interneurons, dorsal and ventral pallidal, entopeduncular, and the reticular part of the substantia nigra neurons were intensely immunolabeled. Motoneurons in all the cranial nerve nuclei and the anterior horn of the spinal cord also revealed intense immunolabeling. On the contrary, pyramidal neurons in the Ammon's horn of the hippocampal formation, granule cells in the olfactory bulb, dentate gyrus and cerebellar cortex, Purkinje cells, neurons in the medial habenular nucleus and the inferior olivary nucleus have not shown immunoreactivity. Axons in the white matter or nerve root of the cranial nerve nuclei were immunolabeled. Glial cells in the white matter also showed immunostaining. Because the substrate of CaM-K Pase is multifunctional CaM-kinase II, I and IV, localization of each CaM-kinase was compared with that of CaM-K Pase. The distribution of CaM-K Pase and these CaM-kinases was found to overlap in various regions in the brain and spinal cord. It was concluded, therefore, that CaM-K Pase could regulate the activity of these CaM-kinases by dephosphorylation, when they existed together in neurons.

The unique histopathological responses of the injured spinal cord. Implications for neuroprotective therapy

Tissue destruction at the primary site of a spinal cord injury leads to persistent necrosis that progressively enlarges the lesion. Steroids attenuate this necrotizing process and promote tissue repair even though such anti-inflammatory drugs interfere with wound healing in non-CNS organs. To address this paradox, the spinal cord of rats and mice was crushed extradurally and the effects of the following anti-inflammatory agents studied by light microscopical image analysis: allopurinol, aminoguanidine, indomethacin, a bacterial lipopolysaccharide, naproxen, and pregnenolone. The contribution of Wallerian degeneration to progressive necrosis was studied in a mutant mouse strain (WldS) that is characterized by delayed Wallerian degeneration. In rats, the anti-inflammatory agents selectively attenuated progressive necrosis and encouraged wound healing. In mice, considerable tissue repair occurred without pharmacological intervention; this wound-healing process was delayed in the mutant WldS strain. Since spinal cord injury results in concomitant tissue necrosis and wound healing, a goal of neuroprotective therapy is to regulate the dynamic balance between these destructive and reparative processes.

Regional differences between the immunohistochemical distribution of Ca2+/calmodulin-dependent protein kinase II alpha and beta isoforms in the brainstem of the rat

The distribution of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) alpha and beta isoforms in the brainstem of adult rats was investigated using an immunohistochemical method with two monoclonal antibodies which specifically recognize the alpha and beta isoform, respectively. We found that these isoforms were differentially expressed by neurons in the substantia nigra, red nucleus, dorsal cochlear nucleus, pontine nuclei and inferior olivary nucleus. Neurons in the inferior olivary nucleus express the alpha isoform, but not the beta isoform. In contrast, neurons in the substantia nigra, red nucleus and pontine nuclei were immunostained with the beta antibody, but not with the alpha antibody. In the dorsal cochlear nucleus, neurons in layers I and II were alpha-immunopositive, whereas neurons in layers III and IV were beta-immunopositive. Therefore, the distribution of the CaM kinase II alpha-immunopositive neurons is completely different from that of CaM kinase II beta-immunopositive neurons. Next we examined the possible coexistence of CaM kinase II alpha isoform and glutamate or that of CaM kinase II beta isoform and glutamic acid decarboxylase (GAD) in the single neuron by double immunofluorescence labelling using a pair of anti-alpha and anti-glutamate antibodies, or a pair of anti-beta and anti-GAD antibodies. The results indicated that neurons expressing anti-alpha immunoreactivity were also immunopositive against anti-glutamate antibody, and neurons expressing beta isoform were also immunopositive against anti-GAD antibody, suggesting that alpha-immunopositive neurons are classified as excitatory-type neurons, and on the contrary, beta-immunopositive neurons are classified as inhibitory-type neurons. In conclusion, the present study confirmed that alpha- and beta-isoforms of CaM kinase II are differentially expressed in the nuclei of the brainstem and have different roles.

Calcium/calmodulin-dependent protein kinase II expression in motor neurons: effect of axotomy

Although Ca2+/calmodulin-dependent (CaM) protein kinase II isoforms are present in the nervous system in high amounts, many aspects of in vivo expression, localization, and function remain unexplored. During development, CaM kinase IIalpha and IIbeta are differentially expressed. Here, we examined CaM kinase II isoforms in Sprague-Dawley rat sciatic motor neurons before and after axotomy. We cut the L4-5 spinal nerves unilaterally and exposed the proximal nerve stumps to a fluoroprobe, to retrogradely label the neurons of origin. Anti-CaM kinase IIbeta antibody showed immunoreactivity in motor neurons, which decreased to low levels by 4 days after axotomy. We found a similar response by in situ hybridization with riboprobes. The decrease in expression of mRNA and protein was confined to fluorescent motor neurons. For CaM kinase IIalpha, in situ hybridization showed that the mRNA was in sciatic motor neurons, with a density unaffected by axotomy. However, these neurons were also enlarged, suggesting an up-regulation of expression. Northern blots confirmed an mRNA increase. We were unable to find CaM kinase IIalpha immunoreactivity before or after axotomy in sciatic motor neuron cell bodies, suggesting that CaM kinase IIalpha is in the axons or dendrites, or otherwise unavailable to the antibody. Using rats with crush lesions, we radiolabeled axonal proteins being synthesized in the cell body and used two-dimensional polyacrylamide gel electrophoresis with Western blots to identify CaM kinase IIalpha as a component of slow axonal transport. This differential regulation and expression of kinase isoforms suggests separate and unique intracellular roles. Because we find CaM kinase IIbeta down-regulates during axonal regrowth, its role in these neurons may be related to synaptic transmission. CaM kinase IIalpha appears to support axonal regrowth.

Experimental spinal cord injury: Wallerian degeneration in the dorsal column is followed by revascularization, glial proliferation, and nerve regeneration

The presence of adequate blood supply is a critical factor in recovery from traumatic injuries. We have examined whether the revascularization of the injured tissues is as crucial a precondition for wound healing in the spinal cord as in other organs. The development of the initial primary lesion (PL) after spinal crush injury in rats is followed by the formation of a unique tunnel-like dorsal column lesion (DCL) that extends rostrocaudally for many millimeters from the primary injury site. The DCL has been shown to result from Wallerian degeneration of the long spinal tracts in the dorsal column. In this study, we compared the processes of revascularization, wound healing, and nerve regeneration in the PL and the DCL by light microscopy after a crush injury of the cord. The spinal cord of 54 adults rats was crushed at T8 with jewelers forceps. The rats were allowed to survive from 3 h up to 8 weeks after spinal cord injury. The PL appeared immediately after injury and the DCL began to develop 6 h later. Infiltration of neutrophils, which is the first sign of the inflammatory responses to injury, began several hours later in the DCL than in the PL. Secondary vascular injury then occurred which resulted in hemorrhage around the DCL and rapid enlargement of the lesion during the remainder of the first week. Subsequent changes in the PL and DCL were entirely different. The PL underwent progressive enlargement and cavitation such that by 8 weeks, the lesion contained only very few cells, vessels, and axons scattered between huge fluid-filled cavities. The DCL, on the other hand, was maximal in size at 1 week and declined significantly in size and cavitation thereafter. By 8 weeks it was highly vascularized, contained abundant nerve fibers, and lacked any trace of cavitation. These findings amplify the current view that ischemia plays a critical role in spinal cord trauma by showing that revascularization precedes tissue repair and nerve regeneration in the dorsal columns. We conclude (a) that a well-vascularized lesion permits the ingrowth of glial and other cells which give rise to a supportive matrix for the nerve regeneration and (b) that procedures which induce revascularization or angiogenesis will ameliorate the cascade of progressive tissue necrosis.

Localization of the calcium/calmodulin-dependent protein phosphatase, calcineurin, in the hindbrain and spinal cord of the rat

The calcium/calmodulin-dependent protein phosphatase calcineurin was localized at the light microscopic level in the rat hindbrain and spinal cord by using an antibody against the alpha-isoform of the catalytic subunit. Calcineurin was highly concentrated in axons, dendrites, and cell bodies of a subpopulation of alpha-motoneurons in hindbrain motor nuclei and the lateral motor column along the length of the spinal cord. These calcineurin-positive alpha-motoneurons appeared to be randomly distributed and represented approximately 25% of the total alpha-motoneuron pool in the motor trigeminal nucleus and the spinal cord lateral motor column. Within the facial nucleus, calcineurin-containing motoneurons were present in the medial and dorsal subdivision but not in the lateral and intermediate subdivision. In addition to the enrichment in motoneurons, calcineurin was enriched in cells of the superficial laminae of the spinal cord dorsal horn and its extension into the medulla, the caudal spinal trigeminal nucleus. Axonal staining in the white matter of the spinal cord was generally weak, except in the dorsolateral funiculus, where strongly calcineurin-positive axons formed a putative ascending tract that appeared to terminate uncrossed in the caudal lateral reticular nucleus of the medulla. This tract may originate from calcineurin-positive cells in the dorsolateral funiculus. We also compared the distribution of calcineurin with calcium/calmodulin-dependent kinase II in the spinal cord and found that the kinase is more widely expressed. Thus, calcineurin is highly restricted to a few locations in the hindbrain and spinal cord. Selective staining in facial subnuclei that innervate phasically active muscles suggests that calcineurin-positive motoneurons represent a subset of alpha-motoneurons innervating a metabolic subtype of muscle fibers, possibly fast-twitch fibers.

Genetic influences on cellular reactions to spinal cord injury: a wound-healing response present in normal mice is impaired in mice carrying a mutation (WldS) that causes delayed Wallerian degeneration

Progressive tissue necrosis is a process unique to the injured mammalian spinal cord which often leads to gradually increasing cavitation and enlargement of the lesion. To evaluate the role of neuronal degeneration in initiating this response, histopathological changes were compared in C57BL and WldS (delayed Wallerian degeneration mutation) mice. The spinal cord was crushed at T8, producing a primary lesion at the site of the trauma and a secondary lesion extending rostrocaudally in the dorsal columns (where long ascending and descending fiber tracts undergo Wallerian degeneration). Cavitation was relatively mild at both sites and developed mainly at the margins of the lesions. In striking contrast to spinal cord injury in rats, progressive necrosis did not occur in mice; instead, the primary and secondary lesion sites became filled in by macrophages and fibroblasts embedded in a well-vascularized collagenous stroma. Quantitative image analysis revealed that the primary lesion decreased dramatically in size and cavitation between 2 and 3 weeks in C57BL, whereas in WldS the reduction in size and cavitation began later (at 4 weeks) and was less complete. The initial development of the secondary lesion began later and its healing was less complete in WldS than C57BL. These results are consistent with the hypothesis that neuronal damage, including Wallerian degeneration, triggers inflammatory responses leading to tissue repair. For this reason, any delay in neuronal degeneration, as in the WldS mutation, results in deficient tissue repair as reflected in the larger size of both primary and dorsal column lesions.

Anatomy, development and lesion-induced plasticity of rodent corticospinal tract

In this review the current knowledge of the anatomy, development and plasticity of the rodent corticospinal tract is summarised. Recent technical advancements, especially in neuronal tracing methods, have provided much new data concerning the anatomy of the corticospinal tract. The rodent corticospinal axons project to the subcortical nuclei via collateral branches. These collateral branches of corticospinal axons are formed by delayed interstitial budding during early postnatal periods. Corticospinal neurons are generated in the ventricular zone during a short time lag, migrate into the cortical plate, and settle in layer V of the cerebral cortex. The migration of corticospinal neurons is experimentally deranged by prenatal exposure to alcohol or genetically affected by the reeler genetic locus (rl), resulting in generation of ectopic corticospinal neurons. Such experimentally or genetically induced ectopic corticospinal neurons are a good model for examining whether target recognition and path finding are affected by the intracortical position of corticospinal neurons. Some chemical molecules (e.g. L1 and B-50/GAP43) are transiently expressed in the corticospinal tract during the perinatal period, while others (e.g. protein kinase C gamma subspecies and alpha CaM kinase II) are permanently expressed in the adult corticospinal tract. The only chemical marker specific for layer V corticofugal neurons is an antibody to a soluble protein, protein 35. Since the corticospinal tract in the rodent is an easily identified group of fibers situated in the most ventral portion of the dorsal funiculus of the spinal cord and exhibits considerable postnatal development, it has often been utilized in the neurological studies on plasticity and regenerative capacity of the lesioned central nervous system. Recently, it has been clarified that growing corticospinal fibers have the ability to penetrate and traverse across the lesion sites under certain special conditions.

Specific distribution of Ca2+/calmodulin-dependent protein kinase II alpha and beta isoforms in some structures of the rat forebrain

The immunohistochemical distribution of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) alpha and beta isoforms in the rat forebrain was examined by using monoclonal antibodies specific to each isoform. The present study confirmed that alpha and beta immunoreactivities are localized only in neuronal elements. At the light microscopic level, specific distribution patterns of these isoforms and staining characteristics were recognized in some regions of the forebrain as follows. Firstly, alpha-immunoreactive neurons were more homogeneously distributed throughout the cellular layers of the cerebral cortex (i.e., layers II-VI) than beta-immunoreactive ones. Secondly, neurons in the globus pallidus were immunostained by the anti-beta antibody, but not by the anti-alpha antibody. Thirdly, neurons in the medial habenular nucleus, the subthalamic nucleus and the reticular thalamic nucleus were more densely stained with the anti-beta antibody than with the anti-alpha antibody. However, marked differences were not observed in the hippocampal formation at the light microscopic level. The electron microscopic analysis of the cerebral cortex demonstrated that subcellular localizations of alpha- and beta-immunoreactive products within the cortical neurons were quite dissimilar: (i) the nucleus was stained only with the anti-alpha antibody, but not with the anti-beta antibody, and (ii) beta-immunoreactive products were more sporadically localized in the cytoplasms of the perikarya and dendrites than the alpha-immunoreactive ones. These regional and subcellular differences between the distribution patterns of alpha and beta immunoreactivities suggest the functional diversity of CaM kinase II alpha and beta isoforms in the central nervous system.

Immunocytochemical localization of calcium/calmodulin-dependent protein kinase II isoforms in the ganglion cells of the rat retina: immunofluorescence histochemistry combined with a fluorescent retrograde tracer

To determine whether or not calcium/calmodulin-dependent protein kinase II (CaM kinase II) is localized in the ganglion cells in the rat retina, we labeled ganglion cells by injection of Fast blue (FB) into the lateral geniculate nucleus and then stained the retina immunohistochemically with monoclonal antibodies which react specifically with the alpha and beta isoforms of CaM kinase II. Eighty and 90% of the FB-labeled ganglion cells in the ganglion cell layer were immunoreactive with the alpha and beta antibodies, respectively, suggesting that both alpha and beta isoforms of CaM kinase II are expressed in most ganglion cells which project to the lateral geniculate nucleus.