Activation of M3-AChR and IP3/Ca2+/PKC signaling pathways by pilocarpine increases glycine-induced currents in ventral horn neurons of the spinal cord.

Our study aimed to determine the effects of pilocarpine and the mechanisms involving muscarinic acetylcholine receptors (mAChRs) on glycine receptors (GlyRs) in neurons of the spinal cord ventral horn. An enzymatic digestion combined with acute mechanical separation was applied to isolate neurons from the spinal cord ventral horn. Patch-clamp recording was then used to investigate the outcomes of pilocarpine. Our results indicate that pilocarpine increased the glycine currents in a concentration-dependent manner, which was blocked by the M3-AChR selective antagonists 4-DAMP and J104129. Pilocarpine also enhanced the glycine currents in nominally Ca2+-free extracellular solution. Conversely, the enhancement of glycine currents by pilocarpine disappeared when intracellular Ca2+ was chelated by BAPTA. Heparin and Xe-C, which are IP3 receptor antagonists, also totally abolished the pilocarpine effect. Furthermore, Bis-IV, a PKC inhibitor, eliminated the pilocarpine effect. Additionally, PMA, a PKC activator, mimicked the pilocarpine effect. These results indicate that pilocarpine may increase the glycine currents by activating the M3-AChRs and IP3/Ca2+/PKC pathways.

Developmental Formation of the GABAergic and Glycinergic Networks in the Mouse Spinal Cord.

Gamma-aminobutyric acid (GABA) and glycine act as inhibitory neurotransmitters. Three types of inhibitory neurons and terminals, GABAergic, GABA/glycine coreleasing, and glycinergic, are orchestrated in the spinal cord neural circuits and play critical roles in regulating pain, locomotive movement, and respiratory rhythms. In this study, we first describe GABAergic and glycinergic transmission and inhibitory networks, consisting of three types of terminals in the mature mouse spinal cord. Second, we describe the developmental formation of GABAergic and glycinergic networks, with a specific focus on the differentiation of neurons, formation of synapses, maturation of removal systems, and changes in their action. GABAergic and glycinergic neurons are derived from the same domains of the ventricular zone. Initially, GABAergic neurons are differentiated, and their axons form synapses. Some of these neurons remain GABAergic in lamina I and II. Many GABAergic neurons convert to a coreleasing state. The coreleasing neurons and terminals remain in the dorsal horn, whereas many ultimately become glycinergic in the ventral horn. During the development of terminals and the transformation from radial glia to astrocytes, GABA and glycine receptor subunit compositions markedly change, removal systems mature, and GABAergic and glycinergic action shifts from excitatory to inhibitory.

Coherence analysis of the calcium activity of putative astrocytic and neuronal cells on the L5 ventral horn and neural output in activated lumbar CPG networks.

Astrocytes are thought to play a crucial role in providing structure to the spinal cord and maintaining efficient synaptic function and metabolism because their fine processes envelop the synapses of neurons and form many neuronal networks within the central nervous system (CNS). To investigate whether putative astrocytes and putative neurons distributed on the ventral horn play a role in the modulation of lumbar locomotor central pattern generator (CPG) networks, we used extracellular recording and optical imaging techniques and recorded the neural output from the left L5 ventral root and the calcium activity of putative astrocytes and neurons in the L5 ventral horn at the same time when activating an isolated L1-L5 spinal cord preparation from rats aged 0-2 days. Optical measurements detected cells that showed a fluorescence intensity change under all experimental conditions, namely, (1) 5-HT + NMDA, (2) TTX, and (3) TTX + Low K+. These cells were semiautomatically identified using an in-house MATLAB-based program, as putative astrocytes and neurons according to the cell classification, i.e., increased or decreased fluorescence intensity change (ΔF/F0), and subjective judgment based on their soma size. Coherence and its phase were calculated according to the calcium activity of the putative astrocytes and putative neurons, and neural output was calculated during fictive locomotion with in-house MATLAB-based programs. We found that the number of putative astrocytes activated by applying low K+ tends not to differ from that activated by applying the protease-activated receptor 1 (PAR1) selective agonist TFLLR-NH2 (TFLLR). Moreover, the calcium activity of several putative astrocytes and neurons synchronized with locomotor-like activity at a frequency range below 0.5 Hz and the time lag between peaks of cellular calcium activity and locomotor-like activity ranged from -1000 to + 1000 ms. These findings presumably indicates that these putative astrocytes and neurons in the left L5 ventral horn require -1000 to + 1000 ms to communicate with lumbar CPG networks and maintain efficient synaptic function and metabolism in activated lumbar CPG networks. This finding suggests the possibility that putative astrocytic and neuronal cells in the L5 ventral horn contribute to generating the rhythms and patterns of locomotor-like activity by activated CPG networks in the first to fifth lumbar spinal cord.

Protective effects of remote ischemic preconditioning against spinal cord ischemia-reperfusion injury in rats.

OBJECTIVES: We aimed to investigate the protective effect of remote ischemic preconditioning against spinal cord ischemia and find a clue to its mechanism by measuring glutamate concentrations in the spinal ventral horn. METHODS: Male Sprague-Dawley rats were divided into 5 groups (n = 6 in each group) as follows: sham; SCI (only spinal cord ischemia); RIPC/SCI (perform remote ischemic preconditioning before spinal cord ischemia); MK-801/RIPC/SCI (administer MK-801, N-methyl-D-aspartate receptor antagonist, before remote ischemic preconditioning); and MK-801/SCI (administer MK-801 without remote ischemic preconditioning). Remote ischemic preconditioning was achieved by brief limb ischemia 80 minutes before spinal cord ischemia. MK-801 (1 mg/kg, intravenous) was administered 60 minutes before remote ischemic preconditioning. The glutamate concentration in the ventral horn was measured by microdialysis for 130 minutes after spinal cord ischemia. Immunofluorescence was also performed to evaluate the expression of N-methyl-D-aspartate receptor 2B subunit in the ventral horn 130 minutes after spinal cord ischemia. RESULTS: The glutamate concentrations in the spinal cord ischemia group were significantly higher than in the sham group at all time points (P < .01). Remote ischemic preconditioning attenuated the spinal cord ischemia-induced glutamate increase. When MK-801 was preadministered before remote ischemic preconditioning, glutamate concentration was increased after spinal cord ischemia (P < .01). Immunofluorescence showed that remote ischemic preconditioning prevented the increase in the expression of N-methyl-D-aspartate receptor 2B subunit on the surface of motor neurons (P = .047). CONCLUSIONS: Our results showed that remote ischemic preconditioning prevented spinal cord ischemia-induced extracellular glutamate increase in ventral horn and suppressed N-methyl-D-aspartate receptor 2B subunit expression.

Conditional RAC1 knockout in motor neurons restores H-reflex rate-dependent depression after spinal cord injury.

A major complication with spinal cord injury (SCI) is the development of spasticity, a clinical symptom of hyperexcitability within the spinal H-reflex pathway. We have previously demonstrated a common structural motif of dendritic spine dysgenesis associated with hyperexcitability disorders after injury or disease insults to the CNS. Here, we used an adeno-associated viral (AAV)-mediated Cre-Lox system to knockout Rac1 protein expression in motor neurons after SCI. Three weeks after AAV9-Cre delivery into the soleus/gastrocnemius of Rac1-"floxed" adult mice to retrogradely infect spinal alpha-motor neurons, we observed significant restoration of RDD and reduced H-reflex excitability in SCI animals. Additionally, viral-mediated Rac1 knockdown reduced presence of dendritic spine dysgenesis on motor neurons. In control SCI animals without Rac1 knockout, we continued to observe abnormal dendritic spine morphology associated with hyperexcitability disorder, including an increase in mature, mushroom dendritic spines, and an increase in overall spine length and spine head size. Taken together, our results demonstrate that viral-mediated disruption of Rac1 expression in ventral horn motor neurons can mitigate dendritic spine morphological correlates of neuronal hyperexcitability, and reverse hyperreflexia associated with spasticity after SCI. Finally, our findings provide evidence of a putative mechanistic relationship between motor neuron dendritic spine dysgenesis and SCI-induced spasticity.

Orexin-A potentiates glycine currents by activating OX1R and IP3/Ca2+/PKC signaling pathways in spinal cord ventral horn neurons.

Orexin-A/B modulates multiple physical functions by activating their receptors (OX1R and OX2R), but its effects in the spinal cord motor control remain unknown. Using acute separation (by digestive enzyme) of cells and patch-clamp recordings, we aimed to investigate the effect and mechanisms of orexin-A on the glycine receptors in the spinal cord ventral horn neurons. Orexin-A potentiated the glycine currents by activating OX1R. In Ca2+-free extracellular solution, orexin-A still increased the glycine currents. While, the orexin-A-induced potentiation was blocked when Ca2+ was chelated by internal infusion of BAPTA, and the orexin-A effect was abolished by the IP3 receptor antagonists heparin and Xe-C. The PKC inhibitor Bis-IV nullified the orexin-A effect. In addition, orexin-A did not cause a further enhancement of the glycine currents after bath application of the PKC activator PMA. In conclusion, after OX1R is activated, a distinct IP3/Ca2+-dependent PKC signaling pathway, is likely responsible for the orexin-A potentiation on glycine currents in the spinal cord ventral horn neurons.

Transplantation of viable mitochondria attenuates neurologic injury after spinal cord ischemia.

OBJECTIVES: Spinal cord ischemia (SCI) is one of the major concerns of postoperative paraplegia during major vascular or aortic surgery. Since mitochondrial dysfunction develops at the early stage of SCI, this study tested the neuronal protective effect of transplantation of viable mitochondria to the ischemic cord in rats. METHODS: SCI was induced by crossclamping of thoracic aorta at T6 level for 25 minutes, followed by release of vascular clip to restore aortic blood flow in the anesthetized rats. Mitochondria (100 µg) were isolated from freshly harvested soleus muscle and delivered via the internal jugular vein before releasing of vascular clip. The motor function was assessed independently up to 7 days after reperfusion. Spinal cords were harvested and analyzed for molecular and histological changes. RESULTS: Whole-body in vivo images acquired by an in vivo imaging system confirmed the enhancement of MitoTracker fluorescence at the regions below crossclamping and in the ischemic cord. Compared with control vehicles, transplantation of mitochondria significantly improved the lower-limb locomotor function of rats subjected to cord ischemia up to 7 days after surgery. Mitochondrial transplantation suppressed the regional endoplasmic reticulum stress in the ischemic cord by attenuating CCAAT-enhancer-binding protein homologous protein expression and restoring binding immunoglobulin protein levels. In accordance, tissue levels of interleukin-6, tumor necrosis factor-α, and caspase-3 were attenuated in the mitochondrial transplanted group. Histologic examination also showed significant increase in numbers of Nissls bodies in the neurons at the ventral horn of ischemic cord following mitochondrial transplantation. CONCLUSIONS: Our study showed that transplantation of freshly isolated mitochondria during the early stage of spinal cord ischemia-reperfusion injury suppressed the oxidative stress in endoplasmic reticulum of the injured cord, thereby reducing neuroapoptosis and improving locomotor function of rats with SCI.

Inositol hexakisphosphate kinase 2 promotes cell death of anterior horn cells in the spinal cord of patients with amyotrophic lateral sclerosis.

We have previously reported that inositol hexakisphosphate kinase (InsP6K)2 mediates cell death. InsP6K2 is abundantly expressed in anterior horn cells of the mammalian spinal cord. We investigated the role of InsP6K2 in spinal cords of patients with amyotrophic lateral sclerosis (ALS). Autopsy specimens of lumbar spinal cords from ten patients with sporadic ALS and five non-neurological disease patients (NNDPs) were obtained. We performed quantitative real-time PCR, immunostaining, and western blotting for InsP6K1, InsP6K2, InsP6K3, protein kinase B (Akt), casein kinase 2 (CK2), and 90-kDa heat-shock protein (HSP90). In contrast to InsP6K1 and InsP6K3 mRNA expression, InsP6K2 levels in anterior horn cells of the spinal cord were significantly increased in ALS patients compared to NNDPs. In ALS patients, InsP6K2 translocated from the nucleus to the cytoplasm. However, we observed a decrease in HSP90, CK2, and Akt activity in ALS patients compared to NNDPs. A previous study reported that InsP6K2 activity is suppressed after binding to HSP90 and subsequent phosphorylation and degradation by CK2, thus decreasing InsP6K2 activity. However, InsP7, which is generated by InsP6K2, can compete with Akt for PH domain binding. Consequently, InsP7 can inhibit Akt phosphorylation. Our results suggest that InsP6K2 is activated in the spinal cord of patients with ALS and may play an important role in ALS by inducing cell death mechanisms via Akt, CK2, and HSP90 pathways.

5-HT2A/B receptor expression in the phrenic motor nucleus in a rat model of ALS (SOD1G93A).

Despite respiratory motor neuron death, ventilation is preserved in SOD1G93A rats. Compensatory respiratory plasticity may counterbalance the loss of these neurons. Phrenic long-term facilitation (pLTF; a form of respiratory plasticity) in naïve rats is 5-HT2 and NADPH oxidase-dependent. Furthermore, 5-HT2A, not 5-HT2B, receptor-induced phrenic motor facilitation is NADPH oxidase-independent in naïve rats. pLTF is NADPH oxidase-dependent in pre-symptomatic, but not end-stage, SOD1G93A rats. Here, we hypothesized that in the putative phrenic motor nucleus (PMN) of SOD1G93A rats vs. wild-type littermates: 1) pre-symptomatic rats would have greater 5-HT2B receptor expression that decreases at end-stage; and 2) 5-HT2A receptor expression would increase from pre-symptomatic to end-stage. Putative PMN 5-HT2A receptor expression was reduced when comparing across (but not within) pre-symptomatic vs. end-stage groups (p < 0.05). In contrast, putative PMN 5-HT2B receptor expression was increased when comparing across pre-symptomatic vs. end-stage groups, and within end-stage groups (p < 0.05). These data suggest a potential role for 5-HT2 receptors in pLTF and breathing in SOD1G93A rats.

Infantile onset progressive cerebellar atrophy and anterior horn cell Degeneration-A novel phenotype associated with mutations in the PLA2G6 gene.

Pontocerebellar hypoplasia (PCH) encompasses a group of neurodegenerative disorders. There are ten known subtypes with common characteristics of pontine and cerebellar hypoplasia or atrophy, neocortical atrophy, and microcephaly. PCH is associated with anterior horn cell degeneration in PCH1a and PCH1b due to mutations in the VRK1 and EXOSC3 genes. Late onset PCH1 has been described in single case reports. The molecular etiology remains mostly unknown. We describe two siblings from a consanguineous Moslem Arabic family with a unique combination of progressive cerebellar atrophy and a SMA-like anterior horn cell degeneration due to a homozygous mutation in the PLA2G6 gene (NM_003560.2). The PLA2G6 gene encodes phospholipase A2 beta, which is involved in the remodeling of membrane phospholipids, signal transduction and calcium signaling, cell proliferation and apoptosis. Mutations in PLA2G6 are known to cause Neurodegeneration with brain iron accumulation 2 (NBIA2): Our patients have some similarities with NBIA2; both are characterized by rapidly progressive psychomotor regression and cerebellar atrophy. However, NBIA2 is not known to exhibit anterior horn cell degeneration. Our patients' phenotype is more consistent with late onset PCH1; thus, indicating that the spectrum of clinical and radiological presentations of PLA2G6 mutations should be extended and that this gene should be included in the molecular evaluation of patients with late onset PCH1.

Autophagy Is a Common Degradation Pathway for Bunina Bodies and TDP-43 Inclusions in Amyotrophic Lateral Sclerosis.

Bunina bodies (BBs) coexisting with TDP-43-immunoreactive (TDP-43-IR) skein-like inclusions (SIs) and round inclusions (RIs) in lower motor neurons are a frequent feature of sporadic amyotrophic lateral sclerosis (sALS). Since previous studies have shown that BBs and TDP-43-IR inclusions are often detected in association with autophagy-related structures (autophagosomes and autolysosomes), we examined the anterior horn cells (AHCs) of the spinal cord from 15 patients with sALS and 6 control subjects, using antibodies against autophagy-related proteins (LC3, cathepsin B, and cathepsin D). Among AHCs with SIs, 43.9% contained BBs, whereas 51.7% of AHCs with RIs did so. The cytoplasm of AHCs showed diffuse immunoreactivity for LC3, cathepsin B and cathepsin D in both sALS and controls. Ultrastructurally, SIs and mature BBs contained autophagosomes and autolysosomes. Mature BBs were localized in the vicinity of SIs. RIs also contained autophagosomes, autolysosomes, and early-stage BBs. These findings suggest that autophagy is a common degradation pathway for BBs and TDP-43-IR inclusions, which may explain their frequent coexistence.

p190RhoGAP Filters Competing Signals to Resolve Axon Guidance Conflicts.

The rich functional diversity of the nervous system is founded in the specific connectivity of the underlying neural circuitry. Neurons are often preprogrammed to respond to multiple axon guidance signals because they use sequential guideposts along their pathways, but this necessitates a strict spatiotemporal regulation of intracellular signaling to ensure the cues are detected in the correct order. We performed a mouse mutagenesis screen and identified the Rho GTPase antagonist p190RhoGAP as a critical regulator of motor axon guidance. Rather than acting as a compulsory signal relay, p190RhoGAP uses a non-conventional GAP-independent mode to transiently suppress attraction to Netrin-1 while motor axons exit the spinal cord. Once in the periphery, a subset of axons requires p190RhoGAP-mediated inhibition of Rho signaling to target specific muscles. Thus, the multifunctional activity of p190RhoGAP emerges from its modular design. Our findings reveal a cell-intrinsic gate that filters conflicting signals, establishing temporal windows of signal detection.

l-Theanine and NEP1-40 promote nerve regeneration and functional recovery after brachial plexus root avulsion.

Brachial plexus root avulsion causes severe sequelae Treatments and prognosis face many problems, including inflammatory reaction, oxidative damage, and myelin related inhibitory effect. l-Theanine has anti-inflammatory, anti-oxidative, and neuroprotective effects. NEP1-40 competitively inhibits Nogo-66 receptor (NgR1) promotes axonal regeneration. Forty-eight Sprague-Dawley rats were randomly assigned into four groups to establish an animal model of brachial plexus root avulsion. Inflammation and oxidative damage were evaluated by spectrophotometry and motor function of the upper limbs was assessed via Terzis grooming test after modeling. Immunofluorescence and hematoxylin and eosin staining were utilized to determine the content of reactive oxygen species, activation of microglial cells, neuroprotection, and nerve regeneration. Compared with the control group, the L-Theanine + NEP1-40 group had significantly decreased myeloperoxidase, malondialdehyde, interleukin-6, reactive oxygen species, and microglial cells, significantly increased score on the Terzis grooming test, increased motor neuron content, and thickened muscle fibers, increased area, and appearance of large and clear motor endplate structures. The results of this study suggest that l-Theanine combined with NEP1-40significantly promoted nerve regeneration after brachial plexus root avulsion, and may be a potential treatment for promoting nerve regeneration. Possible mechanisms underlying these results are alleviation of oxidative damage and inflammatory responses in the injured area and antagonism of myelin inhibition.

Human Oligodendrogenic Neural Progenitor Cells Delivered with Chondroitinase ABC Facilitate Functional Repair of Chronic Spinal Cord Injury.

Treatment of chronic spinal cord injury (SCI) is challenging due to cell loss, cyst formation, and the glial scar. Previously, we reported on the therapeutic potential of a neural progenitor cell (NPC) and chondroitinase ABC (ChABC) combinatorial therapy for chronic SCI. However, the source of NPCs and delivery system required for ChABC remained barriers to clinical application. Here, we investigated directly reprogrammed human NPCs biased toward an oligodendrogenic fate (oNPCs) in combination with sustained delivery of ChABC using an innovative affinity release strategy in a crosslinked methylcellulose biomaterial for the treatment of chronic SCI in an immunodeficient rat model. This combinatorial therapy increased long-term survival of oNPCs around the lesion epicenter, facilitated greater oligodendrocyte differentiation, remyelination of the spared axons by engrafted oNPCs, enhanced synaptic connectivity with anterior horn cells and neurobehavioral recovery. This combinatorial therapy is a promising strategy to regenerate the chronically injured spinal cord.

Systemic overexpression of SQSTM1/p62 accelerates disease onset in a SOD1H46R-expressing ALS mouse model.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by a selective loss of upper and lower motor neurons. Recent studies have shown that mutations in SQSTM1 are linked to ALS. SQSTM1 encodes SQSTM1/p62 that regulates not only autophagy via the association with MAP1LC3/LC3 and ubiquitinated proteins but also the KEAP1-NFE2L2/Nrf2 anti-oxidative stress pathway by interacting with KEAP1. Previously, we have demonstrated that loss of SQSTM1 exacerbates disease phenotypes in a SOD1H46R-expressing ALS mouse model. To clarify the effects of SQSTM1 overexpression in this model, we generated SQSTM1 and SOD1 H46R double-transgenic (SQSTM1;SOD1 H46R ) mice. SQSTM1;SOD1 H46R mice exhibited earlier disease onset and shorter lifespan than did SOD1 H46R mice. Conversely, disease progression after the onset rather slightly but significantly slowed in SQSTM1;SOD1 H46R mice. However, there were observable differences neither in the number of Nissl positive neurons nor in the distribution of ubiquitin-positive and/or SQSTM1-positive aggregates between SOD1 H46R and SQSTM1;SOD1 H46R mice. It was noted that these protein aggregates were mainly observed in neuropil, and partly localized to astrocytes and/or microglia, but not to MAP2-positive neuronal cell bodies and dendrites at the end-stage of disease. Nonetheless, the biochemically-detectable insoluble SQSTM1 and poly-ubiquitinated proteins were significantly and progressively increased in the spinal cord of SQSTM1;SOD1 H46R mice compared to SOD1 H46R mice. These results suggest that overexpression of SQSTM1 in SOD1 H46R mice accelerates disease onset by compromising the protein degradation pathways.

Functional Divergence of Delta and Mu Opioid Receptor Organization in CNS Pain Circuits.

Cellular interactions between delta and mu opioid receptors (DORs and MORs), including heteromerization, are thought to regulate opioid analgesia. However, the identity of the nociceptive neurons in which such interactions could occur in vivo remains elusive. Here we show that DOR-MOR co-expression is limited to small populations of excitatory interneurons and projection neurons in the spinal cord dorsal horn and unexpectedly predominates in ventral horn motor circuits. Similarly, DOR-MOR co-expression is rare in parabrachial, amygdalar, and cortical brain regions processing nociceptive information. We further demonstrate that in the discrete DOR-MOR co-expressing nociceptive neurons, the two receptors internalize and function independently. Finally, conditional knockout experiments revealed that DORs selectively regulate mechanical pain by controlling the excitability of somatostatin-positive dorsal horn interneurons. Collectively, our results illuminate the functional organization of DORs and MORs in CNS pain circuits and reappraise the importance of DOR-MOR cellular interactions for developing novel opioid analgesics.

Triggering of Autophagy by Baicalein in Response to Apoptosis after Spinal Cord Injury: Possible Involvement of the PI3K Activation.

High level apoptosis induced by spinal cord injury (SCI) evokes serious damage because of the loss and dysfunction of motor neurons. Our previous studies showed that inhibition of autophagy evokes the activation of apoptosis. Interestingly, Baicalein, a medicine with anti-apoptosis activity that is derived from the roots of herb Scutellaria baicalensis, largely induces autophagy by activating phosphatidylinositol 3-kinase (PI3K). In this study, we investigated the effects of intraperitoneal injection of Baicalein on autophagy and apoptosis in SCI mice and evaluated the relationship between autophagy and apoptosis. We demonstrated that Baicalein promoted the functional recovery of motor neurons at 7 d after SCI. In addition, Baicalein enhanced neuronal autophagy and the autophagy-related factor PI3K, while inhibiting the p62 protein. Baicalein treatment decreased neuronal apoptosis at 7 d after SCI. Moreover, when inhibiting autophagy, apoptosis was upgraded by Baicalein treatment after injury. Thus, Baicalein attenuated SCI by inducing autophagy to reduce apoptosis in neurons potentially via activating PI3K.

Characterization of calbindin D28k expressing interneurons in the ventral horn of the mouse spinal cord.

BACKGROUND: Expression of the calcium binding protein, calbindin (CB), is well established as a hallmark of Renshaw cells, a class of interneurons found in spatially restricted areas in the ventral spinal cord that directly modulate motor neuron activity. CB expression, however, is not restricted only to Renshaw cells in the ventral horn, and within this population other interneuron subtypes may be identifiable on the basis of cell position and the potential for coexpression of other calcium binding proteins. RESULTS: Here we have quantified the changing CB expression pattern in the ventral spinal cord across postnatal development in the mouse. Fewer neurons express CB as postnatal development progresses, and those neurons frequently coexpress other calcium binding proteins (calretinin and parvalbumin) in subpopulations with distinct spatial distributions. We also found a significant portion of CB-expressing interneurons receive putative synaptic contacts from primary sensory afferents. CONCLUSIONS: These findings suggest CB labels a heterogeneous group of interneurons in the ventral horn, some of which may process sensory information. Based on cellular position, CB expression may be a shared feature of subsets of interneurons arising from multiple ventral progenitor domains. Developmental Dynamics 247:185-193, 2018. © 2017 Wiley Periodicals, Inc.

Endomorphin-2 Decreases Excitatory Synaptic Transmission in the Spinal Ventral Horn of the Rat.

Motor impairment is one of the serious side-effects of morphine, which is an exogenous agonist of the µ-opioid receptor (MOR) as well as a widely used analgesic drug in clinical practice for chronic pain treatment. Endomorphins (EMs, including EM-1 and EM-2), the most effective and specific endogenous agonists of the MOR, exert more potent analgesia in acute and neuropathic pain than other opiates, such as morphine. Although EMs had fewer side-effects comparing to other opiates, motor impairment was still one unwanted reaction which limited its clinical application. In order to prevent and treat the motor impairment, it is critical to reveal the neural mechanisms underlying such locomotion disorder. The purpose of the present study was to reveal the neural mechanisms underlying the effects of EM-2 on the activity of motoneurons in the spinal ventral horn. First, we examine the distribution of EM-2-immunoreactive (IR) primary afferent fibers and their synaptic connections with the motoneurons innervating the skeletal muscles of the lower limb revealed by sciatic nerve retrograde tracing. The results showed that EM-2-IR fibers and terminals were sparsely observed in lamina IX and they formed symmetric synaptic connections with the motoneurons within lamina IX of the spinal ventral horn. Then, whole-cell patch-clamp technique was used to observe the effects of EM-2 on the spontaneous excitatory postsynaptic current (sEPSC) of motoneurons in lamina IX. The results showed that EM-2 could decrease both the frequency and amplitude of the sEPSC of the motoneurons in lamina IX, which was reversed by the MOR antagonist CTOP. These results indicate that EM-2-IR fibers originated from primary afferent fibers form symmetric synaptic connections with motoneurons innervating skeletal muscles of the lower limbs in lamina IX of the spinal ventral horn and EM-2 might exert inhibitory effects on the activities of these motoneurons through both presynaptic and postsynaptic mechanisms.

Tail Nerve Electrical Stimulation and Electro-Acupuncture Can Protect Spinal Motor Neurons and Alleviate Muscle Atrophy after Spinal Cord Transection in Rats.

Spinal cord injury (SCI) often results in death of spinal neurons and atrophy of muscles which they govern. Thus, following SCI, reorganizing the lumbar spinal sensorimotor pathways is crucial to alleviate muscle atrophy. Tail nerve electrical stimulation (TANES) has been shown to activate the central pattern generator (CPG) and improve the locomotion recovery of spinal contused rats. Electroacupuncture (EA) is a traditional Chinese medical practice which has been proven to have a neural protective effect. Here, we examined the effects of TANES and EA on lumbar motor neurons and hindlimb muscle in spinal transected rats, respectively. From the third day postsurgery, rats in the TANES group were treated 5 times a week and those in the EA group were treated once every other day. Four weeks later, both TANES and EA showed a significant impact in promoting survival of lumbar motor neurons and expression of choline acetyltransferase (ChAT) and ameliorating atrophy of hindlimb muscle after SCI. Meanwhile, the expression of neurotrophin-3 (NT-3) in the same spinal cord segment was significantly increased. These findings suggest that TANES and EA can augment the expression of NT-3 in the lumbar spinal cord that appears to protect the motor neurons as well as alleviate muscle atrophy.