BDNF-induced TrkB activation down-regulates the K+-Cl- cotransporter KCC2 and impairs neuronal Cl- extrusion

Sex-Dependent Signaling Pathways Underlying Seizure Susceptibility and the Role of Chloride Cotransporters

Seizure incidence, severity, and antiseizure medication (ASM) efficacy varies between males and females. Differences in sex-dependent signaling pathways that determine network excitability may be responsible. The identification and validation of sex-dependent molecular mechanisms that influence seizure susceptibility is an emerging focus of neuroscience research. The electroneutral cation-chloride cotransporters (CCCs) of the SLC12A gene family utilize Na⁺-K⁺-ATPase generated electrochemical gradients to transport chloride into or out of neurons. CCCs regulate neuronal chloride gradients, cell volume, and have a strong influence over the electrical response to the inhibitory neurotransmitter GABA. Acquired or genetic causes of CCCs dysfunction have been linked to seizures during early postnatal development, epileptogenesis, and refractoriness to ASMs. A growing number of studies suggest that the developmental expression of CCCs, such as KCC2, is sex-dependent. This review will summarize the reports of sexual dimorphism in epileptology while focusing on the role of chloride cotransporters and their associated modulators that can influence seizure susceptibility.

Mechanisms underlying a critical period of respiratory development in the rat

Twenty-five years ago, Filiano and Kinney (1994) proposed that a critical period of postnatal development constitutes one of the three risk factors for sudden infant death syndrome (SIDS). The underlying mechanism was poorly understood. In the last 17 years, much has been uncovered on this period in the rat. Against several expected trends of development, abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory system at P12-13. This results in a transient synaptic imbalance with suppressed excitation and enhanced inhibition, and the response to acute hypoxia is the weakest at this time, both at the cellular and system's levels. The basis for the synaptic imbalance is likely to be contributed by a reduced expression of brain-derived neurotrophic factor (BDNF) and its TrkB receptors in multiple brain stem respiratory-related nuclei during the critical period. Exogenous BDNF or a TrkB agonist partially reverses the synaptic imbalance, whereas a TrkB antagonist accentuates the imbalance. A transient down-regulation of pituitary adenylate cyclase-activating polypeptide (PACAP) at P12 in respiratory-related nuclei also contributes to the vulnerability of this period. Carotid body denervation during this time or perinatal hyperoxia merely delays and sometimes prolongs, but not eliminate the critical period. The rationale for the necessity of the critical period in postnatal development is discussed.

Role of the BDNF-TrkB pathway in KCC2 regulation and rehabilitation following neuronal injury: A mini review

In most mature neurons, low levels of intracellular Cl^- concentrations ([Cl^-]_i) are maintained by channels and transporters, particularly the K⁺-Cl^- cotransporter 2 (KCC2), which is the only Cl^- extruder in most neurons. Recent studies have implicated KCC2 expression in the molecular mechanisms underlying neuronal disorders, such as spasticity, epilepsy and neuropathic pain. Alterations in KCC2 expression have been associated with brain-derived neurotrophic factor (BDNF) and its receptor tropomyosin-related kinase B (TrkB). The present review summarizes recent progress regarding the roles of Cl^- regulators in immature and mature neurons. Moreover, we focus on the role of KCC2 regulation via the BDNF-TrkB pathway in spinal cord injury and rehabilitation, as prior studies have shown that the BDNF-TrkB pathway can affect both the pathological development and functional amelioration of spinal cord injuries. Evidence suggests that rehabilitation using active exercise and mechanical stimulation can attenuate spasticity and neuropathic pain in animal models, likely due to the upregulation of KCC2 expression via the BDNF-TrkB pathway. Moreover, research suggests that such rehabilitation efforts may recover KCC2 expression without the use of exogenous BDNF.

Reciprocal Regulation of KCC2 Trafficking and Synaptic Activity

The main inhibitory neurotransmitter receptors in the adult central nervous system (CNS) are type A γ-aminobutyric acid receptors (GABA_ARs) and glycine receptors (GlyRs). Synaptic responses mediated by GlyR and GABA_AR display a hyperpolarizing shift during development. This shift relies mainly on the developmental up-regulation of the K⁺-Cl^- co-transporter KCC2 responsible for the extrusion of Cl^-. In mature neurons, altered KCC2 function-mainly through increased endocytosis-leads to the re-emergence of depolarizing GABAergic and glycinergic signaling, which promotes hyperexcitability and pathological activities. Identifying signaling pathways and molecular partners that control KCC2 surface stability thus represents a key step in the development of novel therapeutic strategies. Here, we present our current knowledge on the cellular and molecular mechanisms governing the plasma membrane turnover rate of the transporter under resting conditions and in response to synaptic activity. We also discuss the notion that KCC2 lateral diffusion is one of the first parameters modulating the transporter membrane stability, allowing for rapid adaptation of Cl^- transport to changes in neuronal activity.

Involvement of lysophosphatidic acid-induced astrocyte activation underlying the maintenance of partial sciatic nerve injury-induced neuropathic pain

We have previously demonstrated that lysophosphatidic acid (LPA) plays key roles in the initial mechanisms for neuropathic pain (NeuP) development. Here, we examined whether LPA receptor mechanisms and LPA production are related to the glial activation at a late stage after partial sciatic nerve ligation (pSNL) by use of microglial inhibitor, Mac1-saporin or astrocyte inhibitor, and L-α-aminoadipate (L-AA). Although single intrathecal injection of LPA1/3 antagonist, Ki-16425 did not affect the pain threshold at day 7 after the spinal cord injury, repeated treatments of each compound gradually reversed the basal pain threshold to the control level. The intrathecal administration of a microglia inhibitor, Mac-1-saporin reversed the late hyperalgesia and LPA production at day 14 after the pSNL, whereas L-AA inhibited the hyperalgesia, but had no effect on LPA production. The involvement of LPA receptors in astrocyte activation in vivo was evidenced by the findings that Ki-16425 treatments abolished the upregulation of CXCL1 in activated astrocytes in the spinal dorsal horn of mice at day 14 after the pSNL, and that Ki-16425 reversed the LPA-induced upregulation of several chemokine gene expressions in primary cultured astrocytes. Finally, we found that significant hyperalgesia was observed with intrathecal administration of primary cultured astrocytes, which had been stimulated by LPA in a Ki-16425-reversible manner. All these findings suggest that LPA production and LPA1/3 receptor activation through differential glial mechanisms play key roles in the maintenance as well as initiation mechanisms in NeuP.

Studies of the Anti-amnesic Effects and Mechanisms of Single and Combined Use of Donepezil and Ginkgo Ketoester Tablet on Scopolamine-Induced Memory Impairment in Mice

Ginkgo ketoester tablets (GT) and donepezil were a clinically used combination for the treatment of Alzheimer's disease (AD). The aim of the study was undertaken to investigate the antiamnesic effects of the two drugs alone and in combination through in vivo models of the Morris water maze along with in vitro antioxidants, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). The potential mechanisms were speculated by the activities of acetylcholine (ACh), AChE, superoxide dismutase (SOD), and malondialdehyde (MDA) and the protein expression of brain-derived neurotrophic factor (BDNF) and tyrosine protein kinase B (TrkB). The combination group showed a concentration-dependent inhibition of cholinesterase and antioxidation. As far as its mechanism was concerned, the combination of two drugs exerted excellent effects on oxidative stress, cholinergic pathway damage, and inactivation of the BDNF-TrkB signaling pathway. Additionally, to elucidate the binding mechanism of GT active ingredients into the structure of AChE, the results of molecular docking studies indicated that hydrogen and/or hydrophobic bonds might play an important role in their binding process. Thus, the combination of drugs could treat AD perfectly and further verify the scientific rationality of clinical medication.

Dexamethasone protects against arsanilic acid‑induced rat vestibular dysfunction through the BDNF and JNK 1/2 signaling pathways

The brain‑derived neurotrophic factor (BDNF) and c‑Jun NH 2‑terminal kinase (JNK) signaling pathways are therapeutic targets to prevent degeneration in the central nervous system. Dexamethasone (DXMS), a glucocorticoid, protects against vestibular brain injury, however, the molecular mechanisms have yet to be fully elucidated. To investigate whether the BDNF and JNK signaling pathways are involved in the protective effects of DXMS in rats with vestibular dysfunction, a rat model of severe vestibular deficits was established by middle ear injection of arsanilic acid (AA; 100 mg/ml; 0.05 ml). After 3 days, rat symptoms and behavior scores with vestibular disorders were detected. In brain tissues, histopathological alterations, cell apoptosis, expression levels and patterns of BDNF signaling pathway‑associated BDNF, tyrosine receptor kinase B (TrKB) and K+/Cl‑ cotransporter isoform 2 (KCC2), and the expression of apoptosis‑related cleaved‑caspase 3 and the JNK signaling pathway were detected. It was identified that DXMS relieved AA‑induced vestibular dysfunction, leading to improvement in rat behavior scores to normal levels, minimizing brain damage at the histopatholojnnkngical level, reducing cell apoptosis, enhancing the expression of BDNF, TrKB and KCC2, and downregulating cleaved‑caspase 3 and phosphorylated‑JNK1/2 in brain tissues. Together, these findings indicated the protective effect of DXMS on AA‑induced rat vestibular dysfunction, and that activating BDNF and inhibiting JNK singling pathways were the underlying mechanisms. In addition, with additional treatment of mifepristone (RU486), a specific glucocorticoid agonist, all the events elicited by DXMS mentioned above in the AA‑treated rat rats were reversed. In conclusion, DXMS was identified as a therapeutic agent targeting the BDNF and JNK singling pathways for AA‑induced rat vestibular dysfunction.

In Vivo Study on Mechanism Underlying Increased Pharmacological Effects of Phenobarbital in Rats with Glycerol-Induced Acute Renal Failure

The mechanism underlying the increased pharmacological effects of phenobarbital in rats with glycerol-induced acute renal failure (ARF) was examined. In the experiments, a surgical cannula was inserted in the lateral ventricle of the rats for phenobarbital infusion, and the ARF induction was performed by intramuscular administration of 50% glycerol. The onset time of anesthesia by phenobarbital was determined with the tail flick method. In addition, cerebral microsomes were prepared from excised cerebral cortices of sham and ARF rats, and the cerebral expression of the γ-aminobutyric acid (GABA)A receptor and two cation-chloride transporters, KCC2 and NKCC1, was evaluated by Western blotting, as their functions are involved in the anesthetic effects of phenobarbital. When phenobarbital was infused in the ventricle, anesthesia was induced 2.2-times faster in ARF rats than in sham rats, and there was no detectable increase in the cerebral expression of the GABAA receptor in ARF rats. It was additionally noted that the cerebral expression of KCC2 decreased, whereas that of NKCC1 was unaltered in ARF rats. These findings indicated that the anesthetic effects of phenobarbital are potentiated in ARF rats, probably due to imbalanced cerebral expression of KCC2 and NKCC1, suggesting that altered cation-chloride handling in nerve cells is associated.

Double-edged GABAergic synaptic transmission in seizures: The importance of chloride plasticity

GABAergic synaptic inhibition, which is a critical regulator of neuronal excitability, is closely involved in epilepsy. Interestingly, fast GABAergic transmission mediated by Cl- permeable GABAA receptors can bi-directionally exert both seizure-suppressing and seizure-promoting actions. Accumulating evidence suggests that chloride plasticity, the driving force of GABAA receptor-mediated synaptic transmission, contributes to the double-edged role of GABAergic synapses in seizures. Large amounts of Cl- influx can overwhelm Cl- extrusion during seizures not only in healthy tissue in a short-term "activity-dependent" manner, but also in chronic epilepsy in a long-term, irreversible "pathology-dependent" manner related to the dysfunction of two chloride transporters: the chloride importer NKCC1 and the chloride exporter KCC2. In this review, we address the importance of chloride plasticity for the "activity-dependent" and "pathology-dependent" mechanisms underlying epileptic events and provide possible directions for further research, which may be clinically important for the design of GABAergic synapse-targeted precise therapeutic interventions for epilepsy.

The role of convergent ion channel pathways in microglial phenotypes: a systematic review of the implications for neurological and psychiatric disorders

Increases in the activated state of microglia, the main neuroimmune cells, are widely reported in the brains of patients with neurological and psychiatric disorders. Microglia transform from the resting to the activated state by sensing their environment, aided by a variety of ion channels. To examine the effect of ion channels on microglial phenotypes, we conducted a systematic review of immunohistochemical analyses of these neuroimmune cells in animal models following administration of ion channel antagonists, compared to control conditions. A systematic search of the PubMed and Web of Science electronic databases using the PRISMA and WHO methodologies for systematic reviews yielded 15 original peer-reviewed studies. The majority (13 out of 15) of these studies reported a decrease in microglial activated state after ion signaling pharmacological blockade. The studies provide evidence that acute administration of ion channel antagonists leads to a reduction in microglial activation in rodent brains in the models for epilepsy, Parkinson's disease, inflammation, pain, ischemia, and brain and spinal cord injury. Future research should explore microglial-specific druggable targets for neurological and psychiatric disorders. The investigation of acute and chronic administration of ion channel antagonists in microglial phenotypes in primates and the development of microglia-like cells derived from human stem cells could be valuable sources in this direction.

KCC2 Regulates Dendritic Spine Formation in a Brain-Region Specific and BDNF Dependent Manner

KCC2 is the major chloride extruder in neurons. The spatiotemporal regulation of KCC2 expression orchestrates the developmental shift towards inhibitory GABAergic drive and the formation of glutamatergic synapses. Whether KCC2's role in synapse formation is similar in different brain regions is unknown. First, we found that KCC2 subcellular localization, but not overall KCC2 expression levels, differed between cortex and hippocampus during the first postnatal week. We performed site-specific in utero electroporation of KCC2 cDNA to target either hippocampal CA1 or somatosensory cortical pyramidal neurons. We found that a premature expression of KCC2 significantly decreased spine density in CA1 neurons, while it had the opposite effect in cortical neurons. These effects were cell autonomous, because single-cell biolistic overexpression of KCC2 in hippocampal and cortical organotypic cultures also induced a reduction and an increase of dendritic spine density, respectively. In addition, we found that the effects of its premature expression on spine density were dependent on BDNF levels. Finally, we showed that the effects of KCC2 on dendritic spine were dependent on its chloride transporter function in the hippocampus, contrary to what was observed in cortex. Altogether, these results demonstrate that KCC2 regulation of dendritic spine development, and its underlying mechanisms, are brain-region specific.

Pharmaco-resistant Neonatal Seizures: Critical Mechanistic Insights from a Chemoconvulsant Model

Neonatal seizures are harmful to the developing brain and are associated with mortality and long-term neurological comorbidities. Hypoxic-ischemic encephalopathy (HIE) seizures represent a significant proportion of such seizures. Phenobarbital (PB) remains the first line anti-seizure drug (ASD) treatment but fails ~50% of the time. Translational models of neonatal seizures are crucial to investigating mechanisms underlying PB-resistance. A model of PB-resistant ischemic seizures in postnatal day 7 (P7) CD-1 mice reported K-Cl cotransporter 2 (KCC2) degradation that has been shown to be due to activation of the TrkB pathway. We investigated PB-efficacy in a pentylenetetrazole (PTZ) model of neonatal seizures in the same strain and age using identical treatment protocols to gain insights into mechanisms underlying PB-resistance. A single dose of PTZ (80 mg/kg; IP) consistently induced repetitive seizures that did not progress to status epilepticus (SE). PB (25 mg/kg; IP, single dose) significantly suppressed the PTZ-induced seizures. This was associated with significant KCC2 upregulation and stable Na-K-Cl cotransporter 1 (NKCC1) expression at 24h. The TrkB pathway was not activated. PTZ seizure burdens were significantly higher than those reported for ischemic seizures, indicating seizure severity did not dictate the differences in PB-efficacy. Bumetanide (BTN) (0.1-0.2 mg/kg; IP) did not work as an anti-seizure agent, similar to the ischemic model. When investigating mechanisms underlying the emergence of PB-resistance in translational models, the method by which seizures are induced may dictate mechanisms underlying emergence of PB-resistance.

Phosphoregulation of the intracellular termini of K+-Cl- cotransporter 2 (KCC2) enables flexible control of its activity

The pivotal role of K⁺-Cl^- cotransporter 2 (KCC2) in inhibitory neurotransmission and severe human diseases fosters interest in understanding posttranslational regulatory mechanisms such as (de)phosphorylation. Here, the regulatory role of the five bona fide phosphosites Ser³¹, Thr³⁴, Ser⁹³², Thr⁹⁹⁹, and Thr¹⁰⁰⁸ was investigated by the use of alanine and aspartate mutants. Tl⁺-based flux analyses in HEK-293 cells demonstrated increased transport activity for S932D (mimicking phosphorylation) and T1008A (mimicking dephosphorylation), albeit to a different extent. Increased activity was due to changes in intrinsic activity, as it was not caused by increased cell-surface abundance. Substitutions of Ser³¹, Thr³⁴, or Thr⁹⁹⁹ had no effect. Additionally, we show that the indirect actions of the known KCC2 activators staurosporine and N-ethylmaleimide (NEM) involved multiple phosphosites. S31D, T34A, S932A/D, T999A, or T1008A/D abrogated staurosporine mediated stimulation, and S31A, T34D, or S932D abolished NEM-mediated stimulation. This demonstrates for the first time differential effects of staurosporine and NEM on KCC2. In addition, the staurosporine-mediated effects involved both KCC2 phosphorylation and dephosphorylation with Ser⁹³² and Thr¹⁰⁰⁸ being bona fide target sites. In summary, our data reveal a complex phosphoregulation of KCC2 that provides the transporter with a toolbox for graded activity and integration of different signaling pathways.

Uncovering a critical period of synaptic imbalance during postnatal development of the rat visual cortex: role of brain-derived neurotrophic factor

KEY POINTS

With daily electrophysiological recordings and neurochemical analysis, we uncovered a transient period of synaptic imbalance between enhanced inhibition and suppressed excitation in rat visual cortical neurons from the end of the fourth toward the end of the fifth postnatal weeks. The expression of brain-derived neurotrophic factor (BDNF), which normally enhances excitation and suppresses inhibition, was down-regulated during that time, suggesting that this may contribute to the inhibition/excitation imbalance. An agonist of the BDNF receptor tropomyosin-related kinase B (TrkB) partially reversed the imbalance, whereas a TrkB antagonist accentuated the imbalance during the transient period. Monocular lid suture during the transient period is more detrimental to the function and neurochemical properties of visual cortical neurons than before or after this period. We regard the period of synaptic imbalance as the peak critical period of vulnerability, and its existence is necessary for neurons to transition from immaturity to a more mature state of functioning.

ABSTRACT

The mammalian visual cortex is immature at birth and undergoes postnatal structural and functional adjustments. The exact timing of the vulnerable period in rodents remains unclear. The critical period is characterized by inhibitory GABAergic maturation reportedly dependent on brain-derived neurotrophic factor (BDNF). However, most of the studies were performed on experimental/transgenic animals, questioning the relationship in normal animals. The present study aimed to conduct in-depth analyses of the synaptic and neurochemical development of visual cortical neurons in normal and monocularly-deprived rats and to determine specific changes, if any, during the critical period. We found that (i) against a gradual increase in excitation and inhibition with age, a transient period of synaptic and neurochemical imbalance existed with suppressed excitation and enhanced inhibition at postnatal days 28 to 33/34; (ii) during this window, the expression of BDNF and tropomyosin-related kinase B (TrkB) receptors decreased, along with glutamatergic GluN1 and GluA1 receptors and the metabolic marker cytochrome oxidase, whereas that of GABAA Rα1 receptors continued to rise; (iii) monocular deprivation reduced both excitatory and inhibitory synaptic activity and neurochemicals mainly during this period; and (iv) in vivo TrkB agonist partially reversed the synaptic imbalance in normal and monocularly-deprived neurons during this time, whereas a TrkB antagonist accentuated the imbalance. Thus, our findings highlight a transitory period of synaptic imbalance with a negative relationship between BDNF and inhibitory GABA. This brief critical period may be necessary in transitioning from an immature to a more mature state of visual cortical functioning.

Mechanism of BDNF Modulation in GABAergic Synaptic Transmission in Healthy and Disease Brains

In the mature healthy mammalian neuronal networks, γ-aminobutyric acid (GABA) mediates synaptic inhibition by acting on GABA_A and GABA_B receptors (GABA_AR, GABA_BR). In immature networks and during numerous pathological conditions the strength of GABAergic synaptic inhibition is much less pronounced. In these neurons the activation of GABA_AR produces paradoxical depolarizing action that favors neuronal network excitation. The depolarizing action of GABA_AR is a consequence of deregulated chloride ion homeostasis. In addition to depolarizing action of GABA_AR, the GABA_BR mediated inhibition is also less efficient. One of the key molecules regulating the GABAergic synaptic transmission is the brain derived neurotrophic factor (BDNF). BDNF and its precursor proBDNF, can be released in an activity-dependent manner. Mature BDNF operates via its cognate receptors tropomyosin related kinase B (TrkB) whereas proBDNF binds the p75 neurotrophin receptor (p75^NTR). In this review article, we discuss recent finding illuminating how mBDNF-TrkB and proBDNF-p75^NTR signaling pathways regulate GABA related neurotransmission under physiological conditions and during epilepsy.

M-Calpain Activation Facilitates Seizure Induced KCC2 Down Regulation

Potassium chloride co-transporter 2 (KCC2), a major chloride transporter that maintains GABA_A receptor inhibition in mature mammalian neurons, is down-regulated in the hippocampus during epileptogenesis. Impaired KCC2 function accelerates or facilitates seizure onset. Calpain, with two main subtypes of m- and μ-calpain, is a Ca²⁺-dependent cysteine protease that mediates the nonlysosomal degradation of KCC2. Although recent studies have demonstrated that calpain inhibitors exert antiepileptic and neuroprotective effects in animal models of acute and chronic epilepsy, whether calpain activation affects seizure induction through KCC2 degradation remains unknown. Our results showed that: (1) Blockade of calpain by non-selective calpain inhibitor MDL-28170 prevented convulsant stimulation induced KCC2 downregulation, and reduced the incidence and the severity of pentylenetetrazole (PTZ) induced seizures. (2) m-calpain, but not μ-calpain, inhibitor mimicked MDL-28170 effect on preventing KCC2 downregulation. (3) Phosphorylation of m-calpain has been significantly enhanced during seizure onset, which was partly mediated by the calcium independent MAPK/ERK signaling pathway activation. (4) MAPK/ERK signaling blockade also had similar effect as total calpain blockade on both KCC2 downregulation and animal seizure induction. The results indicate that upregulated m-calpain activation by MAPK/ERK during convulsant stimulation down regulates both cytoplasm- and membrane KCC2, and in turn facilitates seizure induction. This finding may provide a foundation for the development of highly effective antiepileptic drugs targeting of m-calpain.

Postnatal Changes in K+/Cl- Cotransporter-2 Expression in the Forebrain of Mice Bearing a Mutant Nicotinic Subunit Linked to Sleep-Related Epilepsy

The Na+/K+/Cl- cotransporter-1 (NKCC1) and the K+/Cl- cotransporter-2 (KCC2) set the transmembrane Cl- gradient in the brain, and are implicated in epileptogenesis. We studied the postnatal distribution of NKCC1 and KCC2 in wild-type (WT) mice, and in a mouse model of sleep-related epilepsy, carrying the mutant β2-V287L subunit of the nicotinic acetylcholine receptor (nAChR). In WT neocortex, immunohistochemistry showed a wide distribution of NKCC1 in neurons and astrocytes. At birth, KCC2 was localized in neuronal somata, whereas at subsequent stages it was mainly found in the somatodendritic compartment. The cotransporters' expression was quantified by densitometry in the transgenic strain. KCC2 expression increased during the first postnatal weeks, while the NKCC1 amount remained stable, after birth. In mice expressing β2-V287L, the KCC2 amount in layer V of prefrontal cortex (PFC) was lower than in the control littermates at postnatal day 8 (P8), with no concomitant change in NKCC1. Consistently, the GABAergic excitatory to inhibitory switch was delayed in PFC layer V of mice carrying β2-V287L. At P60, the amount of KCC2 was instead higher in mice bearing the transgene. Irrespective of genotype, NKCC1 and KCC2 were abundantly expressed in the neuropil of most thalamic nuclei since birth. However, KCC2 expression decreased by P60 in the reticular nucleus, and more so in mice expressing β2-V287L. Therefore, a complex regulatory interplay occurs between heteromeric nAChRs and KCC2 in postnatal forebrain. The pathogenetic effect of β2-V287L may depend on altered KCC2 amounts in PFC during synaptogenesis, as well as in mature thalamocortical circuits.

Dose-dependent reversal of KCC2 hypofunction and phenobarbital-resistant neonatal seizures by ANA12

Neonatal seizures have an incidence of 3.5 per 1000 newborns; while hypoxic-ischemic encephalopathy (HIE) accounts for 50-60% of cases, half are resistant to 1st-line anti-seizure drugs such as phenobarbital (PB). Tyrosine receptor kinase B (TrkB) activation following ischemic injury is known to increase neuronal excitability by downregulation of K-Cl co-transporter 2 (KCC2); a neuronal chloride (Cl-) co-transporter. In this study, three graded doses of ANA12, a small-molecule selective TrkB antagonist, were tested in CD1 mice at P7 and P10 following induction of neonatal ischemia by a unilateral carotid ligation. The PB loading dose remained the same in all treatment groups at both ages. Evaluation criteria for the anti-seizure efficacy of ANA12 were: (1) quantitative electroencephalographic (EEG) seizure burden and power, (2) rescue of post-ischemic KCC2 and pKCC2-S940 downregulation and (3) reversal of TrkB pathway activation following ischemia. ANA12 significantly rescued PB resistant seizures in a dose-dependent manner at P7 and improved PB efficacy at P10. Additionally, female pups responded better to lower doses of ANA12 compared to males. ANA12 significantly reversed post-ischemic KCC2 downregulation and TrkB pathway activation at P7 when PB alone was inefficacious. Rescuing KCC2 hypofunction may be critical for preventing emergence of refractory seizures.

Dexmedetomidine attenuates persistent postsurgical pain by upregulating K+-Cl- cotransporter-2 in the spinal dorsal horn in rats

Background

Dexmedetomidine (DEX) could have an analgesic effect on pain transmission through the modulation of brain-derived neurotrophic factor (BDNF). In addition, KCC2-induced shift in neuronal Cl− homeostasis is crucial for postsynaptic inhibition mediated by GABAA receptors. Accumulating evidence shows that nerve injury, peripheral inflammation and stress activate the spinal BDNF/TrkB signal, which results in the downregulation of KCC2 transport and expression, eventually leads to GAGAergic disinhibition and hyperalgesia. The aim of this experiment was to explore the interaction between DEX and KCC2 at a molecular level in rats in the persistent postsurgical pain (PPSP).

Methods

PPSP in rats was evoked by the skin/muscle incision and retraction (SMIR). Mechanical hypersensitivity was assessed with the Dynamic Plantar Aesthesiometer. Western blot and immunofluorescence assay were used to assess the expressions of related proteins.

Results

In the first part of our experiment, the results revealed that the BDNF/TrkB-KCC2 signal plays a critical role in the development of SMIR-evoked PPSP; the second part showed that intraperitoneal administrations of 40 µg/kg DEX at 15 min presurgery and 1 to 3 days post-surgery significantly attenuated SMIR-evoked PPSP. Simultaneously, SMIR-induced KCC2 downregulation was partly reversed, which coincided with the inhibition of the BDNF/TrkB signal in the spinal dorsal horn. Moreover, intrathecal administrations of KCC2 inhibitor VU0240551 significantly reduced the analgesic effect of DEX on SMIR-evoked PPSP.

Conclusion

The results of our study indicated that DEX attenuated PPSP by restoring KCC2 function through reducing BDNF/TrkB signal in the spinal dorsal horn in rats, which provides a new insight into the treatment of chronic pain in clinical postsurgical pain management.

Chloride transporters and GABA polarity in developmental, neurological and psychiatric conditions

Neuronal chloride regulation is a determinant factor for the dynamic tuning of GABAergic inhibition during and beyond brain development. This regulation is mainly dependent on the two co-transporters K⁺/Cl^- co-transporter KCC2 and Na⁺/K⁺/Cl^- co-transporter NKCC1, whose activity can decrease or increase neuronal chloride concentrations respectively. Altered expression and/or activity of either of these co-transporters has been associated with a wide variety of brain disorders including developmental disorders, epilepsy, schizophrenia and stroke. Here, we review current knowledge on chloride transporter expression and activity regulation and highlight the intriguing potential for existing and future interventions to support chloride homeostasis across a wide range of mental disorders and neurological conditions.

Therapeutic Potential of Oridonin and Its Analogs: From Anticancer and Antiinflammation to Neuroprotection

Oridonin, a diterpenoid natural product commonly used in East Asian herbal medicine, is garnering increased attention in the biomedical community due to its extensive biological activities that include antitumor, anti-inflammatory, antimicrobial, hepatic fibrosis prevention, and neurological effects. Over the past decade, significant progress has been made in structure activity relationship and mechanism of action studies of oridonin for the treatment of cancer and other diseases. This review provides a brief summary on oridonin and its analogs in cancer drug discovery and antiinflammation and highlights its emerging therapeutic potential in neuroprotection applications.

Advances in understanding nociception and neuropathic pain

Pain results from the activation of a subset of sensory neurones termed nociceptors and has evolved as a "detect and protect" mechanism. However, lesion or disease in the sensory system can result in neuropathic pain, which serves no protective function. Understanding how the sensory nervous system works and what changes occur in neuropathic pain are vital in identifying new therapeutic targets and developing novel analgesics. In recent years, technologies such as optogenetics and RNA-sequencing have been developed, which alongside the more traditional use of animal neuropathic pain models and insights from genetic variations in humans have enabled significant advances to be made in the mechanistic understanding of neuropathic pain.

Sensory neuronal P2RX4 receptors controls BDNF signaling in inflammatory pain

Chronic inflammatory and neuropathic pains are major public health concerns. Potential therapeutic targets include the ATP-gated purinergic receptors (P2RX) that contribute to these pathological types of pain in several different cell types. The purinergic receptors P2RX2 and P2RX3 are expressed by a specific subset of dorsal root ganglion neurons and directly shape pain processing by primary afferents. In contrast the P2RX4 and P2RX7 are mostly expressed in myeloid cells, where activation of these receptors triggers the release of various pro-inflammatory molecules. Here, we demonstrate that P2RX4 also controls calcium influx in mouse dorsal root ganglion neurons. P2RX4 is up-regulated in pain-processing neurons during long lasting peripheral inflammation and it co-localizes with Brain-Derived Neurotrophic Factor (BDNF). In the dorsal horn of the spinal cord, BDNF-dependent signaling pathways, phosphorylation of Erk1/2 and of the GluN1 subunit as well as the down regulation of the co-transporter KCC2, which are triggered by peripheral inflammation are impaired in P2RX4-deficient mice. Our results suggest that P2RX4, expressed by sensory neurons, controls neuronal BDNF release that contributes to hyper-excitability during chronic inflammatory pain and establish P2RX4 in sensory neurons as a new potential therapeutic target to treat hyperexcitability during chronic inflammatory pain.

Epilepsy-associated alterations in hippocampal excitability

The hippocampus exhibits a wide range of epilepsy-related abnormalities and is situated in the mesial temporal lobe, where limbic seizures begin. These abnormalities could affect membrane excitability and lead to overstimulation of neurons. Multiple overlapping processes refer to neural homeostatic responses develop in neurons that work together to restore neuronal firing rates to control levels. Nevertheless, homeostatic mechanisms are unable to restore normal neuronal excitability, and the epileptic hippocampus becomes hyperexcitable or hypoexcitable. Studies show that there is hyperexcitability even before starting recurrent spontaneous seizures, suggesting although hippocampal hyperexcitability may contribute to epileptogenesis, it alone is insufficient to produce epileptic seizures. This supports the concept that the hippocampus is not the only substrate for limbic seizure onset, and a broader hyperexcitable limbic structure may contribute to temporal lobe epilepsy (TLE) seizures. Nevertheless, seizures also occur in conditions where the hippocampus shows a hypoexcitable phenotype. Since TLE seizures most often originate in the hippocampus, it could therefore be assumed that both hippocampal hypoexcitability and hyperexcitability are undesirable states that make the epileptic hippocampal network less stable and may, under certain conditions, trigger seizures.

Role of KCC2-dependent potassium efflux in 4-Aminopyridine-induced Epileptiform synchronization

A balance between excitation and inhibition is necessary to maintain stable brain network dynamics. Traditionally, seizure activity is believed to arise from the breakdown of this delicate balance in favor of excitation with loss of inhibition. Surprisingly, recent experimental evidence suggests that this conventional view may be limited, and that inhibition plays a prominent role in the development of epileptiform synchronization. Here, we explored the role of the KCC2 co-transporter in the onset of inhibitory network-induced seizures. Our experiments in acute mouse brain slices, of either sex, revealed that optogenetic stimulation of either parvalbumin- or somatostatin-expressing interneurons induced ictal discharges in rodent entorhinal cortex during 4-aminopyridine application. These data point to a proconvulsive role of GABAA receptor signaling that is independent of the inhibitory input location (i.e., dendritic vs. somatic). We developed a biophysically realistic network model implementing dynamics of ion concentrations to explore the mechanisms leading to inhibitory network-induced seizures. In agreement with experimental results, we found that stimulation of the inhibitory interneurons induced seizure-like activity in a network with reduced potassium A-current. Our model predicts that interneuron stimulation triggered an increase of interneuron firing, which was accompanied by an increase in the intracellular chloride concentration and a subsequent KCC2-dependent gradual accumulation of the extracellular potassium promoting epileptiform ictal activity. When the KCC2 activity was reduced, stimulation of the interneurons was no longer able to induce ictal events. Overall, our study provides evidence for a proconvulsive role of GABAA receptor signaling that depends on the involvement of the KCC2 co-transporter.

K+-Cl- co-transporter 2 (KCC2) - a membrane trafficking perspective

K⁺-Cl^- co-transporter 2 (KCC2/SLC12A5) is a neuronal specific cation chloride co-transporter which is active under isotonic conditions, and thus a key regulator of intracellular Cl^- levels. It also has an ion transporter-independent structural role in modulating the maturation and regulation of excitatory glutamatergic synapses. KCC2 levels are developmentally regulated, and a postnatal upregulation of KCC2 generates a low intracellular chloride concentration that allows the neurotransmitters γ-aminobutyric acid (GABA) and glycine to exert inhibitory neurotransmission through its Cl^- permeating channel. Functional expression of KCC2 at the neuronal cell surface is necessary for its activity, and impairment in KCC2 cell surface transport and/or internalization may underlie a range of neuropathological conditions. Although recent advances have shed light on a range of cellular mechanisms regulating KCC2 activity, little is known about its membrane trafficking itinerary and regulatory proteins. In this review, known membrane trafficking signals, pathways and mechanisms pertaining to KCC2's functional surface expression are discussed.

Retracing your footsteps: developmental insights to spinal network plasticity following injury

During development of the spinal cord, a precise interaction occurs between descending projections and sensory afferents, with spinal networks that lead to expression of coordinated motor output. In the rodent, during the last embryonic week, motor output first occurs as regular bursts of spontaneous activity, progressing to stochastic patterns of episodes that express bouts of coordinated rhythmic activity perinatally. Locomotor activity becomes functionally mature in the 2nd postnatal wk and is heralded by the onset of weight-bearing locomotion on the 8th and 9th postnatal day. Concomitantly, there is a maturation of intrinsic properties and key conductances mediating plateau potentials. In this review, we discuss spinal neuronal excitability, descending modulation, and afferent modulation in the developing rodent spinal cord. In the adult, plastic mechanisms are much more constrained but become more permissive following neurotrauma, such as spinal cord injury. We discuss parallel mechanisms that contribute to maturation of network function during development to mechanisms of pathological plasticity that contribute to aberrant motor patterns, such as spasticity and clonus, which emerge following central injury.

Seizing Control of KCC2: A New Therapeutic Target for Epilepsy

Deficits in GABAergic inhibition result in the abnormal neuronal activation and synchronization that underlies seizures. However, the molecular mechanisms responsible for transforming a normal brain into an epileptic one remain largely unknown. Hyperpolarizing inhibition mediated by type A GABA (GABAA) receptors is dependent on chloride extrusion by the neuron-specific type 2K+-Cl- cotransporter (KCC2). Loss-of-function mutations in KCC2 are a known cause of infantile epilepsy in humans and KCC2 dysfunction is present in patients with both idiopathic and acquired epilepsy. Here we discuss the growing evidence that KCC2 dysfunction has a central role in the development and severity of the epilepsies.

Molecular cloning and biochemical characterization of two cation chloride cotransporter subfamily members of Hydra vulgaris

Cation Chloride Cotransporters (CCCs) comprise secondary active membrane proteins mainly mediating the symport of cations (Na⁺, K⁺) coupled with chloride (Cl⁻). They are divided into K⁺-Cl⁻ outward transporters (KCCs), the Na⁺-K⁺-Cl⁻ (NKCCs) and Na⁺-Cl⁻ (NCCs) inward transporters, the cation chloride cotransporter interacting protein CIP1, and the polyamine transporter CCC9. KCCs and N(K)CCs are established in the genome since eukaryotes and metazoans, respectively. Most of the physiological and functional data were obtained from vertebrate species. To get insights into the basal functional properties of KCCs and N(K)CCs in the metazoan lineage, we cloned and characterized KCC and N(K)CC from the cnidarian Hydra vulgaris. HvKCC is composed of 1,032 amino-acid residues. Functional analyses revealed that hvKCC mediates a Na⁺-independent, Cl⁻ and K⁺ (Tl⁺)-dependent cotransport. The classification of hvKCC as a functional K-Cl cotransporter is furthermore supported by phylogenetic analyses and a similar structural organization. Interestingly, recently obtained physiological analyses indicate a role of cnidarian KCCs in hyposmotic volume regulation of nematocytes. HvN(K)CC is composed of 965 amino-acid residues. Phylogenetic analyses and structural organization suggest that hvN(K)CC is a member of the N(K)CC subfamily. However, no inorganic ion cotransport function could be detected using different buffer conditions. Thus, hvN(K)CC is a N(K)CC subfamily member without a detectable inorganic ion cotransporter function. Taken together, the data identify two non-bilaterian solute carrier 12 (SLC12) gene family members, thereby paving the way for a better understanding of the evolutionary paths of this important cotransporter family.

Molecular and neurochemical substrates of the audiogenic seizure strains: The GASH:Sal model

PURPOSE

Animal models of audiogenic epilepsy are useful tools to understand the mechanisms underlying human reflex epilepsies. There is accumulating evidence regarding behavioral, anatomical, electrophysiological, and genetic substrates of audiogenic seizure strains, but there are still aspects concerning their neurochemical basis that remain to be elucidated. Previous studies have shown the involved of γ-amino butyric acid (GABA) in audiogenic seizures. The aim of our research was to clarify the role of the GABAergic system in the generation of epileptic seizures in the genetic audiogenic seizure-prone hamster (GASH:Sal) strain.

MATERIAL AND METHODS

We studied the K+/Cl- cotransporter KCC2 and β2-GABAA-type receptor (GABAAR) and β3-GABAAR subunit expressions in the GASH:Sal both at rest and after repeated sound-induced seizures in different brain regions using the Western blot technique. We also sequenced the coding region for the KCC2 gene both in wild- type and GASH:Sal hamsters.

RESULTS

Lower expression of KCC2 protein was found in GASH:Sal when compared with controls at rest in several brain areas: hippocampus, cortex, cerebellum, hypothalamus, pons-medulla, and mesencephalon. Repeated induction of seizures caused a decrease in KCC2 protein content in the inferior colliculus and hippocampus and an increase in the pons-medulla. When compared to controls, the basal β2-GABAAR subunit in the GASH:Sal was overexpressed in the inferior colliculus, rest of the mesencephalon, and cerebellum, whereas basal β3 subunit levels were lower in the inferior colliculus and rest of the mesencephalon. Repeated seizures increased β2 both in the inferior colliculus and in the hypothalamus and β3 in the hypothalamus. No differences in the KCC2 gene-coding region were found between GASH:Sal and wild-type hamsters.

CONCLUSIONS

These data indicate that GABAergic system functioning is impaired in the GASH:Sal strain, and repeated seizures seem to aggravate this dysfunction. These results have potential clinical relevance and support the validity of employing the GASH:Sal strain as a model to study the neurochemistry of genetic reflex epilepsy. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Neuronal Chloride Regulation via KCC2 Is Modulated through a GABAB Receptor Protein Complex

GABAB receptors are G-protein-coupled receptors that mediate inhibitory synaptic actions through a series of downstream target proteins. It is increasingly appreciated that the GABAB receptor forms part of larger signaling complexes, which enable the receptor to mediate multiple different effects within neurons. Here we report that GABAB receptors can physically associate with the potassium-chloride cotransporter protein, KCC2, which sets the driving force for the chloride-permeable ionotropic GABAA receptor in mature neurons. Using biochemical, molecular, and functional studies in rodent hippocampus, we show that activation of GABAB receptors results in a decrease in KCC2 function, which is associated with a reduction in the protein at the cell surface. These findings reveal a novel "crosstalk" between the GABA receptor systems, which can be recruited under conditions of high GABA release and which could be important for the regulation of inhibitory synaptic transmission.SIGNIFICANCE STATEMENT Synaptic inhibition in the brain is mediated by ionotropic GABAA receptors (GABAARs) and metabotropic GABAB receptors (GABABRs). To fully appreciate the function and regulation of these neurotransmitter receptors, we must understand their interactions with other proteins. We describe a novel association between the GABABR and the potassium-chloride cotransporter protein, KCC2. This association is significant because KCC2 sets the intracellular chloride concentration found in mature neurons and thereby establishes the driving force for the chloride-permeable GABAAR. We demonstrate that GABABR activation can regulate KCC2 at the cell surface in a manner that alters intracellular chloride and the reversal potential for the GABAAR. Our data therefore support an additional mechanism by which GABABRs are able to modulate fast synaptic inhibition.

KCC2 downregulation facilitates epileptic seizures

GABAA receptor-mediated inhibition depends on the maintenance of low level intracellular [Cl-] concentration, which in adult depends on neuron specific K+-Cl- cotransporter-2 (KCC2). Previous studies have shown that KCC2 was downregulated in both epileptic patients and various epileptic animal models. However, the temporal relationship between KCC2 downregulation and seizure induction is unclear yet. In this study, we explored the temporal relationship and the influence of KCC2 downregulation on seizure induction. Significant downregulation of plasma membrane KCC2 was directly associated with severe (Racine Score III and above) behavioral seizures in vivo, and occurred before epileptiform bursting activities in vitro induced by convulsant. Overexpression of KCC2 using KCC2 plasmid effectively enhanced resistance to convulsant-induced epileptiform bursting activities in vitro. Furthermore, suppression of membrane KCC2 expression, using shRNAKCC2 plasmid in vitro and shRNAKCC2 containing lentivirus in vivo, induced spontaneous epileptiform bursting activities in vitro and Racine III seizure behaviors accompanied by epileptic EEG in vivo. Our findings novelly demonstrated that altered expression of KCC2 is not the consequence of seizure occurrence but likely is the contributing factor.

Complete spinal cord injury (SCI) transforms how brain derived neurotrophic factor (BDNF) affects nociceptive sensitization

Noxious stimulation can induce a lasting increase in neural excitability within the spinal cord (central sensitization) that can promote pain and disrupt adaptive function (maladaptive plasticity). Brain-derived neurotrophic factor (BDNF) is known to regulate the development of plasticity and has been shown to impact the development of spinally-mediated central sensitization. The latter effect has been linked to an alteration in GABA-dependent inhibition. Prior studies have shown that, in spinally transected rats, exposure to regular (fixed spaced) stimulation can counter the development of maladaptive plasticity and have linked this effect to an up-regulation of BDNF. Here it is shown that application of the irritant capsaicin to one hind paw induces enhanced mechanical reactivity (EMR) after spinal cord injury (SCI) and that the induction of this effect is blocked by pretreatment with fixed spaced shock. This protective effect was eliminated if rats were pretreated with the BDNF sequestering antibody TrkB-IgG. Intrathecal (i.t.) application of BDNF prevented, but did not reverse, capsaicin-induced EMR. BDNF also attenuated cellular indices (ERK and pERK expression) of central sensitization after SCI. In uninjured rats, i.t. BDNF enhanced, rather than attenuated, capsaicin-induced EMR and ERK/pERK expression. These opposing effects were related to a transformation in GABA function. In uninjured rats, BDNF reduced membrane-bound KCC2 and the inhibitory effect of the GABAA agonist muscimol. After SCI, BDNF increased KCC2 expression, which would help restore GABAergic inhibition. The results suggest that SCI transforms how BDNF affects GABA function and imply that the clinical usefulness of BDNF will depend upon the extent of fiber sparing.

Brain-derived neurotropic factor and GABAergic transmission in neurodegeneration and neuroregeneration

Neurotoxicity induced by stress, radiation, chemicals, or metabolic diseases, is commonly associated with excitotoxicity, oxidative stress, and neuroinflammation. The pathological process of neurotoxicity induces neuronal death, interrupts synaptic plasticity in the brain, and is similar to that of diverse neurodegenerative diseases. Animal models of neurotoxicity have revealed that clinical symptoms and brain lesions can recover over time via neuroregenerative processes. Specifically, brain-derived neurotropic factor (BDNF) and gamma-aminobutyric acid (GABA)-ergic transmission are related to both neurodegeneration and neuroregeneration. This review summarizes the accumulating evidences that suggest a pathogenic role of BDNF and GABAergic transmission, their underlying mechanisms, and the relationship between BDNF and GABA in neurodegeneration and neuroregeneration. This review will provide a comprehensive overview of the underlying mechanisms of neuroregeneration that may help in developing potential strategies for pharmacotherapeutic approaches to treat neurotoxicity and neurodegenerative disease.

Activation of spinal alpha-7 nicotinic acetylcholine receptor shortens the duration of remifentanil-induced postoperative hyperalgesia by upregulating KCC2 in the spinal dorsal horn in rats

Background Accumulating evidence has shown that the signal from spinal brain-derived neurotrophic factor/tyrosine receptor kinase B-K+-Cl- cotransporter-2 plays a critical role in the process of pain hypersensitivity. The activation of alpha-7 nicotinic acetylcholine receptors could have an analgesic effect on remifentanil-induced postoperative hyperalgesia. Nevertheless, whether intrathecal administration of PNU-120596, an alpha-7 nicotinic acetylcholine receptors selective type II positive allosteric modulator, before surgery could affect the duration of remifentanil-induced postoperative hyperalgesia remains unknown, and the effects of alpha-7 nicotinic acetylcholine receptors activation on the brain-derived neurotrophic factor/tyrosine receptor kinase B-K+-Cl- cotransporter-2 signal in the spinal dorsal horn of rats with remifentanil-induced postoperative hyperalgesia is still enigmatic. Results We demonstrated that the brain-derived neurotrophic factor/tyrosine receptor kinase B-K+-Cl- cotransporter-2 signal played a critical role in the development of remifentanil-induced postoperative hyperalgesia. Intrathecal administration of PNU-120596 (8 µg/kg, 15 min before surgery) was associated with earlier signs of recovery from remifentanil-induced postoperative hyperalgesia. Simultaneously, remifentanil-induced postoperative hyperalgesia-induced K+-Cl- cotransporter-2 downregulation was partly reversed and coincided with a decreased expression of brain-derived neurotrophic factor/tyrosine receptor kinase B in the spinal dorsal horn, approximately correlating with the time course of the nociceptive behavior. Moreover, intrathecal administration of the K+-Cl- cotransporter-2 inhibitor VU0240551 significantly reduced the analgesic effect of PNU-120596 on remifentanil-induced postoperative hyperalgesia. Conclusions The activation of alpha-7 nicotinic acetylcholine receptors induced a shorter duration of remifentanil-induced postoperative hyperalgesia by restoring the brain-derived neurotrophic factor/tyrosine receptor kinase B-K+-Cl- cotransporter-2 signal in the spinal dorsal horn of rats, which provides new insight into treatment in clinical postoperative pain management.

Neuroprotective Effects of Exercise Treatments After Injury: The Dual Role of Neurotrophic Factors

BACKGROUND

Shared connections between physical activity and neuroprotection have been studied for decades, but the mechanisms underlying this effect of specific exercise were only recently brought to light. Several evidences suggest that physical activity may be a reasonable and beneficial method to improve functional recovery in both peripheral and central nerve injuries and to delay functional decay in neurodegenerative diseases. In addition to improving cardiac and immune functions, physical activity may represent a multifunctional approach not only to improve cardiocirculatory and immune functions, but potentially modulating trophic factors signaling and, in turn, neuronal function and structure at times that may be critical for neurodegeneration and regeneration.

METHODS

Research content related to the effects of physical activity and specific exercise programs in normal and injured nervous system have been reviewed.

RESULTS

Sustained exercise, particularly if applied at moderate intensity and early after injury, exerts anti-inflammatory and pro-regenerative effects, and may boost cognitive and motor functions in aging and neurological disorders. However, newest studies show that exercise modalities can differently affect the production and function of brain-derived neurotrophic factor and other neurotrophins involved in the generation of neuropathic conditions. These findings suggest the possibility that new exercise strategies can be directed to nerve injuries with therapeutical benefits.

CONCLUSION

Considering the growing burden of illness worldwide, understanding of how modulation of neurotrophic factors contributes to exercise-induced neuroprotection and regeneration after peripheral nerve and spinal cord injuries is a relevant topic for research, and represents the beginning of a new non-pharmacological therapeutic approach for better rehabilitation of neural disorders.

Rehabilitation Strategies after Spinal Cord Injury: Inquiry into the Mechanisms of Success and Failure

Body-weight supported locomotor training (BWST) promotes recovery of load-bearing stepping in lower mammals, but its efficacy in individuals with a spinal cord injury (SCI) is limited and highly dependent on injury severity. While animal models with complete spinal transections recover stepping with step-training, motor complete SCI individuals do not, despite similarly intensive training. In this review, we examine the significant differences between humans and animal models that may explain this discrepancy in the results obtained with BWST. We also summarize the known effects of SCI and locomotor training on the muscular, motoneuronal, interneuronal, and supraspinal systems in human and non-human models of SCI and address the potential causes for failure to translate to the clinic. The evidence points to a deficiency in neuronal activation as the mechanism of failure, rather than muscular insufficiency. While motoneuronal and interneuronal systems cannot be directly probed in humans, the changes brought upon by step-training in SCI animal models suggest a beneficial re-organization of the systems' responsiveness to descending and afferent feedback that support locomotor recovery. The literature on partial lesions in humans and animal models clearly demonstrate a greater dependency on supraspinal input to the lumbar cord in humans than in non-human mammals for locomotion. Recent results with epidural stimulation that activates the lumbar interneuronal networks and/or increases the overall excitability of the locomotor centers suggest that these centers are much more dependent on the supraspinal tonic drive in humans. Sensory feedback shapes the locomotor output in animal models but does not appear to be sufficient to drive it in humans.

Control of seizures by ketogenic diet-induced modulation of metabolic pathways

Epilepsy is too complex to be considered as a disease; it is more of a syndrome, characterized by seizures, which can be caused by a diverse array of afflictions. As such, drug interventions that target a single biological pathway will only help the specific individuals where that drug's mechanism of action is relevant to their disorder. Most likely, this will not alleviate all forms of epilepsy nor the potential biological pathways causing the seizures, such as glucose/amino acid transport, mitochondrial dysfunction, or neuronal myelination. Considering our current inability to test every individual effectively for the true causes of their epilepsy and the alarming number of misdiagnoses observed, we propose the use of the ketogenic diet (KD) as an effective and efficient preliminary/long-term treatment. The KD mimics fasting by altering substrate metabolism from carbohydrates to fatty acids and ketone bodies (KBs). Here, we underscore the need to understand the underlying cellular mechanisms governing the KD's modulation of various forms of epilepsy and how a diverse array of metabolites including soluble fibers, specific fatty acids, and functional amino acids (e.g., leucine, D-serine, glycine, arginine metabolites, and N-acetyl-cysteine) may potentially enhance the KD's ability to treat and reverse, not mask, these neurological disorders that lead to epilepsy.

Spinal Plasticity and Behavior: BDNF-Induced Neuromodulation in Uninjured and Injured Spinal Cord

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophic factor family of signaling molecules. Since its discovery over three decades ago, BDNF has been identified as an important regulator of neuronal development, synaptic transmission, and cellular and synaptic plasticity and has been shown to function in the formation and maintenance of certain forms of memory. Neural plasticity that underlies learning and memory in the hippocampus shares distinct characteristics with spinal cord nociceptive plasticity. Research examining the role BDNF plays in spinal nociception and pain overwhelmingly suggests that BDNF promotes pronociceptive effects. BDNF induces synaptic facilitation and engages central sensitization-like mechanisms. Also, peripheral injury-induced neuropathic pain is often accompanied with increased spinal expression of BDNF. Research has extended to examine how spinal cord injury (SCI) influences BDNF plasticity and the effects BDNF has on sensory and motor functions after SCI. Functional recovery and adaptive plasticity after SCI are typically associated with upregulation of BDNF. Although neuropathic pain is a common consequence of SCI, the relation between BDNF and pain after SCI remains elusive. This article reviews recent literature and discusses the diverse actions of BDNF. We also highlight similarities and differences in BDNF-induced nociceptive plasticity in naïve and SCI conditions.

The membrane trafficking and functionality of the K+-Cl- co-transporter KCC2 is regulated by TGF-β2

Functional activation of the neuronal K(+)-Cl(-) co-transporter KCC2 (also known as SLC12A5) is a prerequisite for shifting GABAA responses from depolarizing to hyperpolarizing during development. Here, we introduce transforming growth factor β2 (TGF-β2) as a new regulator of KCC2 membrane trafficking and functional activation. TGF-β2 controls membrane trafficking, surface expression and activity of KCC2 in developing and mature mouse primary hippocampal neurons, as determined by immunoblotting, immunofluorescence, biotinylation of surface proteins and KCC2-mediated Cl(-) extrusion. We also identify the signaling pathway from TGF-β2 to cAMP-response-element-binding protein (CREB) and Ras-associated binding protein 11b (Rab11b) as the underlying mechanism for TGF-β2-mediated KCC2 trafficking and functional activation. TGF-β2 increases colocalization and interaction of KCC2 with Rab11b, as determined by 3D stimulated emission depletion (STED) microscopy and co-immunoprecipitation, respectively, induces CREB phosphorylation, and enhances Rab11b gene expression. Loss of function of either CREB1 or Rab11b suppressed TGF-β2-dependent KCC2 trafficking, surface expression and functionality. Thus, TGF-β2 is a new regulatory factor for KCC2 functional activation and membrane trafficking, and a putative indispensable molecular determinant for the developmental shift of GABAergic transmission.

Melatonin attenuates neuronal apoptosis through up-regulation of K(+) -Cl(-) cotransporter KCC2 expression following traumatic brain injury in rats

Traumatic brain injury (TBI) initiates a complex cascade of neurochemical and signaling changes that leads to neuronal apoptosis, which contributes to poor outcomes for patients with TBI. The neuron-specific K(+) -Cl(-) cotransporter-2 (KCC2), the principal Cl(-) extruder in adult neurons, plays an important role in Cl(-) homeostasis and neuronal function. This present study was designed to investigate the expression pattern of KCC2 following TBI and to evaluate whether or not melatonin is able to prevent neuronal apoptosis by modulating KCC2 expression in a Sprague Dawley rat controlled cortical impact model of TBI. The time course study showed decreased mRNA and protein expression of KCC2 in the ipsilateral peri-core parietal cortex after TBI. Double immunofluorescence staining demonstrated that KCC2 is located in the plasma membrane of neurons. In addition, melatonin (10 mg/kg) was injected intraperitoneally at 5 minutes and repeated at 1, 2, 3, and 4 hours after brain trauma, and brain samples were extracted 24 hours after TBI. Compared to the vehicle group, melatonin treatment altered the down-regulation of KCC2 expression in both mRNA and protein levels after TBI. Also, melatonin treatment increased the protein levels of brain-derived neurotrophic factor (BDNF) and phosphorylated extracellular signal-regulated kinase (p-ERK). Simultaneously, melatonin administration ameliorated cortical neuronal apoptosis, reduced brain edema, and attenuated neurological deficits after TBI. In conclusion, our findings suggested that melatonin restores KCC2 expression, inhibits neuronal apoptosis and attenuates secondary brain injury after TBI, partially through activation of BDNF/ERK pathway.

Expanding Spectrum of Sodium Potassium Chloride Co-transporters in the Pathophysiology of Diseases

Sodium potassium chloride co-transporter (NKCC) belongs to cation-dependent chloride co-transporter family, whose activation allows the entry of Na(+), K(+) and 2Cl(-) inside the cell. It acts in concert with K(+) Cl(-) co-transporter (KCC), which extrudes K(+) and Cl(-) ions from cell. NKCC1 is widely distributed throughout the body, while NKCC2 is exclusively present in kidney. Protein kinase A, protein kinase C, Ste20-related proline-alanine-rich kinase, oxidative stress responsive kinases, With No K=lysine kinase and protein phosphatase type 1 control the phosphorylation/dephosphorylation of key threonine residues of in regulatory domain of NKCC1. The selective inhibitors of NKCC1 including bumetanide and furosemide are conventionally employed as diuretics. However, recent studies have indicated that NKCC1 may be involved in the pathophysiology of anxiety, cerebral ischemia, epilepsy, neuropathic pain, fragile X syndrome, autism and schizophrenia. The inhibitors of NKCC1 are shown to produce anxiolytic effects; attenuate cerebral ischemia-induced neuronal injury; produce antiepileptic effects and attenuate neuropathic pain. In the early developing brain, GABAA activation primarily produces excitatory actions due to high NKCC1/KCC2 ratio. However, as the development progresses, the ratio of NKCC1/KCC2 ratio reverses and there is switch in the polarity of GABAA actions and latter acquires the inhibitory actions. The recapitulation of developmental-like state during pathological state may be associated with increase in the expression and functioning of NKCC1, which decreases the strength of inhibitory GABAergic neurotransmission. The present review describes the expanding role and mechanism of NKCC1 in the pathophysiology of different diseases.

Glial Na(+) -dependent ion transporters in pathophysiological conditions

Sodium dynamics are essential for regulating functional processes in glial cells. Indeed, glial Na(+) signaling influences and regulates important glial activities, and plays a role in neuron-glia interaction under physiological conditions or in response to injury of the central nervous system (CNS). Emerging studies indicate that Na(+) pumps and Na(+) -dependent ion transporters in astrocytes, microglia, and oligodendrocytes regulate Na(+) homeostasis and play a fundamental role in modulating glial activities in neurological diseases. In this review, we first briefly introduced the emerging roles of each glial cell type in the pathophysiology of cerebral ischemia, Alzheimer's disease, epilepsy, Parkinson's disease, Amyotrophic Lateral Sclerosis, and myelin diseases. Then, we discussed the current knowledge on the main roles played by the different glial Na(+) -dependent ion transporters, including Na(+) /K(+) ATPase, Na(+) /Ca(2+) exchangers, Na(+) /H(+) exchangers, Na(+) -K(+) -Cl(-) cotransporters, and Na(+) - HCO3- cotransporter in the pathophysiology of the diverse CNS diseases. We highlighted their contributions in cell survival, synaptic pathology, gliotransmission, pH homeostasis, and their role in glial activation, migration, gliosis, inflammation, and tissue repair processes. Therefore, this review summarizes the foundation work for targeting Na(+) -dependent ion transporters in glia as a novel strategy to control important glial activities associated with Na(+) dynamics in different neurological disorders. GLIA 2016;64:1677-1697.

Motor Cortex Excitability and BDNF Levels in Chronic Musculoskeletal Pain According to Structural Pathology

The central sensitization syndrome (CSS) encompasses disorders with overlapping symptoms in a structural pathology spectrum ranging from persistent nociception [e.g., osteoarthritis (OA)] to an absence of tissue injuries such as the one presented in fibromyalgia (FM) and myofascial pain syndrome (MPS). First, we hypothesized that these syndromes present differences in their cortical excitability parameters assessed by transcranial magnetic stimulation (TMS), namely motor evoked potential (MEP), cortical silent period (CSP), short intracortical inhibition (SICI) and short intracortical facilitation (SICF). Second, considering that the presence of tissue injury could be detected by serum neurotrophins, we hypothesized that the spectrum of structural pathology (i.e., from persistent nociception like in OA, to the absence of tissue injury like in FM and MPS), could be detected by differential efficiency of their descending pain inhibitory system, as assessed by the conditioned pain modulation (CPM) paradigm. Third, we explored whether brain-derived neurotrophic factor (BDNF) had an influence on the relationship between motor cortex excitability and structural pathology. This cross-sectional study pooled baseline data from three randomized clinical trials. We included females (n = 114), aged 19-65 years old with disability by chronic pain syndromes (CPS): FM (n = 19), MPS (n = 54), OA (n = 27) and healthy subjects (n = 14). We assessed the serum BDNF, the motor cortex excitability by parameters the TMS measures and the change on numerical pain scale [NPS (0-10)] during CPM-task. The adjusted mean (SD) on the SICI observed in the absence of tissue injury was 56.36% lower than with persistent nociceptive input [0.31(0.18) vs. 0.55 (0.32)], respectively. The BDNF was inversely correlated with the SICI and with the change on NPS (0-10)during CPM-task. These findings suggest greater disinhibition in the motor cortex and the descending pain inhibitory system in FM and MPS than in OA and healthy subjects. Likewise, the inter-hemispheric disinhibition as well as the dysfunction in the descending pain modulatory system is higher in chronic pain without tissue injury compared to a structural lesion. In addition, they suggest that a greater level of serum BDNF may be involved in the processes that mediate the disinhibition of motor cortex excitability, as well as the function of descending inhibitory pain modulation system, independently of the physiopathology mechanism of musculoskeletal pain syndromes.