Dual actions of brain-derived neurotrophic factor on GABAergic transmission in cerebellar Purkinje neurons

Hyperbaric Oxygen Therapy Attenuated the Motor Coordination and Cognitive Impairment of Polyglutamine Spinocerebellar Ataxia SCA17 Mice

Spinocerebellar ataxias (SCAs) are a large and diverse group of autosomal-dominant neurodegenerative diseases. No drugs have been approved for these relentlessly progressive and fatal SCAs. Our previous studies indicate that oxidative stress, neuroinflammation, and neuronal apoptosis are elevated in the SCA17 mice, which are the main therapeutic targets of hyperbaric oxygen treatment (HBOT). HBOT is considered to be an alternative and less invasive therapy for SCAs. In this study, we evaluated the HBOT (2.2 ATA for 14 days) effect and the persistence for the management of SCA17 mice and their wild-type littermates. We found HBOT attenuated the motor coordination and cognitive impairment of SCA17 mice and which persisted for about 1 month after the treatment. The results of several biochemistry and liver/kidney hematoxylin and eosin staining show the HBOT condition has no obvious toxicity in the mice. Immunostaining analyses show that the neuroprotective effect of HBOT could be through the promotion of BDNF production and the amelioration of neuroinflammation. Surprisingly, HBOT executes different effects on the male and female SCA17 mice, including the reduction of neuroinflammation and activation of CaMKII and ERK. This study suggests HBOT is a potential alternative therapeutic treatment for SCA17. Accumulated findings have revealed the similarity in disease pathomechanisms and possible therapeutic strategies in polyQ diseases; therefore, HBOT could be an optional treatment as well as the other polyQ diseases.

Neuropeptides and Their Roles in the Cerebellum

Although more than 30 different types of neuropeptides have been identified in various cell types and circuits of the cerebellum, their unique functions in the cerebellum remain poorly understood. Given the nature of their diffuse distribution, peptidergic systems are generally assumed to exert a modulatory effect on the cerebellum via adaptively tuning neuronal excitability, synaptic transmission, and synaptic plasticity within cerebellar circuits. Moreover, cerebellar neuropeptides have also been revealed to be involved in the neurogenetic and developmental regulation of the developing cerebellum, including survival, migration, differentiation, and maturation of the Purkinje cells and granule cells in the cerebellar cortex. On the other hand, cerebellar neuropeptides hold a critical position in the pathophysiology and pathogenesis of many cerebellar-related motor and psychiatric disorders, such as cerebellar ataxias and autism. Over the past two decades, a growing body of evidence has indicated neuropeptides as potential therapeutic targets to ameliorate these diseases effectively. Therefore, this review focuses on eight cerebellar neuropeptides that have attracted more attention in recent years and have significant potential for clinical application associated with neurodegenerative and/or neuropsychiatric disorders, including brain-derived neurotrophic factor, corticotropin-releasing factor, angiotensin II, neuropeptide Y, orexin, thyrotropin-releasing hormone, oxytocin, and secretin, which may provide novel insights and a framework for our understanding of cerebellar-related disorders and have implications for novel treatments targeting neuropeptide systems.

Rebuilding hippocampus neural circuit with hADSC-derived neuron cells for treating ischemic stroke

Background

Human adipose-derived stem cells (hADSCs) have been demonstrated to be a promising autologous stem cell source for treating various neuronal diseases. Our study indicated that hADSCs could be induced into neuron-like cells in a stepwise manner that are characterized by the positive expression of MAP2, SYNAPSIN 1/2, NF-200, and vGLUT and electrophysiological activity. We first primed hADSCs into neuron-like cells (hADSC-NCs) and then intracerebrally transplanted them into MCAO reperfusion mice to further explore their in vivo survival, migration, integration, fate commitment and involvement in neural circuit rebuilding.

Results

The hADSC-NCs survived well and transformed into MAP2-positive, Iba1- or GFAP-negative cells in vivo while maintaining some proliferative ability, indicated by positive Ki67 staining after 4 weeks. hADSC-NCs could migrate to multiple brain regions, including the cortex, hippocampus, striatum, and hypothalamus, and further differentiate into mature neurons, as confirmed by action potential elicitation and postsynaptic currents. With the aid of a cell suicide system, hADSC-NCs were proven to have functionally integrated into the hippocampal memory circuit, where they contributed to spatial learning and memory rescue, as indicated by LTP improvement and subsequent GCV-induced relapse. In addition to infarction size shrinkage and movement improvement, MCAO-reperfused mice showed bidirectional immune modulation, including inhibition of the local proinflammatory factors IL-1α, IL-1β, IL-2, MIP-1β and promotion proinflammatory IP-10, MCP-1, and enhancement of the anti-inflammatory factors IL-15.

Conclusion

Overall, hADSC-NCs used as an intermediate autologous cell source for treating stroke can rebuild hippocampus neuronal circuits through cell replacement.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00774-x.

A single nucleotide polymorphism-based formula to predict the risk of propofol TCI concentration being over 4 µg mL-1 at the time of loss of consciousness

We aim to develop a formula based on single nucleotide polymorphisms (SNPs) to predict whether the propofol target-controlled infusion (TCI) concentration would be over 4 μg mL^-1 at the time of loss of consciousness (LOC). We recruited 184 patients undergoing thyroid or breast surgeries with propofol anaesthesia. A total of 48 SNPs of CYP2B6, CYP2C9, UGT1A9, HNF4A, ABCB1, ABCC4, ABCG2, GABRA2, GABRA4, GABRB1, GABRB3, GABRG2, GABBR2, GAD1, SLC1A3, BDNF, and NRXN1, previously associated with propofol metabolic and pharmacology pathway, were genotyped. The formula was developed in the training cohort using the least absolute shrinkage and selection operator logistic regression model, and then validated in the testing cohort. The SNPs, GABBR2 rs1167768, GABBR2 rs1571927, NRXN1 rs601010, BDNF rs2049046, GABRA4 rs1512135, UGT1A9 rs11692021, GABBR2 rs2808536, HNF4A rs1884613, GABRB3 rs2017247, and CYP2B6 rs3181842 were selected to construct the SNP-based formula, which was used to calculate the risk score for over 4 μg mL^-1 TCI concentration of propofol at the time of LOC. Patients in the high-risk group were more likely to require a propofol concentration higher than 4 μg mL^-1 and presented a longer LOC latency. The SNP-based formula may significantly improve the safety and effectiveness of propofol-induced anaesthesia.

Gephyrin Interacts with the K-Cl Cotransporter KCC2 to Regulate Its Surface Expression and Function in Cortical Neurons

The K+-Cl- cotransporter KCC2, encoded by the Slc12a5 gene, is a neuron-specific chloride extruder that tunes the strength and polarity of GABAA receptor-mediated transmission. In addition to its canonical ion transport function, KCC2 also regulates spinogenesis and excitatory synaptic function through interaction with a variety of molecular partners. KCC2 is enriched in the vicinity of both glutamatergic and GABAergic synapses, the activity of which in turn regulates its membrane stability and function. KCC2 interaction with the submembrane actin cytoskeleton via 4.1N is known to control its anchoring near glutamatergic synapses on dendritic spines. However, the molecular determinants of KCC2 clustering near GABAergic synapses remain unknown. Here, we used proteomics to identify novel KCC2 interacting proteins in the adult rat neocortex. We identified both known and novel candidate KCC2 partners, including some involved in neuronal development and synaptic transmission. These include gephyrin, the main scaffolding molecule at GABAergic synapses. Gephyrin interaction with endogenous KCC2 was confirmed by immunoprecipitation from rat neocortical extracts. We showed that gephyrin stabilizes plasmalemmal KCC2 and promotes its clustering in hippocampal neurons, mostly but not exclusively near GABAergic synapses, thereby controlling KCC2-mediated chloride extrusion. This study identifies gephyrin as a novel KCC2 anchoring molecule that regulates its membrane expression and function in cortical neurons.SIGNIFICANCE STATEMENT Fast synaptic inhibition in the brain is mediated by chloride-permeable GABAA receptors (GABAARs) and therefore relies on transmembrane chloride gradients. In neurons, these gradients are primarily maintained by the K/Cl cotransporter KCC2. Therefore, understanding the mechanisms controlling KCC2 expression and function is crucial to understand its physiological regulation and rescue its function in the pathology. KCC2 function depends on its membrane expression and clustering, but the underlying mechanisms remain unknown. We describe the interaction between KCC2 and gephyrin, the main scaffolding protein at inhibitory synapses. We show that gephyrin controls plasmalemmal KCC2 clustering and that loss of gephyrin compromises KCC2 function. Our data suggest functional units comprising GABAARs, gephyrin, and KCC2 act to regulate synaptic GABA signaling.

Deletion of TrkB in parvalbumin interneurons alters cortical neural dynamics

Signaling by neurotrophins such as the brain‐derived neurotrophic factor (BDNF) is known to modulate development of interneurons, but the circuit effects of this modulation remain unclear. Here, we examined the impact of deleting TrkB, a BDNF receptor, in parvalbumin‐expressing (PV) interneurons on the balance of excitation and inhibition (E‐I) in cortical circuits. In the mouse olfactory cortex, TrkB deletion impairs multiple aspects of PV neuronal function including synaptic excitation, intrinsic excitability, and the innervation pattern of principal neurons. Impaired PV cell function resulted in aberrant spiking patterns in principal neurons in response to stimulation of sensory inputs. Surprisingly, dampened PV neuronal function leads to a paradoxical decrease in overall excitability in cortical circuits. Our study demonstrates that, by modulating PV circuit plasticity and development, TrkB plays a critical role in shaping the evoked pattern of activity in a cortical network.

Physiology of Cerebellar Reserve: Redundancy and Plasticity of a Modular Machine

The cerebellum is endowed with the capacity for compensation and restoration after pathological injury, a property known as cerebellar reserve. Such capacity is attributed to two unique morphological and physiological features of the cerebellum. First, mossy fibers that convey peripheral and central information run mediolaterally over a wide area of the cerebellum, resulting in the innervation of multiple microzones, commonly known as cerebellar functional units. Thus, a single microzone receives redundant information that can be used in pathological conditions. Secondly, the circuitry is characterized by a co-operative interplay among various forms of synaptic plasticity. Recent progress in understanding the mechanisms of redundant information and synaptic plasticity has allowed outlining therapeutic strategies potentiating these neural substrates to enhance the cerebellar reserve, taking advantage of the unique physiological properties of the cerebellum which appears as a modular and potentially reconfiguring brain structure.

The postnatal GABA shift: A developmental perspective

GABA is the major inhibitory neurotransmitter that counterbalances excitation in the mature brain. The inhibitory action of GABA relies on the inflow of chloride ions (Cl^-), which hyperpolarizes the neuron. In early development, GABA signaling induces outward Cl^- currents and is depolarizing. The postnatal shift from depolarizing to hyperpolarizing GABA is a pivotal event in brain development and its timing affects brain function throughout life. Altered timing of the postnatal GABA shift is associated with several neurodevelopmental disorders. Here, we argue that the postnatal shift from depolarizing to hyperpolarizing GABA represents the final shift in a sequence of GABA shifts, regulating proliferation, migration, differentiation, and finally plasticity of developing neurons. Each developmental GABA shift ensures that the instructive role of GABA matches the circumstances of the developing network. Sensory input may be a crucial factor in determining proper timing of the postnatal GABA shift. A developmental perspective is necessary to interpret the full consequences of a mismatch between connectivity, activity and GABA signaling during brain development.

Coordinated downregulation of KCC2 and GABAA receptor contributes to inhibitory dysfunction during seizure induction

The GABAA receptor (GABAAR) is the main inhibitory receptor in the adult mammalian brain. GABAAR function is dependent on its expression, distribution, and the chloride (Cl-) transmembrane gradient, which is determined by the potassium-chloride cotransporter 2 (KCC2) in the adult brain. KCC2 and GABAAR are downregulated in an activity-dependent manner during seizure induction. Functionally, KCC2 and GABAAR are closely related membrane proteins which modulate GABAergic inhibition. However, it remains unclear how their downregulation during seizure induction is coordinated. This study aimed to assess this interaction. Our results revealed that KCC2 and GABAAR were simultaneously downregulated in both in vivo and in vitro seizure models induced by the convulsant cyclothazide (CTZ), which was at least partly due to structural coupling in hippocampal neuronal membranes. Immunohistochemistry revealed colocalization of gephyrin with KCC2 and co-immunoprecipitation exhibited a direct coupling between GABAAR α1-subunit and KCC2 protein in hippocampal cell membranes. KCC2 specific short hairpin RNA (KCC2-shRNA) was employed to specifically reduce the expression of KCC2 in cultured hippocampal neurons. This resulted in a significant reduction in KCC2-independent GABAergic miniature inhibitory post-synaptic current (mIPSC) amplitude in shKCC2-transfected neurons. Further, pre-treatment with furosemide, a KCC2 inhibitor, during CTZ stimulation followed by washout significantly prevented convulsant stimulation-induced membrane KCC2 downregulation and significantly attenuated GABAAR downregulation concomitant with recovery of suppressed KCC2-independent GABAergic mIPSC amplitude. Our results suggest that the coordinated downregulation of KCC2 and GABAAR during seizure induction exerts a strong functional impact on GABAAR, highlighting an important regulatory mechanism in epilepsy.

Recent Advances in the Treatment of Cerebellar Disorders

Various etiopathologies affect the cerebellum, resulting in the development of cerebellar ataxias (CAs), a heterogeneous group of disorders characterized clinically by movement incoordination, affective dysregulation, and cognitive dysmetria. Recent progress in clinical and basic research has opened the door of the ‘‘era of therapy” of CAs. The therapeutic rationale of cerebellar diseases takes into account the capacity of the cerebellum to compensate for pathology and restoration, which is collectively termed cerebellar reserve. In general, treatments of CAs are classified into two categories: cause-cure treatments, aimed at arresting disease progression, and neuromodulation therapies, aimed at potentiating cerebellar reserve. Both forms of therapies should be introduced as soon as possible, at a time where cerebellar reserve is still preserved. Clinical studies have established evidence-based cause-cure treatments for metabolic and immune-mediated CAs. Elaborate protocols of rehabilitation and non-invasive cerebellar stimulation facilitate cerebellar reserve, leading to recovery in the case of controllable pathologies (metabolic and immune-mediated CAs) and delay of disease progression in the case of uncontrollable pathologies (degenerative CAs). Furthermore, recent advances in molecular biology have encouraged the development of new forms of therapies: the molecular targeting therapy, which manipulates impaired RNA or proteins, and the neurotransplantation therapy, which delays cell degeneration and facilitates compensatory functions. The present review focuses on the therapeutic rationales of these recently developed therapeutic modalities, highlighting the underlying pathogenesis.

Task Force Paper On Cerebellar Transplantation: Are We Ready to Treat Cerebellar Disorders with Cell Therapy?

Restoration of damaged central nervous system structures, functional recovery, and prevention of neuronal loss during neurodegenerative diseases are major objectives in cerebellar research. The highly organized anatomical structure of the cerebellum with numerous inputs/outputs, the complexity of cerebellar functions, and the large spectrum of cerebellar ataxias render therapies of cerebellar disorders highly challenging. There are currently several therapeutic approaches including motor rehabilitation, neuroprotective drugs, non-invasive cerebellar stimulation, molecularly based therapy targeting pathogenesis of the disease, and neurotransplantation. We discuss the goals and possible beneficial mechanisms of transplantation therapy for cerebellar damage and its limitations and factors determining outcome.

Impact of Chronic BDNF Depletion on GABAergic Synaptic Transmission in the Lateral Amygdala

Brain-derived neurotrophic factor (BDNF) has previously been shown to play an important role in glutamatergic synaptic plasticity in the amygdala, correlating with cued fear learning. While glutamatergic neurotransmission is facilitated by BDNF signaling in the amygdala, its mechanism of action at inhibitory synapses in this nucleus is far less understood. We therefore analyzed the impact of chronic BDNF depletion on GABA_A-mediated synaptic transmission in BDNF heterozygous knockout mice (BDNF^+/−). Analysis of miniature and evoked inhibitory postsynaptic currents (IPSCs) in the lateral amygdala (LA) revealed neither pre- nor postsynaptic differences in BDNF^+/− mice compared to wild-type littermates. In addition, long-term potentiation (LTP) of IPSCs was similar in both genotypes. In contrast, facilitation of spontaneous IPSCs (sIPSCs) by norepinephrine (NE) was significantly reduced in BDNF^+/− mice. These results argue against a generally impaired efficacy and plasticity at GABAergic synapses due to a chronic BDNF deficit. Importantly, the increase in GABAergic tone mediated by NE is reduced in BDNF^+/− mice. As release of NE is elevated during aversive behavioral states in the amygdala, effects of a chronic BDNF deficit on GABAergic inhibition may become evident in response to states of high arousal, leading to amygdala hyper-excitability and impaired amygdala function.

Effect of voluntary running on expression of myokines in brains of rats with depression

This study aimed to demonstrate the histopathology and immunoexpression of exercise-derived myokines in dentate gyrus (DG), medial prefrontal cortex (mPFC) and cerebellum of depressed Wistar rats during depression and after practising voluntary running. Depression was developed by forced swimming for 2 weeks. Voluntary running was performed by voluntary running for 3 weeks. Brain sections were processed and immunostained to detect brain-derived neurotrophic factor (BDNF), macrophage migration inhibitory factor (MIF), vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6). ImageJ software was used to measure the optical density (OD). BDNF was expressed in neurons in DG, mPFC and granular and Purkinje cells in cerebellum. MIF was expressed in neurons of sub-granular zone in DG, mPFC and Purkinje cells. VEGF was expressed in many neurons in DG, mPFC and Purkinje cells. IL-6 was expressed in some neurons in DG, in neuropil of mPFC and in Purkinje cells. In depression, the OD of studied myokines significantly decreased in all examined areas. After voluntary running, the OD of myokines significantly increased in all areas. This study defines the immunohistochemical expression of myokines in brain areas in depression and after voluntary running and reveals the involvement of the mPFC and cerebellum in the pathophysiology of depression.

Brain Derived Neurotrophic Factor (BDNF) Delays Onset of Pathogenesis in Transgenic Mouse Model of Spinocerebellar Ataxia Type 1 (SCA1)

Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by an abnormal expansion of CAG repeats in the Ataxin-1 (ATXN1) gene and characterized by motor deficits and cerebellar neurodegeneration. Even though mutant ATXN1 is expressed from an early age, disease onset usually occurs in patient’s mid-thirties, indicating the presence of compensatory factors that limit the toxic effects of mutant ATXN1 early in disease. Brain derived neurotrophic factor (BDNF) is a growth factor known to be important for the survival and function of cerebellar neurons. Using gene expression analysis, we observed altered BDNF expression in the cerebella of Purkinje neuron specific transgenic mouse model of SCA1, ATXN1[82Q] mice, with increased expression during the early stage and decreased expression in the late stage of disease. We therefore investigated the potentially protective role of BDNF in early stage SCA1 through intraventricular delivery of BDNF via ALZET osmotic pumps. Extrinsic BDNF delivery delayed onset of motor deficits and Purkinje neuron pathology in ATXN1[82Q] mice supporting its use as a novel therapeutic for SCA1.

Brain-Derived Neurotrophic Factor Is Required for the Neuroprotective Effect of Mifepristone on Immature Purkinje Cells in Cerebellar Slice Culture

Endogenous γ-aminobutyric acid (GABA)-dependent activity induces death of developing Purkinje neurons in mouse organotypic cerebellar cultures and the synthetic steroid mifepristone blocks this effect. Here, using brain-derived neurotrophic factor (BDNF) heterozygous mice, we show that BDNF plays no role in immature Purkinje cell death. However, interestingly, BDNF haploinsufficiency impairs neuronal survival induced by mifepristone and GABA_A-receptors antagonist (bicuculline) treatments, indicating that the underlying neuroprotective mechanism requires the neurotrophin full expression.

Neurotransplantation therapy

Neurotransplantation may be a promising approach for therapy of cerebellar diseases characterized by a substantial loss of neurons. Neurotransplantation could rescue neurons from degeneration and maintain cerebellar reserve, facilitate cerebellar compensation, or help reconstruct damaged neural circuits by cell substitution. These mechanisms of action can be of varying importance according to the type of cerebellar disease. Neurotransplantation therapy in cerebellar ataxias is still at the stage of experimental studies. There is currently little knowledge regarding cerebellar patients. Nevertheless, data provided by experiments in animal models of cerebellar degeneration and both clinical studies and experiences in patients with other neurologic diseases enable us to suggest basic principles, expectations, limitations, and future directions of neurotransplantation therapy for cerebellar diseases.

Influence of brain-derived neurotrophic factor-tyrosine receptor kinase B signalling in the nucleus tractus solitarius on baroreflex sensitivity in rats with chronic heart failure

KEY POINTS

Impairment of baroreflex function is associated with the progression of chronic heart failure (CHF) and a poor prognosis. The baroreflex desensitization in CHF is at least partly the result of central neuronal network dysfunction. The dorsal medial nucleus tractus solitarius (dmNTS) has long been appreciated as a primary site of baroreceptor afferent termination in the central nervous system. However, the influence of neurotransmitters and neuromodulators in the dmNTS on baroreflex function both in normal and CHF states is not fully understood. The present study provides the first evidence showing a tonic sympatho-inhibitory role for brain-derived neurotrophic factor (BDNF) neurotransmission in the dmNTS. Most importantly, BDNF- tyrosine receptor kinase B (TrkB) signalling in the dmNTS is integral for normal baroreflex function as indicated by the blunting of baroreflex sensitivity (BRS) following the antagonization of TrkB, which inhibited baroreflex gain and range. Furthermore, we found that the tonic sympatho-inhibition of BDNF was withdrawn in the CHF state, thus contributing to the increased sympathetic tone associated with CHF. Consistent with this finding, BDNF/TrkB antagonism had little effect on reducing BRS in CHF animals, which is corroborated by the observation of decreased TrkB expression in the dmNTS during CHF. Taken together, these results implicate a reduction in BDNF-TrkB signalling in the dmNTS during CHF that contributes to sympatho-excitation and baroreflex desensitization. The observation that the BDNF/TrkB pathway is impaired in the dmNTS during CHF provides a novel mechanism for understanding the central alterations that contribute to baroreflex desensitization during CHF.

ABSTRACT

Chronic heart failure (CHF) results in blunting of arterial baroreflex sensitivity (BRS), which arises from alterations to both peripheral baroreceptors and central autonomic nuclei such as the nucleus tractus solitarius (NTS). Although glutamate is known to be an important neurotransmitter released from baroreceptor afferent synapses in the NTS, the influence of other neurotransmitters and neuromodulators remains unclear. Alterations to NTS signalling in CHF remain particularly undefined. The present study aimed to evaluate the role of brain-derived neurotrophic factor (BDNF) and tyrosine receptor kinase B (TrkB) receptor signalling in the NTS on baroreflex control both in healthy and CHF rats. To this end, we microinjected BDNF or the highly selective TrkB receptor antagonist [N2-2-2-oxoazepan-3-yl amino] carbonyl phenyl benzo (b)thiophene-2-carboxamide (ANA-12) into the dorsal medial NTS (dmNTS) of male Sprague-Dawley rats with coronary artery ligation-induced CHF and sham operated controls and recorded blood pressure and renal sympathetic nerve activity responses. We subsequently measured BRS before and after bilateral dmNTS microinjections of ANA-12. In sham rats, BDNF evoked a dose-dependent depressor and sympatho-inhibitory effect and ANA-12 produced the opposite response. Both of these responses were significantly blunted in CHF rats. Furthermore, bilateral microinjection of ANA-12 into the dmNTS greatly diminished baroreflex sensitivity in sham rats, whereas it had less of an effect in CHF rats. We observed decreased levels of TrkB protein and mRNA in the dmNTS of CHF rats. These data indicate that endogenous BDNF signalling in the NTS is integral for the maintenance of BRS and that BDNF/TrkB signalling is impaired in the NTS in the CHF state.

Reducing premature KCC2 expression rescues seizure susceptibility and spine morphology in atypical febrile seizures

Atypical febrile seizures are considered a risk factor for epilepsy onset and cognitive impairments later in life. Patients with temporal lobe epilepsy and a history of atypical febrile seizures often carry a cortical malformation. This association has led to the hypothesis that the presence of a cortical dysplasia exacerbates febrile seizures in infancy, in turn increasing the risk for neurological sequelae. The mechanisms linking these events are currently poorly understood. Potassium-chloride cotransporter KCC2 affects several aspects of neuronal circuit development and function, by modulating GABAergic transmission and excitatory synapse formation. Recent data suggest that KCC2 downregulation contributes to seizure generation in the epileptic adult brain, but its role in the developing brain is still controversial. In a rodent model of atypical febrile seizures, combining a cortical dysplasia and hyperthermia-induced seizures (LHS rats), we found a premature and sustained increase in KCC2 protein levels, accompanied by a negative shift of the reversal potential of GABA. In parallel, we observed a significant reduction in dendritic spine size and mEPSC amplitude in CA1 pyramidal neurons, accompanied by spatial memory deficits. To investigate whether KCC2 premature overexpression plays a role in seizure susceptibility and synaptic alterations, we reduced KCC2 expression selectively in hippocampal pyramidal neurons by in utero electroporation of shRNA. Remarkably, KCC2 shRNA-electroporated LHS rats show reduced hyperthermia-induced seizure susceptibility, while dendritic spine size deficits were rescued. Our findings demonstrate that KCC2 overexpression in a compromised developing brain increases febrile seizure susceptibility and contribute to dendritic spine alterations.

The K(+)-Cl(-) Cotransporter KCC2 and Chloride Homeostasis: Potential Therapeutic Target in Acute Central Nervous System Injury

The K(+)-Cl(-) cotransporter-2 (KCC2) is a well-known member of the electroneutral cation-chloride cotransporters with a restricted expression pattern to neurons. This transmembrane protein mediates the efflux of Cl(-) out of neurons and exerts a critical role in inhibitory γ-aminobutyric acidergic (GABAergic) and glycinergic neurotransmission. Moreover, KCC2 participates in the regulation of various physiological processes of neurons, including cell migration, dendritic outgrowth, spine morphology, and dendritic synaptogenesis. It is important to note that down-regulation of KCC2 is associated with the pathogenesis of multiple neurological diseases, which is of particular relevance to acute central nervous system (CNS) injury. In this review, we aim to survey the pathogenic significance of KCC2 down-regulation under the condition of acute CNS injuries. We propose that further elucidation of the molecular mechanisms regarding KCC2 down-regulation after acute CNS injuries is necessary because of potential promising avenues for prevention and treatment of acute CNS injury.

Anoctamin Calcium-Activated Chloride Channels May Modulate Inhibitory Transmission in the Cerebellar Cortex

Calcium-activated chloride channels of the anoctamin (alias TMEM16) protein family fulfill critical functions in epithelial fluid transport, smooth muscle contraction and sensory signal processing. Little is known, however, about their contribution to information processing in the central nervous system. Here we examined the recent finding that a calcium-dependent chloride conductance impacts on GABAergic synaptic inhibition in Purkinje cells of the cerebellum. We asked whether anoctamin channels may underlie this chloride conductance. We identified two anoctamin channel proteins, ANO1 and ANO2, in the cerebellar cortex. ANO1 was expressed in inhibitory interneurons of the molecular layer and the granule cell layer. Both channels were expressed in Purkinje cells but, while ANO1 appeared to be retained in the cell body, ANO2 was targeted to the dendritic tree. Functional studies confirmed that ANO2 was involved in a calcium-dependent mode of ionic plasticity that reduces the efficacy of GABAergic synapses. ANO2 channels attenuated GABAergic transmission by increasing the postsynaptic chloride concentration, hence reducing the driving force for chloride influx. Our data suggest that ANO2 channels are involved in a Ca2+-dependent regulation of synaptic weight in GABAergic inhibition. Thus, in balance with the chloride extrusion mechanism via the co-transporter KCC2, ANO2 appears to regulate ionic plasticity in the cerebellum.

BDNF signaling in the rat cerebello-vestibular pathway during vestibular compensation: BDNF signaling in vestibular compensation

Vestibular compensation, which is the behavioral recovery from lesions to the peripheral vestibular system, is attributed to plasticity of the central vestibular system. It has been reported that brain-derived neurotrophic factor (BDNF) is expressed and released in an activity-dependent manner. Upon binding to the tyrosine receptor kinase B (TrkB), BDNF can acutely modulate synaptic transmission and plasticity in the central nervous system. To assess the possible contribution of BDNF to this recovery process, we studied the expression of BDNF, TrkB.FL, TrkB.T1 and KCC2 (K(+) -Cl(-) cotransporter isoform 2) in the bilateral medial vestibular nucleus (MVN) and the flocculus of rats at 4 h, 8 h, 1, 3 and 7 days following unilateral labyrinthectomy (UL) using immunohistochemistry, quantitative real-time PCR and western blotting. Our results have shown that, compared with the sham controls and the contra-lesional side, (a) the expression of BDNF and TrkB.FL increased at 4 h in the ipsi-lesional flocculus after UL; (b) the expression of TrkB.T1 decreased at 4 h and KCC2 decreased at 8 h and 1 day in the ipsi-lesional flocculus after UL; and (c) BDNF and TrkB.FL expression was enhanced and KCC2 expression was reduced in the ipsi-lesional MVN at 8 h after UL. Our data supported the hypothesis that BDNF upregulation may reduce the inhibitory effects of the flocculus and commissural inhibition system by regulating inhibitory GABAergic synaptic transmission in floccular Purkinje cells and Purkinje cell terminals in the MVN. Additionally, KCC2 may be a switch in this process.

Sex-specific consequences of early life seizures

Seizures are very common in the early periods of life and are often associated with poor neurologic outcome in humans. Animal studies have provided evidence that early life seizures may disrupt neuronal differentiation and connectivity, signaling pathways, and the function of various neuronal networks. There is growing experimental evidence that many signaling pathways, like GABAA receptor signaling, the cellular physiology and differentiation, or the functional maturation of certain brain regions, including those involved in seizure control, mature differently in males and females. However, most experimental studies of early life seizures have not directly investigated the importance of sex on the consequences of early life seizures. The sexual dimorphism of the developing brain raises the question that early seizures could have distinct effects in immature females and males that are subjected to seizures. We will first discuss the evidence for sex-specific features of the developing brain that could be involved in modifying the susceptibility and consequences of early life seizures. We will then review how sex-related biological factors could modify the age-specific consequences of induced seizures in the immature animals. These include signaling pathways (e.g., GABAA receptors), steroid hormones, growth factors. Overall, there are very few studies that have specifically addressed seizure outcomes in developing animals as a function of sex. The available literature indicates that a variety of outcomes (histopathological, behavioral, molecular, epileptogenesis) may be affected in a sex-, age-, region-specific manner after seizures during development. Obtaining a better understanding for the gender-related mechanisms underlying epileptogenesis and seizure comorbidities will be necessary to develop better gender and age appropriate therapies.

The BDNF/TrkB signaling pathway is involved in heat hyperalgesia mediated by Cdk5 in rats

Background

Cyclin-dependent kinase 5 (Cdk5) has been shown to play an important role in mediating inflammation-induced heat hyperalgesia. However, the underlying mechanism remains unclear. The aim of this study was to determine whether roscovitine, an inhibitor of Cdk5, could reverse the heat hyperalgesia induced by peripheral injection of complete Freund's adjuvant (CFA) via the brain-derived neurotrophic factor (BDNF)-tyrosine kinase B (TrkB) signaling pathway in the dorsal horn of the spinal cord in rats.

Results

Heat hyperalgesia induced by peripheral injection of CFA was significantly reversed by roscovitine, TrkB-IgG, and the TrkB inhibitor K252a, respectively. Furthermore, BDNF was significantly increased from 0.5 h to 24 h after CFA injection in the spinal cord dorsal horn. Intrathecal adminstration of the Cdk5 inhibitor roscovitine had no obvious effects on BDNF levels. Increased TrkB protein level was significantly reversed by roscovitine between 0.5 h and 6 h after CFA injection. Cdk5 and TrkB co-immunoprecipitation results suggested Cdk5 mediates the heat hyperalgesia induced by CFA injection by binding with TrkB, and the binding between Cdk5 and TrkB was markedly blocked by intrathecal adminstration of roscovitine.

Conclusion

Our data suggested that the BDNF-TrkB signaling pathway was involved in CFA-induced heat hyperalgesia mediated by Cdk5. Roscovitine reversed the heat hyperalgesia induced by peripheral injection of CFA by blocking BDNF/TrkB signaling pathway, suggesting that severing the close crosstalk between Cdk5 and the BDNF/TrkB signaling cascade may present a potential target for anti-inflammatory pain.

BDNF and synaptic plasticity, cognitive function, and dysfunction

Among all neurotrophins, brain-derived neurotrophic factor (BDNF) stands out for its high level of expression in the brain and its potent effects on synapses. It is now widely accepted that the main function of BDNF in the adult brain is to regulate synapses, with structural and functional effects ranging from short-term to long-lasting, on excitatory or inhibitory synapses, in many brain regions. The diverse effects of BDNF on brain synapses stem from its complex downstream signaling cascades, as well as the diametrically opposing effects of the pro- and mature form through distinct receptors, TrkB and p75(NTR). Many aspects of BDNF cell biology are regulated by neuronal activity. The synergistic interactions between neuronal activity and synaptic plasticity by BDNF make it an ideal and essential regulator of cellular processes that underlie cognition and other complex behaviors. Indeed, numerous studies firmly established that BDNF plays a critical role in hippocampal long-term potentiation (LTP), a long-term enhancement of synaptic efficacy thought to underlie learning and memory. Converging evidence now strongly suggest that deficits in BDNF signaling contribute to the pathogenesis of several major diseases and disorders such as Huntington's disease, Alzheimer's disease, and depression. Thus, manipulating BDNF pathways represents a viable treatment approach to a variety of neurological and psychiatric disorders.

Stress and trauma: BDNF control of dendritic-spine formation and regression

Chronic restraint stress leads to increases in brain derived neurotrophic factor (BDNF) mRNA and protein in some regions of the brain, e.g. the basal lateral amygdala (BLA) but decreases in other regions such as the CA3 region of the hippocampus and dendritic spine density increases or decreases in line with these changes in BDNF. Given the powerful influence that BDNF has on dendritic spine growth, these observations suggest that the fundamental reason for the direction and extent of changes in dendritic spine density in a particular region of the brain under stress is due to the changes in BDNF there. The most likely cause of these changes is provided by the stress initiated release of steroids, which readily enter neurons and alter gene expression, for example that of BDNF. Of particular interest is how glucocorticoids and mineralocorticoids tend to have opposite effects on BDNF gene expression offering the possibility that differences in the distribution of their receptors and of their downstream effects might provide a basis for the differential transcription of the BDNF genes. Alternatively, differences in the extent of methylation and acetylation in the epigenetic control of BDNF transcription are possible in different parts of the brain following stress. Although present evidence points to changes in BDNF transcription being the major causal agent for the changes in spine density in different parts of the brain following stress, steroids have significant effects on downstream pathways from the TrkB receptor once it is acted upon by BDNF, including those that modulate the density of dendritic spines. Finally, although glucocorticoids play a canonical role in determining BDNF modulation of dendritic spines, recent studies have shown a role for corticotrophin releasing factor (CRF) in this regard. There is considerable improvement in the extent of changes in spine size and density in rodents with forebrain specific knockout of CRF receptor 1 (CRFR1) even when the glucocorticoid pathways are left intact. It seems then that CRF does have a role to play in determining BDNF control of dendritic spines.

Coupling between GABA-A receptor and chloride transporter underlies ionic plasticity in cerebellar Purkinje neurons

Ionic plasticity, a form of synaptic plasticity unique to inhibitory neurotransmission, can be induced in cerebellar Purkinje neurons by brain-derived neurotrophic factor (BDNF). It is expressed as a decrease in synaptic strength of GABA-A transmission onto Purkinje neurons due to reduced transmembrane chloride gradient. By making whole-cell recordings, we found that the effect of BDNF is mediated by neuronal potassium and chloride transporter KCC2 because it is blocked by inhibitors of KCC2 or by raising the intracellular chloride concentration. Under these conditions in which KCC2 activity is reduced, BDNF augments evoked GABA-A currents suggesting a direct facilitatory effect of BDNF on GABA-A receptor. We also found that the effect of BDNF is highly localized at the GABA-A synapse and is secured by physical coupling between GABA-A receptor and KCC2, as revealed by coimmunoprecipitation studies. Based on these results, we hypothesize that the interaction between KCC2 and specific subunit of GABA-A receptor represents a fundamental mechanism rendering the rapid induction of ionic plasticity in individual or input-specific GABA synapses possible. Such a mechanism may be important for the function of Purkinje neurons that are known to express GABA-A receptors with different subunit compositions.