Emergence and fragmentation of the alpha-band driven by neuronal network dynamics

Rhythmic neuronal network activity underlies brain oscillations. To investigate how connected neuronal networks contribute to the emergence of the α-band and to the regulation of Up and Down states, we study a model based on synaptic short-term depression-facilitation with afterhyperpolarization (AHP). We found that the α-band is generated by the network behavior near the attractor of the Up-state. Coupling inhibitory and excitatory networks by reciprocal connections leads to the emergence of a stable α-band during the Up states, as reflected in the spectrogram. To better characterize the emergence and stability of thalamocortical oscillations containing α and δ rhythms during anesthesia, we model the interaction of two excitatory networks with one inhibitory network, showing that this minimal topology underlies the generation of a persistent α-band in the neuronal voltage characterized by dominant Up over Down states. Finally, we show that the emergence of the α-band appears when external inputs are suppressed, while fragmentation occurs at small synaptic noise or with increasing inhibitory inputs. To conclude, α-oscillations could result from the synaptic dynamics of interacting excitatory neuronal networks with and without AHP, a principle that could apply to other rhythms.     

Calcium Channel α2δ1 Proteins Mediate Trigeminal Neuropathic Pain States Associated with Aberrant Excitatory Synaptogenesis

To investigate a potential mechanism underlying trigeminal nerve injury-induced orofacial hypersensitivity, we used a rat model of chronic constriction injury to the infraorbital nerve (CCI-ION) to study whether CCI-ION caused calcium channel α₂δ₁ (Ca_vα₂δ₁) protein dysregulation in trigeminal ganglia and associated spinal subnucleus caudalis and C1/C2 cervical dorsal spinal cord (Vc/C2). Furthermore, we studied whether this neuroplasticity contributed to spinal neuron sensitization and neuropathic pain states. CCI-ION caused orofacial hypersensitivity that correlated with Ca_vα₂δ₁ up-regulation in trigeminal ganglion neurons and Vc/C2. Blocking Ca_vα₂δ₁ with gabapentin, a ligand for the Ca_vα₂δ₁ proteins, or Ca_vα₂δ₁ antisense oligodeoxynucleotides led to a reversal of orofacial hypersensitivity, supporting an important role of Ca_vα₂δ₁ in orofacial pain processing. Importantly, increased Ca_vα₂δ₁ in Vc/C2 superficial dorsal horn was associated with increased excitatory synaptogenesis and increased frequency, but not the amplitude, of miniature excitatory postsynaptic currents in dorsal horn neurons that could be blocked by gabapentin. Thus, CCI-ION-induced Ca_vα₂δ₁ up-regulation may contribute to orofacial neuropathic pain states through abnormal excitatory synapse formation and enhanced presynaptic excitatory neurotransmitter release in Vc/C2.     

Desensitization of Gamma Aminobutyric Acid (GABA) Receptors in Muscle Fibers of the Crab Cancer borealis

Carcinus muscle fibers respond to γ-aminobutyric acid (GABA) with a conductance increase that subsides rather rapidly. In the larger fibers which have low input resistance the decrease may disappear within 2 min. The inhibition of the excitatory postsynaptic potentials (EPSP's) by GABA nevertheless persists as long as the drug is applied. The subsidence of the increased conductance indicates that the membrane of the inhibitory synapses has become desensitized to GABA. The persistence of inhibition of the EPSP's appears to be due to an action of the drug on the presynaptic terminals of the excitatory axons which reduces or blocks the secretory activity that releases the excitatory transmitter.     

Scaffold Protein X11α Interacts with Kalirin-7 in Dendrites and Recruits It to Golgi Outposts

Pyramidal neurons in the mammalian forebrain receive their synaptic inputs through their dendritic trees, and dendritic spines are the sites of most excitatory synapses. Dendritic spine structure is important for brain development and plasticity. Kalirin-7 is a guanine nucleotide-exchange factor for the small GTPase Rac1 and is a critical regulator of dendritic spine remodeling. The subcellular localization of kalirin-7 is thought to be important for regulating its function in neurons. A yeast two-hybrid screen has identified the adaptor protein X11α as an interacting partner of kalirin-7. Here, we show that kalirin-7 and X11α form a complex in the brain, and this interaction is mediated by the C terminus of kalirin-7. Kalirin-7 and X11α co-localize at excitatory synapses in cultured cortical neurons. Using time-lapse imaging of fluorescence recovery after photobleaching, we show that X11α is present in a mobile fraction of the postsynaptic density. X11α also localizes to Golgi outposts in dendrites, and its overexpression induces the removal of kalirin-7 from spines and accumulation of kalirin-7 in Golgi outposts. In addition, neurons overexpressing X11α displayed thinner spines. These data support a novel mechanism of regulation of kalirin-7 localization and function in dendrites, providing insight into signaling pathways underlying neuronal plasticity. Dissecting the molecular mechanisms of synaptic structural plasticity will improve our understanding of neuropsychiatric and neurodegenerative disorders, as kalirin-7 has been associated with schizophrenia and Alzheimer disease.     

ON THE MEASURE OF EXCITABILITY

Recent time-intensity data by Rushton (1932) on the sciatic nerve of the frog are shown to provide additional support to the writer''s suggestion (1932, a) that integrals of the equation See PDF for Equation where V is the applied voltage, p is the local excitatory process and K and k are constants adequately represent the just effective direct current stimuli when the threshold value of p is made a linear function of the voltage of the form h ± α V where h and α are constants. The measurement of excitability is discussed and it is shown that the criteria for "true" measurements are not likely to be found by the agreement of the data with canonical time-intensity functions as suggested by Lapicque (1931) but rather in the establishing of standard experimental conditions. These conditions may permit the use of chronaxie as a measure of excitability, but it seems more likely that the constant k of the above equation will have to be adopted. There is sufficient evidence to cast considerable doubt on the validity of any conclusions drawn from the existing measurements of chronaxie although those derived through a particular technique may be valid. The problem requires a thorough experimental investigation in terms of integrals of the above equation.     

Reduced GABAergic Inhibition in the Basolateral Amygdala and the Development of Anxiety-Like Behaviors after Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is a major public health concern affecting a large number of athletes and military personnel. Individuals suffering from a TBI risk developing anxiety disorders, yet the pathophysiological alterations that result in the development of anxiety disorders have not yet been identified. One region often damaged by a TBI is the basolateral amygdala (BLA); hyperactivity within the BLA is associated with increased expression of anxiety and fear, yet the functional alterations that lead to BLA hyperexcitability after TBI have not been identified. We assessed the functional alterations in inhibitory synaptic transmission in the BLA and one mechanism that modulates excitatory synaptic transmission, the α₇ containing nicotinic acetylcholine receptor (α₇-nAChR), after mTBI, to shed light on the mechanisms that contribute to increased anxiety-like behaviors. Seven and 30 days after a mild controlled cortical impact (CCI) injury, animals displayed significantly greater anxiety-like behavior. This was associated with a significant loss of GABAergic interneurons and significant reductions in the frequency and amplitude of spontaneous and miniature GABA_A-receptor mediated inhibitory postsynaptic currents (IPSCs). Decreases in the mIPSC amplitude were associated with reduced surface expression of α1, β2, and γ2 GABA_A receptor subunits. However, significant increases in the surface expression and current mediated by α₇-nAChR, were observed, signifying increases in the excitability of principal neurons within the BLA. These results suggest that mTBI causes not only a significant reduction in inhibition in the BLA, but also an increase in neuronal excitability, which may contribute to hyperexcitability and the development of anxiety disorders.     

Distribution and Function of Laminins in the Neuromuscular System of Developing, Adult, and Mutant Mice

Laminins, heterotrimers of α, β, and γ chains, are prominent constituents of basal laminae (BLs) throughout the body. Previous studies have shown that laminins affect both myogenesis and synaptogenesis in skeletal muscle. Here we have studied the distribution of the 10 known laminin chains in muscle and peripheral nerve, and assayed the ability of several heterotrimers to affect the outgrowth of motor axons. We show that cultured muscle cells express four different α chains (α1, α2, α4, and α5), and that developing muscles incorporate all four into BLs. The portion of the muscle's BL that occupies the synaptic cleft contains at least three α chains and two β chains, but each is regulated differently. Initially, the α2, α4, α5, and β1 chains are present both extrasynaptically and synaptically, whereas β2 is restricted to synaptic BL from its first appearance. As development proceeds, α2 remains broadly distributed, whereas α4 and α5 are lost from extrasynaptic BL and β1 from synaptic BL. In adults, α4 is restricted to primary synaptic clefts whereas α5 is present in both primary and secondary clefts. Thus, adult extrasynaptic BL is rich in laminin 2 (α2β1γ1), and synaptic BL contains laminins 4 (α2β2γ1), 9 (α4β2γ1), and 11 (α5β2γ1). Likewise, in cultured muscle cells, α2 and β1 are broadly distributed but α5 and β2 are concentrated at acetylcholine receptor–rich “hot spots,” even in the absence of nerves. The endoneurial and perineurial BLs of peripheral nerve also contain distinct laminin chains: α2, β1, γ1, and α4, α5, β2, γ1, respectively. Mutation of the laminin α2 or β2 genes in mice not only leads to loss of the respective chains in both nerve and muscle, but also to coordinate loss and compensatory upregulation of other chains. Notably, loss of β2 from synaptic BL in β2^−/− “knockout” mice is accompanied by loss of α5, and decreased levels of α2 in dystrophic α2^dy/dy mice are accompanied by compensatory retention of α4. Finally, we show that motor axons respond in distinct ways to different laminin heterotrimers: they grow freely between laminin 1 (α1β1γ1) and laminin 2, fail to cross from laminin 4 to laminin 1, and stop upon contacting laminin 11. The ability of laminin 11 to serve as a stop signal for growing axons explains, in part, axonal behaviors observed at developing and regenerating synapses in vivo.     

Mice Lacking α-Tubulin Acetyltransferase 1 Are Viable but Display α-Tubulin Acetylation Deficiency and Dentate Gyrus Distortion

α-Tubulin acetylation at Lys-40, located on the luminal side of microtubules, has been widely studied and used as a marker for stable microtubules in the cilia and other subcellular structures, but the functional consequences remain perplexing. Recent studies have shown that Mec-17 and its paralog are responsible for α-tubulin acetylation in Caenorhabditis elegans. There is one such protein known as Atat1 (α-tubulin acetyltransferase 1) per higher organism. Zebrafish Atat1 appears to govern embryo development, raising the intriguing possibility that Atat1 is also critical for development in mammals. In addition to Atat1, three other mammalian acetyltransferases, ARD1-NAT1, ELP3, and GCN5, have been shown to acetylate α-tubulin in vitro, so an important question is how these four enzymes contribute to the acetylation in vivo. We demonstrate here that Atat1 is a major α-tubulin acetyltransferase in mice. It is widely expressed in mouse embryos and tissues. Although Atat1-null animals display no overt phenotypes, α-tubulin acetylation is lost in sperm flagella and the dentate gyrus is slightly deformed. Furthermore, human ATAT1 colocalizes on bundled microtubules with doublecortin. These results thus suggest that mouse Atat1 may regulate advanced functions such as learning and memory, thereby shedding novel light on the physiological roles of α-tubulin acetylation in mammals.     

Membrane-Derived Phospholipids Control Synaptic Neurotransmission and Plasticity

Synaptic communication is a dynamic process that is key to the regulation of neuronal excitability and information processing in the brain. To date, however, the molecular signals controlling synaptic dynamics have been poorly understood. Membrane-derived bioactive phospholipids are potential candidates to control short-term tuning of synaptic signaling, a plastic event essential for information processing at both the cellular and neuronal network levels in the brain. Here, we showed that phospholipids affect excitatory and inhibitory neurotransmission by different degrees, loci, and mechanisms of action. Signaling triggered by lysophosphatidic acid (LPA) evoked rapid and reversible depression of excitatory and inhibitory postsynaptic currents. At excitatory synapses, LPA-induced depression depended on LPA₁/G_αi/o-protein/phospholipase C/myosin light chain kinase cascade at the presynaptic site. LPA increased myosin light chain phosphorylation, which is known to trigger actomyosin contraction, and reduced the number of synaptic vesicles docked to active zones in excitatory boutons. At inhibitory synapses, postsynaptic LPA signaling led to dephosphorylation, and internalization of the GABA_Aγ2 subunit through the LPA₁/G_α12/13-protein/RhoA/Rho kinase/calcineurin pathway. However, LPA-induced depression of GABAergic transmission was correlated with an endocytosis-independent reduction of GABA_A receptors, possibly by GABA_Aγ2 dephosphorylation and subsequent increased lateral diffusion. Furthermore, endogenous LPA signaling, mainly via LPA₁, mediated activity-dependent inhibitory depression in a model of experimental synaptic plasticity. Finally, LPA signaling, most likely restraining the excitatory drive incoming to motoneurons, regulated performance of motor output commands, a basic brain processing task. We propose that lysophospholipids serve as potential local messengers that tune synaptic strength to precedent activity of the neuron.     

Multi-dimensional modulations of α and γ cortical dynamics following mindfulness-based cognitive therapy in Major Depressive Disorder

To illuminate candidate neural working mechanisms of Mindfulness-Based Cognitive Therapy (MBCT) in the treatment of recurrent depressive disorder, parallel to the potential interplays between modulations in electro-cortical dynamics and depressive symptom severity and self-compassionate experience. Linear and nonlinear α and γ EEG oscillatory dynamics were examined concomitant to an affective Go/NoGo paradigm, pre-to-post MBCT or natural wait-list, in 51 recurrent depressive patients. Specific EEG variables investigated were; (1) induced event-related (de-) synchronisation (ERD/ERS), (2) evoked power, and (3) inter-/intra-hemispheric coherence. Secondary clinical measures included depressive severity and experiences of self-compassion. MBCT significantly downregulated α and γ power, reflecting increased cortical excitability. Enhanced α-desynchronisation/ERD was observed for negative material opposed to attenuated α-ERD towards positively valenced stimuli, suggesting activation of neural networks usually hypoactive in depression, related to positive emotion regulation. MBCT-related increase in left-intra-hemispheric α-coherence of the fronto-parietal circuit aligned with these synchronisation dynamics. Ameliorated depressive severity and increased self-compassionate experience pre-to-post MBCT correlated with α-ERD change. The multi-dimensional neural mechanisms of MBCT pertain to task-specific linear and non-linear neural synchronisation and connectivity network dynamics. We propose MBCT-related modulations in differing cortical oscillatory bands have discrete excitatory (enacting positive emotionality) and inhibitory (disengaging from negative material) effects, where mediation in the α and γ bands relates to the former.     

Contractile Activation in Frog Skeletal Muscle

Contractile activation was studied in frog single muscle fibers treated with tetrodotoxin to block action potentials. The membrane potential in a short segment of the fiber was controlled with a two-electrode voltage clamp, and the contractile response of superficial myofibrils in this segment was observed microscopically. The strength-duration relation for contractile activation was similar to that reported by Adrian, Chandler, and Hodgkin (1969); at 3.9°C, the contraction threshold was –44 mV for long depolarizing pulses (100-ms) and increased to +64 mV for 2-ms depolarizations. Hyperpolarizing postpulses shifted the threshold for 2-ms pulses to more positive values, and a similar, but smaller, effect was produced by hyperpolarizing prepulses. The decay of excitability following subthreshold pulses showed two apparently distinct components; at 3.9°C, excitability fell to 50% of its initial value within 4 ms, while the subsequent decline of excitability proceeded with a half-time of about 20 ms.     

Myelin Abnormalities in the Optic and Sciatic Nerves in Mice With GM1-Gangliosidosis

GM1-gangliosidosis is a glycosphingolipid lysosomal storage disease involving accumulation of GM1 and its asialo form (GA1) primarily in the brain. Thin-layer chromatography and X-ray diffraction were used to analyze the lipid content/composition and the myelin structure of the optic and sciatic nerves from 7- and 10-month old β-galactosidase (β-gal) +/? and β-gal −/− mice, a model of GM1gangliosidosis. Optic nerve weight was lower in the β-gal −/− mice than in unaffected β-gal +/? mice, but no difference was seen in sciatic nerve weight. The levels of GM1 and GA1 were significantly increased in both the optic nerve and sciatic nerve of the β-gal −/− mice. The content of myelin-enriched cerebrosides, sulfatides, and plasmalogen ethanolamines was significantly lower in optic nerve of β-gal −/− mice than in β-gal +/? mice; however, cholesteryl esters were enriched in the β-gal −/− mice. No major abnormalities in these lipids were detected in the sciatic nerve of the β-gal −/− mice. The abnormalities in GM1 and myelin lipids in optic nerve of β-gal −/− mice correlated with a reduction in the relative amount of myelin and periodicity in fresh nerve. By contrast, the relative amount of myelin and periodicity in the sciatic nerves from control and β-gal −/− mice were indistinguishable, suggesting minimal pathological involvement in sciatic nerve. Our results indicate that the greater neurochemical pathology observed in the optic nerve than in the sciatic nerve of β-gal −/− mice is likely due to the greater glycolipid storage in optic nerve.     

α-Synuclein and Its A30P Mutant Affect Actin Cytoskeletal Structure and Dynamics

The function of α-synuclein, a soluble protein abundant in the brain and concentrated at presynaptic terminals, is still undefined. Yet, α-synuclein overexpression and the expression of its A30P mutant are associated with familial Parkinson''s disease. Working in cell-free conditions, in two cell lines as well as in primary neurons we demonstrate that α-synuclein and its A30P mutant have different effects on actin polymerization. Wild-type α-synuclein binds actin, slows down its polymerization and accelerates its depolymerization, probably by monomer sequestration; A30P mutant α-synuclein increases the rate of actin polymerization and disrupts the cytoskeleton during reassembly of actin filaments. Consequently, in cells expressing mutant α-synuclein, cytoskeleton-dependent processes, such as cell migration, are inhibited, while exo- and endocytic traffic is altered. In hippocampal neurons from mice carrying a deletion of the α-synuclein gene, electroporation of wild-type α-synuclein increases actin instability during remodeling, with growth of lamellipodia-like structures and apparent cell enlargement, whereas A30P α-synuclein induces discrete actin-rich foci during cytoskeleton reassembly. In conclusion, α-synuclein appears to play a major role in actin cytoskeletal dynamics and various aspects of microfilament function. Actin cytoskeletal disruption induced by the A30P mutant might alter various cellular processes and thereby play a role in the pathogenesis of neurodegeneration.     

Assembly of a Ca2+-dependent BK channel signaling complex by binding to beta2 adrenergic receptor

Large-conductance voltage and Ca²⁺-activated potassium channels (BKCa) play a critical role in modulating contractile tone of smooth muscle, and neuronal processes. In most mammalian tissues, activation of β-adrenergic receptors and protein kinase A (PKA_c) increases BKCa channel activity, contributing to sympathetic nervous system/hormonal regulation of membrane excitability. Here we report the requirement of an association of the β2-adrenergic receptor (β2AR) with the pore forming α subunit of BKCa and an A-kinase-anchoring protein (AKAP79/150) for β2 agonist regulation. β2AR can simultaneously interact with both BKCa and L-type Ca²⁺ channels (Ca_v1.2) in vivo, which enables the assembly of a unique, highly localized signal transduction complex to mediate Ca²⁺- and phosphorylation-dependent modulation of BKCa current. Our findings reveal a novel function for G protein-coupled receptors as a scaffold to couple two families of ion channels into a physical and functional signaling complex to modulate β-adrenergic regulation of membrane excitability.     

LKB1 Mediates the Development of Conventional and Innate T Cells via AMP-Dependent Kinase Autonomous Pathways

The present study has examined the role of the serine/threonine kinase LKB1 in the survival and differentiation of CD4/8 double positive thymocytes. LKB1-null DPs can respond to signals from the mature α/β T-cell-antigen receptor and initiate positive selection. However, in the absence of LKB1, thymocytes fail to mature to conventional single positive cells causing severe lymphopenia in the peripheral lymphoid tissues. LKB1 thus appears to be dispensable for positive selection but important for the maturation of positively selected thymocytes. LKB1 also strikingly prevented the development of invariant Vα14 NKT cells and innate TCR αβ gut lymphocytes. Previous studies with gain of function mutants have suggested that the role of LKB1 in T cell development is mediated by its substrate the AMP-activated protein kinase (AMPK). The present study now analyses the impact of AMPK deletion in DP thymocytes and shows that the role of LKB1 during the development of both conventional and innate T cells is mediated by AMPK-independent pathways.     

Positions of β2 and β3 subunits in the large-conductance calcium- and voltage-activated BK potassium channel

Large-conductance voltage- and Ca²⁺-gated K⁺ channels are negative-feedback regulators of excitability in many cell types. They are complexes of α subunits and of one of four types of modulatory β subunits. These have intracellular N- and C-terminal tails and two transmembrane (TM) helices, TM1 and TM2, connected by an ∼100-residue extracellular loop. Based on endogenous disulfide formation between engineered cysteines (Cys), we found that in β2 and β3, as in β1 and β4, TM1 is closest to αS1 and αS2 and TM2 is closest to αS0. Mouse β3 (mβ3) has seven Cys in its loop, one of which is free, and this Cys readily forms disulfides with Cys substituted in the extracellular flanks of each of αS0–αS6. We identified by elimination mβ3-loop Cys152 as the only free Cys. We inferred the disulfide-bonding pattern of the other six Cys. Using directed proteolysis and fragment sizing, we determined this pattern first among the four loop Cys in β1. These are conserved in β2–β4, which have four additional Cys (eight in total), except that mβ3 has one fewer. In β1, disulfides form between Cys at aligned positions 1 and 8 and between Cys at aligned positions 5 and 6. In mβ3, the free Cys is at position 7; position 2 lacks a Cys present in all other β2–β4; and the disulfide pattern is 1–8, 3–4, and 5–6. Presumably, Cys 2 cross-links to Cys 7 in all other β2–β4. Cross-linking of mβ3 Cys152 to Cys substituted in the flanks of αS0–S5 attenuated the protection against iberiotoxin (IbTX); cross-linking of Cys152 to K296C in the αS6 flank and close to the pore enhanced protection against IbTX. In no case was N-type inactivation by the N-terminal tail of mβ3 perturbed. Although the mβ3 loop can move, its position with Cys152 near αK296, in which it blocks IbTX binding, is likely favored.     

Involvement of Peripheral Nerves in the Transgenic PLP-α-Syn Model of Multiple System Atrophy: Extending the Phenotype

Multiple system atrophy (MSA) is a fatal, rapidly progressive neurodegenerative disease with (oligodendro-)glial cytoplasmic α-synuclein (α-syn) inclusions (GCIs). Peripheral neuropathies have been reported in up to 40% of MSA patients, the cause remaining unclear. In a transgenic MSA mouse model featuring GCI-like inclusion pathology based on PLP-promoter driven overexpression of human α-syn in oligodendroglia motor and non-motor deficits are associated with MSA-like neurodegeneration. Since α-syn is also expressed in Schwann cells we aimed to investigate whether peripheral nerves are anatomically and functionally affected in the PLP-α-syn MSA mouse model.

Results

To this end, heat/cold as well as mechanical sensitivity tests were performed. Furthermore, in vivo and ex vivo nerve conduction and the G-ratios of the sciatic nerve were analyzed, and thermosensitive ion channel mRNA expression in dorsal root ganglia (DRG) was assessed. The presence of human α-syn in Schwann cells was associated with subtle behavioral impairments. The G-ratio of the sciatic nerve, the conduction velocity of myelinated and unmyelinated primary afferents and the expression of thermosensitive ion channels in the sensory neurons, however, were similar to wildtype mice.

Conclusion

Our results suggest that the PNS appears to be affected by Schwann cell α-syn deposits in the PLP-α-syn MSA mouse model. However, there was no consistent evidence for functional PNS perturbations resulting from such α-syn aggregates suggesting a more central cause of the observed behavioral abnormalities. Nonetheless, our results do not exclude a causal role of α-syn in the pathogenesis of MSA associated peripheral neuropathy.     

α-Actinin-2 Mediates Spine Morphology and Assembly of the Post-Synaptic Density in Hippocampal Neurons

Dendritic spines are micron-sized protrusions that constitute the primary post-synaptic sites of excitatory neurotransmission in the brain. Spines mature from a filopodia-like protrusion into a mushroom-shaped morphology with a post-synaptic density (PSD) at its tip. Modulation of the actin cytoskeleton drives these morphological changes as well as the spine dynamics that underlie learning and memory. Several PSD molecules respond to glutamate receptor activation and relay signals to the underlying actin cytoskeleton to regulate the structural changes in spine and PSD morphology. α-Actinin-2 is an actin filament cross-linker, which localizes to dendritic spines, enriched within the post-synaptic density, and implicated in actin organization. We show that loss of α-actinin-2 in rat hippocampal neurons creates an increased density of immature, filopodia-like protrusions that fail to mature into a mushroom-shaped spine during development. α-Actinin-2 knockdown also prevents the recruitment and stabilization of the PSD in the spine, resulting in failure of synapse formation, and an inability to structurally respond to chemical stimulation of the N-methyl-D-aspartate (NMDA)-type glutamate receptor. The Ca²⁺-insensitive EF-hand motif in α-actinin-2 is necessary for the molecule''s function in regulating spine morphology and PSD assembly, since exchanging it for the similar but Ca²⁺-sensitive domain from α-actinin-4, another α-actinin isoform, inhibits its function. Furthermore, when the Ca²⁺-insensitive domain from α-actinin-2 is inserted into α-actinin-4 and expressed in neurons, it creates mature spines. These observations support a model whereby α-actinin-2, partially through its Ca²⁺-insensitive EF-hand motif, nucleates PSD formation via F-actin organization and modulates spine maturation to mediate synaptogenesis.     

Neurosteroid 3α-Androstanediol Efficiently Counteracts Paclitaxel-Induced Peripheral Neuropathy and Painful Symptoms

Painful peripheral neuropathy belongs to major side-effects limiting cancer chemotherapy. Paclitaxel, widely used to treat several cancers, induces neurological symptoms including burning pain, allodynia, hyperalgesia and numbness. Therefore, identification of drugs that may effectively counteract paclitaxel-induced neuropathic symptoms is crucial. Here, we combined histopathological, neurochemical, behavioral and electrophysiological methods to investigate the natural neurosteroid 3α-androstanediol (3α-DIOL) ability to counteract paclitaxel-evoked peripheral nerve tissue damages and neurological symptoms. Prophylactic or corrective 3α-DIOL treatment (4 mg/kg/2days) prevented or suppressed PAC-evoked heat-thermal hyperalgesia, cold-allodynia and mechanical allodynia/hyperalgesia, by reversing to normal, decreased thermal and mechanical pain thresholds of PAC-treated rats. Electrophysiological studies demonstrated that 3α-DIOL restored control values of nerve conduction velocity and action potential peak amplitude significantly altered by PAC-treatment. 3α-DIOL also repaired PAC-induced nerve damages by restoring normal neurofilament-200 level in peripheral axons and control amount of 2’,3’-cyclic-nucleotide-3’-phosphodiesterase in myelin sheaths. Decreased density of intraepidermal nerve fibers evoked by PAC-therapy was also counteracted by 3α-DIOL treatment. More importantly, 3α-DIOL beneficial effects were not sedation-dependent but resulted from its neuroprotective ability, nerve tissue repairing capacity and long-term analgesic action. Altogether, our results showing that 3α-DIOL efficiently counteracted PAC-evoked painful symptoms, also offer interesting possibilities to develop neurosteroid-based strategies against chemotherapy-induced peripheral neuropathy. This article shows that the prophylactic or corrective treatment with 3α-androstanediol prevents or suppresses PAC-evoked painful symptoms and peripheral nerve dysfunctions in rats. The data suggest that 3α-androstanediol-based therapy may constitute an efficient strategy to explore in humans for the eradication of chemotherapy-induced peripheral neuropathy.