Showing papers in "Neurosignals in 2009"

Physiological roles for G protein-regulated adenylyl cyclase isoforms: insights from knockout and overexpression studies.

Abstract: Cyclic AMP is a universal second messenger, produced by a family of adenylyl cyclase (AC) enzymes. The last three decades have brought a wealth of new information about the regulation of cyclic AMP production by ACs. Nine hormone-sensitive, membrane-bound AC isoforms have been identified in addition to a tenth isoform that lacks membrane spans and more closely resembles the cyanobacterial AC enzymes. New model systems for purifying and characterizing the catalytic domains of AC have led to the crystal structure of these domains and the mapping of numerous interaction sites. However, big hurdles remain in unraveling the roles of individual AC isoforms and their regulation in physiological systems. In this review we explore the latest on AC knockout and overexpression studies to better understand the roles of G protein regulation of ACs in the brain, olfactory bulb, and heart.

Biological mechanism of antidepressant effect of omega-3 fatty acids: how does fish oil act as a 'mind-body interface'?

Abstract: The unsatisfactory results of monoamine-based antidepressant therapy and the high occurrence of somatic symptoms and physical illness in patients with depression imply that the serotonin hypothesis is

Functions and regulatory mechanisms of Gq-signaling pathways.

Abstract: Gq family members of heterotrimeric G protein activate beta isoforms of phospholipase C that hydrolyzes phosphatidylinositol phosphate to diacylglycerol and inositol trisphosphate, leading to the protein kinase C activation and intracellular Ca(2+) mobilization, respectively. To understand the functions and regulatory mechanisms of Gq-signaling pathways, we first introduce the Galphaq-interacting proteins, which function as the effectors and the modulators of Gq. Next, we describe the Pasteurella multocida toxin and YM-254890, which are useful tools to investigate Gq signaling as activator and inhibitor, respectively. Finally, we discuss the physiological function of Gq in developmental brain, especially in neural progenitor cells.

Regulation and Physiological Functions of G12/13-Mediated Signaling Pathways

Abstract: Accumulating data indicate that G12 subfamily (Gα12/13)-mediated signaling pathways play pivotal roles in a variety of physiological processes, while aberrant regulation of this pathway has been identified in various human diseases. It has been demonstrated that Gα12/13-mediated signals form networks with other signaling proteins at various levels, from cell surface receptors to transcription factors, to regulate cellular responses. Gα12/13 have slow rates of nucleotide exchange and GTP hydrolysis, and specifically target RhoGEFs containing an amino-terminal RGS homology domain (RH-RhoGEFs), which uniquely function both as a GAP and an effector for Gα12/13. In this review, we will focus on the mechanisms regulating the Gα12/13 signaling system, particularly the Gα12/13-RH-RhoGEF-Rho pathway, which can regulate a wide variety of cellular functions from migration to transformation.

Molecular mechanisms of go signaling.

Abstract: Go is the most abundant G protein in the central nervous system, where it comprises about 1% of membrane protein in mammalian brains. It functions to couple cell surface receptors to intercellular effectors, which is a critical process for cells to receive, interpret and respond to extracellular signals. Go protein belongs to the pertussis toxin-sensitive Gi/Go subfamily of G proteins. A number of G-protein-coupled receptors transmit stimuli to intercellular effectors through Go. Go regulates several cellular effectors, including ion channels, enzymes, and even small GTPases to modulate cellular function. This review summarizes some of the advances in Go research and proposes areas to be further addressed in exploring the functional role of Go.

Regulation of stem cell pluripotency and neural differentiation by lysophospholipids.

Abstract: Lysophospholipids are bioactive signalling molecules able to act through the binding of their specific G-protein-coupled receptors to exert pleiotropic effects on a wide range of cells. The most widely studied signalling lysophospholipids are lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P). LPA and S1P have been identified to have widespread developmental, physiological and pathological actions in the central nervous system and more recently have been shown to induce biological effects on various stem cell types. This review aims to summarise the current knowledge on LPA and S1P regulation of embryonic and neural stem cell biology.

Heterotrimeric G-Proteins Interact Directly with Cytoskeletal Components to Modify Microtubule-Dependent Cellular Processes

Abstract: A large percentage of current drugs target G-protein-coupled receptors, which couple to well-known signaling pathways involving cAMP or calcium G-proteins themselves may subserve a second messenger f

Structural Determinants Involved in the Formation and Activation of G Protein βγ Dimers

Abstract: Heterotrimeric G proteins, composed of an α, β and γ subunit, represent one of the most important and dynamic families of signaling proteins. As a testament to the significance of G protein signaling, the hundreds of seven-transmembrane-spanning receptors that interact with G proteins are estimated to occupy 1–2% of the human genome. This broad diversity of receptors is echoed in the number of potential heterotrimer combinations that can arise from the 23 α subunit, 7 β subunit and 12 γ subunit isoforms that have been identified. The potential for such vast complexity implies that the receptor G protein interface is the site of much regulation. The historical model for the activation of a G protein holds that activated receptor catalyzes the exchange of GDP for GTP on the α subunit, inducing a conformational change that substantially lowers the affinity of α for βγ. This decreased affinity enables dissociation of βγ from α and receptor. The free form of βγ is thought to activate effectors, until the hydrolysis of GTP by G α (aided by RGS proteins) allows the subunits to re-associate, effectively deactivating the G protein until another interaction with activated receptor.

Expression of p-Akt in sensory neurons and spinal cord after peripheral nerve injury.

Abstract: Akt has been implicated in pro-survival and anti-apoptotic activities in many cell types, including dorsal root ganglion (DRG) and spinal motor neurons. In this immunohistochemical study we have monitored phosphorylated Akt (p-Akt) levels in adult mouse DRGs and spinal cord following unilateral peripheral sciatic nerve transection (axotomy) or carrageenan-induced inflammation. In control animals around half of the lumbar DRG neuron profiles (NPs), mainly small and medium-sized ones, were p-Akt immunoreactive (IR), and of these around 50% expressed calcitonin gene-related peptide and/or isolectin IB4. Two weeks after axotomy, the number of p-Akt-positive NPs was only slightly reduced, but p-Akt immunofluorescence intensity was strongly increased. One third of the ipsilateral p-Akt-IR NPs was galanin positive, but virtually without colocalization with neuropeptide Y. Furthermore, p-Akt-like immunoreactivity significantly increased in intensity in the ipsilateral spinal dorsal horn after axotomy and expanded into deeper layers. Carrageenan-induced peripheral inflammation increased the number of p-Akt-IR NPs after 1 h. Both axotomy and inflammation caused a clear increase in nuclear p-Akt-like immunoreactivity in DRG neurons. Our findings support a role for Akt as a key signaling molecule in sensory neurons and spinal cord after peripheral injury.

The role of neurotrophins in the regulation of myelin development.

Abstract: Neurotrophins comprise a family of growth factors that are expressed in a variety of cell types, and which exert influences on a large range of cellular activities that are important for development and the maintenance of the nervous system, as well as in neurodegenerative and psychiatric disorders. More recently, neurotrophins have been implicated in influencing the dynamic and complex signals that occur between neurons and glial cells, including Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system that regulate myelination. Here we review the recent studies that identify neurotrophins as important regulators of both peripheral and central myelination, highlight some of the many questions that remain to be answered, and identify possibilities for further research.

Signals involved in neural differentiation of human embryonic stem cells.

Abstract: Neural differentiation from embryonic stem cells involves progressive stages of neural induction, expansion and maintenance of neural stem/progenitor cells, and differentiation to neurons and glia. Our understanding of the signals involved in each of these processes is primarily based on our knowledge of neural development during embryogenesis. This review will focus on the signalling pathways that have been identified to play a role in neural differentiation of human embryonic stem cells (hESCs), including their induction to neuroectoderm, maintenance and expansion of hESC-derived neurospheres, differentiation to neurons and specification to specific neuronal lineages. Understanding the signals involved in each of these stages is important for optimising methods to derive specific cell types for transplantation therapies, as well as for providing insight into the mechanisms of human neurogenesis.

PCTK proteins: the forgotten brain kinases?

Abstract: PCTAIRE kinases (PCTKs) are highly conserved serine/threonine kinases that are closely related to cyclin-dependent kinases. They are enriched in post-mitotic neurons of adult brains, suggesting they m

TAM Receptor Signalling and Demyelination

Abstract: The TAM family (Tyro3, Axl and Mer) of receptor protein tyrosine kinases play pivotal roles in a number of major cellular processes: cell survival and proliferation, immunomodulation and phagocytosis. These processes are central to both the initial development and pathological course of human multiple sclerosis. All three receptors and their ligands, Gas6 (growth arrest-specific gene 6) and protein S, are expressed in the central nervous system (CNS), including in oligodendrocytes, the myelin-producing cell of the CNS. Recent studies have shown that Gas6-dependent TAM receptor signalling is an important modulator of oligodendrocyte survival and microglial phenotype both in vitro and in vivo. Multiple lines of evidence allow us to hypothesise that, during a demyelinating challenge, dysfunctional TAM receptor signalling could lead to a 'vicious cycle' of cell death, reduced phagocytosis and deleterious immune hyper-activation. A current challenge in this field is to expand our understanding of TAM receptor signalling from rodent models of central demyelination to human disease.

Effects of Bone Morphogenic Proteins on Neural Precursor Cells and Regulation during Central Nervous System Injury

Abstract: Bone morphogenic proteins (BMPs) are well known for their influence on cell fate determination, proliferation and differentiation during early embryogenesis. Here, we review evidence for BMPs playing an additional, ongoing role in the proliferation and differentiation of neural precursor and progenitor cells in postnatal and adult central nervous system (CNS) and in CNS injury. The effects of BMPs on CNS cells have been studied using primary cultures of neural precursor and oligodendrocyte lineage cells. In addition, transgenic mice have been used to investigate in vivo effects of altering BMP pathway activation, and rodent models of CNS injury have been used to examine endogenous regulation of BMPs. These results have shown that BMPs promote production of astrocytes and inhibit production and maturation of oligodendroglia. The effects of BMPs on neurogenesis could be dependent on the origin of precursor cells or on the specifics of the microenvironment of the cell niche, as there are reports of inhibition and promotion of neurogenesis by BMPs. There is emerging evidence that BMPs are upregulated in several models of CNS injury; however, the effects of this regulation have not been well characterised. Understanding of the function of endogenous BMP regulation is important for determining how modulation of BMP signalling could improve repair following CNS injury.

Neonatal maternal separation increases brain-derived neurotrophic factor and tyrosine kinase receptor B expression in the descending pain modulatory system.

Abstract: Neonatal maternal separation (NMS) could trigger long-term changes in the central neuronal responses to nociceptive stimuli in rats. Stress-induced visceral hyperalgesia is closely associated with the dysfunction of descending pain modulatory systems. Brain-derived neurotrophic factor (BDNF) not only has an important role in long-term synaptic plasticity but also in facilitating descending pain. The present study aimed to investigate changes in the expression of BDNF and its receptor tyrosine kinase receptor B (TrkB) in the amygdala and the rostral ventromedial medulla (RVM) after NMS and colorectal distention (CRD) stimulation in rats. Male Wistar rat pups were subjected to 180 min of daily NMS or not handled for 13 consecutive days. Expression of BDNF and TrkB following NMS and CRD stimulation was determined using immunohistochemistry. The results revealed an increase in the expression of BDNF and TrkB in the amygdala after NMS. An interactive effect of NMS and CRD on the expression of TrkB, but not BDNF, was found in the RVM. Furthermore, a significant interactive effect of NMS and CRD on the colocalization coefficient of TrkB and phospho-extracellular signal-regulated kinase expression in both the amygdala and RVM were found. These data demonstrate that NMS increases BDNF and TrkB expression in the descending pain systems, which may contribute to the development of NMS-induced visceral hyperalgesia.

Diminished presynaptic GABA(B) receptor function in the neocortex of a genetic model of absence epilepsy.

Abstract: Changes in GABAB receptor subunit expression have been recently reported in the neocortex of epileptic WAG/Rij rats that are genetically prone to experience absence seizures. These alterations may lead to hyperexcitability by downregulating the function of presynaptic GABAB receptors in neocortical networks as suggested by a reduction in paired-pulse depression. Here, we tested further this hypothesis by analyzing the effects induced by the GABAB receptor agonist baclofen (0.1–10 μM) on the inhibitory events recorded in vitro from neocortical slices obtained from epileptic (>180 day-old) WAG/Rij and age-matched, non-epileptic control (NEC) rats. We found that higher doses of baclofen were required to depress pharmacologically isolated, stimulus-induced IPSPs generated by WAG/Rij neurons as compared to NEC. We also obtained similar evidence by comparing the effects of baclofen on the rate of occurrence of synchronous GABAergic events recorded by WAG/Rij and NEC neocortical slices treated with 4-aminopyridine + glutamatergic receptor antagonists. In conclusion, these data highlight a decreased function of presynaptic GABAB receptors in the WAG/Rij rat neocortex. We propose that this alteration may contribute to neocortical hyperexcitability and thus to absence seizures.

Nitric oxide as an upstream signal of p38 mediates hypoxia/reoxygenation-induced neuronal death.

Abstract: Nitric oxide (NO) and p38 have been shown to be involved in the ischemia/hypoxia-induced neuronal injury. In this study, we examined the activation patterns of mitogen-activated protein kinases and explored the relationship between NO and p38 in a model of hippocampal neuronal death induced by hypoxia/reoxygenation (H/R). p38 activity increased robustly during hypoxia and after reoxygenation, while the increase of c-Jun amino-terminal kinase and extracellular signal-related kinase activities showed mild tendency. Inhibition of p38 with SB203580 or SB202190 rescued neuronal death, whereas inhibition of extracellular signal-related kinases with PD98059 or c-Jun amino-terminal kinases with SP600125 offered no protection. p38 inhibitors also reduced neuronal death induced by the NO donor S-nitrosoglutathione. L-NAME, a nonspecific NO synthase inhibitor, blocked the p38 activation and rescued H/R-induced neuronal death. These results suggest that NO is an upstream signal of p38 that mediates the H/R-induced neuronal death.

Muscarinic Receptors in Psychiatric Disorders – Can We Mimic ‘Health’?

Abstract: The concept that acetylcholine is involved in the pathophysiologies of psychiatric disorders has existed since the 1950s. There is very strong evidence implicating a dysfunctional muscarinic system in

Antihypoxic effects of neuroglobin in hypoxia-preconditioned mice and SH-SY5Y cells.

Abstract: This work aims at investigating the neuroprotective effects of neuroglobin (Ngb) in vivo and in vitro. RT-PCR and Western blotting were used to examine Ngb mRNA and protein levels in the mouse cortex after acute and repeated exposure to hypoxia. The cDNAs of mouse Ngb were cloned and transfected into SH-SY5Y cells to examine Ngb function in vitro. Expression of Ngb and mRNA was upregulated in the cortex of mice preconditioned by repetitive exposure to hypoxia. Tolerance to hypoxia of Ngb-transformed SH-SY5Y cells was enhanced. These results suggest that Ngb might be involved in hypoxic preconditioning which protects neurons from hypoxic injury.

Novel Regulation of Adenylyl Cyclases by Direct Protein-Protein Interactions: Insights from Snapin and Ric8a

Abstract: Adenosine 3′,5′-cyclic mononucleotide (cAMP) is one of the most important second messengers which govern cellular signal transductions. Adenylyl cyclases (ACs), which are cAMP-synthesizing enzymes, ar

Differential and Synergistic Effect of Nerve Growth Factor and cAMP on the Regulation of Early Response Genes during Neuronal Differentiation

Abstract: Neurotrophin (NT)-driven differentiation is a process involving activation of multiple signalling events. Treatment of PC12 cells with the prototypic NT nerve growth factor (NGF) induces PC12 cell differentiation characterized by neurite outgrowth and expression of differentiation genes. Cyclic AMP (cAMP), one of the second messengers of NGF stimulation, has also been observed to induce neuronal differentiation in PC12 cells. Interestingly, co-treatment of NGF and dibutyryl cAMP (DBcAMP) exhibits a synergistic effect on neurite outgrowth in PC12 cells, but the mechanisms underlying this synergism remain unknown. In the current study, we compared the gene expression profiles of PC12 cells treated with NGF, DBcAMP or both for 12 h to identify differentially regulated genes during the early stage of differentiation. We found that the genes that were differentially regulated by NGF, DBcAMP or both include genes for acquiring neuronal phenotypes, cytoskeleton-binding proteins and cell cycle proteins. Importantly, we identified a subset of genes that was specifically regulated during co-treatment of NGF and cAMP, suggesting that the synergistic effect of NGF and DBcAMP on neurite outgrowth is possibly mediated through transcription regulation. Our observations provide novel insights on the signalling mechanisms underlying the regulation of neuronal differentiation by NGF and cAMP.

Conduction failures in rabbit saphenous nerve unmyelinated fibers.

Abstract: Recent experimental and theoretical data indicate that the functional capabilities of axons with specialized structures are much more diverse than traditionally thought. However, few observations were concerned with the main axons without arborization. In the present study, electrical stimulation of the saphenous nerve at different frequencies (2, 5, 10, 20 Hz) was used to test the role of activity-dependent effects on the pattern of action potentials that propagate along individual unmyelinated fibers (C fibers) within the trunk of the saphenous nerve in rabbits. Three basic types of C fiber responses to repetitive stimulation were observed: type-1 fibers showed an entrained response without conduction failure; type-2 fibers discharged with intermittent conduction failures; while only sporadic conduction failures happened in type 3. The failure modality in type-2 and type-3 fibers is closely related to the conductive distance as well as the frequency and duration of stimuli which lead to a critical level of conduction velocity slowing. A novel fluctuation in interspike intervals was always observed immediately before the occurrence of the failures, implying that the fluctuation of conduction velocity is correlated with imminent failures. Both the 4-aminopyridine-sensitive potassium current and hyperpolarization-activated cation current were recognized to be involved in the regulation of conduction failure patterns. The results confirmed, at least in part, the existence of conduction failures in the main axon of C fibers, suggesting that axonal operations may also be determinants for adaptation phenomenon and information processing in peripheral nervous system.

Current and Future Applications of Transcriptomics for Discovery in CNS Disease and Injury

Abstract: The central nervous system (CNS) displays heterogeneity at regional, cellular and subcellular levels, making analysis of transcriptomic events accompanying neural injury particularly challenging. Microarray technology provides methods for elucidating global changes in neural gene expression and discovery of signalling pathways within this complex biological network. The lack of suitable and sufficient human CNS tissue along with its inherent variability means that diverse animal models of both multiple sclerosis and neurotrauma are vital for examining the pathophysiological changes accompanying neural injury resulting from disease or trauma. Gene expression profiling of these models is providing valuable information about mechanisms of damage, repair and regeneration and candidate treatments. In vitro models of neural injury are also proving useful, and transcriptomics is enhancing our understanding of the properties of neural stem cells with a view to their therapeutic application in neural repair. Thoughtful experimental design and analysis of microarray experiments is crucial for extracting biological meaning from the vast amount of data produced. In this review we discuss the current and emerging application of transcriptomics for the study of neural function in health, disease and injury.

A hematopoietic perspective on the promiscuity and specificity of Galpha16 signaling.

Abstract: Galpha(16), a member of G(q) subfamily, is expressed exclusively in hematopoietic cells, and its expression is highly modulated during lineage differentiation. Although functional redundancy within G(q) subclass members has been observed in many established models, Galpha(16)possesses unique structural and biochemical properties not shared by other family members. Its broad receptor-coupling capacity and unique downstream binding partners and effectors allow the occurrence of both inositol lipid-dependent and -independent signals. Apart from its recognized biological functions in hematopoietic cell responses, the enlistment of complicated signaling pathways further signifies the importance of Galpha(16)in signal integration. This review aims to provide an updated appreciation and rational discussion of Galpha(16) signaling with regard to its promiscuity and specificity.

Cerebellar fastigial nuclear inputs and peripheral feeding signals converge on neurons in the dorsomedial hypothalamic nucleus.

Abstract: Previous studies have indicated that neurons in the dorsomedial hypothalamic nucleus (DMN) receive feeding-related signals from the gastric vagal nerves, glycemia as well as leptin. On the other hand, it is intriguing that the cerebellum participates in regulating nonsomatic visceral activities including food intake via the direct cerebellohypothalamic projections. The present study was designed to examine, by using extracellular recordings in vivo in rats, whether the cerebellar fastigial nucleus (FN) could reach and converge with the feeding-associated gastric vagal, glycemia and leptin signals onto single DMN neurons. Of the 200 DMN neurons recorded, 104 (52%) responded to the cerebellar FN stimulation, in which 95 (91.3%) were also responsive to the gastric vagal stimulation, suggesting a convergence of cerebellar FN and gastric vagal inputs on the DMN neurons. Moreover, a summation of responses was observed (n = 10) when the cerebellar FN and gastric vagal nerve were simultaneously stimulated. Among the 18 DMN neurons receiving convergent inputs from the cerebellar FN and gastric vagal nerves, 16 (88.9%) cells also responded to the systemic administrations of glucose and leptin. These results demonstrated that the cerebellar FN-afferent inputs, together with the feeding signals from the gastric vagal nerves, blood glucose as well as leptin, converge onto single DMN neurons, suggesting that a somatic-visceral integration related to the feeding may occur in the DMN and the cerebellum may actively participate in the feeding regulation through the cerebellar FN-DMN projections.

Dopaminergic Modulation of Afferent Synaptic Transmission in the Semicircular Canals of Frogs

Abstract: Using multiunit recording of action potentials from the whole nerve with the aid of external perfusion, we investigated the effects of dopamine (DOP) agonists that are involved in modulatory actions o

Electrophysiological Effects of Neurotensin on Globus Pallidus Neurons of 6-Hydroxydopamine-Lesioned Rats

Abstract: The globus pallidus is a nucleus in the indirect pathway of the basal ganglia circuits. Neurotensin has been reported to play an important role in the central nervous system. Functional study revealed