Cellular localization of TRPC3 channel in rat brain: preferential distribution to oligodendrocytes

GLP-1 modulated the firing activity of nigral dopaminergic neurons in both normal and parkinsonian mice

The spontaneous firing activity of nigral dopaminergic neurons is associated with some important roles including modulation of dopamine release, expression of tyrosine hydroxylase (TH), as well as neuronal survival. The decreased neuroactivity of nigral dopaminergic neurons has been revealed in Parkinson's disease. Central glucagon-like peptide-1 (GLP-1) functions as a neurotransmitter or neuromodulator to exert multiple brain functions. Although morphological studies revealed the expression of GLP-1 receptors (GLP-1Rs) in the substantia nigra pars compacta, the possible modulation of GLP-1 on spontaneous firing activity of nigral dopaminergic neurons is unknown. The present extracellular in vivo single unit recordings revealed that GLP-1R agonist exendin-4 significantly increased the spontaneous firing rate and decreased the firing regularity of partial nigral dopaminergic neurons of adult male C57BL/6 mice. Blockade of GLP-1Rs by exendin (9-39) decreased the firing rate of nigral dopaminergic neurons suggesting the involvement of endogenous GLP-1 in the modulation of firing activity. Furthermore, the PKA and the transient receptor potential canonical (TRPC) 4/5 channels are involved in activation of GLP-1Rs-induced excitatory effects of nigral dopaminergic neurons. Under parkinsonian state, both the exogenous and endogenous GLP-1 could still induce excitatory effects on the surviving nigral dopaminergic neurons. As the mild excitatory stimuli exert neuroprotective effects on nigral dopaminergic neurons, the present GLP-1-induced excitatory effects may partially contribute to its antiparkinsonian effects.

TRPV1 stimulation increased oxidative neurotoxicity and apoptosis in the glia cell membrane but not in the perinuclear area: An evidence of TRPV1 subtype

Glia are essential neurons of the immune system in the central nervous system. The effective mission of glia depends on their activation, release of cytokines, and oxidative cleaning of debris material from neuronal cells. Accumulating evidence indicates that microglia activation-induced oxidative stress via the activation Ca2+ permeable TRPV1 channel has an essential role in the pathophysiology of neurodegenerative diseases. However, there is scarce information on the cytosolic localization of TRPV1 and the induction of oxidative cytotoxicity in the glia. Hence, we investigated the interactions between cytosolic TRPV1 expression levels and oxidative neurotoxicity in the BV2, C8-D1A, N9 glia, and DBTRG glioblastoma cells. We observed TRPV1 expression in the perinuclear area but not in the cell membrane in the BV2, C8-D1A, and N9 cells. Hence, we observed no activation of TRPV1 on the increase of mitochondrial free reactive oxygen species (mROS) and apoptosis in the cells after the capsaicin stimulation. However, we observed TRPV1 channel expression in the positive control (DBTRG) cell membranes. Hence, the Ca2+ influx, TRPV1 current density, apoptosis, and mROS levels were increased in the DBTRG cells after the capsaicin stimulation, although their levels were diminished by the treatment of the TRPV1 blocker (capsazepine). In conclusion, the presence of TRPV1 in the cell membrane of DBTRG cells induced excessive generation of mROS and apoptosis actions, although the presence of TRPV1 in the perinuclear area did not cause the actions. It seems that there is a subtype of TRPV1 in the perinuclear area, and it is not activated by the capsaicin.

Distribution and Assembly of TRP Ion Channels

In the last several decades, a large family of ion channels have been identified and studied intensively as cellular sensors for diverse physical and/or chemical stimuli. Named transient receptor potential (TRP) channels, they play critical roles in various aspects of cellular physiology. A large number of human hereditary diseases are found to be linked to TRP channel mutations, and their dysregulations lead to acute or chronical health problems. As TRP channels are named and categorized mostly based on sequence homology rather than functional similarities, they exhibit substantial functional diversity. Rapid advances in TRP channel study have been made in recent years and reported in a vast body of literature; a summary of the latest advancements becomes necessary. This chapter offers an overview of current understandings of TRP channel distribution and subunit assembly.

Roles of Microglial Ion Channel in Neurodegenerative Diseases

As the average age and life expectancy increases, the incidence of both acute and chronic central nervous system (CNS) pathologies will increase. Understanding mechanisms underlying neuroinflammation as the common feature of any neurodegenerative pathology, we can exploit the pharmacology of cell specific ion channels to improve the outcome of many CNS diseases. As the main cellular player of neuroinflammation, microglia play a central role in this process. Although microglia are considered non-excitable cells, they express a variety of ion channels under both physiological and pathological conditions that seem to be involved in a plethora of cellular processes. Here, we discuss the impact of modulating microglia voltage-gated, potential transient receptor, chloride and proton channels on microglial proliferation, migration, and phagocytosis in neurodegenerative diseases.

Strategies for Neuroprotection in Multiple Sclerosis and the Role of Calcium

Calcium ions are vital for maintaining the physiological and biochemical processes inside cells. The central nervous system (CNS) is particularly dependent on calcium homeostasis and its dysregulation has been associated with several neurodegenerative disorders including Parkinson’s disease (PD), Alzheimer’s disease (AD) and Huntington’s disease (HD), as well as with multiple sclerosis (MS). Hence, the modulation of calcium influx into the cells and the targeting of calcium-mediated signaling pathways may present a promising therapeutic approach for these diseases. This review provides an overview on calcium channels in neurons and glial cells. Special emphasis is put on MS, a chronic autoimmune disease of the CNS. While the initial relapsing-remitting stage of MS can be treated effectively with immune modulatory and immunosuppressive drugs, the subsequent progressive stage has remained largely untreatable. Here we summarize several approaches that have been and are currently being tested for their neuroprotective capacities in MS and we discuss which role calcium could play in this regard.

2-Aminoethyldiphenyl Borinate: A Multitarget Compound with Potential as a Drug Precursor

BACKGROUND

Boron is considered a trace element that induces various effects in systems of the human body. However, each boron-containing compound exerts different effects.

OBJECTIVE

To review the effects of 2-Aminoethyldiphenyl borinate (2-APB), an organoboron compound, on the human body, but also, its effects in animal models of human disease.

METHODS

In this review, the information to showcase the expansion of these reported effects through interactions with several ion channels and other receptors has been reported. These effects are relevant in the biomedical and chemical fields due to the application of the reported data in developing therapeutic tools to modulate the functions of the immune, cardiovascular, gastrointestinal and nervous systems.

RESULTS

Accordingly, 2-APB acts as a modulator of adaptive and innate immunity, including the production of cytokines and the migration of leukocytes. Additionally, reports show that 2-APB exerts effects on neurons, smooth muscle cells and cardiomyocytes, and it provides a cytoprotective effect by the modulation and attenuation of reactive oxygen species.

CONCLUSION

The molecular pharmacology of 2-APB supports both its potential to act as a drug and the desirable inclusion of its moieties in new drug development. Research evaluating its efficacy in treating pain and specific maladies, such as immune, cardiovascular, gastrointestinal and neurodegenerative disorders, is scarce but interesting.

The role of TRP channels in white matter function and ischaemia

Transient receptor potential (TRP) proteins are a large family of tetrameric non-selective cation channels that are widely expressed in the grey and white matter of the CNS, and are increasingly considered as potential therapeutic targets in brain disorders. Here we briefly review the evidence for TRP channel expression in glial cells and their possible role in both glial cell physiology and stroke. Despite their contribution to important functions, our understanding of the roles of TRP channels in glia is still in its infancy. The evidence reviewed here indicates that further investigation is needed to determine whether TRP channel inhibition can decrease damage or increase repair in stroke and other diseases affecting the white matter.

Physiological and Pathophysiological Roles of Transient Receptor Potential Channels in Microglia-Related CNS Inflammatory Diseases

Central nervous system (CNS) inflammation is a potential therapeutic target for neurodegenerative diseases. In recent years, a number of studies have focused on the links between neurodegenerative diseases and CNS glial cells, especially microglia. Microglia are the main resident immune cells in the CNS and represent approximately 10-15% of all CNS cells. Microglia play an important role in maintaining brain homeostasis at rest by surveying the environment, and engulfing apoptotic cells and debris in the healthy brain. However, under certain pathological conditions, microglia can generate neurotoxic factors, such as pro-inflammatory cytokines and molecules like nitric oxide (NO), which lead to CNS inflammatory diseases. In this review, we discuss the evidence that regulation of microglial ion channels may modulate CNS inflammation and subsequent tissue damage in neurological disorders. In particular, we discuss the role of transient receptor potential (TRP) channels in microglia in both acute and chronic inflammatory conditions, and describe the physiological and pathophysiological roles of TRP channels in CNS inflammatory pathways. Additionally, we describe the benefits of stimulation/inhibition of TRP channels in animal models of microglia-related CNS inflammatory diseases.

TRPC3 is required for the survival, pluripotency and neural differentiation of mouse embryonic stem cells (mESCs)

Transient receptor potential canonical subfamily member 3 (TRPC3) is known to be important for neural development and the formation of neuronal networks. Here, we investigated the role of TRPC3 in undifferentiated mouse embryonic stem cells (mESCs) and during the differentiation of mESCs into neurons. CRISPR/Cas9-mediated knockout (KO) of TRPC3 induced apoptosis and the disruption of mitochondrial membrane potential both in undifferentiated mESCs and in those undergoing neural differentiation. In addition, TRPC3 KO impaired the pluripotency of mESCs. TRPC3 KO also dramatically repressed the neural differentiation of mESCs by inhibiting the expression of markers for neural progenitors, neurons, astrocytes and oligodendrocytes. Taken together, our new data demonstrate an important function of TRPC3 with regards to the survival, pluripotency and neural differentiation of mESCs.

Store-operated calcium entry is essential for glial calcium signalling in CNS white matter

‘Calcium signalling’ is the ubiquitous response of glial cells to multiple extracellular stimuli. The primary mechanism of glial calcium signalling is by release of calcium from intracellular stores of the endoplasmic reticulum (ER). Replenishment of ER Ca²⁺ stores relies on store-operated calcium entry (SOCE). However, despite the importance of calcium signalling in glial cells, little is known about their mechanisms of SOCE. Here, we investigated SOCE in glia of the mouse optic nerve, a typical CNS white matter tract that comprises bundles of myelinated axons and the oligodendrocytes and astrocytes that support them. Using quantitative RT-PCR, we identified Orai1 channels, both Stim1 and Stim2, and the transient receptor potential M3 channel (TRPM3) as the primary channels for SOCE in the optic nerve, and their expression in both astrocytes and oligodendrocytes was demonstrated by immunolabelling of optic nerve sections and cultures. The functional importance of SOCE was demonstrated by fluo-4 calcium imaging on isolated intact optic nerves and optic nerve cultures. Removal of extracellular calcium ([Ca²⁺]_o) resulted in a marked depletion of glial cytosolic calcium ([Ca²⁺]_i), which recovered rapidly on restoration of [Ca²⁺]_o via SOCE. 2-aminoethoxydiphenylborane (2APB) significantly decreased SOCE and severely attenuated ATP-mediated calcium signalling. The results provide evidence that Orai/Stim and TRPM3 are important components of the ‘calcium toolkit’ that underpins SOCE and the sustainability of calcium signalling in white matter glia.

TRPC Channels and Neuron Development, Plasticity, and Activities

In this chapter, we mainly focus on the functions of TRPC channels in brain development, including neural progenitor proliferation, neurogenesis, neuron survival, axon guidance, dendritic morphology, synaptogenesis, and neural plasticity. We also notice emerging advances in understanding the functions of TRPC channels in periphery, especially their functions in sensation and nociception in dorsal root ganglion (DRG). Because TRPC channels are expressed in all major types of glial cells, which account for at least half of total cells in the brain, TRPC channels may act as modulators for glial functions as well. The future challenges for studying these channels could be (1) the detailed protein structures of these channels, (2) their cell type-specific functions, (3) requirement for their specific blockers or activators, and (4) change in the channel conformation in the brain.

Electrophysiological properties of NG2(+) cells: Matching physiological studies with gene expression profiles

NG2(+) glial cells are a dynamic population of non-neuronal cells that give rise to myelinating oligodendrocytes in the central nervous system. These cells express numerous ion channels and neurotransmitter receptors, which endow them with a complex electrophysiological profile that is unique among glial cells. Despite extensive analysis of the electrophysiological properties of these cells, relatively little was known about the molecular identity of the channels and receptors that they express. The generation of new RNA-Seq datasets for NG2(+) cells has provided the means to explore how distinct genes contribute to the physiological properties of these progenitors. In this review, we systematically compare the results obtained through RNA-Seq transcriptional analysis of purified NG2(+) cells to previous physiological and molecular studies of these cells to define the complement of ion channels and neurotransmitter receptors expressed by NG2(+) cells in the mammalian brain and discuss the potential significance of the unique physiological properties of these cells. This article is part of a Special Issue entitled SI:NG2-glia(Invited only).

Brain transient receptor potential channels and stroke

Transient receptor potential (TRP) channels have been increasingly implicated in the pathological mechanisms of CNS disorders. TRP expression has been detected in neurons, astrocytes, oligodendrocytes, microglia, and ependymal cells as well as in the cerebral vascular endothelium and smooth muscle. In stroke, TRPC3/4/6, TRPM2/4/7, and TRPV1/3/4 channels have been found to participate in ischemia-induced cell death, whereas other TRP channels, in particular those expressed in nonneuronal cells, have been less well studied. This review summarizes the current knowledge on the expression and functions of the TRP channels in various cell types in the brain and our current understanding of TRP channels in stroke pathophysiology. In an aging society, the occurrence of stroke is expected to increase steadily, and there is an urgent requirement to improve the current stroke management strategy. Therefore, elucidating the roles of TRP channels in stroke could shed light on the development of novel therapeutic strategies and ultimately improve stroke outcome.

Epsilon toxin from Clostridium perfringens acts on oligodendrocytes without forming pores, and causes demyelination

Epsilon toxin (ET) is produced by Clostridium perfringens types B and D and causes severe neurological disorders in animals. ET has been observed binding to white matter, suggesting that it may target oligodendrocytes. In primary cultures containing oligodendrocytes and astrocytes, we found that ET (10(-9) M and 10(-7) M) binds to oligodendrocytes, but not to astrocytes. ET induces an increase in extracellular glutamate, and produces oscillations of intracellular Ca(2+) concentration in oligodendrocytes. These effects occurred without any change in the transmembrane resistance of oligodendrocytes, underlining that ET acts through a pore-independent mechanism. Pharmacological investigations revealed that the Ca(2+) oscillations are caused by the ET-induced rise in extracellular glutamate concentration. Indeed, the blockade of metabotropic glutamate receptors type 1 (mGluR1) prevented ET-induced Ca(2+) signals. Activation of the N-methyl-D-aspartate receptor (NMDA-R) is also involved, but to a lesser extent. Oligodendrocytes are responsible for myelinating neuronal axons. Using organotypic cultures of cerebellar slices, we found that ET induced the demyelination of Purkinje cell axons within 24 h. As this effect was suppressed by antagonizing mGluR1 and NMDA-R, demyelination is therefore caused by the initial ET-induced rise in extracellular glutamate concentration. This study reveals the novel possibility that ET can act on oligodendrocytes, thereby causing demyelination. Moreover, it suggests that for certain cell types such as oligodendrocytes, ET can act without forming pores, namely through the activation of an undefined receptor-mediated pathway.

Evidence That Erythropoietin Modulates Neuroinflammation through Differential Action on Neurons, Astrocytes, and Microglia

Neuroinflammation is a normal and healthy response to neuronal damage. However, excessive or chronic neuroinflammation exacerbates neurodegeneration after trauma and in progressive diseases such as Alzheimer’s, Parkinson’s, age-related macular degeneration, and glaucoma. Therefore, molecules that modulate neuroinflammation are candidates as neuroprotective agents. Erythropoietin (EPO) is a known neuroprotective agent that indirectly attenuates neuroinflammation, in part, by inhibiting neuronal apoptosis. In this review, we provide evidence that EPO also modulates neuroinflammation upstream of apoptosis by acting directly on glia. Further, the signaling induced by EPO may differ depending on cell type and context possibly as a result of activation of different receptors. While significant progress has been made in our understanding of EPO signaling, this review also identifies areas for future study in terms of the role of EPO in modulating neuroinflammation.

Expression and functional properties of TRPM2 channels in dopaminergic neurons of the substantia nigra of the rat

Transient receptor potential melastatin 2 (TRPM2) channels are sensitive to oxidative stress, and their activation can lead to cell death. Although these channels have been extensively studied in expression systems, their role in the brain, particularly in the substantia nigra pars compacta (SNc), remains unknown. In this study, we assessed the expression and functional properties of TRPM2 channels in rat dopaminergic SNc neurons, using acute brain slices. RT-PCR analysis revealed TRPM2 mRNA expression in the SNc region. Immunohistochemistry demonstrated expression of TRPM2 protein in tyrosine hydroxylase-positive neurons. Channel function was tested with whole cell patch-clamp recordings and calcium (fura-2) imaging. Intracellular application of ADP-ribose (50-400 μM) evoked a dose-dependent, desensitizing inward current and intracellular free calcium concentration ([Ca(2+)](i)) rise. These responses were strongly inhibited by the nonselective TRPM2 channel blockers clotrimazole and flufenamic acid. Exogenous application of H(2)O(2) (1-5 mM) evoked a rise in [Ca(2+)](i) and an outward current mainly due to activation of ATP-sensitive potassium (K(ATP)) channels. Inhibition of K(+) conductance with Cs(+) and tetraethylammonium unmasked an inward current. The inward current and/or [Ca(2+)](i) rise were partially blocked by clotrimazole and N-(p-amylcinnamoyl)anthranilic acid (ACA). The H(2)O(2)-induced [Ca(2+)](i) rise was abolished in "zero" extracellular Ca(2+) concentration and was enhanced at higher baseline [Ca(2+)](i), consistent with activation of TRPM2 channels in the cell membrane. These results provide evidence for the functional expression of TRPM2 channels in dopaminergic SNc neurons. Given the involvement of oxidative stress in degeneration of SNc neurons in Parkinson's disease, further studies are needed to determine the pathophysiological role of these channels in the disease process.

Modulation of canonical transient receptor potential channel 1 in the proliferation of oligodendrocyte precursor cells by the golli products of the myelin basic protein gene

Golli proteins, products of the myelin basic protein gene, function as a new type of modulator of intracellular Ca(2+) levels in oligodendrocyte progenitor cells (OPCs). Because of this, they affect a number of Ca(2+)-dependent functions, such as OPC migration and process extension. To examine further the Ca(2+) channels regulated by golli, we studied the store-operated Ca(2+) channels (SOCCs) in OPCs and acute brain slice preparations from golli knock-out and golli-overexpressing mice. Our results showed that pharmacologically induced Ca(2+) release from intracellular stores evoked a significant extracellular Ca(2+) entry after store depletion in OPCs. They also indicated that, under these pharmacological conditions, golli promoted activation of Ca(2+) influx by SOCCs in cultured OPCs as well as in tissue slices. The canonical transient receptor potential family of Ca(2+) channels (TRPCs) has been postulated to be SOCC subunits in oligodendrocytes. Using a small interfering RNA knockdown approach, we provided direct evidence that TRPC1 is involved in store-operated Ca(2+) influx in OPCs and that it is modulated by golli. Furthermore, our data indicated that golli is probably associated with TRPC1 at OPC processes. Additionally, we found that TRPC1 expression is essential for the effects of golli on OPC proliferation. In summary, our data indicate a key role for golli proteins in the regulation of TRPC-mediated Ca(2+) influx, a finding that has profound consequences for the regulation of multiple biological processes in OPCs. More important, we have shown that extracellular Ca(2+) uptake through TRPC1 is an essential component in the mechanism of OPC proliferation.

TRPM3 is expressed in sphingosine-responsive myelinating oligodendrocytes

Oligodendrocytes are the myelin-forming cells of the CNS and guarantee proper nerve conduction. Sphingosine, one major component of myelin, has recently been identified to activate TRPM3, a member of the melastatin-related subfamily of transient receptor potential (TRP) channels. TRPM3 has been demonstrated to be expressed in brain with unknown cellular distribution. Here, we show for the first time that TRPM3 is expressed in oligodendrocytes in vitro and in vivo. TRPM3 is present during oligodendrocyte differentiation. Immunohistochemistry of adult rat brain slices revealed staining of white matter areas, which co-localized with oligodendrocyte markers. Analysis of the developmental distribution revealed that, prior to myelination, TRPM3 channels are localized on neurons. On oligodendrocytes they are found after the onset of myelination. RT-PCR studies showed that the transcription of TRPM3 splice variants is also developmentally regulated in vitro. Ca(2+) imaging approaches revealed the presence of a sphingosine-induced Ca(2+) entry mechanism in oligodendrocytes - with a pharmacological profile similar to the profile published for heterologously expressed TRPM3. These findings indicate that TRPM3 participates as a Ca(2+)-permeable and sphingosine-activated channel in oligodendrocyte differentiation and CNS myelination.

Differential expression of canonical (classical) transient receptor potential channels in guinea pig enteric nervous system

The canonical transient receptor potential (TRPC) family of ion channels is implicated in many neuronal processes including calcium homeostasis, membrane excitability, synaptic transmission, and axon guidance. TRPC channels are postulated to be important in the functional neurobiology of the enteric nervous system (ENS); nevertheless, details for expression in the ENS are lacking. Reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemistry were used to study the expression and localization of TRPC channels. We found mRNA transcripts, protein on Western blots, and immunoreactivity (IR) for TRPC1/3/4/6 expressed in the small intestinal ENS of adult guinea pigs. TRPC1/3/4/6-IR was localized to distinct subpopulations of enteric neurons and was differentially distributed between the myenteric and submucosal divisions of the ENS. TRPC1-IR was widely distributed and localized to neurons with cholinergic, calretinin, and nitrergic neuronal immunochemical codes in the myenteric plexus. It was localized to both cholinergic and noncholinergic secretomotor neurons in the submucosal plexus. TRPC3-IR was found only in the submucosal plexus and was expressed exclusively by neuropeptide Y-IR neurons. TRPC4/6-IR was expressed in only a small population of myenteric neurons, but was abundantly expressed in the submucosal plexus. TRPC4/6-IR was coexpressed with both cholinergic and nitrergic neurochemical codes in the myenteric plexus. In the submucosal plexus, TRPC4/6-IR was expressed exclusively in noncholinergic secretomotor neurons. No TRPC1/3/4/6-IR was found in calbindin-IR neurons. TRPC3/4/6-IR was widely expressed along varicose nerve fibers and colocalized with synaptophysin-IR at putative neurotransmitter release sites. Our results suggest important roles for TRPC channels in ENS physiology and neuronal regulation of gut function.

Heterogeneous distribution of TRPC proteins in the embryonic cortex

The present study was initiated to gain some information about the tissue distribution of transient receptor potential proteins of C-type (TRPC), a family of voltage-independent cation channels, at the beginning of neurogenesis in the telencephalon of embryonic mice. The mRNAs of all known TRPCs (TRPC1-TRPC7) could be found in the cortex at E13. TRPC1, TRPC3 and TRPC5 were the main isoforms, whereas the mRNAs for TRPC2, TRPC4, TRPC6 and TRPC7 were less abundant. The distribution throughout the cortical wall of TRPC1, TRPC3 and TRPC6 was studied by means of immuno-histochemistry. The data collected pointed to a heterogeneous expression of the channels. Three groups were identified. The first one comprises TRPC1, specifically found in the preplate but only in some post-mitotic neurons. It was mainly observed in a subset of cells distinct from the Cajal-Retzius cells. The second group is composed of TRPC3. It was found in non-neuronal cells and also in dividing (5-bromo-2'-deoxyuridine-positive) cells, indicating that TRPC3 is present in precursor cells. The third group contains TRPC6 detected in neuronal and in dividing non-neuronal cells. Double immunostaining experiments showed that TRPC3-positive cells also express TRPC6. Collectively, this report highlights a specific TRPC expression pattern in the immature cortical wall.

TRPC6 channels promote dendritic growth via the CaMKIV-CREB pathway

The canonical transient receptor potential channels (TRPCs) are Ca(2+)-permeable nonselective cation channels with various physiological functions. Here, we report that TRPC6, a member of the TRPC family, promotes hippocampal neuron dendritic growth. The peak expression of TRPC6 in rat hippocampus was between postnatal day 7 and 14, a period known to be important for maximal dendritic growth. Overexpression of TRPC6 increased phosphorylation of Ca(2+)/calmodulin-dependent kinase IV (CaMKIV) and cAMP-response-element binding protein (CREB) and promoted dendritic growth in hippocampal cultures. Downregulation of TRPC6 by short hairpin RNA interference against TRPC6 suppressed phosphorylation of both CaMKIV and CREB and impaired dendritic growth. Expressing a dominant-negative form of CaMKIV or CREB blocked the TRPC6-induced dendritic growth. Furthermore, inhibition of Ca(2+) influx suppressed the TRPC6 effect on dendritic growth. Finally, in TRPC6 transgenic mice, the phosphorylation of CaMKIV and CREB was enhanced and the dendritic growth was also increased. In conclusion, TRPC6 promoted dendritic growth via the CaMKIV-CREB pathway. Our results thus revealed a novel role of TRPC6 during the development of the central nervous system (CNS).

Immunohistochemical localization of TRPC6 in the rat substantia nigra

Transient receptor potential channels (TRPC) are plasma membrane, nonselective cationic channels and have been proposed as candidates involved in the regulation of cellular Ca2+ influx [D.E. Clapham, L.W. Runnels, C., Strubing, The TRP ion channel family, Nat. Rev. Neurosci. 2 (2001) 387-396; A. Martorana, C. Giampa, Z. DeMarch, M.T. Viscomi, S. Patassini, G. Sancesario, G. Bernardi, F.R. Fusco, Distribution of TRPC1 receptors in dendrites of rat substantia nigra: a confocal and electron microscopy study, Eur. J. Neurosci. 24 (2006) 732-738]. Studies on regional localization patterns of TRPCs are necessary to provide helpful guidelines for correlating current types with particular channels. In this study, we examined the distribution of one particular member of TRPC superfamily, namely, TRPC6, in the substantia nigra of normal rat brain. Single and double label immunohistochemistry were employed to perform both light and confocal microscopy observations. Our single label studies showed that, in the substantia nigra, TRPC6 labeled the perikarya with a diffuse and intense immunoreaction product distributed throughout cell cytoplasm whereas only a light immunostaining was observed in the cell nuclei. No labeling of axon or terminals was observed, although TRPC6 was evenly distributed in the neuropil. Our dual label studies showed a TRPC6 immunoreactivity pattern that was localized into the proximal dendrites and axon hillock of the large dopaminergic neurons identified by TH immunoreaction. Furthermore, our double label immunofluorescence study for TRPC6 and mGluR1 showed a complete co-localization of the two markers in the substantia nigra. Moreover, TRPC6 did not co-localize with synaptophysin. Thus, our study shows the postsynaptic localization of TRPC6 and its association with mGluR1 in the midbrain dopamine neurons.

Immunohistochemical study on the distribution of canonical transient receptor potential channels in rat basal ganglia

In the present study, we examined the localizations of canonical transient receptor potential channels (TRPCs) in rat basal ganglia. The dot-like staining pattern of TRPC5 was observed through the globus pallidus (GP) and caudate-putamen. TRPC7 had a strikingly high level of expression in the neuropil in the GP. In the subthalamic nucleus, strong staining for TRPC5 was observed in the cell bodies, while moderate to high immunoreactivies for TRPC1, TRPC3, TRPC4 and TRPC7 were found in the cell bodies and surrounding neuropil. In the substantia nigra, immunoreactivities for TRPC3 and TRPC7 were prominent in the cell bodies and several processes in the pars compacta and pars reticulata. TRPC6 was expressed in the neuropil, not in the cell bodies. This study may provide useful data for the future investigations on the structural and functional properties of TRPCs.

TRP channels and pain

Since the molecular identification of the capsaicin receptor, now known as TRPV1, transient receptor potential (TRP) channels have occupied an important place in the understanding of sensory nerve function in the context of pain. Several TRP channels exhibit sensitivity to substances previously known to cause pain or pain-like sensations; these include cinnamaldehyde, menthol, gingerol, and icillin. Many TRP channels also exhibit significant sensitivity to increases or decreases in temperature. Some TRP channels are sensitized in vitro by the activation of other receptors such that these channels may be activated by processes, such as inflammation that result in pain. TRP channels are suggested to be involved in processes as diverse as sensory neuron activation events, neurotransmitter release and action in the spinal cord, and release of inflammatory mediators. These functions strongly suggest that specific and selective inhibition of TRP channel activity will be of use in alleviating pain.

Distribution of TRPC4 in developing and adult murine brain

The transient receptor potential (TRP) superfamily comprises of a group of non-selective cation channels that have been implicated in both receptor and store-operated channel functions. The family of classical TRPs (TRPCs) consists of seven members (TRPC1-7), with TRPC4 possibly playing a role in neuronal signaling. We have examined the distribution pattern of TRPC4 mRNA and protein in the developing and postnatal murine brain by using in situ hybridization, Western blotting, and immunocytochemistry. Expression of TRPC4 mRNA starts at embryonic day 14.5 (E14.5) in the developing septal area and cerebellar anlagen. At E16.5, prominent expression is additionally seen in the hippocampal formation and cortical plate. High densities of cells expressing TRPC4 mRNA occur in the adult olfactory bulb and hippocampus, whereas the cortex and septum display lower densities of cells positive for TRPC4 mRNA. Analysis of the adult hippocampal formation has revealed TRPC4 immunoreactivity in hippocampal areas CA1 to CA3 and in the dentate gyrus. Functions consistent with this spatially restricted pattern of expression remain to be revealed.

Distribution of TRPC1 receptors in dendrites of rat substantia nigra: a confocal and electron microscopy study

Transient receptor potential channels (TRPC) are plasma membrane, non-selective cationic channels and have been proposed as candidates involved in the regulation of cellular Ca2+ influx. The expression, at mRNA level, of several TRPCs has been demonstrated recently in dopaminergic neurons of the substantia nigra (SN). The aim of the present study was to characterize the expression of TRPC1, at a protein level, in the substantia nigra neurons and non-excitable cells of Wistar rats. Single-label immunohistochemistry and double-label immunofluorescence were used to study the expression of TRPC1 among substantia nigra dopamine neurons and cellular processes using antibodies against tyrosine hydroxylase (TH), substance P (SP), enkephalin, synaptophysin, vesicular glutamate transporter-2 (Vglut-2), microtubule associated protein-2 and metabotropic glutamate receptor 1 (mGluR1). Moreover, the ultrastructural localization of TRPC1 was investigated by means of electron microscopy. A set of dual label experiments was also performed to investigate the presence of TRPC1 among glial cells. Our results showed that TRPC1 is localized mainly in dendritic processes of dopamine neurons, whereas a relatively small percentage of neuronal somata display a light TRPC1 immunoreactivity. Such results were confirmed by our electron microscopy observations. Our study demonstrates, for the first time, a coexpression of TRPC1 and mGluR1 receptors in dendrites of the substantia nigra dopaminergic neurons. Such observation reinforces the concept of an involvement of TRPC1 in mGluR1-mediated excitatory inputs in rat dopamine neurons.

Cellular localization of TRPC5 in the substantia nigra of rat

Transient receptor potential channels (TRPC) are plasma membrane, non-selective cationic channels and have been proposed as candidates involved in the regulation of cellular Ca2+ influx. TRPC are involved in metabotropic glutamate receptor (mGluR)-mediated excitatory post-synaptic currents (EPSCs) in the dopaminergic neurons of the substantia nigra. We previously observed several subtypes of TRPC to be expressed at an mRNA level in the substantia nigra dopamine neurons. In particular, TRPC1 and TRPC5 are most frequently expressed in the substantia nigra. Our recent immunohistochemical findings showed that TRPC1 are mainly distributed in the dendrites of dopamine neurons. In the present study we have investigated, by means of immunohistochemistry and dual label immunofluorescence, the anatomical distribution of TRPC5 in the substantia nigra, and we have shown their preferential localization into the neuronal nuclei. Our findings suggest a role of TRPs in the calcium signaling system of the nucleus, although its physiological meaning needs further investigations.