Analysis of the mechanism of Sophorae Flavescentis Radix in the treatment of intractable itching based on network pharmacology and molecular docking

OBJECTIVE

Sophorae Flavescentis Radix (Kuh-seng, SFR), a Traditional Chinese Medicine (TCM), is widely used alone or within a TCM formula to treat pruritus, especially histamine-independent intractable itching. In the previous study, potential antipruritic active components of the SFR were screened based on cell membrane immobilized chromatography (CMIC), revealing oxymatrine (OMT) as an antipruritic agent. However, the low oral bioavailability (OB) of OMT cannot explain the antipruritic effect of SFR when administered orally in clinic. In this study, we investigated the antipruritic effects and underlying mechanisms of orally administered SFR.

MATERIALS AND METHODS

A network pharmacology and molecular docking were employed to screen the active components of SFR and predict their binding to disease-related target proteins, while the potential mechanisms were explored with Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. The binding energy between components and target proteins was calculated by molecular docking.

RESULTS

The SFR-components-targets-intractable itching Protein-Protein Interactions (PPI) network was established, and 22 active components and 42 targets were screened. The GO enrichment analysis showed that the key target genes of SFR were related to nuclear receptors, transcription factors, and steroid hormone receptors. The results of the KEGG enrichment pathway analysis include Hepatitis B, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor resistance, advanced glycation end product (AGE)-receptor for AGE (RAGE) signaling pathway in diabetic complications, etc. Molecular docking showed that three key target proteins in the network, the vascular endothelial growth factor A (VEGFA), epidermal growth factor receptor (EGFR) and caspase-3 (CASP3), have higher binding activities with inermine, phaseolin and kushenol O, respectively; the binding energy of each pair is stronger than that of the target protein-corresponding inhibitors.

CONCLUSIONS

The complexity of the SFR-components-targets-intractable itching network demonstrated the holistic treatment effect of SFR on intractable itching. The partial coherence between results screened by CMIC in the previous study and network pharmacology demonstrated the potential of network pharmacology in active component screening. Inermine screened from both CMIC and network pharmacology is a VEGFA inhibitor, which possibly accounts for the antipruritic effect of orally administered SFR.

Neuroanatomical and morphometric study of S100β positive astrocytes in the entorhinal cortex during ageing in the 3xTg-Alzehimer's disease mouse model

Astrocytes contribute to the progression of neurodegenerative diseases, including Alzheimer's disease (AD). Here, we report the neuroanatomical and morphometric analysis of astrocytes in the entorhinal cortex (EC) of the aged wild type (WT) and triple transgenic (3xTg-AD) mouse model of AD. Using 3D confocal microscopy, we determined the surface area and volume of positive astrocytic profiles in male mice (WT and 3xTg-AD) from 1 to 18 months of age. We showed that S100β-positive astrocytes were equally distributed throughout the entire EC in both animal types and showed no changes in Nv (number of cells/mm3) nor in their distribution at the different ages studied. These positive astrocytes, demonstrated an age-dependent gradual increase in their surface area and in their volume starting at 3 months of age, in both WT and 3xTg-AD mice. This last group demonstrated a large increase in both surface area and volume at 18 months of age when the burden of pathological hallmarks of AD is present (69.74% to 76.73% in the surface area and the volume, for WT and 3xTg-AD mice respectively). We observed that these changes were due to the enlargement of the cell processes and to less extend the somata. In fact, the volume of the cell body was increased by 35.82% in 18-month-old 3xTg-AD compared to WT. On the other hand, the increase on the astrocytic processes were detected as soon as 9 months of age where we found an increase of surface area and volume (36.56% and 43.73%, respectively) sustained till 18 month of age (93.6% and 113.78%, respectively) when compared age-matched non-Tg mice. Moreover, we demonstrated that these hypertrophic S100β-positive astrocytes were mainly associated with Aβ plaques. Our results show a severe atrophy in GFAP cytoskeleton in all cognitive areas; whilst within the EC astrocytes independent to this atrophy show no changes in GS and S100β; which can play a key role in the memory impairment.

Astrocytes and major depression: The purinergic avenue

Major depressive disorder (MDD) is one of the most prevalent psychiatric illnesses worldwide which impairs the social functioning of the afflicted patients. Astrocytes promote homeostasis of the CNS and provide defense against various types of harmful influences. Increasing evidence suggests that the number, morphology and function of astrocytes are deteriorated in the depressed brain and the malfunction of the astrocytic purinergic system appears to participate in the pathophysiology of MDD. Adenosine 5'-triphosphate (ATP) released from astrocytes modulates depressive-like behavior in animal models and probably also clinical depression in patients. Astrocytes possess purinergic receptors, such as adenosine A_2A receptors (Rs), and P2X7, P2Y₁, and P2Y₁₁Rs, which mediate neuroinflammation, neuro(glio)transmission, and synaptic plasticity in depression-relevant areas of the brain (e.g. medial prefrontal cortex, hippocampus, amygdala nuclei). By contrast, astrocytic A₁Rs are neuroprotective and immunosuppressive. In the present review, we shall discuss the release of purines from astrocytes, and the expression/function of astrocytic purinergic receptors. Subsequently, we shall review in more detail novel evidence indicating that the dysregulation of astrocytic purinergic signaling actively contributes to the pathophysiology of depression and shall discuss possible therapeutic options based on knowledge recently acquired in this field.

Connexins as therapeutic targets in neurological and neuropsychiatric disorders

Astrocytes represent the reticular part of the central nervous system; gap junctions formed by connexins Cx43, Cx30- and Cx26 provide for homocellular astrocyte-astrocyte coupling, whereas connexins Cx30, Cx32, Cx43, and Cx47 connect astrocytes and oligodendrocytes. Astroglial networks are anatomically and functionally segregated being homologous to neuronal ensembles. Connexons, gap junctions and hemichannels (unpaired connexons) are affected in various neuropathologies from neuropsychiatric to neurodegenerative diseases. Manipulation of astrocytic connexins modulates the size and outreach of astroglial syncytia thus affecting astroglial homeostatic support. Modulation of astrocytic connexin significantly modifies pharmacological profile of many CNS drugs, which represents an innovative therapeutic approach for CNS disorders; this approach is now actively tested in pre-clinical and clinical studies. Wide combination of connexin modulators with CNS drugs open new promising perspectives for fundamental studies and therapeutic strategies.

Anti-Atherosclerosis Effect of Angong Niuhuang Pill via Regulating Th17/Treg Immune Balance and Inhibiting Chronic Inflammatory on ApoE-/- Mice Model of Early and Mid-Term Atherosclerosis

Angong Niuhuang Pill (ANP) is a well-known patented Chinese medicine which is used for hundreds of years for treating the central nervous system diseases. Atherosclerosis is a poly-aetiological chronic inflammatory vascular disease. Preventing inflammation is fundamental for treating atherosclerosis in early stages. In this study, we investigated the protective effects and possible mechanisms of ANP action on a high-fat diet induced early and mid-term atherosclerosis ApoE^-/- mice. The effects of ANP were compared with accepted drug simvastatin. Twelve male C57BL/6J mice were used as the control group, and 60 male ApoE^-/- mice were randomly divided into five groups: Model group, Simvastatin group, Low-, Medium-, and High-dose ANP group these groups received, respectively, saline, simvastatin (3.0mg/kg), low-dose ANP (0.25 g/kg), medium-dose ANP (0.50 g/kg), and high-dose ANP (1.0 g/kg), once every other day for 10 weeks. After administration, serum biochemical indices were detected by the automatic biochemical analyzer, the concentrations of IL-6 and IL-10 in the serum were assayed by ELISA, expression levels of IL-1β, TNF-α, MMP-2, MMP-9, CCL2, and its receptor CCR2 in the full-length aorta, and expression levels of transcription factors Foxp3, RORγt in the spleen were assayed via western blotting and RT-qPCR. Flow cytometry was used to analyze Th17 cells and Treg cells. Pathological and histological analysis was completed on aortic root. ANP decreased LDL/HDL ratio, concentrations of IL-6 while increased IL-10 in serum. Moreover, ANP down-regulated the expression levels of IL-1β, TNF-α, MMP-2, MMP-9, CCL2, and CCR2 receptor in the full-length aorta. In addition, ANP decreased Th17 cells and expression levels of transcription factor RORγt, increased Treg cells and expression levels of transcription factor Foxp3. ANP decreased content of collagen fibers and infiltration of inflammatory cells in the aortic root. In conclusion, we demonstrated that ANP has anti-atherosclerosis effects on a high-fat diet induced ApoE^-/- mice early and mid-term AS model via regulating Th17/Treg balance, inhibiting chronic inflammation, reducing plaque collagen fibers, and reducing inflammatory cells infiltration, to exert its multi-channel multi-target anti-early and mid-term AS effects.

Astroglial vesicular network: evolutionary trends, physiology and pathophysiology

Intracellular organelles, including secretory vesicles, emerged when eukaryotic cells evolved some 3 billion years ago. The primordial organelles that evolved in Archaea were similar to endolysosomes, which developed, arguably, for specific metabolic tasks, including uptake, metabolic processing, storage and disposal of molecules. In comparison with prokaryotes, cell volume of eukaryotes increased by several orders of magnitude and vesicle traffic emerged to allow for communication between distant intracellular locations. Lysosomes, first described in 1955, a prominent intermediate of endo- and exocytotic pathways, operate virtually in all eukaryotic cells including astroglia, the most heterogeneous type of homeostatic glia in the central nervous system. Astrocytes support neuronal network activity in particular through elaborated secretion, based on a complex intracellular vesicle network dynamics. Deranged homeostasis underlies disease and astroglial vesicle traffic contributes to the pathophysiology of neurodegenerative (Alzheimer's disease, Huntington's disease), neurodevelopmental diseases (intellectual deficiency, Rett's disease) and neuroinfectious (Zika virus) disorders. This review addresses astroglial cell-autonomous vesicular traffic network, as well as its into primary and secondary vesicular network defects in diseases, and considers this network as a target for developing new therapies for neurological conditions.

Ammonium increases Ca(2+) signalling and upregulates expression of Cav1.2 gene in astrocytes in primary cultures and in the in vivo brain

AIM

The primary aim of this study was to identify the effects of hyperammonaemia on functional expression of Cav1.2 L-type Ca(2+) channels in astroglia.

METHODS

Primary cultures of mouse astrocytes were used to study effects of chronic treatment (1-5 days) with ammonium chloride, at 1, 3 and 5 mm on depolarization-induced increases in free cytosolic Ca(2+) concentration ([Ca(2+)]i , measured with Fura-2 based microfluorimetry) in control conditions and following treatment with the L-type Ca(2+) channel inhibitor, nifedipine, or with ryanodine receptor inhibitor, ryanodine. Expression of Cav1.2 mRNA was identified with RT-PCR, whereas protein content was determined by Western blotting. Sustained hyperammonaemia in vivo was induced by daily injections of urease (33 units kg body weight(-1), i.p.) for 3 days.

RESULTS

Depolarization-induced [Ca(2+)]i transients sensitive to nifedipine (peak of the response) and to ryanodine (plateau phase) were significantly increased in astrocytes chronically exposed to ammonium. The ammonium-induced increase in Ca(2+) influx in astrocytes resulted from an upregulation of Cav1.2 channel's expression detected at mRNA and protein levels. Increase in Cav1.2 expression was prevented by ouabain antagonist canrenone. Similar upregulation of Cav1.2 gene expression was found in the brains of adult mice subjected to intraperitoneal injection of urease. In transgenic mice tagged with an astrocyte-specific or neurone-specific markers and treated with intraperitoneal injections of urease, the fluorescence-activated cell sorting of neurones and astrocytes demonstrated that Cav1.2 mRNA expression was upregulated in astrocytes, but not in neurones.

CONCLUSIONS

Ammonium-induced deregulation of astroglial Ca(2+) signalling, is, in part, associated with upregulation of Cav1.2 L-type calcium channels.

Astrocytic vesicles and gliotransmitters: Slowness of vesicular release and synaptobrevin2-laden vesicle nanoarchitecture

Neurotransmitters released at synapses activate neighboring astrocytes, which in turn, modulate neuronal activity by the release of diverse neuroactive substances that include classical neurotransmitters such as glutamate, GABA or ATP. Neuroactive substances are released from astrocytes through several distinct molecular mechanisms, for example, by diffusion through membrane channels, by translocation via plasmalemmal transporters or by vesicular exocytosis. Vesicular release regulated by a stimulus-mediated increase in cytosolic calcium involves soluble N-ethyl maleimide-sensitive fusion protein attachment protein receptor (SNARE)-dependent merger of the vesicle membrane with the plasmalemma. Up to 25 molecules of synaptobrevin 2 (Sb2), a SNARE complex protein, reside at a single astroglial vesicle; an individual neuronal, i.e. synaptic, vesicle contains ∼70 Sb2 molecules. It is proposed that this paucity of Sb2 molecules in astrocytic vesicles may determine the slow secretion. In the present essay we shall overview multiple aspects of vesicular architecture and types of vesicles based on their cargo and dynamics in astroglial cells.

Altered expression of Alzheimer's disease-related genes in the cerebellum of autistic patients: a model for disrupted brain connectome and therapy

Autism and Alzheimer's disease (AD) are, respectively, neurodevelopmental and degenerative diseases with an increasing epidemiological burden. The AD-associated amyloid-β precursor protein-α has been shown to be elevated in severe autism, leading to the 'anabolic hypothesis' of its etiology. Here we performed a focused microarray analysis of genes belonging to NOTCH and WNT signaling cascades, as well as genes related to AD and apoptosis pathways in cerebellar samples from autistic individuals, to provide further evidence for pathological relevance of these cascades for autism. By using the limma package from R and false discovery rate, we demonstrated that 31% (116 out of 374) of the genes belonging to these pathways displayed significant changes in expression (corrected P-values <0.05), with mitochondria-related genes being the most downregulated. We also found upregulation of GRIN1, the channel-forming subunit of NMDA glutamate receptors, and MAP3K1, known activator of the JNK and ERK pathways with anti-apoptotic effect. Expression of PSEN2 (presinilin 2) and APBB1 (or F65) were significantly lower when compared with control samples. Based on these results, we propose a model of NMDA glutamate receptor-mediated ERK activation of α-secretase activity and mitochondrial adaptation to apoptosis that may explain the early brain overgrowth and disruption of synaptic plasticity and connectome in autism. Finally, systems pharmacology analyses of the model that integrates all these genes together (NOWADA) highlighted magnesium (Mg(2+)) and rapamycin as most efficient drugs to target this network model in silico. Their potential therapeutic application, in the context of autism, is therefore discussed.

Differentiation of adipose-derived stem cells into Schwann cell phenotype induces expression of P2X receptors that control cell death

Schwann cells (SCs) are fundamental for development, myelination and regeneration in the peripheral nervous system. Slow growth rate and difficulties in harvesting limit SC applications in regenerative medicine. Several molecules, including receptors for neurosteroids and neurotransmitters, have been suggested to be implicated in regulating physiology and regenerative potential of SCs. Adipose-derived stem cells (ASCs) can be differentiated into SC-like phenotype (dASC) sharing morphological and functional properties with SC, thus representing a valid SC alternative. We have previously shown that dASC express γ-aminobutyric-acid receptors, which modulate their proliferation and neurotrophic potential, although little is known about the role of other neurotransmitters in ASC. In this study, we investigated the expression of purinergic receptors in dASC. Using reverse transriptase (RT)-PCR, western blot analyses and immunocytochemistry, we have demonstrated that ASCs express P2X3, P2X4 and P2X7 purinoceptors. Differentiation of ASCs towards glial phenotype was accompanied by upregulation of P2X4 and P2X7 receptors. Using Ca(2+)-imaging techniques, we have shown that stimulation of purinoceptors with adenosine 5'-triphosphate (ATP) triggers intracellular Ca(2+) signals, indicating functional activity of these receptors. Whole-cell voltage clamp recordings showed that ATP and BzATP induced ion currents that can be fully inhibited with specific P2X7 antagonists. Finally, using cytotoxicity assays we have shown that the increase of intracellular Ca(2+) leads to dASC death, an effect that can be prevented using a specific P2X7 antagonist. Altogether, these results show, for the first time, the presence of functional P2X7 receptors in dASC and their link with critical physiological processes such as cell death and survival. The presence of these novel pharmacological targets in dASC might open new opportunities for the management of cell survival and neurotrophic potential in tissue engineering approaches using dASC for nerve repair.

Increased densities of resting and activated microglia in the dentate gyrus follow senile plaque formation in the CA1 subfield of the hippocampus in the triple transgenic model of Alzheimer's disease

Alzheimer's disease (AD) is an irreversible neurodegenerative disease that is characterised by the presence of β-amyloid (Aβ) plaques, neurofibrillary tangles (NFTs) and synaptic loss specifically in brain regions involved in learning and memory such as the neocortex and the hippocampus. Aβ depositions in the form of neuritic plaques trigger activation of microglia that is believed to be a common neuropathological feature of AD brains. As an integral part of the hippocampus, the dentate gyrus (DG) plays an important role in cognitive function. Although post-mortem studies suggest later involvement of the DG into the AD progression, changes in microglia have not been studied in this subfield of the hippocampus. In the present study the numerical density (Nv, #/mm(3)) of both resting (identified by tomato lectin staining) and activated (identified by Mac-1 immunoreactivity) microglia was analysed in the molecular layer (ML) of the DG in the triple transgenic (3xTg-AD) mouse model of AD at different ages (9, 12 and 18 months). The 3xTg-AD mouse model of AD showed a significant increase in the Nv of resting (by 75%) and activated (by 67%) at 18 months of age compared to non-Tg controls. These results indicate a complex microglial remodelling during AD progression.

Increased hippocampal CA1 density of serotonergic terminals in a triple transgenic mouse model of Alzheimer's disease: an ultrastructural study

Alzheimer's disease (AD) is a neurodegenerative pathology that deteriorates mnesic functions and associated brain regions including the hippocampus. Serotonin (5-HT) has an important role in cognition. We recently demonstrated an increase in 5-HT transporter (SERT) fibre density in the hippocampal CA1 in an AD triple transgenic mouse model (3xTg-AD). Here, we analyse the ultrastructural localisation, distribution and numerical density (N_v) of hippocampal SERT axons (SERT-Ax) and terminals (SERT-Te) and their relationship with SERT fibre sprouting and altered synaptic N_v in 3xTg-AD compared with non-transgenic control mice. 3xTg-AD animals showed a significant increase in SERT-Te N_v in CA1 at both, 3 (95%) and 18 months of age (144%), being restricted to the CA1 stratum moleculare (S. Mol; 227% at 3 and 180% at 18 months). 3xTg-AD animals also exhibit reduced N_v of perforated axospinous synapses (PS) in CA1 S. Mol (56% at 3 and 52% at 18 months). No changes were observed in the N_v of symmetric and asymmetrical synapses or SERT-Ax. Our results suggest that concomitant SERT-Te N_v increase and PS reduction in 3xTg-AD mice may act as a compensatory mechanism maintaining synaptic efficacy as a response to the AD cognitive impairment.

Increase in the density of resting microglia precedes neuritic plaque formation and microglial activation in a transgenic model of Alzheimer's disease

The formation of cerebral senile plaques composed of amyloid β peptide (Aβ) is a fundamental feature of Alzheimer's disease (AD). Glial cells and more specifically microglia become reactive in the presence of Aβ. In a triple transgenic model of AD (3 × Tg-AD), we found a significant increase in activated microglia at 12 (by 111%) and 18 (by 88%) months of age when compared with non-transgenic (non-Tg) controls. This microglial activation correlated with Aβ plaque formation, and the activation in microglia was closely associated with Aβ plaques and smaller Aβ deposits. We also found a significant increase in the area density of resting microglia in 3 × Tg-AD animals both at plaque-free stage (at 9 months by 105%) and after the development of A plaques (at 12 months by 54% and at 18 months by 131%). Our results show for the first time that the increase in the density of resting microglia precedes both plaque formation and activation of microglia by extracellular Aβ accumulation. We suggest that AD pathology triggers a complex microglial reaction: at the initial stages of the disease the number of resting microglia increases, as if in preparation for the ensuing activation in an attempt to fight the extracellular Aβ load that is characteristic of the terminal stages of the disease.

Serotonin fibre sprouting and increase in serotonin transporter immunoreactivity in the CA1 area of hippocampus in a triple transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that deteriorates cognitive functions and associated brain regions such as the hippocampus, being the primary cause of dementia. Serotonin (5-HT) is widely present in the hippocampus, being an important neurotransmitter involved in learning and memory. Although recent evidence suggests alterations in 5-HT neurotransmission in AD, it is not clear how hippocampal 5-HT innervation is modified. Here, we studied hippocampal 5-HT innervation by analysing: (i) the expression, density and distribution of 5-HT transporter (SERT)-immunoreactive fibres; (ii) the specific morphological characteristics of serotonergic fibres and their relation to amyloid plaques; and (iii) the total number of 5-HT neurons within the raphe nuclei in triple transgenic mouse model of AD. We used quantitative light microscopy immunohistochemistry comparing transgenic and non-transgenic animals of different ages (3, 6, 9, 12 and 18 months). The transgenic animals showed a significant increase in SERT fibres in the hippocampus in a subfield-, strata- and age-specific manner. The increase in SERT fibres was specific to the CA1 stratum lacunosum-moleculare. An increase in SERT fibres in transgenic animals was observed at 3 months (by 61%) and at 18 months (by 74%). No changes, however, were found in the total number of raphe 5-HT neurons at any age. Our results indicate that triple transgenic mice display changes in the expression of SERT and increased SERT fibres sprouting, which may account for imbalanced serotonergic neurotransmission associated with (or linked to) AD cognitive impairment.

The birth and postnatal development of purinergic signalling

The purinergic signalling system is one of the most ancient and arguably the most widespread intercellular signalling system in living tissues. In this review we present a detailed account of the early developments and current status of purinergic signalling. We summarize the current knowledge on purinoceptors, their distribution and role in signal transduction in various tissues in physiological and pathophysiological conditions.

Extracellular cAMP inhibits P2X receptors in rat sensory neurones through G protein-mediated mechanism

AIM

To identify the mechanisms of P2X(3) receptor inhibition by extracellular cyclic adenosine monophosphate (cAMP) in rat dorsal root ganglion (DRG) neurones.

METHODS

Whole-cell currents were measured in cultured DRG neurones using the combination of voltage and concentration clamp.

RESULTS

We have found that extracellular cAMP inhibits P2X(3)-mediated currents in a concentration- and use-dependent manner. The P2X(3) currents, activated by ATP applied every 4 min, were inhibited by 55% in the presence of 10 microm cAMP and by 81% in the presence of 30 microm cAMP. At 8 min interval between ATP applications the same concentration of cAMP did not alter the currents. Addition of 0.5 mm of guanosine 5'-O-(2-thiodiphosphate) to intracellular solution blocked the inhibitory action of cAMP. The inhibitory effects of cAMP were not mimicked by extracellular application of 30 mum adenosine.

CONCLUSIONS

In this paper, we demonstrate, for the first time, that extracellular application of cAMP to rat sensory neurones inhibits P2X(3) receptors via a G protein-coupled mechanism in a use-dependent manner, thus indicating the neuronal expression of specific plasmalemmal cAMP receptor.

Novel mechanism for temperature-independent transitions in flexible molecules: role of thermodynamic fluctuations

A novel physical mechanism is proposed to explain the temperature-independent transition reactions in molecular systems. The mechanism becomes effective in the case of conformation transitions between quasi-isoenergetic molecular states. It is shown that at room temperatures, stochastic broadening of molecular energy levels predominates the energy of low-frequency vibrations accompanying the transition. This leads to a cancellation of temperature dependence in the stochastically averaged rate constants. As an example, a physical interpretation of temperature-independent onset of P2X{3} receptor desensitization in neuronal membranes is provided.

Evolutionary origins of the purinergic signalling system

Purines appear to be the most primitive and widespread chemical messengers in the animal and plant kingdoms. The evidence for purinergic signalling in plants, invertebrates and lower vertebrates is reviewed. Much is based on pharmacological studies, but important recent studies have utilized the techniques of molecular biology and receptors have been cloned and characterized in primitive invertebrates, including the social amoeba Dictyostelium and the platyhelminth Schistosoma, as well as the green algae Ostreococcus, which resemble P2X receptors identified in mammals. This suggests that contrary to earlier speculations, P2X ion channel receptors appeared early in evolution, while G protein-coupled P1 and P2Y receptors were introduced either at the same time or perhaps even later. The absence of gene coding for P2X receptors in some animal groups [e.g. in some insects, roundworms (Caenorhabditis elegans) and the plant Arabidopsis] in contrast to the potent pharmacological actions of nucleotides in the same species, suggests that novel receptors are still to be discovered.

Evolutionary origins of the purinergic signalling system

Purines appear to be the most primitive and widespread chemical messengers in the animal and plant kingdoms. The evidence for purinergic signalling in plants, invertebrates and lower vertebrates is reviewed. Much is based on pharmacological studies, but important recent studies have utilized the techniques of molecular biology and receptors have been cloned and characterized in primitive invertebrates, including the social amoeba Dictyostelium and the platyhelminth Schistosoma, as well as the green algae Ostreococcus, which resemble P2X receptors identified in mammals. This suggests that contrary to earlier speculations, P2X ion channel receptors appeared early in evolution, while G protein-coupled P1 and P2Y receptors were introduced either at the same time or perhaps even later. The absence of gene coding for P2X receptors in some animal groups [e.g. in some insects, roundworms (Caenorhabditis elegans) and the plant Arabidopsis] in contrast to the potent pharmacological actions of nucleotides in the same species, suggests that novel receptors are still to be discovered.

Neuronismo y reticulismo: neuronal-glial circuits unify the reticular and neuronal theories of brain organization

The neuronal doctrine, which shaped the development of neuroscience, was born from a long-lasting struggle between reticularists, who assumed internal continuity of neural networks and neuronists, who defined the brain as a network of physically separated cellular entities, defined as neurones. Modern views regard the brain as a complex of constantly interacting cellular circuits, represented by neuronal networks embedded into internally connected astroglial syncytium. The neuronal-glial circuits endowed with distinct signalling cascades form a 'diffuse nervous net' suggested by Golgi, where millions of synapses belonging to very different neurones are integrated first into neuronal-glial-vascular units and then into more complex structures connected through glial syncytium. These many levels of integration, both morphological and functional, presented by neuronal-glial circuitry ensure the spatial and temporal multiplication of brain cognitive power.

ARG3.1/ARC expression in hippocampal dentate gyrus astrocytes: ultrastructural evidence and co-localization with glial fibrillary acidic protein

Synaptic efficacy following long-term potentiation (LTP) and memory consolidation is associated with changes in the expression of immediate early genes (IEGs). These changes are often accompanied by increased expression of glial fibrillary acidic protein (GFAP). While the protein products of the majority of IEGs are mainly restricted to the cell body, Arg3.1/Arc product is rapidly delivered to dendrites, where it accumulates close to synaptic sites. Arg3.1/Arc protein was originally considered neurone specific; however, we have recently found Arg3.1/Arc immunoreactivity (Arg3.1/Arc-IR) within glial cells and demonstrated its increased expression after LTP in the hippocampal dentate gyrus (DG). Here, we have further investigated this novel finding, using electron microscopic immunocytochemistry to determine the localization and sub-cellular distribution of Arg3.1/Arc protein in GFAP positive glia (GFAP-IR) in the DG. Arg3.1/Arc labelling was seen prominently in GFAP-IR glial cell bodies and in large- and medium-sized glial filamentous processes. GFAP-labelled medium-small peri-synaptic glial profiles also displayed Arg3.1/Arc-IR; however, the very thin and distal glial filaments only displayed Arc-IR. Arc-IR was distributed throughout the cytoplasm, often associated with GFAP filaments, and along the plasma membrane of glial processes. Peri-synaptic glial Arg3.1/Arc-IR processes were apposed to pre- and/or post-synaptic profiles at asymmetric axospinous synapses. These data, taken with our earlier study which provided evidence for an increase in astrocytic Arg3.1/Arc-IR after the induction of LTP, suggest a role for glial Arg3.1/Arc in structural and synaptic plasticity which may be critical for the maintenance of cognitive functions.

Pathological potential of astroglia

The pathological potential of glial cells was recognized already by Rudolf Virchow, Santiago Ramon y Cajal and Pio Del Rio-Ortega. Many functions and roles performed by astroglia in the healthy brain determine their involvement in brain diseases; as indeed any kind of brain insult does affect astrocytes, and their performance in pathological conditions, to a very large extent, determines the survival of the brain parenchyma, the degree of damage and neurological defect. Astrocytes being in general responsible for overall brain homeostasis are involved in virtually every form of brain pathology. Here we provide an overview of recent developments in identifying the role and mechanisms of the pathological potential of astroglia.

P2X receptors and synaptic plasticity

Adenosine triphosphate (ATP) is released in many synapses in the CNS either together with other neurotransmitters, such as glutamate and GABA, or on its own. Postsynaptic action of ATP is mediated through metabotropic P2Y and ionotropic P2X receptors abundantly expressed in neural cells. Activation of P2X receptors induces fast excitatory postsynaptic currents in synapses located in various brain regions, including medial habenula, hippocampus and cortex. P2X receptors display relatively high Ca2+ permeability and can mediate substantial Ca2+ influx at resting membrane potential. P2X receptors can dynamically interact with other neurotransmitter receptors, including N-methyl-D-aspartate (NMDA) receptors, GABA(A) receptors and nicotinic acetylcholine (ACh) receptors. Activation of P2X receptors has multiple modulatory effects on synaptic plasticity, either inhibiting or facilitating the long-term changes of synaptic strength depending on physiological context. At the same time precise mechanisms of P2X-dependent regulation of synaptic plasticity remain elusive. Further understanding of the role of P2X receptors in regulation of synaptic transmission in the CNS requires dissection of P2X-mediated effects on pre-synaptic terminals, postsynaptic membrane and glial cells.

Cytoplasmic organelles determine complexity and specificity of calcium signalling in adrenal chromaffin cells

Complex and coordinated fluctuations of intracellular free Ca2+ concentration ([Ca2+]c) regulate secretion of adrenaline from chromaffin cells. The physiologically relevant intracellular Ca2+ signals occur either as localized microdomains of high Ca2+ concentrations or as propagating Ca2+ waves, which give rise to global Ca2+ elevations. Intracellular organelles, the endoplasmic reticulum (ER), mitochondria and nuclear envelope, are endowed with powerful Ca2+ transport systems. Calcium uptake and Ca2+ release from these organelles determine the spatial and temporal parameters of Ca2+ signalling events. Furthermore, the ER and mitochondria form close relations with the sites of plasmalemmal Ca2+ entry, creating 'Ca2+ signalling triads' which act as elementary operational units, which regulate exocytosis. Ca2+ ions accumulating in the ER and mitochondria integrate exocytotic activity with energy production and protein synthesis.

Glia: the fulcrum of brain diseases

Neuroglia represented by astrocytes, oligodendrocytes and microglial cells provide for numerous vital functions. Glial cells shape the micro-architecture of the brain matter; they are involved in information transfer by virtue of numerous plasmalemmal receptors and channels; they receive synaptic inputs; they are able to release 'glio'transmitters and produce long-range information exchange; finally they act as pluripotent neural precursors and some of them can even act as stem cells, which provide for adult neurogenesis. Recent advances in gliology emphasised the role of glia in the progression and handling of the insults to the nervous system. The brain pathology, is, to a very great extent, a pathology of glia, which, when falling to function properly, determines the degree of neuronal death, the outcome and the scale of neurological deficit. Glial cells are central in providing for brain homeostasis. As a result glia appears as a brain warden, and as such it is intrinsically endowed with two opposite features: it protects the nervous tissue as long as it can, but it also can rapidly assume the guise of a natural killer, trying to eliminate and seal the damaged area, to save the whole at the expense of the part.

Neuronal-glial networks as substrate for CNS integration

Astrocytes have been considered, for a long time, as the support and house-keeping cells of the nervous system. Indeed, the astrocytes play very important metabolic roles in the brain, but the catalogue of nervous system functions or activities that involve directly glial participation has extended dramatically in the last decade. In addition to the further refining of the signalling capacity of the neuroglial networks and the detailed reassessment of the interactions between glia and vascular bed in the brain, one of the important salient features of the increased glioscience activity in the last few years was the morphological and functional demonstration that protoplasmic astrocytes occupy well defined spatial territories, with only limited areas of morphological overlapping, but still able to communicate with adjacent neighbours through intercellular junctions. All these features form the basis for a possible reassessment of the nature of integration of activity in the central nervous system that could raise glia to a role of central integrator.

Calcium ions and integration in neural circuits

Integration in the nervous system is achieved by signal processing within dynamic functional ensembles formed by highly complex neuronal-glial cellular circuits. The interactions between electrically excitable neuronal networks and electrically non-excitable glial syncytium occur through either chemical transmission, which involves the release of transmitters from presynaptic terminals or from astroglial cells, or via direct intercellular contacts, gap junctions. Calcium ions act as a universal intracellular signalling system, which controls many aspects of neuronal-glial communications. In neurones, calcium signalling events regulate the exocytosis of neurotransmitters and establish the link between excitation of postsynaptic cells and integrative intracellular events, which control synaptic strength, expression of genes and memory function. In glial cells metabotropic receptor mediated release of calcium ions from the intracellular endoplasmic reticulum calcium store provide specific form of glial excitability. Glial calcium signals ultimately result in vesicular secretion of "glio" transmitters, which affect neuronal networks thus closing the glial-neuronal circuits. Cellular signalling through calcium ions therefore can be regarded as a molecular mechanism of integration in the nervous system.

Neurotrophin-3 prevents mitochondrial dysfunction in sensory neurons of streptozotocin-diabetic rats

Sensory neurons from streptozotocin (STZ)-diabetic rats exhibit depolarization of mitochondria and the related induction of reactive oxygen species has been proposed to contribute to the etiology of sensory polyneuropathy in diabetes. There is deficient neurotrophin-3 (NT-3)-dependent neurotrophic support of sensory neurons in diabetes and treatment of STZ-diabetic rats with NT-3 prevents neuropathological alterations in peripheral nerve. Therefore, we hypothesized that loss of NT-3 may contribute to mitochondrial dysfunction in sensory neurons in diabetic sensory neuropathy. The specific aim of this study was to determine whether treatment of STZ-diabetic rats with systemic NT-3 could prevent depolarization of the mitochondrial inner membrane potential (Deltapsi(m)). In vitro studies with cultured DRG neurons from control rats revealed that treatment with 50 ng/ml NT-3 for 6 h enhanced the Deltapsi(m), e.g., a higher polarized membrane potential, compared to untreated neurons (P < 0.05). Studies on DRG sensory neurons from control vs. STZ-diabetic rats demonstrated that NT-3 therapy prevented the diabetes-induced depolarization of Deltapsi(m) (P < 0.05) in parallel with normalization of diabetes-dependent deficits in sensory nerve conduction velocity. Furthermore, alterations in mitochondrial function in vitro and in vivo correlated with the level of activation/expression of Akt in DRG neurons.

Regulation of GABA release by depolarisation-evoked Ca2+ transients at a single hippocampal terminal

We correlated dynamic changes in free cytosolic [Ca2+] ([Ca2+]i) within single presynaptic terminals of cultured hippocampal neurones with the postsynaptic GABA-mediated currents. The local changes in [Ca2+]i and evoked inhibitory postsynaptic currents (eIPSCs) were recorded simultaneously using Fura-2 fluorescence and whole-cell patch-clamp respectively. The Ca2+ signals and eIPSCs were evoked by direct extracellular electrical stimulation of a single presynaptic terminal by short depolarising pulses. The presynaptic Ca2+ transient was graded by varying the amplitude of extracellular stimulating pulses. The probability of the release event, P, estimated for each stimulation strength, reached a maximum (P=1) when the Ca2+ signal became maximal and remained at this level at higher stimulation strength, despite the subsequent decrease in the amplitude of the Ca2+ transient. A gradual, linear increase in stimulation amplitude (Vstim) resulted in a bell-shaped dependence of the averaged amplitudes of Ca2+ signals and corresponding averaged amplitudes of eIPSCs. Analysis of the eIPSC demonstrated that the decrease in both the mean eIPSC amplitude and the mean quantal content of release resulted from a reduction in the probability of multivesicular release, i.e. in the disappearance of failures and in the decrease of individual eIPSC amplitude. The Ca2+ signals of similar amplitude resulted in both random and determinate (non-random) neurotransmitter release. We conclude that depolarisation-induced elevation of [Ca2+]i within the terminal is necessary but not sufficient for activation of vesicular release of neurotransmitter.

Endoplasmic reticulum Ca(2+) homeostasis and neuronal death

The endoplasmic reticulum (ER) is a universal signalling organelle, which regulates a wide range of neuronal functional responses. Calcium release from the ER underlies various forms of intracellular Ca(2+) signalling by either amplifying Ca(2+) entry through voltage-gated Ca(2+) channels by Ca(2+)-induced Ca(2+) release (CICR) or by producing local or global cytosolic calcium fluctuations following stimulation of metabotropic receptors through inositol-1,4,5-trisphosphate-induced Ca(2+) release (IICR). The ER Ca(2+) store emerges as a single interconnected pool, thus allowing for a long-range Ca(2+) signalling via intra-ER tunnels. The fluctuations of intra-ER free Ca(2+) concentration regulate the activity of numerous ER resident proteins responsible for post-translational protein folding and modification. Disruption of ER Ca(2+) homeostasis results in the developing of ER stress response, which in turn controls neuronal survival. Altered ER Ca(2+) handling may be involved in pathogenesis of various neurodegenerative diseases including brain ischemia and Alzheimer dementia.

Ca2+ and mitochondria as substrates for deficits in synaptic plasticity in normal brain ageing

Normal brain ageing is associated with a degree of functional impairment of neuronal activity that results in a reduction in memory and cognitive functions. One mechanism proposed to explain the age-dependent changes was the "Ca(2+) hypothesis of ageing" but data accumulated in the last decade revealed a number of inconsistencies. Two important questions were raised: (a) which are, if any, the most reliable age-associated change in neuronal Ca(2+) homeostasis and (b) are these changes primary, and thus determinant of the ageing phenotype, or are they secondary to other changes in the physiology of the aged neurones. After a brief review of the evidence accumulated for the age-induced changes in synaptic plasticity, we assess the proposal that these changes are, ultimately, determined by changes in the metabolic state of the aged neurones, that are manifest particularly after neuronal stimulation. In this context, it appears that the changes in mitochondrial status and function are of primary importance.

P2X receptor-mediated excitatory synaptic currents in somatosensory cortex

Fast P2X receptor-mediated excitatory postsynaptic current (EPSC) was found in pyramidal neurones of layer V of somatosensory cortex in slices acutely isolated from the brain of 17- to 22-day-old rats. The EPSCs were elicited by field electrical stimulation in the layer VI at 0.1 Hz in the presence of picrotoxin. When the glutamatergic EPSC was blocked by glutamate receptors inhibitors NBQX and D-AP5, a residual EPSC (rEPSC) was recorded from 85% of neurones tested. This rEPSC was not affected by blockers of nicotinic (hexamethonium) and serotonin (Y25130) receptors; however, it was reversibly inhibited by P2X receptors antagonists (NF023, NF279, and PPADS). An application of ATP (20 microM), beta,gamma-methylene ATP (25 microM), and alpha,beta-methylene ATP (20 microM) to acutely isolated pyramidal neurones of layer V evoked inward currents (30 to 400 pA) in 75% of cells tested. We concluded that several subtypes of P2X purinoreceptors participate in synaptic transmission in neocortex.

The endoplasmic reticulum and neuronal calcium signalling

The endoplasmic reticulum (ER) is a multifunctional signalling organelle regulating a wide range of neuronal functional responses. The ER is intimately involved in intracellular Ca(2+) signalling, producing local or global cytosolic calcium fluctuations via Ca(2+)-induced Ca(2+) release (CICR) or inositol-1,4,5-trisphosphate-induced Ca(2+) release (IICR). The CICR and IICR are controlled by two subsets of Ca(2+) release channels residing in the ER membrane, the Ca(2+)-gated Ca(2+) release channels, generally known as ryanodine receptors (RyRs) and InsP(3)-gated Ca(2+) release channels, referred to as InsP(3)-receptors (InsP(3)Rs). Both types of Ca(2+) release channels are expressed abundantly in nerve cells and their activation triggers cytoplasmic Ca(2+) signals important for synaptic transmission and plasticity. The RyRs and InsP(3)Rs show heterogeneous localisation in distinct cellular sub-compartments, conferring thus specificity in local Ca(2+) signals. At the same time, the ER Ca(2+) store emerges as a single interconnected pool fenced by the endomembrane. The continuity of the ER Ca(2+) store could play an important role in various aspects of neuronal signalling. For example, Ca(2+) ions may diffuse within the ER lumen with comparative ease, endowing this organelle with the capacity for "Ca(2+) tunnelling". Thus, continuous intra-ER Ca(2+) highways may be very important for the rapid replenishment of parts of the pool subjected to excessive stimulation (e.g. in small compartments within dendritic spines), the facilitated removal of localised Ca(2+) loads, and finally in conveying Ca(2+) signals from the site of entry towards the cell interior and nucleus.

Ionotropic P2X purinoreceptors mediate synaptic transmission in rat pyramidal neurones of layer II/III of somato-sensory cortex

Fast P2X receptor-mediated excitatory postsynaptic current (EPSC) was identified in pyramidal neurones of layer II/III of somato-sensory cortex in acutely isolated slices obtained from the brain of 17- to 22-day-old rats. The EPSCs were elicited by electrical stimulation of vertical axons originating from layer IV-VI neurones at 0.1 Hz in the presence of bicuculline. When the glutamatergic EPSC was blocked by saturating concentrations of glutamate receptor inhibitors 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo-[f]-quinoxaline-7-sulphonamide (NBQX) and D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5), a small EPSC component was recorded from 90 % of neurones tested. This residual EPSC was not affected by selective blockers of nicotinic (hexamethonium) or serotonin (N-(1-azabicyclo-[2.2.2]oct-3-yl)-6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-8-carboxamide hydrochloride, Y-25130) receptors, but it was reversibly inhibited by the antagonists of P2X receptors NF023 (8,8'-[carbonylbis(imino-3,1-phenylenecarbonylimino)]bis-1,3,5-naphthalene-trisulphonic acid), NF279 (8,8'-[carbonylbis (imino-4,1-phenylenecarbonylimino-4,1-phenylenecarbonylimino)]bis-1,3,5-naphthalene-trisulphonic acid) and PPADS (pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid). Application of ATP (10 microM) or alpha,beta-methylene ATP (10 microM) to pyramidal neurones, acutely isolated from cortical slices, evoked inward currents (30 to 200 pA) in 65 % of cells tested. The relative calcium/caesium permeability (P(Ca)/P(Cs)) of P2X receptors was 12.3 as estimated from the reversal potential of ATP-induced current measured at different extracellular calcium concentrations. We concluded that P2X purinoreceptors are activated during synaptic transmission in neocortex.

Xestospongin C empties the ER calcium store but does not inhibit InsP3-induced Ca2+ release in cultured dorsal root ganglia neurones

The action of Xestospongin C (XeC) on calcium concentration in the cytosol ([Ca2+]i) and within the lumen of endoplasmic reticulum (ER) ([Ca2+]L) was studied using cultured dorsal root ganglia (DRG) neurones. Application of 2.5 microM of XeC triggered a slow [Ca2+]i transient as measured by Fura-2 video-imaging. The kinetics and amplitude of XeC-induced [Ca2+]i response was similar to that triggered by 1 microM thapsigargin (TG). The [Ca2+]L was monitored in cells loaded with low-affinity Ca2+ indicator Mag-Fura-2. The cytosolic portion of Mag-Fura-2 was removed by permeabilisation of the plasmalemma with saponin. Application of XeC to these permeabilised neurones resulted in a slow depletion of the ER Ca2+ store. XeC, however, failed to inhibit inositol 1,4,5-trisphosphate (InsP3)-induced [Ca2+]L responses. We conclude that XeC is a potent inhibitor of sarco(endo)plasmic reticulum calcium ATPase, and it cannot be regarded as a specific inhibitor of InsP3 receptors in cultured DRG neurones.

Diabetes-induced alterations in calcium homeostasis in sensory neurones of streptozotocin-diabetic rats are restricted to lumbar ganglia and are prevented by neurotrophin-3

AIMS/HYPOTHESIS

In diabetic sensory polyneuropathy the earliest and most severe pathophysiology occurs in neurones with the longest axons. The aim of this study was to characterise a diabetes-induced neurodegenerative marker that was selective for sensory neurones with the longest axons. We studied alterations in calcium homeostasis since this occurs in other neurodegenerative diseases.

METHODS

Sensory neurones were cultured from control and streptozotocin-diabetic rats, treated with or without human recombinant neurotrophin-3 (hrNT-3), and neurones from L4-L6 dorsal root ganglia (DRG) which exhibit the longest axons in vivo were compared with those from C5-L3 DRG. Fluorescent video-imaging was used to measure cytoplasmic calcium dynamics.

RESULTS

Streptozotocin diabetes of 8 to 14 weeks, induced an increase in resting internal Ca(2+) concentration ([Ca(2+)](i)), from 67 +/- 7 nmol/l in small neurones and 79 +/- 9 nmol/l in big neurones obtained from control animals to 214 +/- 19 nmol/l in small neurones and 273 +/- 30 nmol/l in big neurones after 14 weeks of diabetes ( p < 0.05) in L4-L6 DRG cultures. Neurones from C5-L3 ganglia and non-neuronal cells were not affected. Treatment of 14-week streptozotocin-diabetic rats with subcutaneous injection of 5 mg/kg NT-3 normalised the increase in resting [Ca(2+)](i). The amplitudes induced by depolarisation, caffeine and ATP [Ca(2+)](i) responses were reduced in small ( < 30 microm diameter) but not big ( > 35 microm diameter) neurones of L4-L6 DRG from streptozotocin-diabetic animals; the C5-L3 DRG were not similarly affected and the changes in the L4-L6 DRG were corrected by NT-3 treatment.

CONCLUSIONS/INTERPRETATION

Altered calcium homeostasis could be an early molecular marker linked to the onset of diabetic sensory neuropathy. This neurodegenerative index can be corrected by NT-3 therapy and should encourage further work aimed at understanding the mechanistic basis of these observations.

Ca(2+) dynamics in the lumen of the endoplasmic reticulum in sensory neurons: direct visualization of Ca(2+)-induced Ca(2+) release triggered by physiological Ca(2+) entry

In cultured rat dorsal root ganglia neurons, we measured membrane currents, using the patch-clamp whole-cell technique, and the concentrations of free Ca(2+) in the cytosol ([Ca(2+)](i)) and in the lumen of the endoplasmic reticulum (ER) ([Ca(2+)](L)), using high- (Fluo-3) and low- (Mag-Fura-2) affinity Ca(2+)-sensitive fluorescent probes and video imaging. Resting [Ca(2+)](L) concentration varied between 60 and 270 microM. Activation of ryanodine receptors by caffeine triggered a rapid fall in [Ca(2+)](L) levels, which amounted to only 40--50% of the resting [Ca(2+)](L) value. Using electrophysiological depolarization, we directly demonstrate the process of Ca(2+)-induced Ca(2+) release triggered by Ca(2+) entry through voltage-gated Ca(2+) channels. The amplitude of Ca(2+) release from the ER lumen was linearly dependent on I(Ca).

Capsaicin-induced depolarisation of mitochondria in dorsal root ganglion neurons is enhanced by vanilloid receptors

Capsaicin, a pungent ingredient of hot chilli peppers, triggered Ca(2+) influx in dorsal root ganglion (DRG) neurons, which express specific vanilloid receptors of type 1, with ED(50)<100 nM. An increase in capsaicin concentration to 10 microM inhibited Ca(2+) clearance from the cytosol, but did not affect the amplitude of intracellular Ca(2+) elevation. In DRG neurons, 10 microM capsaicin also produced a significant drop in mitochondrial membrane potential (Deltapsi), as measured with the mitochondria-specific potentiometric fluorescent dye JC-1. Similar loss of mitochondrial potential upon application of capsaicin was observed in non-neuronal primary (human lymphocytes) and transformed (human myeloid leukaemia cell line, HL-60) cells. The EC(50) values for capsaicin-induced mitochondrial depolarisation were 6.9 microM (DRG neurons), 200 microM (human lymphocytes) and 150 microM (HL-60 cells). Removal of extracellular Ca(2+) or an application of the antioxidant trolox attenuated capsaicin-induced dissipation of Deltapsi in DRG neurons, but not in human lymphocytes and HL-60 cells. Rotenone, an inhibitor of complex I of the mitochondrial respiratory chain, and oligomycin, an inhibitor of F(0)F(1)-ATPase, significantly enhanced the mitochondrial depolarisation produced by capsaicin in DRG neurons. In human lymphocytes and HL-60 cells, only oligomycin potentiated the effect of capsaicin. From our results, we suggest that, in DRG neurons and non-neuronal cells, capsaicin dissipates Deltapsi, possibly due to a direct inhibition of complex I of the mitochondrial respiratory chain. The presence of vanilloid receptor-1 in DRG neurons makes their mitochondria 20-30-fold more sensitive to the depolarising effect of capsaicin compared with non-neuronal cells lacking vanilloid receptor-1. The higher sensitivity of DRG neurons to capsaicin may underlie a selective neurotoxicity of capsaicin towards sensory neurons.