Parvalbumin gates chronic pain through the modulation of firing patterns in inhibitory neurons.

Spinal cord dorsal horn inhibition is critical to the processing of sensory inputs, and its impairment leads to mechanical allodynia. How this decreased inhibition occurs and whether its restoration alleviates allodynic pain are poorly understood. Here, we show that a critical step in the loss of inhibitory tone is the change in the firing pattern of inhibitory parvalbumin (PV)-expressing neurons (PVNs). Our results show that PV, a calcium-binding protein, controls the firing activity of PVNs by enabling them to sustain high-frequency tonic firing patterns. Upon nerve injury, PVNs transition to adaptive firing and decrease their PV expression. Interestingly, decreased PV is necessary and sufficient for the development of mechanical allodynia and the transition of PVNs to adaptive firing. This transition of the firing pattern is due to the recruitment of calcium-activated potassium (SK) channels, and blocking them during chronic pain restores normal tonic firing and alleviates chronic pain. Our findings indicate that PV is essential for controlling the firing pattern of PVNs and for preventing allodynia. Developing approaches to manipulate these mechanisms may lead to different strategies for chronic pain relief.

Induction of antiviral interferon-stimulated genes by neuronal STING promotes the resolution of pain in mice.

Inflammation and pain are intertwined responses to injury, infection, or chronic diseases. While acute inflammation is essential in determining pain resolution and opioid analgesia, maladaptive processes occurring during resolution can lead to the transition to chronic pain. Here we found that inflammation activates the cytosolic DNA-sensing protein stimulator of IFN genes (STING) in dorsal root ganglion nociceptors. Neuronal activation of STING promotes signaling through TANK-binding kinase 1 (TBK1) and triggers an IFN-ß response that mediates pain resolution. Notably, we found that mice expressing a nociceptor-specific gain-of-function mutation in STING exhibited an IFN gene signature that reduced nociceptor excitability and inflammatory hyperalgesia through a KChIP1-Kv4.3 regulation. Our findings reveal a role of IFN-regulated genes and KChIP1 downstream of STING in the resolution of inflammatory pain.

Novel Scorpion Toxin ω-Buthitoxin-Hf1a Selectively Inhibits Calcium Influx via CaV3.3 and CaV3.2 and Alleviates Allodynia in a Mouse Model of Acute Postsurgical Pain.

Venom peptides have evolved to target a wide range of membrane proteins through diverse mechanisms of action and structures, providing promising therapeutic leads for diseases, including pain, epilepsy, and cancer, as well as unique probes of ion channel structure-function. In this work, a high-throughput FLIPR window current screening assay on T-type CaV3.2 guided the isolation of a novel peptide named ω-Buthitoxin-Hf1a from scorpion Hottentotta franzwerneri crude venom. At only 10 amino acid residues with one disulfide bond, it is not only the smallest venom peptide known to target T-type CaVs but also the smallest structured scorpion venom peptide yet discovered. Synthetic Hf1a peptides were prepared with C-terminal amidation (Hf1a-NH2) or a free C-terminus (Hf1a-OH). Electrophysiological characterization revealed Hf1a-NH2 to be a concentration-dependent partial inhibitor of CaV3.2 (IC50 = 1.18 µM) and CaV3.3 (IC50 = 0.49 µM) depolarized currents but was ineffective at CaV3.1. Hf1a-OH did not show activity against any of the three T-type subtypes. Additionally, neither form showed activity against N-type CaV2.2 or L-type calcium channels. The three-dimensional structure of Hf1a-NH2 was determined using NMR spectroscopy and used in docking studies to predict its binding site at CaV3.2 and CaV3.3. As both CaV3.2 and CaV3.3 have been implicated in peripheral pain signaling, the analgesic potential of Hf1a-NH2 was explored in vivo in a mouse model of incision-induced acute post-surgical pain. Consistent with this role, Hf1a-NH2 produced antiallodynia in both mechanical and thermal pain.

A novel Nav1.8-FLPo driver mouse for intersectional genetics to uncover the functional significance of primary sensory neuron diversity.

The recent development of single-cell and single-nucleus RNA sequencing has highlighted the extraordinary diversity of dorsal root ganglia neurons. However, the few available genetic tools limit our understanding of the functional significance of this heterogeneity. We generated a new mouse line expressing the flippase recombinase from the scn10a locus. By crossing Nav1.8Ires-FLPo mice with the AdvillinCre and RC::FL-hM3Dq mouse lines in an intersectional genetics approach, we were able to obtain somatodendritic expression of hM3Dq-mCherry selectively in the Nav1.8 lineage. The bath application of clozapine N-oxide triggered strong calcium responses selectively in mCherry+ neurons. The intraplantar injection of CNO caused robust flinching, shaking, and biting responses accompanied by strong cFos activation in the ipsilateral lumbar spinal cord. The Nav1.8Ires-FLPo mouse model will be a valuable tool for extending our understanding of the in vivo functional specialization of neuronal subsets of the Nav1.8 lineage for which inducible Cre lines are available.

Prolonged Piezo1 Activation Induces Cardiac Arrhythmia.

The rhythmical nature of the cardiovascular system constantly generates dynamic mechanical forces. At the centre of this system is the heart, which must detect these changes and adjust its performance accordingly. Mechanoelectric feedback provides a rapid mechanism for detecting even subtle changes in the mechanical environment and transducing these signals into electrical responses, which can adjust a variety of cardiac parameters such as heart rate and contractility. However, pathological conditions can disrupt this intricate mechanosensory system and manifest as potentially life-threatening cardiac arrhythmias. Mechanosensitive ion channels are thought to be the main proponents of mechanoelectric feedback as they provide a rapid response to mechanical stimulation and can directly affect cardiac electrical activity. Here, we demonstrate that the mechanosensitive ion channel PIEZO1 is expressed in zebrafish cardiomyocytes. Furthermore, chemically prolonging PIEZO1 activation in zebrafish results in cardiac arrhythmias. indicating that this ion channel plays an important role in mechanoelectric feedback. This also raises the possibility that PIEZO1 gain of function mutations could be linked to heritable cardiac arrhythmias in humans.

Pmu1a, a novel spider toxin with dual inhibitory activity at pain targets hNaV 1.7 and hCaV 3 voltage-gated channels.

Venom-derived peptides targeting ion channels involved in pain are regarded as a promising alternative to current, and often ineffective, chronic pain treatments. Many peptide toxins are known to specifically and potently block established therapeutic targets, among which the voltage-gated sodium and calcium channels are major contributors. Here, we report on the discovery and characterization of a novel spider toxin isolated from the crude venom of Pterinochilus murinus that shows inhibitory activity at both hNaV 1.7 and hCaV 3.2 channels, two therapeutic targets implicated in pain pathways. Bioassay-guided HPLC fractionation revealed a 36-amino acid peptide with three disulfide bridges named µ/ω-theraphotoxin-Pmu1a (Pmu1a). Following isolation and characterization, the toxin was chemically synthesized and its biological activity was further assessed using electrophysiology, revealing Pmu1a to be a toxin that potently blocks both hNaV 1.7 and hCaV 3. Nuclear magnetic resonance structure determination of Pmu1a shows an inhibitor cystine knot fold that is the characteristic of many spider peptides. Combined, these data show the potential of Pmu1a as a basis for the design of compounds with dual activity at the therapeutically relevant hCaV 3.2 and hNaV 1.7 voltage-gated channels.

A cellular taxonomy of the adult human spinal cord.

The mammalian spinal cord functions as a community of cell types for sensory processing, autonomic control, and movement. While animal models have advanced our understanding of spinal cellular diversity, characterizing human biology directly is important to uncover specialized features of basic function and human pathology. Here, we present a cellular taxonomy of the adult human spinal cord using single-nucleus RNA sequencing with spatial transcriptomics and antibody validation. We identified 29 glial clusters and 35 neuronal clusters, organized principally by anatomical location. To demonstrate the relevance of this resource to human disease, we analyzed spinal motoneurons, which degenerate in amyotrophic lateral sclerosis (ALS) and other diseases. We found that compared with other spinal neurons, human motoneurons are defined by genes related to cell size, cytoskeletal structure, and ALS, suggesting a specialized molecular repertoire underlying their selective vulnerability. We include a web resource to facilitate further investigations into human spinal cord biology.

Role of T CD4+ cells, macrophages, C-low threshold mechanoreceptors and spinal Cav 3.2 channels in inflammation and related pain-like symptoms in murine inflammatory models.

BACKGROUND AND PURPOSE: T-type calcium channels, mainly the Cav 3.2 subtype, are important contributors to the nociceptive signalling pathway. We investigated their involvement in inflammation and related pain-like symptoms. EXPERIMENTAL APPROACH: The involvement of Cav 3.2 and T-type channels was investigated using genetic and pharmacological inhibition to assess mechanical allodynia/hyperalgesia and oedema development in two murine inflammatory pain models. The location of Cav 3.2 channels involved in pain-like symptoms was studied in mice with Cav 3.2 knocked out in C-low threshold mechanoreceptors (C-LTMR) and the use of ABT-639, a peripherally restricted T-type channel inhibitor. The anti-oedema effect of Cav 3.2 channel inhibition was investigated in chimeric mice with immune cells deleted for Cav 3.2. Lymphocytes and macrophages from either green fluorescent protein-targeted Cav 3.2 or KO mice were used to determine the expression of Cav 3.2 protein and the functional status of the cells. KEY RESULTS: Cav 3.2 channels contributed to the development of pain-like symptoms and oedema in the two murine inflammatory pain models. Our results provided evidence of the involvement of Cav 3.2 channels located on C-LTMRs and spinal cord in inflammatory pain. Cav 3.2 channels located in T cells and macrophages contribute to the inflammatory process. CONCLUSION AND IMPLICATIONS: Cav 3.2 channels play crucial roles in inflammation and related pain, implying that targeting of Cav 3.2 channels with pharmacological agents could be an attractive and readily evaluable strategy in clinical trials, to relieve chronic inflammatory pain in patients.

Centrally expressed Cav3.2 T-type calcium channel is critical for the initiation and maintenance of neuropathic pain.

Cav3.2 T-type calcium channel is a major molecular actor of neuropathic pain in peripheral sensory neurons, but its involvement at the supraspinal level is almost unknown. In the anterior pretectum (APT), a hub of connectivity of the somatosensory system involved in pain perception, we show that Cav3.2 channels are expressed in a subpopulation of GABAergic neurons coexpressing parvalbumin (PV). In these PV-expressing neurons, Cav3.2 channels contribute to a high-frequency-bursting activity, which is increased in the spared nerve injury model of neuropathy. Specific deletion of Cav3.2 channels in APT neurons reduced both the initiation and maintenance of mechanical and cold allodynia. These data are a direct demonstration that centrally expressed Cav3.2 channels also play a fundamental role in pain pathophysiology.

The impact of C-tactile low-threshold mechanoreceptors on affective touch and social interactions in mice.

Affective touch is necessary for proper neurodevelopment and sociability. However, it remains unclear how the neurons innervating the skin detect affective and social behaviors. The C low-threshold mechanoreceptors (C-LTMRs), a specific population of somatosensory neurons in mice, appear particularly well suited, physiologically and anatomically, to perceive affective and social touch. However, their contribution to sociability has not been resolved yet. Our observations revealed that C-LTMR functional deficiency induced social isolation and reduced tactile interactions in adulthood. Conversely, transient increase in C-LTMR excitability in adults, using chemogenetics, was rewarding, promoted touch-seeking behaviors, and had prosocial influences on group dynamics. This work provides the first empirical evidence that specific peripheral inputs alone can drive complex social behaviors. It demonstrates the existence of a specialized neuronal circuit, originating in the skin, wired to promote interactions with other individuals.

The neuronal tyrosine kinase receptor ligand ALKAL2 mediates persistent pain.

The anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase known for its oncogenic potential that is involved in the development of the peripheral and central nervous system. ALK receptor ligands ALKAL1 and ALKAL2 were recently found to promote neuronal differentiation and survival. Here, we show that inflammation or injury enhanced ALKAL2 expression in a subset of TRPV1+ sensory neurons. Notably, ALKAL2 was particularly enriched in both mouse and human peptidergic nociceptors, yet weakly expressed in nonpeptidergic, large-diameter myelinated neurons or in the brain. Using a coculture expression system, we found that nociceptors exposed to ALKAL2 exhibited heightened excitability and neurite outgrowth. Intraplantar CFA or intrathecal infusion of recombinant ALKAL2 led to ALK phosphorylation in the lumbar dorsal horn of the spinal cord. Finally, depletion of ALKAL2 in dorsal root ganglia or blocking ALK with clinically available compounds crizotinib or lorlatinib reversed thermal hyperalgesia and mechanical allodynia induced by inflammation or nerve injury, respectively. Overall, our work uncovers the ALKAL2/ALK signaling axis as a central regulator of nociceptor-induced sensitization. We propose that clinically approved ALK inhibitors used for non-small cell lung cancer and neuroblastomas could be repurposed to treat persistent pain conditions.

Isolation and Culture of Precursor Cells from the Adult Human Spinal Cord.

We demonstrated the presence of neural stem cells and/or progenitor cells in the adult human spinal cord. This chapter provides materials and methods to harvest high-quality samples of thoracolumbar, lumbar, and sacral adult human spinal cord and human dorsal root ganglia isolated from brain-dead patients who had agreed before passing to donate their bodies to science for therapeutic and scientific advances. The methods to culture precursor cells from the adult human spinal cord are also described.

Epigenetics Involvement in Oxaliplatin-Induced Potassium Channel Transcriptional Downregulation and Hypersensitivity.

Peripheral neuropathy is the most frequent dose-limiting adverse effect of oxaliplatin. Acute pain symptoms that are induced or exacerbated by cold occur in almost all patients immediately following the first infusions. Evidence has shown that oxaliplatin causes ion channel expression modulations in dorsal root ganglia neurons, which are thought to contribute to peripheral hypersensitivity. Most dysregulated genes encode ion channels involved in cold and mechanical perception, noteworthy members of a sub-group of potassium channels of the K2P family, TREK and TRAAK. Downregulation of these K2P channels has been identified as an important tuner of acute oxaliplatin-induced hypersensitivity. We investigated the molecular mechanisms underlying this peripheral dysregulation in a murine model of neuropathic pain triggered by a single oxaliplatin administration. We found that oxaliplatin-mediated TREK-TRAAK downregulation, as well as downregulation of other K+ channels of the K2P and Kv families, involves a transcription factor known as the neuron-restrictive silencer factor (NRSF) and its epigenetic co-repressors histone deacetylases (HDACs). NRSF knockdown was able to prevent most of these K+ channel mRNA downregulation in mice dorsal root ganglion neurons as well as oxaliplatin-induced acute cold and mechanical hypersensitivity. Interestingly, pharmacological inhibition of class I HDAC reproduces the antinociceptive effects of NRSF knockdown and leads to an increased K+ channel expression in oxaliplatin-treated mice.

TACAN Is an Ion Channel Involved in Sensing Mechanical Pain.

Mechanotransduction, the conversion of mechanical stimuli into electrical signals, is a fundamental process underlying essential physiological functions such as touch and pain sensing, hearing, and proprioception. Although the mechanisms for some of these functions have been identified, the molecules essential to the sense of pain have remained elusive. Here we report identification of TACAN (Tmem120A), an ion channel involved in sensing mechanical pain. TACAN is expressed in a subset of nociceptors, and its heterologous expression increases mechanically evoked currents in cell lines. Purification and reconstitution of TACAN in synthetic lipids generates a functional ion channel. Finally, a nociceptor-specific inducible knockout of TACAN decreases the mechanosensitivity of nociceptors and reduces behavioral responses to painful mechanical stimuli but not to thermal or touch stimuli. We propose that TACAN is an ion channel that contributes to sensing mechanical pain.

Evaluation of the Spider (Phlogiellus genus) Phlotoxin 1 and Synthetic Variants as Antinociceptive Drug Candidates.

Over the two last decades, venom toxins have been explored as alternatives to opioids to treat chronic debilitating pain. At present, approximately 20 potential analgesic toxins, mainly from spider venoms, are known to inhibit with high affinity the NaV1.7 subtype of voltage-gated sodium (NaV) channels, the most promising genetically validated antinociceptive target identified so far. The present study aimed to consolidate the development of phlotoxin 1 (PhlTx1), a 34-amino acid and 3-disulfide bridge peptide of a Phlogiellus genus spider, as an antinociceptive agent by improving its affinity and selectivity for the human (h) NaV1.7 subtype. The synthetic homologue of PhlTx1 was generated and equilibrated between two conformers on reverse-phase liquid chromatography and exhibited potent analgesic effects in a mouse model of NaV1.7-mediated pain. The effects of PhlTx1 and 8 successfully synthetized alanine-substituted variants were studied (by automated whole-cell patch-clamp electrophysiology) on cell lines stably overexpressing hNaV subtypes, as well as two cardiac targets, the hCaV1.2 and hKV11.1 subtypes of voltage-gated calcium (CaV) and potassium (KV) channels, respectively. PhlTx1 and D7A-PhlTx1 were shown to inhibit hNaV1.1-1.3 and 1.5-1.7 subtypes at hundred nanomolar concentrations, while their affinities for hNaV1.4 and 1.8, hCaV1.2 and hKV11.1 subtypes were over micromolar concentrations. Despite similar analgesic effects in the mouse model of NaV1.7-mediated pain and selectivity profiles, the affinity of D7A-PhlTx1 for the NaV1.7 subtype was at least five times higher than that of the wild-type peptide. Computational modelling was performed to deduce the 3D-structure of PhlTx1 and to suggest the amino acids involved in the efficiency of the molecule. In conclusion, the present structure-activity relationship study of PhlTx1 results in a low improved affinity of the molecule for the NaV1.7 subtype, but without any marked change in the molecule selectivity against the other studied ion channel subtypes. Further experiments are therefore necessary before considering the development of PhlTx1 or synthetic variants as antinociceptive drug candidates.

TRPV1 promotes opioid analgesia during inflammation.

Pain and inflammation are inherently linked responses to injury, infection, or chronic diseases. Given that acute inflammation in humans or mice enhances the analgesic properties of opioids, there is much interest in determining the inflammatory transducers that prime opioid receptor signaling in primary afferent nociceptors. Here, we found that activation of the transient receptor potential vanilloid type 1 (TRPV1) channel stimulated a mitogen-activated protein kinase (MAPK) signaling pathway that was accompanied by the shuttling of the scaffold protein ß-arrestin2 to the nucleus. The nuclear translocation of ß-arrestin2 in turn prevented its recruitment to the µ-opioid receptor (MOR), the subsequent internalization of agonist-bound MOR, and the suppression of MOR activity that occurs upon receptor desensitization. Using the complete Freund's adjuvant (CFA) inflammatory pain model to examine the role of TRPV1 in regulating endogenous opioid analgesia in mice, we found that naloxone methiodide (Nal-M), a peripherally restricted, nonselective, and competitive opioid receptor antagonist, slowed the recovery from CFA-induced hypersensitivity in wild-type, but not TRPV1-deficient, mice. Furthermore, we showed that inflammation prolonged morphine-induced antinociception in a mouse model of opioid receptor desensitization, a process that depended on TRPV1. Together, our data reveal a TRPV1-mediated signaling pathway that serves as an endogenous pain-resolution mechanism by promoting the nuclear translocation of ß-arrestin2 to minimize MOR desensitization. This previously uncharacterized mechanism may underlie the peripheral opioid control of inflammatory pain. Dysregulation of the TRPV1-ß-arrestin2 axis may thus contribute to the transition from acute to chronic pain.

Cav3.2 T-type calcium channels shape electrical firing in mouse Lamina II neurons.

The T-type calcium channel, Cav3.2, is necessary for acute pain perception, as well as mechanical and cold allodynia in mice. Being found throughout sensory pathways, from excitatory primary afferent neurons up to pain matrix structures, it is a promising target for analgesics. In our study, Cav3.2 was detected in ~60% of the lamina II (LII) neurons of the spinal cord, a site for integration of sensory processing. It was co-expressed with Tlx3 and Pax2, markers of excitatory and inhibitory interneurons, as well as nNOS, calretinin, calbindin, PKCγ and not parvalbumin. Non-selective T-type channel blockers slowed the inhibitory but not the excitatory transmission in LII neurons. Furthermore, T-type channel blockers modified the intrinsic properties of LII neurons, abolishing low-threshold activated currents, rebound depolarizations, and blunting excitability. The recording of Cav3.2-positive LII neurons, after intraspinal injection of AAV-DJ-Cav3.2-mcherry, showed that their intrinsic properties resembled those of the global population. However, Cav3.2 ablation in the dorsal horn of Cav3.2GFP-Flox KI mice after intraspinal injection of AAV-DJ-Cav3.2-Cre-IRES-mcherry, had drastic effects. Indeed, it (1) blunted the likelihood of transient firing patterns; (2) blunted the likelihood and the amplitude of rebound depolarizations, (3) eliminated action potential pairing, and (4) remodeled the kinetics of the action potentials. In contrast, the properties of Cav3.2-positive neurons were only marginally modified in Cav3.1 knockout mice. Overall, in addition to their previously established roles in the superficial spinal cord and in primary afferent neurons, Cav3.2 channel appear to be necessary for specific, significant and multiple controls of LII neuron excitability.

Inhibition of Cav 3.2 calcium channels: A new target for colonic hypersensitivity associated with low-grade inflammation.

BACKGROUND AND PURPOSE: Abdominal pain associated with low-grade inflammation is frequently encountered in irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) during remission. Current treatments are not very effective and new therapeutic approaches are needed. The role of CaV 3.2 channels, which are important in other chronic pain contexts, was investigated in a murine model of colonic hypersensitivity (CHS) associated with low-grade inflammation. EXPERIMENTAL APPROACH: Low doses of dextran sulfate sodium (DSS; 0.5%) were chronically administered to C57BL/6j mice in drinking water. Their inflammatory state was assessed by systemic and local measures of IL-6, myeloperoxidase, and lipocalin-2 using elisa. Colonic sensitivity was evaluated by the visceromotor responses to colorectal distension. Functional involvement of CaV 3.2 channels was assessed with different pharmacological (TTA-A2, ABT-639, and ethosuximide) and genetic tools. KEY RESULTS: DSS induced low-grade inflammation associated with CHS in mice. Genetic or pharmacological inhibition of CaV 3.2 channels reduced CHS. Cav3.2 channel deletion in primary nociceptive neurons in dorsal root ganglia (CaV 3.2Nav1.8 KO mice) suppressed CHS. Spinal, but not systemic, administration of ABT-639, a peripherally acting T-type channel blocker, reduced CHS. ABT-639 given intrathecally to CaV 3.2Nav1.8 KO mice had no effect, demonstrating involvement of CaV 3.2 channels located presynaptically in afferent fibre terminals. Finally, ethosuximide, which is a T-type channel blocker used clinically, reduced CHS. CONCLUSIONS AND IMPLICATIONS: These results suggest that ethosuximide represents a promising drug reposition strategy and that inhibition of CaV 3.2 channels is an attractive therapeutic approach for relieving CHS in IBS or IBD.

5-HT2A receptor-dependent phosphorylation of mGlu2 receptor at Serine 843 promotes mGlu2 receptor-operated Gi/o signaling.

The serotonin 5-HT2A and glutamate mGlu2 receptors continue to attract particular attention, given their implication in psychosis associated with schizophrenia and the mechanism of action of atypical antipsychotics and a new class of antipsychotics, respectively. A large body of evidence indicates a functional crosstalk between both receptors in the brain, but the underlying mechanisms are not entirely elucidated. Here, we have explored the influence of 5-HT2A receptor upon the phosphorylation pattern of mGlu2 receptor in light of the importance of specific phosphorylation events in regulating G protein-coupled receptor signaling and physiological outcomes. Among the five mGlu2 receptor-phosphorylated residues identified in HEK-293 cells, the phosphorylation of Ser843 was enhanced upon mGlu2 receptor stimulation by the orthosteric agonist LY379268 only in cells co-expressing the 5-HT2A receptor. Likewise, administration of LY379268 increased mGlu2 receptor phosphorylation at Ser843 in prefrontal cortex of wild-type mice but not 5-HT2A-/- mice. Exposure of HEK-293 cells co-expressing mGlu2 and 5-HT2A receptors to 5-HT also increased Ser843 phosphorylation state to a magnitude similar to that measured in LY379268-treated cells. In both HEK-293 cells and prefrontal cortex, Ser843 phosphorylation elicited by 5-HT2A receptor stimulation was prevented by the mGlu2 receptor antagonist LY341495, while the LY379268-induced effect was abolished by the 5-HT2A receptor antagonist M100907. Mutation of Ser843 into alanine strongly reduced Gi/o signaling elicited by mGlu2 or 5-HT2A receptor stimulation in cells co-expressing both receptors. Collectively, these findings identify mGlu2 receptor phosphorylation at Ser843 as a key molecular event that underlies the functional crosstalk between both receptors.

The Low-Threshold Calcium Channel Cav3.2 Mediates Burst Firing of Mature Dentate Granule Cells.

Mature granule cells are poorly excitable neurons that were recently shown to fire action potentials, preferentially in bursts. It is believed that the particularly pronounced short-term facilitation of mossy fiber synapses makes granule cell bursting a very effective means of properly transferring information to CA3. However, the mechanism underlying the unique bursting behavior of mature granule cells is currently unknown. Here, we show that Cav3.2 T-type channels at the axon initial segment are responsible for burst firing of mature granule cells in rats and mice. Accordingly, Cav3.2 knockout mice fire tonic spikes and exhibit impaired bursting, synaptic plasticity and dentate-to-CA3 communication. The data show that Cav3.2 channels are strong modulators of bursting and can be considered a critical molecular switch that enables effective information transfer from mature granule cells to the CA3 pyramids.