Trigeminal Root Ganglia Research Articles

Bright light activates a trigeminal nociceptive pathway

Bright light can cause ocular discomfort and/or pain; however, the mechanism linking luminance to trigeminal nerve activity is not known. In this study we identify a novel reflex circuit necessary for bright light to excite nociceptive neurons in superficial laminae of trigeminal subnucleus caudalis (Vc/C1). Vc/C1 neurons encoded light intensity and displayed a long delay (>10s) for activation. Microinjection of lidocaine into the eye or trigeminal root ganglion (TRG) inhibited light responses completely, whereas topical application onto the ocular surface had no effect. These findings indicated that light-evoked Vc/C1 activity was mediated by an intraocular mechanism and transmission through the TRG. Disrupting local vasomotor activity by intraocular microinjection of the vasoconstrictive agents, norepinephrine or phenylephrine, blocked light-evoked neural activity, whereas ocular surface or intra-TRG microinjection of norepinephrine had no effect. Pupillary muscle activity did not contribute since light-evoked responses were not altered by atropine. Microinjection of lidocaine into the superior salivatory nucleus diminished light-evoked Vc/C1 activity and lacrimation suggesting that increased parasympathetic outflow was critical for light-evoked responses. The reflex circuit also required input through accessory visual pathways since both Vc/C1 activity and lacrimation were prevented by local blockade of the olivary pretectal nucleus. These findings support the hypothesis that bright light activates trigeminal nerve activity through an intraocular mechanism driven by a luminance-responsive circuit and increased parasympathetic outflow to the eye.

Does herpes zoster ophthalmicus increase the risk of stroke?

Varicella zoster virus (VZV), a ubiquitous human herpesvirus, causes chicken pox on primary infection and then establishes lifelong latency in all cranial nerve, dorsal root, and autonomic ganglia. When VZV-specific cell-mediated immunity declines, such as in elderly and immunocompromised individuals, virus reactivates in one or more ganglia and typically travels peripherally to cause herpes zoster in the corresponding dermatomes. Herpes zoster can be complicated by stroke and has been described clinically as VZV vasculopathy, granulomatous angiitis, post varicella arteriopathy, and herpes zoster ophthalmicus (HZO) with delayed contralateral hemiparesis. The likely mechanism for stroke caused by VZV is direct viral infection of cerebral arteries. This assertion is supported by animal studies identifying afferent fibers from trigeminal and dorsal root ganglia to both intracranial and extracranial blood vessels, providing an anatomic pathway for spread of the virus,1,2 and observations of viral particles, antigens, and DNA in affected arterial vessels in VZV vasculopathy cases.3,4 Several studies have examined varicella and the risk of stroke in children,5,6 but large studies in the adult population regarding the frequency and risk of …

Inwardly rectifying potassium channel Kir4.1 is responsible for the native inward potassium conductance of satellite glial cells in sensory ganglia

Satellite glial cells (SGCs) surround primary afferent neurons in sensory ganglia, and increasing evidence has implicated the K + channels of SGCs in affecting or regulating sensory ganglion excitability. The inwardly rectifying K + (Kir) channel Kir4.1 is highly expressed in several types of glial cells in the central nervous system (CNS) where it has been implicated in extracellular K + concentration buffering. Upon neuronal activity, the extracellular K + concentration increases, and if not corrected, causes neuronal depolarization and uncontrolled changes in neuronal excitability. Recently, it has been demonstrated that knockdown of Kir4.1 expression in trigeminal ganglia leads to neuronal hyperexcitability in this ganglia and heightened nociception. Thus, we investigated the contribution of Kir4.1 to the membrane K + conductance of SGCs in neonatal and adult mouse trigeminal and dorsal root ganglia. Whole cell patch clamp recordings were performed in conjunction with immunocytochemistry and quantitative transcript analysis in various mouse lines. We found that in wild-type mice, the inward K + conductance of SGCs is blocked almost completely with extracellular barium, cesium and desipramine, consistent with a conductance mediated by Kir channels. We then utilized mouse lines in which genetic ablation led to partial or complete loss of Kir4.1 expression to assess the role of this channel subunit in SGCs. The inward K + currents of SGCs in Kir4.1+/− mice were decreased by about half while these currents were almost completely absent in Kir4.1−/− mice. These findings in combination with previous reports support the notion that Kir4.1 is the principal Kir channel type in SGCs. Therefore Kir4.1 emerges as a key regulator of SGC function and possibly neuronal excitability in sensory ganglia.

Molecular Identification of Rapidly Adapting Mechanoreceptors and Their Developmental Dependence on Ret Signaling

In mammals, the first step in the perception of form and texture is the activation of trigeminal or dorsal root ganglion (DRG) mechanosensory neurons, which are classified as either rapidly (RA) or slowly adapting (SA) according to their rates of adaptation to sustained stimuli. The molecular identities and mechanisms of development of RA and SA mechanoreceptors are largely unknown. We found that the "early Ret(+)" DRG neurons are RA mechanoreceptors, which form Meissner corpuscles, Pacinian corpuscles, and longitudinal lanceolate endings. The central projections of these RA mechanoreceptors innervate layers III through V of the spinal cord and terminate within discrete subdomains of the dorsal column nuclei. Moreover, mice lacking Ret signaling components are devoid of Pacinian corpuscles and exhibit a dramatic disruption of RA mechanoreceptor projections to both the spinal cord and medulla. Thus, the early Ret(+) neurons are RA mechanoreceptors and Ret signaling is required for the assembly of neural circuits underlying touch perception.

Ablation of TrpV1 neurons reveals their selective role in thermal pain sensation

Here we make use of neural ablation to investigate the properties of the TrpV1-expressing neurons in the trigeminal and dorsal root ganglia of mice. Resiniferotoxin (RTX), a potent TrpV1 agonist, administered either by direct injection in the ganglion or intrathecally killed approximately 70% of TrpV1 cells and resulted in modest thermal analgesia. Interestingly, after carageenan injection in the hind paw, the analgesic effects of RTX were dramatically increased with mice now paradoxically showing far less response to heat applied at sites of inflammation. This additional carageenan and RTX-induced analgesia was transient, lasting less than 2 days, and likely resulted from deafferentation of remaining TrpV1 neurons. Remarkably, although RTX affected sensitivity to heat, mechanical sensitivity (both of normal and inflamed tissue) was completely unaltered by toxin-mediated silencing of the TrpV1 sensory input. Thus, our data demonstrate that TrpV1 neurons are selectively tuned nociceptors that mediate responses to thermal but not mechanical pain and insinuate a labeled line model for somatosensory coding.

Hyperpolarization-activated cyclic-nucleotide gated 4 (HCN4) protein is expressed in a subset of rat dorsal root and trigeminal ganglion neurons

Hyperpolarization-activated cyclic nucleotide-gated (HCN) cation channels are active at resting membrane potential and thus are likely to contribute to neuronal excitability. Four HCN channel subunits (HCN1-4) have previously been cloned. The aim of the current study was to investigate the immunoreactivity of HCN4 channel protein in rat trigeminal (TG) and dorsal root ganglion (DRG) sensory neurons. HCN4 was present in 9% of TG neurons and 4.7% of DRG neurons, it was distributed in a discrete population of small-diameter neurons in the TG but was located in cells of all sizes in the DRG. Approximately two thirds of HCN4-containing neurons in each ganglia were labelled with antisera raised against the 200-kDa neurofilament (NF200). The remaining HCN4-containing neurons were NF200-negative, were not labelled with antisera raised against calcitonin-gene related peptide (CGRP), and did not bind the isolectin B4 (IB4). HCN4-containing neurons made up more than half of the population of small-diameter primary afferent neurons that did not contain either NF200 or CGRP or bind IB4 in both TG and DRG. This population was not insignificant, comprising 5% of TG neurons and 2% of DRG neurons.

Dopamine D2 receptor mRNA expression is increased in the jugular-nodose ganglia of rats with nitrogen dioxide-induced chronic bronchitis

The bronchodilatatory effect of inhaled dopamine or dopamine D2 receptor agonists in cases of bronchial constriction may involve the suppression of pathologically increased airway sensory nerve activity. The aim of this study is to investigate the regulation of the dopamine D2 receptor mRNA expression in the ganglia of rats with nitrogen dioxide-induced chronic bronchitis compared with that in ganglia of healthy control animals. Rats were exposed to nitrogen dioxide (10ppm, 20d) and dopamine D2 receptor mRNA levels in sensory ganglia (jugular-nodose, trigeminal, cervical dorsal root and thoracic dorsal root ganglia) were examined by quantitative real-time polymerase chain reaction and compared to control tissues. Whereas for trigeminal and dorsal root ganglia the dopamine D2 receptor expression levels showed no difference between both animal groups, there was a significant (p<0.05) increase in the jugular-nodose ganglia with a 2.1-fold factor. The increase of dopamine D2 receptor mRNA in jugular-nodose sensory neurons which innervate the airways may represent a neurochemical basis for the effects seen in man and animal models following topical administration of dopamine or dopamine agonists onto the respiratory epithelium.

Latency-Associated Transcript (LAT) Exon 1 Controls Herpes Simplex Virus Species-Specific Phenotypes: Reactivation in the Guinea Pig Genital Model and Neuron Subtype-Specific Latent Expression of LAT

Herpes simplex virus 1 (HSV-1) and HSV-2 cause similar acute infections but differ in their abilities to reactivate from trigeminal and lumbosacral dorsal root ganglia. During latency, HSV-1 and HSV-2 also preferentially express their latency-associated transcripts (LATs) in different sensory neuronal subtypes that are positive for A5 and KH10 markers, respectively. Chimeric virus studies showed that LAT region sequences influence both of these viral species-specific phenotypes. To further map the LAT region sequences responsible for these phenotypes, we constructed the chimeric virus HSV2-LAT-E1, in which exon 1 (from the LAT TATA to the intron splice site) was replaced by the corresponding sequence from HSV-1 LAT. In intravaginally infected guinea pigs, HSV2-LAT-E1 reactivated inefficiently relative to the efficiency of its rescuant and wild-type HSV-2, but it yielded similar levels of viral DNA, LAT, and ICP0 during acute and latent infection. HSV2-LAT-E1 preferentially expressed the LAT in A5+ neurons (as does HSV-1), while the chimeric viruses HSV2-LAT-P1 (LAT promoter swap) and HSV2-LAT-S1 (LAT sequence swap downstream of the promoter) exhibited neuron subtype-specific latent LAT expression phenotypes more similar to that of HSV-2 than that of HSV-1. Rescuant viruses displayed the wild-type HSV-2 phenotypes of efficient reactivation in the guinea pig genital model and a tendency to express LAT in KH10+ neurons. The region that is critical for HSV species-specific differences in latency and reactivation thus lies between the LAT TATA and the intron splice site, and minor differences in the 5' ends of chimeric sequences in HSV2-LAT-E1 and HSV2-LAT-S1 point to sequences immediately downstream of the LAT TATA.

Involvement of NMDA receptor in nociceptive effects elicited by intrathecal [Tyr 6] γ2-MSH(6-12), and the interaction with nociceptin/orphanin FQ in pain modulation in mice

The mas-related genes (Mrgs, also known as sensory neuron-specific receptors, SNSRs) are specifically expressed in small diameter sensory neurons in the trigeminal and dorsal root ganglia, suggesting an important role of the receptors in pain transmission. The present study aimed to investigate the underlying mechanism of the nociceptive effects after activation of MrgC, and the interaction between MrgC and N/OFQ–NOP receptor system in modulation of nociception in mice. Intrathecal (i.t.) administration of [Tyr 6] γ2-MSH(6-12), the most potent agonist for MrgC receptor, produced a significant hyperalgesic response as assayed by tail withdrawal test and a series of characteristic nociceptive responses, including biting, licking and scratching, in a dose-dependent manner (0.01–10 pmol and 0.01–10 nmol, respectively) in mice. These pronociceptive effects induced by [Tyr 6] γ2-MSH(6-12) were inhibited dose-dependently by co-injection of competitive NMDA receptor antagonist D-APV, non-competitive NMDA receptor antagonist MK-801, and nitric oxide (NO) synthase inhibitor L-NAME. However, the tachykinin NK 1 receptor antagonist L-703,606, and tachykinin NK 2 receptor antagonist MEN-10,376, had no influence on pronociceptive effects elicited by [Tyr 6] γ2-MSH(6-12). In other groups, [Tyr 6] γ2-MSH(6-12)-induced nociceptive responses were bidirectionally regulated by the co-injection of N/OFQ. N/OFQ inhibited nociceptive responses at high doses (0.01–1 nmol), but potentiated the behaviors at low doses (1 fmol–3 pmol). Furthermore, both hyperalgesia and nociceptive responses were enhanced after the co-administration with NOP receptor antagonist [Nphe 1]N/OFQ(1-13)-NH 2. These results suggest that intrathecal [Tyr 6] γ2-MSH(6-12)-induced pronociceptive effects may be mediated through NMDA receptor–NO system in the spinal cord, and demonstrate the interaction between MrgC and N/OFQ–NOP receptor system in pain transmission.

Identification and functional characterization of the promoter of the mouse sodium‐activated sodium channel Nax gene (Scn7a)

Na(x) is a sodium channel, thought to be a descendant of the voltage-gated sodium channel family. Nevertheless, Na(x) is not activated by voltage but rather by augmentation of extracellular sodium over 150 mM. In the brain, it is localized to the circumventricular organs, important regions for salt and water homeostasis in mammals, where it operates as a sodium-level sensor of body fluid. Na(x) channel is expressed in lung, uterus, and heart, and it is also found in trigeminal and dorsal root ganglia and in nonmyelinating Schwann cells, where its physiological role remains unclarified. Here we identified the promoter and transcription start sites of Na(x) sodium channel in dorsal root ganglia neurons from mouse. We report a characterization of the basal TATA-less promoter and the sequence requirements for promoter activity in Neuro 2A neuroblastoma cells and in dorsal root ganglia neurons, where basal promoter activity seems to require NGFI-C and Ebox DNA elements. Finally, we provide evidence that a repression mechanism that inhibits Na(x) expression may be present in certain tissues. These findings provide the basis with which to understand tissue-specific regulation of Na(x) sodium channel gene (Scn7a) expression.

A central role for Islet1 in sensory neuron development linking sensory and spinal gene regulatory programs

We have used conditional knockout strategies in mice to determine the developmental events and gene expression program regulated by the LIM-homeodomain factor Islet1 in developing sensory neurons. Early development of the trigeminal and dorsal root ganglia are grossly normal in the absence of Islet1. However, from E12.5 onward, Islet1 mutant embryos exhibit loss of the nociceptive markers TrkA and Runx1 and a near absence of cutaneous innervation. Proprioceptive neurons characterized by the expression of TrkC/Runx3/Etv1 are relatively spared. Microarray analysis of Islet1 mutant ganglia reveals prolonged expression of developmental regulators normally restricted to early sensory neurogenesis, and ectopic expression of transcription factors normally found in the CNS but not in sensory ganglia. Later excision of Islet1 does not reactivate early genes, but results in decreased expression of transcripts related to specific sensory functions. Together these results establish a central role for Islet1 in the transition from sensory neurogenesis to subtype specification.

Central projections of the sensory innervation of the rat middle meningeal artery

Headaches, especially migraine, involve not only pain but also aspects such as vasodilation of cranial vessels and sensitization of nerve endings, processes dependent on and connected to the central nervous system. To understand pathogenic mechanisms of headache, it is important to elucidate the central projections of sensory nerves that innervate cranial vessels, of which the middle meningeal artery (MMA) is the largest artery supplying the dura mater. In this study, cholera toxin subunit b (CTb) or wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) was applied on the adventitia of MMA. After perfusion fixation, the brainstem, the C1–C4 spinal segments and the trigeminal and C2 dorsal root ganglia were removed and sections from these tissues were processed to visualize transported tracers. Labeled cell bodies were seen ipsilaterally in the trigeminal and C2 dorsal root ganglia. Labeled nerve terminations were found ipsilaterally in the lateral part of the spinal dorsal horn of segments C1–C3 and in the caudal and interpolar parts of the spinal trigeminal nucleus. WGA-HRP labeled terminations were mainly located in laminae I and II, whereas CTb labeled terminations located in laminae III–V. These results indicate that sensory information from the MMA is transmitted through both trigeminal and cervical spinal nerve branches to a region in the central nervous system extending rostrally from the C3 dorsal horn to the interpolar part of the spinal trigeminal nucleus. Our data further substantiates that the sensory innervation of the MMA, in addition to putative nociceptive afferents, include a population of large caliber afferents with an as yet unclear but presumably non-nociceptive role.

Mechanisms of Compartmentalized Expression of Mrg Class G-Protein-Coupled Sensory Receptors

Mrg class G-protein-coupled receptors (GPCRs) are expressed exclusively in sensory neurons in the trigeminal and dorsal root ganglia. Pharmacological activation of Mrg proteins is capable of modulating sensory neuron activities and elicits nociceptive effects. In this study, we illustrate a control mechanism that allows the Runx1 runt domain transcription factor to generate compartmentalized expression of these sensory GPCRs. Expression of MrgA, MrgB, and MrgC subclasses is confined to an "A/B/C" neuronal compartment that expresses Runx1 transiently (or does not express Runx1), whereas MrgD expression is restricted to a "D" compartment with persistent Runx1 expression. Runx1 is initially required for the expression of all Mrg genes. However, during late development Runx1 becomes a repressor for MrgA/B/C genes. As a result, MrgA/B/C expression persists only in the Runx1- "A/B/C" compartment. In delta446 mice, in which Runx1 lacks the C-terminal repression domain, expression of MrgA/B/C genes is dramatically expanded into the Runx1+ "D" compartment. MrgD expression, however, is resistant to Runx1-mediated repression in the "D" compartment. Therefore, the creation of Runx1+ and Runx1- compartments, in conjunction with different responses of Mrg genes to Runx1-mediated repression, results in the compartmentalized expression of MrgA/B/C versus MrgD genes. Within the MrgA/B/C compartment, MrgB4-expressing neurons innervate exclusively the hairy skin. Here we found that Smad4, a downstream component of bone morphological protein-mediated signaling, is required selectively for the expression of MrgB4. Our study suggests a new line of evidence that specification of sensory subtypes is established progressively during perinatal and postnatal development.

Mouse G-protein gamma3 expression in the developing CNS and neural crest cell derivatives

Heterotrimeric G-protein signaling, involving alpha, beta and gamma subunits, plays a number of roles in differentiation and development. Individual gamma subunits interact with a beta subunit and as a heterodimer, is responsible for modulating many G protein-mediated cellular responses. The 12 gamma subunits in mammals have highly variable distribution and expression patterns in adult tissues. gamma3 is abundantly and widely expressed in the brain and when its expression is knocked-out, the mice show increased susceptibility to seizures, reduced body weights and decreased adiposity compared to the wild-type littermates (Schwindinger et al., 2004). Recent evidence has shown the Gng3 gene being strongly induced in activated CD4+ T-cells (Dubeykovskiy et al., 2006) and its involvement in the developing mammalian enteric nervous system (Heanue and Pachnis, 2006). Given this diversity in expression and interest in finding models of human disease, and to extend our previous investigation with zebrafish gamma3 (Kelly et al., 2001), we undertook an analysis to report the temporal and spatial expression patterns of gamma3 mRNA during mouse embryogenesis. Analysis reveals that gamma3 transcripts were first expressed in mid-late embryonic stages. Specifically, signals were predominant in the CNS and in neural crest cell derivatives including but not limited to the trigeminal and dorsal root (spinal) ganglia, and in cells of the adrenal medulla. These data indicate that G protein coupled signaling involving gamma3 participates in a number of physiological roles, not only in the CNS, but also in numerous cells derived from the neural crest.

Expression of the Lingo/LERN gene family during mouse embryogenesis

We have analysed the expression during mouse development of the four member Lingo/ LERN gene family which encodes type 1 transmembrane proteins containing 12 extracellular leucine rich repeats, an immunoglobulin C2 domain and a short intracellular tail. Each family member has a distinct pattern of expression in the mouse embryo as is the case for the related NLRR, FLRT and LRRTM gene families. Lingo1/LERN1 is expressed in the developing trigeminal, facio-acoustic and dorsal root ganglia. An interesting expression pattern is also observed in the somites with expression localising to the inner surface of the dermomyotome in the ventro-caudal lip. Further expression is seen in lateral cells of the hindbrain and midbrain, lateral cells in the motor horn of the neural tube, the otic vesicle epithelium and epithelium associated with the developing gut. Lingo3/ LERN2 is expressed in a broad but specific pattern in many tissues across the embryo. Lingo2/LERN3 is seen in a population of cells lying adjacent to the epithelial lining of the olfactory pit while Lingo4/LERN4 is expressed in the neural tube in a subset of progenitors adjacent to the motor neurons. Expression of all Lingo/ LERN genes increases as the embryo develops but is low in the adult with only Lingo1/LERN1 and Lingo2/LERN3 being detectable in adult brain.

Diverse Herpes Simplex Virus Type 1 Thymidine Kinase Mutants in Individual Human Neurons and Ganglia

Mutations in the thymidine kinase gene (tk) of herpes simplex virus type 1 (HSV-1) explain most cases of virus resistance to acyclovir (ACV) treatment. Mucocutaneous lesions of patients with ACV resistance contain mixed populations of tk mutant and wild-type virus. However, it is unknown whether human ganglia also contain mixed populations since the replication of HSV tk mutants in animal neurons is impaired. Here we report the detection of mutated HSV tk sequences in human ganglia. Trigeminal and dorsal root ganglia were obtained at autopsy from an immunocompromised woman with chronic mucocutaneous infection with ACV-resistant HSV-1. The HSV-1 tk open reading frames from ganglia were amplified by PCR, cloned, and sequenced. tk mutations were detected in a seven-G homopolymer region in 11 of 12 ganglia tested, with clonal frequencies ranging from 4.2 to 76% HSV-1 tk mutants per ganglion. In 8 of 11 ganglia, the mutations were heterogeneous, varying from a deletion of one G to an insertion of one to three G residues, with the two-G insertion being the most common. Each ganglion had its own pattern of mutant populations. When individual neurons from one ganglion were analyzed by laser capture microdissection and PCR, 6 of 14 HSV-1-positive neurons were coinfected with HSV tk mutants and wild-type virus, 4 of 14 were infected with wild-type virus alone, and 4 of 14 were infected with tk mutant virus alone. These data suggest that diverse tk mutants arise independently under drug selection and establish latency in human sensory ganglia alone or together with wild-type virus.

Effects of static magnetic fields on the voltage-gated potassium channel currents in trigeminal root ganglion neurons

To evaluated the effects of moderate-intensity static magnetic fields (SMF) on two types of voltage-gated potassium channel (VGPC) currents: I K,A and I K,V, whole-cell patch-clamp experiments were conducted on acute dissociated rat trigeminal root ganglion (TRG) neurons. The results demonstrated that 125 mT SMF could influence the inactivation kinetics of these two VGPC currents by altering the inactivation rate and velocity. No significant change was observed in the activation properties. These findings supported the hypothesis that biological membrane would be deformed in moderate-intensity SMF and the physiological characteristics of ion channels on the membrane would be influenced. The mechanism underlying the different effects of SMF on the I K,A and I K,V inactivation was also discussed.

Herpes Simplex Virus Type 2 (HSV-2) Establishes Latent Infection in a Different Population of Ganglionic Neurons than HSV-1: Role of Latency-Associated Transcripts

Herpes simplex virus type 1 (HSV-1) and HSV-2 cause very similar acute infections but differ in their abilities to reactivate from trigeminal and dorsal root ganglia. To investigate differences in patterns of viral infection, we colabeled murine sensory ganglia for evidence of HSV infection and for the sensory neuron marker A5 or KH10. During acute infection, 7 to 10% of HSV-1 or HSV-2 antigen-positive neurons were A5 positive and 13 to 16% were KH10 positive, suggesting that both viruses reach each type of neuron in a manner proportional to their representation in uninfected ganglia. In murine trigeminal ganglia harvested during HSV latency, 25% of HSV-1 latency-associated transcript (LAT)- and 4% of HSV-2 LAT-expressing neurons were A5 positive, while 12% of HSV-1 LAT- and 42% of HSV-2 LAT-expressing neurons were KH10 positive. A similar difference was observed in murine dorsal root ganglia. These differences could not be attributed to differences in LAT expression levels in A5- versus KH10-positive neurons. Thus, HSV-1 demonstrated a preference for the establishment of latency in A5-positive neurons, while HSV-2 demonstrated a preference for the establishment of latency in KH10-positive neurons. A chimeric HSV-2 mutant that expresses the HSV-1 LAT exhibited an HSV-1 phenotype, preferentially establishing latency in A5-positive neurons. These data imply that the HSV-1 and HSV-2 LAT regions influence the ability of virus to establish latency in different neuronal subtypes. That the same chimeric virus has a characteristic HSV-1 reactivation phenotype further suggests that LAT-influenced establishment of latency in specific neuronal subtypes could be an important part of the mechanism by which LAT influences viral reactivation phenotypes.

Critical Evaluation of the Colocalization Between Calcitonin Gene-Related Peptide, Substance P, Transient Receptor Potential Vanilloid Subfamily Type 1 Immunoreactivities, and Isolectin B4 Binding in Primary Afferent Neurons of the Rat and Mouse

Calcitonin gene-related peptide (CGRP) and/or substance P (SP) immunoreactivity as well as isolectin B(4) (IB(4)) binding are commonly used to define peptidergic and non-peptidergic nociceptor populations, respectively. Although this demarcation is well supported in the mouse, there is accumulating evidence to suggest it is not so in the rat. Hence, this investigation was undertaken to evaluate and quantify the colocalization of the neuropeptides CGRP and SP with IB(4) binding sites and the transient receptor potential vanilloid subfamily type 1 (TRPV1) channel and to compare this colocalization between trigeminal (TG) and dorsal root ganglia (DRG) in adult rats. These findings illustrate that there is a substantial overlap ( approximately 45% in the DRG and approximately 30% in the TG) between peptidergic neurons (ie, CGRP- and SP-expressing) and neurons that bind IB(4) in rat sensory ganglia. However, there were also significant differences in the colocalization of these markers between the DRG and TG. For instance, in the DRG, significantly more CGRP-immunoreactive neurons also expressed IB(4) binding sites (44.5%) compared with the TG (27.5%). In contrast, significantly fewer CGRP-immunoreactive neurons in the DRG colocalized TRPV1 immunoreactivity (49.2%) compared with the TG (70%). Moreover, we directly assessed the colocalization of CGRP and IB(4) in the TG of rats and mice using a CGRP antibody that recognizes this peptide in both species. Thus, whereas only an approximately 10% overlap was observed in TG neurons of mouse, significantly greater overlap (approximately 35%) was observed in those of rat. These data indicate that in adult rat sensory ganglia, there is not a clear distinction between the peptidergic and non-peptidergic nociceptor subclasses as a function of IB(4) binding. Furthermore, there are significant differences between the TG and DRG in the degree to which commonly utilized nociceptive neuronal markers are co-expressed. Taken together, the present findings dictate prudence when extrapolating experimental conclusions about the neurochemical classification of neurons between sensory ganglia or between species, including humans.

Functional analysis of the α-neurotoxin, BmαTX14, derived from the Chinese scorpion, Buthus martensii Karsch

The gene encoding the BmalphaTX14 (alpha-neurotoxin TX14) protein, derived from the cDNA library of the Chinese scorpion Buthus martensii Karsch, was expressed in Pichia pastoris. The recombinant protein was purified by metal chelate affinity chromatography and gel filtration chromatography. Using patch-clamp technique, electrophysiological activity of rBmalphaTX14 was identified. In the neurons isolated from mice trigeminal root ganglion, the Na+ current amplitude was reduced by 80% under whole cell patch-clamp recording. There were no apparent modifications to the gating mechanism in the presence of rBmalphaTX14. Although BmalphaTX14 shared a high amino acid sequence similarity with other typical alpha-toxins, it has different effects on neurons. Further electrophysiological analysis suggested that rBmalphaTX14 selectively blocked Na+ channels and is a member of a new group of scorpion toxins.