The DRASIC cation channel contributes to the detection of cutaneous touch and acid stimuli in mice.

Cation channels in the DEG/ENaC family are proposed to detect cutaneous stimuli in mammals. We localized one such channel, DRASIC, in several different specialized sensory nerve endings of skin, suggesting it might participate in mechanosensation and/or acid-evoked nociception. Disrupting the mouse DRASIC gene altered sensory transduction in specific and distinct ways. Loss of DRASIC increased the sensitivity of mechanoreceptors detecting light touch, but it reduced the sensitivity of a mechanoreceptor responding to noxious pinch and decreased the response of acid- and noxious heat-sensitive nociceptors. The data suggest that DRASIC subunits participate in heteromultimeric channel complexes in sensory neurons. Moreover, in different cellular contexts, DRASIC may respond to mechanical stimuli or to low pH to mediate normal touch and pain sensation.

A Mouse Model of Chronic Pancreatitis Induced by an Alcohol and High Fat Diet.

BACKGROUND/AIMS: Study of acute pancreatitis in chemically-induced rodent models has provided useful data; models of alcoholic chronic pancreatitis have not been available in mice. The aim of the present study was to characterize a mouse model of chronic pancreatitis induced solely with an alcohol and high fat (AHF) diet. METHODS: Mice were fed a liquid high fat diet containing 6% alcohol as well as a high fat supplement (57% total dietary fat) over a period of five months or as control, normal chow ad libitum. Pain related measures utilized as an index of pain included mechanical sensitivity of the hind paws determined using von Frey filaments and a smooth/rough textured plate. A modified hotplate test contributed information about higher order behavioral responses to visceral hypersensitivity. Mice underwent mechanical and thermal testing both with and without pharmacological treatment with a peripherally restricted µ-opioid receptor agonist, loperamide. RESULTS: Mice on the AHF diet exhibited mechanical and heat hypersensitivity as well as fibrotic histology indicative of chronic pancreatitis. Low dose, peripherally restricted opiate loperamide attenuated both mechanical and heat hypersensitivity. CONCLUSION: Mice fed an alcohol and high fat diet develop histology consistent with chronic pancreatitis as well as opioid sensitive mechanical and heat hypersensitivity.

Inflammatory 'double hit' model of temporomandibular joint disorder with elevated CCL2, CXCL9, CXCL10, RANTES and behavioural hypersensitivity in TNFR1/R2-/- mice.

BACKGROUND: Patients with temporomandibular joint disorders (TMD), reactive arthritis and rheumatoid arthritis often have combined etiology of hereditary and microenvironmental factors contributing to joint pain. Multiple clinical and animal studies indicate 'double-hit' inflammatory insults can cause chronic inflammation. The first inflammatory insult primes the immune system and subsequent insults elicit amplified responses. The present 'double hit' study produced a chronic orofacial pain model in mice with genetic deletion of both TNFα receptors (TNFR1/R2-/-), investigating the main nociceptive signalling pathways in comparisons to wild type mice. METHODS: An initial inflammatory insult was given unilaterally into the temporomandibular joint (TMJ). Secondary hypersensitivity was tested on the skin over the TMJ throughout the experiment. Three weeks later after complete reversal of hypersensitivity, a second inflammatory insult was imposed on the colon. Pharmacological interventions were tested for efficacy after week 10 when hypersensitivity was chronic in TNFR1/R2-/- mice. Serum cytokines were analysed at Days 1, 14, and Week 18. RESULTS: The double hit insult produced chronic hypersensitivity continuing through the 4-month experimental timeline in the absence of TNFα signalling. P2X7 and NMDA receptor antagonists temporarily attenuated chronic hypersensitivity. Serum cytokine/chemokine analysis on Day 14 when CFA induced hypersensitivity was resolved identified increased levels of pro-inflammatory cytokines CCL2, CXCL9, CXCL10, RANTES and decreased levels of anti-inflammatory cytokines IL-1ra and IL-4 in TNFR1/R2-/- compared to WT mice. CONCLUSIONS: These data suggest a causal feed-forward signalling cascade of these little studied cytokines have the potential to cause recrudescence in this orofacial inflammatory pain model in the absence of TNFα signalling. SIGNIFICANCE: Using a mouse model of chronic inflammatory temporomandibular joint disorder, we determined that absence of functional TNFR1/R2 induces aberrant inflammatory signalling caused by other increased pro-inflammatory and decreased anti-inflammatory cytokines that could serve as blood biomarkers and may predict disease progression.

Transient receptor potential vanilloid 1-immunopositive neurons in the mouse are more prevalent within colon afferents compared to skin and muscle afferents.

Previous studies in our laboratories found that isolectin B(4)(IB(4))-positive polymodal nociceptors in the mouse do not express transient receptor potential vanilloid 1 (TRPV1), nor does deletion of TRPV1 compromise the ability of these afferents to detect thermal stimuli. Considering that IB(4)-positive afferents account for over 70% of cutaneous nociceptors and that 30-50% of all mouse primary afferents express TRPV1, it is highly likely that many TRPV1-positive fibers project to non-cutaneous structures. To investigate this issue, Alexa Fluor-conjugated wheat germ agglutinin (WGA) or IB(4) was injected into the nerves innervating quadriceps muscle (femoral) or hindlimb skin (saphenous) of male C57Bl/6 mice. Similarly, Alexa Fluor-conjugated cholera toxin-beta was injected subserosally into the distal colon. Spinal ganglia at the appropriate level (L2-3 for saphenous and femoral nerves; L6 for colon) were processed for TRPV1, calcitonin gene-related peptide (CGRP), neurofilament heavy chain (NHF) and IB(4) visualization and examined on a confocal microscope. Colon afferents contained the highest percentage of both TRPV1- and CGRP-positive neurons, followed by femoral (WGA) and saphenous afferents (WGA and IB(4)). In contrast, NHF staining was more prevalent among femoral afferents, followed by saphenous (WGA) and colon afferents. IB(4) binding was observed in very few colon or saphenous (WGA) afferents, with no femoral afferents binding or transporting IB(4). Considering that the largest percentages of TRPV1-positive neurons observed in this study were within visceral and muscle afferent populations (neurons that typically are not subject to noxious temperatures), these results suggest that TRPV1 may not function primarily as a temperature sensor but rather as a detector of protons, vanilloid compounds or through interactions with other membrane proteins.

Transdermal cannabidiol reduces inflammation and pain-related behaviours in a rat model of arthritis.

BACKGROUND: Current arthritis treatments often have side-effects attributable to active compounds as well as route of administration. Cannabidiol (CBD) attenuates inflammation and pain without side-effects, but CBD is hydrophobic and has poor oral bioavailability. Topical drug application avoids gastrointestinal administration, first pass metabolism, providing more constant plasma levels. METHODS: This study examined efficacy of transdermal CBD for reduction in inflammation and pain, assessing any adverse effects in a rat complete Freund's adjuvant-induced monoarthritic knee joint model. CBD gels (0.6, 3.1, 6.2 or 62.3 mg/day) were applied for 4 consecutive days after arthritis induction. Joint circumference and immune cell invasion in histological sections were measured to indicate level of inflammation. Paw withdrawal latency (PWL) in response to noxious heat stimulation determined nociceptive sensitization, and exploratory behaviour ascertained animal's activity level. RESULTS: Measurement of plasma CBD concentration provided by transdermal absorption revealed linearity with 0.6-6.2 mg/day doses. Transdermal CBD gel significantly reduced joint swelling, limb posture scores as a rating of spontaneous pain, immune cell infiltration and thickening of the synovial membrane in a dose-dependent manner. PWL recovered to near baseline level. Immunohistochemical analysis of spinal cord (CGRP, OX42) and dorsal root ganglia (TNFα) revealed dose-dependent reductions of pro-inflammatory biomarkers. Results showed 6.2 and 62 mg/day were effective doses. Exploratory behaviour was not altered by CBD indicating limited effect on higher brain function. CONCLUSIONS: These data indicate that topical CBD application has therapeutic potential for relief of arthritis pain-related behaviours and inflammation without evident side-effects.

Lack of neurotrophin-4 causes selective structural and chemical deficits in sympathetic ganglia and their preganglionic innervation.

Neurotrophin-4 (NT-4) is perhaps the still most enigmatic member of the neurotrophin family. We show here that NT-4 is expressed in neurons of paravertebral and prevertebral sympathetic ganglia, i.e., the superior cervical (SCG), stellate (SG), and celiac (CG) ganglion. Mice deficient for NT-4 showed a significant reduction (20-30%) of preganglionic sympathetic neurons in the intermediolateral column (IML) of the thoracic spinal cord. In contrast, neuron numbers in the SCG, SG, and CG were unchanged. Numbers of axons in the thoracic sympathetic trunk (TST) connecting the SG with lower paravertebral ganglia were also reduced, whereas axon numbers in the cervical sympathetic trunk (CST) were unaltered. Axon losses in the TST were paralleled by losses of synaptic terminals on SG neurons visualized by electron microscopy. Furthermore, immunoreactivity for the synaptic vesicle antigen SV2 was clearly reduced in the SG and CG. Levels of catecholamines and tyrosine hydroxylase immunoreactivity were dramatically reduced in the SG and the CG but not in the SCG. Despite this severe phenotype in the sympathetic system, blood pressure levels were not reduced and displayed a pattern more typical of deficits in baroreceptor afferents. Numbers of IML neurons were unaltered at postnatal day 4, suggesting a postnatal requirement for their maintenance. In light of these and previous data, we hypothesize that NT-4 provided by postganglionic sympathetic neurons is required for establishing and/or maintaining synapses of IML neurons on postganglionic cells. Impairment of synaptic connectivity may consequently reduce impulse flow, causing a reduction in transmitter synthesis in postganglionic neurons.

The sensory mechanotransduction ion channel ASIC2 (acid sensitive ion channel 2) is regulated by neurotrophin availability.

Almost all sensory neurons of the dorsal root ganglia have a mechanosensitive receptive field in the periphery. We have shown that the sensitivity to mechanical stimuli of a subset of sensory neurons that are slowly adapting mechanoreceptors (SAM) is strongly dependent on the availability of brain-derived neurotrophic factor (BDNF). Here we have investigated whether the ASIC2 sodium channel, recently shown by us to be necessary for normal SAM sensitivity, might be regulated by BDNF and thus partially account for the down-regulation of SAM sensitivity seen in BDNF deficient mice. We show that the mRNA for ASIC2 channels is reduced in the DRG of BDNF deficient mice indicating that BDNF might maintain its expression in vivo. We also made short-term cultures of sensory neurons from adult BDNF deficient mice and used a specific antibody to detect the presence of ASIC2 channels in different classes of sensory neurons. We observed that the channel protein was dramatically down-regulated selectively in medium and large diameter neurons and this expression could be rescued in a dose and time dependent manner by addition of BDNF to the culture (10-100 ng/ml). Drugs that block new transcription or protein synthesis also prevented the rescue effects of BDNF. We observed that ASIC2 channels were down-regulated in sensory neurons taken from neurotrophin-4 and neurotrophin-3 deficient mice; these effects might be due to a selective loss of neurons that normally express large amounts of ASIC2 channels. In summary, our data identify the ASIC2 channel as a target of BDNF signaling in vivo and suggest that the functional down-regulation of sensory mechanotransduction in BDNF deficient mice is in part due to loss of ASIC2 expression.

Deletion of P2X3 receptors blunts gastro-oesophageal sensation in mice.

Prior studies have demonstrated P2X receptor expression in the majority of nodose neurons. Immunoreactivity for P2X receptors has also been seen in putative gastric mechanoreceptors, the intraganglionic laminar endings. We therefore hypothesized that deletion of P2X3 receptors will blunt responses to gastric distension in vagal sensory neurons. Using wildtype and P2X3(-/-) mice, we examined responses to purinergic agonists in retrogradely labelled gastric sensory neurons with patch-clamp techniques. Activation of gastro-oesophageal neurons by fluid distension was studied with intracellular electrodes. Distension-evoked ATP release into the gastric lumen was determined with the luciferase assay and intake and gastric emptying of a solid meal was assessed. ATP triggered inward currents in 80% of gastric nodose neurons. In P2X3(-/-) mice, the peak current density was lower compared to controls. Ten of 14 controls but none of 30 neurons from P2X3(-/-) mice responded to alpha,beta-metATP. Gastro-oesophageal sensory neurons of P2X3(-/-) mice showed a blunted response to fluid distension of oesophagus and stomach. This difference was not explained by differences in distension-evoked ATP release, which did not differ between knockout mice and controls. Food intake during a 3-h period was lower in P2X3(-/-) mice. Gastric emptying of a solid meal was slightly faster in knockout mice after 1.5 h, but did not differ between groups at 3 h. Our data support a role of purinergic signalling in gastric vagal afferents. Considering the role of vagal input in sensations of fullness or nausea, P2X receptors may be interesting treatment targets for dyspeptic symptoms.

A digital three-dimensional atlas of the honeybee antennal lobe based on optical sections acquired by confocal microscopy.

We present a digital atlas of the glomeruli in the antennal lobe of the honeybee, Apis mellifera, accessible to the scientific community via the Internet. The atlas allows the identification of glomeruli in preparations in which the glomeruli can be recognized, be it in sections or in whole-mounts. The high resolution of the anatomical data upon which the atlas is based and its electronic form should prove to be an important tool for anyone involved in the study of the honeybee antennal lobe. Its accessibility via the Internet is a step towards interactive and freely accessible databases of animal brains.

The mammalian sodium channel BNC1 is required for normal touch sensation.

Of the vertebrate senses, touch is the least understood at the molecular level The ion channels that form the core of the mechanosensory complex and confer touch sensitivity remain unknown. However, the similarity of the brain sodium channel 1 (BNC1) to nematode proteins involved in mechanotransduction indicated that it might be a part of such a mechanosensor. Here we show that disrupting the mouse BNC1 gene markedly reduces the sensitivity of a specific component of mechanosensation: low-threshold rapidly adapting mechanoreceptors. In rodent hairy skin these mechanoreceptors are excited by hair movement. Consistent with this function, we found BNC1 in the lanceolate nerve endings that lie adjacent to and surround the hair follicle. Although BNC1 has been proposed to have a role in pH sensing, the acid-evoked current in cultured sensory neurons and the response of acid-stimulated nociceptors were normal in BNC1 null mice. These data identify the BNC1 channel as essential for the normal detection of light touch and indicate that BNC1 may be a central component of a mechanosensory complex.