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Background: Somatosensation depends on primary sensory neurons of the trigeminal and dorsal root ganglia (DRG). Transcriptional profiling of mouse DRG sensory neurons has defined at least 18 distinct neuronal cell types. Using an advillin promoter, we have generated a transgenic mouse line that only expresses diphtheria toxin A (DTA) in sensory neurons in the presence of Cre recombinase. This has allowed us to ablate specific neuronal subsets within the DRG using a range of established and novel Cre lines that encompass all sets of sensory neurons. Methods: A floxed-tdTomato-stop-DTA bacterial artificial chromosome (BAC) transgenic reporter line (AdvDTA) under the control of the mouse advillin DRG promoter was generated. The line was first validated using a Nav1.8Cre and then crossed to CGRPCreER (Calca), ThCreERT2, Tmem45bCre, Tmem233Cre, Ntng1Cre and TrkBCreER (Ntrk2) lines. Pain behavioural assays included Hargreaves’, hot plate, Randall-Selitto, cold plantar, partial sciatic nerve ligation and formalin tests. Results: Motor activity, as assessed by the rotarod test, was normal for all lines tested. Noxious mechanosensation was significantly reduced when either Nav1.8 positive neurons or Tmem45b positive neurons were ablated whilst acute heat pain was unaffected. In contrast, noxious mechanosensation was normal following ablation of CGRP-positive neurons but acute heat pain thresholds were significantly elevated and a reduction in nocifensive responses was observed in the second phase of the formalin test. Ablation of TrkB-positive neurons led to significant deficits in mechanical hypersensitivity in the partial sciatic nerve ligation neuropathic pain model. Conclusions: Ablation of specific DRG neuronal subsets using the AdvDTA line will be a useful resource for further functional characterization of somatosensory processing, neuro-immune interactions and chronic pain disorders.

Background: Sensory neurons play an essential role in almost all pain conditions, and have recently been classified into distinct subsets on the basis of their transcriptomes. Here we have analysed alterations in dorsal root ganglia (DRG) gene expression using microarrays in mouse models related to human chronic pain. Methods: Six different pain models were studied in male C57BL/6J mice: (1) bone cancer pain using cancer cell injection in the intramedullary space of the femur; (2) neuropathic pain using partial sciatic nerve ligation; (3) osteoarthritis pain using mechanical joint loading; (4) chemotherapy-induced pain with oxaliplatin; (5) chronic muscle pain using hyperalgesic priming; and (6) inflammatory pain using intraplantar complete Freund’s adjuvant. Microarray analyses were performed using RNA isolated from dorsal root ganglia and compared to sham/vehicle treated controls. Results: Differentially expressed genes (DEGs) were identified. Known and previously unreported genes were found to be dysregulated in each pain model. The transcriptomic profiles for each model were compared and expression profiles of DEGs within subsets of DRG neuronal populations were analysed to determine whether specific neuronal subsets could be linked to each of the pain models. Conclusions: Each pain model exhibits a unique set of altered transcripts implying distinct cellular responses to different painful stimuli. No simple direct link between genetically distinct sets of neurons and particular pain models could be discerned.

The voltage-gated sodium channel NaV1.7 plays a critical role in pain pathways. Besides action potential propagation, NaV1.7 regulates neurotransmitter release, integrates depolarizing inputs over long periods and regulates transcription. In order to better understand these functions, we generated an epitope-tagged NaV1.7 mouse that showed normal pain behavior. Analysis of NaV1.7 complexes affinity-purified under native conditions by mass spectrometry revealed 267 NaV1.7 associated proteins including known interactors, such as the sodium channel β3 subunit (Scn3b) and collapsin response mediator protein (Crmp2), and novel interactors. Selected novel NaV1.7 protein interactors membrane-trafficking protein synapototagmin-2 (Syt2), G protein-regulated inducer of neurite outgrowth 1 (Gprin1), L-type amino acid transporter 1 (Lat1) and transmembrane P24 trafficking protein 10 (Tmed10) together with Scn3b and Crmp2 were validated using co-immunoprecipitation and functional assays. The information provided with this physiologically normal epitope-tagged mouse should provide useful insights into the pain mechanisms associated with NaV1.7 channel function.

Loss of function of the gene SCN9A, encoding the voltage-gated sodium channel Na(v)1.7, causes a congenital inability to experience pain in humans. Here we show that Na(v)1.7 is not only necessary for pain sensation but is also an essential requirement for odour perception in both mice and humans. We examined human patients with loss-of-function mutations in SCN9A and show that they are unable to sense odours. To establish the essential role of Na(v)1.7 in odour perception, we generated conditional null mice in which Na(v)1.7 was removed from all olfactory sensory neurons. In the absence of Na(v)1.7, these neurons still produce odour-evoked action potentials but fail to initiate synaptic signalling from their axon terminals at the first synapse in the olfactory system. The mutant mice no longer display vital, odour-guided behaviours such as innate odour recognition and avoidance, short-term odour learning, and maternal pup retrieval. Our study creates a mouse model of congenital general anosmia and provides new strategies to explore the genetic basis of the human sense of smell.

Several members of the ADAM (a disintegrin and metalloprotease) family of proteins have been implicated in biological processes ranging from fertilization to myoblast fusion and neural cell fate determination. These proteins have so far been studied mostly in terms of their protease activity, but a considerable amount of evidence suggests that many ADAMs are also important as receptors for cell-surface integrins. We have shown that, for one such member of the family, ADAM23, mRNA transcripts are expressed in neuronal cells throughout the rat brain, at all stages of postnatal development, and that particularly high transcript concentrations are found in the hippocampus and cerebellum. Using an antibody that we raised against the rat ADAM23 disintegrin domain, we found that ADAM23 is present at detectable levels only in nervous system tissue. Our analysis of ADAM23 expression in cultured cerebellar granule cells (CGCs) furthermore suggested that this protein is synthesized as a glycosylated precursor of about 100 kD whose maturation depends on cleavage by furin or a related enzyme. We have also shown ADAM23 to be expressed primarily as a cell-surface protein that appears to be localized to sites of intercellular contact. Taken together, these data are consistent with a model wherein ADAM23 serves to mediate cell–cell interactions within the mammalian CNS. © 2004 Wiley-Liss, Inc.