Environmental cold exposure increases blood flow and affects pain sensitivity in the knee joints of CFA-induced arthritic mice in a TRPA1-dependent manner

BACKGROUND: The effect of cold temperature on arthritis symptoms is unclear. The aim of this study was to investigate how environmental cold affects pain and blood flow in mono-arthritic mice, and examine a role for transient receptor potential ankyrin 1 (TRPA1), a ligand-gated cation channel that can act as a cold sensor. METHODS: Mono-arthritis was induced by unilateral intra-articular injection of complete Freund’s adjuvant (CFA) in CD1 mice, and in mice either lacking TRPA1 (TRPA1 KO) or respective wildtypes (WT). Two weeks later, nociception and joint blood flow were measured following exposure to 10 °C (1 h) or room temperature (RT). Primary mechanical hyperalgesia in the knee was measured by pressure application apparatus; secondary mechanical hyperalgesia by automated von Frey system; thermal hyperalgesia by Hargreaves technique, and weight bearing by the incapacitance test. Joint blood flow was recorded by full-field laser perfusion imager (FLPI) and using clearance of (99m)Technetium. Blood flow was assessed after pretreatment with antagonists of either TRPA1 (HC-030031), substance P neurokinin 1 (NK(1)) receptors (SR140333) or calcitonin gene-related peptide (CGRP) (CGRP(8–37)). TRPA1, TAC-1 and CGRP mRNA levels were examined in dorsal root ganglia, synovial membrane and patellar cartilage samples. RESULTS: Cold exposure caused bilateral primary mechanical hyperalgesia 2 weeks after CFA injection, in a TRPA1-dependent manner. In animals maintained at RT, clearance techniques and FLPI showed that CFA-treated joints exhibited lower blood flow than saline-treated joints. In cold-exposed animals, this reduction in blood flow disappears, and increased blood flow in the CFA-treated joint is observed using FLPI. Cold-induced increased blood flow in CFA-treated joints was blocked by HC-030031 and not observed in TRPA1 KOs. Cold exposure increased TRPA1 mRNA levels in patellar cartilage, whilst reducing it in synovial membranes from CFA-treated joints. CONCLUSIONS: We provide evidence that environmental cold exposure enhances pain and increases blood flow in a mono-arthritis model. These changes are dependent on TRPA1. Thus, TRPA1 may act locally within the joint to influence blood flow via sensory nerves, in addition to its established nociceptive actions

Neuronal circuitry for pain processing in the dorsal horn

Neurons in the spinal dorsal horn process sensory information, which is then transmitted to several brain regions, including those responsible for pain perception. The dorsal horn provides numerous potential targets for the development of novel analgesics and is thought to undergo changes that contribute to the exaggerated pain felt after nerve injury and inflammation. Despite its obvious importance, we still know little about the neuronal circuits that process sensory information, mainly because of the heterogeneity of the various neuronal components that make up these circuits. Recent studies have begun to shed light on the neuronal organization and circuitry of this complex region

Extensive Neuronal Differentiation of Human Neural Stem Cell Grafts in Adult Rat Spinal Cord

BACKGROUND: Effective treatments for degenerative and traumatic diseases of the nervous system are not currently available. The support or replacement of injured neurons with neural grafts, already an established approach in experimental therapeutics, has been recently invigorated with the addition of neural and embryonic stem-derived precursors as inexhaustible, self-propagating alternatives to fetal tissues. The adult spinal cord, i.e., the site of common devastating injuries and motor neuron disease, has been an especially challenging target for stem cell therapies. In most cases, neural stem cell (NSC) transplants have shown either poor differentiation or a preferential choice of glial lineages. METHODS AND FINDINGS: In the present investigation, we grafted NSCs from human fetal spinal cord grown in monolayer into the lumbar cord of normal or injured adult nude rats and observed large-scale differentiation of these cells into neurons that formed axons and synapses and established extensive contacts with host motor neurons. Spinal cord microenvironment appeared to influence fate choice, with centrally located cells taking on a predominant neuronal path, and cells located under the pia membrane persisting as NSCs or presenting with astrocytic phenotypes. Slightly fewer than one-tenth of grafted neurons differentiated into oligodendrocytes. The presence of lesions increased the frequency of astrocytic phenotypes in the white matter. CONCLUSIONS: NSC grafts can show substantial neuronal differentiation in the normal and injured adult spinal cord with good potential of integration into host neural circuits. In view of recent similar findings from other laboratories, the extent of neuronal differentiation observed here disputes the notion of a spinal cord that is constitutively unfavorable to neuronal repair. Restoration of spinal cord circuitry in traumatic and degenerative diseases may be more realistic than previously thought, although major challenges remain, especially with respect to the establishment of neuromuscular connections

P2Y receptors and pain transmission

It is widely accepted that the most important ATP receptors involved in pain transmission belong to the P2X3 and P2X2/3 subtypes, selectively expressed in small diameter dorsal root ganglion (DRG) neurons. However, several types of the metabotropic ATP (P2Y) receptors have also been found in primary afferent neurons; P2Y1 and P2Y2 receptors are typically expressed in small, nociceptive cells. Here we review the results available on the involvement of P2Y receptors in the modulation of pain transmission

Repeated administration of the GABAB receptor positive modulator BHF177 decreased nicotine self-administration, and acute administration decreased cue-induced reinstatement of nicotine seeking in rats

Abstract: Rationale $\gamma$-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain and is implicated in the modulation of central reward processes. Acute or chronic administration of GABA$_B$ receptor agonists or positive modulators decreased self-administration of various drugs of abuse. Furthermore, GABA$_B$ receptor agonists inhibited cue-induced reinstatement of nicotine- and cocaine-seeking behavior. Because of their fewer adverse side effects compared with GABA$_B$ receptor agonists, GABA$_B$ receptor positive modulators are potentially improved therapeutic compounds for the treatment of drug dependence compared with agonists. Objectives and methods: We examined whether the acute effects of the GABA$_B$ receptor positive modulator N-[(1R,2R,4S)-bicyclo[2.2.1]hept-2-yl]-2-methyl-5-[4-(trifluoromethyl)phenyl]-4-pyrimidinamine (BHF177) on nicotine self- administration and food-maintained responding under a fixed-ratio 5 schedule of reinforcement were maintained after repeated administration. The effects of acute BHF177 administration on cue-induced nicotine- and food-seeking behavior, a putative animal model of relapse, were also examined. Results: Repeated administration of BHF177 for 14 days decreased nicotine self-administration, with small tolerance observed during the last 7 days of treatment, whereas BHF177 minimally affected food-maintained responding. Acute BHF177 administration dose-dependently blocked cue-induced reinstatement of nicotine-, but not food-, seeking behavior after a 10-day extinction period. Conclusions: These results showed that BHF177 selectively blocked nicotine self-administration and prevented cueinduced reinstatement of nicotine seeking, with minimal effects on responding for food and no effect on cue-induced reinstatement of food seeking. Thus, GABA$_B$ receptor positive modulators could be useful therapeutics for the treatment of different aspects of nicotine dependence by facilitating smoking cessation by decreasing nicotine intake and preventing relapse to smoking in humans