Peripheral sensitization caused by insulin-like growth factor 1 contributes to pain hypersensitivity after tissue injury.

Sensitization of primary afferent neurons is one of the most important components of pain hypersensitivity after tissue injury. Insulin-like growth factor 1 (IGF-1), involved in wound repair in injured tissue, also plays an important role in maintaining neuronal function. In the present study, we investigated the effect of tissue IGF-1 on nociceptive sensitivity of primary afferent neurons. Local administration of IGF-1 induced thermal and mechanical pain hypersensitivity in a dose-dependent manner, and was attenuated by IGF-1 receptor (IGF1R) inhibition. Tissue but not plasma IGF-1 levels, as determined by enzyme-linked immunosorbent assay, significantly increased after plantar incision. Immunohistochemistry revealed that IGF1R was predominantly expressed in neurons as well as in satellite glial cells in the dorsal root ganglion (DRG). Double-labeling immunohistochemistry showed that IGF1R expression colocalized with peripherin and TRPV1, but not with NF200 in DRG neurons. The IGF1R inhibitor successfully alleviated mechanical allodynia, heat hyperalgesia, and spontaneous pain behavior observed after plantar incision. Expression of phosphorylated Akt in DRG neurons significantly increased after plantar incision and was suppressed by IGF1R inhibition. These results demonstrate that increased tissue IGF-1 production sensitizes primary afferent neurons via the IGF1R/Akt pathway to facilitate pain hypersensitivity after tissue damage.

Induction of CB1 cannabinoid receptor by inflammation in primary afferent neurons facilitates antihyperalgesic effect of peripheral CB1 agonist.

Cannabinoids act on various regions in the nervous system to modulate neuronal activity including nociception. Here, we investigated CB1 receptor expression in primary afferent neurons in the dorsal root ganglion (DRG) and the efficacy of a local (intraplantar) application of the selective CB1 agonist, 2-arachidonyl-2-chloroethylamide (ACEA), on inflammatory thermal hyperalgesia. In situ hybridization showed normal CB1 mRNA expression in 28% of DRG neurons. Peripheral inflammation by CFA (complete Freund's adjuvant) significantly increased the ratio of CB1 mRNA-positive neurons to 43%, primarily with increase in NF200-negative C-fiber nociceptors. Furthermore, CB1 and TRPV1 (transient potential receptor vanilloid subtype-1) co-localization was increased from 41% before inflammation to 67% two days after inflammation. Inflammation also increased CB1 immunoreactivity in DRG neurons and in nerve fibers of the hindpaw dermis, indicating increased CB1 transport from the cell body to the peripheral nerve. The intraplantar application of ACEA attenuated CFA-induced thermal hyperalgesia. The antinociceptive properties of ACEA became more prominent at 2 days after inflammation, compared with those in non-inflamed and inflamed animals at 8 h. These results suggest that CB1 expression in primary afferent neurons is increased by inflammation and that the subsequent increase in CB1 transport to peripheral axons contributes to the increased antihyperalgesic efficacy of locally administered CB1 agonist.

Peripheral inflammation induces up-regulation of TRPV2 expression in rat DRG.

The transient receptor potential vanilloid subfamily member 2 (TRPV2) is a cation channel activated by temperatures above 52 degrees C. To analyze the contribution of TRPV2 to the development of inflammation-induced hyperalgesia, the expression of TRPV2 in primary sensory neurons was analyzed after intraplantar injection of complete Freund's adjuvant (CFA). Using specific antibodies, an increase in TRPV2-expressing neurons was identified after inflammation. TRPV2 expression is concentrated in a subset of medium-sized dorsal root ganglion neurons, independent of transient receptor potential vanilloid subfamily member 1 (TRPV1) expression. A similar distribution of TRPV2 was observed after inflammation. Intraplantar injection of nerve growth factor increased TRPV1 expression but not TRPV2, suggesting that induction of TRPV2 expression is driven by a mechanism distinct from that for TRPV1. Heat hyperalgesia assessment after chemical desensitization of TRPV1 by resiniferatoxin demonstrates a possible role for TRPV2 in inflammation at high temperatures (>56 degrees C). These results suggest that TRPV2 upregulation contributes to peripheral sensitization during inflammation and is responsible for pain hypersensitivity to noxious high temperature stimuli.

NGF and GDNF differentially regulate TRPV1 expression that contributes to development of inflammatory thermal hyperalgesia.

The transient receptor potential ion channel, TRPV1 plays an essential role in the development of inflammatory thermal hyperalgesia. We investigated the dependence of inflammatory TRPV1 induction on neurotrophic factor. Rat dorsal root ganglia (DRG) neurons were classified according to immunostaining for trk-A and IB4 and the effects of antibodies against NGF or GDNF on TRPV1 expression within the groups were then analysed by immunohistochemical means. The data were compared with the time course of trophic factor expression and the effects of their antibodies on thermal hyperalgesia against radiant heat after inflammation. Although the levels of both NGF and GDNF were increased by inflammation, NGF rapidly and transiently increased whereas GDNF increased gradually over a period of approximately one week. TRPV1 expression was increased within both trk-A positive and IB4 positive neurons after inflammation. Increased TRPV1 expression within trk-A positive neurons was prevented by anti-NGF but not by anti-GDNF, whereas TRPV1 induction within the IB4 positive group was blocked by anti-GDNF but not by anti-NGF. Both antibodies prevented the short latency of withdrawing an inflamed paw from radiant heat. These results suggest that inflammation differentially increases both NGF and GDNF, which facilitate TRPV1 expression within distinctive neurons to induce thermal hyperalgesia.

Local inflammation increases vanilloid receptor 1 expression within distinct subgroups of DRG neurons.

Vanilloid receptor 1 (VR1) is essential to the development of inflammatory hyperalgesia. We investigated whether inflammation can increase in VR1 positive neuronal profiles in rat DRG neurons using histochemical methods. We also used size frequency analysis and double staining with several neuronal markers to investigate whether or not inflammation alters VR1 expression. Inflammation induced a 1.5-fold increase in percentage of VR1-like immunoreactivity (LI) positive profiles per total neuronal profiles, suggesting that the number of heat and pH sensitive neurons increase during inflammation. Area frequency histograms showed that VR1 expression increased in small and medium-sized neurons after inflammation. Double labeling of VR1 with NF200 showed that VR1 positive neurons with NF200 positive profiles significantly increased, indicating that the medium-sized VR1 positive neurons were neurons with myelinated A-fibers. Local inflammation thus increases in VR1 protein level within distinct subgroups of DRG neurons that may participate in the development and maintenance of inflammatory hyperalgesia.

Cloning and characterization of a novel GRP78-binding protein in the rat brain.

The full-length cDNA clone of a novel GRP78-binding protein (GBP) was isolated from rat brain using PCR-selected cDNA subtraction. GBP was predominantly expressed in neuronal cells among various brain tissues. GBP mRNA was already detected in the E12 brain and then gradually increased to reach a peak within P0-2 weeks after birth. GBP expression in the brain decreased age-dependently to approximately 30% of the postnatal level at 12 months. GBP encoded 1021 amino acids and was predicted to have two transmembrane regions and glutamic acid- and proline-rich regions. Because the sequence of GBP offered few clues to the possible function, we performed a GST-tagged GBP pull-down assay in PC12 lysates and identified GRP78, one of the heat shock proteins, as a counterpart. Observation of COS7 cells expressing green fluorescent protein- or Myc-tagged GBP showed that GBP was localized in the endoplasmic reticulum-Golgi domain where BODIPY 558/568 (4,4-difluro-5-(2-thienyl)-4-bora-3alpha,4alpha-diaza-S-indacene)-labeled brefeldin A accumulated. To investigate a biological role for GBP, we established Neuro2a cells stably expressing Myc-tagged GBP. Overexpression of GBP did not affect cell growth or morphological features but attenuated the time-dependent decrease in cell viability caused by serum deprivation compared with control cells. After 48 h of serum starvation, Neuro2a cells overexpressing GBP were resistant to the cell death induced by serum withdrawal. These results suggest that GBP would have a relevant functional role in embryonic and postnatal development of the brain.

[Mechanical supports for stunned myocardium after esophagectomy].

Coronary vasospasm can cause a wide spectrum of clinical syndromes ranging from transient myocardial ischemia to irreversible infarction. A 72-year-old male patient had intense vasospasms intraoperatively, which led to stunned myocardium. Though MB fraction of creatine kinase after the spasms was almost within normal limits, postoperative transcutaneous echocardiogram showed diffuse hypokinesis of heart wall motion. He developed low output syndrome, acute respiratory distress syndrome and acute renal failure. He was treated with mechanical supports (intra-aortic balloon pumping, high frequency oscillatory ventilation, and continuous hemodiafiltration), in addition to intravenous administration of cathecolamines, on the first postoperative day. It took 6 days to wean the patient from these mechanical supports and catecholamine infusion. This case suggests stunned myocardium after coronary vasospasm, despite the rapid disappearing ST elevation, and of importance of mechanical supports for the circulatory failure.

[Plasma ionized magnesium concentration following cardiopulmonary bypass].

We performed a retrospective study to analyze plasma ionized magnesium concentration following cardiopulmonary bypass. Severe decrease of ionized magnesium concentration associated with frequent abnormal ECG sign was found in a patient with magnesium-free cardioplegia. Cardioplegia containing 16 mmol.l-1 of magnesium ion maintained ionized magnesium concentration within normal ranges without postoperative magnesium loading. Use of cardioplegia containing magnesium or adequate magnesium supplement is thought to be essential for patients receiving cardiopulmonary bypass.

Upright posture reduces thermogenesis and augments core hypothermia.

UNLABELLED: We recently reported that baroreceptor-mediated reflexes modulate thermoregulatory vasoconstriction during lower abdominal surgery. Accordingly, we examined the hypothesis that postural differences and the related alterations in baroreceptor loading similarly modulate the thermogenic (i.e., shivering) response to hypothermia in humans. In healthy humans (n = 7), cold saline was infused IV (30 mL/kg at 4 degrees C) for 30 min to decrease core temperature. Each participant was studied on 2 separate days, once lying supine and once sitting upright. Tympanic membrane temperature and oxygen consumption were monitored for 40 min after each saline infusion. The decrease in core temperature upon completion of the infusion in the upright posture position was 1.24 degrees C +/- 0.07 degrees C, which was significantly greater than the 1.02 degrees C +/- 0.06 degrees C seen in the supine position. The core temperature was reduced by 0.59 degrees C +/- 0.07 degrees C in the upright position but only by 0.37 degrees C +/- 0.05 degrees C in the supine position when the increase in oxygen consumption signaling thermogenic shivering occurred. Thus, the threshold temperature for thermogenesis was significantly less in the upright than the supine position. The gain of the thermogenic response did not differ significantly between the positions (363 +/- 69 mL. min(-1). degrees C(-1) for upright and 480 +/- 80 mL. min(-1). degrees C(-1) for supine). The skin temperature gradient was significantly larger in the upright than in the supine posture, suggesting that the peripheral vasoconstriction was augmented by upright posture. Plasma norepinephrine concentrations increased in response to cold saline infusion under both conditions, but the increase was significantly larger in the upright than in the supine posture. Baroreceptor unloading thus augments the peripheral vasoconstrictor and catecholamine response to core hypothermia but simultaneously reduces thermogenesis, which consequently aggravated the core temperature decrease in the upright posture. IMPLICATIONS: Upright posture attenuates the thermogenic response to core hypothermia but augments peripheral vasoconstriction. This divergent result suggests that input from the baroreceptor modifies the individual thermoregulatory efferent pathway at a site distal to the common thermoregulatory center or neural pathway.