Upregulated glial cell line-derived neurotrophic factor through cyclooxygenase-2 activation in the muscle is required for mechanical hyperalgesia after exercise in rats.

Unaccustomed strenuous exercise that includes lengthening contraction (LC) often causes delayed onset muscle soreness (DOMS), characterised as muscular mechanical hyperalgesia. Previously we reported that a bradykinin-like substance released from the muscle during exercise plays a pivotal role in triggering the process of muscular mechanical hyperalgesia by upregulating nerve growth factor (NGF) in exercised muscle of rats. We show here that cyclooxygenase (COX)-2 and glial cell line-derived neurotrophic factor (GDNF) are also involved in DOMS. COX-2 inhibitors but not COX-1 inhibitors given orally before LC completely suppressed the development of DOMS, but when given 2 days after LC they failed to reverse the mechanical hyperalgesia. COX-2 mRNA and protein in exercised muscle increased six- to 13-fold in mRNA and 1.7-2-fold in protein 0-12 h after LC. COX-2 inhibitors did not suppress NGF upregulation after LC. Instead, we found GDNF mRNA was upregulated seven- to eight-fold in the exercised muscle 12 h-1 day after LC and blocked by pretreatment of COX-2 inhibitors. In situ hybridisation studies revealed that both COX-2 and GDNF mRNA signals increased at the periphery of skeletal muscle cells 12 h after LC. The accumulation of COX-2 mRNA signals was also observed in small blood vessels. Intramuscular injection of anti-GDNF antibody 2 days after LC partly reversed DOMS. Based on these findings, we conclude that GDNF upregulation through COX-2 activation is essential to mechanical hyperalgesia after exercise.

Bradykinin and nerve growth factor play pivotal roles in muscular mechanical hyperalgesia after exercise (delayed-onset muscle soreness).

Unaccustomed strenuous exercise that includes lengthening contraction (LC) often causes delayed-onset muscle soreness (DOMS), a kind of muscular mechanical hyperalgesia. The substances that induce this phenomenon are largely unknown. Peculiarly, DOMS is not perceived during and shortly after exercise, but rather is first perceived after approximately 1 d. Using B(2) bradykinin receptor antagonist HOE 140, we show here that bradykinin released during exercise plays a pivotal role in triggering the process that leads to muscular mechanical hyperalgesia. HOE 140 completely suppressed the development of muscular mechanical hyperalgesia when injected before LC, but when injected 2 d after LC failed to reverse mechanical hyperalgesia that had already developed. B(1) antagonist was ineffective, regardless of the timing of its injection. Upregulation of nerve growth factor (NGF) mRNA and protein occurred in exercised muscle over a comparable time course (12 h to 2 d after LC) for muscle mechanical hyperalgesia. Antibodies to NGF injected intramuscularly 2 d after exercise reversed muscle mechanical hyperalgesia. HOE 140 inhibited the upregulation of NGF. In contrast, shortening contraction or stretching induced neither mechanical hyperalgesia nor NGF upregulation. Bradykinin together with shortening contraction, but not bradykinin alone, reproduced lasting mechanical hyperalgesia. We also showed that rat NGF sensitized thin-fiber afferents to mechanical stimulation in the periphery after 10-20 min. Thus, NGF upregulation through activation of B(2) bradykinin receptors is essential (though not satisfactory) to mechanical hyperalgesia after exercise. The present observations explain why DOMS occurs with a delay, and why lengthening contraction but not shortening contraction induces DOMS.

Effect of NC-1900, an active fragment analog of arginine vasopressin, and inhibitors of arachidonic acid metabolism on performance of a passive avoidance task in mice.

In this study, we investigated the effect of administration of inhibitors of each of the arachidonic acid metabolism pathways and the effect of co-administration of these inhibitors with NC-1900, a fragment analog of arginine vasopressin, on step-through passive avoidance task performance. All drugs were administered just after the acquisition trial in the passive avoidance task. Intracerebroventricular (i.c.v.) administration of nordihydroguaiaretic acid (NDGA, 1 and 10 microg), a phospholipase A2 (PLA2) and lipoxygenase (LOX) inhibitor, and of arachidonyl trifluoromethyl ketone (ATK, 1 and 10 microg), a specific PLA2 inhibitor caused reductions in latency on the retention trial. The i.c.v. administration of either of baicalein (0.1-10 microg), a 12-LOX inhibitor, or AA-861 (0.1-10 microg), a 5-LOX inhibitor, did not influence the latency. Intraperitoneal administration of indomethacin (20 mg/kg), a non-specific COX inhibitor, or NS-398 (10 mg/kg), a specific COX-2 inhibitor, impaired performance on the retention trial in the task, while piroxicam (20 mg/kg), a specific COX-1 inhibitor, did not. Subcutaneous administration of NC-1900 (0.1 ng/kg) ameliorated the reduction of latency caused by NDGA, ATK, indomethacin, or NS-398. These results suggested that the COX-2 pathway of arachidonic acid metabolism may be important for learning and/or memory in the passive avoidance task in mice, and that the ameliorating effect of NC-1900, in part, is due to mimicking of the effects of metabolites of the COX-2 pathway.

Zaltoprofen, a non-steroidal anti-inflammatory drug, inhibits bradykinin-induced pain responses without blocking bradykinin receptors.

Zaltoprofen, a preferential COX-2 inhibitor, exhibited a potent inhibitory action on the nociceptive responses induced by a retrograde infusion of bradykinin into the right common carotid artery in rats. However, other COX-2 preferential inhibitors such as meloxicam and etodolac did not exhibit any apparent action, and also, preferential COX-1 inhibitors mofezolac and indomethacin, COX-1 and COX-2 inhibitor loxoprofen sodium showed a weak effect. These non-steroidal anti-inflammatory drugs (NSAIDs) except for zaltoprofen, strongly inhibited an acetic acid-induced writhing response related to PGs based on COX-1, at lower doses. Zaltoprofen had a moderate inhibitory effect compared with those of the above-mentioned NSAIDs. These results suggest that the inhibitory effect of zaltoprofen on bradykinin-induced nociceptive responses is not explainable by the inhibition of cyclooxygenase (COX). So, we examined the inhibitory effect of zaltoprofen on bradykinin-induced nociceptive responses by performing several in vitro experiments. Zaltoprofen did not bind to B(1) and B(2) receptors in a radio-ligand binding assay. In the cultured dorsal root ganglion cells of mature mice, zaltoprofen completely inhibited the bradykinin-induced increase of [Ca(2+)](i), which was inhibited by B(2) antagonist D-Arg-[Hyp(3), Thi(5,8), D-Phe(7)]-bradykinin, but not by B(1) antagonist. In addition, the inhibition of zaltoprofen on the increase of [Ca(2+)](i) was observed even under extracellular Ca(2+)-free conditions. The above results suggest that zaltoprofen produces an analgesic action on bradykinin-induced nociceptive responses by blocking the B(2) receptor-mediated pathway in the primary sensory neurons. Taken together, these results suggest that zaltoprofen may serve as a potent and superior analgesic for the treatment of pain.

Zaltoprofen inhibits bradykinin-induced responses by blocking the activation of second messenger signaling cascades in rat dorsal root ganglion cells.

Bradykinin interacts with the bradykinin B2 receptor on dorsal root ganglion (DRG) neurons, setting off a series of reactions inside the cells that ultimately make the vanilloid receptor 1 more sensitive to a normal stimulus by activating various enzymes coupled with second messenger signaling cascades. Zaltoprofen, a propionic acid derivative non-steroidal anti-inflammatory drug (NSAID), was proved to inhibit bradykinin-induced pain responses in vivo experimental systems more potently than indomethacin or other NSAIDs, but the molecular mechanisms underlying its action are not yet fully understood. Currently it appears unlikely that zaltoprofen binds to specific sites on the protein of the bradykinin B2 receptor, hence we have examined the effect of zaltoprofen on bradykinin-induced responses of adult DRG neurons to investigate possible interaction sites. Compared with several other NSAIDs, such as indomethacin, loxoprofen and diclofenac, zaltoprofen most potently inhibits bradykinin-enhancement of capsaicin-induced 45Ca2+ uptake into DRG neurons. Zaltoprofen also significantly inhibits bradykinin-induced 12-lipoxygenase (12-LOX) activity and the slow bradykinin-induced onset of substance P release from DRG neurons. These data indicate zaltoprofen may produce its analgesic effects through the inhibition of bradykinin B2 receptor-mediated bradykinin responses of not only cyclooxygenases (COXs) but also bradykinin induced 12-LOX inhibitors.

Glutamate antagonists attenuate the action of NC-1900, a vasopressin fragment analog, on passive avoidance task performance in mice.

To examine the relationship between glutamate receptors and the action of NC-1900 on a step-through passive avoidance (PA) task in mice, MK-801, an NMDA receptor blocker, and (S)-4-carboxyphenylglycine (4CPG), a group I metabotropic receptor antagonist, were administered intraventricularly (i.c.v.) singly or as co-injections. The i.c.v. injection of MK-801 (0.8 microg) or 4CPG (2 microg) decreased the latency on the PA task. NC-1900 (1 ng/kg, subcutaneously (s.c.)) alone prolonged the latency on the retention trial in the PA task. MK-801 (0.2 and 0.8 microg) or 4CPG (0.5 and 2 microg) significantly inhibited the action of NC-1900, while the s.c. injection of NC-1900 did not affect latency in mice that received i.c.v. co-injection of MK-801 and 4CPG at any of the doses tested. These results suggest that glutamate receptors participate in the action of NC-1900 on learning and memory in PA task performance.

Facilitative effect of a novel AVP fragment analog, NC-1900, on memory retention and recall in mice.

In order to determine the mechanism of action of a new AVP(4-9) analog, NC-1900, on memory processes, memory retention and retrieval tests were conducted in a step-through passive avoidance (PA) task in mice. The administration of NC-1900 facilitated memory retention and retrieval in the PA task through vasopressin1A (V1A) receptors but not V2 receptors. The effect of NC-1900 on memory retention test performance appeared to be due to activation of the protein kinase C (PKC) signaling pathway via V1A receptors; however, the modulation of PKC was not essential for the facilitative effect of the new peptide in the retrieval test. The facilitation of memory retrieval by NC-1900 may also be mediated by other non-PKC-dependent signaling pathways, such as the phospholipase C-inositol trisphosphate pathway.

Effect of pretraining administration of NC-1900, a vasopressin fragment analog, on memory performance in non- or CO2-amnesic mice.

In the present study, we investigated the facilitative effect of NC-1900, a new arginine vasopressin (AVP(1-9)) fragment analog, on memory performance in eight-arm radial maze or passive avoidance (PA) tasks in nonamnesic and amnesic (PA tasks only) mice. In the radial maze, all injections (subcutaneous) were given daily 60 min before each trail. NC-1900 (1 ng/kg)-treated animals showed enhancement of performance, and AVP(4-9) (1 microg/kg), an AVP(1-9) fragment, had similar effects, although the effective dose was 1000-fold higher. In the PA task, all drugs were administrated subcutaneously 60 min before the acquisition trial (Acq.), and the amnesic mice were exposed to CO(2) just after the Acq. NC-1900 (1 ng/kg) enhanced the memory performance of nonamnesic mice and ameliorated CO(2)-induced amnesia. AVP(4-9) (1 microg/kg) had a similar effect, although only at higher doses, while AVP(1-9) (0.1-1 microg/kg) had no effect. The facilitating effect of NC-1900 on nonamnesic mice was inhibited by coinjection [Pmp(1)-Tyr(Me)(2)]-AVP (Pmp,Tyr-AVP; 1 microg/kg), a V(1A) antagonist, but not by OPC-31260, a vasopressin(2) (V(2)) antagonist. The effect of NC-1900 on CO(2)-induced amnesia was also decreased by coinjection of Pmp,Tyr-AVP or [deamino-Pen(1), Me-Tyr(2)]-AVP (10 microg/kg), both of which are V(1) antagonists. These results suggested that NC-1900 has a more potent effect on facilitation of memory via the V(1A) receptor than AVP(4-9) in non- and CO(2)-amnesic conditions.

[The improvement of memory retention and retrieval of a novel vasopressin fragment analog NC-1900].

The effects of a novel vasopressin (AVP) fragment analog NC-1900 (pGlu-Asn-Ser-Pro-Arg-Gly-NH2 acetate) were studied on the performance of memory retention and retrieval in mice. NC-1900 of one time application of 1 hr after the acquired trial (electric shock) extended the latent period of passive avoidance task 21 days after the acquired trial. Though the extended response was also recognized with AVP4-9, the potency was approx. 1/1000 of NC-1900. The potentiation wasn't recognized with vasopressin. NC-1900 showed a significantly high correct answer after 21 days after the last trial in the search task. While, V1 antagonist Pmp1-Tyr (Me)2-AVP shortened the latent period of passive avoidance task. On the other hand, NC-1900 extended the reaction latency 21 days after the acquired trial by the application 1 hr before the retention trial. Though this improvement of memory retrieval was recognized with vasopressin and AVP4-9, the potency was 1/100-1/1000. NC-1900 improved the retrieval 24 h after the CO2 exposure. V1 antagonists Pmp1-Tyr-Me2-AVP or Deamino-Pen1, O-Me-Tyr2-AVP, and PMA had no effects on the retrieval 21 days after the acquired trial. These results suggest that NC-1900 may have the memory retention and retrieval potentiating action, and that phospholipase C-protein kinase C system may be involved in the former action, and the latter action not be involved.