Koichi Tan-No

Background: We have recently demonstrated that intrathecal (i.t.) administration of angiotensinII(AngII) induces nociceptive behaviour in mice accompanied by a phosphorylation of p38 mitogen‐activated protein kinase (MAPK) mediated throughAngIItype 1 (AT₁) receptors. TheN‐terminal fragment ofAngII,Ang (1–7), plays a pivotal role in counterbalancing many of the well‐established actions induced byAngII. However, the role ofAng (1–7) in spinal nociceptive transmission remains unclear. Therefore, we examined whether i.t. administration ofAng (1–7) can inhibit theAngII‐induced nociceptive behaviour in mice.Methods: In the behavioural experiments, the accumulated response time of nociceptive behaviour consisting of scratching, biting and licking in conscious mice was determined during a 25‐min period starting after i.t. injection. The distribution and localization ofAT₁orMas receptors were analysed using aMapAnalyzer and confocal microscope, respectively. Phosphorylation of p38MAPKin the dorsal spinal cord was measured by Western blotting.Results: The nociceptive behaviour induced byAngIIwas dose‐dependently inhibited by the co‐administration ofAng (1–7). The inhibitory effect ofAng (1–7) was reversed by the co‐administration ofA779, aMas receptor antagonist. Western blot analysis showed that the increase in spinal p38MAPKphosphorylation following the i.t. administration ofAngIIwas also inhibited byAng (1–7), and theAng (1–7) induced‐inhibition was prevented byA779.Conclusions: Our data show that the i.t. administration ofAng (1–7) attenuates anAngII‐induced nociceptive behaviour and is accompanied by the inhibition of p38MAPKphosphorylation mediated throughMas receptors.

Background: It has been demonstrated that angiotensin II (Ang II) participates in either the inhibition or the facilitation of nociceptive transmission depending on the brain area. Neuronal Ang II is locally synthesized not only in the brain, but also in the spinal cord. Though the spinal cord is an important area for the modulation of nociception, the role of spinal Ang II in nociceptive transmission remains unclear. Therefore, in order to elucidate the role of Ang II in nociceptive transmission in the spinal cord, we examined the effect of intrathecal (i.t.) administration of Ang II into mice. Results: I.t. administration of Ang II produced a behavioral response in mice mainly consisting of biting and/or licking of the hindpaw and the tail along with slight hindlimb scratching directed toward the flank. The behavior induced by Ang II (3 pmol) was dose-dependently inhibited by intraperitoneal injection of morphine (0.1–0.3 mg/kg), suggesting that the behavioral response is related to nociception. The nociceptive behavior was also inhibited dose-dependently by i.t. co-administration of losartan (0.3–3 nmol), an Ang II type 1 (AT₁) receptor antagonist, and SB 2035 80 (0.1–1 nmol), a p38 MAPK inhibitor. However, the Ang II type 2 (AT₂) receptor antagonist PD123319, the upstream inhibitor of ERK1/2 phosphorylation U0126, and the JNK inhibitor SP600125 had no effect on Ang II-induced nociceptive behavior. Western blot analysis showed that the i.t. injection of Ang II induced phosphorylation of p38 MAPK in the lumbar dorsal spinal cord, which was inhibited by losartan, without affecting ERK1/2 and JNK. Furthermore, we found that AT₁ receptor expression was relatively high in the lumbar superficial dorsal horn. Conclusions: Our data show that i.t. administration of Ang II induces nociceptive behavior accompanied by the activation of p38 MAPK signaling mediated through AT₁ receptors. This observation indicates that Ang II may act as a neurotransmitter and/or neuromodulator in the spinal transmission of nociceptive information.

Intrathecal (i.t.) administration of D -cycloserine (100 and 300 fmol), a partial agonist of the glycine recognition site on the N-methyl- D -aspartate (NMDA) receptor ion-channel complex, produced a behavioral response mainly consisting of biting and/or licking of the hindpaw and the tail along with slight hindlimb scratching directed toward the flank in mice, which peaked at 5 – 10 min and almost disappeared at 15 min after the injection. The behavior induced by D -cycloserine (300 fmol) was dose-dependently inhibited by an intraperitoneal injection of morphine (0.5 – 2 mg/kg), suggesting that the behavioral response is related to nociception. The nociceptive behavior was also dose-dependently inhibited by i.t. co-administration of 7-chlorokynurenic acid (0.25 – 4 nmol), a competitive antagonist of the glycine recognition site on the NMDA receptor ion-channel complex; D -(−)-2-amino-5-phosphonovaleric acid (62.5 – 500 pmol), a competitive NMDA receptor antagonist; MK-801 (62.5 – 500 pmol), an NMDA ion-channel blocker; ifenprodil (0.5 – 8 nmol); arcaine (31 – 125 pmol); and agmatine (0.1 – 10 pmol), all being antagonists of the polyamine recognition site on the NMDA receptor ion-channel complex. However, [ D -Phe7, D -His9]-substance P(6 – 11), a specific antagonist for substance P (NK1) receptors, and MEN-10,376, a tachykinin NK2-receptor antagonist, had no effect on D -cycloserine-induced nociceptive behavior. These results in the mouse spinal cord suggest that D -cycloserine-induced nociceptive behavior is mediated through the activation of the NMDA receptor ion-channel complex by acting on the glycine recognition site and that it does not involve the tachykinin receptor mechanism.

The anti-inflammatory effect of propolis was compared with that of diclofenac, a non-steroidal anti-inflammatory drug, and L-NG-nitro arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, using carrageenin-induced mouse paw edema. When administered 10 min prior to carrageenin injection, propolis (1 : 1000, 1 : 100, p.o.), diclofenac (12.5, 50 mg/kg, p.o.) and L-NAME (10, 100 mg/kg, s.c.) showed a significant anti-inflammatory effect. The anti-inflammatory effects of propolis and L-NAME were significantly inhibited by L-arginine, a precursor of nitric oxide, but not by D-arginine. In contrast, the anti-inflammatory effect produced by diclofenac was not inhibited by either D-arginine or L-arginine. These results indicate that the anti-inflammatory effect of propolis on mouse paw edema acts via the inhibition of nitric oxide production, similar to that of L-NAME but not diclofenac.