Ko Zushida

Role of vanilloid VR1 receptor in thermal allodynia and hyperalgesia in diabetic mice

We examined the role of the vanilloid VR1 receptor in the thermal hyperalgesia and allodynia seen in diabetic mice. Tail-flick latencies at source voltages of 35 and 50 V for a 50-W projection bulb in diabetic mice were significantly shorter than those in non-diabetic mice. Tail-flick latencies at 35 and 50 V in diabetic mice were increased by pretreatment with anti-vanilloid VR1 receptor serum. Intrathecal (i.t.) injection of anti-VR1 serum resulted in a significant increase in the tail-flick latency at 50 V in non-diabetic mice. However, i.t. pretreatment with anti-vanilloid VR1 receptor serum did not affect the tail-flick latency at a heat intensity of 35 V in non-diabetic mice. Thus, it seems likely that thermal allodynia and hyperalgesia in diabetic mice may be due to the sensitization of vanilloid VR1 receptors in primary sensory neurons in the spinal cord.

The antinociceptive effects of endomorphin-1 and endomorphin-2 in diabetic mice.

The antinociceptive effects of endomorphin-1 and endomorphin-2, endogenous mu-opioid receptor agonists, were examined using the tail-flick test in non-diabetic and diabetic mice. Endomorphin-1, at doses of 1 to 10 microg, i.c.v., and endomorphin-2, at doses of 3 to 30 microg, i.c.v., each dose dependently inhibited the tail-flick response in both non-diabetic and diabetic mice. There was no significant difference between the antinociceptive effects of endomorphin-1 in non-diabetic mice and diabetic mice. The antinociceptive effect of endomorphin-2 was greater in non-diabetic mice than in diabetic mice. In non-diabetic mice, the antinociceptive effects of endomorphin-1 and endomorphin-2 were significantly reduced by beta-funaltrexamine, a mu-opioid receptor antagonist, and naloxonazine, a selective mu(1)-opioid receptor antagonist, but not by naltrindole, a delta-opioid receptor antagonist, or nor-binaltorphimine, a kappa-opioid receptor antagonist. In diabetic mice, the antinociceptive effect of endomorphin-2 was significantly reduced by beta-funaltrexamine and naloxonazine. However, these micro-opioid receptor antagonists had no significant effect on the antinociceptive effect of endomorphin-1 in diabetic mice. The antinociception induced by endomorphin-1 in diabetic mice was significantly reduced by naltrindole and 7-benzylidenenaltrexon, a selective delta(1)-opioid receptor antagonist, administered i.c.v. However, nor-binaltorphimine had no significant effect on the antinociceptive effects of endomorphin-1 and endomorphin-2 in diabetic mice. These results indicate that the antinociceptive effects of endomorphin-1 and endomorphin-2 in non-diabetic mice are mediated through the activation of mu(1)-opioid receptors, whereas in diabetic mice, endomorphin-1 and endomorphin-2 may produce antinociception through different actions at delta(1)- and mu(1)-opioid receptors, respectively.

The role of spinal cholecystokinin B receptors in thermal allodynia and hyperalgesia in diabetic mice

We examined the tail-flick response to various heat intensities in diabetic and non-diabetic mice. Heat intensities were set to one of six values by adjusting the source of voltage for a 50-W projection bulb to 20, 25, 35, 50, 65 and 80 V. Tail-flick latencies at source voltages of 35 and 50 V in diabetic mice were significantly shorter than those in non-diabetic mice. However, tail-flick latencies at 25, 65 and 80 V in diabetic mice were not significantly altered. Although tail-flick latencies in non-diabetic mice were not affected by i.t. pre-treatment with CI-988, a selective cholecystokinin B (CCK(B)) receptor antagonist, those at 35 and 50 V in diabetic mice were significantly increased. In non-diabetic mice, i.t. pre-treatment with cholecystokinin octapeptide (CCK-8), at a dose of 0.3 ng, decreased tail-flick latencies at 35 and 50 V. Furthermore, the attenuation of tail-flick latencies induced by i.t. pre-treatment with CCK-8 in non-diabetic mice was reversed by i.t. pre-treatment with CI-988. Protein kinase C (PKC) activator phorbol-12, 13-dibutyrate (PDBu)-induced reduction in the tail-flick latencies at heat intensities of 35 and 50 V in non-diabetic mice was dose-dependently and significantly reversed by i.t. pre-treatment with CI-988. On the other hand, the CCK-8-induced thermal hyperalgesia and allodynia at heat intensities of 35 and 50 V in non-diabetic mice were inhibited when PKC activity was inhibited by i.t. pre-treatment with calphostin C. These results indicate that the thermal allodynia and hyperalgesia in diabetic mice may be due, at least in part, to the activation of CCK(B) receptors followed by the activation of PKC in the spinal cord.

Effect of diabetes on pinacidil-induced antinociception in mice.

The antinociceptive effects of pinacidil, an adenosine triphosphate (ATP)-sensitive K(+)i (K(ATP)) channel opener, were examined using the tail-flick test in non-diabetic and diabetic mice. Pinacidil i.c.v. produced dose-dependent antinociception in both non-diabetic and diabetic mice. There was no significant difference between the antinociceptive effect of i.c.v. pinacidil in non-diabetic mice and diabetic mice. The i.t. administration of pinacidil also produced dose-dependent antinociception in both non-diabetic and diabetic mice, however, the antinociceptive effect of i.t. pinacidil in diabetic mice was significantly greater than that in non-diabetic mice. The antinociceptive effect of i.c.v. or i.t. pinacidil was significantly antagonized by i.c.v. or i.t. glibenclamide, a K(ATP) channel blocker in both non-diabetic and diabetic mice. In non-diabetic mice, the antinociceptive effect of i.c.v. or i.t. administration of pinacidil was significantly antagonized by beta-funaltrexamine, a mu-opioid receptor antagonist, 7-benzylidenenaltrexone, a delta1-opioid receptor antagonist, naltriben, a delta2-opioid receptor antagonist, and nor-binaltorphimine, a kappa-opioid receptor antagonist. In diabetic mice, the antinociceptive effect of i.c.v. pinacidil was significantly reduced by 7-benzylidenenaltrexone, naltriben, and nor-binaltorphimine. However, beta-funaltrexamine had no effect on antinociception induced by i.c.v. pinacidil in diabetic mice. On the other hand, the antinociceptive effect of i.t. pinacidil was significantly antagonized by beta-funaltrexamine, 7-benzylidenenaltrexone, naltriben, and nor-binaltorphimine in diabetic mice. These results indicated that pinacidil produced antinociception through the release of opioid peptides acting at mu-, delta- and kappa-opioid receptors in surpraspinal and spinal cord of non-diabetic mice. On the other hand, in diabetic mice, the antinociception-induced by pinacidil was mediated through the release of opioid peptides acting at delta- and kappa-opioid receptors supraspinally, whereas pinacidil produced antinociception through the release of opioid peptides acting at mu-, delta-, and kappa-opioid receptors spinally.

Modification of the fenvalerate-induced nociceptive response in mice by diabetes.

We examined the effect of diabetes on the fenvalerate-induced nociceptive response in mice. The intrathecal (i.t.) or intraplantar (i.pl.) injection of fenvalerate, a sodium channel activator, induced a characteristic behavioral syndrome mainly consisting of reciprocal hind limb scratching directed towards caudal parts of the body and biting or licking of the hind legs in both non-diabetic and diabetic mice. However, the intensity of such fenvalerate-induced nociceptive responses was significantly greater in diabetic mice than in non-diabetic mice. Calphostin C (3 pmol, i.t.), a selective protein kinase C inhibitor, significantly inhibited intrathecal fenvalerate-induced nociceptive behavior with a rightward shift of the dose-response curve for fenvalerate-induced nociceptive behavior to the level those observed in non-diabetic mice. On the other hand, when non-diabetic mice were pretreated with phorbol-12, 13-dibutyrate (50 pmol, i.t.), the dose-response curve for intrathecal fenvalerate-induced nociceptive behavior was shifted leftward to the level those observed in diabetic mice. These results suggest that the sensitization of sodium channels, probably tetrodotoxin-resistant (TTX-R) sodium channels, by the long-term activation of protein kinase C may play an important role in the enhancement of the duration of fenvalerate-induced nociceptive behavior in diabetic mice.

Antinociceptive effect induced by intraperitoneal administration of vitamin K2 (menatetrenone) in ICR mice

The antinociceptive effect of vitamin K2 (menatetrenone) in mice was examined using tail-flick and formalin test. Menatetrenone at doses of 10, 50 and 100 mg/kg, i.p. produced a dose-dependent and significant inhibition of the tail-flick response in mice. Menatetrenone (50 and 100 mg/kg, i.p.) had no significant effect on the duration of the first phase of the formalin-induced flinching. However, menatetrenone (100 mg/kg, i.p.) significantly inhibited the second phase of the formalin-induced flinching. I.p. administration of menatetrenone (100 mg/kg) significantly reduced the duration of nociceptive responses induced by i.t. injection of bradykinin, but not of substance P, prostaglandin E2 or N-methyl-D-aspartate (NMDA). These present data suggest that i.p. pretreatment with menatetrenone produced dose-dependent antinociceptive effect in mice. This effect may be, at least in part, mediated by the inhibition of bradykinin dependent nociceptive transmission in the spinal cord.

Effect of MK-801 on the antinociceptive effect of [D-Ala2, N-mePhe4, Gly-ol5]enkephalin in diabetic mice

The role of N-methyl-D-aspartate (NMDA) receptors in supraspinal and spinal sites on the reduction of supraspinal micro-opioid receptor-induced antinociception in diabetic mice was examined. The antinociceptive effect of i.c.v. [D-Ala(2), N-MePhe(4), Gly-ol(5)]enkephalin (DAMGO, 20 pmol) in diabetic mice was significantly less than that in non-diabetic mice. The antinociceptive effect of i.c.v. DAMGO (20 pmol) was significantly and dose dependently reduced by i.c.v. (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) in both non-diabetic (0.03-0.3 nmol) and diabetic mice (0.1-3.0 nmol). While the antinociceptive effect of i.c.v. DAMGO (10 pmol) was significantly enhanced by i.c.v NMDA (0.01-0.1 nmol) in non-diabetic mice, the same doses of i.c.v. NMDA had no significant effect on the antinociceptive effect of i.c.v. DAMGO (20 pmol) in diabetic mice. In non-diabetic mice, the antinociceptive effect of DAMGO (20 pmol, i.c.v.) was dose dependently reduced by intrathecal administration of MK-801 (0.1-1.0 nmol). The antinociceptive effect of DAMGO (20 pmol, i.c.v.) was dose-dependently enhanced by MK-801 (0.1-1.0 nmol, i.t.) in diabetic mice. Furthermore, NMDA (0.1 nmol, i.t.) significantly enhanced the antinociceptive effect of DAMGO (10 pmol, i.c.v.) in non-diabetic mice. However, in non-diabetic mice, the antinociceptive effect of DAMGO (40 pmol, i.c.v.) was dose dependently reduced by NMDA (0.03-0.3 nmol, i.t.). These results suggest that NMDA receptor function in supraspinal and spinal sites appear to be modulated differently by the diabetic state, and this functional modulation may play an important role in the reduction of supraspinal micro-opioid receptor-induced antinociception in diabetic animals.

Role of cholecystokinin in the reduction of endomorphin-2-induced antinociception in diabetic mice

We examined the role of cholecystokinin in the reduction of endomorphin-2-induced antinociception in diabetic mice. Endomorphin-1 (1-10 microg, i.c.v.) and endomorphin-2 (3-30 microg, i.c.v.) dose dependently inhibited the tail-flick response in non-diabetic and diabetic mice. There was no significant difference between the antinociceptive effect of endomorphin-1 in non-diabetic and diabetic mice. On the other hand, the antinociceptive effect of endomorphin-2 in diabetic mice was significantly less than that in non-diabetic mice. Cholecystokinin octapeptide (CCK-8) dose dependently reduced the antinociceptive effects of endomorphin-1 and endomorphin-2 in non-diabetic mice. However, in diabetic mice, CCK-8 significantly inhibited the antinociceptive effect of endomorphin-1, but not of endomorphin-2. In non-diabetic mice, CI-988 ((R-[R*,R*])-4-([3-1H-indol]-3-yl)-2-methyl-1-oxo-2-([(tricyclo(3.3.1.1)dec-2-yloxy)carbonyl] amino)propylamino-1-phenyl-ethylamino-4-oxybutanoic acid) had no significant effect on either endomorphin-1- or endomorphin-2-induced antinociception. In diabetic mice, while CI-988 had no significant effect on endomorphin-1-induced antinociception, it dose dependently enhanced the antinociceptive effect of endomorphin-2. The results indicated that the reduction of endomorphin-2-induced antinociception in diabetic mice might be due, at least in part, to the activation of CCK(2) receptors.