Hideki Hitosugi

Streptozotocin-induced diabetes selectively reduces antinociception mediated by μ1-opioid receptors, but not that mediated by μ2-opioid receptors

We assessed the effect of naloxonazine, a selective mu 1-opioid receptor antagonist, on antinociception produced by intrathecal or intracerebroventricular injections of morphine in streptozotocin-induced diabetic mice. The antinociceptive effect of morphine (10 micrograms), administered i.c.v., was significantly less in diabetic mice than in non-diabetic mice. The antinociceptive effect of i.c.v. morphine was significantly reduced in both diabetic and non-diabetic mice following pretreatment with naloxonazine. There were no significant differences in the antinociceptive effect of morphine (1 microgram, i.t.) in diabetic and non-diabetic mice. Furthermore, naloxonazine had no significant effect on the antinociceptive effect of i.t. morphine in either diabetic or non-diabetic mice. On the other hand, the antinociceptive effects of i.c.v. and i.t. morphine were significantly reduced following pretreatment with beta-funaltrexamine, a selective mu-opioid receptor antagonist, in both diabetic and non-diabetic mice. In conclusion, mice with diabetes are selectively hyporesponsive to supraspinal mu 1-opioid receptor-mediated antinociception, but are normally responsive to activation of spinal mu 2-opioid receptors.

Effect of diabetes on the antinociceptive effect of β-endorphin

Abstract We examined whether streptozotocin-induced diabetes can modulate β-endorphin-induced antinociception in mice. While β-endorphin administered i.c.v. produced a dose-dependent inhibition of the tail-flick response in both diabetic and non-diabetic mice, the antinociceptive response was greater in diabetic mice than in non-diabetic mice. The ED 50 value of β-endorphin administered i.c.v. in diabetic mice was significantly lower than that in non-diabetic mice. The antinociceptive effects of β-endorphin administered i.c.v. in both diabetic and non-diabetic mice were significantly antagonized by s.c. administration of naltrindole, a selective δ-opioid receptor antagonist. β-Endorphin administered i.t. also produced a dose-dependent antinociception in both diabetic and non-diabetic mice. However, the ED 50 value of β-endorphin administered i.t. in diabetic mice was significantly higher than that in non-diabetic mice. The antinociceptive effect of β-endorphin administered i.t. in both diabetic and non-diabetic mice were significantly antagonized by s.c. administration of nor-binaltorphimine, a selective κ-opioid receptor antagonist. On the other hand, the antinociceptive potency of DPDPE, a selective δ-opioid agonist, administered i.t. is significantly increased in diabetic mice, as compared with non-diabetic mice, whereas, the antinociceptive potency of U-50,488H, a κ-opioid receptor agonist, administered i.t. is significantly less than in non-diabetic mice. These results suggest that diabetes may modulate β-endorphin-induced antinociception differently at the spinal and supraspinal levels.

Formalin-induced nociceptive responses in diabetic mice

In non-diabetic mice, s.c. injection of formalin to the hindpaw had a biphasic effect: an immediate nociceptive response (first-phase) followed by a tonic response (second-phase). However, only the immediate nociceptive response was observed in diabetic mice. The duration of the first-phase response was significantly longer in diabetic mice than in non-diabetic mice. In diabetic mice, when spantide, an antagonist of substance P, reduced the duration of the nociceptive response in the first-phase to the levels that were observed in non-diabetic mice, the second-phase response appeared. The second phase also became apparent in diabetic mice after pretreatment with naltrindole (3 mg/kg), an antagonist of delta-opioid receptors. These results suggest that a negative control system, which is mediated by delta-opioid receptors and links substance P with somatostatin-mediated nociceptive transmission, may inhibit the formalin-induced second-phase of the nociceptive response in diabetic mice.

Involvement of haloperidol-sensitive σ-sites in antitussive effects

Abstract The effects of selective σ-ligands on the capsaicin-induced cough reflex in rats were studied. Intraperitoneal injection of (+)-N-allylnormetazocine ((+)-SKF-10,047) and N,N′-di(ortho-toly)guanidine (DGT) in doses that ranged from 0.3 to 3.0 mg/kg decreased the number of coughs dose dependently. The antitussive effects of these σ-ligands were significantly attenuated by pretreatment with haloperidol. Pretreatment with haloperidol also markedly reduced the antitussive effects of (±)-pentazocinc and dextromethorphan. These results suggest that haloperidol-sensitive σ-sites may be involved in the regulation of coughs.

Antinociceptive effects of intrathecally administered endothelin-1 in mice

Intrathecal administration of endothelin-1 (ET-1) produced dose-dependent antinociceptive effects in the tail-flick test. The antinociceptive effects of ET-1 were attenuated significantly by pretreatment with naloxone and the delta receptor-selective antagonist naltrindole. The antinociceptive effects of ET-1 were also significantly attenuated by pretreatment with verapamil, an L-type Ca(2+)-channel blocker. These results suggest that the mechanism underlying the antinociceptive effects of ET-1 involves mediation, at least in part, by Ca(2+)-induced release of endogenous opioids, which act on delta-opioid receptors.

δ-Opiod receptor-mediated forced swimming stress-induced antinociception in the formalin test

Forced swimming stress-induced antinociception (FSSIA) was assessed using the formalin test. Male ICR mice, weighing about 30 g, were forced to swin in water at 20°C for 3 min. In unstressed mice, SC injection of formalin (0.5%) to the hindpaw caused a biphasic response: an immediate nociceptive response (first phase) followed by a tonic response (second phase). Although forced swimming stress (FSS) had no effect on the duration of the first-phase response, FSS significantly reduced the duration of the second-phase response. The effect of FSSIA on the second-phase response was blocked by naltrindole (1 mg/kg, SC), a selective δ-opioid receptor antagonist, but not by β-funaltrexamine (20 mg/kg, SC), a selective μ-opioid receptor antagonist. These results indicate that FSS may selectively reduce the second phase of the formalin-induced nociceptive response, primarily through δ-opioid receptors.

Modulation of the formalin-induced nociceptive response by diabetes: possible involvement of intracellular calcium

We examined the involvement of cytosolic calcium in the modulation of the formalin-induced nociceptive response by diabetes. Injection of formalin into the hindpaw of mice produced a biphasic nociceptive response consisting of immediate (first phase) and tonic (second phase) components. Although the duration of the first-phase response was significantly longer in diabetic mice than in non-diabetic mice, the second phase was significantly shorter in diabetic mice. The first-phase response was dose-dependently and significantly reduced by pretreatment with ryanodine, which blocks Ca(2+) release from Ca(2+)/caffeine-sensitive microsomal pools. The second-phase response was also significantly increased when diabetic mice were pretreated with ryanodine. However, ryanodine had no significant effect on either the first-phase or second-phase response in non-diabetic mice. On the other hand, pretreatment with thapsigargin, which inhibits Ca(2+) uptake into the inositol-1,4, 5-trisphosphate-sensitive microsomal Ca(2+) pool, significantly enhanced the first-phase response in non-diabetic mice. Furthermore, thapsigargin significantly and dose-dependently reduced the second phase of the formalin-induced nociceptive response in non-diabetic mice. Thapsigargin administered i.t. did not significantly affect either the first- or the second-phase response in diabetic mice. These results suggest that the change in the formalin-induced nociceptive response in diabetic mice may be due, at least in part, to the modification of nociceptive transmission in the spinal cord by intracellular calcium.

Effect of diabetes on bradykinin-induced thermal hyperalgesia in mice

To investigate the role of protein kinase C in the attenuation of bradykinin-induced thermal hyperalgesia in diabetic mice, we examined the effects of a protein kinase C activator or inhibitor on the i.t. bradykinin-induced hyperalgesia in diabetic and non-diabetic mice. Intrathecal injection of bradykinin caused a transient antinociceptive effect, which diminished within 30 min, and then produced a thermal hyperalgesia, which lasted about 120 min, in non-diabetic mice. Although the duration of the antinociceptive phase was longer in diabetic mice than in non-diabetic mice, the hyperalgesic response was not observed in diabetic mice. The bradykinin-induced hyperalgesia was dose-dependently and significantly enhanced by pretreatment with calphostin C (0.3 to 3 pmol, i.t.), a specific protein kinase C inhibitor, in diabetic mice. However, calphostin C (3 pmol, i.t.) had no significant effect on bradykinin-induced hyperalgesia in non-diabetic mice. On the other hand, pretreatment with phorbol-12, 13-dibutyrate (12.5 to 50 pmol, i.t.), a protein kinase C activator, significantly and dose-dependently reduced bradykinin-induced hyperalgesia in non-diabetic mice. However, phorbol-12, 13-dibutyrate (50 pmol, i.t. ) had no significant effect on bradykinin-induced hyperalgesia in diabetic mice. These results suggest that the change in bradykinin-induced thermal hyperalgesia in diabetic mice may be due, at least in part, to the modification of nociceptive transmission in the spinal cord by the activation of protein kinase C.

Algogenic mediator-induced nociceptive response in diabetic mice

The duration of the somatostatin-, bradykinin- or prostaglandin F2alpha-induced nociceptive response was significantly less in diabetic mice than in non-diabetic mice. Subcutaneous injection of 7-benzylidenenaltrexone (0.1, 0.3 and 1 mg/kg), an antagonist of delta1-opioid receptors, had no significant effect on either somatostatin-, bradykinin- or prostaglandin F2alpha-induced nociceptive responses in non-diabetic mice. 7-Benzylidenenaltrexone (0.1 and 0.3 mg/kg, s.c.) also had no significant effect on somatostatin- or prostaglandin F2alpha-induced nociceptive responses in diabetic mice. However, the bradykinin-induced nociceptive response in diabetic mice was dose-dependently and significantly increased when 7-benzylidenenaltrexone (0.1, 0.3 and 1 mg/kg, s.c.) was injected 10 min before the injection of bradykinin. These results suggest that a spinal delta1-opioid receptor-mediated endogenous antinociceptive system may inhibit the bradykinin-mediated nociceptive responses in the second phase of the formalin-induced nociceptive response in diabetic mice.

The role of spinal δ1-opioid receptors in inhibiting the formalin-induced nociceptive response in diabetic mice

Injection of formalin into the hindpaw of mice produced a biphasic nociceptive response consisting of immediate (first-phase) and tonic (second-phase) components. In diabetic mice, the flinching response of the first phase was increased while that in the second phase was decreased in diabetic mice relative to the results in non-diabetic mice. To examine the role of supraspinal and/or spinal endogenous delta1-opioid receptors in inhibiting the formalin-induced nociceptive response in diabetic mice, we assessed the effect of 7-benzylidenenaltrexone, a selective delta1-opioid receptor antagonist, and naltriben, a selective delta2-opioid receptor antagonist, administered either i.c.v. or i.t., on the formalin-induced flinching response. The second-phase response appeared when diabetic mice were pretreated with 7-benzylidenenaltrexone (0.1 and 0.3 mg/kg, s.c.), but not with naltriben (0.3 and 1 mg/kg, s.c.). On the other hand, while 7-benzylidenenaltrexone (0.1, 0.3 and 1 microg/mouse) administered i.t. had no significant effect on the first phase, it significantly and dose-dependently increased the second phase of the formalin-induced flinching response in diabetic mice. 7-Benzylidenenaltrexone (1 and 3 microg/mouse) administered i.c.v. had no significant effect on either the first- or the second-phase response in both non-diabetic and diabetic mice. These results suggest that a spinal delta1-opioid receptor-mediated endogenous antinociceptive system may inhibit the formalin-induced second phase of the nociceptive response in diabetic mice.