Dong K. Song

Involvement of dynorphin in immobilization stress-induced antinociception in the mouse

The effect of antiserum against [Met(5)]-enkephalin, [Leu(5)]-enkephalin, beta-endorphin, or dynorphin A-(1-13) administered intracerebroventricularly (i.c.v.) or intrathecally (i. t.) on immobilization-induced antinociception was studied in ICR mice. Antinociception was assessed by the tail-flick assay. Immobilization of the mouse increased inhibition of the tail-flick response at least 1 h. The i.c.v. or i.t. injection with antiserum against dynorphin A-(1-13) at the dose of 200 microg significantly attenuated immobilization-induced inhibition of the tail-flick response. However, antiserum against [Met(5)]-enkephalin, [Leu(5)]-enkephalin, or beta-endorphin did not affect the immobilization stress-induced antinociception. Furthermore, i.c.v. or i.t. injection with nor-binaltorphimine (Nor-BNI; from 1 to 20 microg) effectively inhibited immobilization stress-induced inhibition of the tail-flick response in a dose-dependent manner. However, beta-FNA (from 0.5 to 2 microg) or naltrindole (from 1 to 20 microg) administered i.c.v. or i.t. did not affect immobilization stress-induced antinociception. Our results suggest that supraspinally and spinally located dynorphin appears to be involved in the production of immobilization stress-induced antinociception via stimulating kappa-opioid receptors.

Differential modulatory roles of cholera toxin and pertussis toxin in the regulation of pain responses induced by excitatory amino acids administered intrathecally in mice.

The present study was designed to characterize the possible roles of spinally located cholera toxin (CTX)- and pertussis toxin (PTX)-sensitive G-proteins in excitatory amino acids induced pain response. Intrathecal (i.t.) injection of glutamate (20 microg), N-methyl-D-aspartic acid (NMDA; 60 ng), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA; 13 ng), and kainic acid (12 ng) showed pain response. Pretreatment with CTX (0.05 and 0.5 microg, i.t.) attenuated pain response induced by glutamate, NMDA, AMPA and kainic acid administered i.t. in a dose-dependent manner. On the other hand, i.t. pretreatment with PTX further increased the pain response induced by glutamate, NMDA, AMPA and kainic acid administered i.t., especially at the dose of 0.5 microg. Our results suggest that, at the spinal cord level, CTX- and PTX-sensitive G-proteins appear to play opposite roles in modulating the pain response induced by spinally administered. Furthermore, CTX- and PTX-sensitive G-proteins appear to modulate pain response induced by stimuli of both NMDA and non-NMDA glutamate receptors.

Effects of intrathecal or intracerebroventricular pretreatment with pertussis toxin on antinociception induced by β-endorphin or morphine administered intracerebroventricularly in mice

We have previously demonstrated that β-endorphin and morphine, when administered supraspinally, produce antinociception by activating different descending pain inhibitory systems in both rats and mice. However, the signal transduction mechanisms involved in the descending pain-inhibitory systems that are activated by β-endorphin and morphine administered intracerebroventricularly (i.c.v.) have not been characterized. Therefore, in the present study, the effects of intrathecal (i.t.) and i.c.v. pretreatments with pertussis toxin (PTX) on antinociception induced by β-endorphin or by morphine administered i.c.v. were studied in ICR mice. Antinociception was assessed by the tail-flick assay and by the hotplate assay. Intrathecal pretreatment with PTX (0.5 μg) for 6 days effectively reduced the inhibition of the tail-flick response induced by β-endorphin (1 μg) or by morphine (1 μg) administered i.c.v. However, i.t. pretreatment with PTX was not effective in reducing the inhibition of the hot-plate response induced by β-endorphin or by morphine administered i.c.v. Intracerebroventricular pretreatment with PTX (0.5 μg) for 6 days effectively reduced the inhibition of the tail-flick and hot-plate responses induced by morphine (1 μg), but not that induced by β-endorphin (1 μg), administered i.cv. Our results suggest that there are PTX-sensitive G proteins coupled to the spinal descending pain inhibitory systems that are activated by β-endorphin and morphine administered i.c.v. At a supraspinal level, i.cv. morphine- but not β-endorphin-induced antinociception is mediated by PTX-sensitive G proteins.

Involvement of different subtypes of cholecystokinin receptors in opioid antinociception in the mouse

Various doses of sulfated cholecystokinin octapeptide (CCK-8s) injected intracerebroventricularly (ICV) alone did not show any antinociceptive effect. CCK-8s (0.01-1 ng) pretreated ICV for 10 min dose-dependently attenuated the inhibition of the tail flick response induced by ICV-administered morphine (2 micrograms). beta-endorphin (1 microgram), and U50,488H (trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]benzeocetamide), 60 micrograms). However, ICV pretreatment with CCK-8s was not effective in reducing the inhibition of the tail flick response induced by [D-Pen(2)-D-Pen5]enkephalin (DPDPE; 10 micrograms) administered ICV. To determine what subtype(s) of CCK receptors are involved in antagonizing the antinociception induced by these opioids, effect of lorglumide sodium salt (a CCKA receptor antagonist) or PD135,158 N-methyl-D-glucamine salt (a CCKB receptor antagonist) on opioid-induced inhibition of the tail flick response was examined. Various doses of lorglumide sodium salt (lorglumide) or PD135,158 N-methyl-D-glucamine salt (PD135,158) injected ICV alone did not affect the basal tail flick response. The antagonistic effect of CCK-8s on morphine-, beta-endorphin-, and U50,488H-induced inhibition of the tail flick response was blocked in a dose-dependent manner by the co-ICV injection of PD135,158 (0.001-0.1 ng). The co-ICV injection of lorglumide (0.001-0.1 ng) dose-dependently blocked the antagonistic effect of CCK-8s on beta-endorphin- and U50,488H-induced, but not morphine-induced, inhibition of the tail flick response. Our results suggest that both CCKA and CCKB receptors are involved in antagonizing antinociception induced by beta-endorphin and U50,488H administered supraspinally. However, only CCKB (but not CCKA) receptors are involved in antagonizing antinociception induced by morphine administered supraspinally. CCK receptors are not involved in antagonizing the supraspinally administered DPDPE-induced antinociception.

MULTIPLICATIVE INTERACTION BETWEEN INTRATHECALLY AND INTRACEREBROVENTRICULARLY ADMINISTERED MORPHINE FOR ANTINOCICEPTION IN THE MOUSE : INVOLVEMENT OF SUPRASPINAL NMDA BUT NOT NON-NMDA RECEPTORS

Concurrent administration of morphine to both supraspinal and spinal sites produced a multiplicative (synergistic) interaction for antinociception. The purpose of this study was to determine if supraspinal glutaminergic receptors are involved in the multiplicative interaction for antinociception induced by morphine. The antinociception was assessed by the tail-flick test. Effect of MK-801 [(+/-)-5-methyl-10, 11-dihydro-5H-dibenzo (a,d)cyclohepten-5,10-imine maleate], a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, or CNQX (6-Cyano-7-nitroquinoxaline-2,3-dione), a competitive non-NMDA receptor antagonist on inhibition of the tail-flick response induced by a combined i.t. and i.c.v. administration of morphine was studied. Either i.t. or i.c.v. administration of morphine alone at the dose of 0.2 microgram slightly increased inhibition of the tail-flick response. However, concurrent i.t. and i.c.v. injections of morphine at the dose of 0.2 microgram increased the inhibition of the tail-flick response in a synergistic manner. Various doses of MK-801 (0.01-1 microgram) or CNQX (0.05-0.5 microgram) pretreated i.c.v. alone did not show any antinociceptive effect. MK-801 pretreated i.c.v. for 10 min dose-dependently attenuated the inhibition of the tail-flick response induced by concurrent i.t. and i.c.v. injections of morphine. However, CNQX pretreated i.c.v. for 10 min did not affect the inhibition of the tail-flick response induced by concurrent i.t. and i.c.v. injections of morphine. Our results suggest that supraspinal NMDA but not non-NMDA receptors are involved in mediating the antinociception produced by morphine-induced multiplicative interaction between spinal and supraspinal sites.

Differential modulation by muscimol and baclofen on antinociception induced by morphine, β-endorphin, d-Pen2,5-enkephalin and U50,488H administered intracerebroventricularly in the mouse

The present study was designed to investigate the modulatory effects of stimulation of GABAA and GABAB receptors at supraspinal sites on antinociception induced by supraspinally administered μ-, ɛ-, δ-, and κ-opioid receptor agonists. The effects of the GABAA and GABAB receptor agonists, muscimol and baclofen respectively, on the antinociception induced by morphine (a μ-receptor agonist), β-endorphin (an ɛ-receptor agonist), D-Pen2,5-enkephalin (DPDPE, a δ-receptor agonist) and U50,488H ({trans-3,4-di-chloroN-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeocetamide}; a κ-receptor agonist) injected intracerebroventricularly (i.c.v.) were studied. The anti-nociception was assayed using the tail-flick and hot-plate tests. Muscimol at doses of 25–200 ng, administered i.c.v. alone did not affect the latencies of tail-flick and hot-plate thresholds, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by i.c.v. administered morphine (2 μg), β-endorphin (1 μg), DPDPE (10 μg), and U50,488H (60 μg). Baclofen (1.25–10 ng) administered i.c.v. alone did not affect the latencies of the tail-flick and hot-plate responses, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by β-endorphin and U50,488H, without affecting morphine-or DPDPE-induced responses. Our results indicate that activation of GABAA receptors at the supraspinal sites by i.c.v. injection of muscimol antagonizes antinociception induced by supraspinally administered μ-, ɛ-, δ-, and κ-opioid receptor agonists. On the other hand, activation of GABAB receptors at supraspinal sites by i.c.v. baclofen antagonizes antinociception induced by i.c.v. administered ɛ- and κ-opioid agonists, but not μ- or δ-opioid agonists.

Effects of intrathecal injection of nimodipine, ω-conotoxin GVIA, calmidazolium, and KN-62 on the antinociception induced by cold water swimming stress in the mouse

The present study was designed to determine if spinal calcium channels, calmodulin, and calcium/calmodulin-dependent protein kinase II were involved in the production of antinociception induced by cold water swimming stress (CWSS). The effects of intrathecal (i.t.) injection of nimodipine, omega-conotoxin GVIA, calmidazolium, or (S)-5-isoquinolinesulfonic acid, 4-[2-[(5-isoquinolinyl-sulfonyl)methylamino]-3-oxo-3-(4-phenyl-1-piperaz inyl)-propyl]phenyl ester (KN-62) on CWSS-induced antinociception were studied in ICR mice. The antinociception was assessed by the tail-flick test. CWSS produced inhibition of the tail-flick response. Various doses of nimodipine (10-40 ng), omega-conotoxin GVIA (5-40 ng), calmidazolium (10-40 ng), or KN-62 (5-40 ng) injected i.t. alone did not show any antinociceptive effect in the tail-flick test. I.t. pretreatment with omega-conotoxin GVIA, calmidazolium, or KN-62 dose dependently attenuated the CWSS-induced inhibition of the tail-flick response. However, i.t. pretreatment with nimodipine did not affect the inhibition of the tail-flick response induced by CWSS. Our results suggest that spinal N-type calcium channel, calmodulin and calcium/calmodulin-dependent protein kinase II may be involved in the production of antinociception induced by CWSS. On the other hand, CWSS-induced antinociception appears not to be mediated via the spinal L-type calcium channel.

Differential potentiative effects of gaba receptor agonists in the production of antinociception induced by morphine and β-endorphin administered intrathecally in the mouse

The effect of muscimol or baclofen injected intrathecally (i.t.) on the inhibition of the tail-flick response induced by morphine and beta-endorphin administered i.t. was studied in ICR mice. The i.t. injection of muscimol (100 ng) or baclofen (10 ng) alone did not affect the basal inhibition of the tail-flick response. Morphine (0.2 microg) and beta-endorphin (0.1 microg) caused only slight inhibition of the tail-flick response. Baclofen, but not muscimol, injected i.t. enhanced the inhibition of the tail-flick response induced by i.t. administered morphine. Both muscimol and baclofen injected i.t. significantly enhanced i.t. injected beta-endorphin-induced inhibition of the tail-flick response. Our results suggest that the GABA(B), but not GABA(A), receptors located in the spinal cord appear to be involved in enhancing the inhibition of the tail-flick response induced by morphine administered spinally. In addition, both GABA(A) and GABA(B) receptors are involved in enhancing the inhibition of the tail-flick response induced by beta-endorphin administered i.t.