Biomedical subjects

R B Raffa

Publications and source records attributed to R B Raffa.

At least 73 records · Page 4Linked to original sources

PubMed1995

LiCl uncouples signal transduction in morphine-induced supraspinal antinociception in mice.

1. The present study examined whether LiCl antagonism of morphine-induced antinociception in mice occurs at mu-opioid receptors. 2. The antinociceptive ED50 value of intracerebroventricular morphine was maximally increased compared to controls 18 hr after LiCl (10 mmol/kg, s.c.) and remained significantly less (P < 0.05) 7 and 14 days after once-daily LiCl treatment. 3. There was no significant difference in [3H]-[D-Ala2,N-MePhe4,Gly- ol5]enkephalin affinity or receptor density compared to controls (KD = 0.43 nM, Bmax = 54.8 +/- 9.3 pM). 4. These results suggest that LiCl's effect is not on mu-opioid receptors, but rather on some distal site.

Analgesics↗

PubMed1995

Serotonin and norepinephrine uptake inhibiting activity of centrally acting analgesics: structural determinants and role in antinociception.

Although it is well established that the analgesic effects of morphine are mediated by opioid receptors, previous studies have shown that some opioids additionally inhibit the uptake of serotonin and norepinephrine. The present investigation of a diverse group of opioids revealed that structurally identifiable subgroups inhibited the neuronal reuptake of these monoamines. Phenanthrene opioids with an oxygen bridge between C4 and C5, such as morphine and naloxone (group I), did not block norepinephrine or serotonin uptake, whereas phenanthrene opioids without the oxygen bridge and the C6-OH moiety, such as levorphanol and levomethorphan (group II), did inhibit uptake, as did nonphenanthrene opioids, such as d-propoxyphene and methadone (group III). Affinity at the mu opioid receptor correlated with antinociceptive potency (r = 0.87, P < .05). Although the antinociceptive activity of the "active enantiomers" of group II and III compounds also correlated with their affinity at the mu opioid receptor (r = 0.85, P = .007), additional consideration of serotonin uptake inhibiting activity (but not of norepinephrine uptake inhibiting activity) significantly improved the correlation between antinociceptive potency and the in vitro activity of these compounds (r = 0.915, P = .0017). Additionally, for group II and III (but not group I) compounds, smaller differences between enantiomers in antinociceptive potency than in mu receptor affinity were noted, presumably because of the contribution of uptake inhibition to the antinociceptive activity of group II and III compounds. Evidence also is provided suggesting a broader role for the combination of mu opioid affinity and 5-hydroxytryptamine uptake inhibition in the activity of other antinociceptive agents.

Analgesics, Opioid↗

PubMed1994

Differentiation of receptor subtypes by thermodynamic analysis: application to opioid delta receptors.

The temperature dependence of the dissociation constant for the interaction of an opioid delta selective ligand and its receptor was evaluated in three tissues. The change in free energy of this interaction was similar in mouse brain, mouse spinal cord, and NG 108-15 mouse neuroblastoma-rat glioma hybrid cells (delta G(o)' = -13.44, -13.34, and -13.66 kcal.mol-1, respectively). However, the reaction was endothermic and occurred with an increase in entropy in mouse brain and NG 108-15 cells, but it was exothermic and occurred with a negligible change in entropy in mouse spinal cord. These data are consistent with the existence of multiple subtypes of opioid delta receptor, and they further suggest that the opioid delta receptor recently cloned from the NG 108-15 cell line is of the brain subtype. Subtypes of opioid delta receptors may mediate analgesia, but not side-effects, of opiates and thus could be targets for future drug design.

Animals↗

PubMed1994

Lack of glibenclamide or TEA affinity for opioid receptors: further evidence for in vivo modulation of antinociception at K+ channels.

Radioligand binding of the opioid receptor subtype selective ligands, [3H][D-Ala2,N-Me-Phe4, Gly-ol5]-enkephalin (DAMGO) (mu), [3H][D-Pen2,D-Pen5]-enkephalin (DPDPE) (delta) and [3H]U-69,593 (kappa), to rat brain particulate preparations was virtually unaffected by 1-100 microM glibenclamide (Glib) or tetraethylammonium bromide (TEA). These results argue against opioid receptor antagonism by Glib or TEA and support the hypothesis that antagonism of opioid-induced antinociception by Glib or TEA occurs at the level of K+ (possibly ATP-sensitive KATP) channels.

Amino Acid Sequence↗

PubMed1994

G-protein antisense oligodeoxyribonucleotides and mu-opioid supraspinal antinociception.

The present study utilized an in vivo antisense strategy to examine the functional interaction of supraspinal mu-opioid receptors with the G protein subunits Gi1 alpha, Gi2 alpha, Gi3 alpha and Gs alpha. Mice were injected intracerebroventricularly (i.c.v.) with 33-base phosphorothioate oligodeoxyribonucleotides (12.5 micrograms) or with vehicle in equal volume (sterile water, 5 microliters) and the antinociceptive responses to i.c.v. morphine [D-Ala2,NMePhe4,Gly5-ol]enkephalin (DAMGO) or sufentanil were determined 18-24 h later using the tail-flick test. Treatment with antisense to Gi2 alpha, but not the other subunits, significantly attenuated morphine-induced antinociception. The degree of attenuation for the three mu-opioid agonists was in the order morphine > DAMGO > sufentanil, the inverse of their intrinsic efficacy.

Analgesics↗

PubMed1994

Opioid mu receptor subtypes (possibly mu 1 and mu 2) revealed by morphine-induced antinociception vs endothelin-1 in recombinant inbred CXBK mice.

Morphine was administered intracerebroventricularly to normal or recombinant inbred CXBK (mu-opioid receptor deficient) mice and antinociception was determined against two different stimuli. Morphine-induced antinociception against acetylcholine was strain-dependent, whereas against endothelin-1 it was not. The antinociception was mediated via opioid mu receptors (blocked by beta-FNA, but not naltrindole, ICI 174,864 or nor-BNI) through separate pathways, one naloxonazine-sensitive and the other naloxonazine-insensitive. Taken together, these results appear to demonstrate supraspinal morphine-induced antinociception through distinct subtypes of the mu opioid receptor, supporting the possibility of novel subtype-selective therapeutic agents with greater separation between analgesia and side-effects or physical dependence. Furthermore, the methodology described herein provides model systems for the in vivo screening of such agents.

Animals↗

PubMed1994

Etonitazene-induced antinociception in mu1 opioid receptor deficient CXBK mice: evidence for a role for mu2 receptors in supraspinal antinociception.

The prevailing view is that supraspinal mu opioid-mediated antinociception in mice is mediated via the mu 1 subtype. The purpose of the present study was to determine if the highly mu-selective compound etonitazene could produce supraspinal (intracerebroventricular; i.c.v.) antinociception in CXBK mice, which are deficient in brain mu1, but not mu2, opioid receptors. CXBK or normal Crl:CD-1 (ICR)BR mice were administered graded doses of etonitazene i.c.v. and 15 min later antinociception was assessed by a standard radiant-heat or 55 degrees C water tail-flick test. Etonitazene produced dose-related antinociception that was blocked by naloxone and by beta-FNA (demonstrating a mu opioid mechanism), but not by either ICI-174,864 or naltrindole (demonstrating the lack of involvement of delta opioid receptors). These findings suggest that mu2 opioid receptors are important contributors to opioid-induced supraspinal antinociception in mice.

Animals↗

PubMed1994

Low affinity of FMRFamide and four FaRPs (FMRFamide-related peptides), including the mammalian-derived FaRPs F-8-Famide (NPFF) and A-18-Famide, for opioid mu, delta, kappa 1, kappa 2a, or kappa 2b receptors.

The binding affinities at opioid receptor subtypes in rat or guinea pig brain membranes were determined for the neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2), the two mammalian-derived FMRFamide-related peptides F-8-Famide (NPFF; Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe- NH2) and A-18-Famide (Ala-Gly-Glu-Gly-Leu-Ser-Ser-Pro-Phe-Trp-Ser-Leu-Ala-Ala-Pro-Gln-Arg-Phe -NH2), and the two other FMRFamide-related peptides Tyr-Phe-Met-Arg-Phe-NH2 (Tyr-FMRFamide) and Pro-Gln-Arg-Phe-NH2 (Pro-Gln-RFamide). The mu and delta sites were labeled in rat brain membranes using tritiated [D-Ala2, N-MePhe4,Gly-ol5] enkephalin ([3H]DAMGO) and [D-Ala2,D-Leu5]enkephalin ([3H]DADLE), respectively. The kappa sites were labeled in guinea pig brain using [3H]U-69,593 after treatment with BIT and FIT for kappa 1 and [3H]bremazocine after pretreatment with BIT and FIT for kappa 1 and [3H]bremazocine after pretreatment with BIT and FIT for kappa 2. The kappa 2a binding sites were assayed using [Leu5]enkephalin to block kappa 2b sites and the kappa 2b sites were assayed using (-)-(1S,2S)-U50,488 to block kappa 2a sites. Neither FMRFamide nor any of the FMRFamide-related peptides (up to 61.0 microM) displayed significant affinity at any of the subtypes of opioid receptor. Hence, the known ability of FMRFamide and FaRPs to interact with the opioid system does not appear to be related to direct binding to these opioid receptors.

Amino Acid Sequence↗

PubMed1993

Scyliorhinin-I and -II induce reciprocal hindlimb scratching in mice: differentiation of spinal and supraspinal neurokinin receptors in vivo.

Scyliorhinin-I amide (SCY-I) (selective for NK-1 and NK-2 receptors) or scyliorhinin-II amide (SCY-II) (selective for NK-3 receptors) were injected either spinally (i.t.; intrathecally) or supraspinally (i.c.v.; intracerebroventricularly) to mice. Following i.c.v. administration, SCI-I and SCY-II produced potent, dose-related reciprocal hindlimb scratching about equipotently (ED50 = 0.05 and 0.08 nmol, respectively). However, following i.t. administration, only SCY-I elicited greater than 50% response (ED50 = 0.07 nmol). Reciprocal hindlimb scratching is a behavioral response that has not been associated previously with neurokinins. These results might provide the first functional in vivo correlate for the differential localization of neurokinin receptor types within the mammalian central nervous system.

Amino Acid Sequence↗

PubMed1993

Thermodynamic parameters for [D-Pen2,5]enkephalin at delta-opioid receptors in the mouse isolated vas deferens.

Dissociation constants (KA) for [D-Pen2,5]enkephalin (DPDPE) inhibition of the electrically evoked twitch of the mouse isolated vas deferens preparation (MVD) were calculated at five temperatures (25, 30, 34, 37 and 40 degrees C). These values were determined from the equiactive concentrations obtained before (A) and after (A') partial irreversible blockade of a fraction of the receptor population by beta-chlornaltrexamine (beta-CNA) plotted as (1/A') where KA = (slope -1)/intercept. The values of KA tended to increase (approximately doubled) over this temperature range, indicating that the affinity of DPDPE for the opioid delta receptor is an inverse function of temperature. From these results, thermodynamic parameters were calculated from a Van't Hoff plot of 1n(KA) against 1/T. The relative magnitudes of the change in enthalpy (delta Ho' = -6.67 kcal mol-1), the change in entropy (delta So' = +0.009 kcal mol-1 degrees K-1) and the change in free energy (delta Go' = -9.43 kcal mol-1) suggest that the interaction between DPDPE and the delta-opioid receptor in MVD is an exothermic exergonic reaction, predominantly enthalpy-driven and results in an increase in the entropy of the system.

Animals↗

PubMed1993

The combined immunological and antinociceptive defects of beige-J mice: the possible existence of a 'mu-repressin'.

A selective non-responsiveness to the analgesic effects of opioid mu receptor-, but not opioid delta receptor-, mediated antinociception in the tail-flick test has been identified in C57BL/6J-bgJ (beige-J) mice. The beige-J mutation is also known to give rise to multiple immunological disorders and immune cell dysfunctions. A link between these apparently disparate manifestations has been examined in a series of studies using, for example, adoptive transfer of spleen cells. The findings appear to have broad implications for the link between the immune and opioid systems.

Animals↗

PubMed1993

Determination of the drug-receptor dissociation constant of endothelin-1 using photorelaxation of rabbit isolated thoracic aorta.

An in vitro preparation of rabbit thoracic aorta was tested in order to determine whether isometric contractile force induced by endothelin-1 (ET-1) in this preparation is changed when the tissue is exposed to ultraviolet (UV) light. After constriction of an aortic segment to a steady-state level of tension with ET-1, a flash of UV light induced a transient decrease in tension that returned exponentially to equilibrium. This response was endothelium-independent and sensitive to the extracellular sodium concentration. The rate of return to the baseline tension after photorelaxation increased with increasing concentrations of ET-1. UV light had only a slight photorelaxing effect at very low and very high ET-1 concentrations and a much larger effect at concentrations near the A50 value of ET-1. Since an irreversible antagonist does not yet exist for ET-1, the partial irreversible blockade method for getting the dissociation constant (KD) functionally was not possible. The relaxation method, using UV light as a perturbation of ligand-receptor equilibrium, was used instead to obtain KD as well as the forward (k1) and reverse (k2) rate constants of ET-1 in this tissue.

Animals↗

PubMed1993

Complementary and synergistic antinociceptive interaction between the enantiomers of tramadol.

The explanation for the co-existence of opioid and nonopioid components of tramadol-induced antinociception appears to be related to the different, but complementary and interactive, pharmacologies of its enantiomers. The (+) enantiomer had Ki values of only 1.33, 62.4 and 54.0 microM at mu, delta and kappa receptors, respectively. The (-) enantiomer had even lower affinity at the mu and delta sites (Ki = 24.8, 213 and 53.5 microM, respectively. The (+) enantiomer was the most potent inhibitor of serotonin uptake (Ki = 0.53 microM) and the (-) enantiomer was the most potent inhibitor of norepinephrine uptake (Ki = 0.43 microM). Basal serotonin release was preferentially enhanced by the (+) enantiomer and stimulation-evoked norepinephrine release was preferentially enhanced by the (-) enantiomer. The (+) and (-) enantiomers each independently produced centrally mediated antinociception in the acetylcholine-induced abdominal constriction test (ED50 = 14.1 and 35.0 micrograms i.t., respectively). Racemic tramadol was significantly more potent (P < .05) than the theoretical additive effect of the enantiomers (antinociceptive synergy). Synergy was also demonstrated (P < .1) in the mouse 55 degrees C hot-plate test (i.p. route) and (P < .05) the rat Randall-Selitto yeast-induced inflammatory nociception model (i.v. and i.p. routes). Critically, the enantiomers interacted less than synergistically in two side-effects of inhibition of colonic propulsive motility and impairment of rotarod performance. The racemate and the (+) enantiomer were active in a chronic (arthritic) inflammatory pain model. Taken together, these findings provide a rational explanation for the coexistence of dual components to tramadol-induced antinociception and might form the basis for understanding its clinical profile.

Acetylcholine↗

PubMed1992

2-Substituted 1-azabicycloalkanes, a new class of non-opiate antinociceptive agents.

2-Substituted 1-azabicycloalkanes (3- and 5-aryloctahydroindolizines 2 and 11, 3-cyclohexyloctahydroindolizine 12, 4-aryloctahydroquinolizines 13, and 3-arylhexahydropyrrolizines 14) constitute a new class of non-opiate antinociceptive agents. These compounds demonstrated activity in the mouse abdominal constriction test and many were active in the mouse tail-flick test. trans-3-(2-Bromophenyl)octahydroindolizine (2a) did not bind to the opiate receptor nor did it affect arachidonate metabolism. 3-Aryloctahydroindolizines were prepared by catalytic hydrogenation of 1-aryl-3-(2-pyridinyl)-2-propen-1-ones. The X-ray crystal structure of (-)-2a was determined and absolute stereochemistry assigned as 3-R,8a-R.

Analgesics↗

PubMed1992

Opioid efficacy is linked to the LiCl-sensitive, inositol-1,4,5-trisphosphate-restorable pathway.

Previous work demonstrated that a single subcutaneous injection of LiCl (10 mmol/kg; 18 h prior) significantly reduces the antinociceptive action of centrally administered (intracerebroventricular; i.c.v.) morphine in the tail-flick and that inositol-1,4,5-trisphosphate (IP3; 20 micrograms) restores the morphine response in LiCl-pretreated mice, implicating a phosphoinositide second messenger pathway in the mediation of morphine-induced analgesia. We now report that LiCl pretreatment shifted the antinociceptive dose-response curve produced by the opioid agonists morphine, [D-Ala2, MePhe4, Gly5-ol]enkephalin (DAMGO) and sufentanil in inverse order of their intrinsic efficacy. These results implicate the phosphoinositide pathway(s) as important determinant(s) of opioid efficacy and are interpreted as evidence for the existence of a second-messenger reserve for opioids of high efficacy and the possible role of the phosphoinositide pathway in the development of morphine tolerance.

Analgesics↗

PubMed1992

Lack of antinociceptive efficacy of intracerebroventricular [D-Ala2,Glu4]deltorphin, but not [D-Pen2,D-Pen5]enkephalin, in the mu-opioid receptor deficient CXBK mouse.

The antinociceptive efficacy of [D-Pen2,D-Pen5]enkephalin (DPDPE) (delta 1 agonist) and [D-Ala2,Glu4]deltorphin (delta 2 agonist) was evaluated following intracerebroventricular (i.c.v.) or intrathecal (i.t.) administration in CD-1 and CXBK strains of mice using the radiant heat tail-flick test. Following i.c.v. administration, [D-Ala2,Glu4]deltorphin was effective in CD-1, but not CXBK, mice; DPDPE was approximately equiactive in both strains. While i.c.v. [D-Ala2,Glu4]deltorphin did not produce antinociception in the CXBK mouse, it effectively antagonized the antinociceptive actions of i.c.v. DPDPE. [D-Ala2,Glu4]deltorphin was effective following i.t. administration in both strains. These data suggest possible differences in the supraspinal populations of opioid delta receptor subtypes in the CXBK strain. On the basis of previously established selectivity of these agonists, the CXBK mouse may have a predominate population of supraspinal opioid delta 1, rather than delta 2, receptors.

Analgesics↗

PubMed1992

Morphine antinociception is mediated through a LiCl-sensitive, IP3-restorable pathway.

Pretreatment (18 h) of mice with a single s.c. injection of LiCl (10 mmol/kg) reduced the antinociceptive action of centrally administered (i.c.v.) morphine in the tail-flick test (ED50 = 7.7 micrograms) compared to vehicle-treated controls (ED50 = 1.8 micrograms). The coadministration of inositol-1,4,5-trisphosphate (IP3; 20 micrograms) with morphine restored the morphine-induced antinociception (ED50 = 2.4 micrograms) in LiCl-pretreated mice to control levels. These finding implicate a LiCl-sensitive (possibly phosphoinositide) second messenger pathway in the mediation of morphine-induced analgesia.

Analgesics↗

PubMed1992

Etoperidone, trazodone and MCPP: in vitro and in vivo identification of serotonin 5-HT1A (antagonistic) activity.

The Ki values for etoperidone, trazodone and MCPP (m-chlorophenylpiperazine dihydrochloride) at 5-HT1A sites (using rat cerebral cortical synaptosomes and [3H]8-OH-DPAT) were determined to be 20.2, 23.6 and 18.9 nM, respectively. In an effort to elucidate the functional nature of the interaction at 5-HT1A sites in vivo, the ability of each compound to elicit reciprocal forepaw treading (RFT) or to block the RFT induced by 8-OH-DPAT in reserpinized rats was tested. Specifically, 8-OH-DPAT (1.0 mg/kg SC)-challenged or non-challenged (control) reserpinized (1.0 mg/kg SC) rats were administered etoperidone, trazodone or MCPP (IP) and scored for the elicitation of RFT (indicative of 5-HT1A agonistic activity) or for block of RFT induced by 8-OH-DPAT (indicative of 5-HT1A antagonistic activity). Reference compounds confirmed the specificity of the test. We report that etoperidone, trazodone and MCPP inhibited 8-OH-DPAT-induced RFT (ID50 = 17.4, 23.8 and 13.4 mg/kg, respectively). Only marginal RFT was produced in non-challenged animals by etoperidone and trazodone at a high dose (40 mg/kg). Taken together, the results suggest a predominant antagonistic activity of etoperidone, trazodone and MCPP at 5-HT1A receptor sites in rat central nervous system. However, one cannot rule out the possibility that these compounds are weak partial agonists. This activity may be relevant to the antidepressant action of these compounds.

8-Hydroxy-2-(di-n-propylamino)tetralin↗