enkephalin--ala(2)-mephe(4)-gly(5)- and Body-Weight

The current study aimed to evaluate the contribution(s) of specific opioid receptor systems to the analgesic and detrimental effects of morphine, observed after spinal cord injury in prior studies.. We used specific opioid receptor agonists to assess the effects of μ- (DAMGO), δ- (DPDPE) and κ- (GR89696) opioid receptor activation on locomotor (Basso, Beattie and Bresnahan scale, tapered beam and ladder tests) and sensory (girdle, tactile and tail-flick tests) recovery in a rodent contusion model (T12). We also tested the contribution of non-classic opioid binding using [+]- morphine.. First, a dose-response curve for analgesic efficacy was generated for each opioid agonist. Baseline locomotor and sensory reactivity was assessed 24 h after injury. Subjects were then treated with an intrathecal dose of a specific agonist and re-tested after 30 min. To evaluate the effects on recovery, subjects were treated with a single dose of an agonist and both locomotor and sensory function were monitored for 21 days.. All agonists for the classic opioid receptors, but not the [+]- morphine enantiomer, produced antinociception at a concentration equivalent to a dose of morphine previously shown to produce strong analgesic effects (0.32 μmol). DAMGO and [+]- morphine did not affect long-term recovery. GR89696, however, significantly undermined the recovery of locomotor function at all doses tested.. On the basis of these data, we hypothesize that the analgesic efficacy of morphine is primarily mediated by binding to the classic μ-opioid receptor. Conversely, the adverse effects of morphine may be linked to activation of the κ-opioid receptor. Ultimately, elucidating the molecular mechanisms underlying the effects of morphine is imperative to develop safe and effective pharmacological interventions in a clinical setting.. USA.. Grant DA31197 to MA Hook and the NIDA Drug Supply Program.

Topics: Analgesics, Opioid; Analysis of Variance; Animals; Body Weight; Disease Models, Animal; Dose-Response Relationship, Drug; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Locomotion; Male; Morphine; Pain Measurement; Piperazines; Pyrrolidines; Rats; Rats, Sprague-Dawley; Recovery of Function; Severity of Illness Index; Spinal Cord Injuries

A diaryl ether derivative, (6-(4-{[(3-methylbutyl)amino]methyl}phenoxy)nicotinamide, was prepared and investigated for its biochemical properties at cloned opioid receptors and its pharmacological effects on animal feeding. The compound displaced [(3)H]DAMGO binding of human mu-opioid receptor, [(3)H]U-69593 of human kappa-opioid receptor, and [(3)H]DPDPE of human delta-opioid receptor with IC(50) values of 0.5+/-0.2 nM, 1.4+/-0.2 nM, and 71+/-15 nM, respectively. The compound also potently inhibited [(3)H]DAMGO binding of cloned mouse and rat mu-opioid receptors (IC(50) approximately 1 nM), and acted as a competitive antagonist in a cAMP functional assay using cultured cells expressing human or mouse mu-opioid receptors. Following a single oral administration in diet-induced obese mice (at 10 or 50 mg/kg) or rats (at 1, 3, or 10 mg/kg), the compound caused a dose-dependent suppression of acute food intake and body weight gain in both species. Importantly, the anorectic efficacy of the compound was mostly diminished in mice deficient in the mu-opioid receptor. Our results suggest an important role for the mu-opioid receptor subtype in animal feeding regulation and support the development of mu-selective antagonists as potential agents for treating human obesity.

Topics: Animals; Appetite Depressants; Body Weight; Dose-Response Relationship, Drug; Eating; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Humans; Male; Mice; Mice, Inbred C57BL; Narcotic Antagonists; Rats; Receptors, Opioid, mu

The intracerebroventricular (i.c.v.) infusion of beta-endorphin can cause either a decrease in blood pressure in normal rats or an increase in obese rats. Diet-induced obesity is associated with an increase of hypothalamic mu opioid receptors. Since beta-endorphins act by opioid receptors, we investigated the effect of CNS mu as well as kappa opioid receptor agonist and antagonist on mean blood pressure (MAP), heart rate (HR) and renal sympathetic nerve activity (RSNA) in male Wistar rats fed either a high fat (HF) (40% fat by weight) or a regular low fat (control) (4% fat by weight) diet. After a 12-week-feeding period the animals were implanted with i.c.v. cannulas and 3-5 days later they were anesthetized and instrumented to record MAP, HR and RSNA. HF rats have higher MAP and the i.c.v. injection of a mu opioid agonist (DAMGO) initially decreased the MAP and then increased MAP, HR and RSNA in the normal animals. The increase was greater in HF animals. The i.c.v. injection of the mu antagonist (beta-FNA) resulted in a significantly greater decrease in MAP in HF animals. beta-FNA increased the RSNA in the HF rats but decreased it in the normal rats. The kappa agonist (dynorphin) decreased MAP in normal rats followed by a return to baseline, but not in HF rats. The kappa antagonist, nor-binaltorphimine (N-BP), increased MAP and RSNA in normal rats and to a lesser extent in HF rats. These findings suggest that rats given a high fat diet have higher blood pressures and a greater mu opioid-mediated responsiveness with a greater mu opioid-mediated autonomic tone. Additionally there is a decreased kappa responsiveness and tone in the HF rats. Both these changes, increased mu and decreased kappa responsiveness could strongly contribute to the increased blood pressure in obese animals.

Topics: Animals; Blood Pressure; Body Weight; Central Nervous System; Diet; Dose-Response Relationship, Drug; Dynorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Male; Obesity; Rats; Rats, Wistar; Receptors, Opioid, kappa; Receptors, Opioid, mu; Time Factors

The effect of repeated morphine administration on conditioned place preference (CPP) using a novel treatment schedule, i.e., drug treatment was always contingent with the conditioned environmental stimuli, was investigated. We also examined whether changes in the mu- and kappa-opioid receptor binding occurred in the brain of morphine-treated animals. Intraperitoneal (i.p.) administration of morphine (2 and 10 mg/kg) induced a place preference after 8 daily conditioning trials (4 morphine injections on alternate trials), the level of preference being the same with the two doses of the opiate. No change in place preference was observed in the morphine-treated rats at 2 mg/kg, when animals were further trained up to a total of 32 conditioning trials (16 morphine injections). Conversely, after 20 conditioning trials (10 morphine injections), a stronger CPP response developed in the morphine-treated rats at 10 mg/kg. Signs of morphine withdrawal were never detected in morphine-treated rats during the experiment. Loss of body weight (index of opiate dependence) was not observed either 24 h or 48 h after the last morphine administration. mu- and kappa-opioid receptor density and affinity were not affected by repeated morphine administrations at either dose. The results demonstrate that no tolerance develops to the rewarding properties of morphine. Indeed, a sensitisation effect may occur at increasing doses of the opiate. Furthermore, changes in the rewarding effect of morphine are not dependent upon alterations in opioid receptors involved in the reinforcing mechanisms.

Topics: Analysis of Variance; Animals; Behavior, Animal; Benzeneacetamides; Body Weight; Disease Models, Animal; Drug Tolerance; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Injections, Intraperitoneal; Male; Morphine; Morphine Dependence; Narcotics; Pyrrolidines; Rats; Rats, Sprague-Dawley; Receptors, Opioid, kappa; Receptors, Opioid, mu

The highest maximum binding capacities at the mu-sites of rabbit brain are in the striatum, with intermediate levels in the diencephalon, mesencephalon, cerebellum and cortex and low levels in the pons-medulla and hippocampus. For the delta-site the highest maximum binding capacity is also in the striatum; there are almost equally low levels in the other brain regions. At the kappa-sites the maximum binding capacities are highest in the diencephalon; there are intermediate levels in the cortex and striatum, and low levels in the mesencephalon, cerebellum, hippocampus and pons-medulla. The KD values lack reproducibility; there are no regional variations at the kappa-site as estimated with [3H](-)-bremazocine, but the possibility cannot be excluded that there are regional variations in the KD values for [3H][D-Ala2,MePhe4,Gly-ol5]enkephalin at the mu-site or for [3H][D-Ala2,D-Leu5]enkephalin at the delta-site. It may be important to use saturation analysis in future investigations of the distributions of the binding sites.

Topics: Analgesics; Animals; Benzomorphans; Binding, Competitive; Body Weight; Brain Chemistry; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; In Vitro Techniques; Male; Membranes; Nerve Tissue Proteins; Rabbits; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu

The effect of the administration of thyroxine (T4) (1 mg/kg, s.c.), to male Sprague-Dawley rats on alternate days for 18 days, on the binding of opioid ligands, [3H]Tyr-D-Ala-Gly-MePhe-Gly-ol (DAGO, mu receptors), [3H]Tyr-D-Ser-Gly-Phe-Leu-Thr (DSTLE, delta receptors) and [3H]ethylketocyclazocine (EKC, kappa receptors) to membranes of regions of the brain was determined. The chronic administration of thyroxine to rats decreased their rate of gain of body weight, increased colonic temperature and increased systolic blood pressure and heart rate, in comparison to vehicle-injected rats. The administration of thyroxine also increased the serum concentration of triiodothyronine (total T3) and thyroxine, when compared to vehicle-injected rats. The binding of [3H]DAGO to membranes of the striatum of rats treated with thyroxine was greater than in vehicle-treated rats; however, the binding to membranes of pons and medulla, amygdala, hypothalamus, midbrain and cortex in the two treatment groups did not differ. The increased binding of [3H]DAGO in rats treated with thyroxine was due to an increase in the Bmax value. The binding of [3H]DSTLE in the midbrain, hypothalamus, pons and medulla and striatum of rat treated with thyroxine and vehicle-injected rats did not differ but it was significantly less in the amygdala of rats injected with thyroxine than in vehicle-injected rats. The decreased binding in the amygdala was due to changes in the Kd value of [3H]DSTLE.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Pressure; Body Weight; Brain; Chromatography, High Pressure Liquid; Cyclazocine; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalins; Ethylketocyclazocine; Heart Rate; Hyperthyroidism; Male; Membranes; Oligopeptides; Rats; Rats, Inbred Strains; Receptors, Opioid; Thyroxine

The effect of chronic administration of methimazole (0.05% w/v) in drinking water for 32 days to male Sprague-Dawley rats on the binding of opioid ligands, 3H-Tyr-D-Ala-Gly-MePhe-Gly-ol (DAGO, mu-receptors), 3H-Tyr-D-Ser-Gly-Phe-Leu-Thr (DSTLE, delta-receptors) and 3H-ethylketocyclazocine (EKC, kappa-receptors) to membranes of brain regions was determined. Chronic administration of methimazole to rats decreased their rate of body weight gain, colonic temperature, systolic blood pressure and heart rate in comparison to vehicle-treated rats. Administration of methimazole also decreased the serum concentration of triiodothyronine (total T3) and T4 when compared to vehicle-treated rats. The binding of 3H-DAGO to membranes of amygdala, pons and medulla, striatum, midbrain and cortex of methimazole-treated rats was greater than vehicle-treated rats, however, the binding to membranes of hypothalamus in the two treatment groups did not differ. The binding of 3H-DSTLE in amygdala and hypothalamus of methimazole-treated rats did not differ but it was significantly greater in pons and medulla, midbrain, cortex and striatum of methimazole-treated rats than vehicle-treated rats. The binding of 3H-EKC to membranes of pons and medulla was lower and of striatum and cortex of methimazole-treated rats was significantly greater than vehicle-treated rats, but the binding to membranes of amygdala, hypothalamus, and midbrain of the two treatment groups did not differ. The results indicate that brain, mu-, delta- and kappa-opioid receptors are differentially altered in hypothyroidism.

Topics: Animals; Body Temperature; Body Weight; Brain Chemistry; Cyclazocine; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalins; Ethylketocyclazocine; Heart Rate; Hypothyroidism; Male; Methimazole; Oligopeptides; Rats; Rats, Inbred Strains; Receptors, Opioid; Triiodothyronine

beta-Chlornaltrexamine (beta-CNA) is a non-equilibrium opioid receptor antagonist which alkylates and inactivates opioid receptors. Because opioid peptides are thought to contribute to the regulation of food intake, we examined the effects of intracerebroventricular (icv) injections of beta-CNA on the food intake and body weight of male rats. We also tested the ability of beta-CNA to block food intake stimulated by selective agonists of kappa, mu and delta opioid receptors: dynorphin A2 (DYN), Tyr-D-Ala-Gly-(Me)Phe-Gly-ol (DAGO), and [(D-Ser2,Leu5]-enkephalin-Thr6 (DSLET). Treatment with beta-CNA caused a long-term (2-4 days) reduction in daily food intake and a concomitant reduction in body weight. An additional experiment indicated that the weight loss after beta-CNA treatment could be completely accounted for by the reduction in intake. beta-CNA treatment also abolished or greatly attenuated the feeding effects of DAGO, DSLET and DYN, even when these peptides were tested 26 hours after beta-CNA administration. The long duration of the effects of beta-CNA suggests that this compound will be a useful pharmacological tool in further study of the opioid feeding system.

Topics: Animals; Body Weight; Dynorphins; Eating; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, Leucine; Enkephalins; Male; Naltrexone; Oligopeptides; Rats; Rats, Inbred Strains; Receptors, Opioid