Multiple opiate receptors of brain and spinal cord in opiate addiction

Preoperative screening for illicit drug use in patients undergoing emergency surgery: A prospective observational study

Knowledge of illicit drug users (IDUs) is important because of the comorbidity related to drug use. In this prospective, observational study, we screened 1007 patients undergoing emergency surgery and found that 75 of them (7.5%) were IDUs The results of preoperative screening showed that the rates of HIV and syphilis infection were significantly higher in IDUs (HIV (+) 2.6%, syphilis (+) 10.7%) than in non-IDUs (HIV (+) 0, syphilis (+) 0.5%). Intraoperative consumption of remifentanil (IDUs: 1.85 ± 1.30 vs. non-IDUs: 1.31 ± 0.86, p = 0.009), midazolam (IDUs: 4.82 ± 1.52 vs. non-IDUs: 4.15 ± 1.81, p = 0.002), and atracurium (IDUs: 31.5 ± 15.1 vs. non-IDUs: 25.5 ± 11.9, p = 0.006) and the proportion of patients requiring postoperative fentanyl (IDUs: 15 (20.0%) vs. non-IDUs: 95 (1.2%), p = 0.031) were significantly increased in IDUs compared to non-IDUs. Postoperative complications were observed in 22.7% (17/75) of patients who were IDUs, which was significantly increased when compared with non-IDUs (6.0%, 56/932, p < 0.001). The mortality rate within 30 days after surgery was similar between the two groups. These findings suggested that the IDUs were associated with increased rates of HIV and syphilis infection; greater consumption of intraoperative opioids, sedatives, and muscle relaxants; increased postoperative complications and a similar mortality rate within 30 days after surgery when compared with non-IDUs.

Feeding and reward: perspectives from three rat models of binge eating

Research has focused on understanding how overeating can affect brain reward mechanisms and subsequent behaviors, both preclinically and in clinical research settings. This work is partly driven by the need to uncover the etiology and possible treatments for the ongoing obesity epidemic. However, overeating, or non-homeostatic feeding behavior, can occur independent of obesity. Isolating the variable of overeating from the consequence of increased body weight is of great utility, as it is well known that increased body weight or obesity can impart its own deleterious effects on physiology, neural processes, and behavior. In this review, we present data from three selected animal models of normal-weight non-homeostatic feeding behavior that have been significantly influenced by Bart Hoebel's 40+-yr career studying motivation, feeding, reinforcement, and the neural mechanisms that participate in the regulation of these processes. First, a model of sugar bingeing is described (Avena/Hoebel), in which animals with repeated, intermittent access to a sugar solution develop behaviors and brain changes that are similar to the effects of some drugs of abuse, serving as the first animal model of food addiction. Second, another model is described (Boggiano) in which a history of dieting and stress can perpetuate further binge eating of palatable and non-palatable food. In addition, a model (Boggiano) is described that allows animals to be classified as having a binge-prone vs. binge-resistant behavioral profile. Lastly, a limited access model is described (Corwin) in which non-food deprived rats with sporadic limited access to a high-fat food develop binge-type behaviors. These models are considered within the context of their effects on brain reward systems, including dopamine, the opioids, cholinergic systems, serotonin, and GABA. Collectively, the data derived from the use of these models clearly show that behavioral and neuronal consequences of bingeing on a palatable food, even when at a normal body weight, are different from those that result from simply consuming the palatable food in a non-binge manner. These findings may be important in understanding how overeating can influence behavior and brain chemistry.

Acute delta- and kappa-opioid agonist pretreatment potentiates opioid antagonist-induced suppression of water consumption

The primary objective of this study was to determine whether pretreatment with kappa- and delta-opioid agonists potentiates naltrexone-induced suppression of water consumption following 24h of deprivation. This study also examined the temporal effects of agonist-induced antinociception using the tail-flick and hot-plate tests. Adult male Sprague-Dawley rats were water deprived 20 h and then given an injection (s.c. or i.c.) of an opioid agonist or saline. Drugs included the mu-opioid agonists morphine and DAMGO ([d-Ala2,NMePhe4,Gly-ol5]-enkephalin), the kappa-opioid agonists spiradoline, bremazocine, and U69,593, and the delta-opioid agonists BW 373U86 and DPDPE ([D-Pen2, D-Pen5]-enkephalin). Three hours and forty-five minutes later, animals received a single dose of naltrexone (0.1-30 mg/kg, s.c.) or saline. Fifteen minutes later, animals were allowed free access to water for 30 min. For the tail-flick and hot-plate tests, animals were given a single injection of agonist and tested in both procedures every 30 min for up to 2h, then hourly up to 6h post-injection. Naltrexone dose-dependently suppressed fluid consumption 24h after deprivation. The effects of naltrexone on drinking were potentiated following pretreatment with at least one dose of the agonists tested except BW 373U86. With the exception of BW 373U86, DAMGO, and DPDPE, all of the opioid agonists produced significant antinociception in the hot-plate test. Only BW 373U86 failed to have an antinociceptive effect in the tail-flick test. By 4h after treatment, drug-induced antinociception had largely waned, suggesting the potentiation of naltrexone-induced drinking suppression was not a result of a direct interaction with the agonists. In conclusion, kappa-opioid and delta-opioid receptors appear to contribute to the manifestation of acute opioid dependence, albeit to a lesser degree than mu-opioid receptors.

Proteomic analysis of spinal protein expression in rats exposed to repeated intrathecal morphine injection

Repeated administration of morphine for treating severe chronic pain may lead to neuroadaptive changes in the spinal cord that are thought to underlie molecular mechanisms of the development of morphine tolerance and physical dependence. Here, we employed a 2-D gel-based proteomic technique to detect the global changes of the spinal cord protein expression in rats that had developed morphine tolerance. Morphine tolerance at the spinal cord level was induced by repeated intrathecal injections of morphine (20 microg/10 microL) twice daily for 5 days and evaluated by measurements of paw withdrawal latencies and maximal possible analgesic effect at day 5. After behavioral tests, the lumbar enlargement segments of spinal cord were harvested and proteins resolved by 2-DE. We found that eight proteins were significantly up-regulated or down-regulated in spinal cord after morphine tolerance development, including proteins involved in targeting and trafficking of the glutamate receptors and opioid receptors, proteins involved in oxidative stress, and cytoskeletal proteins, some of which were confirmed by Western blot analysis. Morphine-induced expressional changes of these proteins in the spinal cord might be involved in the central mechanisms that underlie the development of morphine tolerance. It is very likely that these identified proteins may serve as potential molecular targets for prevention of the development of morphine tolerance and physical dependence.

Sensitivity of neuronal nicotinic acetylcholine receptors to the opiate antagonists naltrexone and naloxone: receptor blockade and up-regulation

In HEK293 cells stably expressing alpha4beta2 nAChRs, naltrexone, but not naloxone, blocked alpha4beta2 nAChRs via an open-channel blocking mechanism. In primary hippocampal cultures, naltrexone inhibited alpha7 nAChRs up-regulated by nicotine, and in organotypic hippocampal cultures naltrexone caused a time-dependent up-regulation of functional alpha7 nAChRs that was detected after removal of the drug. These results indicate that naltrexone could be used as a smoking cessation aid.

Effects of U-50,488H on isolated atria from rats chronically treated with the kappa-opioid agonist, U-50,488H

The present investigation was aimed at determining if chronic activation of kappa- or mu-opioid receptors induce development of tolerance and dependence to kappa-opioid agonists on the isolated left atria of the rat. Tolerance to a kappa-agonist (specific tolerance) was induced by chronic administration of U-50,488H, a selective kappa-agonist (15 mg kg(-1) i.p. twice a day for 4 days). The animals were rendered tolerant to morphine by subcutaneous implantation of morphine pellets (75 mg per pellet) for 7 days. Tolerance to U-50,488H was observed after its chronic administration and was revealed as a rightward shift of the concentration-response curve, it was accompanied by a decrease in the maximum response and in the slope. Preparations from morphine-treated rats were not tolerant to the selective kappa-agonist, that is, there was no cross-tolerance between mu- and kappa-agonists. Dependence to the kappa-agonist was tested by administration in the organ bath of Mr-2266 (preferential kappa-antagonist) or nor-binaltorphimine (nor-BNI; selective kappa-antagonist). The administration in the organ bath of the kappa-antagonists Mr-2266 or nor-BNI to preparations from U-50,488H-treated rats induced an increase in atrial force of contraction. In contrast, the administration of the kappa-antagonists to preparations from control rats induced a decrease in atrial force of contraction. These findings demonstrate that left atria from chronically U-50488H-treated rats exhibit tolerance to the negative inotropic effects of U-50,488H as well as opioid withdrawal after nor-BNI.

A role of nitric oxide in WIN 55,212-2 tolerance in mice

The role of nitric oxide (NO) in the development of cannabinoid tolerance was examined by using N(omega)-nitro-L-arginine methyl ester (L-NAME) as an inhibitor of NO synthase. R(+)-[2,3-Dihydro-5-methyl-3 [(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazin-yl]-(1-napht halenyl)methanone mesylate (WIN 55,212-2), a cannabinoid receptor agonist, or L-NAME plus WIN 55,212-2 was acutely or chronically injected i.p. to mice and analgesia, body temperature and immobility were measured. A single injection of WIN 55,212-2 induced time- and dose-dependent analgesia, hypothermia and catalepsy. L-NAME (50 mg/kg), which per se was ineffective, administered 20 min before WIN 55,212-2 did not modify the analgesic, hypothermic and cataleptic responses to the cannabinoid. When WIN 55,212-2 was administered once a day, the animals became completely tolerant to the analgesic, hypothermic and cataleptic effects within five, seven and nine days respectively. L-NAME injected once daily 20 min before WIN 55,212-2 inhibited the development of tolerance to the hypothermic and cataleptic actions but not to the analgesic action of WIN 55,212-2. Since L-NAME given chronically by itself did not modify the analgesia, hypothermia and catalepsy induced by acute administration of WIN 55,212-2, our findings suggest L-NAME acts with some selectivity on the mechanisms involved in cannabinoid tolerance.

Modulation of rat brain cannabinoid receptors after chronic morphine treatment

Intraperitoneal injection of delta9-THC (7.5 mg/kg) in rats made tolerant to morphine by s.c. implantation of morphine pellets had a much greater analgesic effect than in placebo pellet plus delta9-THC treatment. To investigate whether this was due to some change in cannabinoid receptor levels and/or expression induced by chronic morphine, we designed this autoradiographic binding study coupled with in situ hybridization on sagittal sections of the treated rat brains. Binding showed a significant increase in CB1 receptor density (15%) specifically in the caudate-putamen, in parallel with a significant enhancement of CB1 mRNA in the same area (20%). We suggest that morphine chronic treatment leads to a functional modulation between the opioid and cannabinoid systems at least for analgesia in a specific area, in this case the striatum.

Effects of chronic U-50,488H treatment on the isolated right atrium of the rat

The aim of the present investigation was to determine if chronic activation of kappa-opioid receptor induces development of tolerance and dependence to kappa-opioid agonists on the isolated right atrium of the rat. Tolerance to the kappa-agonist was induced by chronic administration of U-50,488H, a selective kappa-agonist (15 mg/kg i.p. twice a day for 4 days). The rats were killed on day 5. Tolerance to U-50,488H was observed after its chronic administration and was revealed as a rightward shift of the concentration-response curve; it was accompanied by a decrease in the maximum response and in the slope. Withdrawal to the kappa-agonist was induced by administration of Mr-2266 (preferentially kappa-antagonist) or nor-binaltorphimine (nor-bni; selective kappa-antagonist) to the organ bath. The administration of the kappa-antagonists Mr-2266 or nor-bni to preparations from tolerant rats in the organ bath induced an increase in auricular contraction frequency. In contrast, the administration of the kappa-antagonists to preparations from vehicle-treated rats induced a decrease in auricular contraction frequency. These findings demonstrate that the hearts of rats that had received chronic U-50,488H treatment develop tolerance to the cardiac effects of U-50,488H and exhibit excitatory reactions to kappa-antagonist's precipitated withdrawal.

Time course of the changes in central nitric oxide synthase activity following chronic treatment with morphine in the mouse: reversal by naltrexone

1. The time course of the effect of chronic administration of morphine on the activity of nitric oxide synthase (NOS) in the brain regions and spinal cord of the mouse was determined. The effect of naltrexone by itself on the NOS activity and that induced by morphine also were determined. 2. Male Swiss Webster mice were implanted subcutaneously with a pellet containing 25 mg of morphine free base for 4 days. Placebo pellet implanted mice served as controls. 3. Twenty-four hours after treatment with morphine, NOS activity decreased in the cerebellum, midbrain, cortex and remainder of the brain as well as in the spinal cord. Forty-eight and 72 hr after the treatment with morphine, NOS activity increased in the cerebellum and cortex, but no change was observed in the other brain regions and spinal cord. Twenty-four hours after morphine pellet removal (withdrawal), NOS activity in all brain regions and the spinal cord has returned to normal. 4. Implantation of a pellet containing 10 mg of naltrexone did not alter NOS activity in any brain region or spinal cord for 24, 48 and 72 hr or 24 hr after removal of the pellet. 5. Implantation of a naltrexone pellet in conjunction with a morphine pellet blocked the changes in NOS activity in the brain region and spinal cord induced by morphine. 6. It is concluded that the initial decrease in NOS activity by morphine may be related to enhanced motor activity, whereas the increase in NOS activity in certain brain regions may be associated with tolerance-physical dependence development. Additionally, the changes in central NOS activity by morphine appear to be mediated by opioid receptors because they were blocked by concurrent treatment with naltrexone.

Effects of multiple intracerebroventricular injections of [D-Pen2,D-Pen5]enkephalin and [D-Ala2,Glu4]deltorphin II on tolerance to their analgesic action and on brain delta-opioid receptors

Male Swiss-Webster mice were injected intracerebroventricularly (i.c.v.) with [D-Pen2,D-Pen5]enkephalin (DPDPE), a delta 1-opioid receptor agonist (20 micrograms per mouse) twice a day for either 2 or 4 days. Vehicle injected mice served as controls. Treatment of mice with DPDPE for 2 or 4 days decreased its analgesic response by 44 and 76%, respectively in comparison to vehicle injected mice. Treatment of mice with DPDPE for 2 or 4 days decreased density (Bmax) of [3H]DPDPE to bind to brain homogenates by 77 and 76%, respectively, in comparison to vehicle injected controls but the apparent dissociation constant (kd) values were not altered. The effects of i.c.v. injections of [D-Ala2,Glu4]deltorphin II (deltorphin II), a delta 2-opioid receptor agonist (20 micrograms per mouse) twice a day for either 2 or 4 days on its analgesic response as well as on brain receptors for [3H]DPDPE were also determined. The analgesic response to deltorphin II decreased by 51 and 78%, respectively in mice treated with deltorphin II for 2 or 4 days, respectively. Two or four days treatment with deltorphin II decreased the Bmax of [3H]DPDPE by 76 and 87%, respectively. The 2-day treatment also increased the Kd value by 58%, but the 4-day treatment with deltorphin II had no effect on the Kd of [3H]DPDPE to bind to brain membranes. Thus, multiple injections of delta 1- or delta 2-opioid receptor agonists results in the development of tolerance to their analgesic action and the intensity of tolerance increases with the duration of treatment. Both delta 1- and delta 2-opioid receptor agonist, on chronic administration, result in the down-regulation of delta 1-opioid receptors labeled with [3H]DPDPE.

Effect of low pH treatment on opioid peptides binding to their receptors and functional coupling of G-proteins to adenylyl cyclase in the rat spinal cord

Because low pH treatment is known to alter the coupling of G-proteins to brain receptors, and little is known about such an effect in the spinal cord, the present study was undertaken to examine whether preincubation of rat spinal cord membranes at low pH (pH 4.5) alters opioid receptor binding characteristics and sodium fluoride (NaF)-stimulated adenylyl cyclase (AC) activity (as a function of G, mediated). [3H][D-Ala2,MePhe4,Gly-ol]enkephalin (DAMGO) and [3H]ethylketocyclazosine (EKC) were used to label mu- and kappa-opioid receptors, respectively. AC activity was determined using ATP as substrate and cAMP formed was quantified. Low pH treatment of membranes did not affect the mu- and kappa-opioid binding characteristics in rat spinal cord. However, the low pH treatment significantly reduced the NaF-stimulated AC activity in rat spinal cord. It is concluded that low pH treatment causes selective changes in the functional coupling of Gs-proteins to AC without affecting the opioid receptor binding characteristics in the spinal cord.

Non-competitive antagonism of N-methyl-D-aspartate receptor inhibits tolerance to the analgesic action of U-50,488H, a kappa-opiate receptor agonist in the rat

1. The effect of dizocilpine (MK-801), a non-competitive inhibitor of N-methyl-D-aspartate (NMDA) receptor on the development of tolerance to the analgesic and hypothermic actions of U-50,488H, a highly selective kappa-opiate receptor agonist, was determined in the rat. 2. Male Sprague-Dawley rats were made tolerant to the pharmacological actions of U-50,488H by twice daily intraperitoneal (i.p.) injections of the drug (25 mg/kg) for 4 days. 3. Multiple injections of U-50,488H resulted in the development of tolerance to its analgesic and hypothermic actions in the rat. MK-801 injected 10 min before each injection of U-50,488H, dose-dependently inhibited the development of tolerance to the analgesic action but the tolerance to the hypothermic action of U-50,488H was unaffected. 4. Multiple injections of U-50,488H decreased the body weight gain. MK-801 dose-dependently decreased the gain in body weight further. 5. The results indicate that non-competitive antagonism of the NMDA receptor by MK-801 can selectively inhibit the tolerance to the analgesic action of U-50,488H in the rat, however, such an effect was associated with significant decreases in normal gain in body weight.

Attenuation of tolerance to, and physical dependence on, morphine in the rat by inhibition of nitric oxide synthase

1. The effect of NG-monomethyl-L-arginine (NMMA), an inhibitor of nitric oxide synthase (NOS), on the development of tolerance to and physical dependence on morphine was determined in the rat. 2. Male Sprague-Dawley rats were rendered tolerant to and dependent on morphine by the subcutaneous implantation of four morphine pellets (each containing 75 mg morphine base) during a 3 day period. Placebo pellet implanted rats served as controls. 3. Chronic administration of morphine resulted in the development of tolerance to the analgesic action of morphine. Twice daily injections of NMMA (4 or 8 mg/kg) attenuated the tolerance to morphine as evidenced by higher analgesic response in NMMA treated than in vehicle treated morphine tolerant rats. 4. Chronic administration of morphine also resulted in the development of physical dependence as evidenced by the appearance of a variety of symptoms including stereotyped jumping response following naltrexone injection. Concurrent treatment with NMMA inhibited naltrexone-induced jumping response but other responses like fecal boli formation, wet dog shakes, teeth chattering, rearing and ejaculations were not modified. 5. It is concluded that inhibition of NOS can attenuate the development of tolerance to, and physical dependence on, morphine in the rat. However, it appears that higher doses of NOS inhibitors are required in the rat than in the mouse for blockade of both tolerance and physical dependence processes.

Cloning and characterization of the promoter region of the mouse mu opioid receptor gene

Opioid compounds have potent analgesic and euphoric properties. They act with specific cell-membrane receptors which have been pharmacologically defined into three major classes, mu, kappa and delta. These receptors are highly regulated with respect to their gene expression, resulting in a temporally and spatially specific pattern of distribution for each receptor. To characterize the promoter sequence of the mu opioid receptor (MOR) gene, a mouse genomic DNA library was screened under high stringency with a rat MOR (MOR-1) cDNA probe and genomic sequences for the mouse MOR gene were isolated. From one genomic clone, a 2.3-kb EcoRI fragment, which hybridized to the 5'-end of the rat MOR-1 cDNA probe, was subcloned and sequenced. This fragment contains 1.3 kb of sequence upstream of the initiation codon, extends downstream through exon 1 and includes a portion of intron 1. Primer extension analysis using mouse brain poly (A)+ RNA identified a transcription initiation site 793 bp upstream from the translation start site. Chimeric constructs of mouse MOR deletion fragments fused to a luciferase reporter gene were transfected into a human neuroblastoma cell line, SK-N-SH, which constitutively expresses endogenous MOR. These transient expression studies indicated that the 0.2-kb region upstream from the transcription initiation site possesses a functional promoter, which directs the expression of the reporter gene in vitro and may possess promoter activity for the mouse MOR gene in vivo.

Effects of NMDA receptor blockade and nitric oxide synthase inhibition on the acute and chronic actions of delta 9-tetrahydrocannabinol in mice

The present studies examined the hypothesis that the N-methyl-D-aspartate (NMDA) receptor-nitric oxide (NO) pathway might be involved in the acute and chronic actions of delta 9-tetrahydrocannabinol (THC). The ability of dizocilpine (MK-801), a competitive NMDA receptor antagonist and NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthase enzyme to modify the analgesic and hypothermic responses following the acute and chronic treatment of animals with THC was determined in male Swiss-Webster mice. Intraperitoneal administration of THC (5, 10 and 20 mg/kg) produced dose-dependent analgesic and hypothermic effects. MK-801 at 0.1 mg/kg i.p. attenuated the analgesic but not the hypothermic responses to THC (10 and 20 mg/kg, i.p.). The effects of various doses of MK-801 (0.03, 0.1 and 0.3 mg/kg, i.p.) on the analgesic and hypothermic responses to a 10 mg/kg, i.p. dose of THC was also determined. All the doses of MK-801 antagonized the analgesic but not the hypothermic effects of THC. The chronic treatment of animals with THC (10 mg/kg, i.p.) twice daily for 4 days produced tolerance to its analgesic and hypothermic effects. Pretreatment of animals with MK-801 (0.03-0.30 mg/kg, i.p.) did not affect the development of tolerance to the analgesic or the hypothermic action of THC. The pretreatment of animals with L-NMMA (2-8 mg/kg, i.p.), did not alter the analgesic or hypothermic effects of THC. Also, it did not modify the tolerance to its pharmacological actions.(ABSTRACT TRUNCATED AT 250 WORDS)

Supraspinal delta opioid receptor mRNA levels are not altered in [D-Ala2]deltorphin II tolerant mice

Delta opioid receptor (DOR) mRNA levels were studied in mice rendered tolerant to [D-Ala2]deltorphin II by 4 days of repeated intracerebroventricular administration (10 micrograms, [tid]). ED50 determinations on day 5 revealed a 10-fold loss in [D-Ala2]deltorphin II potency with the tail-flick test. Utilization of a microdissection technique followed by quantitative solution hybridization of RNA extracts from mouse brain revealed mean levels of DOR mRNA ranging from 3.9 pg/micrograms RNA in the caudate-putamen to 0.4 pg/micrograms RNA in the cerebellum. DOR mRNA levels were not different when RNA extracts from tolerant and non-tolerant mice were compared. These data suggest that altered DOR mRNA levels are not one of the adaptive changes that occur with delta opioid ([D-Ala2]deltorphin II) tolerance.

Evidence for a bidirectional cross-tolerance between morphine and delta 9-tetrahydrocannabinol in mice

Male Swiss-Webster mice were rendered tolerant to morphine by subcutaneous implantation of a morphine pellet, each containing 75 mg morphine base, for 3 days. Mice implanted with placebo pellets served as controls. A high degree of tolerance to the analgesic effect of morphine developed as evidenced by decreased analgesic response to various doses of morphine. delta 9-Tetrahydrocannabinol (5, 10 and 20 mg/kg i.p.) produced dose-dependent analgesic and hypothermic effects in mice implanted with placebo pellets. A significant decrease in the analgesic effects of tetrahydrocannabinol was observed in morphine-tolerant mice as compared to placebo controls. Mice were rendered tolerant to delta 9-tetrahydrocannabinol by injecting the drug (5, 10, or 20 mg/kg i.p.) twice daily for 4 days. Vehicle-injected mice served as controls. Tolerance to the analgesic and hypothermic effects of delta 9-tetrahydrocannabinol in mice injected chronically with the drug was evidenced by the decreases in the intensity of these responses when compared to those observed in vehicle-injected controls. Morphine produced dose-dependent analgesic and hypothermic effects in mice injected chronically with vehicle but the intensity of these effects was significantly lower in mice injected chronically with delta 9-tetrahydrocannabinol. These results indicate that a possible interaction exists between delta 9-tetrahydrocannabinol and the mu-opioid receptors and that a substantial tolerance to analgesic and hypothermic effects of morphine develops in delta 9-tetrahydrocannabinol-tolerant mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of morphine tolerance and abstinence on the binding of [3H]MK-801 to brain regions and spinal cord of the rat

The effect of chronic administration of morphine to rats on the N-methyl-D-aspartate (NMDA) receptors labeled with [3H]MK-801, a non-competitive antagonist, was determined in brain regions and spinal cord. Male Sprague-Dawley rats were rendered tolerant to and physically dependent on morphine by subcutaneous implantation of 6 morphine pellets during a 7-day period. Each pellet contained 75 mg of morphine free base. Animals serving as controls were similarly implanted with placebo pellets. This procedure resulted in the development of a high degree of tolerance and physical dependence on morphine. Two sets of rats were used. In one, the pellets were left intact at the time of sacrifice (tolerant) and in the other the pellets were removed 16 h prior to sacrificing (abstinent). The binding constants, Bmax and Kd values of [3H]MK-801 were determined in cortex, hippocampus, hypothalamus, corpus striatum, midbrain and spinal cord. In the absence of glycine and glutamate, [3H]MK-801 bound to tissue membranes at a single high affinity site. The Bmax and Kd values of [3H]MK-801 were not altered in any of the tissues of the morphine abstinent rats. The Bmax value of [3H]MK-801 was significantly decreased in cerebral cortex of morphine tolerant rats as compared to their placebo controls but the Kd values did not change. In other brain regions and spinal cord of morphine tolerant rats and their placebo controls, the Bmax and Kd values of [3H]MK 801 did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of morphine tolerance and abstinence on the binding of [3H]naltrexone to discrete brain regions and spinal cord of the rat

1. The effect of morphine tolerance and abstinence on the binding of [3H]naltrexone to discrete brain regions and spinal cord of the rat was determined. 2. Male Sprague-Dawley rats were implanted s.c. under light ether anesthesia with six morphine pellets for a 7-day period. Each pellet contained 75 mg of morphine base. Rats implanted with six placebo pellets each served as controls. 3. This procedure resulted in the development of tolerance to morphine as evidenced by decreased analgesic response to various doses of morphine. 4. The binding characteristics (Bmax or Kd values) of [3H]naltrexone, an opiate receptor antagonist, were determined in various tissues of morphine tolerant and abstinent rats. In the tolerant rats, the pellets were left in place at the time of sacrificing, whereas in the abstinent rats, the pellets were removed 18 hr prior to sacrificing. 5. The binding of [3H]naltrexone to opiate receptors on membranes prepared from brain regions (hypothalamus, hippocampus, cortex, pons and medulla, midbrain, corpus striatum and amygdala) and spinal cord of rats from various treatment groups was determined. 6. [3H]Naltrexone bound to tissue membranes at a single high affinity binding sites. The Bmax values of [3H]naltrexone to bind to opiate receptors on the membranes of amygdala and striatum were increased significantly in morphine tolerant rats when compared to the placebo controls, but the Kd values did not differ. 7. The Bmax and Kd values of [3H]naltrexone did not differ in any other brain region or spinal cord of morphine tolerant rats and their placebo controls. The binding constants of [3H]naltrexone were unaffected in morphine abstinent rats. 8. Previously we had shown that the binding of [3H]D-Ala2, MePhe4, Gly-ol5 enkephalin (DAMGO), a highly specific agonist for mu-opiate receptors was decreased in cortex, pons and medulla and spinal cord of morphine tolerant but not in the abstinent rats. In addition, delta and kappa receptors are unaffected in morphine tolerant and abstinent rats. 9. The results suggest that direction of change, as well as, the brain areas for mu-agonist and -antagonist opiate binding sites are affected differentially in morphine tolerant rats.

Effects of morphine withdrawal syndrome on endo-oligopeptidase (EC 3.4.22.19) activity

Endo-oligopeptidase (EC 3.4.22.19), an enzyme capable of generating enkephalin by single cleavage from enkephalin-containing peptides, was examined in several areas of the central nervous system (CNS) as well as in the immune and endocrine tissues of rats chronically treated with morphine and submitted to naloxone-induced withdrawal. A specific fluorogenic substrate was used to determine the endopeptidase 22.19 activity. A non-uniform increase in endopeptidase 22.19 activity was detected in the CNS. The highest increase in endopeptidase 22.19 specific activity was found in the dorsal hippocampus (about 3.5-fold higher than control), followed by occipital and frontal cortex, substantia nigra, thalamus and hypothalamus. In peripheral tissues, a significant decrease of endopeptidase 22.19 was observed in the pineal gland, whereas the morphine withdrawal syndrome caused a slight but significant increase in lymphoid tissues such as lymph nodes and thymus. These findings are indicative of a possible participation of endopeptidase 22.19 in naloxone-induced withdrawal.

Effects of naltrexone pellet implantation on morphine tolerance and physical dependence in the rat

1. The effect of naltrexone pellets containing either 10 or 30 mg of naltrexone base on the development of tolerance and physical dependence on morphine was assessed in male Sprague-Dawley rats. Tolerance-dependence on morphine was induced by s.c. implantation of six morphine pellets, each containing 75 mg morphine base for 7 days. 2. Naltrexone pellet implantation blocked the development of tolerance to the analgesic and hyperthermic effects of morphine. Similarly, naltrexone pellet implantation reversed morphine withdrawal-induced body weight loss. The effect of pellets containing 10 and 30 mg naltrexone did not differ. 3. The effect of naltrexone (10 mg) pellet implantation on various signs of naltrexone-precipitated withdrawal such as body weight loss, hypothermia and increases in urinary and fecal output was investigated. Naltrexone pellet implantation did not alter the naltrexone-precipitated withdrawal-induced body weight loss. Concurrent naltrexone pellet implantation blocked the naltrexone-precipitated withdrawal-induced hypothermia, increased fecal and urinary output in morphine-dependent rats. 4. These results indicate that a single pellet of 10 mg of naltrexone can effectively block morphine tolerance and physical dependence in the rat. Such a procedure may be useful in studying biochemical, endocrinological and immunological mechanisms involved in opioid addiction processes.

Effects of naltrexone on the binding of [3H]D-Ala2, MePhe4, Gly-ol5-enkephalin to brain regions and spinal cord and pharmacological responses to morphine in the rat

1. The effects of naltrexone pellet implantation and removal on the analgesic and hypothermic effects of morphine and the binding of 3H-D-Ala2, MePhe4, Gly-ol5-enkephalin (DAMGO) to mu-opiate receptors in rat brain regions and spinal cord were determined. 2. Male Sprague-Dawley rats were implanted subcutaneously with a pellet containing 10 mg of naltrexone for 7 days. Placebo pellet implanted rats served as controls. The pellets were removed on day 8, and the analgesic and hyperthermic effects were determined in the rat 24 hr later. Morphine produced a dose-dependent analgesic and hyperthermic responses in rats implanted with placebo pellets. Enhanced analgesic and hyperthermic responses to morphine were produced in rats implanted with naltrexone pellets. 3. The binding constants (Bmax and Kd values) of [3H]DAMGO in regions of the brain (amygdala, hypothalamus, striatum, midbrain, hippocampus, pons + medulla and cortex), and spinal cord of rats with naltrexone pellet left intact or removed were determined. The Bmax values of [3H]DAMGO were increased in all brain regions and spinal cord of rats in which the naltrexone pellets were left in place or removed prior to sacrificing. However, the Kd values of [3H]DAMGO were unaffected by naltrexone treatment. 4. It is concluded that enhanced analgesic and hyperthermic response to morphine is produced in rats implanted with naltrexone pellets and such alterations in the pharmacological responses are due to up-regulation of mu-opiate receptors in all the brain regions and spinal cord. Additionally whether the pellets were left intact (receptors blocked) or removed (receptors not blocked), the mu-opiate receptors were up-regulated in spinal cord and all the regions of the brain.

Evidence for the role of nitric oxide in kappa-opiate tolerance in mice

The hypothesis that inhibition of nitric oxide (NO) synthase with subsequent decrease in the production of NO might attenuate the development of kappa-opiate tolerance was examined. Concurrent treatment of NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA) (2-8 mg/kg, i.p.) along with U-50,488H (25 mg/kg, i.p.) twice daily for 4 days dose-dependently attenuated the development of tolerance to the analgesic and hypothermic effects of U-50,488H (25 mg/kg, i.p.). L-NMMA by itself did not modify the analgesic and hypothermic effects of acute administration of U-50,488H. A potential role for NO in the development of kappa-opiate tolerance is suggested.

Biochemical and behavioral studies on the interaction between mu- and kappa-opiate agonists in mice

Male Swiss-Webster mice were rendered tolerant to morphine by subcutaneous implantation of a morphine pellet, each containing 75 mg morphine base, for 3 days. Mice implanted with placebo pellets served as controls. A high degree of tolerance to the analgesic effect of morphine developed as evidenced by decreased analgesic response to various doses of morphine. A selective kappa-opiate agonist, U-50,488H (8, 16 and 32 mg/kg, i.p.) produced dose-dependent analgesic and hypothermic effects in mice implanted with placebo pellets. A significant decrease in the analgesic and hypothermic effects of U-50,488H was observed in morphine tolerant mice as compared to placebo-treated mice. Mice were rendered tolerant to U-50,488H by injecting the drug (25 mg/kg, i.p.) twice daily for 4 days. Vehicle injected mice served as controls. Tolerance to the analgesic and hypothermic effects of U-50,488H in mice injected chronically with the drug was evidenced by the decreases in the intensity of these responses when compared to those observed in vehicle injected controls. Morphine produced a dose-dependent analgesic and hypothermic effects in mice injected chronically with vehicle but the intensity of these effects was significantly lower in mice injected chronically with U-50,488H. These results indicate that a substantial tolerance to analgesic and hypothermic effects of U-50,488H develops in morphine tolerant mice. The effect of chronic injections of U-50,488H on the binding of [3H]ethylketocyclazocine (EKC) and [3H]D-Ala2,MePhe4,Gly-ol5-enkephalin (DAMGO) to whole brain and spinal cord kappa- and mu-opiate receptors was determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for the behavioral supersensitivity of dopamine D2 receptors without receptor up-regulation in morphine-abstinent rats

The effect of morphine tolerance-dependence and abstinence on the characteristics of dopamine D2 receptors in brain regions and spinal cord was determined in the rat. Male Sprague-Dawley rats were implanted s.c. under light ether anesthesia with 6 morphine pellets for a 7-day period, each containing 75 mg of morphine free base. Rats implanted with placebo pellets served as controls. This procedure resulted in the development of tolerance to morphine as evidenced by decreased analgesic response to a challenge dose of morphine. Similarly, the development of physical dependence was evidenced by a decrease in body weight and colonic temperature after morphine pellet removal (withdrawal). The binding characteristics (Bmax and Kd values) of [3H]spiroperidol to dopamine D2 receptors were determined in the tissues of morphine-tolerant and morphine-abstinent rats. In the tolerant rats, the pellets were left intact at the time of sacrificing, whereas, in the abstinent rats the pellets were removed 18 h prior to sacrificing. The binding of [3H]spiroperidol was determined in membranes prepared from brain regions (hypothalamus, hippocampus, cortex, pons and medulla, midbrain, corpus striatum and amygdala) and spinal cord of rats from various treatment groups. [3H]Spiroperidol bound to brain regions and spinal cord at a single high affinity site. The Bmax or the Kd values in brain regions and spinal cord of morphine-tolerant and -abstinent rats did not differ from their respective placebo controls. The behavioral responses to a selective dopamine D2 receptor agonist, 2-bromo-alpha-ergocryptine were also determine in the morphine-abstinent rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Naltrexone-induced alterations of the distribution of morphine in brain regions and spinal cord of the rat

The effects of naltrexone injected intravenously (i.v.) on the pharmacological actions and distribution of i.v. injected morphine in brain regions and spinal cord of male Sprague-Dawley rats were determined. Naltrexone (0.625- and 2.5-mg/kg doses) antagonized the analgesic and hyperthermic effects of morphine (10-mg/kg dose). For distribution studies, naltrexone (0.625- and 2.5-mg/kg doses) was co-administered with morphine via indwelling catheters. Rats were sacrificed at various times after drug injection and the concentration of morphine in brain regions (hypothalamus, hippocampus, cortex, pons and medulla, amygdala, midbrain and corpus striatum), spinal cord and serum was determined by radioimmunoassay. The concentration of morphine in various brain regions was found to be time dependent. Initially, at 5 min, the highest concentration of morphine was found in the hypothalamus and the lowest in the striatum. In cortex and spinal cord, the concentration of morphine was significantly higher in comparison to the other brain regions at 30- and 60-min time points. Co-administration of lower dose of naltrexone (0.625 mg/kg) did not significantly alter the distribution of morphine in brain regions and spinal cord with some exceptions. The higher dose of naltrexone (2.5 mg/kg) increased the concentration of morphine in several brain regions and spinal cord. The ratio of the concentration of morphine in brain region or spinal cord to serum was decreased by naltrexone. It is concluded that naltrexone also alters the distribution of morphine in the central nervous system.

The effect of U-50,488H tolerance-dependence and abstinence on the levels of dynorphin (1-13) in brain regions, spinal cord, pituitary gland and peripheral tissues of the rat

Male Sprague-Dawley rats were rendered tolerant to and physically dependent on U-50,488H, a kappa-opiate agonist, by injecting 25 mg/kg of the drug intraperitoneally twice a day for 4 days. Two sets of rats were used. Rats labeled as tolerant-dependent were injected with U-50,488H (25 mg/kg) 1 h before sacrificing on day 5, whereas the abstinent rats were sacrificed on day 5 without the injection of U-50,488H. Of all the tissues on day 5 without the injection of U-50,488H. Of all the tissues examined, the pituitary gland had the highest level of dynorphin (1-13), whereas the heart had the lowest level. The levels of dynorphin (1-13) increased in the hypothalamus, hippocampus and pons/medulla of U-50,488H tolerant-dependent rats, whereas in abstinent rats the levels of dynorphin (1-13) were elevated only in the midbrain. The levels of dynorphin (1-13) in the pituitary gland of U-50,488H tolerant-dependent or abstinent rats were unchanged. In peripheral tissues, the levels of dynorphin (1-13) in the heart of U-50,488H tolerant-dependent rats were increased. In the abstinent rats they were elevated in the adrenals, spleen, and the heart but were decreased in the kidneys. Compared to morphine tolerant-dependent and abstinent rats, significant differences in the levels of dynorphin (1-13) in tissues of 50,488H tolerant-dependent and abstinent rats were observed and may explain many pharmacological differences in the mu- and kappa-opiate induced tolerance-dependence and abstinence processes.

Abstinence from U-50,488H, a kappa-opiate receptor agonist, decreases the binding of [3H]DPAT to 5-HT1A receptors in the hypothalamus of the rat

The effect of trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]-benzene-acetamide methane sulfonate (U-50,488H), a kappa-opiate agonist-induced tolerance and abstinence on 5-HT1A receptors was determined in regions of the brain and spinal cord of the rat. The administration of U-50,488H (25 mg/kg, i.p., twice daily) to male Sprague-Dawley rats for 4 days resulted in the development of almost complete tolerance to its analgesic and hypothermic effects. On day 5, the animals were divided into tolerant and abstinent groups and sacrificed. The brain and spinal cord were excised from all groups of rats and the brain was dissected into 6 regions, namely, amygdala, hypothalamus, striatum, midbrain, pons+medulla and cortex. The 5-HT1A receptors were characterized by using [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]DPAT) as the ligand. The binding constants (Bmax and Kd values) of [3H]DPAT in regions of the brain and spinal cord of rats tolerant to U-50,488H and vehicle did not differ. However, the Bmax value of [3H]DPAT in the hypothalamus of U-50,488H-abstinent rats was decreased but the Kd value did not change. In the other regions of the brain and spinal cord of U-50,488H-abstinent rats, the Bmax and Kd values of [3H]DPAT were unaffected. Subcutaneous administration of DPAT produced hypothermic response in vehicle- and U-50,488H-treated rats. The intensity of this effect was more marked in U-50,488H-abstinent group. It is concluded that 5-HT1A receptors are down-regulated in the hypothalamus of U-50,488H-abstinent rats but the hypothermic response to 5-HT1A agonist is intensified.

Distribution of morphine in brain regions, spinal cord and serum following intravenous injection to morphine tolerant rats

In order to determine the possible contribution of altered distribution of morphine in the morphine tolerance process, the distribution of morphine was studied in brain regions and spinal cord, following its intravenous administration. Male Sprague-Dawley rats were made tolerant to morphine by implanting 6 morphine pellets, each containing 75 mg of morphine base, for 7 days. Seventy-two hours after the removal of the pellets, a time when serum morphine levels were negligible or absent and yet tolerance to the pharmacological effects of morphine was present, morphine (10 mg/kg, i.v.) was injected in placebo and morphine pellet implanted rats. At various times (5, 30, 60, 120 and 360 min) after the injection of morphine, brain regions (hypothalamus, cortex, hippocampus, midbrain, pons and medulla, striatum and amygdala), spinal cord and serum were collected. The level of morphine in the tissues was determined by using a highly sensitive and specific radioimmunoassay (RIA) method. Five minutes after morphine injection, the concentration of morphine was the highest in the hypothalamus and the lowest in amygdala. The concentration of morphine in hypothalamus, pons and medulla, hippocampus and midbrain of morphine tolerant rats was smaller than in placebo pellet implanted rats. The tissue to serum ratio of morphine in the hypothalamus, hippocampus, striatum, midbrain and cortex were also smaller in morphine tolerant than in non-tolerant rats. The concentration of morphine in brain regions with time did not exhibit linearity. At other time intervals like 30 and 60 min, the concentration of morphine in several brain regions and spinal cord was significantly higher in morphine tolerant than in non-tolerant rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous opiates: 1991

This paper is the fourteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1991 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.