Morphine In Brain Research Articles

Cortical 3α-hydroxy-5α-pregnan-20-one levels after acute administration of Δ9-tetrahydrocannabinol, cocaine and morphine

The neuroactive steroid, 3alpha-hydroxy-5alpha-pregane-20-one (allopregnanolone) is a potent modulator of GABA(A) receptor function. Moreover, pharmacologically relevant concentrations of allopregnanolone are found in brain during physiological conditions (stress, pregnancy and menstrual cycle) and pharmacological challenge (ethanol, fluoxetine, olanzapine). Enhanced levels of neurosteroids are thought to contribute to the therapeutic effects of fluoxetine and various effects of ethanol via GABA(A) receptors. Moreover, neurosteroids influence rewarding effects of ethanol in some models and modulate activation of the hypothalamic pituitary adrenal (HPA) axis. Thus, it is possible that enhanced allopregnanolone levels are involved in the effects of abused drugs. To determine if other abused drugs elicit alterations in brain neurosteroid levels, Delta9-tetrahydrocannabinol (Delta9-THC), cocaine and morphine were administered to male rats. Cortical brain tissue and plasma were collected and analyzed for steroid concentrations using radioimmunoassays. Delta9-THC (5 mg/kg, IP) elevated cortical allopregnanolone levels to pharmacologically active levels, while morphine (15 mg/kg, SC) produced a small but significant increase. Cocaine (30 mg/kg, IP) did not alter allopregnanolone levels, nor did lower doses of Delta9-THC or morphine. Plasma progesterone levels were elevated in both Delta9-THC and cocaine-treated animals. Some, but not all, drugs of abuse produce increases in cortical allopregnanolone levels. In addition, increases in plasma steroid precursor levels do not always translate into increases in brain allopregnanolone levels.

Altered brain exposure of morphine in experimental meningitis studied with microdialysis

During pathologic conditions such as meningitis and traumatic brain injury the function of the blood-brain barrier (BBB) is disturbed. In the present study we examined the cerebral pharmacokinetic pattern of morphine in the intact brain and during experimentally induced meningitis using a pig model. Secondly, the use of intracerebral microdialysis as a potential tool for monitoring damage in the BBB by studying the pharmacokinetics of morphine is addressed. Six pigs were studied under general anaesthesia. One occipital and two frontal microdialysis probes and one pressure transducer were inserted into the brain tissue. Another probe was placed into the jugularis interna. Morphine 1 mg kg(-1) was administered as a 10-min infusion, and morphine concentrations were then measured for 3 h. Meningitis was subsequently induced by injecting lipopoly-saccharide into the cisterna magna. When meningitis was established, the morphine experiment was repeated. The unbound area under the concentration-time curve (AUCu) ratio of morphine in brain to blood was 0.47 (0.19) during the control period, and 0.95 (0.20) (P < 0.001) during meningitis. The increase in the brain/blood AUCu ratio during meningitis implies decreased active efflux and increased passive diffusion of morphine over the BBB. The half-life of morphine in brain was longer than in blood during both periods, and was unaffected by meningitis. This study demonstrates that the morphine exposure to the brain is significantly increased during meningitis as compared with the control situation.

Amperometric determination of morphine on cobalt hexacyanoferrate modified electrode in rat brain microdialysates

The analysis of morphine in biological fluids is of vital interest in monitoring opiate abuse and in drug abuse research. In this paper, a cobalt hexacyanoferrate (CoHCF) chemically modified electrode (CME) was prepared. The electrochemical behavior of morphine at this modified electrode has been studied by cyclic voltammetry (CV). The results indicated that the modified electrode exhibited efficiently electrocatalytic oxidation for morphine with relatively high sensitivity and stability. The CoHCF CME was employed as the detector of high-performance liquid chromatography (HPLC). The peak current was linearly related to the morphine concentration in the range of 1.0×10 −6 M to 5.0×10 −4 M at +0.60 V (vs. Ag/AgCl) with a detection limit of 5.0×10 −7 M (S/N of 3). Typical intra-day reproducibility ( n=5) of 2.0% and inter-day reproducibility ( n=5) of 3.8% were obtained at the 2.0×10 −5 M level. This method was for the first time applied to study the pharmacokinetics of morphine in rat brain after an intravenous administration of morphine (25 mg kg −1).

Effects of diltiazem and MK-801 on morphine analgesia and pharmacokinetics in mice

The effects of diltiazem, an L-type calcium channel blocker, and MK-801, a non-competitive N-methyl- d-aspartate (NMDA) receptor antagonist on morphine analgesia and pharmacokinetics were examined in mice. Mice received a subcutaneous injection of morphine (3.2 mg/kg) 30 min after a subcutaneous injection of diltiazem or MK-801. Diltiazem (20–60 mg/kg) potentiated morphine analgesia and increased serum morphine levels in a dose-dependent manner. MK-801 (0.3 mg/kg) significantly attenuated morphine analgesia but had no significant effect on serum or brain morphine levels. These results suggest that a modification of morphine metabolism is involved, at least in part, in the ability of diltiazem to enhance morphine analgesia, whereas MK-801 attenuates morphine analgesia without affecting morphine pharmacokinetics.

Morphine-Induced Dependence and Sensitization Are Altered in Mice Deficient in AMPA-Type Glutamate Receptor-A Subunits

AMPA-type glutamate receptors have been suggested to be involved in the neurobiological mechanisms of drug addiction. We have made use of two mouse lines, which both have modulated AMPA receptor responses. The first line is entirely deficient in glutamate receptor-A (GluR-A) subunits (A-/- knock-out line) and, in the second one, the Q582 residue of GluR-A subunits is replaced by an arginine residue (R/R mutants), which reduces the calcium permeability and channel conductance of the receptors containing this mutated subunit. Mice of both lines are healthy, but they show slightly increased locomotor activity. Acute morphine administration enhanced locomotor activity of the GluR-A-/- and GluR-A(R/R) mice, at least as much as that of their wild-type littermates. Only in the GluR-A-/- mice did we observe reduced tolerance development in tail-flick antinociception and less severe naloxone-precipitated withdrawal symptoms after treatment with increasing morphine doses, without differences in plasma and brain morphine levels when compared with wild type. Repeated daily morphine administration sensitized the locomotor activity responses in the GluR-A-/- and GluR-A(R/R) mice only when given in the measuring cages, whereas the wild-type mice showed slightly increased responses also when the repeated treatment was given in their home cages. Normal or even enhanced context-dependent sensitization was observed also with repeated amphetamine administration in the GluR-A subunit-deficient mice. The results indicate that AMPA receptors are involved in the acute and chronic effects of morphine, including context-independent sensitization, and that the GluR-A subunit itself is important for morphine tolerance and dependence.

Intraperitoneal injection of antisense peptide nucleic acids targeted to the mu receptor decreases response to morphine and receptor protein levels in rat brain

To determine the effectiveness of peptide nucleic acids (PNAs) in vivo, we designed and synthesized PNAs antisense to the mu receptor, the molecular target of morphine for inducing antinociception. Responsiveness of rats to morphine and the levels of mu receptor expression after treatment was measured. We delivered intraperitoneal injections of antisense PNAs targeted to the mu receptor (AS-MOR), mismatch PNAs (AS-MOR MM), antisense PNAs targeted to the neurotensin receptor subtype 1 (AS-NTR1), or saline and then challenged the rats with 5 mg/kg morphine (intraperitonally) or neurotensin directly into the periaqueductal gray region of the brain. To avoid tolerance, separate groups of animals were tested at 24, 48, and 72 h post-PNA treatment. Only animals treated with the AS-MOR showed a reduction in their antinociceptive response to morphine. The lack of effect of morphine on the AS-MOR rats was profound at 24 and 48 h, but animals tested at 72 h were similar to control groups. At 24 h the AS-MOR rats had a significant 55% decrease in the levels of mu receptor in their periaqueductal gray region, while AS-MOR MM rats showed no significant change. Lastly, the AS-MOR rats continued to show a normal antinociceptive response to neurotensin. This study, therefore, provides additional support for the use of PNAs to target proteins within brain by systemically administered PNAs.

Characteristic glucuronidation pattern of physiologic concentration of morphine in rat brain

Formation of conjugated metabolites from morphine at a very low level in brain was studied in vitro in rats. Incubation of a low concentration of 3H-morphine with brain homogenate followed by two successive high-performance liquid chromatographic analyses showed that endogenous morphine is converted by brain enzymes to its 3- and 6-glucuronides (M-3-G and M-6-G), and codeine glucuronide (Cod-G). However, the formation of morphine-6-sulfate was likely to be low if it was produced at all. All of the cerebral hemisphere, brain stem and cerebellum were capable of producing M-3-G, M-6-G and Cod-G, although there were differences in selectivity. The capacity of the brain for glucuronide formation was far less than that of the liver, but UDP-glucuronosyltransferase in brain was much more selective in forming M-6-G and Cod-G than liver enzymes.

Lipopolysaccharide increases endogenous morphine levels in rat brain

The present study was designed to determine whether whole body injection of lipopolysaccharide increases endogenous rat brain morphine levels. High performance liquid chromatography coupled to electrochemical detection and gas-chromatography mass spectrometry reveal that the resting brain morphine level is 7.0±3.2 ng/g wet weight. In a time dependent manner, intraperitoneal injection of lipopolysaccharide (10 μg), leads to an increase of brain morphine level with a peak reaching after 36 h post injection. After 72 h following the lipopolysaccharide-injection, morphine levels increased to 66.0±5.4 ng/g brain wet weight ( P<0.001). Furthermore, 96 h of fasting also increased the brain morphine level to 44.0±3.6 ng/g of brain wet weight. These results suggest that rat brain morphinergic processes respond to organismic challenges after a significant latent period.

Effect Of Uranyl Nitrate‐Induced Renal Failure On Morphine Disposition And Antinociceptive Response In Rats

1. The aims of the present study were to administer morphine (14.0 mumol/kg, s.c.) to male Hooded Wistar rats and to determine the effect of uranyl nitrate-induced renal failure on: (i) the antinociceptive effect of morphine; (ii) the pharmacokinetics of morphine and morphine-3-glucuronide (M3G); and (iii) the relationship between antinociceptive effect and the pharmacokinetics of morphine in plasma and brain. 2. Renal failure was induced by a single s.c. injection of uranyl nitrate and kinetic/dynamic studies were performed 10 days after its administration, when creatinine clearance was 17% of the control group. Antinociceptive effect was measured by the tail-flick method at various times up to 2 h post-drug administration. Concentrations of morphine and M3G in plasma and brain and concentrations of creatinine in urine and serum were determined by specific HPLC methods. 3. After morphine administration, the area under the antinociceptive effect-time curve was decreased by 44% in renal failure rats. There were no differences between control and renal failure rats in: (i) plasma morphine concentration-time curves; (ii) brain morphine concentration-time curves; and (iii) plasma M3G concentration-time curves. Morphine-6-glucuronide was not detected in any plasma or brain sample from rats administered morphine and no M3G was detected in brain. 4. For both control and renal failure rats, the relationships between antinociceptive effect and plasma morphine concentration were characterized by counterclockwise hysteresis loops, probably reflecting a delay for the relatively polar morphine to cross the blood-brain barrier. The relationship between antinociceptive effect and brain morphine concentration in control rats revealed no evidence of acute tolerance and was described by a sigmoidal function. In contrast, the relationship in renal failure rats was characterized by clockwise hysteresis, which is consistent with acute tolerance development.

Genetic Determinants of Morphine Activity and Thermal Responses in 15 Inbred Mouse Strains

Mice from 15 standard inbred strains were tested for sensitivity to two effects of acute morphine administration, open-field activity, and body temperature changes, at doses of 0, 4, 8, 16, and 32 mg/kg, IP. Large strain differences were consistently observed, indicating a substantial degree of genetic determination of these traits. For morphine-induced activity, some strains were markedly insensitive to all doses (e.g., C3H/He, CE), while others showed increases and some decreases at the same morphine dose. For thermal responses, one strain was insensitive to all doses employed (C3H/He), while others showed marked hypothermia and some hyperthermia at the same dose. Although strains differed in brain morphine concentrations at time of behavioral testing, pharmacokinetic differences were unrelated to both measures of morphine sensitivity. Correlations among strain means (estimates of genetic correlations) were rather high across doses within each measure, indicating that strain differences to a given effect of morphine were rather stable across doses. This suggests substantial commonality in genetically mediated mechanisms across the dose range used for activity, and also for thermal responses. In contrast, genetic correlations between activity and thermal responses were not significant at any dose, indicating that these two traits are largely genetically independent.

The effect of ethanol drinking on opioid analgesia and receptors in mice

Recent studies suggest substantial interactions between opioids and ethanol (EtOH). Both in vivo and in vitro experiments indicate that EtOH can regulate opioid systems and that opioids can modify EtOH consumption. In the present studies, we examined if EtOH consumption altered opioid receptors and the potency of opioid analgesics. Mice were given unlimited access to 6–7% EtOH alone for 7 days or were allowed to drink increasing concentrations (3–6%) of EtOH over 13–14 days. Controls had access to water. The EtOH groups drank significantly less volume than controls, although there were no significant differences in body weight or baseline nociception. The analgesic (tail flick) potency of SC morphine was decreased by ∼1.6–2.0-fold in EtOH-treated mice. A single acute dose of EtOH (1 g/kg) that produced blood alcohol levels in excess of that for 7 day exposure to EtOH, did not change morphine's analgesic ED 50, suggesting that chronic exposure to EtOH was necessary for the reduction in potency. The change in morphine potency was not due to pharmacokinetic differences because EtOH consumption did not modify the concentration of morphine in brain and spinal cord. The analgesic potency of a δ-opioid receptor agonist (ICV DSLET) was also decreased by ∼2-fold. Saturation binding studies indicated no changes in the density or affinity of brain and spinal cord δ-opioid ([ 3H]DPDPE, [ 3H]DSLET, [ 3H]DeltorphinII) and μ-opioid ([ 3H]DAMGO) receptors. Similarly, there was no significant effect of EtOH on δ-opioid receptor mRNA in either brain or spinal cord preparations. Taken together, these data suggest that EtOH consumption decreases the analgesic potency of opioids in mice through a mechanism that is unrelated to pharmacokinetics or opioid receptor changes in brain and cord.

The effect of old age on the disposition and antinociceptive response of morphine and morphine-6 β-glucuronide in the rat

The aims of this study were to examine the effect of old age on the pharmacokinetics of morphine and morphine-6 β-glucuronide (M6G) and their relationships to antinociceptive activity. Morphine (21.0 μmol/kg) or M6G (21.7 μmol/kg) were administered s.c. to young adult and aged male Hooded-Wistar rats. Antinociceptive effect was measured by the tail-flick method at various times up to 2.5 h or 6.5 h after morphine or M6G administration, respectively, and concentrations of morphine, morphine-3 β-glucuronide (M3G) and M6G in plasma and brain were determined by HPLC. Creatinine clearance was significantly lower by 33% or 21% in aged compared to young adult rats receiving morphine or M6G, respectively. After morphine administration, the areas under the (i) antinociceptive effect-time curve, (ii) plasma morphine concentration-time curve, and (iii) brain morphine concentration-time curve were not different between young adult and aged rats. However, the AUC for plasma M3G was five-fold higher in the aged relative to young adult rats, which could not be accounted for by only a 33% lower creatinine clearance. M6G was not detected in any plasma or brain sample from rats administered morphine and no M3G was detected in brain. For M6G administration, the areas under the (i) antinociceptive effect-time curve, and (ii) plasma M6G concentration-time curve were 1.8- and 1.6-fold higher in aged compared to young adult rats, respectively. Concentrations of M6G in brain were below the limit of quantification. No morphine or M3G was detected in any of the plasma or brain samples of rats administered M6G. The results demonstrate no change in morphine antinociception and pharmacokinetics with age, and suggest that blood-brain barrier permeability and receptor sensitivity to morphine are not altered in aged rats. Accumulation of M3G in plasma of aged rats is probably due to diminished renal clearance of M3G in addition to a reduction in the biliary excretion of M3G. The heightened sensitivity of the aged rats to M6G is probably due to the observed altered kinetics of M6G rather than a pharmacodynamic change.

Concentration-effect relationships of morphine and morphine-6 beta-glucuronide in the rat.

1. The aims of the present study were to determine the relationship between the antinociceptive effect and concentrations of morphine and morphine-6 beta-glucuronide (M6G) in plasma and in the brain. 2. Morphine (14.0 and 28.0 mumol/kg) or M6G (8.67 and 17.3 mumol/kg) were administered s.c. to male Hooded-Wistar rats. The antinociceptive effect was measured by the thermal tail-flick method at various times up to 2 h and concentrations of morphine, morphine-3 beta-glucuronide (M3G) and M6G in plasma and in the brain were determined. 3. With a two-fold increment in morphine dose, the areas under the antinociceptive effect-, plasma morphine concentration- and brain morphine concentration-time curves increased by 1.9-, 2.3- and 2.3-fold, respectively. The area under the plasma M3G concentration-time curve increased 2.7-fold. Morphine-6 beta-glucuronide was not detected in any sample. For M6G, doubling of the dose led to a 1.7-fold increase in the area under the curve for plasma-time M6G concentrations but an 8.7-fold increase in the area under the curve for the antinociception-time effect. Concentrations of M6G in the brain were below the limit of quantification. The relationship between antinociceptive effect and plasma morphine or M6G were characterized by counter-clockwise hysteresis loops, probably reflecting a delay in crossing the blood-brain barrier. 4. Morphine-6 beta-glucuronide was approximately equipotent to morphine on the basis of dose, but substantially more potent on the basis of brain concentration.

Modulation of immunoreactive protein kinase C-α and β isoforms and G proteins by acute and chronic treatments with morphine and other opiate drugs in rat brain

The abundance of protein kinase C-alpha and beta isoforms (PKC-alphabeta), PKC-alpha messenger (m) RNA and guanine nucleotide-binding G protein subunits (G alpha(i1/2), G alpha(o), and G beta) were quantitated in the rat cerebral cortex after acute and chronic treatments with various opiate drugs. Acute (100 mg/kg for 2 h) and chronic (10 to 100 mg/kg for 5 days) treatment with morphine decreased similarly the immunoreactivity of PKC-alphabeta (28% and 32%, respectively). Acute (2 h) and chronic treatment (5 days) with other mu-agonists heroin (30 mg/kg and 10 to 30 mg/kg) and methadone (30 mg/kg and 5 to 30 mg/kg) also induced similar decreases of PKC-alphabeta (acute: 25% and 23%; chronic: 28% and 18%). After the chronic treatments, spontaneous (48 h) or naloxone (2 mg/kg)-precipitated opiate withdrawal (2 h) resulted in up-regulation of PKC-alphabeta above control levels (30-38%), and in the case of morphine withdrawal in a concomitant marked increase in the expression of PKC-alpha mRNA levels (2.3-fold). Acute (2 h) treatments with pentazocine (80 mg/kg, mixed kappa/delta-agonist and mu-antagonist), spiradoline (30 mg/kg, selective kappa-agonist) and [D-Pen2, D-Pen5] enkephalin (14 nmol i.c.v., selective delta-agonist) induced significant decreases of PKC-alphabeta (19-33%). Chronic (5 days) treatment with pentazocine (10 to 80 mg/kg), but not spiradoline (2 to 30 mg/kg), also induced a similar decrease of PKC-alphabeta (35%). In pentazocine- or spiradoline-dependent rats, naloxone (2 mg/kg) did not induce up-regulation of brain PKC-alphabeta. Acute (10 mg/kg for 2 h) and chronic (2x10 mg/kg for 5 and 14 days) treatment with naloxone did not alter PKC-alphabeta immunoreactivity. Chronic, but not acute, treatment with mu-agonists (morphine, heroin and methadone) increased the immunoreactivities of G alpha(i1/2) (33-37%), G alpha(o), (25-41%) and G beta (10-33%) protein subunits. In heroin- and methadone-dependent rats naloxone (2 mg/kg)-precipitated withdrawal (2 h) did not modify the up-regulation of these G proteins induced by chronic mu-opiate treatment. In marked contrast to mu-agonists, chronic treatment with high doses of pentazocine and spiradoline or acute treatment with [D-Pen2, D-Pen5] enkephalin did not result in up-regulation of these G protein subunits. After chronic treatment with mu-agonists, significant negative correlations were found when the percentage changes in immunoreactivity of PKC-alphabeta were related to the percentage changes in immunoreactivity of G alpha(i1/2), (r = -0.53, n = 29) and G beta (r = -0.41, n = 24) in the same brains. PKC-alphabeta abundance did not correlate significantly with the density of G alpha(o) (r = -0.21, n = 28). Together the results indicate that the brain PKC-alphabeta system may play a major regulatory role in opiate tolerance and dependence. Moreover, the possible in vivo cross-communication between this regulatory enzyme and specific inhibitory G proteins may also be of relevance in the cellular and molecular processes of opiate addiction.

Relationship between analgesia and extracellular morphine in brain and spinal cord in awake rats

Extracellular concentrations of morphine from the dorsal spinal cord, the periaqueductal gray (PAG) including the dorsal raphé, and the lateral hypothalamus were measured by microdialysis in awake rats after intraperitoneal (i.p.) administration of 2.5, 5.0 and 10 mg/kg morphine. Morphine concentrations in all areas showed similar time courses: morphine was detected in the first dialysate sample (13–15 min) and maximal concentrations were reached at 45 min after injection. When in vivo recoveries of morphine from the spinal cord and brain areas were taken into account, no significant differences between morphine concentrations in the various areas were found. The relationship between extracellular morphine concentrations and morphine-induced analgesic behavior was investigated by simultaneously measuring morphine in the dialysate and its analgesic effect in the paw-withdrawal and tail-flick tests. In all areas sampled, the extracellular concentrations of morphine at different times after i.p. injection, significantly correlated with the magnitude of behavioral analgesia assessed by either test. The highest correlation was obtained between extracellular concentrations of morphine in the spinal cord and PAG and behavioral analgesia assessed in the paw-withdrawal test. Our data indicate that, after systemic injection, morphine is evenly distributed throughout the spinal cord and brain including potential anatomical sites of morphine's analgesic action. We estimate that the minimal extracellular morphine concentration in spinal cord that is required to produce a significant increase in nociceptive threshold is approximately 100 pg/25 μl, which corresponds to a tissue concentration of about 100 ng/g of morphine.

Endogenous morphine

This review surveys the discovery of endogenous alkaloids in mammals. The formation of morphine in mammalian brain was assumed in 1970. The existence of morphine was demonstrated by radioimmunoassay. Identification of morphine was performed by spectroscopic methods. The isolation of mammalian morphine raises the question of biosynthesis. Recently, it has been shown that the biosynthetic pathway is similar to that that exists in poppy.

Modulation of Endogenous Opiate Production: Effect of Fasting

The endogenous opiate alkaloid content in tissues from fed, 24 h and 48 h fasted rats was determined. Plasma morphine and codeine concentrations did not change in response to fasting. Morphine levels in the spleen increased 3-fold after 24 h of fasting and were lower than fed rats by 48 h of fasting; no change was detected in spleen codeine levels. Brain morphine levels were elevated 5-fold after 24 h of fasting and were two-fold higher than those of fed rats after 48 h of fasting. Brain codeine levels did not change with fasting. These results indicate that opiate alkaloids are endogenously produced in rodent tissues, particularly in the spleen, liver, and adrenals. The synthesis of morphine, in the spleen and brain, is maximally stimulated after 24 h of fasting, without alterations in tissue codeine synthesis. These suggest differential regulation of the endogenous synthetic pathways of morphine and codeine in response to the stress of fasting.

Alteration of D1 and D2 dopaminergic receptor kinetics in specific rat brain regions following repeated administration of opiates.

The present study was conducted to investigate the effects of repeated administration of opiates on the binding characteristics of D1 and D2 dopamine receptors in specific rat brain regions. Male Sprague-Dawley rats (150-175 g) were adapted for 1 week under controlled conditions (22 +/- 1 degree C, 40% relative humidity, 12 h light:12 h dark illumination cycle). After the adaptation period, rats were randomly assigned into six groups (n = 15/group) for two sets of experiments; one for D1 and the other for D2 receptor binding evaluation. In each set, group 1 served as saline control, group 2 was treated with morphine (1 mg/kg/day for 7 days) and group 3 was treated with naloxone (2 mg/kg/day for 7 days). Following the third day of morphine injection, rats showed restlessness, hyperactivity, increased urination, diarrhea, lacrimation, irritability and squealing on touch, head and body shakes and salivation just prior to morphine dosage. These observed signs are typical for morphine withdrawal. One hour after the last injection, rats were sacrificed by decapitation, brains were removed and kept at -70 degrees C. The frozen brains were further dissected into cortex (CTX), hypothalamus (HYPO), hippocampus (HIPP) and midbrain (MID), pooled (5/pool), homogenized and used for radioreceptor assays. For D1 binding study, 3H-SCH-23390 was used as ligand and for D2 receptor binding 3H-YM-09151-2 was employed. Following repeated morphine or naloxone treatment, Bmax values for 3H-SCH-23390 binding to membranes of HYPO and MID were increased and decreased, respectively, whereas Kd values were significantly decreased in both HYPO and MID of morphine and naloxone-treated animals. In rat brain CTX, both morphine and naloxone decreased Kd and Bmax values of 3H-SCH-23390 binding, however the decrease in Bmax values noted after morphine administration was not statistically significant. Decrease in both Bmax and Kd values of dopamine D1 receptors were observed after naloxone but not morphine treatment in HIPP. Morphine administration increased the density of D2 receptors in HIPP and MID and decreased the affinity of 3H-YM-09151-2 binding in CTX, HIPP and MID. Naloxone treatment resulted in increased number of 3H-YM-09151-2 binding sites in CTX, HYPO and HIPP. While naloxone treatment increased Kd values of 3H-YM-09151-2 in HYPO and HIPP, it decreased these values in CTX and MID. It is concluded that repeated intermittent treatment with opiates induces alterations in D1 and D2 dopamine receptors binding properties and that these changes are regionally specific.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphine analgesia in the formalin test: Evidence for forebrain and midbrain sites of action

A mapping study was performed to determine where in the rat brain morphine acts to produce Analgesia in the formalin test, which is an animal model of prolonged pain associated with tissue injury. A single dose (5 nmol) of morphine was bilaterally microinjected into a wide range of brain areas throughout the midbrain and forebrain. Strong Analgesia was elicited from the posterior hypothalamic area, the periaqueductal gray and ventral tegmental area. Other sites from which Analgesia was elicited were the nucleus accumbens and a few sites in the retrorubral field and caudate-putamen. Analgesia from the periaqueductal gray or nucleus accumbens was accompanied by decreased locomotor activity and catalepsy, whereas Analgesia from the posterior hypothalamic area or ventral tegmentum was accompanied by a noticeable increase in locomotor activity and rearing. Morphine into various thalamic nuclei had no effect. These results indicate that the primary sites of action of morphine in the formalin test are robably the posterior hypothalamic area and periaqueductal gray, with an additional contribution from regions innervated by tegmental dopamine cells.

Ion-pair extraction and liquid chromatographic analysis of morphine in rat brain and plasma

A highly efficient and reproducible two-step liquid—liquid ion-pair extraction technique for the isolation of morphine from biological samples is described. A rapid normal phase high-performance liquid chromatographic procedure coupled with amperometric electrochemical detection has also been developed for subsequent quantification of morphine. Extraction involves the disruption of brain tissue or plasma in methanol, centrifugation, evaporation and reconstitution in ethyl acetate containing 10 m M di-(2-ethylhexyl) phosphoric acid, a liquid cation-exchanger, and back-extraction into 170 m M orthophosphoric acid. An acidic eluent consisting of acetonitrile—76 m M orthophosphoric acid—ammonia buffer (pH 3.0) (15:85, v/v) in combination with a strong cation-exchange column allows complete separation of morphine and the internal standard, nalbuphine. The limit of detection for morphine is 1.3 ng on-column.