Neurochemical bases for narcotic tolerance and dependence

Acute pain management in patients with prior opioid consumption: a case-controlled retrospective review

The patient with a history of current opioid consumption presenting in the acute postoperative setting presents a challenge for pain management. Standard treatment dosages and strategies are often ineffective in providing pain relief. This retrospective case-control study reviews 4 years' experience of the Acute Pain Service (APS) at our institution providing care for 202 chronic pain and opioid-consuming (CPOC) patients, 6.6% of 3058 patients undergoing urologic, gynecologic, orthopedic and general surgical procedures. Controls matched for age, gender, date and type of surgery, and postoperative pain relief modality were found for 180 (89%) of these patients. Patients were provided patient-controlled analgesia (PCA), or epidural opioid analgesia (EOA with boluses of preservative-free morphine or bupivacaine (1:16% + 2 micrograms/ml fentanyl (B/F)). Records were reviewed for patient demographics, diagnoses, surgical procedures, pre-operative opioid use, days-on-service, analgesic requirement, pain scores and incidence of moderate/severe side effects. Patient demographics were similar between CPOC and control groups. When considering PCA alone, mean 24-h usage in controls was 42.8 (32.0) mg morphine (MS) equivalents differing significantly from CPOC patients' use of 135.8 (68.5) mg MS equivalents (P = 0.0001). EOA and B/F case studies showed similar results. Moderate sedation was experienced by 50% of CPOC patients receiving PCA. Differences in opioid usage, side effects, pain scores, sedation and prescribed treatment with anxiolytics were shown between CPOC patients and matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Cross-tolerance between systemic and epidural morphine in cancer patients

Cross-tolerance to epidural morphine after prior systemic morphine therapy was studied in 26 cancer patients treated for relief of pain secondary to metastatic disease. A 'tolerance index' was calculated for each patient by multiplying the duration of previous morphine therapy with the daily dose just prior to the study and then compared with changes in the following variables measured after epidural morphine administration: with pain scores on a scale from 0 (no pain) to 10 (maximal pain), heart rate, blood pressure, respiratory rate and minute volume, arterial blood gas tensions of oxygen and carbon dioxide and arterial pH. There was no significant analgesic cross-tolerance to epidural morphine, but clear evidence for cross-tolerance regarding morphine's respiratory depressant action. The duration of the previous morphine therapy exerted a greater influence on the development of ventilatory cross-tolerance than the dose.

Blockade of tolerance to morphine analgesia by cocaine

Tolerance to morphine analgesia was induced in male Sprague-Dawley rats by s.c. implantation of a morphine base pellet (75 mg) on the first and second day and determining the magnitude of tolerance 72 h after the first implant by s.c. injection of a test dose of morphine (5 mg/kg). Implantation of a cocaine hydrochloride pellet (25 mg), concurrently with morphine pellets or of a cocaine hydrochloride (50 mg) pellet after the development of tolerance, blocked both the development and expression of morphine analgesic tolerance. In morphine-pelleted animals pretreatment for 3 days with desipramine or zimelidine or phenoxybenzamine but not haloperidol produced no significant morphine tolerance. Pretreatment with a combination of desipramine and zimelidine, however, was as effective as cocaine in blocking morphine tolerance. Alpha-Methyl-p-tyrosine methyl ester counteracted the effect of cocaine in blocking morphine tolerance and potentiated the tolerance development. Blockade of morphine tolerance by cocaine was reinforced and facilitated by pretreatment with fenfluramine or p-chlorophenylalanine ethyl ester and to a lesser extent by clonidine and haloperidol. Acute administration of fenfluramine or zimelidine or a combination of desipramine and zimelidine or alpha-methyl-p-tyrosine methyl ester or p-chlorophenylalanine ethyl ester did not significantly affect morphine analgesia. The study suggests an important role of the concomitant depletion of both central noradrenaline and serotonin in the blockade of morphine tolerance by cocaine and stresses the importance of the counter-balancing functional relationship between these two neurotransmitters in the central nervous system.

Morphine inhibition of calcium fluxes, neurotransmitter release and protein and lipid phosphorylation in brain slices and synaptosomes

Morphine (1-100 microM) was found to inhibit several concomitant events in brain slices and synaptosomes which are augmented by depolarizing agents. Thus, 45Ca2+ uptake, amino acid neurotransmitter release, increases in 3',5' cyclic AMP levels and 32Pi incorporation to proteins and lipids induced by veratrine (25 microM) and by potassium (56 mM), were each inhibited in a dose related manner. These inhibitory actions of morphine were all prevented by naloxone (1 microM). Evidence is presented that morphine binding to a receptor on the synaptic membrane affects intracellular mechanisms involved in neurotransmitter release possibly via a second messenger system. An enhancing action of GTP on the inhibitory influences of morphine suggests that its actions are mediated at least in part, via a coupling of the receptor to adenyl cyclase in the outer membrane. This is supported by its inhibitory action on the capacity of depolarizing agents to increase cyclic AMP levels.

Macromolecular changes in brain stem of morphinized rats

Incorporation of [3H]valine into trichloroacetic acid-(TCA)-precipitable, water-soluble or membrane-bound material of whole brain and brain-stem did not differ significantly in morphine-intoxicated, morphine abstinent and control rats. The animals were intoxicated with morphine (final dose 340 mg/kg b.w.) for 15 days, using an ingestion method with no impairment of the caloric intake compared to controls. Abstinent rats were withdrawn from morphine for 2 days after 13 days of intoxication. Measurements of [3H]valine or [14C]valine incorporated into soluble or membrane-bound brain stem proteins failed to demonstrate any significant changes in specific protein bands from morphinized rats. Separation was achieved by polyacrylamide gel electrophoresis with or without sodium-dodecyl sulphate (SDS) or by isoelectric focusing. After immunoabsorption chromatography to remove those proteins antigenically similar to serum proteins, an increase in the staining intensity and in incorporation of [3H]valine into two protein bands (with isoelectric points (Ip:s) 5.75 and 7.7) was seen in brain stem from long-term morphine-intoxicated rats. The results show that macromolecular interactions are involved in long-term morphine actions.

Accumulation of peptide Tyr-D-Ala-Gly by choroid plexus during ventriculocisternal perfusion of rat brain

Accumulation of Tyr-D-Ala-Gly (TAG) in choroid plexus was studied with ventriculocisternal perfusion of anesthetized rats. The choroid plexus of the lateral ventricles and the fourth ventricle accumulated TAG against a concentration gradient with regards to cerebrospinal fluid (CSF) but not plasma. This accumulation was inhibited by some metabolic inhibitors and peptides which had the same effect on accumulation of TAG in isolated choroid plexus. These results indicate that the active transport of TAG is present in the epithelium facing CSF. This active accumulation was affected by morphine. Reserpine, which is a chemical denervation of sympathetic nerves has no effect on the active accumulation of TAG. Thus, all these results suggest that, in vivo accumulation of TAG in choroid plexus during ventriculocisternal perfusion is similar to in vitro accumulation of TAG in isolated plexus.

Morphine suppression of neurotransmitter release evoked by sensory stimulation in vivo

The effects of morphine and naloxone on the release of acetylcholine and amino acid neurotransmitters from sensorimotor cortex were studied employing an in vivo superfusion cannula. Morphine (20 mg/kg) reduced the spontaneous release of acetylcholine but had no detectable effect on the spontaneous release of amino acids. It also suppressed the release of acetylcholine and amino acid neurotransmitters evoked by sensory stimulation of the contralateral sensorimotor cortex via the brachial plexus. Naloxone (5 mg/kg) prevented all of these inhibitory actions of morphine. Naloxone also caused a significant increase in spontaneous acetylcholine release.

Physical dependence in the rat induced by slow release morphine: dose-response, time course and brain biogenic amines

1. Physical dependence was induced in rats by administration of a slow release morphine emulsion (morphine SR), and assessed by scoring abstinence signs and temperature changes after i.p. administration of naloxone (5 mg/kg). Three groups of rats received doses of 75, 100 or 150 mg/kg of morphine SR. Dependence was evaluated in each of these groups after 24, 48 and 72 h. 2. The effect of these treatments at the different times on brain levels of serotonin, 5-hydroxyindoleacetic acid, noradrenaline and dopamine was determined. 3. A ceiling level of dependence was reached 24 h after 75 and 100 mg/kg and 48 h after 150 mg/kg of morphine SR. 4. These different treatments produced no significant effect on the brain levels of noradrenaline, dopamine or serotonin. The levels of 5-hydroxyindoleacetic acid were significantly raised in morphine-dependent rats and the changes correlated well with the changes in abstinence behaviour and temperature after naloxone. 5. The results suggest that a relationship exists between serotonin turnover and physical dependence on morphine.