Morphine tolerance in arthritic rats and serotonergic system

To understand whether chronic inflammation alters the development of morphine tolerance, the tail-flick test was used to evaluate the analgesic effect of morphine (75 mg tablet, s.c.) in the arthritic rats at the day 9-12 after the inoculation with Freund's adjuvant. Spinal cord monoamines and amino acid neurotransmitters were concomitantly measured. Chronic inflammation attenuated the antinociceptive effect of morphine as tolerance developed faster in the arthritic rats compared to the vehicle-treated controls. In addition, ratio of 5-hydroxyindole-3-acetic acid/5-hydroxytryptamine (5-HIAA/5-HT) increased in the lumbar spinal cord of arthritic rats without any change in the concentrations of norepinephrine, glutamate, aspartate or GABA. Interestingly, increased serotonin turnover in the spinal cord was observed in both control and arthritic rats 24 hours after morphine treatment. Overall, the results suggest a significant role of serotonin up-regulation in the spinal cord during chronic pain and the development of morphine tolerance.     

Dopaminergic and cholinergic muscarinic receptor effects of L-alphacetylmethadol (LAAM) and its metabolites

In isolated rat hearts L-alphacetylmethadol (LAAM) produced a concentration-dependent decrease in the spontaneous beating rate. This effect was completely prevented by 1.0 microM atropine. Chronic treatment of rats with LAAM increased the number of striatal dopamine receptors measured by [3H]spiroperidol binding. The affinity of these binding sites for [3H]spiroperidol was unchanged by LAAM treatment. There were no significant changes in the number or affinity of binding sites for the labeled muscarinic antagonist [3H]quinuclidinyl benzilate ([3H]QNB) with chronic LAAM treatment. The ability of LAAM, nor-LAAM, or dinor-LAAM to antagonize the binding of [3H]spiroperidol (40 pM) or [3H]QNB (125 pM) to striatal membrane fragments was tested. The measured affinity constants for LAAM and metabolites were 100-3000 times higher than the affinity constants of unlabeled spiroperidol at [3H]spiroperidol binding sites. The affinity constants of LAAM and metabolites at muscarinic binding sites were 10-20 times higher than pilocarpine and 5000-8000 times higher than atropine. These results suggest that LAAM can produce some of its effects by acting as a weak agonist at muscarinic receptor sites.     

Morphine withdrawal modifies antinociceptive effects of acute morphine in rats

Repeated opioid use is known to cause tolerance of antinociceptive effects. Whether opioid abstinence modifies antinociceptive effects is unknown. Here we reported that morphine withdrawal for 18 h and 4 days after repeated morphine treatment largely reduced tail-flick latencies compared with control, while the rats showed severe withdrawal syndromes. However, the latencies and withdrawal syndromes were restored to control level at 20 days withdrawal. Similarly, antinociceptive effects of acute morphine were decreased at 18 h and further decreased at 4 days but restored to control level at 20 days withdrawal. Behavioral stress that was given to the rats at 18 h withdrawal further reduced tail-flick latencies and antinociceptive effects. Conversely, the glucocorticoid receptor antagonist RU38486 increased tail-flick latencies and antinociceptive effects at 4 days withdrawal. These results suggest that morphine withdrawal could evoke behavioral stress to modify antinociceptive effects, implicating a significant influence of opioid abstinence on chronic pain treatment.     

Cumulation of active metabolites of levo-alpha-acetylmethadol in the rat fetus and neonate

Levo-alpha-acetylmethadol (LAAM, 0.2 or 2.0 mg/kg/day) was orally administered to female Sprague-Dawley rats for one month prior to and throughout pregnancy. The rats were killed on the 18th day of gestation along with a group of 18-day pregnant females given a single oral 2.0 mg/kg dose of LAAM 24 hours earlier. Although cumulation of LAAM or its active metabolites was not seen in plasma or brain of pregnant rats given drug chronically, significant cumulation was observed in whole fetus and in fetal brain. In addition, a 2–3 fold elevation in the concentrations, and an even greater elevation of total content, was noted in the newborn pup. These data suggest that opiate intoxication soon after birth may be a factor responsible for the increased morbidity and mortality of rat pups prenatally exposed to LAAM.     

Morphine stimulates prolactin release in normal but not in castrated male rats

Morphine (200 micrograms/rat) was injected intraventricularly (i.v.t.) into normal and into long-term castrated (4 weeks) adult male rats. Animals were killed 10, 20, 40 and 60 min after treatment. In normal animals, the treatment with morphine resulted in a significant increase of serum prolactin concentrations at all time intervals considered. However, the i.v.t. injection of 200 micrograms morphine/rat into castrated rats did not exert any significant effect on prolactin release at any time interval considered. When morphine (200 micrograms/rat) was administered i.v.t. together with the specific opioid receptor blocker naloxone (7.5 or 15 micrograms/rat) the stimulatory effect of morphine on prolactin release was diminished at 10 min, and totally blocked at 20 min. Naloxone given alone did not influence serum prolactin concentrations. The results suggest that the presence of endogenous androgens is essential to permit the stimulatory effect of morphine on prolactin release.     

Morphine induces aggression but not analgesia in the naked mole-rat (Heterocephalus glaber)

1. The antinociceptive effect in the mole-rat of morphine (1, 10, 20 or 30 mg/kg) and nefopam (10 or 20 mg/kg) was studied. 2. In the hotplate test, morphine had no analgesic effect. A reduced response latency after morphine (10 and 20 mg/kg) could possibly be explained by hyperactivity and excited behaviour. 3. After morphine (10, 20 and 30 mg/kg) most of the animals died after fighting when kept in colony cages. Aggressive behaviour and death was prevented by naloxone, or by keeping the animals in single cages. 4. Nefopam (20 mg/kg) significantly increased the latency for the nociceptive response. 5. It was concluded that in the mole-rat, opioid systems in the CNS may not be involved in the regulation of nociception, but in the regulation of agonistic and motor behaviour.     

The Role of Mitogen-Activated Protein Kinase (MAPK) in Morphine Tolerance and Dependence

Despite the existence of a large body of information on the subject, the mechanisms of morphine tolerance and dependence are not yet fully understood. There is substantial evidence indicating that mitogen-activated protein kinase (MAPK), a family including extracellular signal-regulated protein kinase, p38 MAPK, and c-Jun N-terminal kinase, can be activated by chronic morphine treatment in the central and peripheral nervous systems and that application of a MAPK inhibitor reduces morphine tolerance and dependence. While the exact mechanism is not completely understood, recent evidence suggests that the activation of MAPK induced by long-term morphine exposure may participate in tolerance and dependence by regulating the downstream targets, such as calcitonin gene-related peptide, substance P, nitric oxide, transient receptor potential vanilloid 1, and proinflammatory cytokines. In this review, we focus on the current understanding of the role of MAPK signaling pathways in morphine tolerance and dependence.     

Morphine dependent rats: Blockade of precipitated abstinence by calcium

In rats made dependent on morphine, brain levels of calcium were significantly lowered. Naloxone administration to such rats produced characteristic abstinence signs. Prior treatment with calcium markedly reduced naloxone-induced abstinence signs and prevented morphine-induced lowering of brain calcium. It is suggested that the antagonistic actions of calcium and morphine may be related to their effects on morphine-sensitive adenylate cyclase activity.     

Morphine self-administration added to food conditioning: methodological variant in rats]

Rats with permanent intra-jugular cannula are submitted to an alimentary operant reinforcement schedule with fixed ratio type FR 1, FR5, then FR 20. As a result, the animals are self administering (together with the alimentary inducer) a slow (about 5 sec) intravenous infusion of morphine (0.05 mg/kg). 20 per cent only of the experimental population exhibit a psychogenic dependance afterward. On the other hand, the animals for which morphine self-administration has been substituted to the alimentary reinforcement without respecting a transitory period combining both types of reinforcement have never shown any tendancy toward morphine self-administration. The lack of positive results could be related to the marked duration of the self-injection.     

Bioinformatic challenges for the next decade(s)

The science of bioinformatics has developed in the wake of methods to determine the sequences of the informational macromolecules--DNAs, RNAs and proteins. But in a wider sense, the biological world depends in its every process on the transmission of information, and hence bioinformatics is the fundamental core of biology. We here give a consideration of some of the key problems of bioinformatics in the coming decade, and perhaps longer.     

Morphine release and displacement by naloxone in vivo in morphine naive and withdrawn rats

Male Long-Evans rats, implanted in the lateral cerebroventricle with chronic indwelling push-pull cannulae, were perfused (10 μl/min) for 120 min: 20 min with 1.5 × 10^?6M morphine in sterile isotonic saline containing 2.3 mM CaCl₂ (vehicle); 40 min with vehicle; 20 min with 1.5 × 10^?6M morphine; 10 min with vehicle and 30 min with 1 × 10^?6M naloxone in vehicle. These rats and drug-naive rats were implanted s.c. with 2 × 50 mg morphine pellets. After 72 hr the pellets were removed and 18–24 hr later the above perfusion procedure was repeated. The amount of morphine collected in the perfusate during the washout with naloxone was elevated, compared to the amount collected during the corresponding time of the washout with vehicle for both naive and withdrawn groups. The enhanced morphine release during the washout with naloxone did not differ significantly between the naive and withdrawn rats. However, significantly less morphine was recovered in the perfusate collected during the vehicle washout from the withdrawn rats, compared to that collected from the naive rats. The data suggest that $\text{in vivo}$ morphine is specifically bound to receptors and is sensitive to naloxone displacement. It is also concluded that morphine is differentially taken up or otherwise disposed of by brains of rats which are in opiate withdrawal.     

Separation of hepatic n-demethylase-inducing and opioid dependence-producing doses of levo-alpha-acetylmethadol in the pregnant rat

A 2.0 mg per kg oral dose of l-alpha-acetylmethadol (LAAM) administered daily to female rats prior to mating and throughout pregnancy increased ethylmorphine N-demethylase activity in liver microsomes of the dams measured 24 h after parturition. This dose of LAAM decreased maternal weight gain during gestation and increased postnatal mortality. However, 0.05 mg LAAM per kg was sufficient to produce dependence in the dams without affecting hepatic drug metabolism, gestational weight gain or neonatal mortality. The data indicate that it is not necessary to use doses of LAAM which can affect drug metabolizing enzymes in dams and increase pup mortality to maintain opioid-type physical dependence.     

Critical challenges and advances in recombinant adeno-associated virus (rAAV) biomanufacturing

Gene therapy is a promising therapeutic approach for genetic and acquired diseases nowadays. Among DNA delivery vectors, recombinant adeno-associated virus (rAAV) is one of the most effective and safest vectors used in commercial drugs and clinical trials. However, the current yield of rAAV biomanufacturing lags behind the necessary dosages for clinical and commercial use, which embodies a concentrated reflection of low productivity of rAAV from host cells, difficult scalability of the rAAV-producing bioprocess, and high levels of impurities materialized during production. Those issues directly impact the price of gene therapy medicine in the market, limiting most patients’ access to gene therapy. In this context, the current practices and several critical challenges associated with rAAV gene therapy bioprocesses are reviewed, followed by a discussion of recent advances in rAAV-mediated gene therapy and other therapeutic biological fields that could improve biomanufacturing if these advances are integrated effectively into the current systems. This review aims to provide the current state-of-the-art technology and perspectives to enhance the productivity of rAAV while reducing impurities during production of rAAV.     

Pulmonary lymphangioleiomyomatosis (LAM): progress and current challenges

Lymphangioleiomyomatosis (LAM), a rare lung disease, is characterized by the progressive proliferation, migration, and differentiation of smooth muscle (SM)-like LAM cells, which lead to the cystic destruction of the lung parenchyma, obstruction of airways and lymphatics, and loss of pulmonary function. LAM is a disease predominantly affecting women and is exacerbated by pregnancy; only a lung transplant can save the life of a patient. It has been discovered that in LAM, somatic or genetic mutations of tumor suppressor genes tuberous sclerosis complex 1 (TSC1) or TSC2 occur and the TSC1/TSC2 protein complex functions as a negative regulator of the mTOR/S6K1 signaling pathway. These two pivotal observations paved the way for the first rapamycin clinical trial for LAM. The recent discoveries that TSC1/TSC2 complex functions as an integrator of signaling networks regulated by growth factors, insulin, nutrients, and energy heightened the interest regarding this rare disease because the elucidation of disease-relevant mechanisms of LAM will promote a better understanding of other metabolic diseases such as diabetes, cancer, and cardiovascular diseases. In this review, we will summarize the progress made in our understanding of TSC1/TSC2 cellular signaling and the molecular mechanisms of LAM; we will also highlight some of the lesser explored directions and challenges in LAM research.     

Five (or so) challenges for species distribution modelling

Species distribution modelling is central to both fundamental and applied research in biogeography. Despite widespread use of models, there are still important conceptual ambiguities as well as biotic and algorithmic uncertainties that need to be investigated in order to increase confidence in model results. We identify and discuss five areas of enquiry that are of high importance for species distribution modelling: (1) clarification of the niche concept; (2) improved designs for sampling data for building models; (3) improved parameterization; (4) improved model selection and predictor contribution; and (5) improved model evaluation. The challenges discussed in this essay do not preclude the need for developments of other areas of research in this field. However, they are critical for allowing the science of species distribution modelling to move forward.     

Endpoints in myelin-deficient (MD) rats

Health problems in some animal models remain unexplained, rendering in vivo studies ethically challenging, especially when experimental animals are prone to sudden death. Over the last 3 decades, the myelin-deficient (md) rat, a strain with severe dysmyelination due to mutant proteolipid protein, has been key to important discoveries in mechanisms of myelination and glial cell biology. The usefulness of this mutant rat, however, has been limited by sudden death during the fourth week of life. Timely euthanasia has been difficult because the cause of these mortalities remains unexplained and the endpoint not determined. In this clinicopathologic study, we determined that sudden onset of hindlimb paralysis inevitably leads to paralysis of the urinary bladder and then breathing difficulties because of severe injury to the spinal cord in the midthoracic region with concurrent narrowing of the vertebral canal due to fracture of a vertebral body. Sudden onset of hindlimb paralysis likely is related to seizures and severe muscle spasms that begin to occur at the end of the third week of life. Once seizure activity begins, we recommend frequent monitoring of md rats for hindlimb paralysis and distention of the urinary bladder as indication of endpoints mandating prompt euthanasia.