Pharmacokinetics and pharmacodynamics of cannabis-based medicine in a patient population included in a randomized, placebo-controlled, clinical trial

Information on the pharmacokinetics (PK) and pharmacodynamics (PD) of orally administered cannabis-based medicine (CBM) in capsule formulation in patient populations is sparse. In this exploratory study, we aimed to evaluate the PK and PD in a probable steady state of CBM in neuropathic pain and spasticity in a population of patients with multiple sclerosis (MS). Of 134 patients participating in a randomized, double-blinded, placebo-controlled, trial, 23 patients with MS (17 female) mean age 52 years (range 21-67) were enrolled in this substudy. They received oral capsules containing Δ9 -tetrahydrocannabinol (THC, n = 4), cannabidiol (CBD, n = 6), a combination (THC&CBD, n = 4), or placebo (n = 9). Maximum doses were 22.5 mg (THC) and 45 mg (CBD) a day divided into three administrations. PD parameters were evaluated for pain and spasticity. Blood samples were analyzed using an ultra-high-performance liquid chromatography-tandem mass spectrometer after protein precipitation and phospholipid removal. PK parameters were estimated using computerized modeling. The variation in daily dose and PK between individuals was considerable in a steady state, yet comparable with previous reports from healthy controls. Based on a simulation of the best model, the estimated PK parameters (mean) for THC (5 mg) were Cmax 1.21 ng/mL, Tmax 2.68 h, and half-life 2.75 h, and for CBD (10 mg) were Cmax 2.67 ng/mL, Tmax 0.10 h, and half-life 4.95 h, respectively. No effect was found on the PD parameters, but the placebo response was considerable. More immediate adverse events were registered in the active treatment groups compared with the placebo group.

Distribution of morphine and methadone to the brain in a developmental chicken embryo model

The use and/or misuse of opioids by pregnant women would expose the fetuses to these drugs during critical stages of development with serious effects for the newborn, like the neonatal abstinence syndrome (NAS). We have revisited an established chicken model for NAS to describe the distribution of morphine and methadone to the brain and explore its validity as a valuable alternative to rodent models. For this purpose, chicken eggs were injected with a single dose of 10 mg/kg or 20 mg/kg morphine or 20 mg/kg methadone onto the chorioallantoic membrane (CAM) on embryonal day 13. Whole brains and lungs were harvested and the concentrations of morphine, methadone and their subsequent metabolites (morphine-3-glucuronide and EDDP, respectively) determined in the brain and lungs at different time points using LC-MS/MS. Morphine and methadone, as well as their metabolites, were detected both in the brain and lungs, with significantly higher concentrations in the lungs. Pharmacokinetic modelling showed that the distribution of morphine to the brain followed a first-order absorption with transit compartments and linear elimination, with concentrations linearly dependent on dose. Moreover, methadone, but not morphine, reduced μ receptor (the main morphine receptor) binding, which can be of relevance for opioid tolerance. The present study is the first to report the brain distribution of morphine, which can be described by standard pharmacokinetic processes, and methadone in the developing chicken embryo. The present findings supplement the already established model and support the use of this chicken model to study NAS.

Heroin metabolism in human blood and its impact for the design of an immunotherapeutic approach against heroin effects

Immunotherapeutic interventions that block drug effects by binding drug molecules to specific antibodies in the bloodstream have shown promising effects in animal studies. For heroin, which effects are mainly mediated by the metabolites 6-acetylmorphine (6-AM; also known as 6-monoacetylmorphine or 6-MAM) and morphine, the optimal antibody specificity has been discussed. In rodents, 6-AM specific antibodies have been recommended based on the rapid metabolism of heroin to 6-AM in the bloodstream. Since the metabolic rate of heroin in blood is unsettled in humans, we examined heroin metabolism with state-of-the-art analytical methodology (UHPLC-MS/MS) in freshly drawn human whole blood incubated with a wide range of heroin concentrations (1-500 μM). The half-life of heroin was highly concentration dependent, ranging from 1.2-1.7 min for concentrations at or above 25 μM, and gradually increasing to approximately 20 min for 1 μM heroin. At concentrations that can be attained in the bloodstream shortly after an i.v. injection, approximately 70% was transformed into 6-AM within 3 min, similar to previous observations in vivo. Our results indicate that blood enzymes play a more important role for the rapid metabolism of heroin in humans than previously assumed. This points to 6-AM as an important target for an efficient immunotherapeutic approach to block heroin effects in humans.

Increased heroin intake and relapse vulnerability in intermittent relative to continuous self-administration: Sex differences in rats

BACKGROUND AND PURPOSE

Studies using intermittent-access drug self-administration show increased motivation to take and seek cocaine and fentanyl, relative to continuous access. In this study, we examined the effects of intermittent- and continuous-access self-administration on heroin intake, patterns of self-administration and cue-induced heroin-seeking, after forced or voluntary abstinence, in male and female rats. We also modelled brain levels of heroin and its active metabolites.

EXPERIMENTAL APPROACH

Rats were trained to self-administer a palatable solution and then heroin (0.075 mg·kg^-1 per inf) either continuously (6 h·day^-1 ; 10 days) or intermittently (6 h·day^-1 ; 5-min access every 30-min; 10 days). Brain levels of heroin and its metabolites were modelled using a pharmacokinetic software. Next, heroin-seeking was assessed after 1 or 21 abstinence days. Between tests, rats underwent either forced or voluntary abstinence. The oestrous cycle was measured using a vaginal smear test.

KEY RESULTS

Intermittent access exacerbated heroin self-administration and was characterized by a burst-like intake, yielding higher brain peaks of heroin and 6-monoacetylmorphine concentrations. Moreover, intermittent access increased cue-induced heroin-seeking during early, but not late abstinence. Heroin-seeking was higher in females after intermittent, but not continuous access, and this effect was independent of the oestrous cycle.

CONCLUSIONS AND IMPLICATIONS

Intermittent heroin access in rats resembles critical features of heroin use disorder: a self-administration pattern characterized by repeated large doses of heroin and higher relapse vulnerability during early abstinence. This has significant implications for refining animal models of substance use disorder and for better understanding of the neuroadaptations responsible for this disorder.

LINKED ARTICLES

This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Does the preparation for intravenous administration affect the composition of heroin injections? A controlled laboratory study

AIMS

To study whether the preparation procedure, and its acidic and heating conditions, used by heroin users to prepare heroin for intravenous administration affects the final composition of the fluid to be injected.

METHODS

Samples from different seizures of illegal heroin provided by the Norwegian police were prepared by adding water and ascorbic acid before heating under controlled conditions in the laboratory. Further, three seizures were prepared with different amounts of ascorbic or citric acid relative to their diacetylmorphine content. Pure diacetylmorphine base or salt was also submitted to the procedure applying two different heating intensities. The seizures and the final product after preparation were analysed for diacetylmorphine, 6-acetylmorphine and morphine using liquid chromatography with tandem mass spectrometry (LC-MS-MS).

RESULTS

After preparation, a decrease of 19.8% (25th and 75th percentiles = -29.2 and -15.3) in the initial diacetylmorphine content was observed. Both the 6-acetylmorphine and morphine content increased but, due to their low content in the initial product, diacetylmorphine still represented 83.9% (25th and 75th percentiles = 77.3 and 88.0) of the sum of these three opioids in the final solution. The loss of water during preparation caused an increase in the concentration of diacetylmorphine, 6-acetylmorphine and morphine, depending on the heating intensity applied. The content of these opioids was affected by the quantity and type of acid added in relation to the heroin purity and the level of diacetylmorphine dissolved being proportional to the amount of ascorbic acid, but not citric acid, in the sample with high heroin purity.

CONCLUSIONS

Preparation of heroin for intravenous injection appears to change the amount or concentration of diacetylmorphine and its active metabolites, 6-acetylmorphine and morphine in the final product, depending on heroin purity, amount and type of acid used or heating conditions. These circumstances can contribute to unintentional variations in the potency of the final injected solution, and therefore affect the outcome after injection.

Management of mixed acute rejection driven by a de novo donor-specific complement-binding anti-DQB1*03:01 antibody and intraepithelial CD8 T-cells in a kidney recipient: a case report

Mixed acute rejection is a clinicopathological entity that is difficult to accurately diagnose, and so may be under-reported. Allografts are lost more often than in either humoral or cellular rejection. The diagnosis requires both histological and immunological studies on renal biopsy and blood specimens from the transplant recipient to provide the required rescue therapy to abolish the allogeneic response against the graft. We present a clinical case report of an active mixed acute rejection driven by a de novo donor-specific complement-binding anti-DQB1*03:01 antibody and intraepithelial CD8 T-cells in a patient with a kidney transplant. The patient was diagnosed, treated, and followed up as per the local institution's procedure with a full recovery of graft function. Our case emphasises the challenge of a mixed acute rejection and supports the need to improve the post-transplant outcome of recipients and their grafts.

Identification of peripheral CD154+ T cells and HLA-DRB1 as biomarkers of acute cellular rejection in adult liver transplant recipients

Decreasing graft rejection and increasing graft and patient survival are great challenges facing liver transplantation (LT). Different T cell subsets participate in the acute cellular rejection (ACR) of the allograft. Cell-mediated immunity markers of the recipient could help to understand the mechanisms underlying acute rejection. This study aimed to analyse different surface antigens on T cells in a cohort of adult liver patients undergoing LT to determine the influence on ACR using multi-parametric flow cytometry functional assay. Thirty patients were monitored at baseline and during 1 year post-transplant. Two groups were established, with (ACR) and without (NACR) acute cellular rejection. Leukocyte, total lymphocyte, percentages of CD4+ CD154+ and CD8+ CD154+ T cells, human leukocyte antigen (HLA) mismatch between recipient-donor and their relation with ACR as well as the acute rejection frequencies were analysed. T cells were stimulated with concanavalin A (Con-A) and surface antigens were analysed by fluorescence activated cell sorter (FACS) analysis. A high percentage of CD4+ CD154+ T cells (P = 0·001) and a low percentage of CD8+ CD154+ T cells (P = 0·002) at baseline were statistically significant in ACR. A receiver operating characteristic analysis determined the cut-off values capable to stratify patients at high risk of ACR with high sensitivity and specificity for CD4+ CD154+ (P = 0·001) and CD8+ CD154+ T cells (P = 0·002). In logistic regression analysis, CD4+ CD154+ , CD8+ CD154+ and HLA mismatch were confirmed as independent risk factors to ACR. Post-transplant percentages of both T cell subsets were significantly higher in ACR, despite variations compared to pretransplant. These findings support the selection of candidates for LT based on the pretransplant percentages of CD4+ CD154+ and CD8+ CD154+ T cells in parallel with other transplant factors.

Association of a CAMK2A genetic variant with logical memory performance and hippocampal volume in the elderly

Calcium/Calmodulin-dependent kinase alpha (αCaMKII) has been shown to play an essential role in synaptic plasticity and in learning and memory in animal models. However, there is little evidence for an involvement in specific memories in humans. Here we tested the potential involvement of the αCaMKII coding gene CAMK2A in verbal logical memory in two Caucasian populations from Germany, in a sample of 209 elderly people with cognitive impairments and a sample of 142 healthy adults. The association of single nucleotide polymorphisms (SNPs) located within the genomic region of CAMK2A with verbal logical memory learning and retrieval from the Wechsler Memory Scale was measured and hippocampal volume was assessed by structural MRI. In the elderly people, we found the minor allele of CAMK2A intronic SNP rs919741 to predict a higher hippocampal volume and better logical memory retrieval. This association was not found in healthy adults. The present study may provide evidence for an association of a genetic variant of the CAMK2A gene specifically with retrieval of logical memory in elderly humans. This effect is possibly mediated by a higher hippocampal volume.

The role of 6-acetylmorphine in heroin-induced reward and locomotor sensitization in mice

We have previously demonstrated that heroin's first metabolite, 6-acetylmorphine (6-AM), is an important mediator of heroin's acute effects. However, the significance of 6-AM to the rewarding properties of heroin still remains unknown. The present study therefore aimed to examine the contribution of 6-AM to heroin-induced reward and locomotor sensitization. Mice were tested for conditioned place preference (CPP) induced by equimolar doses of heroin or 6-AM (1.25-5 μmol/kg). Psychomotor activity was recorded during the CPP conditioning sessions for assessment of drug-induced locomotor sensitization. The contribution of 6-AM to heroin reward and locomotor sensitization was further examined by pretreating mice with a 6-AM specific antibody (anti-6-AM mAb) 24 hours prior to the CPP procedure. Both heroin and 6-AM induced CPP in mice, but heroin generated twice as high CPP scores compared with 6-AM. Locomotor sensitization was expressed after repeated exposure to 2.5 and 5 μmol/kg heroin or 6-AM, but not after 1.25 μmol/kg, and we found no correlation between the expression of CPP and the magnitude of locomotor sensitization for either opioid. Pretreatment with anti-6-AM mAb suppressed both heroin-induced and 6-AM-induced CPP and locomotor sensitization. These findings provide evidence that 6-AM is essential for the rewarding and sensitizing properties of heroin; however, heroin caused stronger reward compared with 6-AM. This may be explained by the higher lipophilicity of heroin, providing more efficient drug transfer to the brain, ensuring rapid increase in the brain 6-AM concentration.

Comparison of (+)- and (-)-Naloxone on the Acute Psychomotor-Stimulating Effects of Heroin, 6-Acetylmorphine, and Morphine in Mice

Toll-like receptor 4 (TLR4) signaling is implied in opioid reinforcement, reward, and withdrawal. Here, we explored whether TLR4 signaling is involved in the acute psychomotor-stimulating effects of heroin, 6-acetylmorphine (6-AM), and morphine as well as whether there are differences between the three opioids regarding TLR4 signaling. To address this, we examined how pretreatment with (+)-naloxone, a TLR4 active but opioid receptor (OR) inactive antagonist, affected the acute increase in locomotor activity induced by heroin, 6-AM, or morphine in mice. We also assessed the effect of pretreatment with (-)-naloxone, a TLR4 and OR active antagonist, as well as the pharmacokinetic profiles of (+) and (-)-naloxone in the blood and brain. We found that (-)-naloxone reduced acute opioid-induced locomotor activity in a dose-dependent manner. By contrast, (+)-naloxone, administered in doses assumed to antagonize TLR4 but not ORs, did not affect acute locomotor activity induced by heroin, 6-AM, or morphine. Both naloxone isomers exhibited similar concentration versus time profiles in the blood and brain, but the brain concentrations of (-)-naloxone reached higher levels than those of (+)-naloxone. However, the discrepancies in their pharmacokinetic properties did not explain the marked difference between the two isomers' ability to affect opioid-induced locomotor activity. Our results underpin the importance of OR activation and do not indicate an apparent role of TLR4 signaling in acute opioid-induced psychomotor stimulation in mice. Furthermore, there were no marked differences between heroin, 6-AM, and morphine regarding involvement of OR or TLR4 signaling.

Levels of heroin and its metabolites in blood and brain extracellular fluid after i.v. heroin administration to freely moving rats

BACKGROUND AND PURPOSE

Heroin, with low affinity for μ-opioid receptors, has been considered to act as a prodrug. In order to study the pharmacokinetics of heroin and its active metabolites after i.v. administration, we gave a bolus injection of heroin to rats and measured the concentration of heroin and its metabolites in blood and brain extracellular fluid (ECF).

EXPERIMENTAL APPROACH

After an i.v. bolus injection of heroin to freely moving Sprague-Dawley rats, the concentrations of heroin and metabolites in blood samples from the vena jugularis and in microdialysis samples from striatal brain ECF were measured by ultraperformance LC-MS/MS.

KEY RESULTS

Heroin levels decreased very fast, both in blood and brain ECF, and could not be detected after 18 and 10 min respectively. 6-Monoacetylmorphine (6-MAM) increased very rapidly, reaching its maximal concentrations after 2.0 and 4.3 min, respectively, and falling thereafter. Morphine increased very slowly, reaching its maximal levels, which were six times lower than the highest 6-MAM concentrations, after 12.6 and 21.3 min, with a very slow decline during the rest of the experiment and only surpassing 6-MAM levels at least 30 min after injection.

CONCLUSIONS AND IMPLICATIONS

After an i.v. heroin injection, 6-MAM was the predominant opioid present shortly after injection and during the first 30 min, not only in the blood but also in rat brain ECF. 6-MAM might therefore mediate most of the effects observed shortly after heroin intake, and this finding questions the general assumption that morphine is the main and most important metabolite of heroin.

A monoclonal antibody specific for 6-monoacetylmorphine reduces acute heroin effects in mice

Immunotherapy against drugs of abuse is being studied as an alternative treatment option in addiction medicine and is based on antibodies sequestering the drug in the bloodstream and blocking its entry into the brain. Producing an efficient vaccine against heroin has been considered particularly challenging because of the rapid metabolism of heroin to multiple psychoactive molecules. We have previously reported that heroin's first metabolite, 6-monoacetylmorphine (6-MAM), is the predominant mediator for heroin's acute behavioral effects and that heroin is metabolized to 6-MAM primarily prior to brain entry. On this basis, we hypothesized that antibody sequestration of 6-MAM is sufficient to impair heroin-induced effects and therefore examined the effects of a monoclonal antibody (mAb) specific for 6-MAM. In vitro experiments in human and rat blood revealed that the antibody was able to bind 6-MAM and block the metabolism to morphine almost completely, whereas the conversion of heroin to 6-MAM remained unaffected. Mice pretreated with the mAb toward 6-MAM displayed a reduction in heroin-induced locomotor activity that corresponded closely to the reduction in brain 6-MAM levels. Intraperitoneal and intravenous administration of the anti-6-MAM mAb gave equivalent protection against heroin effects, and the mAb was estimated to have a functional half-life of 8 to 9 days in mice. Our study implies that an antibody against 6-MAM is effective in counteracting heroin effects.

C1q-fixing human leukocyte antigen assay in immunized renal patients: correlation between Luminex SAB-C1q and SAB-IgG

BACKGROUND

There is no consensus about the impact of thresholds of complement-fixing antibody assays. Recently, a C1q-SAB assay has been developed to identify complement-fixing HLA antibodies with high sensitivity and specificity. Our aim was to determine the correlation between IgG single antigens beads (SAB) and C1q-SAB assay results among patients on the renal waiting list.

PATIENTS AND METHODS

Serum samples from immunized renal waiting list patients as well as negative and positive controls were valided by Luminex (LMX). These sera, which were positive for 166 antibody specificities, were tested for HLA class I in parallel by LMX-IgG and LMX-C1q.

RESULTS

Comparison of antibody detection revealed no correlation based on median fluorescent intensity (MFI), levels between the IgG SAB and the C1qSAB assay (P > .05). IgG-positive sera with MFIs as low as 700 were able to fix C1q, whereas other sera with MFIs as high 14,500 did not. Furthermore, there appeared to be disparities in the profiles of class I antigens able to fix C1q-SAB. In our series, only 34% class I IgG SAB antibodies were also C1qSAB+. In several patients, we detected C1qSAB+ against IgGSAB- that was surely due to IgM antibodies. So, the C1qSAB assay detected IgM antibodies that fix complement.

CONCLUSION

These data suggested that the C1q-SAB assay could be an important method to evaluate pretransplant virtual crossmatch and to define nonpermitted specificities (C1q-fixing) in kidney transplantation.

Genetic polymorphisms of tumour necrosis factor alpha (TNF-α) promoter gene and response to TNF-α inhibitors in Spanish patients with inflammatory bowel disease

Tumour necrosis factor alpha (TNF-α) has an important role in inflammatory response. Alterations in the regulation of TNF-α have been implicated in a variety of inflammatory disorders, including Inflammatory bowel disease (IBD). Indeed, a common treatment for IBD is the use of TNF-α inhibitors. Polymorphisms in the TNF-α promoter region are known to affect the level of gene expression. Our aim was to investigate the influence of these single nucleotide polymorphisms (SNPs) in TNF-α promoter gene play in the risk of IBD in a Spanish population and their individual response to anti-TNF-α treatment. DNA samples from patients with IBD and controls were screened for TNF-α -238G/A (rs361525) and -308G/A (rs1800629) SNPs by PCR-SSOP using a microbeads luminex assay and compared with response to TNF-α inhibitors. There were not statistical differences in -238G/A and -308G/A allele and genotype frequencies between patients. However, we found an increased frequency of -308A allele and -308GA genotype in these nonresponders patients to TNF-α inhibitors with respect to responders patients (Pc < 0.05). This -308GA genotype has been classified as high producer of this cytokine. This fact could actually be interesting to explain the different response of patients with IBD with respect to TNF-α inhibitors. TNF-α promoter gene polymorphism does not seem to play a role in IBD susceptibility, but particular TNF-α genotypes may be involved in the different responses to TNF-α inhibitor treatment in Spanish patients with IBD.

Pharmacokinetic modeling of subcutaneous heroin and its metabolites in blood and brain of mice

High blood-brain permeability and effective delivery of morphine to the brain have been considered as explanations for the high potency of heroin. Results from Andersen et al. indicate that 6-monoacetylmorphine (6-MAM), and not morphine, is the active metabolite responsible for the acute effects observed for heroin. Here, we use pharmacokinetic modeling on data from the aforementioned study to calculate parameters of the distribution of heroin, 6-MAM and morphine in blood and brain tissue after subcutaneous heroin administration in mice. The estimated pharmacokinetic parameters imply that the very low heroin and the high 6-MAM levels observed both in blood and brain in the original experiment are likely to be caused by a very high metabolic rate of heroin in blood. The estimated metabolic rate of heroin in brain was much lower and cannot account for the low heroin and high 6-MAM levels in the brain, which would primarily reflect the concentrations of these compounds in blood. The very different metabolic rates for heroin in blood and brain calculated by the model were confirmed by in vitro experiments. These results show that heroin's fast metabolism in blood renders high concentrations of 6-MAM which, due to its relatively good blood-brain permeability, results in high levels of this metabolite in the brain. Thus, it is the high blood metabolism rate of heroin and the blood-brain permeability to 6-MAM, and not to heroin, which could account for the highly efficient delivery of active metabolites to the brain after heroin administration.

Increased locomotor activity induced by heroin in mice: pharmacokinetic demonstration of heroin acting as a prodrug for the mediator 6-monoacetylmorphine in vivo

We investigated the relative importance of heroin and its metabolites in eliciting a behavioral response in mice by studying the relationship between concentrations of heroin, 6-monoacetylmorphine (6MAM), and morphine in brain tissue and the effects on locomotor activity. Low doses (subcutaneous) of heroin (< or =5 micromol/kg) or 6MAM (< or =15 micromol/kg) made the mice run significantly more than mice given equimolar doses of morphine. There were no differences in the response between heroin and 6MAM, although we observed a shift to the left of the dose-response curve for the maximal response of heroin. The behavioral responses were abolished by pretreatment with 1 mg/kg naltrexone. Heroin was detected in brain tissue after injection, but the levels were low and its presence too short-lived to be responsible for the behavioral response observed. The concentration of 6MAM in brain tissue increased shortly after administration of both heroin and 6MAM and the concentration changes during the first hour roughly reflected the changes in locomotor activity. Both the maximal and the total concentration of 6MAM were higher after administration of heroin than after administration of 6MAM itself. The morphine concentration increased slowly after injection and could not explain the immediate behavioral response. In summary, the locomotor activity response after injection of heroin was mediated by 6MAM, which increased shortly after administration. Heroin acted as an effective prodrug. The concentration of morphine was too low to stimulate the immediate response observed but might have an effect on the later part of the heroin-induced behavioral response curve.

Different time schedules affect conditioned place preference after morphine and morphine-6-glucuronide administration

A number of studies have investigated the reward potential of morphine, using the Conditioned Place Preference (CPP) procedure. The morphine-metabolite morphine-6-glucuronide (M6G) is known to have analgesic activity comparable to morphine, but its reward properties are unclear. An unbiased two compartment counterbalanced procedure was used to investigate the induction of CPP by morphine or M6G in C57BL/6J-Bom mice using different conditioning schedules. The conditioning sessions took place either immediately after the injections and lasted either 20 or 40 min, or were delayed until 15 min after the injections and lasted for 20 min. Locomotor activity was recorded during the conditioning sessions. Morphine induced CPP when the 20-minute conditioning sessions were conducted directly after the injections, but not when they were delayed. M6G induced CPP when the 20-minute conditioning sessions were delayed, but not when the animals were conditioned directly after the injections. Neither morphine nor M6G induced CPP after 40-minute direct conditioning sessions. M6G had a biphasic effect on locomotor activity, with an initial decrease followed by excitation. This study indicates that M6G has rewarding effects, and might contribute to the development of addiction after heroin or morphine administration. However, in any attempts to explore the reward properties of M6G, the choice of time schedule should be carefully considered.

Conditioned place preference induced by morphine and morphine-6-glucuronide in mice☆

Morphine-6-glucuronide (M6G), an active metabolite of morphine has been shown to produce analgesia and fewer side effects than morphine, and the introduction of M6G as a new drug for treatment of postoperative pain is planned in 2007. Following morphine intake in humans, the metabolites morphine-3-glucuronide (M3G) and M6G are present in substantial concentrations and for longer periods than the parent drug. The possible reward effects of the morphine glucuronides have previously not been well studied. In the present study, conditioned place preference (CPP) was recorded after conditioning with subcutaneous injections of 5, 10, 20, 30 or 50 micromol/kg morphine or M6G, or 240 or 500 micromol/kg M3G in C57BL/6J-Bom mice, using a biased two compartment ("closed" and "open") counterbalanced paradigm. CPP was induced after treatment with both morphine and M6G with dose dependent increase up to 30 micromol/kg after treatment in the "closed" compartment. No dose response was observed in the "open" compartment, with maximal CPP after 10 micromol/kg morphine or M6G. M3G caused a tendency of condition place aversion (CPA), although not statistically significant. In the present study morphine and M6G demonstrated comparable reward effects, at doses that differed depending on which compartment the mice were conditioned in. M3G showed a tendency to exhibit aversive properties.

Determination of bradykinin and arg-bradykinin in rat muscle tissue by microdialysis and capillary column-switching liquid chromatography with mass spectrometric detection

Quantification of bradykinin peptides in limited amounts of rat muscle tissue dialysate has been performed using a packed capillary LC-ESI-TOF-MS method. The micro dialysate samples (450 microL) with added internal standard were loaded onto a 1 mm x 5 mm loading column packed with 5 microm Kromasil C18 particles by a carrier solution of 0.1% formic acid in ACN/water (5:95, v/v) at a flow rate of 250 microL/min for online preconcentration of the analytes. Back-flushed elution onto a 150 mm x 0.5 mm Zorbax C18 column packed with 5 microm particles was conducted using a linear solvent ACN/H2O gradient containing 0.1% formic acid. (Tyr8)-bradykinin was used as an internal standard and was added to the dialysis sample prior to injection. Baseline separation of bradykinin, arg-bradykinin and (tyr8)-bradykinin was achieved within 10 min. Positive ESI was performed in the m/z range of 200-1300. The method was validated in the range 0.2-1.0 ng/mL dialysate, yielding correlation coefficients of 0.995 and 0.990 for bradykinin and arg-bradykinin, respectively. The within-assay and between-assay precisions were between 4.3-9.6% and 6.2-10.6%, respectively. Both arg-bradykinin and bradykinin were detected in dialysate from rat muscle tissue, at concentrations of 0.1 and 0.4 ng/mL for bradykinin and arg-bradykinin, respectively, confirming the presence of arg-bradykinin in rat muscles.

Kinin peptides in human trapezius muscle during sustained isometric contraction and their relation to pain

To determine the muscular concentration of bradykinin and kallidin during static contraction, microdialysis probes were implanted bilaterally in the trapezius muscles of healthy women. Three hours after probe implantation, 200 μM of the angiotensin-converting enzyme (ACE) inhibitor enalaprilat were added to the perfusion solution in one of the sides for 30 min. Thirty minutes later, the subjects performed a sustained bilateral shoulder abduction at 10% of the maximal voluntary contraction until exhaustion. This protocol was repeated twice, with an interval of at least 17 days. High intersession repeatability was observed in the concentration of bradykinin but not of kallidin. Enalaprilat induced a significant increase in bradykinin levels in the dialysate, without affecting kallidin levels. The sustained contraction induced a significant increase in dialysate levels of both kinin peptides. The contraction also induced a significant increase in pain ratings, as measured by a visual analog scale. During contraction, positive correlations were found between pain ratings and levels of kinin peptides in dialysate, predominantly in the side previously perfused with enalaprilat. Subjects with the higher pain ratings also showed larger increases in kinin peptides in the side previously perfused with enalaprilat. The present results show that both plasma and tissue kinin-kallikrein are activated during muscle contraction, but that their metabolic pathways are differently regulated during rest and contraction, because they showed a different response to ACE inhibition. They also indicate that intramuscular kinin peptides levels, and ACE activity, may contribute to muscle pain.

Contraction-related factors affect the concentration of a kallidin-like peptide in rat muscle tissue

In order to study the effects of the manipulation of various factors related to muscular activity on the concentration of kinins in muscular tissue, a microdialysis probe was implanted in the adductor muscle of the hindlimb in anaesthetized rats. After collection of baseline samples, the perfusion fluid was changed to a Ringer solution containing sodium lactate (10 or 20 mM), adenosine (50 or 100 microM) or a lower pH (7.0 or 6.6). Whereas perfusion with lactate did not have any significant effect on the concentration of kinins in the dialysate, the perfusion with a lower pH or with adenosine dose-dependently increased the kinin content in the samples. In a second microdialysis experiment, by using specific radioimmunoassays (RIA) for bradykinin and kallidin, we observed that about 70 % of the total kinins dialysed from rat muscle are a kallidin-like peptide. Also, the simultaneous perfusion with 100 microM caffeine totally abolished the increase in kinin levels induced by the perfusion at pH 6.6. In a third experiment, soleus muscles from rat were stimulated in vitro during 30 min in the presence or absence of 77 microM caffeine. Electrically stimulated contraction, but not the addition of 10 mU ml(-1) insulin, induced an increase in the concentration of the kallidin-like peptide in the buffer. This effect was totally prevented by the addition of the adenosine antagonist caffeine. These results show that a kallidin-like peptide is released from rat muscle, and that its production is enhanced by muscle activity. Furthermore, the increase in kinin peptides during muscle contraction may be mediated by an increase in adenosine levels.

Chronic L-deprenyl treatment alters brain monoamine levels and reduces impulsiveness in an animal model of Attention-Deficit/Hyperactivity Disorder

Effects of chronic L-deprenyl administration on hyperactive behaviour and brain monoamine levels were studied in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. SHR were hyperactive, impulsive and had impaired sustained attention when tested with a multiple 2-min fixed interval (FI) 5-min extinction (EXT) schedule of reinforcement. Even low, 0.25 mg/kg, doses of chronically-administered L-deprenyl reduced the impulsiveness (bursts of responses with short interresponse times) of SHR, without altering the general hyperactivity or the impaired sustained attention. The drug had no effect on WKY behaviour. The levels of noradrenaline (NA), dopamine (DA), serotonin (5-hydroxytryptamine, 5-HT) and their metabolites, measured in neostriatum, nucleus accumbens and frontal cortex, showed that L-deprenyl effectively inhibited monoamine oxidase (MAO) activity. These results suggest that impulsiveness is a behavioural component that may be operating independent of the other components, like hyperactivity and deficient sustained attention, and that can be reduced by chronic MAO-B inhibition with L-deprenyl in this strain of rats. The positive effect of L-deprenyl on impulsiveness is discussed as due either to normalization of an asymmetric dopaminergic activity in the nucleus accumbens, or to a restoration of normal DA function in the prefrontal cortex.

Short term storage of samples containing monoamines: ascorbic acid and glutathione give better protection against degradation than perchloric acid

In order to study the protection of monoamines from degradation during short-time storage, the effect of three different antioxidants on the degradation of dopamine, dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) was analyzed after 5 and 20 h. The results showed that dopamine was still quite stable after 20 h storage at room temperature, but that about 95% of 5-HIAA had disappeared. The best protection against degradation of all three substances was achieved when 15% v/v of a solution containing 1-2 mM ascorbic acid or 40 mM glutathione was added to the sample, resulting in near 100% protection after 20 h. Perchloric acid actually accelerated the degradation of 5-HIAA.

Extracellular adenosine levels in neostriatum and hippocampus during rest and activity periods of rats

Adenosine is an inhibitory modulator in the mammalian brain with a possible role in sleep regulation, which is mainly indicated by pharmacological studies showing that adenosine or its analogs can induce sedation and sleep, whereas adenosine antagonists, like caffeine and theophylline, are potent behavioral and neuronal stimulants. In contrast to these pharmacological findings, data on endogenous adenosine in relation to sleep and waking are sparse. Therefore, we have now used in vivo microdialysis to investigate the extracellular levels of adenosine in the neostriatum and hippocampus of freely moving rats. Adenosine was monitored over a time course of 24 h, during which the animals were exposed to a 12 h day/night rhythm with lights-off from 19.00 to 07.00. In this lights-off period, i.e. the rats' active period, the maximal levels of neostriatal and hippocampal extracellular adenosine were higher than during the lights-on period. In contrast to the neostriatum, extracellular levels of hippocampal adenosine tended to increase towards the end of the lights-off period, reaching its maximal level at 07.00, and decreasing again within the following hour. The changes of hippocampal adenosine levels were related to behavior, since significant increases in "sleep-like" behavior, as well as decreases in overall movements and consummatory behavior, were observed when adenosine levels had reached their maxima in the hippocampus; no such relationship was found with respect to the neostriatum. These results are in keeping with a role of endogenous adenosine in the regulation of sleep and wakefulness, and point to a specific role of adenosine in the hippocampus. They also raise the possibility that adenosine may be involved in different behavioral processes dependent on the area of the brain, as well as the type of adenosine receptor involved. Finally, given the known evidence for neuroprotective actions of adenosine, its accumulation in the hippocampus as a function of behavioral activity may serve to prevent or repair the neural degenerative consequences of such activity. It is proposed that adenosine's sleep-promoting effects result from its signalling to cease behavioral activity in order to prevent excessive activity-related changes, and thus allow other restorative sleep-related processes to take over.

Relationship between dopamine release in nucleus accumbens and place preference induced by substance P injected into the nucleus basalis magnocellularis region

The activity of the neurotransmitter dopamine in the nucleus accumbens is considered to be an important element in the central processing of reinforcement. Unilateral administration of the neurokinin substance P into the area of the nucleus basalis magnocellularis of rats was found to be reinforcing, as assessed by the conditioned place preference paradigm. Simultaneous in vivo microdialysis showed that administration of substance P into the area of the nucleus basalis magnocellularis could increase extracellular concentrations of dopamine in the contralateral nucleus accumbens. Only those animals in which the administration of substance P induced this increase in dopamine levels acquired place preference. Furthermore, the changes in extracellular dopamine levels after substance P administration had a bimodal time course with an acute increase (to about 160% of baseline) during the first hour after injection, with a low (to 120-130%) and enduring increase occurring thereafter. Interestingly, during this second increase there were indications for positive correlations with the degree of place preference induced by substance P. Further positive correlations with place preference were found in the levels of the serotonergic metabolite 5-hydroxyindoleacetic acid. In contrast to dopamine, these were observed ipsi- and contralateral to the side of substance P administration. By combining the methods of in vivo microdialysis and conditioned place preference it was shown that the reinforcing effect induced by unilateral substance P injection in the nucleus basalis magnocellularis is related to dopaminergic (and possibly serotonergic) mechanisms in the nucleus accumbens.

Substance P decreases extracellular concentrations of acetylcholine in neostriatum and nucleus accumbens in vivo: possible relevance for the central processing of reward and aversion

It has been shown that peripherally administered substance P has reinforcing effects and can promote functional recovery after unilateral partial lesion of the nigrostriatal system. Furthermore, peripheral injection of substance P induces an increase in extracellular striatal dopamine. To obtain further information about the central mechanisms of these properties we used the in vivo microdialysis technique to investigate changes in the extracellular concentrations of acetylcholine in neostriatum and nucleus accumbens after intraperitoneal (i.p.) administration of substance P or vehicle in freely moving rats. The i.p. administration of 50 micrograms/kg substance P induced a steady, long-lasting decrease in the extracellular concentrations of acetylcholine in neostriatum, while no changes were observed in the nucleus accumbens. In comparison, substance P in a dose of 250 micrograms/kg i.p. acutely decreased the extracellular levels of acetylcholine in both nuclei. Interestingly, after the administration of vehicle, an acute increase in acetylcholine levels was observed in the nucleus accumbens, but not in the neostriatum. This effect did not occur after the injection of substance P indicating that the neurokinin blocked the increase in acetylcholine levels induced by the vehicle injection. These effects of substance P on striatal acetylcholine are discussed with respect to their relationship with dopamine and endogenous opiates, and with respect to the functional role of substance P, such as in reward, aversion, motor activity, and functional recovery.

Different effects of scopolamine on extracellular acetylcholine levels in neostriatum and nucleus accumbens measured in vivo: possible interaction with aversive stimulation

The in vivo microdialysis technique was used to measure extracellular concentrations of acetylcholine (ACh) in the neostriatum (NS) and nucleus accumbens (NAc) of freely moving rats after intraperitoneal administration of the muscarinic receptor antagonist scopolamine (0.5 mg/kg) or vehicle. Simultaneously, behavior was monitored. The administration of scopolamine induced an increase in extracellular ACh levels in the NS, which reached a maximum of about 185% within one hour after injection and returned to baseline values about three hours after injection. In the NAc, an increase of similar time-course was observed; however, this increase reached a maximum of 250%, which was significantly higher than the one observed in NS. These changes in ACh levels were accompanied by enhanced locomotion, rearing and grooming; however, the behavioral changes were of shorter time-course than those of extracellular ACh. The injection of vehicle did not affect ACh levels in NS, but induced a significant increase (60%) in the NAc. The levels of behavioral activity after vehicle injection did not differ from pre-injection levels. These results suggest, that the cholinergic systems in the NAc and NS are differently affected by peripheral administration of both scopolamine and vehicle. The differential effects of scopolamine in NS and NAc could reflect pharmacodynamic differences between these two striatal brain areas, perhaps due to a higher density of cholinergic interneurons or muscarinic autoreceptors in the NAc in comparison to the NS. However, the increase of extracellular ACh observed after vehicle injection suggests that factors such as aversive stimulation through the injection procedure can increase ACh release in the NAc and that such a mechanism can interact within the action of scopolamine. Thus, the stronger action of scopolamine on extracellular ACh in the NAc might be an additive effect of the drug with that of the injection procedure.

Behavioral indices of moderate nigro-striatal 6-hydroxydopamine lesion: a preclinical Parkinson's model

Asymmetries in turning and scanning were investigated in rats with different degrees of neostriatal dopamine depletion after unilateral injections of 6-hydroxydopamine into the substantia nigra. Animals with severe lesions, i.e., residual dopamine levels of < 20%, spontaneously turned ipsiversive and showed more scanning behavior with the side ipsilateral to the lesion. These asymmetries were reversed by the dopamine receptor agonist apomorphine. Animals with less severe dopamine depletion, i.e., residual dopamine levels of 20-65%, did not show an asymmetry in spontaneous turning, but an ipsilateral asymmetry in scanning was still observed, indicating a greater sensitivity of this measure for moderate striatal dopamine depletions. Furthermore, in animals with residual dopamine levels of 45-65%, the dopamine receptor agonist apomorphine did not lead to a behavioral reversal as with severe lesions, but induced ipsilateral scanning and ipsiversive turning. These ipsiversive asymmetries are discussed in relation to asymmetries in self-regulatory mechanisms of the nigro-striatal dopamine system, such as dopamine autoreceptors controlling the release of this transmitter. Dopamine receptor-stimulated behavioral asymmetry in animals with moderate depletions of dopamine is suggested as a preclinical model to study mechanisms affected in the early state of Parkinson's disease.

Sequence-specific effects of neurokinin substance P on memory, reinforcement, and brain dopamine activity

There is ample evidence that the neurokinin substance P (SP) can have neurotrophic as well as memory-promoting effects. This paper outlines a recent series of experiments dealing with the effects of SP and its N- and C-terminal fragments on memory, reinforcement, and brain monoamine metabolism. It was shown that SP, when applied peripherally (IP), promotes memory (inhibitory avoidance learning) and is reinforcing (place preference task) at the same dose of 37 nmol/kg. Most important, however, is the finding that these effects seemed to be encoded by different SP sequences, since the N-terminal SP1-7 (185 nmol/kg) enhanced memory, whereas C-terminal hepta- and hexapeptide sequences of SP proved to be reinforcing in a dose equimolar to SP. These differential behavioral effects were paralleled by selective and site-specific changes in dopamine (DA) activity, as both SP and its C-, but not N-terminus, increased extracellular DA in the nucleus accumbens (NAc), but not in the neostriatum. The neurochemical changes lasted at least 2 h after injection. These results show that the reinforcing action of peripheral administered SP may be mediated by its C-terminal sequence, and that this effect could be related to DA activity in the NAc. Direct application of SP (0.74 pmol) into the region of the nucleus basalis magnocellularis (NBM) was also memory-promoting and reinforcing, and again, these effects were differentially produced by the N-terminus and C-terminus, supporting the proposed structure-activity relationship for SP's effects on memory and reinfrocement. These results may provide a hypothetical link between the memory-modulating and reinforcing effects of SP and the impairment in associative functioning accompanying certain neurodegenerative processes.

Peripherally administered substance P affects extracellular dopamine concentrations in the neostriatum but not in the nucleus accumbens under anesthesia

The in situ microdialysis technique was used in urethane-anesthetized rats to monitor changes in the extracellular concentrations of dopamine and its metabolites in neostriatum and nucleus accumbens after the peripheral administration of substance P (50 or 250 micrograms/kg, IP). Four to five hours after urethane anesthesia a decrease of extracellular dopamine and its metabolites was observed which continued in the nucleus accumbens in the following 3 h. The administration of substance P induced a decrease in extracellular concentration of dopamine in neostriatum. This neurochemical change after substance P was not accompanied by parallel alterations in extracellular concentrations of dopamine metabolites. No effects of substance P were observed on dopamine or its metabolites in nucleus accumbens. These data are discussed in relation with the contrasting effects of substance P on awake rats and the possible changes in striatal dopamine activity induced by anesthetics.

The C-terminal fragment of substance P enhances dopamine release in nucleus accumbens but not in neostriatum in freely moving rats

The in vivo microdialysis technique was used to study the effects of carboxyl or amino terminal sequences of substance P on the extracellular concentrations of dopamine, its metabolites dihydroxyphenylacetic acid and homovanillic acid, as well as on 5-hydroxyindoleacetic acid, in neostriatum and nucleus accumbens of freely moving rats. The i.p. administration of 37 nmol/kg of the substance P C-terminal heptapeptide analog [pGlu5, MePhe8, Sar9]SP5-11 (DiMe-C7) caused an increase in extracellular dopamine concentrations in nucleus accumbens but not in neostriatum. The administration of the equimolar dose of the heptapeptide N-terminal fragment substance P 1-7 (SP1-7) did not have an effect in either structure. No changes were observed in the extracellular concentrations of the metabolites after the administration of either substance. These results are discussed with respect to the reinforcing effects of substance P and its C-terminal sequence, which may be mediated via dopamine release in the nucleus accumbens.

Effects of substance P on extracellular dopamine in neostriatum and nucleus accumbens

Microdialysis was used to monitor changes in dopamine release in the neostriatum and nucleus accumbens after peripheral administration of substance P in freely moving rats. Substance P in a dose of 50 micrograms/kg produced a steady moderate increase in dopamine levels in the neostriatum, which persisted for at least 5 h. In contrast, a dose of 250 micrograms/kg caused an acute increase in dopamine levels in the nucleus accumbens, which lasted about 2 h. These data suggest that the peripheral administration of substance P can influence dopamine release in mesolimbic and mesostriatal terminals.

Effects of different handling-stimulation procedures and benzodiazepines on two-way active avoidance acquisition in rats

The acquisition of two-way active (shuttlebox) avoidance involves a conflict situation which can be used as an animal model of anxiety, since it is sensitive to manipulations of the animal's emotivity/reactivity. The results from the present study (experiment 1) add relevant support to that proposal, since diazepam (2 and 4 mg/kg) and the triazolobenzodiazepine alprazolam (1, 1.25 and 1.5 mg/kg) significantly improved avoidance performance in shuttlebox acquisition in rats in agreement with previous data. In another study (experiment 2), a mild stressful (10-day) handling procedure (i.e. handling which tends to increase the emotional reactivity of the animals, as showed in experiment 3) was found to affect such behaviour in an opposite direction to that of the two benzodiazepines. Conversely, when an habituating handling procedure (i.e. handling which leads to less reactive animals; experiment 3) was used, the acquisition of shuttlebox avoidance was improved (experiment 4). The results are discussed in relation with previous data showing that the particular parameters used in the exposure to stressful stimuli may lead to either sensitization or habituation of anxious responses.

Lateralized changes in behavior and striatal dopamine release following unilateral tactile stimulation of the perioral region: a microdialysis study

Intracranial microdialysis was used to measure dopamine (DA) release in the ventrolateral neostriatum of freely moving rats before and after unilateral tactile stimulation was applied to the orofacial region. Several behavioral parameters which have been linked to changes in nigrostriatal DA transmission (scanning, or snout contact with the walls of the observation chamber, turning and locomotion) were measured as well. Orofacial stimulation was followed by an asymmetrical increase in DA release with concentrations of transmitter higher in the neostriatum ipsilateral to the side of stimulation. Asymmetrical scanning behavior was observed during the time period when DA release was asymmetric, with rats favoring use of the side of the face contralateral to increased DA release. Increases in the DA metabolites DOPAC and HVA were found in the striatum ipsilateral to stimulation, but were delayed 40 min following the increase in DA.