Tear gasses CN, CR, and CS are potent activators of the human TRPA1 receptor

The TRPA1 channel is activated by a number of pungent chemicals, such as allylisothiocyanate, present in mustard oil and thiosulfinates present in garlic. Most of the known activating compounds contain reactive, electrophilic chemical groups, reacting with cysteine residues in the active site of the TRPA1 channel. This covalent modification results in activation of the channel and has been shown to be reversible for several ligands. Commonly used tear gasses CN, CR and CS are also pungent chemicals, and in this study we show that they are extremely potent and selective activators of the human TRPA1 receptor. To our knowledge, these are the most potent TRPA1 agonists known to date. The identification of the molecular target for these tear gasses may open up possibilities to alleviate the effects of tear gasses via treatment with TRPA1 antagonists. In addition these results may contribute to the basic knowledge of the TRPA1 channel that is gaining importance as a pharmacological target.

Differences in nociceptive behavioral performance between C57BL/6J, 129S6/SvEv, B6 129 F1 and NMRI mice

The interpretation of knockout and transgenic mouse studies in pain research critically depends on detailed knowledge of the performance profile of the background strains. Pain-related behavior was compared between four relevant mouse strains (C57BL/6J, 129S6/SvEv, B6 129 F1 and NMRI mice of both sexes) using an extended test battery that included an unusual variety of assays for thermal and mechanical acute nociception, and inflammatory and neuropathic pain. Strain- and gender-dependent differences were demonstrated in many of these nociceptive assays. Particularly, C57BL and 129 mice, which serve as the default genetic backgrounds for experiments in genetically altered mice, display quite different patterns of nociceptive performance. Compared to C57BL/6J mice, 129S6/SvEv animals are less sensitive to inflammatory pain conditions (thermal sensitivity after carrageenan subplantar injection; flinch behavior after formalin injection), while the opposite is observed in the neuropathic pain condition and the visceral pain model. These data may be of special interest for genetic studies, where issues related to the background phenotype may confound their interpretation.

P2X currents in peritoneal macrophages of wild type and P2X4 -/- mice

In this study the ATP-induced (P2X) currents in isolated peritoneal macrophages of wild type (WT) and P2X(4) knockout (P2X(4)(-/-)) mice were studied by means of whole-cell patch clamp in order to (1) survey the P2X currents of native macrophages and (2) to investigate the expression of P2X(4)-like currents in the WT versus P2X(4)(-/-) mice. Three types of currents were observed in the isolated macrophages: (1) in approximately 10% of both WT and P2X(4)(-/-) macrophages a fast activating and inactivating P2X1-like current was recorded with low concentrations (0.1-1 microM) of ATP; (2) 85% of wild type and 100% of P2X(4)(-/-) macrophages exhibited a non-desensitizing P2X(7)-like current activated at high concentrations of ATP (10mM). The identity of the P2X(7) current was confirmed using the specific blocker A-740003; (3) 88.6% of the WT but none of the P2X(4)(-/-) macrophages showed a small P2X(4)-like current that desensitized slowly upon ATP application at intermediate concentrations (3-300 microM). Several observations indicated that the slowly desensitizing current in WT macrophages was P2X(4). The EC50 value of 5.3 microM ATP was as expected for P2X(4) and the current induced by 3-300 microM ATP was absent in P2X(4)(-/-) mice. Upon application of 3 microM ivermectin, a P2X(4)-selective modulator, the amplitude of this current was increased and the desensitization was inhibited in WT cells. In addition, this current was facilitated by 10 microM Zn(2+) but inhibited by Cu(2+) (in contrast to P2X(2)). We conclude that the P2X(4) and P2X(7) currents are functionally expressed in recruited peritoneal macrophages of WT mice and that the P2X(4)-like current is absent in P2X(4)(-/-) mice.

Vesicular glutamate transporter VGLUT2 expression levels control quantal size and neuropathic pain

Uptake of L-glutamate into synaptic vesicles is mediated by vesicular glutamate transporters (VGLUTs). Three transporters (VGLUT1-VGLUT3) are expressed in the mammalian CNS, with partial overlapping expression patterns, and VGLUT2 is the most abundantly expressed paralog in the thalamus, midbrain, and brainstem. Previous studies have shown that VGLUT1 is necessary for glutamatergic transmission in the hippocampus, but the role of VGLUT2 in excitatory transmission is unexplored in glutamatergic neurons and in vivo. We examined the electrophysiological and behavioral consequences of loss of either one or both alleles of VGLUT2. We show that targeted deletion of VGLUT2 in mice causes perinatal lethality and a 95% reduction in evoked glutamatergic responses in thalamic neurons, although hippocampal synapses function normally. Behavioral analysis of heterozygous VGLUT2 mice showed unchanged motor function, learning and memory, acute nociception, and inflammatory pain, but acquisition of neuropathic pain, maintenance of conditioned taste aversion, and defensive marble burying were all impaired. Reduction or loss of VGLUT2 in heterozygous and homozygous VGLUT2 knock-outs led to a graded reduction in the amplitude of the postsynaptic response to single-vesicle fusion in thalamic neurons, indicating that the vesicular VGLUT content is critically important for quantal size and demonstrating that VGLUT2-mediated reduction of excitatory drive affects specific forms of sensory processing.

A modeling approach to the analysis of nerve regenerative experiments

Many experiments aiming at the investigation of nerve repair involve elaborate testing over a certain time period. Data arising from such experiments are often analyzed by time-point. Such a cross-sectional approach is often very inefficient. In this paper, we consider a case study in which repeated measurements of two response variables assumed to be Poisson distributed are obtained. We show how a repeated measures modeling approach, based on generalized linear models, can handle both responses in one model and improve the inference in the nerve repair experiments. The benefits of the model as well as problems that can occur are illustrated and discussed.

Differences in behavioural test battery performance between mice with hippocampal and cerebellar lesions

Effects of hippocampal or cerebellar lesions have been described extensively, but the ability of behavioural tests for laboratory mice to distinguish between such lesions has not been studied in detail. We compared the behavioural consequences of large bilateral hippocampal and hemispheric cerebellar lesions with eight commonly used tests that included elements of neuromotor performance, exploratory behaviour, and learning and memory ability. Dissociation between the effects of the different lesions was most obviously demonstrated by neuromotor impairment in cerebellum-lesioned mice (typically in the rotarod task) and hyperactivity in hippocampus-lesioned mice (typically in cage activity recordings). Several of the behavioural variables derived from the test battery correlated differently with the size of the hippocampal and cerebellar lesions. In contrast, no absolute dissociation between the effects of these lesions was found in the Morris maze, a reportedly hippocampus-dependent learning and memory task. The contextual fear conditioning task, on the other hand, did reveal a selective decrease of context-dependent freezing in hippocampus-lesioned mice, whereas cerebellum-lesioned animals displayed an increase in freezing responses. By and large, the present battery of tests does allow differentiation between the effects of cerebellar and hippocampal lesions in laboratory mice.

Reduction of Abeta levels in the Sprague Dawley rat after oral administration of the functional gamma-secretase inhibitor, DAPT: a novel non-transgenic model for Abeta production inhibitors

Considerable effort has been made to develop drugs that delay or prevent neurodegeneration. These include inhibitors of Abeta-generating proteases for the treatment of Alzheimer's disease. Testing the amyloid hypothesis in vivo requires molecules that are capable of entering the CNS and that produce a substantial reduction in brain Abeta levels. Plaque-developing APP transgenic mice are currently widely used as an in vivo model of choice as these animals produce readily measurable amounts of human Abeta. They are very useful in the testing of a variety of amyloid-lowering approaches but their use for compound screening is often limited by their cost. Transgenic animals also require extensive, time-consuming breeding programs and can show high inter-animal differences in the expression level of the transgene. Hence, we considered it important to develop and characterize a new and simple non-transgenic animal model for testing Abeta modulation. For this purpose, Wild-type adult Sprague Dawley rats were treated with DAPT, a functional gamma-secretase inhibitor, and the Abeta40 and Abeta42 levels in brain-tissue and body fluids were assessed. We showed that DAPT, given orally, significantly lowered Abeta40 and Abeta42 peptide levels in brain extract, CSF, and the plasma dose- and time-dependently. We can conclude that our data establish the usefulness of the wild-type rat model for testing small-molecule inhibitors of Abeta production.

4-Phenyl-4-[1H-imidazol-2-yl]-piperidine derivatives, a novel class of selective δ-opioid agonists

A novel series of 4-phenyl-4-[1H-imidazol-2-yl]-piperidine derivatives has been prepared and their synthesis described herein. In vitro affinities for delta-, mu-, and kappa-opioid receptors, as well as the functional activity in the [(35)S]GTPgammaS assay are reported. The most potent and selective delta-opioid agonist 18a exhibited a K(i) of 18 nM, and was >258-fold and 28-fold selective over mu- and kappa-receptors, respectively; the compound is a full agonist with an EC(50) value of 14 nM.

A multiparametric assay for quantitative nerve regeneration evaluation

We introduce an assay for the semi-automated quantification of nerve regeneration by image analysis. Digital images of histological sections of regenerated nerves are recorded using an automated inverted microscope and merged into high-resolution mosaic images representing the entire nerve. These are analysed by a dedicated image-processing package that computes nerve-specific features (e.g. nerve area, fibre count, myelinated area) and fibre-specific features (area, perimeter, myelin sheet thickness). The assay's performance and correlation of the automatically computed data with visually obtained data are determined on a set of 140 semithin sections from the distal part of a rat tibial nerve from four different experimental treatment groups (control, sham, sutured, cut) taken at seven different time points after surgery. Results show a high correlation between the manually and automatically derived data, and a high discriminative power towards treatment. Extra value is added by the large feature set. In conclusion, the assay is fast and offers data that currently can be obtained only by a combination of laborious and time-consuming tests.

Method for the determination of the levels of β-amyloid peptide in the CSF sampled from freely moving rats

INTRODUCTION

In the present study, a model was developed to determine the effect of secretase inhibition on beta-amyloid peptide (Abeta) levels in the cerebrospinal fluid (CSF) of freely moving adult rats.

METHODS

Rats were chronically implanted with a cannula into the cisterna magna and CSF samples were collected at different time points from the same animal without anaesthesia. The levels of CSF Abeta were measured by a sandwich ELISA assay.

RESULTS

Administration of DAPT, a functional gamma-secretase inhibitor, resulted in a substantial reduction of Abeta40 and Abeta42, confirming the in vivo functionality of the CSF as a biomarker source for endogenous APP processing modulation by secretase inhibitors.

DISCUSSION

Thus, the present work provides clear evidence for the usefulness of CSF sampling from the freely moving rat model for testing the effectiveness of small molecule inhibitors of Abeta production.

A Behavioral and Pharmacological Validation of the Acetone Spray Test in Gerbils with a Chronic Constriction Injury

Cold and mechanical allodynia are important symptoms in patients with neuropathic pain. The study of cold allodynia in animals can help us to understand the underlying pathophysiological mechanisms of neuropathic pain and to validate drugs. The evaluation of cold allodynia in gerbils with a chronic constriction injury of the sciatic nerve on the cold plate is not always stable. We developed a new application method of acetone using a specific spray technique with an Eppendorf multistepper pipette. The chronic constriction injury of the sciatic nerve in gerbils resulted in a long-lasting mechanical and acetone spray-induced hyperreactivity throughout the testing period, which is clearly different from what was seen in sham-operated animals. The acetone spray test incorporates a multimodal stimulus different from direct cold stimulation. The reactivity to the acetone spray coincides in time and strength with the reactivity observed in mechanical allodynia in gerbils and with mechanical and thermal allodynia in other species. Furthermore, a pharmacological validation of the acetone spray test by different reference compounds was performed. Different compounds effective in neuropathic pain models in rodents influence the hyperreactivity to the acetone spray after acute and chronic administration. This study indicates that the multimodal acetone spray test is a valuable tool in the study of neuropathic pain in rodents.

IMPLICATIONS

The acetone spray test is a multimodal and valuable tool in the evaluation of neuropathic pain behavior in gerbils.

Development of a specific ELISA for the quantitative study of amino-terminally truncated beta-amyloid peptides

Clinical studies for disease modifying drugs in Alzheimer's disease are in real need for a sensitive biochemical diagnostic and therapeutic marker. Encouraging results have been obtained by measuring levels of pathology related proteins such as amyloid beta (Abeta) peptides and tau proteins in cerebrospinal fluid (CSF) and plasma of patients. We and other research groups have shown that truncated Abeta11-40 and Abeta11-42 is also a potential marker and that it is produced and deposited in the brains of patients and transgenic mouse models. Because of a lack of quantitative methods for specific measurement of the truncated Abeta it has not been possible to evaluate the true value of this potential biomarker. To overcome these limitations we developed a novel monoclonal antibody-based sandwich enzyme-linked immunosorbent assay (ELISA) to measure Abeta11-40 and Abeta11-42 levels in biological materials. For this purpose monoclonal antibodies were produced that react specifically with amyloid precursor protein (APP) products generated by cleavage at position 11 of the Abeta sequence. The assay has the sensitivity, selectivity and dynamic range to allow specific, direct quantitation of truncated Abeta11 peptides in cell culture medium, cerebrospinal fluid and brain tissue extracts.

Preparation and physicochemical characterization of biodegradable nerve guides containing the nerve growth agent sabeluzole

The objective of this study was to develop and characterize a biodegradable drug-loaded nerve guide for peripheral nerve regeneration. Sabeluzole, a nerve growth agent, was selected as model compound. Four biodegradable polymers were selected for this study: a copolymer of polylactic acid and polycaprolactone (PCL); a copolymer of polyglycolic acid and polycaprolactone PCL; a copolymer of PCL/polydioxanone (PDO) and PDO. Placebo and drug loaded nerve guides were obtained by melt compression and melt extrusion. It was observed that melt compression and melt extrusion are feasible techniques to prepare the nerve guides. Based on the physicochemical characterization, all samples show absence of crystalline sabeluzole, indicating the formation of an amorphous dispersion. The in vitro release measurements show that the release of sabeluzole is complete, reproducible and can be controlled by the proper selection of the polymer. The release mechanism for all samples follows Fickian release behaviour.

Is the Second Phase of the Formalin Test Useful to Predict Activity in Chronic Constriction Injury Models? A Pharmacological Comparison in Different Species

This study presents data of several reference drugs in rats and gerbils for both the second phase of the formalin test and the cold allodynia in animals with a constriction injury of the sciatic nerve. A pharmacological validation of the formalin test and the CCI model in gerbils was performed. It was evaluated whether the second phase of the formalin test could be used as a pharmacological screening to predict outcome in the cold plate test in CCI animals. Male Sprague Dawley and Wistar rats and male gerbils were used for both tests. For the formalin test, animals were injected in the right hind paw (5% formalin rat: 0.05 microl; gerbil: 0.01 microl) and flinching and licking or biting were recorded. For CCI testing, a Bennett operation was performed on the left hind paw 7 days before testing. Cold plate allodynia was evaluated before and after drug treatment. In rats, a good correlation between both test conditions for morphine, fentanyl, MK-801 and flunarizine was found. Clonidine tends to have more activity in the second phase of the formalin test, whereas baclofen, tramadol, amitryptiline, ketamine and topiramate demonstrate to be more active in the cold plate. In gerbils, a good correlation between both test conditions for fentanyl and ketoprofen was found. Tramadol and CP-96345 tend to have more activity in the second phase of the formalin test, whereas morphine, SR-48968, SR-142801 and R116301 demonstrates to be more active in the cold plate test. In the present acute test conditions, there is a correlation in the pharmacological activity in rats and gerbils for the tested compounds a correlation between the second phase of the formalin test and the cold allodynia in CCI animals is found. Comparing to human data the screening drugs tested in this study show a correlation between animal and human studies in these specific circumstances. Further validation studies are needed to make these correlations clinical applicable.

Internal and External Factors Affecting the Development of Neuropathic Pain in Rodents. Is It All About Pain?

It is important to know the factors that will influence animal models of neuropathic pain. A good reproducibility and predictability in different strains of animals for a given test increases the clinical relevance and possible targeting. An obligatory requirement for enabling comparisons of results of different origin is a meticulous definition of the specific sensitivities of a model for neuropathic pain and a description of the test conditions. Factors influencing neuropathic pain behavior can be subdivided in external and internal factors. The most important external factors are; timing of the measurement of pain after induction of neuropathy, circadian rhythms, seasonal influences, air humidity, influence of order of testing, diet, social variables, housing and manipulation, cage density, sexual activity, external stress factors, and influences of the experimenter. The internal factors are related to the type of animal, its genetic background, gender, age, and the presence of homeostatic adaptation mechanisms to specific situations or stress. In practice, the behavioral presentations to pain depend on the combination of genetic and environmental factors such as accepted social behavior. It also depends on the use of genetic manipulation of the animals such as in transgenic animals. These make the interpretation of data even more difficult. Differences of pain behavior between in- and outbred animals will be better understood by using modern analysis techniques. Substrains of animals with a high likelihood for developing neuropathic pain make the unraveling of specific pathophysiological mechanisms possible. Concerning the effect of stress on pain, it is important to differentiate between external and internal stress such as social coping behavior. The individual dealing with this stress is species sensitive, and depends on the genotype and the social learning. In the future, histo-immunological and genetic analysis will highlight similarities of the different pathophysiological mechanisms of pain between different species and human subjects. The final objective for the study of pain is to describe the genetics of the eliciting pain mechanisms in humans and to look for correlations with the knowledge from basic research. Therefore, it is necessary to know the genetic evolution of the different mechanisms in chronic pain. In order to be able to control the clinical predictability of a putative treatment the evolutionary pharmacogenomic structure of specific transmitters and receptors must be clarified.

Opioid tolerance and dependence: an inevitable consequence of chronic treatment?

Although opioids provide effective analgesia, largely unsubstantiated concerns about opioid-induced tolerance, physical dependence and addiction have limited their appropriate use. As a consequence, many patients receive inadequate treatment for both malignant and non-malignant pain. However, it has been shown that analgesic tolerance develops less frequently during chronic opioid administration in a clinical context than in animal experiments, and that instituting an appropriate dosing regimen can minimise withdrawal symptoms. Early studies had suggested that addiction might result from chronic opioid therapy, though more recent data indicate a low risk in patients with no history of drug abuse. New treatment regimens may also reduce the risk of tolerance, physical dependence and addiction. Long-acting preparations, such as transdermal fentanyl and possibly some forms of other slow release opioids, which maintain constant opioid concentrations in the plasma, minimise the occurrence of the 'between-dose' symptoms such as withdrawal and opioid-induced euphoria. This review discusses the development of tolerance, physical dependence and addiction during opioid therapy, and the influence of these factors on the choice of treatment.

Functional study of rat 5-HT2A receptors using antisense oligonucleotides

We studied the effects in rats of a 6-day intracerebroventricular (i.c.v) infusion of four different end-capped phosphorothioate-modified antisense oligonucleotides (AOs), specifically targeting different regions of the 5-hydroxytryptamine2A (5-HT2A) receptor mRNA, on central 5-HT2A receptor expression and 5-HT2A receptor-mediated behaviours. Only one of the AOs (sequence 4), directed against the 5'-untranslated region (from + 557 to + 577), specifically affected central 5-HT2A receptor expression and receptor-mediated behaviour. This AO (sequence 4) reduced binding of the 5-HT2A agonist 1-(2,5-dimethoxy-4-[125I]iodophenyl)-2-aminopropane ([125I]DOI) up to 25% in cortical areas, as measured by quantitative autoradiography. Cortical binding of the antagonist [3H]ketanserin was not affected. As the specific AO treatment presumably affects the synthesis of new receptor, we hypothesize that this newly synthesized receptor represents the major part of the functionally active, G protein coupled receptor. A 5-day infusion of AO (sequence 4) resulted in profound inhibition of the head-twitch response (HTR) to 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). In contrast, treatment with vehicle, sense oligonucleotides (SOs) and other AOs (sequences 1, 2 and 3) caused an increased DOM-induced HTR as well as a spontaneous HTR. The latter was abolished by treatment with the 5-HT2 receptor antagonist, ritanserin. Systematic investigation of the surgical and infusion procedures revealed that the enhanced HTR already appeared following drilling of the skull. This wounding can probably damage the blood-brain barrier and cause a stress-induced increase in serotonergic transmission. AO (sequence 4) treatment also abolished the spontaneous HTR. AO (sequence 4) treatment allowed the identification of specific central 5-HT2A receptor-mediated behaviours in the complex serotonergic syndrome induced by tryptamine in rats. Only bilateral convulsions and body tremors were significantly inhibited. The backward locomotion, hunched back and Straub tail were not affected, nor was cyanosis, an index of vasoconstriction induced by peripheral 5-HT2A receptor activation. Labelling of central 5-HT2C receptors by [3H]mesulergine, and 5-HT2C receptor-mediated anxiety were not attenuated by AO or SO treatment. Rats treated with AO (sequence 4) showed increased locomotor activity and a strong reactivity towards touching. We hypothesize that the down-regulation of functional 5-HT2A receptors may shift the balance between various 5-HT receptor subtypes. Our analysis of the behavioural consequences of AO treatment and the use of different AOs and SOs has shown that specific receptor-mediated behaviour can be identified.

Morphine and d-amphetamine nullify each others' hypothermic effects in mice

We have examined the effects of the psychostimulant d-amphetamine and the neuroleptic haloperidol on hypothermia induced by intraperitoneal injection of the centrally penetrating opioids morphine, fentanyl and sufentanil and the peripherally acting opioid loperamide. Measuring rectal body temperatures, dose-response relationships were established for all compounds. Morphine and sufentanil produced hyperthermia at low doses and dose-related hypothermia at higher doses. Fentanyl and loperamide produced dose-related hypothermia. Fixed doses of each opioid producing significant hypothermia were selected for interaction studies. The psychostimulant d-amphetamine was found t o produce biphasic effects with low doses inducing hypothermia and higher doses inducing hyperthemia. Haloperidol produced dose-related hypothermia. The selected doses of the opioids were then injected followed after 15 min. by injection of hypothermia producing doses of d-amphetamine or haloperidol. Hypothermia induced by morphine, fentanyl and sufentanil was reversed by d-amphetamine whereas loperamide-induced hypothermia was unaffected. Rebound hyperthermia was also measured with fentanyl and sufentanil. Haloperidol increased the hypothermic effects of morphine, fentanyl and sufentanil but not of loperamide. In conclusion, the central stimulating effects of opioids and amphetamine may combine resulting in thermogenesis and reversal of hypothermia. Central mechanisms of opioid-induced hypothermia in mice are influenced by drugs which alter the dopamine system, whereas peripheral mechanisms are unaffected. A possible clinical implication for this dopaminergic interaction may be toxicity associated with hyperpyrexia caused by psychostimulant misuse, which is increasingly occurring concomitantly with abuse of opioids.

Role of 5-HT(2) receptors in the tryptamine-induced 5-HT syndrome in rats

We distinguished the functions of the different 5-hydroxytryptamine-2 (5-HT(2)) receptor (5-HT(2)R) subtypes in the tryptamine-induced 5-HT syndrome in rats using (1) the 5-HT(2A)R antagonist R93274 (N-[(3-p-fluorophenyl-1-propyl)-4-methyl-4-piperidinyl]-4-amino-5-iodo-2-methoxybenzamide), the 5-HT(2A/C)R antagonist R99647 (2-(dimethylaminomethyl)2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine), the 5-HT(2B/C)R antagonist SB-242084 (6-chloro-5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-indoline), and several 5-HT(2)R antagonists (ketanserin, risperidone, pipamperone and mianserin); and (2) chronic 5-HT(2)R activation by 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). In contrast to SB-242084, the selective 5-HT(2A)R antagonist R93274 as well as the non-selective 5-HT(2A)R antagonists (R99647, ketanserin, risperidone, pipamperone and mianserin) significantly inhibited tryptamine-induced forepaw treading and tremors, and reversed peripherally mediated cyanosis into hyperaemia; only the 5-HT(2A/C)R antagonists R99647 and mianserin inhibited the tryptamine-induced hunched back. Intermittent DOM administration (intravenously every 48 h for 12 days) did not change the centrally mediated tryptamine-induced forepaw treading, tremors and hunched back at 1, 4 or 7 days after the last DOM pretreatment. The DOM-induced head twitch response, measured immediately after every DOM injection, was not affected. In contrast, peripherally mediated cyanosis was reversed into hyperaemia in 75, 11 and 20% of all pretreated rats at 1, 4 and 7 days, respectively, after the last DOM administration. Taken together, these finding suggest that central 5-HT(2A)Rs mediate tryptamine-induced forepaw treading and tremors, that peripheral 5-HT Rs mediate tryptamine-induced cyanosis, and that 5-HT(2A)Rs mediate tryptamine-induced hunched back. Peripheral 5-HT(2C)Rs are more sensitive to desensitization after intermittent treatment with an agonist than central 5-HT(2A)Rs.

Probing opioid receptor-ligand interactions by employment of indolizidin-9-one amino acid as a constrained Gly(2)-Gly(3) surrogate in a leucine-enkephalin mimic

The relationship between the conformation and biological activity of Leu-enkephalin was studied using (2S,6R,8S)-9-oxo-8-N-(Boc)amino-1-azabicyclo[4.3.0]nonane-2-carboxylic acid [(2S,6R,8S)-1, I(9)AA] as a constrained Gly(2)-Gly(3) dipeptide surrogate. [I(9)AA](2,3)-Leu-enkephalin 12 was assembled using solid-phase peptide synthesis on Merrifield resin with TBTU as the coupling reagent. The in vitro assays indicated that [I(9)AA](2,3)-Leu-enkephalin 12 exhibited affinities for the mu- and delta-opioid receptors that were three orders of magnitude lower than that of Leu-enkephalin, as well as partial agonist character for both receptors. In in vivo assays for spinal analgesia, the indolizidinone analog 12 showed significantly enhanced duration of action, indicating an increased metabolic stability. Conformational analysis was performed using NMR and CD spectroscopy. The amide temperature coefficients and 3J(NH-CalphaH) coupling constants for 12 could not support a hydrogen-bonded beta-turn structure; however, its CD spectrum indicated a turn conformation. Incorporation of indolizidinone amino acid 1 into Leu-enkephalin thus provided additional support for the importance of a turn conformation for the biological activity of the native peptide.

Comparison of the analgesic and intestinal effects of fentanyl and morphine in rats

Clinical studies report a low incidence of intestinal side effects with transdermally administered fentanyl (TTS-fentanyl) in comparison with oral morphine. To support these clinical data, analgesic and intestinal effects of both opioids were compared in rats. After subcutaneous injection, analgesia in the tail withdrawal reaction test was obtained at a peak effect dose of 0.032 mg/kg with fentanyl and 8.0 mg/kg with morphine. This analgesic dose exceeded the ED50 for inhibition of castor oil-induced diarrhea only slightly (1.1 x) in the case of fentanyl (0.028 mg/kg) but markedly (36 x) in the case of morphine (0.22 mg/kg). To reverse completely the antidiarrheal effect of equivalent analgesic doses of the opioids (their ED50S for analgesia lasting 2 hours), much more naloxone was required in the case of morphine (5.4 mg/kg) than in the case of fentanyl (0.19 mg/kg). After oral administration, the difference between both opioids was less pronounced. Analgesia was obtained at 0.85 mg/kg with fentanyl and 32 mg/kg with morphine. This analgesic dose only slightly (1.7 x) exceeded the antidiarrheal dose in the case of fentanyl (0.49 mg/kg) but significantly (6.2 x) in the case of morphine (5.2 mg/ kg). To reverse completely the antidiarrheal effect of equivalent analgesic oral doses of the opioids (their ED50S for analgesia lasting 2 hours), more naloxone was required in the case of morphine (11 mg/kg) than in the case of fentanyl (2.0 mg/kg). Rapid penetration of fentanyl into the brain is thought to be responsible for small dissociation between the analgesic and intestinal effect of this lipophilic opioid. The present data provide preclinical evidence to support the relatively low incidence of intestinal side effects observed clinically with the use of TTS-fentanyl in comparison with orally administered morphine.