Planarians require an intact brain to behaviorally react to cocaine, but not to react to nicotine

Cotinine influences the effect of high and low nicotine concentrations on planarian motility differently

Previous work from our laboratory showed that cotinine, a nicotine metabolite, reverses three nicotine-induced behavioral effects in freshwater planarians: motility decrease, seizure-like movements, and withdrawal-like behaviors. The present work explored whether cotinine, a nicotine metabolite, antagonized the nicotine-induced effects on planarian motility in a concentration-dependent manner. We found that nicotine decreased planarian motility at nicotine concentrations above 60 μM but increased planarian velocity at concentrations equal to or below 50 μM, in agreement with previous data. Cotinine did not affect planarian motility at a concentration range between 250 and 2750 μM. Furthermore, we found that cotinine alleviated the 100 μM nicotine-induced motility decrease in a concentration-dependent manner and reversed the low nicotine concentration motility increase, albeit in a concentration-independent manner. The apparent concentration-dependent alleviation of >60 μM nicotine-induced motility decrease by cotinine suggests an orthosteric relationship between nicotine and cotinine. On the other hand, the evident concentration-independent cotinine alleviation of the increase in motility induced by 50 μM nicotine suggests an allosteric relationship. Our data is consistent with the existing literature about the relationship between nicotine and cotinine in various models, reinforcing the case for the usefulness of the planarian model in pharmacological studies.

Schild Analysis of the Interaction between Parthenolide and Cocaine Suggests an Allosteric Relationship for Their Effects on Planarian Motility

The freshwater planarian is an emerging animal model in neuroscience due to its centralized nervous system that closely parallels closely parallels the nervous system of vertebrates. Cocaine, an abused drug, is the 'founding member' of the local anesthetic family. Parthenolide, a sesquiterpene lactone, acts as a behavioral and physiological antagonist of cocaine in planarians and rats, respectively. Previous work from our laboratory showed that both parthenolide and cocaine reduced planarian motility and that parthenolide reversed the cocaine-induced motility decrease at concentrations where parthenolide does not affect the movement of the worms. However, the exact mechanism of the cocaine/parthenolide antagonism is unknown. Here, we report the results of a Schild analysis to explore the parthenolide/cocaine relationship in the planarian Girardia tigrina. The Schild slopes of a family of concentration-response curves of parthenolide ± a single concentration of cocaine and vice versa were -0.55 and -0.36, respectively. These slopes were not statistically different from each other. Interestingly, the slope corresponding to the parthenolide ± cocaine (but not the cocaine ± parthenolide) data set was statistically different from -1. Our data suggest an allosteric relationship between cocaine and parthenolide for their effect on planarian motility. To the best of our knowledge, this is the first study about the mechanism of action of the antagonism between cocaine and parthenolide. Further studies are needed to determine the specific nature of the parthenolide/cocaine target(s) in this organism.

Neurophysiological measurements of planarian brain activity: a unique model for neuroscience research

Planarians are well-known model organisms for regeneration and developmental biology research due to their remarkable regenerative capacity. Here, we aim to advocate for the use of planaria as a valuable model for neurobiology, as well. Planarians have most of the major qualities of more developed organisms, including a primal brain. These traits combined with their exceptional regeneration capabilities, allow neurobiological experiments not possible in any other model organism, as we demonstrate by electrophysiological recording from planaria with two heads that control a shared body. To facilitate planarian neuroscience research, we developed an extracellular multi-unit recording procedure for the planarians fragile brain (Dugesia japonica). We created a semi-intact preparation restrained with fine dissection pins, enabling hours of reliable recording, via a suction electrode. Here, we demonstrate the feasibility and potential of planarian neurophysiological research by characterizing the neuronal activity during simple learning processes and responses to various stimuli. In addition, we examined the use of linalool as anesthetic agent to allows recordings from an intact, large worm and for fine electrophysiological approaches such as intracellular recording. The demonstrated ability for neurophysiological measurements, along with the inherent advantages of planarians, promotes this exceptional model organism for neuroscience research.

The complexities of ligand/receptor interactions: Exploring the role of molecular vibrations and quantum tunnelling

Molecular vibrations and quantum tunneling may link ligand binding to the function of pharmacological receptors. The well-established lock-and-key model explains a ligand's binding and recognition by a receptor; however, a general mechanism by which receptors translate binding into activation, inactivation, or modulation remains elusive. The Vibration Theory of Olfaction was proposed in the 1930s to explain this subset of receptor-mediated phenomena by correlating odorant molecular vibrations to smell, but a mechanism was lacking. In the 1990s, inelastic electron tunneling was proposed as a plausible mechanism for translating molecular vibration to odorant physiology. More recently, studies of ligands' vibrational spectra and the use of deuterated ligand analogs have provided helpful information to study this admittedly controversial hypothesis in metabotropic receptors other than olfactory receptors. In the present work, based in part on published experiments from our laboratory using planarians as an experimental organism, I will present a rationale and possible experimental approach for extending this idea to ligand-gated ion channels.

Kratom pharmacology: Clues from planarians exposed to mitragynine

Mitragynine (MG), the most prevalent bioactive alkaloid in kratom, displays nanomolar affinity for µ, κ and δ opioid receptors and produces opioid-dependent antinociception and dependence in rats. Here, using a battery of behavioral assays, we investigated MG effects in planarians. Acute MG exposure (< 100 μM) did not affect planarian motility or environmental preference, but reduced motility was detected during abstinence from chronic MG (1, 10 μM). MG (10 μM) produced place conditioning effects that were reduced by naltrexone (10  μΜ). These results suggest that MG produces opioid-sensitive reinforcing effects in planarians and MG pharmacology is conserved across different species.

Ecotoxicity Assays Using Freshwater Planarians

Freshwater planarians are free-living flatworms known for their regenerative ability. Being easily cultured under laboratory conditions, they are recognized test model organisms in regeneration, developmental biology, and neuropharmacological research. Also, they have been recently employed in toxicity testing where they displayed an array of sensitive and reliable responses to environmental stressors. Here, we outline simple and easy-to-follow protocols to evaluate effects of environmental contaminants and other stressors on survival, behavior (feeding and locomotor activity), and regeneration of freshwater planarians. These endpoints are comparable with responses of well-established ecotoxicological model species.

Biochemical and behavioral effects induced by cocaine exposure to Daphnia magna

Illicit drugs and their metabolites have been identified as emerging aquatic pollutants. Cocaine (COC) is one of the most used illicit drug worldwide. After human consumption, COC enters the aquatic ecosystems, where it is commonly detected in ng L^-1 concentration range. Although a number of studies have shown that the exposure to environmental concentrations of COC can induce diverse biochemical, molecular and histological effects on aquatic organisms, the information of COC-induced behavioral alterations is scant. Thus, the present study aimed at exploring both biochemical and behavioral effects induced by the exposure to two environmental concentrations (50 ng L^-1 and 500 ng L^-1) of COC on the freshwater cladoceran Daphnia magna. Specimens were exposed to selected COC concentrations for 21 days and the effects on the oxidative status, including the amount of reactive oxygen species and the activity of antioxidant (SOD, CAT and GPx) and detoxifying (GST) enzymes, and swimming activity were investigated after 7, 14 and 21 days of treatment, while effects on reproductive success was assessed after 21-days only.. Exposure to COC induced an overproduction of reactive oxygen species and a modulation of the activity of defense enzymes. Moreover, COC affected the swimming behavior and altered the reproductive success of treated specimens. Our results highlighted that environmental concentrations of COC can cause adverse effects at different levels of the biological hierarchy in a zooplanktonic species, confirming the potential threat due to this illicit drug for the aquatic community.

Occurrence, control and fate of contaminants of emerging concern in environmental compartments in Brazil

This is the first review to present data obtained in Brazil over the years regarding contaminants of emerging concern (CEC) and to contrast it with contamination in other countries. Data gathered indicated that caffeine, paracetamol, atenolol, ibuprofen, cephalexin and bisphenol A occur in the μg L^-1 range in streams near urban areas. While endocrine disruptors are frequently detected in surface waters, highest concentrations account for 17α-ethynylestradiol and 17β-estradiol. Organochlorine pesticides are the most frequently found and persistent in sediments in agricultural regions. Moreover, in tropical agricultural fields, pesticide volatilization and its implications to ecosystem protection must be better investigated. The reality represented here for Brazil may be transposed to other developing countries due to similarities related to primitive basic sanitation infrastructure and economic and social contexts, which contribute to continuous environmental contamination by CEC. Municipal wastewater treatment facilities in Brazil, treat up to the secondary stage and lead to limited CEC removal. This is also true for other nations in Latin America, such as Argentina, Colombia and Mexico. Therefore, it is an urgent priority to improve sanitation infrastructure and, then, the implementation of tertiary treatment shall be imposed.

Predator odor produces anxiety-like behavioral phenotype in planarians that is counteracted by fluoxetine

Avoidant behavior is a characteristic feature post-traumatic stress disorder (PTSD) and is modeled in mammals with predator odor. Light avoidance is a hallmark behavioral reaction in planarians. We hypothesized that planarians exposed to frog extract would display enhanced light avoidance that is prevented by fluoxetine. Enhanced light avoidance (i.e., less time spent in light compartment of a dish split into light and dark sides) after a 30-min frog extract exposure (0.0001-0.01%) manifested 15 min post-exposure, persisted for at least 24 h, and was counteracted by fluoxetine (10 μM). These results suggest conservation of an anxiety-like behavioral phenotype.

Behavioral Research with Planaria

This article serves as a brief primer on planaria for behavior scientists. In the 1950s and 1960s, McConnell's planarian laboratory posited that conditioned behavior could transfer after regeneration, and through cannibalization of trained planaria. These studies, the responses, and replications have been collectively referred to as the "planarian controversy." Successful behavioral assays still require refinement with this organism, but they could add valuable insight into our conceptualization of memory and learning. We discuss how the planarian's distinctive biology enables an examination of biobehavioral interaction models, and what behavior scientists must consider if they are to advance behavioral research with this organism. Suggestions for academics interested in building planaria learning laboratories are offered.

Exposure to cocaine and its main metabolites altered the protein profile of zebrafish embryos

Illicit drugs have been identified as emerging aquatic pollutants because of their widespread presence in freshwaters and potential toxicity towards aquatic organisms. Among illicit drug residues, cocaine (COC) and its main metabolites, namely benzoylecgonine (BE) and ecgonine methyl ester (EME), are commonly detected in freshwaters worldwide at concentration that can induce diverse adverse effects to non-target organisms. However, the information of toxicity and mechanisms of action (MoA) of these drugs, mainly of COC metabolites, to aquatic species is still fragmentary and inadequate. Thus, this study was aimed at investigating the toxicity of two concentrations (0.3 and 1.0 μg/L) of COC, BE and EME similar to those found in aquatic ecosystems on zebrafish (Danio rerio) embryos at 96 h post fertilization through a functional proteomics approach. Exposure to COC and both its metabolites significantly altered the protein profile of zebrafish embryos, modulating the expression of diverse proteins belonging to different functional classes, including cytoskeleton, eye constituents, lipid transport, lipid and energy metabolism, and stress response. Expression of vitellogenins and crystallins was modulated by COC and both its main metabolites, while only BE and EME altered proteins related to lipid and energy metabolism, as well as to oxidative stress response. Our data confirmed the potential toxicity of low concentrations of COC, BE and EME, and helped to shed light on their MoA on an aquatic vertebrate during early developmental period.

Environmental concentrations of cocaine and its main metabolites modulated antioxidant response and caused cyto-genotoxic effects in zebrafish embryo cells

Illicit drugs have been recently identified as a serious environmental problem because of the growing evidence regarding their occurrence in aquatic environment and potential toxicity towards non-target organisms. Among them, cocaine (COC) and its main metabolites, namely benzoylecgonine (BE) and ecgonine methyl ester (EME), are commonly measured in freshwaters worldwide at levels that might cause diverse sub-lethal effects to aquatic organisms. Thus, the present study was aimed at investigating the potential adverse effects induced by the exposure to environmental concentrations (0.04, 0.4, 4 and 40 nM) of COC, BE, and EME on zebrafish (Danio rerio) embryos at 96 h post fertilization. Cytotoxicity was assessed by the Trypan Blue exclusion method, while primary and fixed genetic damages were evaluated by the Single Cell Gel Electrophoresis (SCGE) assay, and the DNA diffusion assay together with the Micronucleus test, respectively. The involvement of oxidative stress in the mechanism of action (MoA) of all tested drugs was assessed by measuring the activity of defense enzymes (SOD, CAT, GPx, and GST) and the expression of their encoding genes. Exposure to COC and both metabolites significantly reduced cell viability, increased DNA fragmentation and promoted the onset of apoptotic cells and micronuclei in zebrafish embryos. Results from oxidative stress-related endpoints and gene expression suggested that the observed genotoxicity may be caused by an overproduction of free radicals that imbalanced the oxidative status of embryos. The integration of biomarker responses into a synthetic index showed that at each tested concentration, BE and EME had a similar toxicity and were both more toxic than COC. Our data confirmed the potential toxicity of environmental concentrations of COC, BE, and EME, suggesting the need of further in-depth studies to shed light on their MoA and long-term toxicity towards non-target aquatic species.

Cotinine antagonizes the behavioral effects of nicotine exposure in the planarian Girardia tigrina

Nicotine is one of the most addictive drugs abused by humans. Our laboratory and others have demonstrated that nicotine decreases motility and induces seizure-like behavior in planarians (pSLM, which are vigorous writhing and bending of the body) in a concentration-dependent manner. Nicotine also induces withdrawal-like behaviors in these worms. Cotinine is the major nicotine metabolite in humans, although it is not the final product of nicotine metabolism. Cotinine is mostly inactive in vertebrate nervous systems and is currently being explored as a molecule which possess most of nicotine's beneficial effects and few of its undesirable ones. It is not known whether cotinine is a product of nicotine metabolism in planarians. We found that cotinine by itself does not seem to elicit any behavioral effects in planarians up to a concentration of 1mM. We also show that cotinine antagonizes the aforementioned nicotine-induced motility decrease and also decreases the expression of nicotine-induced pSLMs in a concentration-dependent manner. Also cotinine prevents the manifestation of some of the withdrawal-like behaviors induced by nicotine in our experimental organism. Thus, we obtained evidence supporting that cotinine antagonizes nicotine in this planarian species. Possible explanations include competitive binding of both compounds at overlapping binding sites, at different nicotinic receptor subtypes, or maybe allosteric interactions.

Effect of Donepezil, Tacrine, Galantamine and Rivastigmine on Acetylcholinesterase Inhibition in Dugesia tigrina

Dugesia tigrina is a non-parasitic platyhelminth, which has been recently utilized in pharmacological models, regarding the nervous system, as it presents a wide sensitivity to drugs. Our trials aimed to propose a model for an in vivo screening of substances with inhibitory activity of the enzyme acetylcholinesterase. Trials were performed with four drugs commercialized in Brazil: donepezil, tacrine, galantamine and rivastigmine, utilized in the control of Alzheimer's disease, to inhibit the activity of acetylcholinesterase. We tested five concentrations of the drugs, with an exposure of 24 h, and the mortality and the inhibition of acetylcholinesterase planarian seizure-like activity (pSLA) and planarian locomotor velocity (pLMV) were measured. Galantamine showed high anticholinesterasic activity when compared to the other drugs, with a reduction of 0.05 μmol·min(-1) and 63% of convulsant activity, presenting screw-like movement and hypokinesia, with pLMV of 65 crossed lines during 5 min. Our results showed for the first time the anticholinesterasic and convulsant effect, in addition to the decrease in locomotion induced by those drugs in a model of invertebrates. The experimental model proposed is simple and low cost and could be utilized in the screening of substances with anticholinesterasic action.

Guarana provides additional stimulation over caffeine alone in the planarian model

The stimulant effect of energy drinks is primarily attributed to the caffeine they contain. Many energy drinks also contain other ingredients that might enhance the tonic effects of these caffeinated beverages. One of these additives is guarana. Guarana is a climbing plant native to the Amazon whose seeds contain approximately four times the amount of caffeine found in coffee beans. The mix of other natural chemicals contained in guarana seeds is thought to heighten the stimulant effects of guarana over caffeine alone. Yet, despite the growing use of guarana as an additive in energy drinks, and a burgeoning market for it as a nutritional supplement, the science examining guarana and how it affects other dietary ingredients is lacking. To appreciate the stimulant effects of guarana and other natural products, a straightforward model to investigate their physiological properties is needed. The planarian provides such a system. The locomotor activity and convulsive response of planarians with substance exposure has been shown to provide an excellent system to measure the effects of drug stimulation, addiction and withdrawal. To gauge the stimulant effects of guarana we studied how it altered the locomotor activity of the planarian species Dugesia tigrina. We report evidence that guarana seeds provide additional stimulation over caffeine alone, and document the changes to this stimulation in the context of both caffeine and glucose.

Levamisole enhances the rewarding and locomotor-activating effects of cocaine in rats

BACKGROUND

The Drug Enforcement Agency estimates that 80% of cocaine seized in the United States contains the veterinary pharmaceutical levamisole (LVM). One problem with LVM is that it is producing life-threatening neutropenia in an alarming number of cocaine abusers. The neuropharmacological profile of LVM is also suggestive of an agent with modest reinforcing and stimulant effects that could enhance cocaine's addictive effects.

METHODS

We tested the hypothesis that LVM (ip) enhances the rewarding and locomotor stimulant effects of cocaine (ip) using rat conditioned place preference (CPP) and locomotor assays. Effects of LVM by itself were also tested.

RESULTS

LVM (0-10 mg/kg) produced CPP at 1mg/kg (P<0.05) and locomotor activation at 5mg/kg (P < 0.05). For CPP combination experiments, a statistically inactive dose of LVM (0.1 mg/kg) was administered with a low dose of cocaine (2.5 mg/kg). Neither agent produced CPP compared to saline (P > 0.05); however, the combination of LVM and cocaine produced enhanced CPP compared to saline or either drug by itself (P < 0.01). For locomotor experiments, the same inactive dose of LVM (0.1mg/kg, ip) was administered with low (10 mg/kg) and high doses (30 mg/kg) of cocaine. LVM (0.1 mg/kg) enhanced locomotor activation produced by 10mg/kg of cocaine (P < 0.05) but not by 30 mg/kg (P>0.05).

CONCLUSIONS

LVM can enhance rewarding and locomotor-activating effects of low doses of cocaine in rats while possessing modest activity of its own.

A review of ecological effects and environmental fate of illicit drugs in aquatic ecosystems

Although illicit drugs are detected in surface waters throughout the world, their environmental fate and ecological effects are not well understood. Many illicit drugs and their breakdown products have been detected in surface waters and temporal and spatial variability in use translates into "hot spots and hot moments" of occurrence. Illicit drug occurrence in regions of production and use and areas with insufficient wastewater treatment are not well studied and should be targeted for further study. Evidence suggests that illicit drugs may not be persistent, as their half-lives are relatively short, but may exhibit "pseudo-persistence" wherein continual use results in persistent occurrence. We reviewed the literature on the ecological effects of these compounds on aquatic organisms and although research is limited, a wide array of aquatic organisms, including bacteria, algae, invertebrates, and fishes, have receptors that make them potentially sensitive to these compounds. In summary, illicit drugs occur in surface waters and aquatic organisms may be affected by these compounds; research is needed that focuses on concentrations of illicit drugs in areas of production and high use, environmental fate of these compounds, and effects of these compounds on aquatic ecosystems at the concentrations that typically occur in the environment.

Functional analysis of Girardia tigrina transcriptome seeds pipeline for anthelmintic target discovery

BACKGROUND

Neglected diseases caused by helminth infections impose a massive hindrance to progress in the developing world. While basic research on parasitic flatworms (platyhelminths) continues to expand, researchers have yet to broadly adopt a free-living model to complement the study of these important parasites.

METHODS

We report the high-coverage sequencing (RNA-Seq) and assembly of the transcriptome of the planarian Girardia tigrina across a set of dynamic conditions. The assembly was annotated and extensive orthology analysis was used to seed a pipeline for the rational prioritization and validation of putative anthelmintic targets. A small number of targets conserved between parasitic and free-living flatworms were comparatively interrogated.

RESULTS

240 million paired-end reads were assembled de novo to produce a strictly filtered predicted proteome consisting of over 22,000 proteins. Gene Ontology annotations were extended to 16,467 proteins. 2,693 sequences were identified in orthology groups spanning flukes, tapeworms and planaria, with 441 highlighted as belonging to druggable protein families. Chemical inhibitors were used on three targets in pharmacological screens using both planaria and schistosomula, revealing distinct motility phenotypes that were shown to correlate with planarian RNAi phenotypes.

CONCLUSIONS

This work provides the first comprehensive and annotated sequence resource for the model planarian G. tigrina, alongside a prioritized list of candidate drug targets conserved among parasitic and free-living flatworms. As proof of principle, we show that a simple RNAi and pharmacology pipeline in the more convenient planarian model system can inform parasite biology and serve as an efficient screening tool for the identification of lucrative anthelmintic targets.

Stereochemistry and neuropharmacology of a 'bath salt' cathinone: S-enantiomer of mephedrone reduces cocaine-induced reward and withdrawal in invertebrates

Knowledge about the neuropharmacology of mephedrone (MEPH) applies primarily to the racemate, or street form of the drug, but not to its individual enantiomers. Here, through chemical isolation of MEPH enantiomers and subsequent behavioral characterization in established invertebrate (planarian) assays, we began separating adverse effects of MEPH from potential therapeutic actions. We first compared stereotypical and environmental place conditioning (EPC) effects of racemic MEPH, S-MEPH, and R-MEPH. Stereotypy was enhanced by acute treatment (100-1000 μM) with each compound; however, S-MEPH was less potent and efficacious than racemate and R-MEPH. Both R-MEPH (10, 100, 250 μM) and racemate (100 μM) produced EPC, but S-MEPH was ineffective at all concentrations (10-100 μM). After showing that S-MEPH lacked rewarding efficacy, we investigated its ability to alter three of cocaine's behavioral effects (EPC, withdrawal, and stereotypy). Cocaine (1 μM) produced EPC that was abolished when S-MEPH (100 μM) was administered after cocaine conditioning. Spontaneous withdrawal from chronic cocaine exposure caused a reduction in motility that was not evident during acute or continuous cocaine treatment but was attenuated by S-MEPH (100 μM) treatment during the cocaine abstinence interval. Acute stereotypy produced by 1 mM cocaine, nicotine or racemic MEPH was not affected by S-MEPH (10-250 μM). The present results obtained using planarian assays suggest that the R-enantiomer of MEPH is predominantly responsible for its stimulant and rewarding effects and the S-enantiomer is capable of antagonizing cocaine's addictive-like behaviors without producing rewarding effects of its own.

Ethanol and cocaine: environmental place conditioning, stereotypy, and synergism in planarians

More than 90% of individuals who use cocaine also report concurrent ethanol use, but only a few studies, all conducted with vertebrates, have investigated pharmacodynamic interactions between ethanol and cocaine. Planaria, a type of flatworm often considered to have the simplest 'brain,' is an invertebrate species especially amenable to the quantification of drug-induced behavioral responses and identification of conserved responses. Here, we investigated stereotypical and environmental place conditioning (EPC) effects of ethanol administered alone and in combination with cocaine. Planarians displayed concentration-related increases in C-shaped movements following exposure to ethanol (0.01-1%) (maximal effect: 9.9±1.1 C-shapes/5 min at 0.5%) or cocaine (0.1-5 mM) (maximal effect: 42.8±4.1 C-shapes/5 min at 5 mM). For combined administration, cocaine (0.1-5 mM) was tested with submaximal ethanol concentrations (0.01, 0.1%); the observed effect for the combination was enhanced compared to its predicted effect, indicating synergism for the interaction. The synergy with ethanol was specific for cocaine, as related experiments revealed that combinations of ethanol and nicotine did not result in synergy. For EPC experiments, ethanol (0.0001-1%) concentration-dependently increased EPC, with significant environmental shifts detected at 0.01 and 1%. Cocaine (0.001-1 μM) produced an inverted U-shaped concentration-effect curve, with a significant environmental shift observed at 0.01 μM. For combined exposure, variable cocaine concentrations (0.001-1 μM) were administered with a statistically ineffective concentration of ethanol (0.0001%). For each concentration of cocaine, the environmental shift was enhanced by ethanol, with significance detected at 1 μM. Cocaethylene, a metabolite of cocaine and ethanol, also produced C-shapes and EPC. Lidocaine (0.001-10 μM), an anesthetic and analog of cocaine, did not produce EPC or C-shaped movements. Evidence from planarians that ethanol produces place-conditioning effects and motor dysfunction, and interacts synergistically with cocaine, suggests that aspects of ethanol neuropharmacology are conserved across species.

Flatworm models in pharmacological research: the importance of compound stability testing

Flatworms possess adult pluripotent stem cells, which make them extraordinary experimental model organisms to assess in vivo the undesirable effects of substances on stem cells. Currently, quality practices, implying evaluation of the stability of the test compound under the proposed experimental conditions, are uncommon in this research field. Nevertheless, performing a stability study during the rational design of in vivo assay protocols will result in more reliable assay results. To illustrate the influence of the stability of the test substance on the final experimental outcome, we performed a short-term International Conference on Harmonization (ICH)-based stability study of cyclophosphamide in the culture medium, to which a marine flatworm model Macrostomum lignano is exposed. Using a validated U(H)PLC method, it was demonstrated that the cyclophosphamide concentration in the culture medium at 20°C is lowered to 80% of the initial concentration after 21days. The multiwell plates, flatworms and diatoms, as well as light exposure, did not influence significantly the cyclophosphamide concentration in the medium. The results of the stability study have practical implications on the experimental set-up of the carcinogenicity assay like the frequency of medium renewal. This case study demonstrates the benefits of applying appropriate quality guidelines already during fundamental research increasing the credibility of the results.

Levamisole and cocaine synergism: a prevalent adulterant enhances cocaine's action in vivo

Levamisole is estimated by the Drug Enforcement Agency (DEA) to be present in about 80% of cocaine seized in the United States and linked to debilitating, and sometimes fatal, immunologic effects in cocaine abusers. One explanation for the addition of levamisole to cocaine is that it increases the amount of product and enhances profits. An alternative possibility, and one investigated here, is that levamisole alters cocaine's action in vivo. We specifically investigated effects of levamisole on cocaine's stereotypical and place-conditioning effects in an established invertebrate (planarian) assay. Acute exposure to levamisole or cocaine produced concentration-dependent increases in stereotyped movements. For combined administration of the two agents, isobolographic analysis revealed that the observed stereotypical response was enhanced relative to the predicted effect, indicating synergism for the interaction. In conditioned place preference (CPP) experiments, cocaine produced a significant preference shift; in contrast, levamisole was ineffective at all concentrations tested. For combination experiments, a submaximal concentration of cocaine produced CPP that was enhanced by inactive concentrations of levamisole, indicating synergism. The present results provide the first experimental evidence that levamisole enhances cocaine's action in vivo. Most important is the identification of synergism for the levamisole/cocaine interaction, which now requires further study in mammals.

Opioid receptor types involved in the development of nicotine physical dependence in an invertebrate (Planaria) model

Recent data suggest that opioid receptors are involved in the development of nicotine physical dependence in mammals. Evidence in support of a similar involvement in an invertebrate (Planaria) is presented using the selective opioid receptor antagonist naloxone, and the more receptor subtype-selective antagonists CTAP (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2) (μ, MOR), naltrindole (δ, DOR), and nor-BNI (norbinaltorphimine) (κ, KOR). Induction of physical dependence was achieved by 60-min pre-exposure of planarians to nicotine and was quantified by abstinence-induced withdrawal (reduction in spontaneous locomotor activity). Known MOR and DOR subtype-selective opioid receptor antagonists attenuated the withdrawal, as did the non-selective antagonist naloxone, but a KOR subtype-selective antagonist did not. An involvement of MOR and DOR, but not KOR, in the development of nicotine physical dependence or in abstinence-induced withdrawal was thus demonstrated in a sensitive and facile invertebrate model.