A reverse-phase HPLC and fluorescence detection method for measurement of 5-hydroxytryptamine (serotonin) in Planaria

The role of alternative toxicological trials in drug discovery programs: The case of Caenorhabditis elegans and other methods

The discovery of a new drug requires over a billion dollars and around 12 years of research efforts, and toxicity is the leading reason for failure to approve candidate drugs. Many alternative methods have been validated to detect toxicity as early as possible to diminish the waste of resources and efforts in medicinal chemistry research, and in vivo alternative methods are especially valuable for the amount of information they can give at little cost and in a short time. In this work, we present a review of the literature published between the years 2000 and 2021 of in vivo alternative methods of toxicity screening employed in medicinal chemistry, which we believe will be useful because, in addition to shortening research times, these studies provide much additional information aside from the toxicity of drug candidate compounds. These in vivo models include zebrafish, Artemia salina, Galleria mellonella, Drosophila melanogaster, planarians, and Caenorhabditis elegans as highlights. The most published ones in the last decade were zebrafish, D. melanogaster and C. elegans due to their reliability, ease and cost-effectiveness of implementation and flexibility. Special attention is given to C. elegans because of its rising popularity, a wide range of uses including toxicity screening, and active effects measurement, from antioxidant effects to anthelmintic and antimicrobial activities, and its fast and reliable results. Over time, C. elegans also became a viable high-throughput (HTS) automated drug screening option. Additionally, this manuscript lists briefly the other screening methods used for the initial toxicological analyses and the role of alternative in vivo methods in these scenarios, classifying them as in silico, in vitro and alternative in vivo models, the latter of which have been receiving a growing increase in interest in recent years.

l-Cysteine-Terminated Triangular Silver Nanoplates/MXene Nanosheets are Used as Electrochemical Biosensors for Efficiently Detecting 5-Hydroxytryptamine

5-Hydroxytryptamine (5-HT) is an important neurotransmitter, and its content in the human body is of great significance to human health. In this study, an l-cysteine-terminated triangular silver nanoplate loaded on a MXene (two-dimensional transition metal carbide or nitride) (Tri-AgNP/l-Cys/MXene) electrochemical sensor was used to detect 5-HT. As an electrically active amino acid with a sulfhydryl group, l-cysteine (l-Cys) forms a more stable Ag-S bond with silver nanoparticles, which can selectively substitute trisodium citrate (TSC) in TSC-capped triangular silver nanoplates (Tri-Ag-NP/TSC). Due to the good conductivity, biocompatibility, and large surface area, MXenes provide a good platform for loading Tri-AgNP/l-Cys. Under optimized conditions, the concentration range for detecting 5-HT with the sensor is 0.5-150 μM, and the limit of detection (LOD) is 0.08 μM (S/N = 3). For detecting 5-HT in actual serum samples, the sensor also showed a good recovery rate (95.38-102.3%), and the relative standard deviation was 2.2-3.4%.

Electrochemical Sensing of Serotonin by a Modified MnO2-Graphene Electrode

The development of MnO₂-graphene (MnO_2-GR) composite by microwave irradiation method and its application as an electrode material for the selective determination of serotonin (SE), popularly known as "happy chemical", is reported. Anchoring MnO₂ nanoparticles on graphene, yielded MnO₂-GR composite with a large surface area, improved electron transport, high conductivity and numerous channels for rapid diffusion of electrolyte ions. The composite was characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and scanning electron microscopy (SEM) for assessing the actual composition, structure and morphology. The MnO₂-GR composite modified glassy carbon electrode (GCE) exhibited an excellent electrochemical activity towards the detection of SE in phosphate buffer saline (PBS) at physiological pH of 7.0. Under optimum conditions, the modified electrode could be applied to the quantification of serotonin by square wave voltammetry over a wide linear range of 0.1 to 800 µM with the lowest detection limit of 10 nM (S/N = 3). The newly fabricated sensor also exhibited attractive features such as good anti-interference ability, high reproducibility and long-term stability.

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.

Nanomaterial based electrochemical sensing of the biomarker serotonin: a comprehensive review

This review (with 131 references) summarizes the progress made in the past years in the field of nanomaterial based sensing of serotonin (5-HT). An introduction summarizes the significant role of 5-HT as a biomarker for several major diseases, methods for its determination and the various kinds of nanomaterials for use in electrochemical sensing process relies principally on a precise choice of electrodes. The next main section covers nanomaterial based methods for sensing 5-HT, with subsections on electrodes modified with carbon nanotubes, graphene related materials, gold nanomaterials, and by other nanomaterials. A concluding section discusses future perspectives and current challenges of 5-HT determination. Graphical abstract Conceptual design of electrochemical sensing process of the biomarker serotonin by using nanomaterials and the role of 5-HTas biomarker in the body from preclinical to clincal.

Mu Opioid Receptor Agonist DAMGO Produces Place Conditioning, Abstinence-induced Withdrawal, and Naltrexone-Dependent Locomotor Activation in Planarians

Unlike the behavioral effects planarians display when exposed to cocaine, amphetamines, cathinones, ethanol and sucrose, effects of opioid receptor agonists, especially mu opioid receptor agonists, are poorly defined in these flatworms. Here, we tested the hypothesis that planarians exposed to a selective mu opioid receptor agonist, DAMGO (0.1, 1, 10 µM), would display a triad of opioid-like effects (place conditioning, abstinence-induced withdrawal, and motility changes). DAMGO was selected versus morphine because of its greater mu opioid receptor selectivity. In place conditioning and abstinence experiments, the planarian light/dark test (PLDT) was utilized (i.e., planarians are placed into a petri dish containing water that is split into light and dark compartments and time spent in the compartments is determined). Planarians conditioned with DAMGO (1 µM) spent more time on the drug-paired side compared to water controls. In abstinence experiments, planarians exposed to DAMGO for 30 min were removed and then placed into water, where light avoidance (e.g. defensive responding) and depressant-like effects (i.e., decreased motility) were quantified. Compared to water controls, DAMGO-withdrawn planarians spent less time in the light (10 µM) and displayed decreased motility (1, 10 µM). Acute DAMGO exposure (1 µM) produced hypermotility that was antagonized by naltrexone (1, 10, 100 µM). In contrast, acute exposure to the kappa opioid receptor agonist U50,488H (0.1, 1, 10 µM) resulted in decreased motility. Our results show that a mu opioid agonist produces mammalian-like behavioral responses in planarians that may be related to addiction and suggest opioid-like behavioral effects are conserved in invertebrates.

An HPLC-ECD method for monoamines and metabolites quantification in cuttlefish (cephalopod) brain tissue

The cuttlefish belongs to the mollusk class Cephalopoda, considered as the most advanced marine invertebrates and thus widely used as models to study the biology of complex behaviors and cognition, as well as their related neurochemical mechanisms. Surprisingly, methods to quantify the biogenic monoamines and their metabolites in cuttlefish brain remain sparse and measure a limited number of analytes. This work aims to validate an HPLC-ECD method for the simultaneous quantification of dopamine, serotonin, norepinephrine and their main metabolites in cuttlefish brain. In comparison and in order to develop a method suitable to answer both ecological and biomedical questions, the validation was also carried out on a phylogenetically remote species: mouse (mammals). The method was shown to be accurate, precise, selective, repeatable and sensitive over a wide range of concentrations for 5-hydroxyindole-3-acetic acid, serotonin, dopamine, 3,4-dihydroxyphenylacetic acid and norepinephrine in the both extracts of cuttlefish and mouse brain, though with low precision and recovery for 4-hydroxy-3-methoxyphenylethylene glycol. Homovanillic acid, accurately studied in rodents, was not detectable in the brain of cuttlefish. Overall, we described here the first fully validated HPLC method for the routine measurement of both monoamines and metabolites in cuttlefish brain. Copyright © 2016 John Wiley & Sons, Ltd.

Highly sensitive isotope-dilution liquid-chromatography-electrospray ionization-tandem-mass spectrometry approach to study the drug-mediated modulation of dopamine and serotonin levels in Caenorhabditis elegans

Dopamine (DA) and serotonin (SRT) are monoamine neurotransmitters that play a key role in regulating the central and peripheral nervous system. Their impaired metabolism has been implicated in several neurological disorders, such as Parkinson's disease and depression. Consequently, it is imperative to monitor changes in levels of these low-abundant neurotransmitters and their role in mediating disease. For the first time, a rapid, specific and sensitive isotope-dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of DA and SRT in the nematode Caenorhabditis elegans (C. elegans). This model organism offers a unique approach for studying the effect of various drugs and environmental conditions on neurotransmitter levels, given by the conserved DA and SRT biology, including synaptic release, trafficking and formation. We introduce a novel sample preparation protocol incorporating the usage of sodium thiosulfate in perchloric acid as extraction medium that assures high recovery of the relatively unstable neurotransmitters monitored. Moreover, the use of both deuterated internal standards and the multiple reaction monitoring (MRM) technique allows for unequivocal quantification. Thereby, to the best of our knowledge, we achieve a detection sensitivity that clearly exceeds those of published DA and SRT quantification methods in various matrices. We are the first to show that exposure of C. elegans to the monoamine oxidase B (MAO-B) inhibitor selegiline or the catechol-O-methyltransferase (COMT) inhibitor tolcapone, in order to block DA and SRT degradation, resulted in accumulation of the respective neurotransmitter. Assessment of a behavioral output of the dopaminergic system (basal slowing response) corroborated the analytical LC-MS/MS data. Thus, utilization of the C. elegans model system in conjunction with our analytical method is well-suited to investigate drug-mediated modulation of the DA and SRT system in order to identify compounds with neuroprotective or regenerative properties.

Chemical sensing of neurotransmitters

This review focuses on the chemosensors for neurotransmitters published for the last 12 years, covering biogenic amines (dopamine, epinephrine, norepinephrine, serotonin, histamine and acetylcholine), amino acids (glutamate, aspartate, GABA, glycine and tyrosine), and adenosine.

Cue competition effects in the planarian

The learning abilities of planarian worms (Dugesia tigrina) were assessed by using a number of Pavlovian conditioning paradigms. Experiment 1 showed that planaria were susceptible to basic conditioning in that they readily developed a conditioned response to a change in ambient luminance when it was consistently paired with an electric shock over a number of trials. In Experiment 2, the change in luminance was presented in a compound with a vibration stimulus during conditioning. Subsequent tests revealed poor conditioning of the elements compared with control groups in which the animals were conditioned in the presence of the elements alone, an instance of overshadowing. In Experiment 3, pre-training of one of the elements before compound conditioning resulted in blocking of learning about the other element. These results add to other studies that have reported cue competition effects in animal species belonging to different phyla (chordate, mollusk, arthropod), suggesting that learning in these phyla could be ruled by similar principles. The results are discussed adopting an evolutionary-comparative approach.

Nicotine behavioral pharmacology: clues from planarians

BACKGROUND

Nicotine is one of the world's most addictive substances and the primary reason that humans inhale tobacco smoke. The pharmacological effects of nicotine can be investigated in planarians, aquatic flatworms that possess an integrated neural network including cephalic ganglia that some consider the earliest 'brain' and spinal cord. Here, we tested the hypothesis that nicotine exposure elicits mammalian-like behaviors in planarians.

METHODS

Planarian motility and stereotypy (C-shape hyperkinesias) were quantified following acute nicotine exposure. During repeated nicotine exposure, we investigated the presence of withdrawal, tolerance, behavioral sensitization, and environmental place conditioning.

RESULTS

Acute nicotine exposure increased stereotypical activity and elicited biphasic effects on motility. A low concentration (0.01 mM) increased motility whereas higher concentrations (0.3-10mM) elicited the opposite effect. Planarians exposed to nicotine (0.03 mM) for 60 min and then tested in water displayed reduced motility that was not observed during exposure to water, acute nicotine, or continuous nicotine. Nicotine-treated planarians withdrawn from the drug for 3 days before being challenged with nicotine displayed behavioral sensitization at low concentrations (0.1, 0.3mM) but tolerance at higher concentrations (1, 3mM). Planarians conditioned with nicotine in the ambient light (non-preferred environment) displayed a reduction in their natural preference for a dark environment.

CONCLUSIONS

The present results suggest nicotine elicits mammalian-like effects in planarians, including decreased motility and increased stereotypy following acute administration and abstinence-induced withdrawal, behavioral sensitization, tolerance, and place conditioning during repeated exposure.

Effects of dimethylsulfoxide on behavior and antioxidant enzymes response of planarian Dugesia japonica

In this study, the toxicity, behavioral and antioxidant activity effects of dimethylsulfoxide (DMSO) on planarian Dugesia japonica were investigated. The results showed that the mortality was directly proportional to the DMSO concentration, and planarian locomotor velocity decreased as the concentration of DMSO increased. The recovery of the motility for planarians pre-exposed to DMSO was found to be time- and dose-dependent, and only those pre-exposed to 0.1-3% DMSO resulted in full recovery. The antioxidant enzymes of planarians in response to long-term DMSO stress was also altered in a time- and dose-dependent manner. Planarians revealed more tolerance to DMSO toxicity at low DMSO (0.1%) level in short- and long-term DMSO stress, in which an efficient antioxidant system was involved and the motility was not affected.

Development of an LC-MS/MS method for the analysis of serotonin and related compounds in urine and the identification of a potential biomarker for attention deficit hyperactivity/hyperkinetic disorder

Serotonin is a major neurotransmitter and affects various functions both in the brain and in the rest of the body. It has been demonstrated that altered serotinergic function is implicated in various psychiatric disorders including depression and schizophrenia. Serotonin has also been implicated along with dopamine in attention deficit-hyperkinetic disorder (AD-HKD). This study provides a versatile validated method for the analysis of serotonin, hydroxyindole acetic acid and dopamine in urine using LC-MS/MS. This method was then used to quantify these analytes in a test group of 17 children diagnosed with severe AD-HKD. This group was compared to a matched control group to investigate the possibility that one of these compounds may be a potential biomarker for this condition. The developed method provided good linear calibration curves for the multiplex assay of analytes in urine (0.05-3.27 nmol/L; R(2) ≥ 0.9977). Acceptable inter-day repeatability was achieved for all analytes with RSD values (n = 9) ranging from 1.1% to 9.3% over a concentration range of 0.11-3.27 μmol/L in urine. Excellent limits of detection (LOD) and limits of quantitation (LOQ) were achieved with LODs of 8.8-18.2 nmol/L and the LOQs of 29.4-55.7 nmol/L for analytes in urine. Recoveries were in the ranges of 98-104%, 100-106% and 91-107% for serotonin, 5-HIAA and dopamine, respectively. An appropriate sample clean-up procedure for urine was developed to ensure efficient recovery and reproducibility on analysis. Evaluation of matrix effects was also carried out and the influence of ion suppression on analytical results reported. Confirmatory analysis was carried out on a linear trap quadrupole-Orbitrap mass spectrometer to obtain high mass accuracy data of the target analytes in the clinical samples.

First evidence that drugs of abuse produce behavioral sensitization and cross sensitization in planarians

Behavioral sensitization in mammals, including humans, is sensitive to factors such as administration route, testing environment, and pharmacokinetic confounds, unrelated to the drugs themselves that are difficult to eliminate. Simpler animals less susceptible to these confounding influences may be advantageous substitutes for studying sensitization. We tested this hypothesis by determining whether planarians display sensitization and cross sensitization to cocaine and glutamate. Planarian hyperactivity was quantified as the number of C-like hyperkinesias during a 1-min drug exposure. Planarians exposed initially to cocaine (or glutamate) on day 1 were challenged with cocaine (or glutamate) after 2 or 6 days of abstinence. Acute cocaine or glutamate produced concentration-related hyperactivity. Cocaine or glutamate challenge after 2 and 6 days of abstinence enhanced the hyperactivity, indicating the substances produced planarian behavioral sensitization. Cross-sensitization experiments showed that cocaine produced greater hyperactivity in planarians earlier exposed to glutamate than in glutamate-naive planarians, and vice versa. Behavioral responses were pharmacologically selective because neither scopolamine nor caffeine produced planarian behavioral sensitization despite causing hyperactivity after initial administration, and acute gamma-aminobutyric acid did not cause hyperactivity. Demonstration of pharmacologically selective behavioral sensitization in planarians suggests that these flatworms represent a sensitive in-vivo model to study cocaine behavioral sensitization and to screen potential abuse-deterrent therapeutics.

5-HT(1A)-like receptor activation inhibits abstinence-induced methamphetamine withdrawal in planarians

No pharmacological therapy is approved to treat methamphetamine physical dependence, but it has been hypothesized that serotonin (5-HT)-enhancing drugs might limit the severity of withdrawal symptoms. To test this hypothesis, we used a planarian model of physical dependence that quantifies withdrawal as a reduction in planarian movement. Planarians exposed to methamphetamine (10 μM) for 60 min, and then placed (tested) into drug-free water for 5 min, displayed less movement (i.e., withdrawal) than either methamphetamine-naïve planarians tested in water or methamphetamine-exposed planarians tested in methamphetamine. A concentration-related inhibition of withdrawal was observed when methamphetamine-exposed planarians were placed into a solution containing either methamphetamine and 5-HT (0.1-100 μM) or methamphetamine and the 5-HT(1A) receptor agonist 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT) (10, 20 μM). Planarians with prior methamphetamine exposure displayed enhanced withdrawal when tested in a solution of the 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridyl)cyclohexanecarboxamide (WAY 100635) (1 μM). Methamphetamine-induced withdrawal was not affected by the 5-HT(2B/2C) receptor agonist meta-chlorophenylpiperazine (m-CPZ) (0.1-20 μM). These results provide pharmacological evidence that serotonin-enhancing drugs inhibit expression of methamphetamine physical dependence in an invertebrate model of withdrawal, possibly through a 5-HT(1A)-like receptor-dependent mechanism.

Agmatine: identification and inhibition of methamphetamine, kappa opioid, and cannabinoid withdrawal in planarians

Agmatine blocks morphine physical dependence in mammals, but its effects on withdrawal signs caused by other abused drugs have been less studied. One of the reasons is that withdrawal to some of these drugs is difficult to quantify in mammals. An alternative to mammals is planarians, a type of flatworm. Planarians possess mammalian-like neurotransmitters and display withdrawal from amphetamines, benzodiazepines, cannabinoids, cocaine, and opioids. The withdrawal is manifested as a reduction in locomotor behavior following discontinuation of drug exposure. In the present study, our goal was to identify agmatine in planarians and to determine if planarians exposed to agmatine display withdrawal to methamphetamine, a cannabinoid receptor agonist (WIN 55,212-2), or a kappa-opioid receptor agonist (U-50,488H). Neurochemical experiments revealed that the concentration of agmatine in planarians was 185 +/- 33.7 pmol per mg of planarian weight (dry weight). In behavioral experiments, withdrawal (i.e., reduced locomotor activity) was observed when planarians exposed to each drug (10 microM) for 60 min were placed into water. The withdrawal was attenuated when methamphetamine- or U-50,488H-exposed planarians were tested in agmatine (100 microM). Withdrawal was inhibited similarly when planarians coexposed to agmatine (100 microM) plus methamphetamine (10 microM), WIN 55,212-2 (10 microM), or U-50,488H (10 microM) were tested in water. Arginine, the metabolic precursor to agmatine, was ineffective. Our results identify endogenous agmatine in planarians and demonstrate that agmatine exposure blocks withdrawal to three different drugs in planarians. This suggests that a change in agmatine signaling is a common mechanism in the withdrawal caused by these drugs, at least in planarians.

Neuropharmacology and behavior in planarians: translations to mammals

Planarians are the simplest animals to exhibit a body plan common to all vertebrates and many invertebrates, characterized by bilateral rather than radial symmetry, dorsal and ventral surfaces, and a rostrocaudal axis with a head and a tail, including specialized sense organs and an aggregate of nerve cells in the head. Neurons in planarian more closely resemble those of vertebrates than those of advanced invertebrates, exhibiting typical vertebrate features of multipolar shape, dendritic spines with synaptic boutons, a single axon, expression of vertebrate-like neural proteins, and relatively low spontaneously generated electrical activity. Here we report the most relevant contribution to the knowledge of the neuropharmacology of planarians, with particular reference to the behavioral consequences of the exposure to drugs acting on neural transmission. Neurochemical and histochemical data indicate the presence of several neurotransmitter-receptor systems in planarians. Moreover, a variety of experimental studies characterized specific behavioral patterns of these animals following the exposure to drugs acting on neural transmission. There is also evidence of the interactions between discrete neurotransmitter-receptor systems in modulating behavior in planarians. Finally, the model has proved efficacy for investigating the neurotoxicology of the dopamine neurons, and for the initial screening of the neuroprotective potential of drugs. In conclusion, these findings indicate that interactions between discrete neurotransmitter-receptor systems occur very early along phylogeny, although they may have evolved from very fundamental behaviors, such as motor activity in planarian, to more complex and integrated functions in vertebrates.

Identification and distribution of tryptophan hydroxylase (TPH)-positive neurons in the planarian Dugesia japonica

We identified a full-length tryptophan hydroxylase (TPH) gene of planarian Dugesia japonica from a head EST database, and named it DjTPH. Based on whole-mount in situ hybridization and immunofluorescence analyses, DjTPH mRNA and protein were mainly expressed in the nervous system, especially ventral nerve cords and eye pigment cells. Furthermore, DjTPH immunoreactivity was clearly detected at commissure axonal connections in the ventral nerve cords. 5-HT was significantly decreased in DjTPH-knockdown planarians compared with control animals. These results suggest that DjTPH is required for 5-HT biosynthesis, and DjTPH antibody is a useful marker for serotonergic neurons in planarians.

Flumazenil-sensitive dose-related physical dependence in planarians produced by two benzodiazepine and one non-benzodiazepine benzodiazepine-receptor agonists

Two benzodiazepine (midazolam and clorazepate) and one non-benzodiazepine (zolpidem) benzodiazepine-receptor agonists produced dose-related physical dependence, as evidenced by abstinence-induced decrease in planarian locomotor velocity (pLMV) when drug-exposed planarians were placed into drug-free water, but not when they were placed into drug-containing water (i.e., an abstinence-induced withdrawal, since the effect was only obtained in the removal of drug and not in the continued presence of drug). We have previously shown that the decrease in pLMV is associated with specific and transient withdrawal signs. In the present study, the selective benzodiazepine-receptor antagonist flumazenil significantly antagonized (P<0.05), by co-application, the ability of each agonist to produce the withdrawal. These results: (1) suggest that benzodiazepine-receptor agonists, for two different chemical categories, produce dose-related physical dependence manifested as abstinence-induced withdrawal in this simple and convenient model, and (2) in the absence of cloning or radioligand binding literature, suggest a possible specific interaction site (receptor?) for these compounds in planarians.

An NMDA antagonist (LY 235959) attenuates abstinence-induced withdrawal of planarians following acute exposure to a cannabinoid agonist (WIN 55212-2)

The mechanisms that facilitate the development and expression of cannabinoid physical dependence in humans and other mammals are poorly understood. The present experiments used a planarian model to provide evidence that pharmacological antagonism of NMDA receptors significantly attenuates the development of cannabinoid physical dependence. Abstinence-induced withdrawal from the cannabinoid agonist WIN 55212-2 (10 microM) was manifested as a significant (P<0.05) decrease in the rate of planarian spontaneous locomotor velocity (pLMV) when WIN 55212-2 (10 microM)-exposed planarians were placed into drug-free water. No change in pLMV occurred when WIN 55212-2 (10 microM)-exposed planarians were placed into water containing WIN 55212-2 (10 microM). WIN 55212-2 (10 microM)-exposed planarians placed into water containing LY 235959 (1 or 10 microM) did not display withdrawal (no significant difference, P>0.05, in pLMV). In addition, withdrawal was not observed (no significant difference, P>0.05, in pLMV) in planarians that were co-exposed to a solution containing WIN 55212-2 (10 microM) and LY 235959 (10 microM). The present results reveal that NMDA receptor activation mediates the development of cannabinoid physical dependence and the expression of cannabinoid withdrawal in planarians.

Measurement of glutamate and aspartate in Planaria

INTRODUCTION

The major excitatory neurotransmitters in the mammalian central nervous system are glutamate and aspartate. We developed a rapid and efficient method for the extraction and measurement of these amino acids in Planaria--a valuable model for mammalian processes because of their simple, centralized nervous system and similar neurotransmitter systems.

METHOD

The method utilized buffer extraction (perchloric acid containing 0.025% of L-cystine and Na2EDTA), simple derivatization, high-pressure liquid chromatography (HPLC), and fluorescence detection.

RESULTS

The mean+/-S.E.M. amounts of glutamate and aspartate were 322.6+/-43.6 and 188.6+/-27.6 pmol/mg-planarian, respectively.

DISCUSSION

The method provides the ability to investigate changes in glutamate and aspartate in response to drug administration or withdrawal.