Acutely applied MDMA enhances long-term potentiation in rat hippocampus involving D1/D5 and 5-HT2 receptors through a polysynaptic mechanism.

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is a drug of abuse that induces learning and memory deficit. However, there are no experimental data that correlate the behavioral evidence with models of synaptic plasticity such as long-term potentiation (LTP) or long-term depression (LTD). Using field potential recordings in rat hippocampal slices of young rats, we found that acute application of MDMA enhances LTP in CA3-CA1 synapses without affecting LTD. Using specific antagonists and paired-pulse facilitation protocols we observed that the MDMA-dependent increase of LTP involves presynaptic 5-HT2 serotonin receptors and postsynaptic D1/D5 dopamine receptors. In addition, the inhibition of PKA suppresses the MDMA-dependent increase in LTP, suggesting that dopamine receptor agonism activates cAMP-dependent intracellular pathways. We propose that MDMA exerts its LTP-altering effect involving a polysynaptic interaction between serotonergic and dopaminergic systems in hippocampal synapses. Our results are compatible with the view that the alterations in hippocampal LTP could be responsible for MDMA-dependent cognitive deficits observed in humans and animals.

Comparación farmacocinética de Sinemet y Grifoparkin (levodopa/carbidopa 250/25 mg) en pacientes con enfermedad de Parkinson avanzada: un estudio con dosis única / Pharmacokinetic comparison of Sinemet and Grifoparkin (levodopa/carbidopa 250/25 mg) in Parkinson s disease: a single dose study

BACKGROUND: There are doubts wether generic medications have the same bioavailability and efficacy compared with the original drugs developed by pharmaceutical companies with research capabilities. AIM: To compare the pharmacokinetics and clinical (motor) responses of Sinemet and Grifoparkin (generic carbidopa/levodopa 250/25 mg) in patients with advanced Parkinson's disease. PATIENTS AND METHODS: Patients were randomly assigned to Sinemet (15 patients 62 +/- 12 years old; mean disease duration 11 +/- 7 years) or Grifoparkin (15 patients, 64 +/- 11 years old; mean disease duration 12 +/- 4 years) groups. Medication and food were withheld 12 h before the study. Fifteen blood samples were collected (starting 9 AM) immediately before (sample 1, t = 0 min) and after (samples 2-15, t = 20-360 min) oral administration of a single dose of Sinemet or Grifoparkin, and plasmatic L-DOPA was quantified using HPLC with electrochemical detection. Additionally, each patient was clinically evaluated every 20 minutes, using the tapping test and the unified Parkinson's disease scale Hoehn & Yarh. RESULTS: Tmax (time at which the maximal L-DOPA concentration was reached) were 69 +/- 12 min and 64 +/- 11 min for Sinemet and Grifoparkin respectively (NS). Cmax (maximal L-DOPA concentration reached) was 3161 +/- 345 ng/ml for Sinemet and 3274 +/- 520 ng/ml for Grifoparkin (NS). The t1/2 (half life time), CL (clearance) and volume of distribution (Vd) values calculated were 159 +/- 32 min, 51.7 +/- 5.1 1/h and 3.6 +/- 1.2 l/kg for Sinemet and 161 +/- 48 min, 58.7 +/- 8 l/h and 3.0 +/- 0.7 l/kg for Grifoparkin (NS). UPDRS-III value for the best on state and for the worst off state were 23 +/- 11 and 50 +/- 19 for Sinemet and 20 +/- 7 and 46 +/- 13 for Grifoparkin respectively (NS). CONCLUSION: The results obtained showed that both drugs are bioequivalent in patients with advanced Parkinson's disease.

p-Methylthioamphetamine and 1-(m-chlorophenyl)piperazine, two non-neurotoxic 5-HT releasers in vivo, differ from neurotoxic amphetamine derivatives in their mode of action at 5-HT nerve endings in vitro.

The mechanism underlying the serotoninergic neurotoxicity of some amphetamine derivatives, such as p-chloroamphetamine (pCA) and 3,4-methylenedioxymethamphetamine (MDMA), is still debated. Their main acute effect, serotonin (5-HT) release from nerve endings, involves their interaction with 5-HT transporters (SERTs), as substrates. Although this interaction is required for the neurotoxic effects, 5-HT release alone may not be sufficient to induce long-term 5-HT deficits. Some non-neurotoxic compounds, including p-methylthioamphetamine (MTA) and 1-(m-chlorophenyl)piperazine (mCPP), have 5-HT releasing properties in vivo and in brain slices comparable to that of neurotoxic amphetamine derivatives. We measured 5-HT release in superfused rat brain synaptosomes preloaded with [3H]5-HT, a model that distinguishes a releasing effect from reuptake inhibition. MTA and mCPP induced much lower release than pCA and MDMA. The striking difference between our findings in synaptosomes and those obtained in vivo or in brain slices is probably related to a different compartmentalisation of 5-HT in the different experimental models. Studies in synaptosomes, where the vesicular storage of 5-HT is predominant, could therefore bring to light differences between neurotoxic and non-neurotoxic 5-HT releasing agents which cannot be appreciated in other experimental models and might be useful to identify the mechanisms responsible for the neurotoxicity induced by amphetamine derivatives.

ALEPH-2, a suspected anxiolytic and putative hallucinogenic phenylisopropylamine derivative, is a 5-HT2a and 5-HT2c receptor agonist.

To assess the pharmacodynamic profile of ALEPH-2, a phenylisopropylamine derivative with alleged anxiolytic and hallucinogenic properties, Xenopus laevis oocytes were microinjected with either of the rat cRNA for the 5-HT2A or the 5-HT2C receptor. Concentration-response curves were obtained following the exposure of the oocytes to varying concentrations of either ALEPH-2 or 5-hydroxytryptamine (5-HT) for 10 s. ALEPH-2 is a partial agonist on the 5-HT2A receptor with a similar potency to 5-HT. In contrast, ALEPH-2 is a full 5-HT2C receptor agonist and is about 15-fold less potent than 5-HT. Pre-application of 1 microM ritanserin antagonized the responses induced by 5-HT and ALEPH-2 to the same extent; however, the 5-HT2A receptor is more sensitive to ritanserin blockade than the 5-HT2C receptor.

Effects of 5-HT-releasing agents on the extracellullar hippocampal 5-HT of rats. Implications for the development of novel antidepressants with a short onset of action.

The effects of two selective 5-HT-releasing agents, 4-methylthioamphetamine (MTA) and 5-methoxy-6-methyl-2-aminoindan (MMAI), on the extracellular 5-HT concentration in the dorsal hippocampus was determined by microdialysis in anesthetized rats. After i.p. administration of 1 or 5 mg/kg of either compound, a rapid and significant increase of 5-HT basal release was observed. MTA (5 mg/kg) induced a maximal increase of about 2000% over the basal value 40 min after injection, which declined slowly, whereas MMAI (5 mg/kg) induced a maximal response of about 1350% which showed a rapid decline. Monoamine oxidase-A inhibitory properties of MTA, and MMAI's lack of similar properties might account for the difference between the two compounds. In agreement with previous information, a much lower increase in hippocampal 5-HT was observed in response to systemic fluoxetine. This difference in the magnitude of the response after MTA or MMAI and fluoxetine indicates that different mechanisms of action are operating. Based on evidence showing that an acute enhancement of 5-HT neurotransmission might result in the rapid appearance of therapeutic effects of serotonergic antidepressants, we suggest that MTA and MMAI might serve as leads for a novel family of compounds with a short onset of action useful for treating depression.

Dopaminergic pharmacology and antioxidant properties of pukateine, a natural product lead for the design of agents increasing dopamine neurotransmission.

The dopaminergic and antioxidant properties of pukateine [(R)-11-hydroxy-1,2-methylenedioxyaporphine, PUK], a natural aporphine derivative, were analyzed in the rat central nervous system. At dopamine (DA) D1 ([3H]-SCH 23390) and D2 ([3H]-raclopride) binding sites, PUK showed IC50 values in the submicromolar range (0.4 and 0.6 microM, respectively). When the uptake of tritiated dopamine was assayed by using a synaptosomal preparation, PUK showed an IC50 = 46 microM. In 6-hydroxydopamine unilaterally denervated rats, PUK (8 mg/kg but not 4 mg/kg) elicited a significant contralateral circling, a behavior classically associated with a dopaminergic agonist action. When perfused through a microdialysis probe inserted into the striatum, PUK (340 microM) induced a significant increase in dopamine levels. In vitro experiments with a crude rat brain mitochondrial suspension showed that PUK did not affect monoamine oxidase activities, at concentrations as high as 100 microM. PUK potently (IC50 = 15 microM) and dose-dependently inhibited the basal lipid peroxidation of a rat brain membrane preparation. As a whole, PUK showed a unique profile of action, comprising an increase in extracellular DA, an agonist-like interaction with DA receptors, and antioxidant activity. Thus, PUK may be taken as a lead compound for the development of novel therapeutic strategies for Parkinson disease.

Effects of the D3 preferring dopamine agonist pramipexole on sleep and waking, locomotor activity and striatal dopamine release in rats.

Quantitation of 2 h sessions after administration of the D3 preferring dopamine (DA) agonist pramipexole (10-500 microg/kg) showed dose-related effects on wakefulness (W), slow wave sleep (SWS) and REM sleep in rats. The 30 microg/kg dose of the DA agonist increased SWS and REM sleep and reduced W during the first recording hour, while the 500 microg/kg dose augmented W. On the other hand, W was increased while SWS and REMS were decreased after the 500 microg/kg dose during the second recording hour. The mixed D2- and D3 receptor antagonist YM-09151-2 (30-500 microg/kg), which per se affected sleep variables prevented the increase of REMS induced by pramipexole. Furthermore, the highest doses (500-1000 microg/kg) of the DA antagonist effectively antagonized the increase of W and reduction of SWS induced by the 500 microg/kg dose of the DA agonist. Pramipexole (30-100 microg/kg) induced a decrease of locomotor activity during the 2 h recording period. In addition, the 500 microg/kg dose gave rise to an initial reduction of motor behavior which was reverted 2 h later. Pramipexole (30 and 500 microg/kg) did not significantly affect striatal DA release during the first two hours following drug administration, as measured by microdialysis. It is tentatively suggested that D3 receptor could be involved in the pramipexole-induced increase of sleep and reduction of locomotor activity. On the other hand, the increase of W and of motor behavior after relatively high doses could be related to activation of postsynaptic D2 receptor.

Monoamine oxidase inhibitory properties of some methoxylated and alkylthio amphetamine derivatives: structure-activity relationships.

The monoamine oxidase (MAO) inhibitory properties of a series of amphetamine derivatives with different substituents at or around the para position of the aromatic ring were evaluated. In in vitro studies in which a crude rat brain mitochondrial suspension was used as the source of MAO, several compounds showed a strong (IC50 in the submicromolar range), selective, reversible, time-independent, and concentration-related inhibition of MAO-A. After i.p. injection, the compounds induced an increase of serotonin and a decrease of 5-hydroxyindoleacetic acid in the raphe nuclei and hippocampus, confirming the in vitro results. The analysis of structure-activity relationships indicates that: molecules with amphetamine-like structure and different substitutions on the aromatic ring are potentially MAO-A inhibitors; substituents at different positions of the aromatic ring modify the potency but have little influence on the selectivity; substituents at the para position such as amino, alkoxyl, halogens, or alkylthio produce a significant increase in the activity; the para-substituent must be an electron donor; bulky groups next to the para substituent lead to a decrease in the activity; substituents located at positions more distant on the aromatic ring have less influence and, even when the substituent is a halogen (Cl, Br), an increase in the activity of the compound is obtained. Finally, the MAO-A inhibitory properties of some of the compounds evaluated are discussed in relation to: (a) potential antidepressant activity, and (b) their reported hallucinogenic, neurotoxic, or anxiolytic effects.

(+/-)-1-(2,5-Dimethoxy-4-ethylthiophenyl)-2-aminopropane (ALEPH-2), a novel putative anxiolytic agent lacking affinity for benzodiazepine sites and serotonin-1A receptors.

Serotonergic behavioral responses, effects on motor activity and core temperature, and binding properties of the novel putative anxiolytic amphetamine derivative (+/-)1-(2,5-dimethoxy-4-ethylthio-phenyl)-2-aminopropane (ALEPH-2), were examined in rodents in order to elucidate the mechanism underlying its anxiolytic-like effect. After peripheral administration in rats, ALEPH-2 induced some symptoms of the serotonergic syndrome, e.g. forepaw treading and flat body posture. Additionally, a decrease in motor activity was observed. No significant effects on the number of head shakes were observed after injection, although high inter-subject variability was noted. Higher doses of ALEPH-2, in the range exhibiting anxiolytic properties (4mg/kg), elicited significant hypothermia in mice. The affinity of the drug for 5-HT2A/2C receptors ([3H]ketanserin sites) was in the nanomolar range (Ki = 173 nM), whereas for 5-HT1A, benzodiazepine sites, and GABAA receptors, the affinity was micromolar of lower. Based on these results the mechanism of action and the anxiolytic-like properties of ALEPH-2 are discussed.

Behavioral effects of the putative anxiolytic (+/-)-1-(2,5-dimethoxy-4-ethylthiophenyl)-2-aminopropane (ALEPH-2) in rats and mice.

Behavioral effects of the phenethylamine derivative (+/-)-1-(2,5-dimethoxy-4-ethylthiophenyl)-2-aminopropane (ALEPH-2) were studied in mice and rats. Murine locomotor activity, measured with a photocell actometer, was markedly depressed following IP injection of 2 and 6 mg/kg of the drug. The same doses of the drug also decreased frequency and duration of head dipping and the number of rearings in the hole board apparatus. In the murine elevated plus maze 2 and 6 mg/kg of ALEPH-2 increased the percentage of both open arm entries and time. The total number of entries into the enclosed arms was not significantly affected by the drug. In the rat, 2-12 mg/kg ALEPH-2, IP, decreased photobeam counts in the actometer in a dose-dependent fashion. Both 2 and 4 mg/kg of the drug increased the percentage of open arm entries, but only the highest dose significantly increased the percentage of time spent on the open arms. The dose of 4 mg/kg ALEPH-2 also significantly decreased the total number of enclosed arm entries. Finally, in a recently developed model of anxiety and memory, the elevated T-maze, the doses of 2 and 4 mg/kg ALEPH-2 did not change inhibitory avoidance of the open arms. Nevertheless, the highest dose had an amnestic effect on this task, repeated 72 h later in the absence of drug. In addition, this dose significantly increased the latency to escape from the open arms and had an amnestic effect measured 72 h later. Overall, these results indicate that ALEPH-2 possesses anxiolytic, amnestic as well as sedative and/or motor depressant actions.

Sleep and waking in 5,7-DHT-lesioned or (-)-pindolol-pretreated rats after administration of buspirone, ipsapirone, or gepirone.

The effects of partial 5-HT1A receptor agonists buspirone (0.010-4.0 mg/kg), ipsapirone (0.010-6.0 mg/kg), and gepirone (0.025-4.0 mg/kg) on sleep and waking were studied in vehicle-treated and 5,7-dihydroxytryptamine (5,7-DHT)-injected rats. 5,7-DHT-treated animals showed a marked and significant serotonin and 5-HIAA depletion in the raphe regions of the pons and upper brain stem, cerebral cortex, hippocampus, and striatum. Subcutaneous administration of the partial agonists to both the vehicle-infused and the 5,7-DHT-treated animals significantly increased waking (W) and reduced light sleep (LS), slow-wave sleep (SWS), and REM sleep (REMS). Pretreatment with (-)pindolol (2.0 mg/kg) reversed the effects of buspirone and gepirone on W and non-REM sleep (LS + SWS) whereas REMS remained suppressed. (-)-Pindolol failed to reverse the effects of ipsapirone on sleep and W. The present results tend to indicate that increased W after acute administration of buspirone, ipsapirone, or gepirone depends upon the activation of postsynaptic 5-HT1A receptors. The well-known anxiolytic action observed after chronic administration of the azapirones seems to be related to mechanisms other that these involved in their stimulant effect.

Depletion of brain serotonin by 5,7-DHT: effects on the 8-OH-DPAT-induced changes of sleep and waking in the rat.

The effect of 5-HT1A receptor agonist 8-OH-DPAT on sleep and wakefulness was studied in rats with selective serotonin depletion after ICV administration of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT). Injection of 8-OH-DPAT to vehicle-treated animals induced biphasic effects, such that low doses (0.010 mg/kg) which act perferentially on the somatodendritic autoreceptor decreased wakefulness (W) and increased slow wave sleep (SWS), while higher doses (0.375 mg/kg) which stimulate postsynaptic receptors caused opposite effects. REM sleep was suppressed irrespective of the dosage given. Injection of the 0.010 mg/kg dose in the 5,7-DHT-treated rats did not result in significant changes in sleep or W. On the other hand, the 0.375 mg/kg dose produced changes in sleep variables which were similar to those described in the vehicle-treated animals. Our findings tend to indicate that increased SWS after low doses of 8-OH-DPAT depends upon the activation of inhibitory somatodendritic 5-HT1A receptors, while increased W after higher doses of the compound is related to stimulation of postsynaptic receptors.

Monoamine oxidase inhibitory effects of some 4-aminophenethylamine derivatives.

The in vitro and ex vivo monoamine oxidase (MAO) inhibitory effects of (+/-)4-dimethylamino-alpha-methyl-phenethylamine (4-DMAA) and (+/-)4-methylamino-alpha-methyl-phenethylamine (4-MAA) were reassessed, in comparison with the previously unstudied achiral parent compound, 4-dimethyl-aminophenethylamine (4-DMAPEA) and with a salt of 4-DMAA enriched in the levo isomer, ("-")-4-DMAA, using amiflamine [S-(+)-4-dimethylamino-alpha,2-dimethylphenethylamine] as positive control. The in vitro studies confirmed that 4-amino-alpha-methylphenethylamine derivatives are highly selective and reversible MAO-A inhibitors. Furthermore, ("-")-4DMAA was less active than the racemic mixture. The side chain-unsubstituted compound, 4-DMAPEA, proved to be a nonselective and reversible MAO inhibitor. The ex vivo results, in which catecholamines, serotonin (5-HT) and their metabolites were measured in two brain regions after i.p. administration, confirmed the results obtained in vitro. These results are consistent with the suggestion that the 4-amino group contributes to MAO inhibitory effects of alpha-methyl-phenethylamines, and show that the presence and orientation of an alpha-methyl side chain substituent may be important when determining the potency and selectivity of these compounds. All compounds tested could be quantified by HPLC with electrochemical detection.

4-Dimethylaminophenethylamine, a sensitive, specific, electrochemically detectable monoamine oxidase-B substrate.

4-Dimethylaminophenethylamine (DMAPEA) was characterized as an MAO substrate. This compound was unaffected by MAO-A, while its oxidation by MAO-B was linear as a function of both time and enzyme concentration, with Km = 5.8 microM and Vmax = 21.2 pmol/min/mg protein, using a crude rat brain mitochondrial suspension as source of MAO. Both DMAPEA and its oxidation product, 4-dimethylaminophenylacetic acid (DMAPAA), can be detected electrochemically at 0.85 V. The high MAO-B affinity and selectivity of DMAPEA, together with its low oxidation potential, make this molecule a unique tool to determine MAO-B activity in a wide variety of tissue preparations using HPLC-ED.