Inhibition of serotonin transporters by cocaine and meprylcaine through 5-TH2C receptor stimulation facilitates their seizure activities

Discriminative stimulus properties of the atypical antipsychotic amisulpride: comparison to its isomers and to other benzamide derivatives, antipsychotic, antidepressant, and antianxiety drugs in C57BL/6 mice

RATIONALE

Racemic (RS)-amisulpride (Solian^®) is an atypical antipsychotic drug used to treat schizophrenia and dysthymia. Blockade of dopamine D₂/D₃ and/or serotonin 5-HT₇ receptors is implicated in its pharmacological effects. While the (S)-amisulpride isomer possesses a robust discriminative cue, discriminative stimulus properties of (RS)-amisulpride have not been evaluated.

OBJECTIVES

The present study established (RS)-amisulpride as a discriminative stimulus and assessed amisulpride-like effects of amisulpride stereoisomers, other benzamide derivatives, and antipsychotic, antidepressant, and anxiolytic drugs.

METHODS

Adult, male C57BL/6 mice were trained to discriminate 10 mg/kg (RS)-amisulpride from vehicle in a two-lever food-reinforced operant conditioning task.

RESULTS

(RS)-Amisulpride's discriminative stimulus was dose-related, time-dependent, and stereoselective. (S)-Amisulpride (an effective dose of 50% (ED₅₀) = 0.21 mg/kg) was three times more potent than (RS)-amisulpride (ED₅₀ = 0.60 mg/kg) or (R)-amisulpride (ED₅₀ = 0.68 mg/kg). (RS)-Amisulpride generalized fully to the structurally related atypical antipsychotic/antidysthymia drug sulpiride (Sulpor^®; ED₅₀ = 7.29 mg/kg) and its (S)-enantiomer (ED₅₀ = 9.12 mg/kg); moderate to high partial generalization [60-75% drug lever responding (%DLR)] occurred to the benzamide analogs tiapride (Tiapridal^®) and raclopride, but less than 60% DLR to metoclopramide (Reglan^®), nemonapride (Emilace^®), and zacopride. Antipsychotic, antidepressant, and antianxiety drugs from other chemical classes (chlorpromazine, quetiapine, risperidone, and mianserin) produced 35-55% amisulpride lever responding. Lastly, less than 35% DLR occurred for clozapine, olanzapine, aripiprazole imipramine, chlordiazepoxide, and bupropion.

CONCLUSIONS

(RS)-Amisulpride generalized to some, but not all benzamide derivatives, and it failed to generalize to any other antipsychotic, antidepressant, or antianxiety drugs tested. Interestingly, the (R)-isomer shared very strong stimulus properties with (RS)-amisulpride. This finding was in contrast to findings from Donahue et al. (Eur J Pharmacol 734:15-22, 2014), which found that the (R)-isomer did not share very strong stimulus properties when the (S)-isomer was the training drug.

Potential functional and pathological side effects related to off-target pharmacological activity

Most pharmaceutical companies test their discovery-stage proprietary molecules in a battery of in vitro pharmacology assays to try to determine off-target interactions. During all phases of drug discovery and development, various questions arise regarding potential side effects associated with such off-target pharmacological activity. Here we present a scientific literature curation effort undertaken to determine and summarize the most likely functional and pathological outcomes associated with interactions at 70 receptors, enzymes, ion channels and transporters with established links to adverse effects. To that end, the scientific literature was reviewed using an on-line database, and the most commonly reported effects were summarized in tabular format. The resultant table should serve as a practical guide for research scientists and clinical investigators for the prediction and interpretation of adverse side effects associated with molecules interacting with components of this screening battery.

Cocaine use as an independent predictor of seizures after aneurysmal subarachnoid hemorrhage

OBJECTIVE

Seizures are relatively common after aneurysmal subarachnoid hemorrhage (aSAH). Seizure prophylaxis is controversial and is often based on risk stratification; middle cerebral artery (MCA) aneurysms, associated intracerebral hemorrhage (ICH), poor neurological grade, increased clot thickness, and cerebral infarction are considered highest risk for seizures. The purpose of this study was to evaluate the impact of recent cocaine use on seizure incidence following aSAH.

METHODS

Prospectively collected data from aSAH patients admitted to 2 institutional neuroscience critical care units between 1991 and 2009 were reviewed. The authors analyzed factors that potentially affected the incidence of seizures, including patient demographic characteristics, poor clinical grade (Hunt and Hess Grade IV or V), medical comorbidities, associated ICH, intraventricular hemorrhage (IVH), hydrocephalus, aneurysm location, surgical clipping and cocaine use. They further studied the impact of these factors on "early" and "late" seizures (defined, respectively, as occurring before and after clipping/coiling).

RESULTS

Of 1134 aSAH patients studied, 182 (16%) had seizures; 81 patients (7.1%) had early and 127 (11.2%) late seizures, with 26 having both. The seizure rate was significantly higher in cocaine users (37 [26%] of 142 patients) than in non-cocaine users (151 [15.2%] of 992 patients, p = 0.001). Eighteen cocaine-positive patients (12.7%) had early seizures compared with 6.6% of cocaine-negative patients (p = 0.003); 27 cocaine users (19%) had late seizures compared with 10.5% non-cocaine users (p = 0.001). Factors that showed a significant association with increased risk for seizure (early or late) on univariate analysis included younger age (< 40 years) (p = 0.009), poor clinical grade (p = 0.029), associated ICH (p = 0.007), and MCA aneurysm location (p < 0.001); surgical clipping was associated with late seizures (p = 0.004). Following multivariate analysis, age < 40 years (OR 2.04, 95% CI 1.355-3.058, p = 0.001), poor clinical grade (OR 1.62, 95% CI 1.124-2.336, p = 0.01), ICH (OR 1.95, 95% CI 1.164-3.273, p = 0.011), MCA aneurysm location (OR 3.3, 95% CI 2.237-4.854, p < 0.001), and cocaine use (OR 2.06, 95% CI 1.330-3.175, p = 0.001) independently predicted seizures.

CONCLUSIONS

Cocaine use confers a higher seizure risk following aSAH and should be considered during risk stratification for seizure prophylaxis and close neuromonitoring.

Elevated serotonergic signaling amplifies synaptic noise and facilitates the emergence of epileptiform network oscillations

Serotonin fibers densely innervate the cortical sheath to regulate neuronal excitability, but its role in shaping network dynamics remains undetermined. We show that serotonin provides an excitatory tone to cortical neurons in the form of spontaneous synaptic noise through 5-HT3 receptors, which is persistent and can be augmented using fluoxetine, a selective serotonin re-uptake inhibitor. Augmented serotonin signaling also increases cortical network activity by enhancing synaptic excitation through activation of 5-HT2 receptors. This in turn facilitates the emergence of epileptiform network oscillations (10-16 Hz) known as fast runs. A computational model of cortical dynamics demonstrates that these two combined mechanisms, increased background synaptic noise and enhanced synaptic excitation, are sufficient to replicate the emergence fast runs and their statistics. Consistent with these findings, we show that blocking 5-HT2 receptors in vivo significantly raises the threshold for convulsant-induced seizures.

A systematic review of evidence on the association between cocaine use and seizures

BACKGROUND

Institutional monographs/medical textbooks mention seizures as a neurological complication of cocaine, but no systematic reviews (SRs) have been published on this issue. We aimed to conduct a SR of the literature on the relationship between cocaine use and seizures and to summarize the biological plausibility of that relationship.

METHODS

The pathophysiological mechanisms that may underlie an association between cocaine and seizures were summarized; a SR was then performed using three databases (EMBASE, Medline, PsycINFO) and the Cochrane-library to search for published papers (1980-2012) aimed at quantifying the associations between cocaine use and seizures. The inclusion criteria for selection were: articles based on clinical trials, cohort, case-control (CC) or cross-sectional (CS) studies, participants ≥ 14 years old and not pregnant, and use of cocaine in the last 72 h. Information was extracted, evaluated and cross-checked independently by two researchers.

RESULTS

Of the 1243 potentially relevant articles initially identified; one CC and 22 CS studies were finally selected. The CC study did not find cocaine use to be a risk-factor for seizures. In addition to the limitations of the CS design, these studies had important methodological weaknesses and biases.

CONCLUSIONS

Despite its biological plausibility, no rigorous scientific evidence supports a causal relationship between cocaine use and seizures. The misinterpretation of the role of cocaine may have important implications in medical services. Well-conducted studies are urgently needed.

Assessment of the convulsant liability of antidepressants using zebrafish and mouse seizure models

In the past, antidepressants have been thought to possess proconvulsant properties. This assumption remains controversial, however, because anticonvulsant effects have been attributed to certain antidepressants. To date, it remains unclear which antidepressants can be used for the treatment of patients with epilepsy with depression. The present study was designed to determine the anticonvulsant and/or proconvulsant effects of three antidepressants (citalopram, reboxetine, bupropion) against pilocarpine- and pentylenetetrazole-induced acute seizures in larval zebrafish and mice. In zebrafish, all antidepressants were anticonvulsant in the pentylenetetrazole model. In addition, citalopram was anticonvulsant in the zebrafish pilocarpine model, whereas reboxetine and bupropion were without significant effect. In mice all three antidepressants increased some thresholds for pentylenetetrazole-induced convulsive-like behaviors at varying doses, whereas thresholds for pilocarpine-induced convulsive-like behaviors were generally lowered, particularly at the highest doses tested. In general we conclude that the convulsant liability of antidepressants is model and concentration dependent.

Homeostasis of glucose in the rainbow trout (Oncorhynchus mykiss Walbaum): the role of serotonin

In this study, we evaluated, for the first time, the 5-HT (serotonin)-mediated control of glucose homeostasis in the rainbow trout Oncorhynchus mykiss. Intraperitoneal administration of 5-HT increased plasma levels of glucose, adrenaline and noradrenaline. By contrast, intracerebroventricular administration of 5-HT did not cause any significant variation in plasma levels of glucose. The release of endogenous 5-HT following intraperitoneal administration of d-fenfluramine led to a significant increase in plasma levels of glucose and adrenaline. Intraperitoneal administration of (1) MIAN (a 5-HT2 receptor antagonist) did not block either the hyperglycaemic action or the increase in plasma levels of adrenaline induced by 5-HT, but did block the increase in plasma levels of noradrenaline, and (2) 5-CT (a 5-HT1 agonist) increased the plasma levels of glucose and of adrenaline, without altering those of noradrenaline. Administration of TFMPP (a 5-HT1B agonist) did not increase the plasma levels of glucose, and the hyperglycaemic action of 5-HT was not blocked by antagonists of 5-HT1A (WAY 100635), 5-HT1D (BRL 15572), 5-HT2B (SB 204741) or 5-HT7 (pimozide) receptors. It was demonstrated that, in rainbow trout, peripheral 5-HT, but not brain 5-HT intervenes in the modulation of glucose homeostasis with a hyperglycaemic effect. This effect is associated with the release of adrenaline and activation of 5-HT1-like receptors. As far as could be determined in the present study, these 5-HT1-like receptors are unrelated to either the 5-HT1A, 5-HT1B or 5-HT1D receptor subtypes of mammals. The 5-HT2-type receptors may mediate the release of noradrenaline, but not of adrenaline, and furthermore, do not appear to play an important role in the hyperglycaemic effect exerted by 5-HT.

Predictive factors for generalized seizures after deliberate citalopram overdose

AIMS

Seizures are a recognized complication of citalopram overdose. The present study sought to establish risk factors for seizures in this high-risk patient group, including stated dose ingested, co-ingested drugs or ethanol, and electrolyte disturbances.

METHODS

A retrospective casenote review was carried out of patients who attended the Emergency Department due to citalopram overdose between January 2000 and July 2007 inclusive. Stepwise logistic regression analysis considered age, gender, stated citalopram dose, acute ethanol consumption, co-ingested drugs, administration of activated charcoal, and hyponatraemia.

RESULTS

There were 241 patients (177 women), and the median (interquartile range) stated citalopram dose was 300 mg (200 to 600 mg). Generalized seizures occurred in 18 patients (7.5%). Logistic regression analysis found co-ingested tricyclic antidepressants or venlafaxine predicted seizures with odds ratio = 15 (95% confidence interval 3, 75). In the absence of co-ingested drugs, the minimum citalopram dose associated with seizures was 400 mg. Odds ratio for seizures = 1.1 (95% confidence interval 1.0, 1.2) for every 100 mg increment in citalopram dose. Seizures were associated with a greater need for invasive ventilatory support, higher creatine kinase activity, and prolonged hospital stay.

CONCLUSIONS

Generalized seizures are an important manifestation of citalopram toxicity, and cannot be explained solely by electrolyte disturbances or co-ingestion of other drugs or ethanol. The strongest predictors of seizures in this patient series were ingestion of high citalopram dosages and co-ingestion of drugs capable of lowering seizure threshold.

Chronically administered fluoxetine enhances the anticonvulsant activity of conventional antiepileptic drugs in the mouse maximal electroshock model

Interactions between chronically administered fluoxetine and valproate, carbamazepine, phenytoin, or phenobarbital were studied in the maximal electroshock test in mice. Fluoxetine administered for 14 days at doses up to 20 mg/kg failed to affect the electroconvulsive threshold. Nevertheless the drug (at 15 and 20 mg) enhanced the anticonvulsant activity of valproate, carbamazepine, and phenytoin. When applied at 20 mg/kg, it potentiated the protective action of phenobarbital. Fluoxetine, antiepileptic drugs, and their combinations did not produce significant adverse effects evaluated in the chimney test (motor coordination) and passive-avoidance task (long-term memory). Chronically applied fluoxetine significantly increased the brain concentrations of valproate, carbamazepine, phenobarbital and phenytoin, indicating a pharmacokinetic contribution to the observed pharmacodynamic interactions. In conclusion, long-term treatment with fluoxetine exhibited some favorable effects on the anticonvulsant properties of conventional antiepileptic drugs, resulting, however, from pharmacokinetic interactions.