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Due to the role of astrocytes and microglia in the pathophysiology of epilepsy and limited studies of antiseizure medication (ASM) effects on glial cells, we studied tiagabine (TGB) and zonisamide (ZNS) in an astrocyte-microglia co-culture model of inflammation. Different concentrations of ZNS (10, 20, 40, 100 µg/ml) or TGB (1, 10, 20, 50 µg/ml) were added to primary rat astrocytes co-cultures with 5–10% (M5, physiological conditions) or 30–40% (M30, pathological inflammatory conditions) microglia for 24 h, aiming to study glial viability, microglial activation, connexin 43 (Cx43) expression and gap-junctional coupling. ZNS led to the reduction of glial viability by only 100 µg/ml under physiological conditions. By contrast, TGB revealed toxic effects with a significant, concentration-dependent reduction of glial viability under physiological and pathological conditions. After the incubation of M30 co-cultures with 20 µg/ml TGB, the microglial activation was significantly decreased and resting microglia slightly increased, suggesting possible anti-inflammatory features of TGB under inflammatory conditions. Otherwise, ZNS caused no significant changes of microglial phenotypes. The gap-junctional coupling was significantly decreased after the incubation of M5 co-cultures with 20 and 50 µg/ml TGB, which can be related to its anti-epileptic activity under noninflammatory conditions. A significant decrease of Cx43 expression and cell–cell coupling was found after the incubation of M30 co-cultures with 10 µg/ml ZNS, suggesting additional anti-seizure effects of ZNS with the disruption of glial gap-junctional communication under inflammatory conditions. TGB and ZNS differentially regulated the glial properties. Developing novel ASMs targeting glial cells may have future potential as an "add-on" therapy to classical ASMs targeting neurons. [ABSTRACT FROM AUTHOR]

Tiagabine has been associated with reports of status epilepticus as well as encephalopathy, even when used within therapeutic doses. Vagus nerve stimulation (VNS) has been used successfully to reduce seizure frequency in the outpatient setting as well as in the acute setting of status epilepticus. It is also theorized to reduce cortical synchronization. We present a case of a patient on adjunctive tiagabine therapy who developed sudden onset encephalopathy and rhythmic delta activity soon after vagus nerve stimulation was turned off in preparation for magnetic resonance imaging. The bilateral rhythmic delta activity significantly reduced in burden after VNS was turned back on and encephalopathy also gradually improved to baseline. We hypothesize that vagus nerve stimulation successfully interrupted diffuse hypersynchrony, in the form of bilateral rhythmic delta activity, caused by tiagabine. To our knowledge, this is the first report of such a phenomenon.

HRMS (ESI): I m i / I z i [M + H] SP + sp calcd for C SB 16 sb H SB 17 sb Br SB 2 sb O SB 2 sb : 398.9590; found: 398.9599. HRMS (ESI): I m i / I z i [M + H] SP + sp calcd for C SB 30 sb H SB 31 sb NO SB 2 sb S SB 2 sb : 502.1869; found: 502.1872. Naphthalen-1-yl 2-(3-(Benzyloxy)propyl)oxirane-2-carboxylate (8) Compound B 15 b (4.1 g, 15 mmol) was dissolved in a mixed solution of CF SB 3 sb CO SB 2 sb H (15 mL) and CH SB 2 sb Cl SB 2 sb (30 mL). Then the crude product was dissolved in dry CH SB 2 sb Cl SB 2 sb (30 mL) at 0 °C, Ph SB 3 sb P (1.8 g, 7 mmol) and CBr SB 4 sb (2.3 g, 7 mmol) were then added. [Extracted from the article]

Hyperbaric oxygen (HBO2) inhibits GABAergic neurotransmission in the brain, which can lead to the development of seizure disorders known as oxygen epilepsy. HBO2-induced deficiency in GABAergic transmission, resulting from a decrease in the level of synaptic GABA, can be compensated by the inhibition of neuronal and glial GABA transporters (GAT). In the present study, we compared the anticonvulsant efficacy of two types of GAT inhibitors—tiagabine (TGB), a GAT-1 inhibitor, and SNAP 5114, a GAT-2/3 inhibitor. The anticonvulsant effects were assessed after drug administration into the lateral cerebral ventricle of rats 30 min before the onset of HBO2 exposure at a pressure of 5 ATA. In separate experiments, GABA concentration in the rat striatum was measured while breathing HBO2 at 5 ATA after GAT inhibition with TGB or SNAP 5114. GAT-1 or GAT-2/3 inhibition prevented the development of oxygen epilepsy in rats. TGB proved to be more effective in preventing oxygen seizures compared to SNAP 5114. TGB + SNAP 5114 co-application elicited an additive anticonvulsant effect. Oxygen seizures arose when the brain GABA content was reduced by 30–40% of the baseline level. GAT-1 inhibition with TGB increased extracellular GABA content 2.9-fold and with SNAP 5114 1.7-fold. Thus, GAT-1 and GAT-2/3 inhibition elevated GABA to a level sufficient to restore its inhibitory neurotransmission impaired in HBO2, and prevented the development of hyperbaric oxygen seizures. [ABSTRACT FROM AUTHOR]

Tiagabine (Tia), a new-generation antiseizure drug that mimics the GABAergic signaling by inhibiting GABA transporter type-1, is the least studied molecule in chronic epilepsy models with comorbid neurobehavioral and neuroinflammatory parameters. Therefore, the current study investigated the effects of Tia in a real-time manner on electroencephalographic (EEG) activity, behavioral manifestations and mRNA expression in pentylenetetrazole (PTZ)-kindled mice. Male BALB/c mice were treated with tiagabine (0.5, 1 and 2 mg/kg) for 21 days with simultaneous PTZ (40 mg/kg) injection every other day for a total of 11 injections and monitored for seizure progression with synchronized validation through EEG recordings from cortical electrodes. The post-kindling protection from anxiety and memory deficit was verified by a battery of behavioral experiments. Isolated brains were evaluated for oxidative alterations and real-time changes in mRNA expression for BDNF/TrkB, GAT-1 and GAT-3 as well as neuroinflammatory markers. Experimental results revealed that Tia at the dose of 2 mg/kg maximally inhibited the development of full bloom seizure and reduced epileptic spike discharges from the cortex. Furthermore, Tia dose-dependently exerted the anxiolytic effects and protected from PTZ-evoked cognitive impairment. Tia reduced lipid peroxidation and increased superoxide dismutase and glutathione levels in the brain via augmentation of GABAergic modulation. PTZ-induced upregulated BDNF/TrkB signaling and pro-inflammatory cytokines were mitigated by Tia with upregulation of GAT-1 and GAT-3 transporters in whole brains. In conclusion, the observed effects of Tia might have resulted from reduced oxidative stress, BDNF/TrkB modulation and mitigated neuroinflammatory markers expression leading to reduced epileptogenesis and improved epilepsy-related neuropsychiatric effects.

Tiagabine has been associated with reports of status epilepticus as well as encephalopathy, even when used within therapeutic doses. Vagus nerve stimulation (VNS) has been used successfully to reduce seizure frequency in the outpatient setting as well as in the acute setting of status epilepticus. It is also theorized to reduce cortical synchronization. We present a case of a patient on adjunctive tiagabine therapy who developed sudden onset encephalopathy and rhythmic delta activity soon after vagus nerve stimulation was turned off in preparation for magnetic resonance imaging. The bilateral rhythmic delta activity significantly reduced in burden after VNS was turned back on and encephalopathy also gradually improved to baseline. We hypothesize that vagus nerve stimulation successfully interrupted diffuse hypersynchrony, in the form of bilateral rhythmic delta activity, caused by tiagabine. To our knowledge, this is the first report of such a phenomenon., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier Inc.)

The aim of the present study was to investigate various aspects of tiagabine (TGB) effectiveness in Bulgarian patients with drug-resistant epilepsy. This open, prospective study recruited the patients with epilepsy attending the Clinic of Neurology at the University Hospital of Plovdiv, Bulgaria. The patients completed diaries about the seizure frequency, severity, and adverse events. There were regular documented visits at 3 or 6 months during the first year of treatment with TGB and at 6 months or 1 year afterwards, with dynamic assessment of seizure frequency, severity, adverse events, and EEG recordings. TGB was applied as an add-on treatment in 43 patients (24 males, mean age 39 years). There was relatively mild and transient dynamic improvement of seizure severity, satisfactory seizure frequency reduction in 32.6% of participants, stable mean seizure frequency reduction (40-50%) from month 6 to month 24 and a stable response rate (52.3-50%) during the same period. New seizure types (myoclonic, myoclonic-atonic) occurred in 2 patients. The final clinical efficacy was higher in patients with initial monotherapy. There were adverse events (dizziness/vertigo, sedation, memory impairment, loss of appetite and weight, confusion, psychosis, insomnia, transient diplopia, lymphadenomegaly, rash, nausea, depression, anxiety, tremor of hands, unstable gait, legs edema, thrombocytopenia, cervical muscles tightening) in 26.19% of patients. In conclusion, TGB treatment is associated with low and transient improvement of seizure severity, good and stable improvement of seizure frequency, possible worsening of seizure control, possible appearance of new seizure types, and acceptable safety and tolerability.

The recently obtained cryo-electron microscopy structure (PDB code: 7SK2) of the human γ-aminobutyric acid transporter type 1 (hGAT-1) in complex with the antiepileptic drug, tiagabine, revealed a rather unexpected binding mode for this inhibitor in an inward-open state of the transporter. The simultaneously released crystal structures of the modified dopamine transporter with mutations mimicking hGAT-1 indicated an alternative binding mode for the tiagabine analogues that were found to block the transporter in an outward-open state, which is more consistent with the results of previous biological and molecular modeling studies. In view of the above discrepancies, our study compares different hypothetical tiagabine binding modes using classical and accelerated molecular dynamics simulations, as well as MM-GBSA free binding energy (dG) calculations. The results indicate that the most stable and energetically favorable binding mode of tiagabine is the one where the nipecotic acid fragment is located in the main binding site (S1) and the aromatic rings are arranged within the S2 site of the hGAT-1 transporter in an outward-open state, confirming the previous molecular modelling findings. The position of tiagabine bound to hGAT-1 in an inward-open state, partially within the intracellular release pathway, was significantly less stable and the dG values calculated for this complex were higher. Furthermore, analysis of the cryo-electron map for the 7SK2 structure shows that the model does not appear to fit into the map optimally at the ligand binding site. These findings suggest that the position of tiagabine found in the 7SK2 structure is rather ambiguous and requires further experimental verification. The identification of the main, high-affinity binding site for tiagabine and its analogues is crucial for the future rational design of the GABA transporter inhibitors.

The proposed study is the development of the RP-HPLC method for simultaneous quantification of tiagabine (TBN) and its related substance - A (TBN RS-A). The method was validated for its applicability both in bulk drug and tablet dosage form. For an isocratic elution, a mobile phase comprising of methanol: 0.1 mM acetate buffer mixture (65:45 v/v, pH 5.6) was used at 1 ml/min flow rate and ProntoSIL ODS C18 column (250mm × 4.5 mm; 5μm) column. At 240 nm as max, sharp peaks of TBN RS-A and TBN were observed at 3.7 and 5.2 min respectively. As per the ICH guidelines, the method was validated. Validation of the method was done as per the guidelines of ICH. Linear regression for the calibration curve was carried out for concentration ranges of 75-450 and 1-6 μg/mL respectively for TBN and TBN RS-A. The respective detection limits (LOQ and LOD) of the TBN and RS-A were found to be (2.014 and 0.032 μg/ml) and (6.103 and 0.098 μg/ml). The method was successfully extended for stability-indicating studies under different stress conditions. [ABSTRACT FROM AUTHOR]

Hyperbaric oxygen (HBO2) inhibits the GABAergic function in the brain, leading to the development of convulsive reactions in the form of paroxysmal discharges on the EEG, as well as movement disorders, in a manner similar to a generalized epileptic seizure. We hypothesize that HBO2-induced deficiency of GABAergic neurotransmission due to suppression of GABA synthesis, can be overcome by blocking GABA clearance from the synaptic cleft and slowing down its enzymatic degradation. The present study aimed to explore the development of seizures in rats at 5 ATA of oxygen pressure after tiagabine-mediated blockade of GABA transporters and vigabatrin-mediated inhibition of GABA-transaminase. The data obtained in this study are as follows: (1) both vigabatrin-mediated inhibition of GABA transaminase and tiagabine-mediated inhibition of GABA transporters prevented the development of seizures in rats at 5 ATA of oxygen pressure; (2) HBO2-induced oxygen seizures arose with a decrease in the brain GABA concentration by 30–40% vs. the basal level; (3) vigabatrin-mediated inhibition of GABA transaminase prevented a decrease in the rat striatum GABA level at 5 ATA of oxygen pressure. Thus, a slowdown in synaptic GABA clearance or attenuation of enzymatic GABA degradation can compensate an HBO2-induced reduction in GABA synthesis, as well as raise the GABA concentration to a level sufficient for the restoration of GABAergic function, preventing thereby the development of convulsive syndrome. [ABSTRACT FROM AUTHOR]

The external globus pallidus (GP) is a GABAergic node involved in motor control regulation and coordinates firing and synchronization in the basal ganglia-thalamic-cortical network through inputs and electrical activity. In Parkinson's disease, high GABA levels alter electrical activity in the GP and contribute to motor symptoms. Under normal conditions, GABA levels are regulated by GABA transporters (GATs). GAT type 1 (GAT-1) is highly expressed in the GP, and pharmacological blockade of GAT-1 increases the duration of currents mediated by GABA A receptors and induces tonic inhibition. The functional contribution of the pathway between the GP and the reticular thalamic nucleus (RTn) is unknown. This pathway is important since the RTn controls the flow of information between the thalamus and cortex, suggesting that it contributes to cortical dynamics. In this work, we investigated the effect of increased GABA levels on electrical activity in the RTn by obtaining single-unit extracellular recordings from anesthetized rats and on the motor cortex (MCx) by corticography. Our results show that high GABA levels increase the spontaneous activity rate of RTn neurons and desynchronize oscillations in the beta frequency band in the MCx. Our findings provide evidence that the GP exerts tonic control over RTn activity through the GP-reticular pathway and functionally contributes to cortical oscillation dynamics. Keywords: Motor control, Globus pallidus, Beta band, Tonic inhibition, Reticular thalamic nucleus, Synchronization, Author(s): Nelson Villalobos[sup.1,2], Salvador Almazán-Alvarado[sup.3] and Victor Manuel Magdaleno-Madrigal[sup.3,4] Introduction The reticular thalamic nucleus (RTn) articulates oscillations in large neuronal assemblies [15, 31]. GABAergic neurons in the RTn receive collaterals [...]

Posttraumatic stress disorder (PTSD) has been associated with abnormal regulation of the hypothalamic-pituitary-adrenal gland axis (HPA). Women demonstrate a more robust HPA response and are twice as likely to develop PTSD than men. The role of sex hormones in PTSD remains unclear. We investigated whether post-trauma chronic treatment with the GABA-ergic agent tiagabine and dopamine-mimetic pramipexole affected the behavioral outcome and plasma levels of corticosterone, testosterone, or 17β-estradiol in female and male mice. These medications were investigated due to their potential capacity to restore GABA-ergic and dopaminergic deficits in PTSD. Animals were exposed to a single prolonged stress procedure (mSPS). Following 13 days treatment with tiagabine (10 mg/kg) or pramipexole (1 mg/kg) once daily, the PTSD-like phenotype was examined in the fear conditioning paradigm. Plasma hormones were measured almost immediately following the conditioned fear assessment. We report that the exposure to mSPS equally enhanced conditioned fear in both sexes. However, while males demonstrated decreased plasma corticosterone, its increase was observed in females. Trauma elevated plasma testosterone in both sexes, but it had no significant effects on 17β-estradiol. Behavioral manifestation of trauma was reduced by pramipexole in both sexes and by tiagabine in females only. While neither compound affected corticosterone in stressed animals, testosterone levels were further enhanced by tiagabine in females. This study shows sex-dependent efficacy of tiagabine but not pramipexole in a mouse model of PTSD-like symptoms and a failure of steroid hormones’ levels to predict PTSD treatment efficacy.

Posttraumatic stress disorder (PTSD) has been associated with abnormal regulation of the hypothalamic-pituitary-adrenal gland axis (HPA). Women demonstrate a more robust HPA response and are twice as likely to develop PTSD than men. The role of sex hormones in PTSD remains unclear. We investigated whether post-trauma chronic treatment with the GABA-ergic agent tiagabine and dopamine-mimetic pramipexole affected the behavioral outcome and plasma levels of corticosterone, testosterone, or 17β-estradiol in female and male mice. These medications were investigated due to their potential capacity to restore GABA-ergic and dopaminergic deficits in PTSD. Animals were exposed to a single prolonged stress procedure (mSPS). Following 13 days treatment with tiagabine (10 mg/kg) or pramipexole (1 mg/kg) once daily, the PTSD-like phenotype was examined in the fear conditioning paradigm. Plasma hormones were measured almost immediately following the conditioned fear assessment. We report that the exposure to mSPS equally enhanced conditioned fear in both sexes. However, while males demonstrated decreased plasma corticosterone, its increase was observed in females. Trauma elevated plasma testosterone in both sexes, but it had no significant effects on 17β-estradiol. Behavioral manifestation of trauma was reduced by pramipexole in both sexes and by tiagabine in females only. While neither compound affected corticosterone in stressed animals, testosterone levels were further enhanced by tiagabine in females. This study shows sex-dependent efficacy of tiagabine but not pramipexole in a mouse model of PTSD-like symptoms and a failure of steroid hormones' levels to predict PTSD treatment efficacy. [ABSTRACT FROM AUTHOR]

Background: Before the deposition of amyloid-beta plaques and the onset of learning memory deficits, patients with Alzheimer's disease (AD) experience olfactory dysfunction, typified by a reduced ability to detect, discriminate, and identify odors. Rodent models of AD, such as the Tg2576 and APP/PS1 mice, also display impaired olfaction, accompanied by aberrant in vivo or in vitro gamma rhythms in the olfactory pathway. However, the mechanistic relationships between the electrophysiological, biochemical and behavioral phenomena remain unclear. Methods: To address the above issues in AD models, we conducted in vivo measurement of local field potential (LFP) with a combination of in vitro electro-olfactogram (EOG), whole-cell patch and field recordings to evaluate oscillatory and synaptic function and pharmacological regulation in the olfactory pathway, particularly in the olfactory bulb (OB). Levels of protein involved in excitation and inhibition of the OB were investigated by western blotting and fluorescence staining, while behavioral studies assessed olfaction and memory function. Results: LFP measurements demonstrated an increase in gamma oscillations in the OB accompanied by altered olfactory behavior in both APP/PS1 and 3xTg mice at 3–5 months old, i.e. an age before the onset of plaque formation. Fewer olfactory sensory neurons (OSNs) and a reduced EOG contributed to a decrease in the excitatory responses of M/T cells, suggesting a decreased ability of M/T cells to trigger interneuron GABA release indicated by altered paired-pulse ratio (PPR), a presynaptic parameter. Postsynaptically, there was a compensatory increase in levels of GABAAR α1 and β3 subunits and subsequent higher amplitude of inhibitory responses. Strikingly, the GABA uptake inhibitor tiagabine (TGB) ameliorated abnormal gamma oscillations and levels of GABAAR subunits, suggesting a potential therapeutic strategy for early AD symptoms. These findings reveal increased gamma oscillations in the OB as a core indicator prior to onset of AD and uncover mechanisms underlying aberrant gamma activity in the OB. Conclusions: This study suggests that the concomitant dysfunction of both olfactory behavior and gamma oscillations have important implications for early AD diagnosis: in particular, awareness of aberrant GABAergic signaling mechanisms might both aid diagnosis and suggest therapeutic strategies for olfactory damage in AD. [ABSTRACT FROM AUTHOR]

Tiagabine is an antiepileptic drug used for the treatment of partial seizures in humans. Recently, this drug has been found useful in several non-epileptic conditions, including anxiety, chronic pain and sleep disorders. Since tachycardia—an impairment of cardiac rhythm due to cardiac ion channel dysfunction—is one of the most commonly reported non-neurological adverse effects of this drug, in the present paper we have undertaken pharmacological and numerical studies to assess a potential cardiovascular risk associated with the use of tiagabine. A chemical interaction of tiagabine with a model of human voltage-gated ion channels (VGICs) is described using the molecular docking method. The obtained in silico results imply that the adverse effects reported so far in the clinical cardiological of tiagabine could not be directly attributed to its interactions with VGICs. This is also confirmed by the results from the isolated organ studies (i.e., calcium entry blocking properties test) and in vivo (electrocardiogram study) assays of the present research. It was found that tachycardia and other tiagabine-induced cardiac complications are not due to a direct effect of this drug on ventricular depolarization and repolarization.

Background The γ-aminobutyric acid (GABA) transporter GAT1 is involved in GABA transport across the biological membrane in and out of the synaptic cleft. The efficiency of this Na+ coupled GABA transport is regulated by an electrochemical gradient, which is directed inward under normal conditions. However, in certain pathophysiological situations, including strong depolarization or an imbalance in ion homeostasis, the GABA influx into the cytoplasm is increased by re-uptake transport mechanism. This mechanism may lead to extra removal of extracellular GABA which results in numerous neurological disorders such as epilepsy. Thus, small molecule inhibitors of GABA re-uptake may enhance GABA activity at the synaptic clefts. Methods In the present study, various GRID-independent molecular descriptor (GRIND) models have been developed to shed light on the 3D structural features of human GAT1 (hGAT1) inhibitors using nipecotic acid and N-diarylalkenyl piperidine analogs. Further, a binding hypothesis has been developed for the selected GAT1 antagonists by molecular docking inside the binding cavity of hGAT1 homology model. Results Our results indicate that two hydrogen bond acceptors, one hydrogen bond donor and one hydrophobic region at certain distances from each other play an important role in achieving high inhibitory potency against hGAT1. Our docking results elucidate the importance of the COOH group in hGAT1 antagonists by considering substitution of the COOH group with an isoxazol ring in compound 37, which subsequently leads to a three order of magnitude decrease in biological activity of 37 (IC50 = 38 µM) as compared to compound 1 (IC50 = 0.040 µM). Discussion Our docking results are strengthened by the structure activity relationship of the data series as well as by GRIND models, thus providing a significant structural basis for understanding the binding of antagonists, which may be useful for guiding the design of hGAT1 inhibitors.

Brain responses to transcranial magnetic stimulation (TMS) recorded by electroencephalography (EEG) are emergent noninvasive markers of neuronal excitability and effective connectivity in humans. However, the underlying physiology of these TMS‐evoked EEG potentials (TEPs) is still heavily underexplored, impeding a broad application of TEPs to study pathology in neuropsychiatric disorders. Here we tested the effects of a single oral dose of three antiepileptic drugs with specific modes of action (carbamazepine, a voltage‐gated sodium channel (VGSC) blocker; brivaracetam, a ligand to the presynaptic vesicle protein VSA2; tiagabine, a gamma‐aminobutyric acid (GABA) reuptake inhibitor) on TEP amplitudes in 15 healthy adults in a double‐blinded randomized placebo‐controlled crossover design. We found that carbamazepine decreased the P25 and P180 TEP components, and brivaracetam the N100 amplitude in the nonstimulated hemisphere, while tiagabine had no effect. Findings corroborate the view that the P25 represents axonal excitability of the corticospinal system, the N100 in the nonstimulated hemisphere propagated activity suppressed by inhibition of presynaptic neurotransmitter release, and the P180 late activity particularly sensitive to VGSC blockade. Pharmaco‐physiological characterization of TEPs will facilitate utilization of TMS‐EEG in neuropsychiatric disorders with altered excitability and/or network connectivity. [ABSTRACT FROM AUTHOR]

Background: The γ-aminobutyric acid (GABA) transporter GAT1 is involved in GABA transport across the biological membrane in and out of the synaptic cleft. The efficiency of this Na+ coupled GABA transport is regulated by an electrochemical gradient, which is directed inward under normal conditions. However, in certain pathophysiological situations, including strong depolarization or an imbalance in ion homeostasis, the GABA influx into the cytoplasm is increased by re-uptake transport mechanism. This mechanism may lead to extra removal of extracellular GABA which results in numerous neurological disorders such as epilepsy. Thus, small molecule inhibitors of GABA re-uptake may enhance GABA activity at the synaptic clefts. Methods: In the present study, various GRID-independent molecular descriptor (GRIND) models have been developed to shed light on the 3D structural features of human GAT1 (hGAT1) inhibitors using nipecotic acid and N-diarylalkenyl piperidine analogs. Further, a binding hypothesis has been developed for the selected GAT1 antagonists by molecular docking inside the binding cavity of hGAT1 homology model. Results: Our results indicate that two hydrogen bond acceptors, one hydrogen bond donor and one hydrophobic region at certain distances from each other play an important role in achieving high inhibitory potency against hGAT1. Our docking results elucidate the importance of the COOH group in hGAT1 antagonists by considering substitution of the COOH group with an isoxazol ring in compound 37, which subsequently leads to a three order of magnitude decrease in biological activity of 37 (IC50 = 38 µM) as compared to compound 1 (IC50 = 0.040 µM). Discussion: Our docking results are strengthened by the structure activity relationship of the data series as well as by GRIND models, thus providing a significant structural basis for understanding the binding of antagonists, which may be useful for guiding the design of hGAT1 inhibitors. [ABSTRACT FROM AUTHOR]