Synergistic Effect of ß-Lapachone and Aminooxyacetic Acid on Central Metabolism in Breast Cancer.

The compound ß-lapachone, a naturally derived naphthoquinone, has been utilized as a potent medicinal nutrient to improve health. Over the last twelve years, numerous reports have demonstrated distinct associations of ß-lapachone and NAD(P)H: quinone oxidoreductase 1 (NQO1) protein in the amelioration of various diseases. Comprehensive research of NQO1 bioactivity has clearly confirmed the tumoricidal effects of ß-lapachone action through NAD+-keresis, in which severe DNA damage from reactive oxygen species (ROS) production triggers a poly-ADP-ribose polymerase-I (PARP1) hyperactivation cascade, culminating in NAD+/ATP depletion. Here, we report a novel combination strategy with aminooxyacetic acid (AOA), an aspartate aminotransferase inhibitor that blocks the malate-aspartate shuttle (MAS) and synergistically enhances the efficacy of ß-lapachone metabolic perturbation in NQO1+ breast cancer. We evaluated metabolic turnover in MDA-MB-231 NQO1+, MDA-MB-231 NQO1-, MDA-MB-468, and T47D cancer cells by measuring the isotopic labeling of metabolites from a [U-13C]glucose tracer. We show that ß-lapachone treatment significantly hampers lactate secretion by ~85% in NQO1+ cells. Our data demonstrate that combinatorial treatment decreases citrate, glutamate, and succinate enrichment by ~14%, ~50%, and ~65%, respectively. Differences in citrate, glutamate, and succinate fractional enrichments indicate synergistic effects on central metabolism based on the coefficient of drug interaction. Metabolic modeling suggests that increased glutamine anaplerosis is protective in the case of MAS inhibition.

Protective Effects of Aminooxyacetic Acid on Colitis Induced in Mice with Dextran Sulfate Sodium.

As a known inhibitor of pyridoxal phosphate-dependent transaminase glutamic-oxaloacetic transaminase 1 (GOT1), aminooxyacetic acid (AOAA) has been pointed out to have potential pharmacological effects in antiepileptic, anticonvulsant, antibacterial, cancer cell proliferation inhibition, and acute myocardial infarction (MI) relief. However, its role in inflammatory bowel disease (IBD) has not been reported. Through the in vivo experiment of dextran sulfate sodium- (DSS-) induced colitis in mice, it was found that AOAA significantly attenuated the symptoms, signs, and pathological changes of colitis. In addition, AOAA treatment prevented gut barrier damages by enhancing the expression of zona occludens- (ZO-) 1, occludin, claudin-1, and E-cadherin and recovering the upregulation of the most abundant intermediate filament protein (vimentin). Moreover, the release of interleukin- (IL-) 1ß, IL-6, and tumour necrosis factor- (TNF-) α was suppressed, yet the level of IL-10 was upregulated by AOAA treatment compared to the model group. Furthermore, it was shown that AOAA administration boosted M2-like phenotype and effectively reduced M1 macrophage phenotype in the lamina propria of mouse colonic epithelium. Similarly, the effect of AOAA was verified in vitro. AOAA effectively inhibited the classically activated M1 macrophage phenotype and proinflammatory cytokine (IL-1ß, TNF-α, and IL-6) expression induced by lipopolysaccharide (LPS) and promoted M2-like phenotype. Collectively, this study reveals for the first time that short-term treatment of AOAA can significantly alleviate DSS-induced acute colitis by regulating intestinal barrier function and macrophage polarization, which provides a theoretical basis for the potential use of AOAA in the treatment of IBD.

Mental retardation in Down syndrome: Two ways to treat.

Mental retardation is a progressive condition in Down syndrome: intelligence starts to decline linearly within the first year. This phenomenon could be related to the overproduction of a toxic compound, hydrogen sulfide. Indeed, a gene located on chromosome 21 controls the production of cystathionine-ß-synthase, an enzyme involved in hydrogen sulfide production in the central nervous system. It has recently been demonstrated that excess cystathionine-ß-synthase levels are needed and sufficient to induce cognitive phenotypes in mouse models of Down syndrome. Thus, two therapeutic options might be used in Down syndrome patients: the use of a specific cystathionine ß-synthase inhibitor and the use of an effective antidote to reduce hydrogen sulfide toxicity. Prenatal treatment of Down syndrome fetuses is also suggested.

Impact of Pharmacological Inhibition of Hydrogen Sulphide Production in the SOD1G93A-ALS Mouse Model.

A number of factors can trigger amyotrophic lateral sclerosis (ALS), although its precise pathogenesis is still uncertain. In a previous study done by us, poisonous liquoral levels of hydrogen sulphide (H2S) in sporadic ALS patients were reported. In the same study very high concentrations of H2S in the cerebral tissues of the familial ALS (fALS) model of the SOD1G93A mouse, were measured. The objective of this study was to test whether decreasing the levels of H2S in the fALS mouse could be beneficial. Amino-oxyacetic acid (AOA)-a systemic dual inhibitor of cystathionine-ß-synthase and cystathionine-γ lyase (two key enzymes in the production of H2S)-was administered to fALS mice. AOA treatment decreased the content of H2S in the cerebral tissues, and the lifespan of female mice increased by approximately ten days, while disease progression in male mice was not affected. The histological evaluation of the spinal cord of the females revealed a significant increase in GFAP positivity and a significant decrease in IBA1 positivity. In conclusion, the results of the study indicate that, in the animal model, the inhibition of H2S production is more effective in females. The findings reinforce the need to adequately consider sex as a relevant factor in ALS.

Metabolic control of TH17 and induced Treg cell balance by an epigenetic mechanism.

Metabolism has been shown to integrate with epigenetics and transcription to modulate cell fate and function. Beyond meeting the bioenergetic and biosynthetic demands of T-cell differentiation, whether metabolism might control T-cell fate by an epigenetic mechanism is unclear. Here, through the discovery and mechanistic characterization of a small molecule, (aminooxy)acetic acid, that reprograms the differentiation of T helper 17 (TH17) cells towards induced regulatory T (iTreg) cells, we show that increased transamination, mainly catalysed by GOT1, leads to increased levels of 2-hydroxyglutarate in differentiating TH17 cells. The accumulation of 2-hydroxyglutarate resulted in hypermethylation of the Foxp3 gene locus and inhibited Foxp3 transcription, which is essential for fate determination towards TH17 cells. Inhibition of the conversion of glutamate to α-ketoglutaric acid prevented the production of 2-hydroxyglutarate, reduced methylation of the Foxp3 gene locus, and increased Foxp3 expression. This consequently blocked the differentiation of TH17 cells by antagonizing the function of transcription factor RORγt and promoted polarization into iTreg cells. Selective inhibition of GOT1 with (aminooxy)acetic acid ameliorated experimental autoimmune encephalomyelitis in a therapeutic mouse model by regulating the balance between TH17 and iTreg cells. Targeting a glutamate-dependent metabolic pathway thus represents a new strategy for developing therapeutic agents against TH17-mediated autoimmune diseases.

Targeting glutamine metabolism and the focal adhesion kinase additively inhibits the mammalian target of the rapamycin pathway in spheroid cancer stem-like properties of ovarian clear cell carcinoma in vitro.

Ovarian cancer is one of the leading causes of death in the world, which is linked to its resistance to chemotherapy. Strategies to overcome chemoresistance have been keenly investigated. Culturing cancer cells in suspension, which results in formation of spheroids, is a more accurate reflection of clinical cancer behavior in vitro than conventional adherent cultures. By performing RNA-seq analysis, we found that the focal adhesion pathway was essential in spheroids. The phosphorylation of focal adhesion kinase (FAK) was increased in spheroids compared to adherent cells, and inhibition of FAK in spheroids resulted in inhibition of the downstream mammalian target of the rapamycin (mTOR) pathway in ovarian clear cell carcinomas. This result also suggested that only using a FAK inhibitor might have limitations because the phosphorylation level of FAK could not be reduced to the level in adherent cells, and it appeared that some combination therapies might be necessary. We previously reported that glutamine and glutamate concentrations were higher in spheroids than adherent cells, and we investigated a synergistic effect targeting glutamine metabolism with FAK inhibition on the mTOR pathway. The combination of AOA, a pan-transaminase inhibitor, and PF 573228, a FAK inhibitor, additively inhibited the mTOR pathway in spheroids from ovarian clear cell carcinomas. Our in vitro study proposed a rationale for the positive and negative effects of using FAK inhibitors in ovarian clear cell carcinomas and suggested that targeting glutamine metabolism could overcome the limitation of FAK inhibitors by additively inhibiting the mTOR pathway.

Effect of the Inhibition of Hydrogen Sulfide Synthesis on Ischemic Injury and Oxidative Stress Biomarkers in a Transient Model of Focal Cerebral Ischemia in Rats.

OBJECTIVE: Hydrogen sulfide (H2S) plays multiple roles in the function of the central nervous system in physiological and pathological conditions, such as cerebral ischemia. Recent studies have reported controversial results about the role of H2S in cerebral ischemia. The aim of this study was to evaluate the effects of amino-oxyacetic acid (AOAA), an inhibitor of H2S synthesis, on ischemic injury in an experimental model of stroke. METHODS: Using laser Doppler monitoring, cerebral ischemia was induced by transient middle cerebral artery occlusion (MCAO) for 1 hour in rats. AOAA (.025, .05, .1, and .5 mmol/kg intraperitoneally [i.p.]) was injected at the beginning of MCAO. Infarct volume, cerebral edema, and activity of antioxidant enzymes were measured using the standard methods 24 hours after ischemia. RESULTS: The administration of AOAA at doses .025, .05, and .1 mmol/kg significantly reduced the infarct volume (P < .001). Furthermore, .025 and .05 mmol/kg of AOAA significantly reduced brain edema and improved the neurological outcome (P < .001). The administration of AOAA did not significantly change the malondialdehyde content, activities of superoxide dismutase, or glutathione peroxidase antioxidant enzymes in the brain tissue (P > .05). CONCLUSION: The results showed that AOAA administered at a low dose has protective effects; however, at higher doses it did not exert any protective effect against cerebral ischemia and even worsened the ischemic injury. This finding suggests that H2S might be both beneficial and harmful in cerebral ischemic injury depending on its concentration in transient model of focal cerebral ischemia.

The therapeutic potential of cystathionine ß-synthetase/hydrogen sulfide inhibition in cancer.

SIGNIFICANCE: Cancer represents a major socioeconomic problem; there is a significant need for novel therapeutic approaches targeting tumor-specific pathways. RECENT ADVANCES: In colorectal and ovarian cancers, an increase in the intratumor production of hydrogen sulfide (H2S) from cystathionine ß-synthase (CBS) plays an important role in promoting the cellular bioenergetics, proliferation, and migration of cancer cells. It also stimulates peritumor angiogenesis inhibition or genetic silencing of CBS exerts antitumor effects both in vitro and in vivo, and potentiates the antitumor efficacy of anticancer therapeutics. CRITICAL ISSUES: Recently published studies are reviewed, implicating CBS overexpression and H2S overproduction in tumor cells as a tumor-growth promoting "bioenergetic fuel" and "survival factor," followed by an overview of the experimental evidence demonstrating the anticancer effect of CBS inhibition. Next, the current state of the art of pharmacological CBS inhibitors is reviewed, with special reference to the complex pharmacological actions of aminooxyacetic acid. Finally, new experimental evidence is presented to reconcile a controversy in the literature regarding the effects of H2S donor on cancer cell proliferation and survival. FUTURE DIRECTIONS: From a basic science standpoint, future directions in the field include the delineation of the molecular mechanism of CBS up-regulation of cancer cells and the delineation of the interactions of H2S with other intracellular pathways of cancer cell metabolism and proliferation. From the translational science standpoint, future directions include the translation of the recently emerging roles of H2S in cancer into human diagnostic and therapeutic approaches.

Therapeutic effect of Yokukansan on social isolation-induced aggressive behavior of zinc-deficient and pair-fed mice.

In patients with dementia including Alzheimer's disease, hallucinations, agitation/aggression and irritability are known to frequently occur and as distressing behavioral and psychological symptoms of dementia (BPSD). On the basis of the evidence on clinical efficacy and safety of Yokukansan, a traditional Japanese herbal medicine, on BPSD, in the present study, Yokukansan was examined in the therapeutic effects on social isolation-induced aggressive behavior of zinc-deficient and pair-fed mice. Yokukansan was p.o. administered for 7 days as a drinking water to isolated mice fed a zinc-deficient diet for 10 days, which exhibited aggressive behavior, and isolated pair-fed mice fed a control diet of the amount consumed by zinc-deficient mice for 10 days, which exhibited aggressive behavior. Aggressive behavior was evaluated by the resident-intruder test. Yokukansan (312 mg/kg/day) attenuated both aggressive behaviors of zinc-deficient and pair-fed mice. Because Yokukansan can suppress abnormal glutamatergic neuron activity, MK-801, an N-methyl-D-aspartate (NMDA) receptor blocker, and aminooxyacetic acid (AOAA), a γ-amino butyric acid (GABA) transaminase blocker, were also examined in the effects on social isolation-induced aggressive behavior. MK-801 (0.1 mg/kg) or AOAA (23 mg/kg) was i.p. injected into isolated aggressive mice. Thirty minutes later, the resident-intruder test was performed to evaluate the effect of the drugs. Both drugs attenuated aggressive behavior of zinc deficient mice, but not that of pair-fed mice. These results suggest that Yokukansan ameliorates social isolation-induced aggressive behavior of zinc-deficient and pair-fed mice through the action against glutamatergic neurotransmitter system and other neurotransmitter systems.

Effects of hydrogen sulfide on a rat model of sepsis-associated encephalopathy.

To investigate the interaction and involvement of sodium hydrosulfide (NaHS), a H(2)S donor, on hippocampus of rats suffering from sepsis-associated encephalopathy, rats were subjected to cecal ligation and puncture (CLP)-induced sepsis. Adult male Sprague-Dawley rats were randomly divided into four groups: Sham group, CLP group, CLP+NaHS group and CLP+aminooxyacetic acid (AOAA, an inhibitor of H(2)S formation) group. The four groups were observed at 3, 6, 9, 12 h after treatment. We examined hippocampal H(2)S synthesis and the expression of cystathionine-ß-synthetase (CBS), a major enzyme involved in the H(2)S synthesis in hippocampus. CBS expression was detected by reverse transcription polymerase chain reaction (RT-PCR). The concentrations of inflammatory cytokines (TNF-α, IL-1ß) were determined in hippocampus by using enzyme-linked immunosorbent assay (ELISA). Neuronal damage was studied by histological examination of hippocampus. In CLP group, H(2)S synthesis was significantly increased in hippocampus compared with sham group and it peaked 3 h after CLP (P<0.05). Sepsis also resulted in a significantly upregulated CBS mRNA in hippocampus. The levels of TNF-α and IL-1ß in the hippocampus were substantially elevated at each time point of measurement (P<0.05), and they also reached a peak value at about 3 h. Administration of NaHS significantly aggravated sepsis-associated hippocampus inflammation, as evidenced by TNF-α and IL-1ß activity and histological changes in hippocampus. In septic rats pretreated with AOAA, sepsis-associated hippocampus inflammation was reduced. It is concluded that the rats subjected to sepsis may suffer from brain injury and elevated pro-inflammatory cytokines are responsible for the process. Furthermore, administration of H(2)S can increase injurious effects and treatment with AOAA can protect the brain from injury.

Targeting aspartate aminotransferase in breast cancer.

INTRODUCTION: Glycolysis is increased in breast adenocarcinoma cells relative to adjacent normal cells in order to produce the ATP and anabolic precursors required for survival, growth and invasion. Glycolysis also serves as a key source of the reduced form of cytoplasmic nicotinamide adenine dinucleotide (NADH) necessary for the shuttling of electrons into mitochondria for electron transport. Lactate dehydrogenase (LDH) regulates glycolytic flux by converting pyruvate to lactate and has been found to be highly expressed in breast tumours. Aspartate aminotransferase (AAT) functions in tandem with malate dehydrogenase to transfer electrons from NADH across the inner mitochondrial membrane. Oxamate is an inhibitor of both LDH and AAT, and we hypothesised that oxamate may disrupt the metabolism and growth of breast adenocarcinoma cells. METHODS: We examined the effects of oxamate and the AAT inhibitor amino oxyacetate (AOA) on 13C-glucose utilisation, oxygen consumption, NADH and ATP in MDA-MB-231 cells. We then determined the effects of oxamate and AOA on normal human mammary epithelial cells and MDA-MB-231 breast adenocarcinoma cell proliferation, and on the growth of MDA-MB-231 cells as tumours in athymic BALB/c female mice. We ectopically expressed AAT in MDA-MB-231 cells and examined the consequences on the cytostatic effects of oxamate. Finally, we examined the effect of AAT-specific siRNA transfection on MDA-MB-231 cell proliferation. RESULTS: We found that oxamate did not attenuate cellular lactate production as predicted by its LDH inhibitory activity, but did have an anti-metabolic effect that was similar to AAT inhibition with AOA. Specifically, we found that oxamate and AOA decreased the flux of 13C-glucose-derived carbons into glutamate and uridine, both products of the mitochondrial tricarboxylic acid cycle, as well as oxygen consumption, a measure of electron transport chain activity. Oxamate and AOA also selectively suppressed the proliferation of MDA-MB-231 cells relative to normal human mammary epithelial cells and decreased the growth of MDA-MB-231 breast tumours in athymic mice. Importantly, we found that ectopic expression of AAT in MDA-MB-231 cells conferred resistance to the anti-proliferative effects of oxamate and that siRNA silencing of AAT decreased MDA-MB-231 cell proliferation. CONCLUSIONS: We conclude that AAT may be a valid molecular target for the development of anti-neoplastic agents.

Gamma-aminobutyric acid and mefloquine-induced seizures in mice.

The role of GABAergic mechanism in the convulsant effect of mefloquine was investigated in mice. Mefloquine dose dependently induced tonic seizures in mice. Aminooxyacetic acid, diaminobutyric acid and muscimol significantly protected mice against mefloquine-induced seizures by significantly delaying the onset and decreasing the incidence of the seizures. Bicuculline and picrotoxin significantly enhanced the seizure producing effect of mefloquine and also significantly antagonised the protective effect of muscimol against the seizures. Phenobarbitone and diazepam effectively protected mice against mefloquine-induced seizures. Phenytoin did not alter mefloquine-induced seizures. These data indicate that GABA mechanisms might be involved in seizures produced by mefloquine in mice.

Aminooxyacetic acid-induced accumulation of GABA enhances clonidine hypotension.

The effect of 2-oxoglutarate aminotransferase inhibitor, aminooxyacetic acid (AOAA) on hypotension induced by clonidine in spontaneously hypertensive rats (SHR) was examined. AOAA given 15 min before clonidine significantly intensified clonidine--induced reduction of blood pressure. This effect reached its maximum within 120 min after AOAA administration, when AOAA itself had no influence on blood pressure. Our data suggest that the activation of functional state of GABAergic system by GABA accumulation potentiates clonidine hypotension.

The synergistic protective effect of propranolol & aminooxyacetic acid against picrotoxin-induced myoclonus in rats.

The effect of propranolol was assessed against myoclonus induced by picrotoxin (a known GABA antagonist) in a dose of 3 mg/kg and allylglycine (the inhibitor of GABA synthesis and release) in a dose of 150 mg/kg. A dose-dependent (0.5-2 mg/kg) protective effect was found against both models. Pretreatment of rats with a GABA-reducing dose (100 mg/kg, nonmyoclonic) of allylglycine produced no change in the effect of propranolol against picrotoxin-induced myoclonus. Propranolol thus inhibited myoclonic responses when both the receptor activity and the functional pool of GABA were impaired, suggesting that it produces as antimyoclonic action without the involvement of GABA. However, the drug seems to show a synergistic action with GABA-ergic agents, as greater protection was observed in rats treated concurrently with propranolol and amino-oxyacetic acid, an inhibitor of GABA degradation.

Evaluation of amino-oxyacetic acid as a palliative in tinnitus.

Amino-oxyacetic acid (AOAA) was evaluated as a palliative in tinnitus. Sixty-six patients with tinnitus presumed to be of cochlear origin were given either a placebo or 75 mg of AOAA four times a day for 1 week. Response was evaluated by both audiometric measurement of tinnitus loudness and subjective rating by patients of change or no change in tinnitus severity. Because loudness measurements and self-rating have not been shown to be independent, and since the aim of clinical treatment of tinnitus is the alleviation of subjective distress, greater weight was given to the patient's self-rating. A total of 21% of all patients reported a subjective decrease in tinnitus severity, usually within 3 to 4 days after the start of AOAA use. Patients with tinnitus caused by presbycusis or Meniere's disease were the most likely to respond to AOAA treatment with a reduction in tinnitus severity, whereas those with drug-induced tinnitus were the least likely to respond. Nausea and dysequilibrium were the most common side effects of AOAA use. Of the 21% of patients who responded to AOAA, 71% developed some type of side effect. Amino-oxyacetic acid produces a reduction in the severity of tinnitus in about 20% of patients; however, the incidence of side effects makes the drug unacceptable for clinical use.

The superiority of the Goodwin procedure over the traditional procedure in measuring the loudness level of tinnitus.

The results of two procedures for measuring the loudness level of tinnitus will be presented. The traditional procedure yielded significantly smaller loudness matches, when expressed in decibel sensation level (i.e., dB SL), than did the Goodwin procedure. The Goodwin procedure is more sensitive to pharmacologically induced changes in tinnitus loudness than is the traditional procedure. The Goodwin method correlates well with changes in patient's subjective rating of tinnitus severity. The Goodwin match has a larger reliability coefficient. Nonlinear correlation also indicates that the Goodwin procedure is superior to the traditional method.

Synergistic anticonvulsant action of diazepam & clonazepam with amino-oxyacetic acid against isoniazid-induced convulsions in rats.

The protective effect of two benzodiazepine compounds, diazepam and clonazepam was tested against isoniazid (INH)- induced convulsions in rats pretreated with the gamma-amino-butyric acid (GABA) transaminase inhibitor viz., aminooxyacetic acid (AOAA), and the result was compared with that produced by the two drugs independently. Rats treated 6 h and not 30 min previously with AOAA showed a dose-dependent inhibition of INH-induced convulsions. In these animals both diazepam and clonazepam showed a greater protective effect than that produced by them alone. It is suggested from these findings that, even if their anticonvulsant mechanisms are distinct, with or without the involvement of GABA, AOAA and the benzodiazepine compounds seem to act synergistically against INH-induced convulsions.

[Experimental study of the antiepileptic activity of fenibut and its combinations with sodium valproate and aminooxyacetic acid]. / Eksperimental'noe izuchenie protivoépileticheskoi aktivnosti fenibuta i ego kombinatsii s val'proatom natriia i aminooksiuksusnoi kislotoi.

The antiepileptic activity of GABA-mimetics (phenibut, sodium valproate and aminooxyacetic acid/AOAA/) was studied in experiments on the model of hippocampal penicillin-induced epilepsy in rats. The effects of the drugs were studied in experiments with a mirror epileptogenic focus which forms in the hippocampus contralateral to the penicillin-damaged hippocampus. All the drugs suppressed the activity of the epileptogenic focus after injections in the focus region. At systemic administration of the drugs the antiepileptic activity was found only with sodium valproate and AOAA. Phenibut enhanced the antiepileptic effect of sodium valproate and the toxic effects of AOAA at parenteral administration.

Role of the substantia nigra in GABA-mediated anticonvulsant actions.

The relationship between cerebral GABA content and susceptibility to seizures is addressed from the point of view of specific brain loci at which GABA synapses may control convulsive activity. The substantia nigra (SN) has been identified as a critical site at which GABA-agonist drugs act to reduce susceptibility to a number of types of experimentally induced generalized seizures. Moreover, the ability of GABA-elevating agents to protect against seizures in the maximal electroshock model is directly correlated with increases in GABA specifically in the nerve-terminal compartment of SN. Studies with 2-deoxyglucose indicate that a marked increase in metabolic activity in SN is a common feature of several types of generalized seizures; it is possible that some of this increased activity is associated with GABAergic nerve terminals that become activated in an attempt to suppress seizure spread. Because GABA has been shown to inhibit nigral efferents, it is likely that GABA terminals inhibit nigral projections that are permissive or facilitative to seizure propagation. In support of this, bilateral destruction of SN attenuated clonic and tonic chemoconvulsant and electroshock seizures. Other treatments capable of reducing nigral output, namely opiate agonists (morphine and D-Ala-Met-enkephalin), and substance P antagonist analogs, were also found to have anticonvulsant effects when applied bilaterally into SN. Thus, the seizure-facilitating nigral efferents may be subject to inhibition by both GABA and opiates and may normally be driven by substance P. Of the various outputs from SN, the GABAergic projections to thalamus, reticular formation and/or superior colliculus are most likely responsible for influencing seizure propagation. Experimental evidence does not indicate a significant role of pars compacta nigrostriatal dopamine neurons for controlling the various types of seizures subject to nigral influence. We propose that the inhibition of the GABAergic outputs from SN pars reticulata can suppress the progression of seizure discharge through circuits involving the target areas of these outputs. Because chemical or electrical stimulation of SN does not initiate convulsions, it appears that seizure activity generated elsewhere in the brain may be amplified or sustained by activity in these nigral outputs.