Regulation of GABAergic inputs to CA1 pyramidal neurons by nicotinic receptors and kynurenic acid

Kynurenine, Kynurenic Acid, Quinolinic Acid and Interleukin-6 Levels in the Serum of Patients with Autism Spectrum Disorder

Background and Objectives: It is known that inflammatory processes play a role in the pathogenesis of autism spectrum disorder (ASD). It is also reported that immune activation induces the kynurenine pathway (KP), as known as the tryptophan destruction pathway. In our study, we aimed to investigate whether the serum levels of KP products and interleukin (IL)-6 activating indolamine 2-3 dioxygenase (IDO) enzyme are different in healthy developing children and children with ASD. Materials and Methods: Forty-three ASD children aged 2-9 were included in this study. Forty-two healthy developing children, similar to the patient group in terms of age and gender, were selected as the control group. Serum levels of kynurenic acid, kynurenine, quinolinic acid and IL-6 were analyzed using the ELISA method. ASD severity was evaluated with the Autism Behavior Checklist (ABC). Results: The mean age of children with ASD was 42.4 ± 20.5 months, and that of healthy controls was 48.1 ± 15.8 months. While the serum levels of kynurenic acid, kynurenine and interleukin-6 were higher in the group with ASD (p < 0.05), there was no significant difference (p > 0.05) in terms of the quinolinic acid level. There was no significant difference between the ABC total and subscale scores of children with ASD and biochemical parameters (p > 0.05). Conclusions: We conclude that these biomarkers must be measured in all ASD cases. They may be important for the diagnosis of ASD.

Targeting Members of the Chemokine Family as a Novel Approach to Treating Neuropathic Pain

Neuropathic pain is a debilitating condition that affects millions of people worldwide. Numerous studies indicate that this type of pain is a chronic condition with a complex mechanism that tends to worsen over time, leading to a significant deterioration in patients' quality of life and issues like depression, disability, and disturbed sleep. Presently used analgesics are not effective enough in neuropathy treatment and may cause many side effects due to the high doses needed. In recent years, many researchers have pointed to the important role of chemokines not only in the development and maintenance of neuropathy but also in the effectiveness of analgesic drugs. Currently, approximately 50 chemokines are known to act through 20 different seven-transmembrane G-protein-coupled receptors located on the surface of neuronal, glial, and immune cells. Data from recent years clearly indicate that more chemokines than initially thought (CCL1/2/3/5/7/8/9/11, CXCL3/9/10/12/13/14/17; XCL1, CX3CL1) have pronociceptive properties; therefore, blocking their action by using neutralizing antibodies, inhibiting their synthesis, or blocking their receptors brings neuropathic pain relief. Several of them (CCL1/2/3/7/9/XCL1) have been shown to be able to reduce opioid drug effectiveness in neuropathy, and neutralizing antibodies against them can restore morphine and/or buprenorphine analgesia. The latest research provides irrefutable evidence that chemokine receptors are promising targets for pharmacotherapy; chemokine receptor antagonists can relieve pain of different etiologies, and most of them are able to enhance opioid analgesia, for example, the blockade of CCR1 (J113863), CCR2 (RS504393), CCR3 (SB328437), CCR4 (C021), CCR5 (maraviroc/AZD5672/TAK-220), CXCR2 (NVPCXCR220/SB225002), CXCR3 (NBI-74330/AMG487), CXCR4 (AMD3100/AMD3465), and XCR1 (vMIP-II). Recent research has shown that multitarget antagonists of chemokine receptors, such as CCR2/5 (cenicriviroc), CXCR1/2 (reparixin), and CCR2/CCR5/CCR8 (RAP-103), are also very effective painkillers. A multidirectional strategy based on the modulation of neuronal-glial-immune interactions by changing the activity of the chemokine family can significantly improve the quality of life of patients suffering from neuropathic pain. However, members of the chemokine family are still underestimated pharmacological targets for pain treatment. In this article, we review the literature and provide new insights into the role of chemokines and their receptors in neuropathic pain.

Kynurenine pathway abnormalities are state-specific but not diagnosis-specific in schizophrenia and bipolar disorder

Schizophrenia (SCZ) and bipolar disorder (BD) are associated with immunological dysfunctions that have been hypothesized to lead to clinical symptomatology in particular through kynurenine pathway abnormalities. The aim of this study was thus to investigate the impact of serum kynurenine metabolite levels on diagnosis, clinical state, symptom severity and clinical course in a large French transdiagnostic cohort of SCZ and BD patients. Four patient groups (total n = 507) were included in a cross-sectional observational study: 1) hospitalized acute bipolar patients (n = 205); 2) stable bipolar outpatients (n = 116); 3) hospitalized acute schizophrenia patients (n = 111) and 4) stable schizophrenia outpatients (n = 75), in addition to healthy controls (HC) (n = 185). The quantitative determination of serum kynurenine metabolites was performed using liquid chromatography-tandem mass spectrometry. Kynurenine levels were lower in all patients combined compared to HC while ANCOVA analyses did not reveal inter-diagnostic difference between SCZ and BD. Interestingly, hospitalized patients of both diagnostic groups combined displayed significantly lower kynurenine levels than stabilized outpatients. Psychotic symptoms were associated with lower quinaldic acid (F = 9.18, p=<.001), which is KAT-driven, whereas a longer duration of illness contributed to abnormalities in tryptophan (F = 5.41, p = .023), kynurenine (F = 16.93, p=<.001), xanthurenic acid (F = 9.34, p = .002), quinolinic acid (F = 9.18, p = .003) and picolinic acid (F = 4.15, p = .043), metabolized through the KMO-branch. These data confirm illness state rather than diagnosis to drive KP alterations in SCZ and BD. Lower levels of KP metabolites can thus be viewed as a transdiagnostic feature of SCZ and BD, independently associated with acute symptomatology and a longer duration of illness. Quinaldic acid has seldomly been investigated by previous studies and appears an important state marker in SCZ and BD. As serum samples are used in this study, it is not possible to extrapolate these findings to the brain.

The tryptophan catabolite or kynurenine pathway in schizophrenia: meta-analysis reveals dissociations between central, serum, and plasma compartments

The tryptophan catabolite (TRYCAT) pathway is implicated in the pathophysiology of schizophrenia (SCZ) since the rate-limiting enzyme indoleamine-dioxygenase (IDO) may be induced by inflammatory and oxidative stress mediators. This systematic review searched PubMed, Web of Science, and Google Scholar for papers published from inception until August 2021 and meta-analyzed the association between SCZ and TRYCATs in the central nervous system (CNS) and peripheral blood. We included 61 studies comprising 2813 patients and 2948 healthy controls. In the CNS we found a significant (p < 0.001) increase in the kynurenine/tryptophan (KYN/TRP) (standardized mean difference, SMD = 0.769, 95% confidence interval, CI: 0.456; 1.082) and kynurenic acid (KA)/KYN + TRP (SMD = 0.697, CI: 0.478-0.917) ratios, KA (SMD = 0.646, CI: 0.422; 0.909) and KYN (SMD = 1.238; CI: 0.590; 1.886), while the 3OH-kynurenine (3HK) + KYN-3-monooxygenase (KMO)/KYN ratio was significantly reduced (SMD = -1.089, CI: -1.682; -0.496). There were significant differences between KYN/TRP, (KYN + KA)/TRP, (3HK + KMO)/KYN, KA, and KYN levels among the CNS and peripheral blood, and among serum and plasma KYN. The only useful peripheral marker of CNS TRYCATs findings was the increased KYN/TRP ratio in serum (SMD = 0.211, CI: 0.056; 0.366, p = 0.007), but not in plasma. There was no significant increase in a neurotoxic composite score based on KYN, 3HK, and picolinic, xanthurenic, and quinolinic acid. SCZ is accompanied by increased IDO activity in the CNS and serum, and reduced KMO activity and a shift towards KA production in the CNS. This CNS TRYCATs profile indicates neuroprotective, negative immunoregulatory and anti-inflammatory effects. Peripheral blood levels of TRYCATs are dissociated from CNS findings except for a modest increase in serum IDO activity.

Morphological and biochemical repercussions of Toxoplasma gondii infection in a 3D human brain neurospheres model

Background

Toxoplasmosis is caused by the parasite Toxoplasma gondii that can infect the central nervous system (CNS), promoting neuroinflammation, neuronal loss, neurotransmitter imbalance and behavioral alterations. T. gondii infection is also related to neuropsychiatric disorders such as schizophrenia. The pathogenicity and inflammatory response in rodents are different to the case of humans, compromising the correlation between the behavioral alterations and physiological modifications observed in the disease. In the present work we used BrainSpheres, a 3D CNS model derived from human pluripotent stem cells (iPSC), to investigate the morphological and biochemical repercussions of T. gondii infection in human neural cells.

Methods

We evaluated T. gondii ME49 strain proliferation and cyst formation in both 2D cultured human neural cells and BrainSpheres. Aspects of cell morphology, ultrastructure, viability, gene expression of neural phenotype markers, as well as secretion of inflammatory mediators were evaluated for 2 and 4 weeks post infection in BrainSpheres.

Results

T. gondii can infect BrainSpheres, proliferating and inducing cysts formation, neural cell death, alteration in neural gene expression and triggering the release of several inflammatory mediators.

Conclusions

BrainSpheres reproduce many aspects of T. gondii infection in human CNS, constituting a useful model to study the neurotoxicity and neuroinflammation mediated by the parasite. In addition, these data could be important for future studies aiming at better understanding possible correlations between psychiatric disorders and human CNS infection with T. gondii.

•

T. gondii infects, proliferates and induce cysts formation in neurospheres.

•

T. gondii infection induces neural cell death in neurospheres.

•

T. gondii infection promotes alteration in neural gene expression in neurospheres.

•

T. gondii infection promotes release of inflammatory mediators in neurospheres.

Neuroinflammation and the Kynurenine Pathway in CNS Disease: Molecular Mechanisms and Therapeutic Implications

Diseases of the central nervous system (CNS) remain a significant health, social and economic problem around the globe. The development of therapeutic strategies for CNS conditions has suffered due to a poor understanding of the underlying pathologies that manifest them. Understanding common etiological origins at the cellular and molecular level is essential to enhance the development of efficacious and targeted treatment options. Over the years, neuroinflammation has been posited as a common link between multiple neurological, neurodegenerative and neuropsychiatric disorders. Processes that precipitate neuroinflammatory conditions including genetics, infections, physical injury and psychosocial factors, like stress and trauma, closely link dysregulation in kynurenine pathway (KP) of tryptophan metabolism as a possible pathophysiological factor that 'fuel the fire' in CNS diseases. In this study, we aim to review emerging evidence that provide mechanistic insights between different CNS disorders, neuroinflammation and the KP. We provide a thorough overview of the different branches of the KP pertinent to CNS disease pathology that have therapeutic implications for the development of selected and efficacious treatment strategies.

Relationships and Interactions between Ionotropic Glutamate Receptors and Nicotinic Receptors in the CNS

Although ionotropic glutamate receptors and nicotinic receptors for acetylcholine (ACh) have usually been studied separately, they are often co-localized and functionally inter-dependent. The objective of this review is to survey the evidence for interactions between the two receptor families and the mechanisms underlying them. These include the mutual regulation of subunit expression, which change the NMDA:AMPA response balance, and the existence of multi-functional receptor complexes which make it difficult to distinguish between individual receptor sites, especially in vivo. This is followed by analysis of the functional relationships between the receptors from work on transmitter release, cellular electrophysiology and aspects of behavior where these can contribute to understanding receptor interactions. It is clear that nicotinic receptors (nAChRs) on axonal terminals directly regulate the release of glutamate and other neurotransmitters, α7-nAChRs generally promoting release. Hence, α7-nAChR responses will be prevented not only by a nicotinic antagonist, but also by compounds blocking the indirectly activated glutamate receptors. This accounts for the apparent anticholinergic activity of some glutamate antagonists, including the endogenous antagonist kynurenic acid. The activation of presynaptic nAChRs is by the ambient levels of ACh released from pre-terminal synapses, varicosities and glial cells, acting as a 'volume neurotransmitter' on synaptic and extrasynaptic sites. In addition, ACh and glutamate are released as CNS co-transmitters, including 'cholinergic' synapses onto spinal Renshaw cells. It is concluded that ACh should be viewed primarily as a modulator of glutamatergic neurotransmission by regulating the release of glutamate presynaptically, and the location, subunit composition, subtype balance and sensitivity of glutamate receptors, and not primarily as a classical fast neurotransmitter. These conclusions and caveats should aid clarification of the sites of action of glutamate and nicotinic receptor ligands in the search for new centrally-acting drugs.

The role of anthranilic acid in the increase of depressive symptoms and major depressive disorder during treatment for hepatitis C with pegylated interferon-α2a and oral ribavirin

BACKGROUND

Tryptophan metabolism via the kynurenine pathway is considered the link between the immune and endocrine systems. Dysregulation of serotonergic transmission can stem from the direct influence of interferon-α on the activity of serotonergic receptors 5-HT1A and 5-HT2A, and from its indirect effect on tryptophan metabolism. Induction of the kynurenine pathway increases the concentration of neurotoxic kynurenine metabolites, and the activity of kynurenine derivatives is linked to the onset of depression. The aim of our study was to evaluate the relationships between depressive symptoms and kynurenine, tryptophan, anthranilic acid and kynurenic acid concentrations, indolamine 2,3-dioxygenase (IDO) activity and tryptophan availability to the brain.

METHODS

The study followed a prospective longitudinal cohort design. We evaluated 101 patients with chronic hepatitis C who were treated with pegylated interferon-α2a, and 40 controls who were awaiting treatment. We evaluated the relationships between total score on the Montgomery-Åsberg Depression Rating Scale and kynurenine, tryptophan, anthranilic acid and kynurenic acid concentrations, IDO activity and tryptophan availability to the brain. A logistic regression model was adapted for the diagnosis of major depressive disorder at each time point, taking into account changes in parameters of the kynurenine pathway between a given time point and the baseline measurement.

RESULTS

Of the treated patients, 44% fulfilled the criteria for major depressive disorder at least once during the 24 weeks of treatment. Anthranilic acid concentrations were significantly increased compared to baseline for all time points except week 2. Tryptophan availability showed a significant decrease (β = -0.09, p = 0.01) only in week 12 of treatment. Over time, kynurenine, tryptophan and anthranilic acid concentrations, as well as IDO activity and tryptophan availability to the brain, were significantly associated with total score on the Montgomery-Åsberg Depression Rating Scale. A logistic regression model revealed that participants with decreased tryptophan availability to the brain at 12 weeks of treatment and participants with increased anthranilic acid concentrations at week 24 of treatment were at increased risk for diagnosis of major depressive disorder (odds ratios 2.92 and 3.59, respectively).

LIMITATIONS

This study had an open-label design in a population receiving naturalistic treatment.

CONCLUSION

The present study provides the first direct evidence of the role of anthranilic acid in the pathogenesis of inflammation-induced major depressive disorder during treatment for hepatitis C with pegylated interferon-α2a.

Neuromodulation of Glial Function During Neurodegeneration

Glia, a non-excitable cell type once considered merely as the connective tissue between neurons, is nowadays acknowledged for its essential contribution to multiple physiological processes including learning, memory formation, excitability, synaptic plasticity, ion homeostasis, and energy metabolism. Moreover, as glia are key players in the brain immune system and provide structural and nutritional support for neurons, they are intimately involved in multiple neurological disorders. Recent advances have demonstrated that glial cells, specifically microglia and astroglia, are involved in several neurodegenerative diseases including Amyotrophic lateral sclerosis (ALS), Epilepsy, Parkinson's disease (PD), Alzheimer's disease (AD), and frontotemporal dementia (FTD). While there is compelling evidence for glial modulation of synaptic formation and regulation that affect neuronal signal processing and activity, in this manuscript we will review recent findings on neuronal activity that affect glial function, specifically during neurodegenerative disorders. We will discuss the nature of each glial malfunction, its specificity to each disorder, overall contribution to the disease progression and assess its potential as a future therapeutic target.

Nicotine smoking concentrations modulate GABAergic synaptic transmission in murine medial prefrontal cortex by activation of α7* and β2* nicotinic receptors

Nicotine is the major addictive component of cigarettes, reaching a brain concentration of ~300 nM during smoking of a single cigarette. The prefrontal cortex (PFC) mechanisms underlying temporary changes of working memory during smoking are incompletely understood. Here, we investigated whether 300 nM nicotine modulates γ-aminobutyric acid (GABA) ergic synaptic transmission from pyramidal neurons of the output layer (V) of the murine medial PFC. We used patch clamp in vitro recording from C57BL/6 mice in the whole-cell configuration to investigate the effect of nicotine on pharmacologically isolated GABAergic postsynaptic currents (IPSCs) in the absence or presence of methyllycaconitine (MLA) or dihydro-β-erythroidine (DHβE), selective antagonists of α7- and β2-containing (α7* and β2*) nicotinic acetylcholine receptors (AChRs), respectively. Our results indicated that nicotine, alone or in the presence of MLA, decreases electrically evoked IPSC (eIPSC) amplitude, whereas in the presence of DHβE, nicotine elicited either an eIPSCs amplitude increase or a decrease. In the presence of DHβE, nicotine increased membrane conductance leaving the paired pulse ratio unchanged in all conditions, suggesting a non-β2* mediated effect. In the presence of MLA, nicotine decreased the mean spontaneous IPSC (sIPSC) frequency but increased their rise time, suggesting a non-α7* AChR-mediated synaptic modulation. Also, in the presence of DHβE, nicotine decreased both eIPSC rise and decay times. No receptors other than α7* and β2* appear to be involved in the nicotine effect. Our results indicate that nicotine smoking concentrations modulate GABAergic synaptic currents through mixed pre- and post-synaptic mechanisms by activation of α7* and β2* AChRs.

Peripheral Biomarkers for First-Episode Psychosis-Opportunities from the Neuroinflammatory Hypothesis of Schizophrenia

OBJECTIVE

Schizophrenia is a disabling disorder of unknown aetiology, lacking definite diagnostic method and cure. A reliable biological marker of schizophrenia is highly demanded, for which traceable immune mediators in blood could be promising candidates. We aimed to gather the best findings of neuroinflammatory markers for first-episode psychosis (FEP).

METHODS

We performed an extensive narrative review of online literature on inflammation-related markers found in human FEP patients only.

RESULTS

Changes to cytokine levels have been increasingly reported in schizophrenia. The peripheral levels of IL-1 (or its receptor antagonist), soluble IL-2 receptor, IL-4, IL-6, IL-8, and TNF-α have been frequently reported as increased in FEP, in a suggestive continuum from high-risk stages for psychosis. Microglia and astrocytes establish the link between this immune signalling and the synthesis of noxious tryptophan catabolism products, that cause structural damage and directly hamper normal neurotransmission. Amongst these, only 3-hydroxykynurenine has been consistently described in the blood of FEP patients.

CONCLUSION

Peripheral molecules stemming from brain inflammation might provide insightful biomarkers of schizophrenia, as early as FEP or even prodromal phases, although more time- and clinically-adjusted studies are essential for their validation.

LC-MS/MS-based quantification of tryptophan metabolites and neurotransmitters in the serum and brain of mice

l-Tryptophan (Trp) metabolites and related neurotransmitters play crucial roles in physiological functions, and their imbalances are implicated in the pathology of depression, Alzheimer's disease and other diseases. Measurement of Trp metabolites and related neurotransmitters possesses a great potential to elucidate the disease mechanisms and evaluate the outcomes of therapeutic interventions. A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for simultaneous determination of Trp, l-kynurenine (Kyn), kynurenic acid (Kyna), 3-hydroxykynurenine (3-HK), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), norepinephrine (NE), l-glutamic acid (Glu), γ-aminobutyric acid (GABA) and acetylcholine (ACh) in mice serum and the brain tissues in a single chromatographic run. Samples were spiked with the internal standard, mixed with trifluoroacetic acid to precipitate protein and analyzed by LC-MS/MS. Chromatographic separation was achieved using a Restek Ultra Aqueous C18 column in combination with a gradient elution within 8 min. Mass spectrometric detection was performed using multiple reaction monitoring with electrospray ionization source in positive mode. The method exhibited good selectivity and correlation coefficient values for the calibration curves of each analyte were >0.99. The limit of detection and quantification ranged from 0.96 to 24.48 nmol/L and 3.42 to 244.82 nmol/L, respectively. The intra- and inter-day precision were ≤13.92%. All analytes were stable in prepared samples at room temperature in the autosampler for 24 h. This method was successfully applied to the analysis of biological samples from control and chronic mild stress (CMS) induced depression mice. It was found that Kyn and 3-HK pathways were enhanced by CMS, while the levels of Trp, Kyna, 5-HIAA, Glu, GABA and ACh were significantly reduced. The changes in 5-HT and NE levels were not uniform in the periphery and the brain. This method can therefore be applied to analyze Trp metabolites and related neurotransmitters levels to monitor disease states, study the mechanisms and outcomes of therapeutic interventions.

Reduced protein expressions of cytomembrane GABAARβ3 at different postnatal developmental stages of rats exposed prenatally to valproic acid

Decreased inhibition plays an extremely important role in pathogenesis of autism spectrum disorder (ASD). Therefore, we aimed to determine whether expression levels of the γ-aminobutyric acid type A receptor β3 subunit (GABAARβ3), K+-Cl- cotransporter 2 (KCC2), and Na+-K+-Cl- cotransporter 1 (NKCC1) related to inhibition transmission are changed in a sodium valproate-induced rat model of ASD. Decreased expression levels of membrane GABAARβ3 (m-GABAARβ3) and KCC2 as well as increased endocytosis of GABAARs were found in the model group. However, there were no significant differences in expression of total GABAARβ3 and NKCC1 between the control and model groups. In addition, we observed growth retardation, impaired spatial memory, limited exploration, increased anxiety, and reduced sociability in the model group. These results suggest alterations in m-GABAARβ3 levels, KCC2 levels, and trafficking of GABAARs in rats prenatally exposed to valproic acid and advance our understanding of the pathogenesis of ASD.

Astrocytic and microglial nicotinic acetylcholine receptors: an overlooked issue in Alzheimer's disease

It is increasingly recognized that astrocytes and microglia-associated dysfunction contribute to AD pathology. In addition, glial nicotinic acetylcholine receptors (nAChRs) play a role in AD-related phenomena, such as neuron survival, synaptic plasticity, and memory. From mechanistic point of view, the glial regulation of pro-inflammatory cytokines, as common contributors in AD, is modulated by nAChRs. Astrocytic and microglial nAChRs contribute to Aβ metabolism, including Aβ phagocytosis and degradation as well as Aβ-related oxidative stress and neurotoxicity. These receptors are also involved in neurotransmission and gliotransmission through indirect interaction with N-Methyl-D-aspartate (NMDA) and a-amino-3-hydroxy-5-methyl-4 isoxazolepropionic acid (AMPA) receptors as well as gamma-aminobutyric acid (GABA) and intracellular calcium regulation. In addition, glial nAChRs participate in trophic factors-induced neuroprotection. This review gathers the most recent advances along with the previous data on astrocytic and microglial nAChRs role in AD pathogenesis.

Dual effects of a 2-benzylquinuclidinium derivative on α7-containing nicotinic acetylcholine receptors in rat hippocampal interneurons

Nicotinic acetylcholine receptors (nAChRs) are widely distributed in the brain. Particularly α7-containing nAChRs, associated with several physiological roles and pathologies, are one of the most abundant. Here, we studied 2-(4-hexyloxybenzyl)-1-methylquinuclidin-1-ium iodide (designated as 8d), on ion currents elicited by choline, ICh, (Ch, a selective agonist for α7-containing nAChRs), recorded in interneurons from the stratum radiatum of the rat hippocampal CA1 region by using the whole-cell voltage-clamp technique. The 8d-concentration/Ch-response relationship exhibited high and low inhibitory affinities for α7-containing nAChRs, with IC50 values of 0.59 and 6.80 μM, respectively. Interestingly, 8d in a range of 3-10 μM exerted opposite effects: a short early potentiation and a long late inhibition of the ICh; and 8d alone elicited a non-decaying inward current. Furthermore, potentiation and inhibition of the ICh by 8d depended on the membrane potential, both being stronger at -20 than at -70 mV; indicating that 8d interacts with at least two sites into the ion channel/receptor complex: one for potentiating and another for inhibiting the α7-containing nAChRs. These results suggest that 8d may act as agonist, antagonist and positive modulator of α7-containing nAChRs in hippocampal interneurons.

Molecular biomarkers in drug-resistant epilepsy: Facts & possibilities

Despite great advances in our understanding of the process of epileptogenesis we are yet to develop reliable biomarkers that have the potential to accurately localize the epileptogenic zone (EZ), and to resolve the issue of heterogeneity in epilepsy surgery outcome. Inability to precisely localize the epileptogenic foci is one of the reason why more than 30% of these DRE patients are not benefited. Molecular and cellular biomarkers in combination with imaging and electrical investigations will provide a more specific platform for defining epileptogenic zone. Potential molecular biomarkers of epileptogenesis including markers of inflammation, synaptic alterations and neurodegeneration may also have the potential for localizing EZ. At molecular level components derived from epileptogenic tissues, such as metabolites, proteins, mRNAs and miRNAs that are significantly altered can serve as biomarkers and can be clubbed with existing techniques to preoperatively localize the EZ. Neurosurgeons across the world face problems while defining the margins of the epileptogenic tissues to be resected during surgery. In this review we discuss molecular biomarkers reported so far in the context of epileptogenesis and some of the unexplored markers which may have the potential to localize EZ during surgery. We also discuss "Intelligent knife" technique that couples electrosurgery and mass spectrometry allowing near-real-time characterization of human tissue and may prove to be instrumental in defining the margins of the epileptogenic zone during surgery.

Bupropion-induced inhibition of α7 nicotinic acetylcholine receptors expressed in heterologous cells and neurons from dorsal raphe nucleus and hippocampus

The pharmacological activity of bupropion was compared between α7 nicotinic acetylcholine receptors expressed in heterologous cells and hippocampal and dorsal raphe nucleus neurons. The inhibitory activity of bupropion was studied on GH3-α7 cells by Ca2+ influx, as well as on neurons from the dorsal raphe nucleus and interneurons from the stratum radiatum of the hippocampal CA1 region by using a whole-cell voltage-clamp technique. In addition, the interaction of bupropion with the α7 nicotinic acetylcholine receptor was determined by [3H]imipramine competition binding assays and molecular docking. The fast component of acetylcholine- and choline-induced currents from both brain regions was inhibited by methyllycaconitine, indicating the participation of α7-containing nicotinic acetylcholine receptors. Choline-induced currents in hippocampal interneurons were partially inhibited by 10 µM bupropion, a concentration that could be reached in the brain during clinical administration. Additionally, both agonist-induced currents were reversibly inhibited by bupropion at concentrations that coincide with its inhibitory potency (IC50=54 µM) and binding affinity (Ki=63 µM) for α7 nicotinic acetylcholine receptors from heterologous cells. The [3H]imipramine competition binding and molecular docking results support a luminal location for the bupropion binding site(s). This study may help to understand the mechanisms of actions of bupropion at neuronal and molecular levels related with its therapeutic actions on depression and for smoking cessation.

Neonatal nicotine exposure increases excitatory synaptic transmission and attenuates nicotine-stimulated GABA release in the adult rat hippocampus

Developmental exposure to nicotine has been linked to long-lasting changes in synaptic transmission which may contribute to behavioral abnormalities seen in offspring of women who smoke during pregnancy. Here, we examined the long-lasting effects of developmental nicotine exposure on glutamatergic and GABAergic neurotransmission, and on acute nicotine-induced glutamate and GABA release in the adult hippocampus, a structure important in cognitive and emotional behaviors. We utilized a chronic neonatal nicotine treatment model to administer nicotine (6 mg/kg/day) to rat pups from postnatal day (P) 1-7, a period that falls developmentally into the third human trimester. Using whole-cell voltage clamp recordings from CA1 pyramidal neurons in hippocampal slices, we measured excitatory and inhibitory postsynaptic currents in neonatally control- and nicotine-treated young adult males. Neonatal nicotine exposure significantly increased AMPA receptor-mediated spontaneous and evoked excitatory signaling, with no change in glutamate release probability in adults. Conversely, there was no increase in spontaneous GABAergic neurotransmission in nicotine-males. Chronic neonatal nicotine treatment had no effect on acute nicotine-stimulated glutamate release in adults, but acute nicotine-stimulated GABA release was significantly attenuated. Thus, neonatal nicotine exposure results in a persistent net increase in excitation and a concurrent loss of nicotinic acetylcholine receptor (nAChR)-mediated regulation of presynaptic GABA but not glutamate release, which would exacerbate excitation following endogenous or exogenous nAChR activation. Our data underscore an important role for nAChRs in hippocampal excitatory synapse development, and suggest selective long-term changes at specific presynaptic nAChRs which together could explain some of the behavioral abnormalities associated with maternal smoking.

Neuroprogression in schizophrenia: Pathways underpinning clinical staging and therapeutic corollaries

OBJECTIVE

Whilst dopaminergic dysfunction remains a necessary component involved in the pathogenesis of schizophrenia, our current pharmacological armoury of dopamine antagonists does little to control the negative symptoms of schizophrenia. This suggests other pathological processes must be implicated. This paper aims to elaborate on such theories.

METHODS

Data for this review were sourced from the electronic database PUBMED, and was not limited by language or date of publication.

RESULTS

It has been suggested that multiple 'hits' may be required to unveil the clinical syndrome in susceptible individuals. Such hits potentially first occur in utero, leading to neuronal disruption, epigenetic changes and the establishment of an abnormal inflammatory response. The development of schizophrenia may therefore potentially be viewed as a neuroprogressive response to these early stressors, driven on by changes in tryptophan catabolite (TRYCAT) metabolism, reactive oxygen species handling and N-methyl d-aspartate (NMDA) circuitry. Given the potential for such progression over time, it is prudent to explore the new treatment strategies which may be implemented before such changes become established.

CONCLUSIONS

Outside of the dopaminergic model, the potential pathogenesis of schizophrenia has yet to be fully elucidated, but common themes include neuropil shrinkage, the development of abnormal neuronal circuitry, and a chronic inflammatory state which further disrupts neuronal function. Whilst some early non-dopaminergic treatments show promise, none have yet to be fully studied in appropriately structured randomized controlled trials and they remain little more than potential attractive targets.

Localization and function of dopamine receptors in the subthalamic nucleus of normal and parkinsonian monkeys

The subthalamic nucleus (STN) receives a dopaminergic innervation from the substantia nigra pars compacta, but the role of this projection remains poorly understood, particularly in primates. To address this issue, we used immuno-electron microscopy to localize D1, D2, and D5 dopamine receptors in the STN of rhesus macaques and studied the electrophysiological effects of activating D1-like or D2-like receptors in normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated parkinsonian monkeys. Labeling of D1 and D2 receptors was primarily found presynaptically, on preterminal axons and putative glutamatergic and GABAergic terminals, while D5 receptors were more significantly expressed postsynaptically, on dendritic shafts of STN neurons. The electrical spiking activity of STN neurons, recorded with standard extracellular recording methods, was studied before, during, and after intra-STN administration of the dopamine D1-like receptor agonist SKF82958, the D2-like receptor agonist quinpirole, or artificial cerebrospinal fluid (control injections). In normal animals, administration of SKF82958 significantly reduced the spontaneous firing but increased the rate of intraburst firing and the proportion of pause-burst sequences of firing. Quinpirole only increased the proportion of such pause-burst sequences in STN neurons of normal monkeys. In MPTP-treated monkeys, the D1-like receptor agonist also reduced the firing rate and increased the proportion of pause-burst sequences, while the D2-like receptor agonist did not change any of the chosen descriptors of the firing pattern of STN neurons. Our data suggest that dopamine receptor activation can directly modulate the electrical activity of STN neurons by pre- and postsynaptic mechanisms in both normal and parkinsonian states, predominantly via activation of D1 receptors.

The KMO allele encoding Arg452 is associated with psychotic features in bipolar disorder type 1, and with increased CSF KYNA level and reduced KMO expression

The kynurenine pathway metabolite kynurenic acid (KYNA), modulating glutamatergic and cholinergic neurotransmission, is increased in cerebrospinal fluid (CSF) of patients with schizophrenia or bipolar disorder type 1 with psychotic features. KYNA production is critically dependent on kynurenine 3-monooxygenase (KMO). KMO mRNA levels and activity in prefrontal cortex (PFC) are reduced in schizophrenia. We hypothesized that KMO expression in PFC would be reduced in bipolar disorder with psychotic features and that a functional genetic variant of KMO would associate with this disease, CSF KYNA level and KMO expression. KMO mRNA levels were reduced in PFC of bipolar disorder patients with lifetime psychotic features (P=0.005, n=19) or schizophrenia (P=0.02, n=36) compared with nonpsychotic patients and controls. KMO genetic association to psychotic features in bipolar disorder type 1 was studied in 493 patients and 1044 controls from Sweden. The KMO Arg(452) allele was associated with psychotic features during manic episodes (P=0.003). KMO Arg(452) was studied for association to CSF KYNA levels in an independent sample of 55 Swedish patients, and to KMO expression in 717 lymphoblastoid cell lines and 138 hippocampal biopsies. KMO Arg(452) associated with increased levels of CSF KYNA (P=0.03) and reduced lymphoblastoid and hippocampal KMO expression (P≤0.05). Thus, findings from five independent cohorts suggest that genetic variation in KMO influences the risk for psychotic features in mania of bipolar disorder patients. This provides a possible mechanism for the previous findings of elevated CSF KYNA levels in those bipolar patients with lifetime psychotic features and positive association between KYNA levels and number of manic episodes.

Network beyond IDO in psychiatric disorders: revisiting neurodegeneration hypothesis

The involvement of immune system activation in the pathophysiology of certain psychiatric disorders is well documented. Inflammatory molecules such as pro-inflammatory cytokines could enhance the activity of the indoleamine 2,3-dioxygenase (IDO) enzyme which is the first rate-limiting enzyme of the tryptophan degradation pathway, the kynurenine pathway. The increased tryptophan degradation could induce serotonin depletion and depressive mood. On the other hand, the downstream metabolites from this pathway, such as 3-hydroxykynurenine, quinolinic acid and kynurenic acid, are neuroactive metabolites which can modulate several neurotransmissions, such as glutamatergic, GABAergic, dopaminergic and noradrenergic neurotransmissions, which in turn induce changes in neuronal-glial network and neuropsychiatric consequences. In this issue, we have revised the previous 'neurodegeneration hypothesis,' which explained the involvement of cytokines and IDO pathway interaction in depression, with a further extended view related to the network beyond IDO, the network between immune molecules, tryptophan metabolites and different neurotransmitters, in depression and other major psychiatric disorders such as schizophrenia, bipolar disorder and childhood psychiatric disorders.

Inflammation and the two-hit hypothesis of schizophrenia

The high societal and individual cost of schizophrenia necessitates finding better, more effective treatment, diagnosis, and prevention strategies. One of the obstacles in this endeavor is the diverse set of etiologies that comprises schizophrenia. A substantial body of evidence has grown over the last few decades to suggest that schizophrenia is a heterogeneous syndrome with overlapping symptoms and etiologies. At the same time, an increasing number of clinical, epidemiological, and experimental studies have shown links between schizophrenia and inflammatory conditions. In this review, we analyze the literature on inflammation and schizophrenia, with a particular focus on comorbidity, biomarkers, and environmental insults. We then identify several mechanisms by which inflammation could influence the development of schizophrenia via the two-hit hypothesis. Lastly, we note the relevance of these findings to clinical applications in the diagnosis, prevention, and treatment of schizophrenia.

Contribution of CA3 and CA1 pyramidal neurons to the tonic α7 nAChR-dependent glutamatergic input to CA1 pyramidal neurons

The Schaffer collaterals are among the major glutamatergic inputs to CA1 pyramidal neurons, the primary output of the hippocampus, which also receive sparse recurrent inputs from pyramidal neurons in the CA1 field. Although tonically active α7 nicotinic acetylcholine receptors (nAChRs) have been shown to sustain spontaneous glutamate transmission to CA1 pyramidal neurons in hippocampal slices under resting conditions, it remains to be determined whether these receptors are those expressed by CA3 or CA1 pyramidal neurons. This study was designed to test the hypothesis that the CA3 field of the hippocampus is a significant source of α7 nAChR-sustained glutamatergic transmission to CA1 pyramidal neurons. To this end, spontaneous excitatory postsynaptic currents (EPSCs) were recorded from CA1 and CA3 pyramidal neurons in intact rat hippocampal slices as well as from CA1 pyramidal neurons in CA3-ablated slices under various experimental conditions. Surgical removal of the CA3 region from the slices reduced by 20% the frequency of spontaneous EPSCs recorded from CA1 pyramidal neurons. This finding is in agreement with the concept that the CA3 field contributes significantly to the maintenance of spontaneous glutamatergic synaptic activity in CA1 pyramidal neurons. In addition, the α7 nAChR antagonist methyllycaconitine (MLA, 10nM) reduced the frequency of spontaneous EPSCs recorded from CA1 pyramidal neurons by 30% in intact slices and 12% in CA3-ablated slices. Taken together, these results demonstrate that tonically active α7 nAChRs in CA3 pyramidal neurons and/or in the Mossy fibers that innervate the CA3 pyramidal neurons do in fact contribute to the maintenance of glutamatergic synaptic activity in CA1 pyramidal neurons of hippocampal slices under resting conditions.

Post-ischemic treatment with L-kynurenine sulfate exacerbates neuronal damage after transient middle cerebral artery occlusion

Since brain ischemia is one of the leading causes of adult disability and death, neuroprotection of the ischemic brain is of particular importance. Acute neuroprotective strategies usually have the aim of suppressing glutamate excitotoxicity and an excessive N-methyl-d-aspartate (NMDA) receptor function. Clinically tolerated antagonists should antagonize an excessive NMDA receptor function without compromising the normal synaptic function. Kynurenic acid (KYNA) an endogenous metabolite of the tryptophan metabolism, may be an attractive neuroprotectant in this regard. The manipulation of brain KYNA levels was earlier found to effectively enhance the histopathological outcome of experimental ischemic/hypoxic states. The present investigation of the neuroprotective capacity of L-kynurenine sulfate (L-KYNs) administered systemically after reperfusion in a novel distal middle cerebral artery occlusion (dMCAO) model of focal ischemia/reperfusion revealed that in contrast with earlier results, treatment with L-KYNs worsened the histopathological outcome of dMCAO. This contradictory result indicates that post-ischemic treatment with L-KYNs may be harmful.

Schizophrenia is primed for an increased expression of depression through activation of immuno-inflammatory, oxidative and nitrosative stress, and tryptophan catabolite pathways

Schizophrenia and depression are two common and debilitating psychiatric conditions. Up to 61% of schizophrenic patients have comorbid clinical depression, often undiagnosed. Both share significant overlaps in underlying biological processes, which are relevant to the course and treatment of both conditions. Shared processes include changes in cell-mediated immune and inflammatory pathways, e.g. increased levels of pro-inflammatory cytokines and a Th1 response; activation of oxidative and nitrosative stress (O&NS) pathways, e.g. increased lipid peroxidation, damage to proteins and DNA; decreased antioxidant levels, e.g. lowered coenzyme Q10, vitamin E, glutathione and melatonin levels; autoimmune responses; and activation of the tryptophan catabolite (TRYCAT) pathway through induction of indoleamine-2,3-dioxygenase. Both show cognitive and neurostructural evidence of a neuroprogressive process. Here we review the interlinked nature of these biological processes, suggesting that schizophrenia is immunologically primed for an increased expression of depression. Such a conceptualization explains, and incorporates, many of the current perspectives on the nature of schizophrenia and depression, and has implications for the nature of classification and treatment of both disorders. An early developmental etiology to schizophrenia, driven by maternal infection, with subsequent impact on offspring immuno-inflammatory responses, creates alterations in the immune pathways, which although priming for depression, also differentiates the two disorders.

Schizophrenia: linking prenatal infection to cytokines, the tryptophan catabolite (TRYCAT) pathway, NMDA receptor hypofunction, neurodevelopment and neuroprogression

In 1995, the macrophage-T lymphocyte theory of schizophrenia (Smith and Maes, 1995) considered that activated immuno-inflammatory pathways may account for the higher neurodevelopmental pathology linked with gestational infections through the detrimental effects of activated microglia, oxidative and nitrosative stress (O&NS), cytokine-induced activation of the tryptophan catabolite (TRYCAT) pathway and consequent modulation of the N-methyl d-aspartate receptor (NMDAr) and glutamate production. The aim of the present paper is to review the current state-of-the art regarding the role of the above pathways in schizophrenia. Accumulating data suggest a powerful role for prenatal infection, both viral and microbial, in driving an early developmental etiology to schizophrenia. Models of prenatal rodent infection show maintained activation of immuno-inflammatory pathways coupled to increased microglia activation. The ensuing activation of immuno-inflammatory pathways in schizophrenia may activate the TRYCAT pathway, including increased kynurenic acid (KA) and neurotoxic TRYCATs. Increased KA, via the inhibition of the α7 nicotinic acetylcholine receptor, lowers gamma-amino-butyric-acid (GABA)ergic post-synaptic current, contributing to dysregulated glutamatergic activity. Hypofunctioning of the NMDAr on GABAergic interneurons will contribute to glutamatergic dysregulation. Many susceptibility genes for schizophrenia are predominantly expressed in early development and will interact with these early developmental driven changes in the immuno-inflammatory and TRYCAT pathways. Maternal infection and subsequent immuno-inflammatory responses are additionally associated with O&NS, including lowered antioxidants such as glutathione. This will contribute to alterations in neurogenesis and myelination. In such a scenario a) a genetic or epigenetic potentiation of immuno-inflammatory pathways may constitute a double hit on their own, stimulating wider immuno-inflammatory responses and thus potentiating the TRYCAT pathway and subsequent NMDAr dysfunction and neuroprogression; and b) antipsychotic-induced changes in immuno-inflammatory, TRYCAT and O&NS pathways would modulate the CNS glia-neuronal interactions that determine synaptic plasticity as well as myelin generation and maintenance.

Acetylcholinesterase inhibition reveals endogenous nicotinic modulation of glutamate inputs to CA1 stratum radiatum interneurons in hippocampal slices

The involvement of brain nicotinic acetylcholine receptors (nAChRs) in the neurotoxicological effects of soman, a potent acetylcholinesterase (AChE) inhibitor and a chemical warfare agent, is not clear. This is partly due to a poor understanding of the role of AChE in brain nAChR-mediated functions. To test the hypothesis that AChE inhibition builds sufficient acetylcholine (ACh) in the brain and facilitates nAChR-dependent glutamate transmission, we used whole-cell patch-clamp technique to record spontaneous glutamate excitatory postsynaptic currents (EPSCs) from CA1 stratum radiatum interneurons (SRI) in hippocampal slices. First, the frequency, amplitude and kinetics of EPSCs recorded from slices of control guinea pigs were compared to those recorded from slices of guinea pigs after a single injection of the irreversible AChE inhibitor soman (25.2μg/kg, s.c.). Second, EPSCs were recorded from rat hippocampal slices before and after their superfusion with the reversible AChE inhibitor donepezil (100nM). The frequency of EPSCs was significantly higher in slices taken from guinea pigs 24h but not 7 days after the soman injection than in slices from control animals. In 52% of the rat hippocampal slices tested, bath application of donepezil increased the frequency of EPSCs. Further, exposure to donepezil increased both burst-like and large-amplitude EPSCs, and increased the proportion of short (20-100ms) inter-event intervals. Donepezil's effects were suppressed significantly in presence of 10μM mecamylamine or 10nM methyllycaconitine. These results support the concept that AChE inhibition is able to recruit nAChR-dependent glutamate transmission in the hippocampus and such a mechanism can contribute to the acute neurotoxicological actions of soman.

Kynurenic acid, by targeting α7 nicotinic acetylcholine receptors, modulates extracellular GABA levels in the rat striatum in vivo

Kynurenic acid (KYNA) is an astrocyte-derived non-competitive antagonist of the α7 nicotinic acetylcholine receptor (α7nAChR) and inhibits the NMDA receptor (NMDAR) competitively. The main aim of the present study was to examine the possible effects of KYNA (30 - 1000 nm), applied locally by reverse dialysis for 2 h, on extracellular GABA levels in the rat striatum. KYNA concentration-dependently reduced GABA levels, with 300 nm KYNA causing a maximal reduction to ~60% of baseline concentrations. The effect of KYNA (100 nm) was prevented by co-application of galantamine (5 μm), an agonist at a site of the α7nAChR that is very similar to that targeted by KYNA. Infusion of 7-chlorokynurenic acid (100 nm), an NMDAR antagonist acting selectively at the glycineB site of the receptor, affected neither basal GABA levels nor the KYNA-induced reduction in GABA. Inhibition of endogenous KYNA formation by reverse dialysis of (S)-4-(ethylsulfonyl)benzoylalanine (ESBA; 1 mm) increased extracellular GABA levels, reaching a peak of 156% of baseline levels after 1 h. Co-infusion of 100 nm KYNA abolished the effect of ESBA. Qualitatively and quantitatively similar, bi-directional effects of KYNA on extracellular glutamate were observed in the same microdialysis samples. Taken together, the present findings suggest that fluctuations in endogenous KYNA levels, by modulating α7nAChR function, control extracellular GABA levels in the rat striatum. This effect may be relevant for a number of physiological and pathological processes involving the basal ganglia.

Kynurenic acid as an antagonist of α7 nicotinic acetylcholine receptors in the brain: facts and challenges

Kynurenic acid (KYNA), a major tryptophan metabolite, is a glutamate receptor antagonist, which is also reported to inhibit α7 nicotinic acetylcholine receptors (α7nAChRs). Due to variations in experimental approaches, controversy has arisen regarding the ability of KYNA to directly influence α7nAChR function. Here we summarize current concepts of KYNA neurobiology and review evidence pertaining to the proposed role of KYNA as an endogenous modulator of α7nAChRs and synaptic transmission. As dysfunction of α7nAChRs plays a major role in the pathophysiology of central nervous system disorders, elucidation of KYNA's action on this receptor subtype has significant therapeutic implications.

Kynurenic acid inhibits glutamatergic transmission to CA1 pyramidal neurons via α7 nAChR-dependent and -independent mechanisms

Glutamatergic hypofunction and elevated levels of kynurenic acid (KYNA) in the brain are common features of patients with schizophrenia. In vivo studies indicate that in the hippocampus KYNA decreases glutamate levels, presumably via inhibition of α7 nicotinic receptors (nAChRs). Here we tested the hypothesis that basal synaptic glutamate activity in the hippocampus is regulated by tonically active α7 nAChRs and is sensitive to inhibition by KYNA. To this end, spontaneous excitatory postsynaptic currents (EPSCs), sensitive to AMPA receptor antagonist CNQX (10 μM), were recorded from CA1 pyramidal neurons at -70 mV in rat hippocampal slices. The α7 nAChR antagonists α-bungarotoxin (α-BGT, 100 nM) and methyllycaconitine (MLA, 1-50 nM), and the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV, 50 μM) reduced the frequency of EPSCs. MLA and α-BGT had no effect on miniature EPSCs (mEPSCs). The effect of MLA decreased in the presence of APV (50 μM), with 1 nM MLA becoming completely ineffective. KYNA (1-20 μM) suppressed the frequency of EPSCs, without affecting mEPSCs. The effect of KYNA decreased in the presence of MLA (1 nM) or α-BGT (100 nM), with 1 μM KYNA being devoid of any effect. In the presence of both MLA (10 nM) and APV (50 μM) higher KYNA concentrations (5-20 μM) still reduced the frequency of EPSCs. These results suggest that basal synaptic glutamate activity in CA1 pyramidal neurons is maintained in part by tonically active α7 nAChRs and NMDA receptors and is inhibited by micromolar concentrations of KYNA, acting via α7 nAChR-dependent and -independent mechanisms.

Lack of modulation of nicotinic acetylcholine alpha-7 receptor currents by kynurenic acid in adult hippocampal interneurons

Kynurenic acid (KYNA), a classical ionotropic glutamate receptor antagonist is also purported to block the α7-subtype nicotinic acetylcholine receptor (α7* nAChR). Although many published studies cite this potential effect, few have studied it directly. In this study, the α7*-selective agonist, choline, was pressure-applied to interneurons in hippocampal subregions, CA1 stratum radiatum and hilus of acute brain hippocampal slices from adolescent to adult mice and adolescent rats. Stable α7* mediated whole-cell currents were measured using voltage-clamp at physiological temperatures. The effects of bath applied KYNA on spontaneous glutamatergic excitatory postsynaptic potentials (sEPSC) as well as choline-evoked α7* currents were determined. In mouse hilar interneurons, KYNA totally blocked sEPSC whole-cell currents in a rapid and reversible manner, but had no effect on choline-evoked α7* whole-cell currents. To determine if this lack of KYNA effect on α7* function was due to regional and/or species differences in α7* nAChRs, the effects of KYNA on choline-evoked α7* whole-cell currents in mouse and rat stratum radiatum interneurons were tested. KYNA had no effect on either mouse or rat stratum radiatum interneuron choline-evoked α7* whole-cell currents. Finally, to test whether the lack of effect of KYNA was due to unlikely slow kinetics of KYNA interactions with α7* nAChRs, recordings of a7*-mediated currents were made from slices that were prepared and stored in the presence of 1 mM KYNA (>90 minutes exposure). Under these conditions, KYNA had no measurable effect on α7* nAChR function. The results show that despite KYNA-mediated blockade of glutamatergic sEPSCs, two types of hippocampal interneurons that express choline-evoked α7* nAChR currents fail to show any degree of modulation by KYNA. Our results indicate that under our experimental conditions, which produced complete KYNA-mediated blockade of sEPSCs, claims of KYNA effects on choline-evoked α7* nAChR function should be made with caution.