BDNF enhancement of postsynaptic NMDA receptors is blocked by ethanol

Activation of mediodorsal thalamic dopamine receptors inhibited nicotine-induced anxiety in rats: A possible role of corticolimbic NMDA neurotransmission and BDNF expression

The present study aimed to evaluate the functional interaction between the dopaminergic and glutamatergic systems of the mediodorsal thalamus (MD), the ventral hippocampus (VH), and the prefrontal cortex (PFC) in nicotine-induced anxiogenic-like behaviors. Brain-derived neurotrophic factor (BDNF) level changes were measured in the targeted brain areas following the drug treatments. The percentage of time spent in the open arm (% OAT) and open arm entry (% OAE) were calculated in the elevated plus maze (EPM) to measure anxiety-related behaviors in adult male Wistar rats. Systemic administration of nicotine at a dose of 0.5 mg/kg induced an anxiogenic-like response associated with decreased BDNF levels in the hippocampus and the PFC. Intra-MD microinjection of apomorphine (0.1-0.3 μg/rat) induced an anxiogenic-like response, while apomorphine inhibited nicotine-induced anxiogenic-like behaviors associated with increased hippocampal and PFC BDNF expression levels. Interestingly, the blockade of the VH or the PFC NMDA receptors via the microinjection of D-AP5 (0.3-0.5 μg/rat) into the targeted sites reversed the inhibitory effect of apomorphine (0.5 μg/rat, intra-MD) on the nicotine response and led to the decrease of BDNF levels in the hippocampus and the PFC. Also, the microinjection of a higher dose of D-AP5 (0.5 μg/rat, intra-PFC) alone produced an anxiogenic effect. These findings suggest that the functional interaction between the MD dopaminergic D1/D2-like and the VH/PFC glutamatergic NMDA receptors may be partially involved in the anxiogenic-like effects of nicotine, likely via the alteration of BDNF levels in the hippocampus and the PFC.

Role of BDNF in Neuroplasticity Associated with Alcohol Dependence

Abstract

Chronic alcohol consumption is characterized by disturbances of neuroplasticity. Brain-derived neurotrophic factor (BDNF) is believed to be critically involved in this process. Here we aimed to review actual experimental and clinical data related to BDNF participation in neuroplasticity in the context of alcohol dependence. As has been shown in experiments with rodents, alcohol consumption is accompanied by the brain region-specific changes of BDNF expression and by structural and behavioral impairments. BDNF reverses aberrant neuroplasticity observed during alcohol intoxication. According to the clinical data parameters associated with BDNF demonstrate close correlation with neuroplastic changes accompanying alcohol dependence. In particular, the rs6265 polymorphism within the BDNF gene is associated with macrostructural changes in the brain, while peripheral BDNF concentration may be associated with anxiety, depression, and cognitive impairment. Thus, BDNF is involved in the mechanisms of alcohol-induced changes of neuroplasticity, and polymorphisms within the BDNF gene and peripheral BDNF concentration may serve as biomarkers, diagnostic or prognostic factors in treatment of alcohol abuse.

BDNF shifts excitatory-inhibitory balance in the paraventricular nucleus of the hypothalamus to elevate blood pressure

Presympathetic neurons in the paraventricular nucleus of the hypothalamus (PVN) play a key role in cardiovascular regulation. We have previously shown that brain-derived neurotrophic factor (BDNF), acting in the PVN, increases sympathetic activity and blood pressure and serves as a key regulator of stress-induced hypertensive responses. BDNF is known to alter glutamatergic and GABA-ergic signaling broadly in the central nervous system, but whether BDNF has similar actions in the PVN remains to be investigated. Here, we tested the hypothesis that increased BDNF expression in the PVN elevates blood pressure by enhancing N-methyl-d-aspartate (NMDA) receptor (NMDAR)- and inhibiting GABA_A receptor (GABA_AR)-mediated signaling. Sprague-Dawley rats received bilateral PVN injections of AAV2 viral vectors expressing green fluorescent protein (GFP) or BDNF. Three weeks later, cardiovascular responses to PVN injections of NMDAR and GABA_AR agonists and antagonists were recorded under α-chloralose-urethane anesthesia. In addition, expressions of excitatory and inhibitory signaling components in the PVN were assessed using immunofluorescence. Our results showed that NMDAR inhibition led to a greater decrease in blood pressure in the BDNF vs. GFP group, while GABA_AR inhibition led to greater increases in blood pressure in the GFP group compared to BDNF. Conversely, GABA_AR activation decreased blood pressure significantly more in GFP vs. BDNF rats. In addition, immunoreactivity of NMDAR1 was upregulated, while GABA_AR-α1 and K⁺/Cl^- cotransporter 2 were downregulated by BDNF overexpression in the PVN. In summary, our findings indicate that hypertensive actions of BDNF within the PVN are mediated, at least in part, by augmented NMDAR and reduced GABA_AR signaling.NEW & NOTEWORTHY We have shown that BDNF, acting in the PVN, elevates blood pressure in part by augmenting NMDA receptor-mediated excitatory input and by diminishing GABA_A receptor-mediated inhibitory input to PVN neurons. In addition, we demonstrate that elevated BDNF expression in the PVN upregulates NMDA receptor immunoreactivity and downregulates GABA_A receptor as well as KCC2 transporter immunoreactivity.

Neural Mechanisms Underlying the Rewarding and Therapeutic Effects of Ketamine as a Treatment for Alcohol Use Disorder

Alcohol use disorder (AUD) is the most prevalent substance use disorder and causes a significant global burden. Relapse rates remain incredibly high after decades of attempting to develop novel treatment options that have failed to produce increased rates of sobriety. Ketamine has emerged as a potential treatment for AUD following its success as a therapeutic agent for depression, demonstrated by several preclinical studies showing that acute administration reduced alcohol intake in rodents. As such, ketamine's therapeutic effects for AUD are now being investigated in clinical trials with the hope of it being efficacious in prolonging sobriety from alcohol in humans (ClinicalTrials.gov, Identifier: NCT01558063). Importantly, ketamine's antidepressant effects only last for about 1-week and because AUD is a lifelong disorder, repeated treatment regimens would be necessary to maintain sobriety. This raises questions regarding its safety for AUD treatment since ketamine itself has the potential for addiction. Therefore, this review aims to summarize the neuroadaptations related to alcohol's addictive properties as well as ketamine's therapeutic and addictive properties. To do this, the focus will be on reward-related brain regions such as the nucleus accumbens (NAc), dorsal striatum, prefrontal cortex (PFC), hippocampus, and ventral tegmental area (VTA) to understand how acute vs. chronic exposure will alter reward signaling over time. Additionally, evidence from these studies will be summarized in both male and female subjects. Accordingly, this review aims to address the safety of repeated ketamine infusions for the treatment of AUD. Although more work about the safety of ketamine to treat AUD is warranted, we hope this review sheds light on some answers about the safety of repeated ketamine infusions.

BDNF increases synaptic NMDA receptor abundance by enhancing the local translation of Pyk2 in cultured hippocampal neurons

The effects of brain-derived neurotrophic factor (BDNF) in long-term synaptic potentiation (LTP) are thought to underlie learning and memory formation and are partly mediated by local protein synthesis. Here, we investigated the mechanisms that mediate BDNF-induced alterations in the synaptic proteome that are coupled to synaptic strengthening. BDNF induced the synaptic accumulation of GluN2B-containing NMDA receptors (NMDARs) and increased the amplitude of NMDAR-mediated miniature excitatory postsynaptic currents (mEPSCs) in cultured rat hippocampal neurons by a mechanism requiring activation of the protein tyrosine kinase Pyk2 and dependent on cellular protein synthesis. Single-particle tracking using quantum dot imaging revealed that the increase in the abundance of synaptic NMDAR currents correlated with their enhanced stability in the synaptic compartment. Furthermore, BDNF increased the local synthesis of Pyk2 at the synapse, and the observed increase in Pyk2 protein abundance along dendrites of cultured hippocampal neurons was mediated by a mechanism dependent on the ribonucleoprotein hnRNP K, which bound to Pyk2 mRNA and dissociated from it upon BDNF application. Knocking down hnRNP K reduced the BDNF-induced synaptic synthesis of Pyk2 protein, whereas its overexpression enhanced it. Together, these findings indicate that hnRNP K mediates the synaptic distribution of Pyk2 synthesis, and hence the synaptic incorporation of GluN2B-containing NMDARs, induced by BDNF, which may affect LTP and synaptic plasticity.

Prefrontal cortical trkB, glucocorticoids, and their interactions in stress and developmental contexts

The tropomyosin/tyrosine receptor kinase B (trkB) and glucocorticoid receptor (GR) regulate neuron structure and function and the hormonal stress response. Meanwhile, disruption of trkB and GR activity (e.g., by chronic stress) can perturb neuronal morphology in cortico-limbic regions implicated in stressor-related illnesses like depression. Further, several of the short- and long-term neurobehavioral consequences of stress depend on the developmental timing and context of stressor exposure. We review how the levels and activities of trkB and GR in the prefrontal cortex (PFC) change during development, interact, are modulated by stress, and are implicated in depression. We review evidence that trkB- and GR-mediated signaling events impact the density and morphology of dendritic spines, the primary sites of excitatory synapses in the brain, highlighting effects in adolescents when possible. Finally, we review the role of neurotrophin and glucocorticoid systems in stress-related metaplasticity. We argue that better understanding the long-term effects of developmental stressors on PFC trkB, GR, and related factors may yield insights into risk for chronic, remitting depression and related neuropsychiatric illnesses.

Ventral Tegmental Area GABA Neurons Are Resistant to GABA(A) Receptor-Mediated Inhibition During Ethanol Withdrawal

The neural mechanisms underlying alcohol dependence are not well-understood. GABAergic neurons in the ventral tegmental area (VTA) are a relevant target for ethanol. They are inhibited by ethanol at physiologically-relevant levels in vivo and display marked hyperexcitability during withdrawal. In the present study, we examined the effects of the GABA(A) receptor agonist muscimol on VTA neurons ex vivo following withdrawal from acute and chronic ethanol exposure. We used standard cell-attached mode electrophysiology in the slice preparation to evaluate the effects of muscimol on VTA GABA neuron firing rate following exposure to acute and chronic ethanol in male CD-1 GAD-67 GFP mice. In the acute condition, the effect of muscimol on VTA neurons was evaluated 24 h and 7 days after a single in vivo dose of saline or ethanol. In the chronic condition, the effect of muscimol on VTA neurons was evaluated 24 h and 7 days after either 2 weeks of twice-daily IP ethanol or saline or following exposure to chronic intermittent ethanol (CIE) vapor or air for 3 weeks. VTA GABA neuron firing rate was more sensitive to muscimol than DA neuron firing rate. VTA GABA neurons, but not DA neurons, were resistant to the inhibitory effects of muscimol recorded 24 h after a single ethanol injection or chronic ethanol exposure. Administration of the NMDA receptor antagonist MK-801 before ethanol injection restored the sensitivity of VTA GABA neurons to muscimol inhibition. Seven days after ethanol exposure, VTA GABA neuron firing rate was again susceptible to muscimol's inhibitory effects in the acute condition, but the resistance persisted in the chronic condition. These findings suggest that VTA GABA neurons exclusively undergo a shift in GABA(A) receptor function following acute and chronic exposure. There appears to be transient GABA(A) receptor-mediated plasticity after a single exposure to ethanol that is mediated by NMDA glutamate receptors. In addition, the resistance to muscimol inhibition in VTA GABA neurons persists in the dependent condition, which may contribute to the the hyperexcitability of VTA GABA neurons and inhibition of VTA DA neurons during withdrawal as well as the motivation to seek alcohol.

The Mammalian Circadian Clock Exhibits Chronic Ethanol Tolerance and Withdrawal-Induced Glutamate Hypersensitivity, Accompanied by Changes in Glutamate and TrkB Receptor Proteins

BACKGROUND

Alcohol tolerance and withdrawal-induced effects are criteria for alcohol use disorders listed by the DSM-V. Although tolerance and withdrawal have been studied over many decades, there is still uncertainty regarding mechanistic distinctions that characterize these different forms of ethanol (EtOH)-induced plasticity. Previously, we demonstrated that the suprachiasmatic nucleus (SCN) circadian clock develops both acute and rapid tolerance to EtOH inhibition of glutamate-induced circadian phase shifts. Here, we demonstrate that chronic EtOH tolerance and withdrawal-induced glutamate hypersensitivity occur in vitro and that rapid tolerance, chronic tolerance, and glutamate hypersensitivity have distinct cellular changes.

METHODS

We use single-unit extracellular electrophysiological recordings to determine whether chronic tolerance to EtOH inhibition of glutamatergic phase shifts and withdrawal-induced glutamate hypersensitivity develop in the SCN. We use Western blotting to compare phosphorylation state and total expression of N-methyl-D-aspartate (NMDA) receptor subunits and associated proteins in the SCN after mice were exposed to varying EtOH consumption paradigms.

RESULTS

Chronic tolerance developed after a minimum of 8 days of 4 h/d EtOH access, as indicated by a decreased sensitivity to EtOH inhibition of glutamate-induced phase shifts. We also observed an increased sensitivity to glutamate-induced phase shifts in SCN tissue following withdrawal. We demonstrated an increase in the ratio of NR2B:NR2A NMDA receptor subunit expression after 21 days, but not after 10 days of EtOH drinking. This increase persisted during EtOH withdrawal, along with an increase in NR2B Y1472 phosphorylation, mature brain-derived neurotrophic factor, and phosphorylated TrkB.

CONCLUSIONS

These results demonstrate that multiple tolerance forms and withdrawal-induced glutamate hypersensitivity occur in the SCN and that these different forms of EtOH-induced plasticity are accompanied by distinct changes in cellular physiology. Importantly, this study further demonstrates the power of using the SCN as a model system to investigate EtOH-induced plasticity.

The RNA-Binding Protein hnRNP K Mediates the Effect of BDNF on Dendritic mRNA Metabolism and Regulates Synaptic NMDA Receptors in Hippocampal Neurons

Brain-derived neurotrophic factor (BDNF) is an important mediator of long-term synaptic potentiation (LTP) in the hippocampus. The local effects of BDNF depend on the activation of translation activity, which requires the delivery of transcripts to the synapse. In this work, we found that neuronal activity regulates the dendritic localization of the RNA-binding protein heterogeneous nuclear ribonucleoprotein K (hnRNP K) in cultured rat hippocampal neurons by stimulating BDNF-Trk signaling. Microarray experiments identified a large number of transcripts that are coimmunoprecipitated with hnRNP K, and about 60% of these transcripts are dissociated from the protein upon stimulation of rat hippocampal neurons with BDNF. In vivo studies also showed a role for TrkB signaling in the dissociation of transcripts from hnRNP K upon high-frequency stimulation (HFS) of medial perforant path-granule cell synapses of male rat dentate gyrus (DG). Furthermore, treatment of rat hippocampal synaptoneurosomes with BDNF decreased the coimmunoprecipitation of hnRNP K with mRNAs coding for glutamate receptor subunits, Ca²⁺- and calmodulin-dependent protein kinase IIβ (CaMKIIβ) and BDNF. Downregulation of hnRNP K impaired the BDNF-induced enhancement of NMDA receptor (NMDAR)-mediated mEPSC, and similar results were obtained upon inhibition of protein synthesis with cycloheximide. The results demonstrate that BDNF regulates specific populations of hnRNP-associated mRNAs in neuronal dendrites and suggests an important role of hnRNP K in BDNF-dependent forms of synaptic plasticity.

Radix Puerariae modulates glutamatergic synaptic architecture and potentiates functional synaptic plasticity in primary hippocampal neurons

ETHNOPHARMACOLOGICAL RELEVANCE

Neurologic disorders are frequently characterized by synaptic pathology, including abnormal density and morphology of dendritic spines, synapse loss, and aberrant synaptic signaling and plasticity. Therefore, to promote and/or protect synapses by the use of natural molecules capable of modulating neurodevelopmental events, such as, spinogenesis and synaptic plasticity, could offer a preventive and curative strategy for nervous disorders associated with synaptic pathology. Radix Puerariae, the root of Pueraria monatana var. lobata (Willd.) Sanjappa&Pradeep, is a Chinese ethnomedicine, traditionally used for the treatment of memory-related nervous disorders including Alzheimer's disease. In the previous study, we showed that the ethanolic extracts of Radix Puerariae (RPE) and its prime constituent, puerarin induced neuritogenesis and synapse formation in cultured hippocampal neurons, and thus could improve memory functions.

AIMS OF THE STUDY

In the present study, we specifically investigated the abilities of RPE and puerarin to improve memory-related brain disorders through modulating synaptic maturation and functional potentiation.

MATERIALS AND METHODS

Rat embryonic (E19) brain neurons were cultured in the absence or presence of RPE or puerarin. At predetermined times, cells were live-stained with DiO or fixed and immunostained to visualize neuronal morphologies, or lysed for protein harvesting. Morphometric analyses of dendritic spines and synaptogenesis were performed using Image J software. Functional pre- and postsynaptic plasticity was measured by FM1-43 staining and whole-cell patch clamping, respectively. RPE or puerarin-mediated changes in actin-related protein 2 were assessed by Western blotting. Neuronal survivals were measured using propidium iodide exclusion assay.

RESULTS

RPE and puerarin both: (1) promoted a significant increase in the numbers, and maturation, of dendritic spines; (2) modulated the formation of glutamatergic synapses; (3) potentiated synaptic transmission by increasing the sizes of reserve vesicle pools at presynaptic terminals; (4) enhanced NMDA receptor-mediated postsynaptic currents, and (5) increased cell viability against naturally occurring cell death. Moreover, upregulation of actin-related protein 2 (ARP2) in RPE and puerarin treated brain neurons suggest that RPE and puerarin induced synaptic plasticity might be associated, at least in part, with ARP2-mediated actin-dependent regulation of spinogenesis.

CONCLUSIONS

Our findings indicate that RPE and puerarin might play a substantial role in the morphological and functional maturation of brain neurons and suggest that RPE and puerarin are potentially valuable preventative therapeutics for memory-related nervous disorders.

Does genetic BDNF deficiency in rats interact with neurotransmitter control of prepulse inhibition? Implications for schizophrenia

Several studies have suggested a role of BDNF in the development of schizophrenia. For example, post-mortem studies have shown significantly reduced levels of BDNF protein expression in the brain of schizophrenia patients. We investigated the relationship between reduced levels of BDNF in the brain and the regulation of prepulse inhibition (PPI), a behavioral endophenotype of schizophrenia. We used BDNF heterozygous mutant rats which display a 50% decrease of mature BDNF protein levels. Previously, we observed normal baseline PPI and responses to the dopamine D1/D2 receptor agonist, apomorphine, in these rats. Here, we focused on the effects of the NMDA receptor antagonist, MK-801, its interaction with mGluR2/3 and mGluR5 receptors, and the PPI response to serotonergic drugs. MK-801 administration caused a dose-dependent reduction of PPI and increase of startle amplitudes. Baseline PPI and the effect of 0.02-0.1mg/kg of MK-801 were not significantly altered in male or female BDNF heterozygous rats, although the MK-801-induced increase in startle levels was reduced. Co-treatment with the mGluR2/3 agonist, LY379,268, or the mGluR5 antagonist, MPEP, did not alter the effect of MK-801 on PPI in controls or BDNF mutant rats. Treatment with the serotonin-1A receptor agonist, 8-OH-DPAT, the serotonin-2A receptor agonist, DOI, or the serotonin releaser, fenfluramine, induced differential effects on PPI and startle but these effects were not different between the genotypes. These results show that a significant decrease of BDNF protein expression does not lead to reduced PPI at baseline or changes in the regulation of PPI via NMDA receptors or serotonergic mechanisms. These findings in a genetic rat model of BDNF deficiency do not support a role for similar reductions of BDNF levels in schizophrenia in the disruption of PPI, widely reported as an endophenotype of the illness. The potential implications of these results for our understanding of changes in PPI and BDNF expression in schizophrenia are discussed.

Ethanol Modulates the Spontaneous Complex Spike Waveform of Cerebellar Purkinje Cells Recorded in vivo in Mice

Cerebellar Purkinje cells (PCs) are sensitive to ethanol, but the effect of ethanol on spontaneous complex spike (CS) activity in these cells in vivo is currently unknown. Here, we investigated the effect of ethanol on spontaneous CS activity in PCs in urethane-anesthetized mice using in vivo patch-clamp recordings and pharmacological manipulation. Ethanol (300 mM) induced a decrease in the CS-evoked pause in simple spike (SS) firing and in the amplitude of the afterhyperpolarization (AHP) under current clamp conditions. Under voltage-clamp conditions, ethanol significantly decreased the area under the curve (AUC) and the number of CS spikelets, without changing the spontaneous frequency of the CSs or the instantaneous frequency of the CS spikelets. Ethanol-induced a decrease in the AUC of spontaneous CSs was concentration dependent. The EC₅₀ of ethanol for decreasing the AUC of spontaneous CSs was 168.5 mM. Blocking N-methyl-D-aspartate receptors (NMDARs) failed to prevent the ethanol-induced decreases in the CS waveform parameters. However, blockade of cannabinoid receptor 1 (CB1) significantly suppressed the ethanol-induced effects on the CS-evoked pause in SS firing, amplitude of the AHP, spikelet number and the AUC of CSs. Moreover, a CB1 receptor agonist not only reduced the number of spikelets and the AUC of CSs, but also prevented the ethanol-induced inhibition of CS activity. Our results indicate that ethanol inhibits CS activity via activation of the CB1 receptor in vivo in mice, suggesting that excessive ethanol intake inhibits climbing fiber (CF)–PC synaptic transmission by modulating CB1 receptors in the cerebellar cortex.

Cross-Species Integrative Functional Genomics in GeneWeaver Reveals a Role for Pafah1b1 in Altered Response to Alcohol

Identifying the biological substrates of complex neurobehavioral traits such as alcohol dependency pose a tremendous challenge given the diverse model systems and phenotypic assessments used. To address this problem we have developed a platform for integrated analysis of high-throughput or genome-wide functional genomics studies. A wealth of such data exists, but it is often found in disparate, non-computable forms. Our interactive web-based software system, Gene Weaver (http://www.geneweaver.org), couples curated results from genomic studies to graph-theoretical tools for combinatorial analysis. Using this system we identified a gene underlying multiple alcohol-related phenotypes in four species. A search of over 60,000 gene sets in GeneWeaver's database revealed alcohol-related experimental results including genes identified in mouse genetic mapping studies, alcohol selected Drosophila lines, Rattus differential expression, and human alcoholic brains. We identified highly connected genes and compared these to genes currently annotated to alcohol-related behaviors and processes. The most highly connected gene not annotated to alcohol was Pafah1b1. Experimental validation using a Pafah1b1 conditional knock-out mouse confirmed that this gene is associated with an increased preference for alcohol and an altered thermoregulatory response to alcohol. Although this gene has not been previously implicated in alcohol-related behaviors, its function in various neural mechanisms makes a role in alcohol-related phenomena plausible. By making diverse cross-species functional genomics data readily computable, we were able to identify and confirm a novel alcohol-related gene that may have implications for alcohol use disorders and other effects of alcohol.

Assessing ethanol's actions in the suprachiasmatic circadian clock using in vivo and in vitro approaches

Research over the past decade has demonstrated substantial interactions between the circadian system and the processes through which alcohol affects behavior and physiology. Here we summarize the results of our collaborative efforts focused on this intersection. Using a combination of in vivo and in vitro approaches, we have shown that ethanol affects many aspects of the mammalian circadian system, both acutely as well as after chronic administration. Conversely, we have shown circadian influences on ethanol consumption. Importantly, we are beginning to delve into the cellular mechanisms associated with these effects. We are also starting to form a picture of the neuroanatomical bases for many of these actions. Finally, we put our current findings into perspective by suggesting new avenues of inquiry for our future efforts.

Neurotrophin levels at admission did not change significantly upon alcohol deprivation and were positively correlated with the BMI and LDL levels

BACKGROUND

The neurotrophins brain-derived neurotrophic factor (BDNF) and neurotrophic factor 3 (NT3) could play a role in addictive behavior. Interactions between BDNF and dopamine transmission influence the alcohol intake. It has been hypothesized that extensive alcohol consumption leads to diminished circulating BDNF levels and impaired BDNF-mediated protective mechanisms. What is more, alcohol dependency causes changes in lipid metabolism which in turn may influence the neurotrophin system.

METHODS

In this study, we tested the hypothesis that alcohol withdrawal increases the serum levels of BDNF in alcoholic patients and investigated correlations between serum BDNF and NT3 and alcohol in breath as well as with the body-mass-index (BMI), lipoprotein profiles and lifestyle factors in 110 male in-patients diagnosed with alcohol addiction on the first day after admission and at discharge.

RESULTS

The intoxication level (alcohol in breath at admission) was significantly correlated with liver enzymes and BDNF concentrations (R = .28; p = .004). Patients with positive breath-alcohol test at admission had about 9 times higher NT3 levels and higher liver enzyme concentration levels than nonintoxicated subjects. Alcohol intoxicated patients with pathological aspartate aminase (ASAT) levels had even higher NT3 level (F = 5.41; p = .022). The concentration of NT3 was positively associated with the (BMI) (admission R = .36; p = .004; discharge R = .33; p = .001), and the obese patients had 3 to 5 times higher NT3 concentration than the others. Low-density lipoprotein (LDL) concentration levels were found to positively correlate with NT3 concentration levels (admission R = .025; p = .015 discharge R = .24; p = .23).

CONCLUSION

Other than expected, the levels of NT3 and to a lesser extent BDNF levels, were found to be significantly increased in acute alcohol abuse. Alcohol deprivation did not significantly change the serum neurotrophin levels at admission. NT3 levels were positively correlated with the BMI and LDL levels. Because of expected difference between genders, we recommend investigating these correlations further in patients of both genders.

Alcohol and NMDA receptor: current research and future direction

The brain is one of the major targets of alcohol actions. Most of the excitatory synaptic transmission in the central nervous system is mediated by N-methyl-D-aspartate (NMDA) receptors. However, one of the most devastating effects of alcohol leads to brain shrinkage, loss of nerve cells at specific regions through a mechanism involving excitotoxicity, oxidative stress. Earlier studies have indicated that chronic exposure to ethanol both in vivo and in vitro, increases NR1 and NR2B gene expression and their polypeptide levels. The effect of alcohol and molecular changes on the regulatory process, which modulates NMDAR functions including factors altering transcription, translation, post-translational modifications, and protein expression, as well as those influencing their interactions with different regulatory proteins (downstream effectors) are incessantly increasing at the cellular level. Further, I discuss the various genetically altered mice approaches that have been used to study NMDA receptor subunits and their functional implication. In a recent countable review, epigenetic dimension (i.e., histone modification-induced chromatin remodeling and DNA methylation, in the process of alcohol related neuroadaptation) is one of the key molecular mechanisms in alcohol mediated NMDAR alteration. Here, I provide a recount on what has already been achieved, current trends and how the future research/studies of the NMDA receptor might lead to even greater engagement with many possible new insights into the neurobiology and treatment of alcoholism.

Modulatory effects of the novel TrkB receptor agonist 7,8-dihydroxyflavone on synaptic transmission and intrinsic neuronal excitability in mouse visual cortex in vitro

7,8-Dihydroxyflavone (7,8 DHF) is a new recently identified TrkB receptor agonist, which possesses a potent neurotrophic activity and shares many physiological properties with the neurotrophin "Brain Derived Neurotrophic Factor" (BDNF). However, its precise mechanism of action at the cellular level has not been clarified yet. In the present study we explored the effects of this agent on synaptic and intrinsic neuronal properties by performing whole-cell patch clamp recordings from layer 2/3 pyramidal neurons. Incubation of acute cortical slices with 7,8-DHF (20 µM) for 30 min caused a selective reduction in the strength of GABAergic inhibition. The amplitude of evoked inhibitory postsynaptic currents (eIPSCs) was significantly reduced to 48.2±8.9% of the control level. This might be a result of decreased presynaptic γ-aminobutyric acid (GABA) release, as suggested by the reduced frequency of miniature inhibitory postsynaptic currents (mIPSCs) (control: 10.7±0.7 Hz, 7,8 DHF: 7.9±0.6 Hz) and increased Paired-Pulse Ratio (PPR) (50±8.9%). Conversely, the glutamatergic transmission was unaffected. Moreover, 7,8-DHF was able to alter the intrinsic neuronal excitability, by significantly increasing spike frequency and input resistance (control: 243.75±23.4 MΩ, 7,8 DHF: 338.5±25.1 MΩ). Remarkably, all reported effects were abolished in presence of the TrkB receptor antagonist K252a indicating a direct involvement of TrkB receptors in the action of 7,8-DHF. These data indicate that 7,8-DHF might be one promising candidate for the development of a new class of drugs called "BDNF mimetics" for the future treatment of cognitive disorders and neurodegenerative diseases.

Sex differences in neuroadaptation to alcohol and withdrawal neurotoxicity

Recent work suggests that sex differences exist with regard to both the nature of neuroadaptation to alcohol during the development of dependence, and possibly, the neurodegenerative consequences of alcohol dependence. Volumetric studies in human samples show that females may demonstrate increased volumetric brain loss with equal or lesser dependence histories than males. Furthermore, animal studies demonstrate sex differences in glutamatergic, GABAergic, and adenosinergic receptor signaling and endocrine responses following prolonged alcohol exposure. These differences may influence the development of dependence, neuronal function, and viability, particularly during alcohol withdrawal. The present review discusses the current state of knowledge in this regard. It is concluded that there exists a clear need for a more extensive examination of potential sex differences in neurodegenerative consequences of alcohol dependence in men and women, particularly with regard to the role that alterations in amino acid signaling and hypothalamic-pituitary-adrenal axis function may play. Furthermore, we note the need for expanded examination of the unique role that alcohol withdrawal-associated neuronal activity may have in the development of dependence-associated neurotoxicity.

Long-term consequences of developmental alcohol exposure on brain structure and function: therapeutic benefits of physical activity

Developmental alcohol exposure both early in life and during adolescence can have a devastating impact on normal brain structure and functioning, leading to behavioral and cognitive impairments that persist throughout the lifespan. This review discusses human work as well as animal models used to investigate the effect of alcohol exposure at various time points during development, as well as specific behavioral and neuroanatomical deficits caused by alcohol exposure. Further, cellular and molecular mediators contributing to these alcohol-induced changes are examined, such as neurotrophic factors and apoptotic markers. Next, this review seeks to support the use of aerobic exercise as a potential therapeutic intervention for alcohol-related impairments. To date, few interventions, behavioral or pharmacological, have been proven effective in mitigating some alcohol-related deficits. Exercise is a simple therapy that can be used across species and also across socioeconomic status. It has a profoundly positive influence on many measures of learning and neuroplasticity; in particular, those measures damaged by alcohol exposure. This review discusses current evidence that exercise may mitigate damage caused by developmental alcohol exposure and is a promising therapeutic target for future research and intervention strategies.

Neurochemical and neurostructural plasticity in alcoholism

The behavioral manifestations of alcoholism are primarily attributable to the numerous and lasting adaptations that occur in the brain as a result of chronic heavy alcohol consumption. As will be reviewed here, these adaptations include alcohol-induced plasticity in chemical neurotransmission, density and morphology of dendritic spines, as well as neurodegeneration and cerebral atrophy. Within the context of these neuroadaptations that have been observed in both human and animal studies, we will discuss how these changes potentially contribute to the cognitive and behavioral dysfunctions that are hallmark features of alcoholism, as well as how they reveal novel potential pharmacological targets for the treatment of this disorder.

Glucocorticoid and polyamine interactions in the plasticity of glutamatergic synapses that contribute to ethanol-associated dependence and neuronal injury

Stress contributes to the development of ethanol dependence and is also a consequence of dependence. However, the complexity of physiological interactions between activation of the hypothalamic-pituitary-adrenal (HPA) axis and ethanol itself is not well delineated. Emerging evidence derived from examination of corticotropin-releasing factor systems and glucocorticoid receptor systems in ethanol dependence suggests a role for pharmacological manipulation of the HPA axis in attenuating ethanol intake, though it is not clear how activation of the HPA axis may promote ethanol dependence or contribute to the neuroadaptative changes that accompany the development of dependence and the severity of ethanol withdrawal. This review examines the role that glucocorticoids, in particular, have in promoting ethanol-associated plasticity of glutamatergic synapses by influencing expression of endogenous linear polyamines and polyamine-sensitive polypeptide subunits of N-methyl-D-aspartate (NMDA)-type glutamate receptors. We provide evidence that interactions among glucocorticoid systems, polyamines and NMDA receptors are highly relevant to both the development of ethanol dependence and to behavioral and neuropathological sequelae associated with ethanol withdrawal. Examination of these issues is likely to be of critical importance not only in further elucidating the neurobiology of HPA axis dysregulation in ethanol dependence, but also with regard to identification of novel therapeutic targets that may be exploited in the treatment of ethanol dependence.

Acute ethanol disrupts photic and serotonergic circadian clock phase-resetting in the mouse

BACKGROUND

Alcohol dependence is associated with impaired circadian rhythms and sleep. Ethanol administration disrupts circadian clock phase-resetting, suggesting a mode for the disruptive effect of alcohol dependence on the circadian timing system. In this study, we extend previous work in C57BL/6J mice to: (i) characterize the suprachiasmatic nucleus (SCN) pharmacokinetics of acute systemic ethanol administration, (ii) explore the effects of acute ethanol on photic and nonphotic phase-resetting, and (iii) determine if the SCN is a direct target for photic effects.

METHODS

First, microdialysis was used to characterize the pharmacokinetics of acute intraperitoneal (i.p.) injections of 3 doses of ethanol (0.5, 1.0, and 2.0 g/kg) in the mouse SCN circadian clock. Second, the effects of acute i.p. ethanol administration on photic phase delays and serotonergic ([+]8-OH-DPAT-induced) phase advances of the circadian activity rhythm were assessed. Third, the effects of reverse-microdialysis ethanol perfusion of the SCN on photic phase-resetting were characterized.

RESULTS

Peak ethanol levels from the 3 doses of ethanol in the SCN occurred within 20 to 40 minutes postinjection with half-lives for clearance ranging from 0.6 to 1.8 hours. Systemic ethanol treatment dose-dependently attenuated photic and serotonergic phase-resetting. This treatment also did not affect basal SCN neuronal activity as assessed by Fos expression. Intra-SCN perfusion with ethanol markedly reduced photic phase delays.

CONCLUSIONS

These results confirm that acute ethanol attenuates photic phase-delay shifts and serotonergic phase-advance shifts in the mouse. This dual effect could disrupt photic and nonphotic entrainment mechanisms governing circadian clock timing. It is also significant that the SCN clock is a direct target for disruptive effects of ethanol on photic shifting. Such actions by ethanol could underlie the disruptive effects of alcohol abuse on behavioral, physiological, and endocrine rhythms associated with alcoholism.

EphA activation overrides the presynaptic actions of BDNF

The adult pattern of neural connectivity is shaped by repulsive and attractive factors, many of which are modulated by activity. Although much is known about the actions of these factors when studied in isolation, little is known about how they interact. To address this question, we examined the effects of sequential or coapplication of brain-derived neurotrophic factor (BDNF) and Fc-conjugated ephrin-A5 or EphA5 in cultured embryonic hippocampal neurons. BDNF promotes neurite outgrowth and synapse formation, and when applied acutely, it elicits an increase in ongoing synaptic activity. Members of the ephrin family of ligands and receptors can be repulsive and prevent formation of synaptic contacts. Acute exposure to either ephrin-A5-Fc or EphA5-Fc transiently enhanced synaptic activity when applied alone, but when applied prior to BDNF, they dramatically reduced the electrophysiological effects of the neurotrophin. Conversely, BDNF had no effect on subsequently applied ephrin-A5-Fc or EphA5-Fc. Consistent with this, ephrin-A5-Fc also prevented BDNF-induced activation of p42/44 MAPK. The effect of ephrin-A5-Fc appears to be presynaptic, as it prevented the BDNF-induced increase in spontaneous miniature postsynaptic current frequency, whereas EphA5-Fc did not. These results suggest that these factors can be categorized differently, with the contact-mediated activation of EphA receptors by ephrin-A5 overriding the diffusion-mediated effect of BDNF.

Kalrn promoter usage and isoform expression respond to chronic cocaine exposure

Background

The long-term effects of cocaine on behavior are accompanied by structural changes in excitatory glutamatergic synapses onto the medium spiny neurons of the striatum. The Kalrn gene encodes several functionally distinct isoforms; these multidomain guanine nucleotide exchange factors (GEFs) contain additional domains known to interact with phosphatidylinositides as well as with a number of different proteins. Through their activation of Rho proteins and their interactions with other proteins, the different Kalirin isoforms affect cytoskeletal organization. Chronic exposure of adult male rodents to cocaine increases levels of Kalirin 7 in the striatum. When exposed chronically to cocaine, mice lacking Kalirin 7, the major adult isoform, fail to show an increase in dendritic spine density in the nucleus accumbens, show diminished place preference for cocaine, and exhibit increased locomotor activity in response to cocaine.

Results

The use of alternate promoters and 3'-terminal exons of the mouse Kalrn gene were investigated using real-time quantitative polymerase chain reaction. While the two most distal full-length Kalrn promoters are used equally in the prefrontal cortex, the more proximal of these promoters accounts for most of the transcripts expressed in the nucleus accumbens. The 3'-terminal exon unique to the Kalirin 7 isoform accounts for a greater percentage of the Kalrn transcripts in prefrontal cortex than in nucleus accumbens. Western blot analyses confirmed these differences. Chronic cocaine treatment increases usage of the promoter encoding the Δ-Kalirin isoforms but does not alter full-length Kalirin promoter usage. Usage of the 3'-terminal exon unique to Kalirin 7 increases following chronic cocaine exposure.

Conclusions

Kalrn promoter and 3'-terminal exon utilization are region-specific. In the nucleus accumbens, cocaine-mediated alterations in promoter usage and 3'-terminal exon usage favor expression of Kalirin 7 and Δ-Kalirin 7. The Δ-isoform, which lacks a Sec14p domain and four of the nine spectrin-like repeats found in full-length Kalirin isoforms, increases spine headsize without increasing dendritic spine numbers. Thus cocaine-mediated changes in alternative splicing of the Kalrn gene may contribute importantly to the behavioral, morphological and biochemical responses observed.

Ethanol modulates mammalian circadian clock phase resetting through extrasynaptic GABA receptor activation

Ethanol modulates the actions of multiple neurotransmitter systems, including GABA. However, its enhancing effects on GABA signaling typically are seen only at high concentrations. In contrast, although GABA is a prominent neurotransmitter in the circadian clock of the suprachiasmatic nucleus (SCN), we see ethanol modulation of clock phase resetting at low concentrations (<50 mM). A possible explanation is that ethanol enhances GABAergic signaling in the SCN through activating GABA(A) receptors that contain the delta subunit (GABA(Adelta) receptors), which are sensitive to low ethanol concentrations. Therefore, we investigated whether ethanol acts on GABA(Adelta) receptors in the SCN. Here we show that acute application of the GABA(Adelta) receptor antagonist, RO15-4513, to mouse hypothalamic slices containing the SCN prevents ethanol inhibition of nighttime glutamate-induced (photic-like) phase delays of the circadian clock. Diazepam, which enhances activity of GABA(A) receptors containing the gamma subunit (GABA(Agamma) receptors), does not modulate these phase shifts. Moreover, we find that RO15-4513 prevents ethanol enhancement of daytime serotonergic (non-photic) phase advances of the circadian clock. Furthermore, diazepam phase-advances the SCN circadian clock when applied alone in the daytime, while ethanol has no effect by itself at that time. These data support the hypothesis that ethanol acts on GABA(Adelta) receptors in the SCN to modulate photic and non-photic circadian clock phase resetting. They also reveal distinct modulatory roles of different GABA(A) receptor subtypes in circadian clock phase regulation.

Presynaptic and postsynaptic NMDA receptors mediate distinct effects of brain-derived neurotrophic factor on synaptic transmission

In addition to its effects on neuronal survival and differentiation, brain-derived neurotrophic factor (BDNF) plays an important role in modulating synaptic transmission and plasticity in many brain areas, most notably the neocortex and hippocampus. These effects may underlie a role for BDNF in learning and memory as well as developmental plasticity. Consistent with localization of the tropomyosin-related kinase B receptor to both sides of the synapse, BDNF appears to have pre- and postsynaptic effects, but the underlying cellular mechanisms are unclear and it is not known whether pre- and postsynaptic modulations by BDNF occur simultaneously. To address these issues, we recorded dual-component (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid [AMPA] and N-methyl-D-aspartate [NMDA]) miniature excitatory postsynaptic currents (mEPSCs) from cortical and hippocampal pyramidal neurons and dentate gyrus granule cells from acute brain slices. BDNF had no effect on the fast component of mEPSC decay or on the peak amplitude, suggesting that BDNF did not modulate postsynaptic AMPA receptors, although BDNF rapidly modulated NMDA receptors, as seen by an enhancement of the slow component of mEPSC decay that was prevented by blocking postsynaptic NMDA receptors. At the same time, BDNF acted presynaptically to enhance mEPSC frequency. Surprisingly, the effect on frequency was also NMDA receptor dependent, but required activation of presynaptic, not postsynaptic, NMDA receptors. BDNF also enhanced action potential-dependent glutamate release via presynaptic NMDA receptors, an effect that was unmasked when voltage-gated calcium channels were partially inhibited. Our results indicate that BDNF acutely modulates presynaptic release and postsynaptic responsiveness through simultaneous effects on pre- and postsynaptic NMDA receptors.

BDNF modulation of NMDA receptors is activity dependent

Brain-derived neurotrophic factor (BDNF), a potent modulator of synaptic transmission, is known to influence associative synaptic plasticity and refinement of neural connectivity. We now show that BDNF modulation of glutamate currents in hippocampal neurons exhibits the additional property of use dependence, a postsynaptic mechanism resulting in selective modulation of active channels. We demonstrate selectivity by varying the repetition rate of iontophoretically applied glutamate pulses during BDNF exposure. During relatively high-frequency glutamate pulses (0.1 Hz), BDNF application elicited a doubling of the glutamate current. During low-frequency pulses (0.0033 Hz), however, BDNF evoked a dramatically diminished response. This effect was apparently mediated by calcium because manipulations that prevented elevation of intracellular calcium largely eliminated the action of BDNF on glutamate currents. To confirm N-methyl-D-aspartate (NMDA) receptor involvement and assess spatial requirements, we made cell-attached single-channel recordings from somatic NMDA receptors. Inclusion of calcium in the pipette was sufficient to produce enhancement of channel activity by BDNF. Substitution of EGTA for calcium prevented BDNF effects. We conclude that BDNF modulation of postsynaptic NMDA receptors requires concurrent neuronal activity potentially conferring synaptic specificity on the neurotrophin's actions.

Ethanol-BDNF interactions: still more questions than answers

Brain-derived neurotrophic factor (BDNF) has emerged as a regulator of development, plasticity and, recently, addiction. Decreased neurotrophic activity may be involved in ethanol-induced neurodegeneration in the adult brain and in the etiology of alcohol-related neurodevelopmental disorders. This can occur through decreased expression of BDNF or through inability of the receptor to transduce signals in the presence of ethanol. In contrast, recent studies implicate region-specific up-regulation of BDNF and associated signaling pathways in anxiety, addiction and homeostasis after ethanol exposure. Anxiety and depression are precipitating factors for substance abuse and these disorders also involve region-specific changes in BDNF in both pathogenesis and response to pharmacotherapy. Polymorphisms in the genes coding for BDNF and its receptor TrkB are linked to affective, substance abuse and appetitive disorders and therefore may play a role in the development of alcoholism. This review summarizes historical and pre-clinical data on BDNF and TrkB as it relates to ethanol toxicity and addiction. Many unresolved questions about region-specific changes in BDNF expression and the precise role of BDNF in neuropsychiatric disorders and addiction remain to be elucidated. Resolution of these questions will require significant integration of the literature on addiction and comorbid psychiatric disorders that contribute to the development of alcoholism.

Acute ethanol modulates glutamatergic and serotonergic phase shifts of the mouse circadian clock in vitro

Alcohol abuse is associated with sleep problems, which are often linked to circadian rhythm disturbances. However, there is no information on the direct effects of ethanol on the mammalian circadian clock. Acute ethanol inhibits glutamate signaling, which is the primary mechanism through which light resets the mammalian clock in the suprachiasmatic nucleus (SCN). Glutamate and light also inhibit circadian clock resetting induced by nonphotic signals, including 5-HT. Thus, we investigated the effects of acute ethanol on both glutamatergic and serotoninergic resetting of the mouse SCN clock in vitro. We show that ethanol dose-dependently inhibits glutamate-induced phase shifts and enhances serotonergic phase shifts. The inhibition of glutamate-induced phase shifts is not affected by excess glutamate, glycine or d-serine, but is prevented by excess brain-derived neurotrophic factor (BDNF). BDNF is known to augment glutamate signaling in the SCN and to be necessary for glutamate/light-induced phase shifts. Thus, ethanol may inhibit glutamate-induced clock resetting at least in part by blocking BDNF enhancement of glutamate signaling. Ethanol enhancement of serotonergic phase shifts is mimicked by treatments that suppress glutamate signaling in the SCN, including antagonists of glutamate receptors, BDNF signaling and nitric oxide synthase. The combined effect of ethanol with these treatments is not additive, suggesting they act through a common pathway. Our data indicate further that the interaction between 5-HT and glutamate in the SCN may occur downstream from nitric oxide synthase activation. Thus, acute ethanol disrupts normal circadian clock phase regulation, which could contribute to the physiological and psychological problems associated with alcohol abuse.

Brain-derived neurotrophic factor rapidly increases NMDA receptor channel activity through Fyn-mediated phosphorylation

Brain-derived neurotrophic factor (BDNF) is a potent modulator of hippocampal synaptic plasticity. Previously, we found that one of the targets of BDNF modulation is NR2B-containing NMDA receptors. Furthermore, exposure to the trophin rapidly increases NMDA receptor activity and enhances tyrosine phosphorylation of NR2B in cortical and hippocampal postsynaptic densities (PSDs), potentially linking receptor phosphorylation to synaptic plasticity. To define the specific NR2B residue(s) regulated by BDNF, we focused on tyrosine 1472, phosphorylation of which increases after LTP. BDNF rapidly increased phosphorylation in cortical PSDs. The tyrosine kinase Fyn is critical since BDNF-dependent phosphorylation was abolished in Fyn knockout mice. Single-channel patch clamp recordings showed that Fyn is required for the increase in NMDA receptor activity elicited by BDNF. Collectively, our results suggest that BDNF enhances phosphorylation of NR2B tyrosine 1472 through activation of Fyn, leading to alteration of NMDA receptor activity and increased synaptic transmission.

Modulation of NMDA receptors by AKT kinase

The aim of the present work was to assess whether Akt modulates NMDA receptor function in cerebellar neurons in culture. Forskolin increases cAMP and activates Akt and NMDA receptors. In neurons treated with forskolin, intracellular calcium increased to 296 +/- 38% and this was completely prevented by inhibition of Akt. This indicates that, in these neurons, cAMP modulates NMDA receptors via Epac and Akt. Brain derived neurotrophic factor (BDNF) increases phosphorylation (and activity) of Akt to 350 +/- 60% of basal and also potentiates the increase of calcium and in cGMP induced by NMDA. BDNF-induced potentiation of NMDA receptor function is completely prevented by inhibition of PI3 kinase or of Akt. This indicates that BDNF modulates NMDA receptor function via PI3 kinase and Akt. Activation of NMDA receptors also leads to phosphorylation and activation of Akt which, in turn, potentiates NMDA receptor activation. The results reported indicate that when Akt activity increases the activation of NMDA receptors by its agonists also increases. Akt may play important roles in the modulation of NMDA receptor responses by other neurotransmitters and modulators and in the adaptation of NMDA receptor function to the physiological environmental conditions.

Blockade and enhancement of glutamate receptor responses in Xenopus oocytes by methylated arsenicals

Pentavalent and trivalent organoarsenic compounds belong to the major metabolites of inorganic arsenicals detected in humans. Recently, the question was raised whether the organic arsenicals represent metabolites of a detoxification process or methylated species with deleterious biological effects. In this study, the effects of trivalent arsenite (AsO(3) (3-); iA(III)), the pentavalent organoarsenic compounds monomethylarsonic acid (CH(3)AsO(OH)(2); MMA(V)) and dimethylarsinic acid ((CH(3))(2)AsO(OH); DMA(V)) and the trivalent compounds monomethylarsonous acid (CH(3)As(OH)(2), MMA(III)) and dimethylarsinous acid ((CH(3))(2)As(OH); DMA(III)) were tested on glutamate receptors and on voltage-operated potassium and sodium channels heterologously expressed in Xenopus oocytes. Membrane currents of ion channels were measured by conventional two-electrode voltage-clamp techniques. The effects of arsenite were tested in concentrations of 1-1,000 micromol/l and the organic arsenical compounds were tested in concentrations of 0.1-100 micromol/l. We found no significant effects on voltage-operated ion channels; however, the arsenicals exert different effects on glutamate receptors. While MMA(V) and MMA(III) significantly enhanced ion currents through N-methyl-D: -aspartate (NMDA) receptor ion channels with threshold concentrations <10 micromol/l, DMA(V) and DMA(III) significantly reduced NMDA-receptor mediated responses with threshold concentrations <0.1 micromol/l; iA(III) had no effects on glutamate receptors of the NMDA type. MMA(III) and DMA(V) significantly reduced ion currents through alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor ion channels with threshold concentrations <10 micromol/l (MMA(III)) and <1 micromol/l (DMA(V)). MMA(V) and iA(III) had no significant effects on glutamate receptors of the AMPA type. The effects of MMA(V), MMA(III), DMA(V) and DMA(III )on glutamate receptors point to a neurotoxic potential of these substances.