Brain-derived neurotrophic factor mitigates chronic ethanol-induced attenuation of gamma-aminobutyric acid responses in cultured cerebellar granule cells

Emerging evidence for endogenous neurosteroid modulation of pro-inflammatory and anti-inflammatory pathways that impact neuropsychiatric disease

This mini-review presents emerging evidence that endogenous neurosteroids modulate both pro- and anti-inflammatory signaling by immune cells and brain cells that contribute to depression, alcohol use disorders, and other inflammatory conditions. We first review the literature on pregnenolone and allopregnanolone inhibition of proinflammatory neuroimmune pathways in the periphery and the brain - effects that are independent of GABAergic mechanisms. We follow with evidence for neurosteroid enhancement of anti-inflammatory and protective pathways in brain and immune cells. These studies draw clinical relevance from a large body of evidence that pro-inflammatory immune signaling is dysregulated in many brain disorders and the fact that neurosteroids inhibit the same inflammatory pathways that are activated in depression, alcohol use disorders and other inflammatory conditions. Thus, we describe evidence that neurosteroid levels are decreased and neurosteroid supplementation has therapeutic efficacy in these neuropsychiatric conditions. We conclude with a perspective that endogenous regulation of immune balance between pro- and anti-inflammatory pathways by neurosteroid signaling is essential to prevent the onset of disease. Deficits in neurosteroids may unleash excessive pro-inflammatory activation which progresses in a feed-forward manner to disrupt brain networks that regulate stress, emotion and motivation. Neurosteroids can block various inflammatory pathways in mouse and human macrophages, rat brain and human blood and therefore provide new hope for treatment of intractable conditions that involve excessive inflammatory signaling.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

The Role of Alteration of Glutamic Acid and Gaba in Learning and Memory Impairment of Rats Induced by Aluminum

Aluminum exposure has been reported to be related to learning and memory impairment. This study examines the role of aluminum in alterating amino acids of the cerebral cortex of rats. The Step-down type tests were performed to investigate the alteration of learning and memory of rats induced by aluminum. The amino acids in the cerebral cortex were detected by high performance liquid chromatography (HLPC). Results show that the amounts of aluminum in the cerebral cortex increased by 5.0mgAl3+/(Kg·BW) group and 10.0mg Al3+/(Kg·BW) group. In the Step-down type test, the EN1 increased significantly in the Al3+ 10.0mg/(Kg·BW) group. The latency shortened obviously and the EN2 increased significantly in the 10.0mg Al3+/(Kg·BW) group. The content of Glu (Glutamic acid) increased but the content of GABA (gamma-aminobutyric acid) decreased significantly in the 10.0mg Al3+/(Kg·BW) group. This present study shows evidence that the disorder of amino acid neurotransmitters system plays an important role in the impairment of learning and memory of rats induced by aluminum.

Depression of extra-cellular GABA and increase of NMDA-induced nitric oxide following acute intra-nuclear administration of alcohol in the cerebellar nuclei of the rat

Gamma-aminobutyric acid (GABA) and nitric oxide are two key-transmitters in cerebellar nuclei, the major output of cerebellar circuitry. The aims of this study were to investigate the effects of acute intra-cerebellar administration of ethanol (20 mM) on extra-cellular levels of GABA and on the NMDA-induced nitric oxide (NO) production using microdialysis in the rat. We also studied: (i) the effects of a pre-administration of DNQX, a specific antagonist of AMPA receptors, on NO production, (ii) the effects of a pre-administration of 7-NI (7-nitroindazole, an inhibitor of neuronal nitric oxide synthase NOS) and APV (D-2-amino-5-phosphonovaleric acid, a specific blocker of the NMDA type glutamate receptors) on the actions of alcohol/NMDA on glutamate receptors, and (iii) the in vivo interaction between DNQX, ethanol and NMDA receptor activation. We found that ethanol decreased the amount of extra-cellular GABA, and that this effect was counterbalanced by administration of tiagabine 1 mg/kg, a potent inhibitor of GAT-1 GABA transporter, given by the i.p. route. In loco administration of NMDA increased the levels of NO, as previously reported. A pre-administration of DNQX (500 microM) increased significantly the production of NO up to toxic levels, as well as ethanol administration. A pre-administration of 7-NI or APV reduced significantly the amounts of NO when NMDA and alcohol were infused simultaneously. The combination of ethanol with DNQX was associated with a marked enhancement of the concentrations of NO. The activity of GAT-1 in cerebellar nuclei and around this target, including in glial cells expressing GAT-1 activated by ambient GABA, seems to be spared by ethanol. Tiagabine could be considered as a candidate for future investigational treatments of acute ethanol-induced dysfunction of cerebellar nuclei. We found a potentiation of the production of NO when AMPA antagonists are given simultaneously to ethanol. The hypothesis of AMPA neurotoxicity, which has convincing arguments during chronic exposure, is challenged in this model of acute cerebellar nuclear toxicity of alcohol.

Ethanol regulation of γ-aminobutyric acidA receptors: genomic and nongenomic mechanisms

gamma-Aminobutyric acid(A) (GABA(A)) receptors are ligand-gated ion channels that, predominantly, mediate inhibitory synaptic transmission in the CNS. These receptors are pentameric complexes that are comprised of subunits from several classes (alpha, beta, gamma, delta, ), with each class consisting of several isoforms. Chronic ethanol consumption alters GABA(A) receptor function producing cellular tolerance to GABA and ethanol, cross-tolerance to benzodiazepines and barbiturates, and sensitization to inverse agonists. Recent studies have clearly demonstrated that GABA(A) receptors play an important role in ethanol dependence and functional properties of GABA(A) receptor are altered following chronic ethanol administration. However, the exact mechanisms that account for alterations in GABA(A) receptor function following chronic ethanol administration have not been resolved. The mechanisms responsible for adaptation of GABA(A) receptors to chronic ethanol exposure may involve ethanol-induced changes in cell surface expression, subcellular localization, synaptic localization, receptor phosphorylation, neurosteroids, and/or changes in GABA(A) receptor subunit composition. In this review, we provide an overview of recent data pertaining to mechanisms that could be responsible for altered properties and expression of GABA(A) receptors following chronic ethanol administration.

BDNF enhancement of postsynaptic NMDA receptors is blocked by ethanol

The neurotrophin brain-derived neurotrophic factor (BDNF) modulates several distinct aspects of synaptic transmission. Physiological and biochemical evidence implicates the NMDA glutamate receptor as one of the targets for BDNF modulation. In the present studies, murine brain slices containing hippocampus and neocortex were used to study the effects of BDNF on excitatory neurotransmission. Acute exposure to BDNF rapidly and reversibly enhanced the magnitude of NMDA-mediated, but not AMPA receptor-mediated, synaptic currents, specifically enhancing the activity of NMDA receptors containing the NR2B subunit. This effect of BDNF was dependent on activation of trkB neurotrophin receptors because similar effects were not seen with the related neurotrophins NT-3 or NGF. Furthermore, activation of trkB receptors in the postsynaptic neuron was required, as BDNF-induced potentiation was blocked by postsynaptic injection of a trk tyrosine kinase inhibitor. Interestingly, the effect of BDNF was also completely blocked by pretreatment with ethanol, even at concentrations of ethanol that had minimal direct effects on NMDA-mediated responses. These results provide a potential mechanism for the proposed role for BDNF in activity-dependent synaptic plasticity and, potentially, learning and memory processes.