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Neurosteroids are rapidly emerging as important new therapies in neuropsychiatry, with one such agent, brexanolone, already approved for treatment of postpartum depression, and others on the horizon. These steroids have unique properties, including neuroprotective effects that could benefit a wide range of brain illnesses including depression, anxiety, epilepsy, and neurodegeneration. Over the past 25 years, our group has developed ex vivo rodent models to examine factors contributing to several forms of neurodegeneration in the retina. In the course of this work, we have developed a model of acute closed angle glaucoma that involves incubation of ex vivo retinas under hyperbaric conditions and results in neuronal and axonal changes that mimic glaucoma. We have used this model to determine neuroprotective mechanisms that could have therapeutic implications. In particular, we have focused on the role of both endogenous and exogenous neurosteroids in modulating the effects of acute high pressure. Endogenous allopregnanolone, a major stress-activated neurosteroid in the brain and retina, helps to prevent severe pressure-induced retinal excitotoxicity but is unable to protect against degenerative changes in ganglion cells and their axons under hyperbaric conditions. However, exogenous allopregnanolone, at a pharmacological concentration, completely preserves retinal structure and does so by combined effects on gamma-aminobutyric acid type A receptors and stimulation of the cellular process of macroautophagy. Surprisingly, the enantiomer of allopregnanolone, which is inactive at gamma-aminobutyric acid type A receptors, is equally retinoprotective and acts primarily via autophagy. Both enantiomers are also equally effective in preserving retinal structure and function in an in vivo glaucoma model. These studies in the retina have important implications for the ongoing development of allopregnanolone and other neurosteroids as therapeutics for neuropsychiatric illnesses.

Objective: Isoliquiritigenin (ILTG) is a chalcone compound that exhibits hypnotic effects via gamma-aminobutyric acid type A (GABAA) receptors. The ventrolateral preoptic area (VLPO) is a sleep-promoting center that contains a large number of GABA-releasing cells. There are two cell types in the VLPO: one generates a low-threshold spike (LTS), whereas the other lacks an LTS (non-LTS). Method: Whole-cell patch-clamp technology was used to detect the firing and currents of LTS and non-LTS cells in the VLPO. Results: Bath administration of ILTG (10 μM) increased the firing rate of VLPO LTS cells, reversed by flumazenil (5 μM), a GABAA benzodiazepine site antagonist. However, the firing rate of VLPO non-LTS cells was inhibited by ILTG (10 μM), also reversed by flumazenil (5 μM). No differences were detected regarding resting membrane potential (RMP) amplitude, spike threshold, afterhyperpolarization (AHP) amplitude, or action potential duration (APD50) after ILTG (10 μM) perfusion in VLPO LTS cells. RMP amplitude was more hyperpolarized and spike threshold was higher after ILTG (10 μM) application in VLPO non-LTS cells. In addition, ILTG significantly reduced the frequency of miniature inhibitory postsynaptic currents (mIPSCs) in VLPO LTS cells. ILTG significantly increased the amplitude of mIPSCs in VLPO non-LTS cells. Conclusions: This study revealed that ILTG suppresses presynaptic GABA release on VLPO LTS cells, thereby increasing their excitability. ILTG enhances postsynaptic GABAA receptor function on VLPO non-LTS cells, thereby decreasing their excitability. These results suggest that ILTG may produce hypnotic effects by modulating the GABAergic synaptic transmission properties of these two cell types.

Background: Parkinson's disease (PD) is one of the most common neurodegenerative disorders which is characterized by progressive loss of dopaminergic neurons in substantia nigra. Therefore, drugs or natural agents that have suppressive effects on dopaminergic cell death may reduce the progression of such disorder. Here, the effect of natural product alpha-pinene was evaluated on 6-hydroxydopamine (6-OHDA)-induced damage in SH-SY5Y human dopaminergic cell line as an in vitro model of PD. Methods: The cells were incubated by 150 μM 6-OHDA alone or accompanied with different concentration of alpha-pinene (10–180 μM). Cell viability was determined by MTT assay. The amount of intracellular reactive oxygen species (ROS) and mitochondrial membrane potential were measured by fluorescence spectrophotometry. In addition, the components of molecular apoptotic pathway such as cytochrome c release, Bax, Bcl-2, and caspase-3 levels were measured by immunoblotting. Gamma-aminobutyric acid (GABA) antagonist, bicuculline, was used to find the role of GABA Type A (GABAA) receptors in the signaling of alpha-pinene. Results: The data showed that 6-OHDA produced cell damage, decreased mitochondrial membrane potential, increased intracellular ROS and cytochrome c release, as well as increased Bax/Bcl-2 ratio and caspase-3 activity. Moreover, alpha-pinene (70 μM) significantly inhibited cellular and molecular abnormalities. Blockage of GABAA receptor significantly suppressed the protective effect of alpha-pinene. Conclusion: The results suggest that alpha-pinene has a protective effect against dopaminergic toxicity, and at least in part, its antioxidant and antiapoptotic properties are probably involved in such protection.

Background: Mefenamic acid (MFA), a common analgesic, causes central nervous system (CNS) toxicity at high doses with a proposed activity on the Gamma-aminobutyric acid (GABA) system. However, it remains unknown whether flumazenil (FMZ), a GABA type A receptor (GABAAR) antagonist, can reverse MFA toxicity. Methods: The behavioral and neurophysiological effects of MFA were investigated in mice with and without FMZ pre-treatment. The elevated zero maze (EZM) and marble burying tests were used to assess anxiety-like behaviors and burying activities, respectively. The standard bar test was used to evaluate catalepsy, while the actophotometer test was used to measure locomotor activity. Seizure intensity was scored, and fatalities were counted. Results: Without FMZ pre-treatment, MFA induced behavioral and neurophysiological effects in a dose-dependent manner as follows: At a dose of 20 mg/kg, i.p, MFA-treated mice exhibited anxiety-like behaviors, which was determined by a significant increase in the time spent in the closed areas and a significant decrease in the number of entries to the open areas of the EZM apparatus. These mice also showed a significant decrease in the burying activity, manifested as a significant decrease in the number of buried marbles. At 40 mg/kg, i.p., MFA-treated mice showed catalepsy that was associated with a significant decrease in locomotor activity. At a dose of 80 mg/kg, i.p., mice developed fatal tonic-clonic seizures (seizure score = 4). Pre-treatment with FMZ (5 mg/kg, i.p.) significantly reversed the anxiety-like behaviors and restored marble-burying activity. Additionally, FMZ prevented catalepsy, significantly restored locomotor activity, reduced seizure intensity (seizure score = 0.3) and significantly reduced mortalities. Conclusions: The present study’s findings indicate that activation of the GABAAR is involved in the CNS toxicity of MFA, and FMZ reverses MFA toxicity by interfering with this receptor.

Background: Parkinson's disease (PD) is one of the most common neurodegenerative disorders which is characterized by progressive loss of dopaminergic neurons in substantia nigra. Therefore, drugs or natural agents that have suppressive effects on dopaminergic cell death may reduce the progression of such disorder. Here, the effect of natural product alpha-pinene was evaluated on 6-hydroxydopamine (6-OHDA)-induced damage in SH-SY5Y human dopaminergic cell line as an in vitro model of PD. Methods: The cells were incubated by 150 μM 6-OHDA alone or accompanied with different concentration of alpha-pinene (10–180 μM). Cell viability was determined by MTT assay. The amount of intracellular reactive oxygen species (ROS) and mitochondrial membrane potential were measured by fluorescence spectrophotometry. In addition, the components of molecular apoptotic pathway such as cytochrome c release, Bax, Bcl-2, and caspase-3 levels were measured by immunoblotting. Gamma-aminobutyric acid (GABA) antagonist, bicuculline, was used to find the role of GABA Type A (GABAA) receptors in the signaling of alpha-pinene. Results: The data showed that 6-OHDA produced cell damage, decreased mitochondrial membrane potential, increased intracellular ROS and cytochrome c release, as well as increased Bax/Bcl-2 ratio and caspase-3 activity. Moreover, alpha-pinene (70 μM) significantly inhibited cellular and molecular abnormalities. Blockage of GABAA receptor significantly suppressed the protective effect of alpha-pinene. Conclusion: The results suggest that alpha-pinene has a protective effect against dopaminergic toxicity, and at least in part, its antioxidant and antiapoptotic properties are probably involved in such protection. [ABSTRACT FROM AUTHOR]

Gamma-aminobutyric type A receptor (GABA AR) is a member of the Cys-loop family of pentameric ligand gated ion channels (pLGICs). It has been identified as a key target for many clinical drugs. In the present study, we construct the structure of human 2α 12β 2γ 2 GABA AR using a homology modeling method. The structures of ten benzodiazepine type drugs and two non-benzodiazepine type drugs were then docked into the potential benzodiazepine binding site on the GABA AR. By analyzing the docking results, the critical residues His102 (α 1), Phe77 (γ 2) and Phe100 (α 1) were identified in the binding site. To gain insight into the binding affinity, molecular dynamics (MD) simulations were performed for all the receptor–ligand complexes. We also examined single mutant GABA AR (His102A) in complexes with the three drugs (flurazepam, eszopiclone and zolpidem) to elucidate receptor–ligand interactions. For each receptor–ligand complex (with flurazepam, eszopiclone and zolpidem), we calculated the average distance between the C α of the mutant residue His102A (α 1) to the center of mass of the ligands. The results reveal that the distance between the C α of the mutant residue His102A (α 1) to the center of flurazepam is larger than that between His102 (α 1) to flurazepam in the WT type complex. Molecular mechanic-generalized Born surface area (MM-GBSA)-based binding free energy calculations were performed. The binding free energy was decomposed into ligand-residue pairs to create a ligand-residue interaction spectrum. The predicted binding free energies correlated well ( R2 = 0.87) with the experimental binding free energies. Overall, the major interaction comes from a few groups around His102 (α 1), Phe77 (γ 2) and Phe100 (α 1). These groups of interaction consist of at least of 12 residues in total with a binding energy of more than 1 kcal mol −1. The simulation study disclosed herein provides a meaningful insight into GABA AR–ligand interactions and helps to arrive at a binding mode hypothesis with implications for drug design. [ABSTRACT FROM AUTHOR]