GABA: A critical player for regulating synaptic plasticity and adult neurogenesis

During aging, the decrease of cognitive ability is believed to be the cause of age related neuronal damage and reduced proliferation and differentiation of adult-born neural precursor cells. To modulate the synaptic plasticity and adult neurogenesis, it is of immense importance to enhance the potential of resident neural stem cells of hippocampus and sub ventricular zone (SVZ). The necessity to restore brain functions is enormous in the neurodegenerative disease like Alzheimer, Parkinson diseases, stress induced cognitive dysfunction, depression and age-associated and HIV-associated dementia. As a pioneer transmitter, Gamma Amino Butaric Acid (GABA) influences the activity dependent adult neurogenesis and excites immature neurons in adult hippocampus. GABA holds the key for making adult immature neuron to mature functional neuron hence plays critical role in adult neurogenesis.This review aims to discuss about the spatio-temporal expression of various subunit of GABA-A receptor and how these subunits intimately modulates the synaptic plasticity. During developmental period GABAergic neurons mature at early stages and regulate overall neural activity much before the activity of glutamate. Not only during development but also during adult neurogenesis GABA plays a significant role in neurite outgrowth and establishing well network.

Prawdopodobna dysfunkcja receptorów GABA-A u pacjentów z zaburzeniami neurorozwojowymi uwarunkowanymi wariantami patogennymi w genie GNAO1.

Wprowadzenie i cel: Spektrum fenotypowe zaburzeń neurorozwojowych związanych z wariantami patogennymi w genie GNAO1 obejmuje encefalopatię rozwojowo-padaczkową (ERP) i szereg zaburzeń ruchowych (ZR). Powyższe objawy kliniczne są związane z zaburzeniami presynaptycznego autohamującego działania neuroprzekaźników na receptory: muskarynowy M2/M4, α2-adrenergiczny, opioidowy μ/δ, gabaergiczny GABA-B. Dokonano analizy korelacji fenotyp-genotyp u pacjentów z wariantami patogennymi w genie GNAO1 celem zidentyfikowania nowych powiązań pomiędzy objawami klinicznymi a określonymi zaburzeniami neuroprzekaźnictwa. Materiał i metody: Przebieg kliniczny choroby oceniano u dwóch pacjentów polskiego pochodzenia ze zidentyfikowanymi wariantami patogennymi w genie GNAO1 de novo. W obu przypadkach diagnozę postawiono na podstawie sekwencjonowania całoeksomowego (WES) na platformie Illumina. Wyniki: U pierwszego pacjenta z objawami ERP został zidentyfikowany wariant typu utraty funkcji w genie GNAO1 (c.607G>A). U tego pacjenta ZR (choreatetoza, dystonia ogniskowa) współistniały z napadami padaczkowymi. U drugiego pacjenta ta sama prezentacja kliniczna ZR, bez współistniejącej padaczki, była spowodowana przez patogenny wariant o nieznanej funkcji (c.709G>A). U obu pacjentów stwierdzono nadwrażliwość na wyższe dawki benzodiazepin, a u drugiego również na wyższe dawki baklofenu. U pierwszego pacjenta obserwowano wczesny początek ERP (2. tyg. ż.) z dobrą odpowiedzią na leczenie wigabatryną i następującym rozwojem nadmiernej reakcji zaskoczenia od 3 r. ż., z paradoksalną reakcją na leczenie klonazepamem. Wnioski: Przeprowadzona analiza korelacji fenotyp-genotyp u dwóch pacjentów z zaburzeniami neurorozwojowymi związanymi z wariantami patogennymi w genie GNAO1 zidentyfikowała reakcje na zastosowane leczenie lub reakcje nadwrażliwości na leki, które mogą wskazywać na zaburzenia czynnościowe nie tylko receptorów GABA-B, ale również GABA-A. Potrzebne są dalsze badania funkcjonalne.

Electrical activity between skin cells regulates melanoma initiation

Oncogenes can only initiate tumors in certain cellular contexts, which is referred to as oncogenic competence. In melanoma, whether cells in the microenvironment can endow such competence remains unclear. Using a combination of zebrafish transgenesis coupled with human tissues, we demonstrate that GABAergic signaling between keratinocytes and melanocytes promotes melanoma initiation by BRAFV600E. GABA is synthesized in melanoma cells, which then acts on GABA-A receptors on keratinocytes. Electron microscopy demonstrates synapse-like structures between keratinocytes and melanoma cells, and multi-electrode array analysis shows that GABA acts to inhibit electrical activity in melanoma/keratinocyte co-cultures. Genetic and pharmacologic perturbation of GABA synthesis abrogates melanoma initiation in vivo. These data suggest that electrical activity across the skin microenvironment determines the ability of oncogenes to initiate melanoma.

Complex regulation of Gephyrin splicing is a determinant of inhibitory postsynaptic diversity

Gephyrin (GPHN) regulates the clustering of postsynaptic components at inhibitory synapses and is involved in pathophysiology of neuropsychiatric disorders. Here, we uncover an extensive diversity of GPHN transcripts that are tightly controlled by splicing during mouse and human brain development. Proteomic analysis reveals at least a hundred isoforms of GPHN incorporated at inhibitory Glycine and GABA-A receptors containing synapses. They exhibit different localization and postsynaptic clustering properties, and altering the expression level of one isoform is sufficient to affect the number, size, and density of inhibitory synapses in cerebellar Purkinje cells. Furthermore, we discovered that splicing defects reported in neuropsychiatric disorders are carried by multiple alternative GPHN transcripts, demonstrating the need for a thorough analysis of the GPHN transcriptome in patients. Overall, we show that alternative splicing of GPHN is an important genetic variation to consider in neurological diseases and a determinant of the diversity of postsynaptic inhibitory synapses.

PASSIFLORA INCARNATA NO AUXÍLIO FARMACOTERAPEUTICO DOS TRANSTORNOS DE ANSIEDADE E NAS DESORDENS DO SONO

Introdução: A Passiflora reúne cerca de 400 espécies de maracujá, a maioria originária da região Neotropical (América), sendo aproximadamente 120 nativas do Brasil. Passiflora incarnata, conhecida por flor da paixão ou planta do maracujá, é uma planta medicinal utilizada na preparação de infusões, tinturas e remédios fitoterápicos para acalmar o nervosismo e combater a ansiedade e a insônia. A Passiflora tem na sua composição passiflorina, flavonoides, C-glicosídeos e alcaloides, com propriedades sedativa, calmante, sonífera e hipnótica, sendo por isso útil no tratamento da ansiedade, tensão nervosa, insônia e dificuldade de concentração. Objetivo: Apresentar a detecção qualitativa da ação da Passiflora incarnata em relação as desordens do sono bem como nos transtornos de ansiedade. Metodologia: O presente trabalho configurou-se com um estudo de caso do tipo comparativo e abordagem qualitativa através da revisão sistemática da literatura que possibilitou a construção de referencial teórico sobre assuntos que estão relacionados ao tema em questão, utilizando dados de artigos científicos das plataformas digitais PubMed (National Library of Medicine) e SciELO (Scientific Electronic Library Online). Resultados: Um estudo clínico, randomizado e controlado, avaliou o uso do extrato de P. incarnata no tratamento de desordens da ansiedade. Foram obtidos resultados semelhantes entre os grupos tratados com o oxazepam (30 mg/dia) e com o medicamento a base de extrato de P. incarnata (45 gotas/dia), durante quatro semanas. Além do efeito sedativo, este atua no tratamento de desordens da ansiedade. O flavonóide Chrysin demonstrou possuir alta afinidade, in vitro, aos receptores benzodiazepínicos. Em altas doses, prolongou o efeito hipnótico induzido por pentobarbital. Em outro estudo pré-clínico, também foi demonstrado, in vitro, a ligação aos receptores GABA A e B. Conclusão: Dessa forma acredita-se que os flavonóides presentes na espécie vegetal sejam os principais responsáveis pelas atividades farmacológicas. Estes constituintes, em sinergismo com os alcalóides também presentes no vegetal, promovem ações depressoras inespecíficas do Sistema Nervoso Central (SNC) contribuindo, assim, para a ação sedativa e tranquilizante. Estudos farmacodinâmicos disponíveis suportam o uso como sedativo e ansiolítico. O sinergismo entre os componentes da espécie vegetal é relatado como um importante fator responsável para a ação farmacológica.

Phenotypic effects from the expression of a deregulated AtGAD1 transgene and GABA pathway suppression mutants in maize

Glutamate decarboxylase (GAD; EC 4.1.1.15) catalyzes the irreversible decarboxylation of glutamate to produce γ-aminobutyric acid (GABA); a ubiquitous non-protein amino acid involved in the regulation of several aspects of plant metabolism and physiology. To study the function of GAD and GABA in maize, we have; 1) introduced native and deregulated forms of AtGAD1 into maize with the intent of increasing the synthesis of GABA and 2) introduced constructs into maize designed to suppress the activity of several GABA shunt, GABA transport and GABA pathway genes. Maize plants expressing the deregulated AtGAD1 exhibit a severe chlorosis and retarded growth phenotype and have high levels of GABA, and Ca++/CaM-independent GAD activity. Plants expressing the suppression constructs for GABA biosynthetic and transport pathway genes had no observable phenotype whereas a knockout of GABA catabolic pathway genes led to growth and developmental defects under standard growth conditions. The implications of this study to our understanding of the action and function of GABA and GAD in crops are discussed.

Genetic Code Expansion and Click-Chemistry Labeling to Visualize GABA-A Receptors by Super-Resolution Microscopy

Fluorescence labeling of difficult to access protein sites, e.g., in confined compartments, requires small fluorescent labels that can be covalently tethered at well-defined positions with high efficiency. Here, we report site-specific labeling of the extracellular domain of γ-aminobutyric acid type A (GABA-A) receptor subunits by genetic code expansion (GCE) with unnatural amino acids (ncAA) combined with bioorthogonal click-chemistry labeling with tetrazine dyes in HEK-293-T cells and primary cultured neurons. After optimization of GABA-A receptor expression and labeling efficiency, most effective variants were selected for super-resolution microscopy and functionality testing by whole-cell patch clamp. Our results show that GCE with ncAA and bioorthogonal click labeling with small tetrazine dyes represents a versatile method for highly efficient site-specific fluorescence labeling of proteins in a crowded environment, e.g., extracellular protein domains in confined compartments such as the synaptic cleft.

When Are Depolarizing GABAergic Responses Excitatory?

The membrane responses upon activation of GABA(A) receptors critically depend on the intracellular Cl− concentration ([Cl−]i), which is maintained by a set of transmembrane transporters for Cl−. During neuronal development, but also under several pathophysiological conditions, the prevailing expression of the Cl− loader NKCC1 and the low expression of the Cl− extruder KCC2 causes elevated [Cl−]i, which result in depolarizing GABAergic membrane responses. However, depolarizing GABAergic responses are not necessarily excitatory, as GABA(A) receptors also reduces the input resistance of neurons and thereby shunt excitatory inputs. To summarize our knowledge on the effect of depolarizing GABA responses on neuronal excitability, this review discusses theoretical considerations and experimental studies illustrating the relation between GABA conductances, GABA reversal potential and neuronal excitability. In addition, evidences for the complex spatiotemporal interaction between depolarizing GABAergic and glutamatergic inputs are described. Moreover, mechanisms that influence [Cl−]i beyond the expression of Cl− transporters are presented. And finally, several in vitro and in vivo studies that directly investigated whether GABA mediates excitation or inhibition during early developmental stages are summarized. In summary, these theoretical considerations and experimental evidences suggest that GABA can act as inhibitory neurotransmitter even under conditions that maintain substantial depolarizing membrane responses.