N-butyl-ß-carboline-3-carboxylate (ß-CCB) systemic administration promotes remyelination in the cuprizone demyelinating model in mice.

Demyelination is generated in several nervous system illnesses. Developing strategies for effective clinical treatments requires the discovery of promyelinating drugs. Increased GABAergic signaling through γ-aminobutyric acid type A receptor (GABAAR) activation in oligodendrocytes has been proposed as a promyelinating condition. GABAAR expressed in oligodendroglia is strongly potentiated by n-butyl-ß-carboline-3-carboxylate (ß-CCB) compared to that in neurons. Here, mice were subjected to 0.3% cuprizone (CPZ) added in the food to induce central nervous system demyelination, a well-known model for multiple sclerosis. Then ß-CCB (1 mg/Kg) was systemically administered to analyze the remyelination status in white and gray matter areas. Myelin content was evaluated using Black-Gold II (BGII) staining, immunofluorescence (IF), and magnetic resonance imaging (MRI). Evidence indicates that ß-CCB treatment of CPZ-demyelinated animals promoted remyelination in several white matter structures, such as the fimbria, corpus callosum, internal capsule, and cerebellar peduncles. Moreover, using IF, it was observed that CPZ intake induced an increase in NG2+ and a decrease in CC1+ cell populations, alterations that were importantly retrieved by ß-CCB treatment. Thus, the promyelinating character of ß-CCB was confirmed in a generalized demyelination model, strengthening the idea that it has clinical potential as a therapeutic drug.

ß-carbolines that enhance GABAA receptor response expressed in oligodendrocytes promote remyelination in an in vivo rat model of focal demyelination.

Demyelination is typically followed by a remyelination process through mature oligodendrocytes (OLs) differentiated from precursor cells (OPCs) recruited into the lesioned areas, however, this event usually results in uncompleted myelination. Potentiation of the remyelination process is an important target for designing effective therapeutic strategies against white matter loss. Here, it was evaluated the remyelinating effect of different ß-carbolines that present differential allosteric modulation on the GABAA receptor expressed in OLs. For this, we used a focalized demyelination model in the inferior cerebellar peduncle (i.c.p.) of rats (DRICP model), in which, demyelination by ethidium bromide (0.05%) stereotaxic injection was confirmed histologically by staining with Black-Gold II (BGII) and toluidine blue. In addition, a longitudinal analysis with diffusion-weighted magnetic resonance imaging (dMRI) was made by computing fractional anisotropy (FA), apparent diffusion coefficient (ADC) and diffusivity parameters to infer i.c.p. microstructural changes. First, dMRI analysis revealed FA decreases together with ADC and radial diffusivity (RD) increases after demyelination, which correlates with histological BGII observations. Then, we evaluated the effect produced by three allosteric GABAA receptor modulators, the N-butyl-ß-carboline-3-carboxylate (ß-CCB), ethyl 9H-pyrido [3,4-b]indole-3-carboxylate (ß-CCE), and 4-ethyl-6,7-dimethoxy-9H-pyrido [3,4-b]indole-3-carboxylic acid methyl ester (DMCM). The results indicated that daily systemic ß-CCB (1 mg/Kg) or ß-CCE (1 mg/Kg) administration for 2 weeks, but not DMCM (0.35 mg/Kg), in lesioned animals increased FA and decreased ADC or RD, suggesting myelination improvement. This was supported by BGII staining analysis that showed a recovery of myelin content. Also, it was quantified by immunohistochemistry both NG2+ and CC1+ cellular population in the different experimental sceneries. Data indicated that either ß-CCB or ß-CCE, but not DMCM, produced an increase in the population of CC1+ cells in the lesioned area. Finally, it was also calculated the g-ratio of myelinated axons and observed a similar value in those lesioned animals treated with ß-CCB or ß-CCE compared to controls. Thus, using the DRICP model, it was observed that either ß-CCB or ß-CCE, positive modulators of the GABAA receptor in OLs, had a potent promyelinating effect.

Potential contributions of the intrinsic retinal oscillations recording using non-invasive electroretinogram to bioelectronics.

Targeted electric signal use for disease diagnostics and treatment is emerging as a healthcare game-changer. Besides arrhythmias, treatment-resistant epilepsy and chronic pain, blindness, and perhaps soon vision loss, could be among the pathologies that benefit from bioelectronic medicine. The electroretinogram (ERG) technique has long demonstrated its role in diagnosing eye diseases and early stages of neurodegenerative diseases. Conspicuously, ERG applications are all based on light-induced responses. However, spontaneous, intrinsic activity also originates in retinal cells. It is a hallmark of degenerated retinas and its alterations accompany obesity and diabetes. To the extent that variables extracted from the resting activity of the retina measured by ERG allow the predictive diagnosis of risk factors for type 2 diabetes. Here, we provided a comparison of the baseline characteristics of intrinsic oscillatory activity recorded by ERGs in mice, rats, and humans, as well as in several rat strains, and explore whether zebrafish exhibit comparable activity. Their pattern was altered in neurodegenerative models including the cuprizone-induced demyelination model in mice as well as in the Royal College of Surgeons (RCS-/-) rats. We also discuss how the study of their properties may pave the way for future research directions and treatment approaches for retinopathies, among others.

GABAA Receptors Expressed in Oligodendrocytes Cultured from the Neonatal Rat Contain α3 and γ1 Subunits and Present Differential Functional and Pharmacological Properties.

Oligodendrocytes (OLs) express functional GABAA receptors (GABAARs) that are activated by GABA released at synaptic contacts with axons or by ambient GABA in extrasynaptic domains. In both instances, the receptors' molecular identity has not been fully defined. Furthermore, data on their structural diversity in different brain regions and information on age-dependent changes in their molecular composition are scant. This lack of knowledge has delayed access to a better understanding of the role of GABAergic signaling between neurons and OLs. Here, we used functional, and pharmacological analyses, as well as gene and protein expression of GABAAR subunits, to explore the subunit combination that could explain the receptor functional profile expressed in OLs from the neonate rat. We found that GABAAR composed of α3ß2γ1 subunits mimicked the characteristics of the endogenous receptor when expressed heterologously in Xenopus laevis oocytes. Either α3 or γ1 subunit silencing by small interfering RNA transfection changed the GABA-response characteristics in oligodendrocyte precursor cells, indicating their participation in the endogenous receptor conformation. Thus, α3 subunit silencing shifted the mean EC50 for GABA from 75.1 to 46.6 µM, whereas γ1 silencing reduced the current amplitude response by 55%. We also observed that ß-carbolines differentially enhance GABA responses in oligodendroglia as compared with those in neurons. These results contribute to defining the molecular and pharmacological properties of GABAARs in OLs. Additionally, the identification of ß-carbolines as selective enhancers of GABAARs in OLs may help to study the role of GABAergic signaling during myelination. SIGNIFICANCE STATEMENT: GABAergic signaling through GABAA receptors (GABAARs) expressed in the oligodendroglial lineage contributes to the myelination control. Determining the molecular identity and the pharmacology of these receptors is essential to define their specific roles in myelination. Using GABAAR subunit expression and silencing, we identified that the GABAAR subunit combination α3ß2γ1 conforms the bulk of GABAARs in oligodendrocytes from rat neonates. Furthermore, we found that these receptors have differential pharmacological properties that allow specific positive modulation by ß-carbolines.

Expression and Function of GABA Receptors in Myelinating Cells.

Myelin facilitates the fast transmission of nerve impulses and provides metabolic support to axons. Differentiation of oligodendrocyte progenitor cells (OPCs) and Schwann cell (SC) precursors is critical for myelination during development and myelin repair in demyelinating disorders. Myelination is tightly controlled by neuron-glia communication and requires the participation of a wide repertoire of signals, including neurotransmitters such as glutamate, ATP, adenosine, or γ-aminobutyric acid (GABA). GABA is the main inhibitory neurotransmitter in the central nervous system (CNS) and it is also present in the peripheral nervous system (PNS). The composition and function of GABA receptors (GABARs) are well studied in neurons, while their nature and role in glial cells are still incipient. Recent studies demonstrate that GABA-mediated signaling mechanisms play relevant roles in OPC and SC precursor development and function, and stand out the implication of GABARs in oligodendrocyte (OL) and SC maturation and myelination. In this review, we highlight the evidence supporting the novel role of GABA with an emphasis on the molecular identity of the receptors expressed in these glial cells and the possible signaling pathways involved in their actions. GABAergic signaling in myelinating cells may have potential implications for developing novel reparative therapies in demyelinating diseases.