GABA in developing rat skeletal muscle and motor neurons

Neurochemical and Morphological Comparisons of Motor Nerve Organoids and Spinal-Cord Explants

Organoids are multicellular structures formed in vitro from populations of individual cells allowing modeling of structural and functional aspects of organs and tissues in normal and diseased states. They offer unique opportunities to model and treat disease. Using a mouse embryonic stem cell line, we have cultured organoids that express markers of spinal cord motor neurons as well as motor neurons found within the peripheral nervous system. The morphology and select neurotransmitter content of the organoids and spinal cord explants were compared at different developmental time points. We found indications of maturation in the organoids over time, mirrored by similar trends in the spinal cord explants. Although the organoids contained the same neurotransmitters as the spinal cord explants, the developmental changes of these neurotransmitter levels were less marked in organoids. Given these differences, further work is required to optimize organoid growth conditions to better reproduce in vivo models when using organoids to study development.

Impairment of Skeletal Muscle Contraction by Inhibitors of GABA Transporters

γ-Aminobutyric acid (GABA) has a significant impact on the functioning of not only the central but also the peripheral part of the nervous system. Recently, various elements of the GABAergic signaling system have been discovered in the area of the neuromuscular junction of mammals. At the same time, the functional activity of membrane-bound GABA transporters (GATs) and their role in neuromuscular transmission have not been identified. In the present study, performed on a neuromuscular preparation of the mouse diaphragm, the effect of GABA transporter inhibitors (nipecotic acid and β-alanine) on the force of muscle contraction was assessed. It was found that in the presence of both compounds in the bathing solution, the force of contractions caused by stimulation of the motor nerve dropped by 30-50%. However, when the muscle was stimulated directly, no effect of GABA transporter inhibitors on the contractile force was observed. The depressant effect of β-alanine induced by nerve stimulation was completely abolished by the GABAB receptor blocker CGP 55845. GABA transporters were detected at the neuromuscular junction using immunohistochemistry. Thus, our results indicate that GABA transporters are localized in the area of the neuromuscular junction, and their activity affects the muscle contraction force. This influence is most likely due to the removal of GABA released during nerve stimulation and activating GABA receptors, which leads to a decrease in the contraction force of the striated muscles.

GABA Receptors and Kv7 Channels as Targets for GABAergic Regulation of Acetylcholine Release in Frog Neuromuscular Junction

Effects of gamma-aminobutyric acid (GABA) and some selective GABAergic ligands on the quantal acetylcholine (ACh) release in the frog neuromuscular contacts were investigated using combination of microelectrode technique with fluorescent and immunohistochemical assays. Significant attenuation of ACh release was observed in the presence of GABA as well as selective GABAA and GABAB receptor agonists. Neither GABAA nor GABAB antagonists abolished to full extent this effect of GABA. Fluorescent assay allowed to detect the GABA-induced opening of K+ channels, which was inhibited by XE-991, a selective antagonist of Kv7 type. Electrophysiological recordings of endplate potentials in the presence of XE-991 confirmed the contribution of Kv7 type potassium channels to the effects of GABA on ACh release that was not associated with GABAA and GABAB receptors activation. Note that XE-991 effectively precluded the action of retigabine, neuronal Kv7 channel opener, on ACh release. Immunohistochemical assay revealed that frog mature skeletal muscle fibers contain a significant amount of GABA, and substantial amount of GABA can be released in the extracellular space at the muscle contractions induced by prolonged high-frequency nerve stimulation. Besides, some binding sites for exogenous GABA were detected on the plasma membranes. It is concluded that GABA, in addition to affecting GABAA and GABAB receptors, can directly activate Kv7 channels, thereby negatively modulating the evoked ACh release. Endogenous GABA may serve as a retrograde regulator of neurotransmitter exocytosis.

Increased endocytosis rate and enhanced lysosomal pathway of silica-coated superparamagnetic nanoparticles into M-HeLa cells compared with cultured primary motor neurons

The unique properties of superparamagnetic iron oxide nanoparticles (SPIONs) enable their use as magnetic biosensors, targeted drug delivery, magnetothermia, magnetic resonance imaging, etc. Today, SPIONs are the only type of metal oxide nanoparticles approved for biomedical application. In this work, we analyzed the cellular response to the previously reported luminescent silica coated SPIONs of the two cell types: M-HeLa cells and primary motor neuron culture. Both internalization pathways and intracellular fate of SPIONs have been compared for these cell lines using fluorescence and transmission electron microscopy. We also applied a pharmacological approach to analyze the endocytosis pathways of SPIONs into the investigated cell lines. The penetration of SPIONs into M-HeLa cells is already noticeable within 30 s of incubation through both caveolin-dependent endocytosis and micropinocytosis. However, incubation for a longer time (1 h at least) is required for the internalization of SPIONs into motor neuron culture cells provided by dynamin-dependent endocytosis and macropinocytosis. The intracellular colocalization assay reveals that the lysosomal internalization pathway of SPIONs is also dependent on the cell type. The lysosomal pathway is much more pronounced for M-HeLa cells compared with motor neurons. The emphasized differences in cellular responses of the two cell lines open up new opportunities in the application of SPIONs in the diagnostics and therapy of cancer cells.

Multitissue transcriptomics demonstrates the systemic physiology of methionine deficiency in broiler chickens

Methionine (Met) supplementation is common practice in broilers to support nutrition, yet there are gaps in the understanding of its role in systemic physiology. Furthermore, several different Met sources are available that may have different physiological effects. This study evaluated the mode of action of Met deficiency (no Met-supplementation) and supplementation (0.25% DL- or L-Met, 0.41% liquid methionine hydroxy analog-free acid (MHA-FA)), and of Met source (DL-, L- or MHA-FA) in broiler chickens, via host transcriptomics. Biological pathway activation modeling was performed to predict the likely phenotypic effects of differentially expressed genes (DEGs) in tissue samples from the jejunum, liver and breast obtained at 10, 21 and 34/35 d of age from three experiments in a combined analysis. Animal performance data showed that Met deficiency reduced BW, daily BW gain, daily feed intake, and breast yield, and increased feed conversion ratio in all experiments (P < 0.05). Effects of Met deficiency on gene expression were least evident in the jejunum and most evident in the liver and breast, as evidenced by the number of DEG and activated pathways. Activated pathways suggested Met deficiency was associated with inhibited protein turnover, gut barrier integrity, and adaptive immunity functions in the jejunum, that predicted reduced breast yield. There was an interaction with age; in Met-deficient birds, there were 333 DEGs in the jejunum of starter vs finisher birds suggesting young birds were more sensitive to Met deficiency than older birds. In the liver, Met deficiency activated pathways associated with lipid turnover, amino acid metabolism, oxidative stress, and the immune system, whereas in breast, it activated pathways involved in metabolic regulation, hemostasis, the neuronal system, and oxidative stress, again predicting a negative impact on breast yield. In the starter phase, supplementation with DL-Met compared to MHA-FA inhibited gamma-aminobutyric acid activity and oxidative stress in breast tissue. When data from all tissues were integrated, increased expression of a liver gene (ENSGALG00000042797) was found to be correlated with the expression of several genes that best explained variation due to the Met deficiency in jejunum and breast muscle. Some of these genes were involved in anti-oxidant systems. Overall, the findings indicate that impaired growth performance due to Met deficiency results from an array of tissue-specific molecular mechanisms in which oxidative stress plays a key systemic role. Young birds are more sensitive to Met-deficiency and DL-Met was a preferential source of Met than L- or MHA-FA during the starter phase.

Integrated metabolomics and transcriptomics analyses reveal the key genes regulating differential metabolites of longissimus dorsi muscle in castrated South Sichuan black goats (Capra hircus)

The main aim of the current work was to explore the differential metabolites and differentially expressed genes of longissimus dorsi muscle (LDM) between castrated and uncastrated fattening male South Sichuan black goats (Capra hircus). Then, the key genes regulating important differential metabolites (DMs) in castrated male goats were observed by integrated metabolomics and transcriptomics analyses. In addition, we evaluated the effects of castration on blood constituents, dressing percentage, and water holding capacity of LDM in male black goats. The results showed that the concentrations of alkaline phosphatase (ALP), total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol (LDL-C) were significantly increased and testosterone was significantly decreased in castrated male goats compared with the uncastrated male goats, while dressing percentage of black goats and water holding capacity of longissimus dorsi muscle were not significant differences. Through metabolomics and transcriptomics analyses, 23 important KEGG pathways, 13 important DMs, 32 important differentially expressed genes (DEGs), and 13 key genes related to the "Metabolism" and "Organismal systems" pathways were screened. Lipid accumulation may be elevated in the blood of fattening South Sichuan black goats after castration. Castration might play a positive role in energy provision, intercellular signaling, muscle function, softening of meat, disease reduction, and anti-oxidation of LDM. P4HA2, AKR1B1, GPT2, L2HGDH, ENSCHIG00000021660, ENSCHIG00000023861, DGAT2, ULK1, SLC38A3, PLA2G4A, SLC6A1, ENSCHIG00000026624, and ND2 might be the key genes regulating important DMs in the KEGG pathways related to "Metabolism" and "Organismal systems" of castrated male goats compared with the uncastrated male goats.

Mitochondria-Targeted Delivery Strategy of Dual-Loaded Liposomes for Alzheimer's Disease Therapy

Liposomes modified with tetradecyltriphenylphosphonium bromide with dual loading of α-tocopherol and donepezil hydrochloride were successfully designed for intranasal administration. Physicochemical characteristics of cationic liposomes such as the hydrodynamic diameter, zeta potential, and polydispersity index were within the range from 105 to 115 nm, from +10 to +23 mV, and from 0.1 to 0.2, respectively. In vitro release curves of donepezil hydrochloride were analyzed using the Korsmeyer-Peppas, Higuchi, First-Order, and Zero-Order kinetic models. Nanocontainers modified with cationic surfactant statistically better penetrate into the mitochondria of rat motoneurons. Imaging of rat brain slices revealed the penetration of nanocarriers into the brain. Experiments on transgenic mice with an Alzheimer's disease model (APP/PS1) demonstrated that the intranasal administration of liposomes within 21 days resulted in enhanced learning abilities and a reduction in the formation rate of Aβ plaques in the entorhinal cortex and hippocampus of the brain.

Differentiation of Myoblasts in Culture: Focus on Serum and Gamma-Aminobutyric Acid

There are many facts about the possible role of gamma-aminobutyric acid (GABA) in the development and differentiation of cells not only in nervous but also in muscle tissue. In the present study, a primary culture of rat skeletal muscle myocytes was used to evaluate the correlation between the content of GABA in the cytoplasm and the processes of myocyte division and their fusion into myotubes. The effect of exogenous GABA on the processes of culture development was also estimated. Since the classical protocol for working with myocyte cultures involves the use of fetal bovine serum (FBS) to stimulate cell division (growth medium) and horse serum (HS) to activate the differentiation process (differentiation medium), the studies were carried out both in the medium with FBS and with HS. It was found that cells grown in medium supplemented with FBS contain more GABA compared to cultures growing in medium supplemented with HS. Addition of exogeneous GABA leads to a decrease in the number of myotubes formed in both media, while the addition of an amino acid to the medium supplemented with HS had a more pronounced inhibitory effect. Thus, we have obtained data indicating that GABA is able to participate in the early stages of skeletal muscle myogenesis by modulating the fusion process.