Effects of Homocysteine and its Derivatives on Spontaneous Network Activity in the Hippocampus of Neonatal Rat Pups

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Homocysteine is a sulfur-containing amino acid, which at high concentrations has neurotoxic effects and induces impairments to the development of the nervous system. Homocysteine is rapidly oxidized in the plasma, forming disulfide bonds with proteins and other low molecular weight thiols; it also undergoes transformation into the into homocysteine thiolactone. On chronic exposure, the neurotoxicity of homocysteine is therefore mediated mainly by its derivatives. The aim of the present work was to investigate the effects of homocysteine and its derivatives – homocystine and homocysteine thiolactone – on spontaneous network activity in the hippocampus of rats in the first week after birth. Giant depolarizing potentials (GDP) and multiple action potentials (MAP) were recorded using an extracellular electrode in hippocampal field CA3. All three study compounds were found to induce increases in the frequency of GDP and MAP at concentrations of 100 and 500 μM, homocystine producing the most significant increase in neuron network activity. The effects of homocysteine, homocystine, and homocysteine thiolactone on the spontaneous network activity of neurons were completely eliminated on blockade of NMDA and AMPA receptors. Thus, homocysteine and its derivatives lead to increased spontaneous network activity of hippocampal neurons in neonatal rats, which can induce impairments to the formation of the neural networks of the hippocampus in conditions of chronic hyperhomocysteinemia, and could also induce hyperexcitability and the risk of developing epilepsy in the postnatal period

Mast Cell Mediators as Pain Triggers in Migraine: Comparison of Histamine and Serotonin in the Activation of Primary Afferents in the Meninges in Rats

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. The meninges around the brain are characterized by an abundant blood supply, a high density of sensory nerves, and large numbers of mast cells. In migraine, the commonest neurological disorder, activation of trigeminal nerve fibers in the meninges is the initial trigger mechanism for generating pain signals. The recently suggested concept of the neuroimmune synapse suggests that mast cell transmitters can activate receptor proteins in close-lying nerve endings, leading to the generation of nociceptive spike activity. Serotonin and histamine, presumptive triggers for migraine, are classical transmitters released on activation of mast cells. Our recent research has identifi ed powerful activation of primary afferents by serotonin, mediated mainly via 5-HT3 receptors. However, the role of histamine in meningeal neuroimmune synapses has received little study. The present study therefore used recording of spike activity from primary afferents in the meninges in rats to study the role of histamine as a possible trigger for pain in migraine. Results from testing a wide range of histamine concentrations identified only a minimal (about 12%) effect with 10 μM histamine on the nociceptive activity of the trigeminal nerve. More detailed cluster analysis showed that the proportion of fibers reacting to histamine was no more than 29%, increases in spike activity in these fibers being significantly lower than on exposure to serotonin. Longer (4 h) exposure to histamine also produces no significant change in trigeminal nerve activity. The results do not exclude a stimulatory role for histamine in migraine but suggest that this mast cell transmitter has an action other than activation of the trigeminal nerve

Short chain fatty acids and colon motility in a mouse model of irritable bowel syndrome

Background: Irritable bowel syndrome (IBS) is defined as a multifactorial disorder associated with visceral hypersensitivity, altered gut motility and dysfunction of the brain-gut axis. Gut microbiota and its metabolites are proposed as possible etiological factors of IBS. Short chain fatty acids (SCFAs) induce both inhibitory and stimulatory action on colon motility, however, their effects on the IBS model were not investigated. The aim of our study was to investigate the level of SFCAs in feces and their effects on colon motility in a mouse model of IBS. Methods: IBS model was induced in mice by intracolonic infusion of 1% acetic acid during the early postnatal period. Mice colon hypersensitivity was assessed by the threshold of the abdominal withdrawal reflex in response to colorectal distention. Colon contractility was studied using proximal colon specimens in isometric conditions. Transit rates were assessed by the pellet propulsion in the isolated colon. Concentrations of SCFAs in feces were measured using gas–liquid chromatography. Results: The concentration of SCFAs in feces of IBS model mice was higher compared to the control group. Visceral sensitivity to colorectal distension and colonic transit rate were increased indicating IBS with predominant diarrhea. The frequency and amplitude of spontaneous contractions of proximal colon segments from IBS mice were higher, but carbachol induced contractions were lower compared to control. During acute application of SCFAs (sodium propionate, sodium acetate or butyric acid) dose-dependently (0.5–30 mM) decreased tonic tension, frequency and amplitude of spontaneous and carbachol-evoked contractions. In the mouse IBS group the inhibitory effects SCFAs on spontaneous and carbachol-evoked contractions were less pronounced. At the same time intraluminal administration of butyrate (5 mM) increased the transit rate in the colon of both groups, but its stimulatory effect was more pronounced in mouse IBS model group. Conclusion: Our data indicate that the increased transit rate in the mouse IBS model group is associated with a disbalance of activating and inhibiting action of SCFAs due to chronically elevated SCFA levels, which may impact the pathogenesis of IBS with predominant diarrhea syndrome

Effects of hyperhomocysteinemia on the platelet-driven contraction of blood clots

Hyperhomocysteinemia (HHcy) is associated with thrombosis, but the mechanistic links between them are not understood. We studied effects of homocysteine (Hcy) on clot contraction in vitro and in a rat model of HHcy. Incubation of blood with exogenous Hcy for 1 min enhanced clot contraction, while 15-min incubation led to a dose-dependent suppression of contraction. These effects were likely due to direct Hcy-induced platelet activation followed by exhaustion, as revealed by an increase in fibrinogen-binding capacity and P-selectin expression determined by flow cytometry. In the blood of rats with HHcy, clot contraction was enhanced at moderately elevated Hcy levels (10-50 µM), while at higher Hcy levels (>50 µM), the onset of clot contraction was delayed. HHcy was associated with thrombocytosis combined with a reduced erythrocyte count and hypofibrinogenemia. These data suggest that in HHcy, platelets get activated directly and indirectly, leading to enhanced clot contraction that is facilitated by the reduced content and resilience of fibrin and erythrocytes in the clot. The excessive platelet activation can lead to exhaustion and impaired contractility, which makes clots larger and more obstructive. In conclusion, HHcy modulates blood clot contraction, which may comprise an underappreciated pro- or antithrombotic mechanism

Characterization of gut contractility and microbiota in patients with severe chronic constipation

© 2020 Yarullina et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Chronic constipation (CC) is one of the most common gastrointestinal disorders worldwide. Its pathogenesis, however, remains largely unclear. The purpose of the present work was to gain an insight into the role of contractility and microbiota in the etiology of CC. To this end, we studied spontaneous and evoked contractile activity of descending colon segments from patients that have undergone surgery for refractory forms of CC. The juxta-mucosal microbiota of these colon samples were characterized with culture-based and 16S rRNA sequencing techniques. In patients with CC the spontaneous colonic motility remained unchanged compared to the control group without dysfunction of intestinal motility. Moreover, contractions induced by potassium chloride and carbachol were increased in both circular and longitudinal colonic muscle strips, thus indicating preservation of contractile apparatus and increased sensitivity to cholinergic nerve stimulation in the constipated intestine. In the test group, the gut microbiota composition was assessed as being typically human, with four dominant bacterial phyla, namely Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria, as well as usual representation of the most prevalent gut bacterial genera. Yet, significant inter-individual differences were revealed. The phylogenetic diversity of gut microbiota was not affected by age, sex, or colonic anatomy (dolichocolon, megacolon). The abundance of butyrate-producing genera Roseburia, Coprococcus, and Faecalibacterium was low, whereas conventional probiotic genera Lactobacillus and Bifidobacteria were not decreased in the gut microbiomes of the constipated patients. As evidenced by our study, specific microbial biomarkers for constipation state are absent. The results point to a probable role played by the overall gut microbiota at the functional level. To our knowledge, this is the first comprehensive characterization of CC pathogenesis, finding lack of disruption of motor activity of colonic smooth muscle cells and insufficiency of particular members of gut microbiota usually implicated in CC