Suppression of spontaneous firing in inferior colliculus neurons during sound processing

Spontaneous activity is a well-known neural phenomenon that occurs throughout the brain and is essential for normal development of auditory circuits and for processing of sounds. Spontaneous activity could interfere with sound processing by reducing the signal-to-noise ratio. Multiple studies have reported that spontaneous activity in auditory neurons can be suppressed by sound stimuli. The goal of this study was to determine the stimulus conditions that cause this suppression and to identify possible underlying mechanisms. Experiments were conducted in the inferior colliculus (IC) of awake little brown bats using extracellular and intracellular recording techniques. The majority of IC neurons (82%) fired spontaneously, with a median spontaneous firing rate of 6 spikes/s. After offset of a 4 ms sound, more than half of these neurons exhibited suppression of spontaneous firing that lasted hundreds of milliseconds. The duration of suppression increased with sound level. Intracellular recordings showed that a short (<50 ms) membrane hyperpolarization was often present during the beginning of suppression, but it was never observed during the remainder of the suppression. Beyond the initial 50 ms period, the absence of significant changes in input resistance during suppression suggests that suppression is presynaptic in origin. Namely, it may occur on presynaptic terminals and/or elsewhere on presynaptic neurons. Suppression of spontaneous firing may serve as a mechanism for enhancing signal-to-noise ratios during signal processing.     

Endocannabinoids contribute to metabotropic glutamate receptor-mediated inhibition of GABA release onto hippocampal CA3 pyramidal neurons in an isolated neuron/bouton preparation

Retrograde synaptic signaling by endogenous cannabinoids (endocannabinoids) is a recently discovered form of neuromodulation in various brain regions. In hippocampus, it is well known that endocannabinoids suppress presynaptic inhibitory neurotransmitter release in CA1 region. However, endocannabinoid signaling in CA3 region remains to be examined. Here we investigated whether presynaptic inhibition can be caused by activation of postsynaptic group I metabotropic glutamate receptors (mGluRs) and following presynaptic cannabinoid receptor type 1 (CB1 receptor) using mechanically dissociated rat hippocampal CA3 pyramidal neurons with adherent functional synaptic boutons. Application of group I mGluR agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) reversibly suppressed spontaneous inhibitory postsynaptic currents (IPSCs). In the presence of tetrodotoxin (TTX), frequency of miniature IPSCs was significantly reduced by DHPG, while there were no significant changes in minimum quantal size and sensitivity of postsynaptic GABA_A receptors to the GABA_A receptor agonist muscimol, indicating that this suppression was caused by a decrease in GABA release from presynaptic nerve terminals. Application of CB1 synthetic agonist WIN55212-2 (mesylate(R)-(+)-[2,3-dihydro-5-methyl-3-[4-morpholino)methyl]pyrrolo-[1,2,3-de]-1,4-benzoxazin-6-yl](1-naphthyl)methanone) or endocannabinoid 2-arachidonoylglycerol also suppressed the spontaneous IPSC. The inhibitory effect of DHPG on spontaneous IPSCs was abolished by SR-141716 (5-(4-chlorophenyl)-1-(2,4-dichloro-phenyl)-4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide), a CB1 receptor antagonist. Furthermore, postsynaptic application of GDP-βS blocked the DHPG-induced inhibition of spontaneous IPSCs, indicating the involvement of endcannabinoid-mediated retrograde synaptic signaling. These results provide solid evidence for retrograde signaling from postsynaptic group I mGluRs to presynaptic CB1 receptors, which induces presynaptic inhibition of GABA release in rat hippocampal CA3 region.     

Oxytocin and vasopressin enhance synaptic transmission in the hypoglossal motor nucleus of young rats by acting on distinct receptor types

Hypoglossal (XII) motoneurons innervate extrinsic and intrinsic muscles of the tongue and control behaviors such as suckling, swallowing, breathing or chewing. In young rats, XII motoneurons express V1a vasopressin and oxytocin receptors. Previous studies have shown that activation of these receptors induces direct powerful excitation in XII motoneurons. In addition, by activating V1a receptors vasopressin can also enhance inhibitory synaptic transmission in the XII nucleus. In the present work, we have further characterized the effect of these neuropeptides on synaptic transmission in the XII nucleus. We have used brainstem slices of young rats and whole-cell patch clamp recordings. Oxytocin enhanced the frequency of spontaneous inhibitory postsynaptic currents by a factor of two and a half. GABAergic and glycinergic events were both affected. The oxytocin effect was mediated by uterine-type oxytocin receptors. Vasopressin and oxytocin also increased the frequency of excitatory synaptic currents, the enhancement being sixfold for the former and twofold for the latter compound. These effects were mediated by V1a and oxytocin receptors, respectively. Miniature synaptic events were unaffected by either vasopressin or oxytocin. This indicates that the peptide-dependent facilitation of synaptic currents was mediated by receptors located on the somatodendritic membrane of interneurons or premotor neurons, and not by receptors sited on axon terminals contacting XII motoneurons. Accordingly, recordings obtained from non-motoneurons located near the border of the XII nucleus showed that part of these cells possess functional V1a and oxytocin receptors whose activation leads to excitation. Some of these neurons could be antidromically activated following electrical stimulation of the XII nucleus, suggesting that they may act as premotor neurons. We propose that in young rats, oxytocin and vasopressin may function as neuromodulators in brainstem motor circuits responsible of tongue movements.     

Effect of duramycin on chloride transport and intracellular calcium concentration in cystic fibrosis and non-cystic fibrosis epithelia

Oliynyk I, Varelogianni G, Roomans GM, Johannesson M. Effect of duramycin on chloride transport and intracellular calcium concentration in cystic fibrosis and non‐cystic fibrosis epithelia. APMIS 2010; 118: 982–90. The lantibiotic duramycin (Moli1901, Lancovutide) has been suggested as a drug of choice in the treatment for cystic fibrosis (CF). It has been proposed that duramycin may stimulate chloride secretion through Ca²⁺‐activated Cl^? channels (CaCC). We investigated whether duramycin exhibited any effect on Cl^? efflux and intracellular Ca²⁺ concentration ([Ca²⁺]_i) in CF and non‐CF epithelial cells. Duramycin did stimulate Cl^? efflux from CF bronchial epithelial cells (CFBE) in a narrow concentration range (around 1 μM). However, 100 and 250 μM of duramycin inhibited Cl^? efflux from CFBE cells. An inhibitor of the CF transmembrane conductance regulator (CFTR_inh‐172) and a blocker of the capacitative Ca²⁺ entry, gadolinium chloride, inhibited the duramycin‐induced Cl^? efflux. No effect on Cl^? efflux was observed in non‐CF human bronchial epithelial cells (16HBE), human airway submucosal gland cell line, human pancreatic epithelial cells, CF airway submucosal gland epithelial cells, and CF pancreatic cells. The [Ca²⁺]_i was increased by 3 μM duramycin in 16HBE cells, but decreased after 1, and 3 μM of duramycin in CFBE cells. The results suggest that the mechanism responsible for the stimulation of Cl^? efflux by duramycin is mainly related to unspecific changes of the cell membrane or its components rather than to effects on CaCC.     

Intracellular signaling pathways in IgE-dependent mast cell activation

Mast cells (MCs) are both central effectors and signaling cells in allergic reactions. Their key role in the immunopathology of asthma and other allergic diseases has been well documented. Molecular events leading to MC activation have not been yet fully established, however. Recent studies emphasize the key role of the protein tyrosine kinases Lyn and Fyn in MC signal transduction. The finding that Lyn kinase negatively regulates MC degranulation and that Fyn kinase enhances this effector response is of great importance. This creates new possibilities for therapeutic intervention in asthma and other allergic diseases. This review summarizes current knowledge on MC intracellular signaling and discusses the most recent strategies for the treatment of allergic diseases based on MC signaling pathway inhibition.     

创伤失血性休克的治疗进展

目的：探讨创伤失血性休克的治疗现状,从而有效地指导临床工作.方法：应用PubMed、SpringerLink、中国知网医学全文期刊等数据库,查阅近年来相关文献,总结创伤失血性休克的治疗方法及其临床疗效.结果：现阶段,创伤失血性休克的治疗以限制性液体复苏、改善微循环为主,抗炎性介质、抗氧自由基、抗内毒素及中医中药等治疗显示出较好的临床前景,但仍处于辅助地位.结论：把液体复苏、免疫、炎症反应调控和抗氧化等临床治疗手段与细胞内氧复苏相结合是休克治疗领域发展的方向.     

Cellular mechanisms of motor control in the vibrissal system

In this article we discuss the experimental advantages that the vibrissal motor system offers for analysis of motor control and the specializations of this system related to the unique characteristics of whisker movements. Whisker movements are often rhythmic, fast, and bilateral. Movements of individual whiskers have simple characteristics, whereas, movements of the entire vibrissae array are complex and sophisticated. In the last few years, powerful methods for high precision tracking of whisker movements have become available. The whisker musculature is arranged to permit forward movements of individual whiskers and consists—depending on the species—mainly or exclusively of fast contracting, fast fatigable muscle fibers. Whisker motor neurons are located in the lateral facial nucleus and their cellular properties might contribute to the rhythmicity of whisking. Numerous structures provide input to the lateral facial nucleus, the most mysterious and important one being the putative central pattern generator (CPG). Although recent studies identified candidate structures for the CPG, the precise identity and the functional organization of this structure remains uncertain. The vibrissa motor cortex (VMC) is the largest motor representation in the rodent brain, and recent work has clarified its localization, subdivisions, cytoarchitectonics, and connectivity. Single-cell stimulation experiments in VMC allow determining the cellular basis of cortical motor control with unprecedented precision. The functional significance of whisker movements remains to be determined.     

Effects of intracellular pH and Ca2+ on the activity of stretch-sensitive cation channels in leech neurons

The effects of intracellular pH and calcium on the activity of the leech mechanosensitive cation channels have been studied. These channels exhibited two activity modes denoted as spike-like (SL) and multiconductance (MC). In the absence of mechanical stimulation, acidification of the intracellular side of membrane patches from 7.2 to 6.2 reversibly increased the mean channel open time as well as the opening frequency in the SL mode. Channels in MC mode were activated by a pH_i reduction from 7.2 to 6.2, but were inhibited at pH_i 5.5. Unlike MC mode, SL mode was strongly activated by intracellular Ca²⁺. Fura-2 imaging experiments showed that intracellular calcium was induced to increase by hypotonic cell swelling. The major component of this response did not require extracellular calcium. A component of the swelling-induced calcium response was sensitive to blockers of stretch-sensitive cation channels. The results indicate that the two activity modes of mechanosensitive channels of leech neurons respond differently to changes of intracellular pH and calcium. The sensitivity of the channel to micromolar concentrations of internal free calcium, along with its permeability to this ion, is consistent with a role in the amplification of mechanically induced Ca²⁺ signals in leech neurons.     

桑黄液体发酵生产多糖工艺研究

目的 考察不同培养条件对桑黄菌液体发酵生产多糖的影响.方法 通过正交试验设计,对不同培养基种类、起始pH值、发酵温度和摇床转速进行优化,在此工艺基础上,采用5L发酵罐进行发酵放大试验.结果 采用添加0.3 9/L维生素B1和0.3 g/L维生素B2的PD培养基,起始pH值5,发酵温度28℃,摇床转速180 r/min条件下,桑黄菌摇瓶发酵液中胞内多糖和胞外多糖分别为5.80、2.37 g/L;5 L发酵罐发酵液中桑黄胞内多糖和胞外多糖分别为5.85、2.30 g/L.结论 桑黄液体发酵可获得桑黄多糖,本实验结果为桑黄液体发酵工业化生产提供参考.     

Rhodiola rosea extract protects human cortical neurons against glutamate and hydrogen peroxide-induced cell death through reduction in the accumulation of intracellular calcium

The aim of this study was to investigate the neuroprotective effects of a titolated extract from Rhodiola rosea L. (RrE) and of salidroside (Sa), one of the major biologically active compounds extracted from this medicinal plant, against oxidative stressor hydrogen peroxide (H₂O₂) and glutamate (GLU)‐induced cell apoptosis in a human cortical cell line (HCN 1‐A) maintained in culture. The results obtained indicate that exposure of differentiated HCN 1‐A neurons to GLU or H₂O₂ resulted in concentration‐dependent cell death. A 24 h pre‐treatment with RrE significantly increased cell survival and significantly prevented the plasma membrane damage and the morphological disruption caused by GLU or H₂O₂, indicating that neurons treated with RrE were protected from the neurotoxicity induced by the oxidative stressor used. In addition, RrE significantly reduced H₂O₂ or GLU‐induced elevation of intracellular free Ca²⁺ concentration. The results obtained have also shown that Sa caused similar effects in all experimental models used; however, the potency of the action was lower than that of the extract containing corresponding quantities of Sa. These findings indicate that RrE has a neuroprotective effect in cortical neurons and suggest that the antioxidant activity of the RrE, due to the structural features of the synergic active principles they contain, may be responsible for its ability to stabilize cellular Ca²⁺ homeostasis. Copyright © 2011 John Wiley & Sons, Ltd.