Endocannabinoid signaling and synaptic plasticity in the brain

Repetitive firing neuron or activation of synaptic transmission plays an important role in the modulation of synaptic efficacy, such as long-term potentiation (LTP) and long-term depression (LTD). These activity-dependent changes in synaptic efficacy are thought to be critical to learning and memory; however, the underlying mechanisms remain to be defined. Endogenous cannabinoids (eCBs) are diffusible modulators that are released from depolarized postsynaptic neurons and act on presynaptic terminals. Persistent release of eCBs can lead to long-term modulation of synaptic plasticity in the brain. Given a broad distribution of eCB receptors in the brain, the eCB signaling system could contribute to use-dependent modification of brain functions.     

Endocannabinoid signaling in the brain: biosynthetic mechanisms in the limelight

Studies of the endocannabinoid system in the CNS have been mostly focused on endocannabinoid receptors and inactivating mechanisms. Until recently, very little was known about the role of biosynthetic enzymes in endocannabinoid signaling. New data from the recent development of pharmacological and genetic tools for the study of these enzymes point to their fundamental role in determining where and when endocannabinoids function, and raise the possibility of new intriguing and previously unsuspected concepts in the general strategy of endocannabinoid signaling. However, even with these new tools, the cross-talk between anandamide and 2-arachidonoylglycerol biosynthesis makes it difficult to dissect one from the other, and data will need to be interpreted with this in mind.     

Chemical dependencies of learning in the rabbit olfactory bulb: acquisition of the transient spatial pattern change depends on norepinephrine

Intracerebral cannulas were implanted in both olfactory bulbs of 6 rabbits. A surface electrode-array (8 X 8) was implanted epidurally on the lateral surface of the left bulb. Each rabbit was conditioned to respond to sniffing to an odor paired with cutaneous shock while receiving continuous intrabulbar infusion of either vehicle or propranolol (100 microM at 1 microliter/hr) in vehicle. After two training sessions to the original odor, a response to a new odor was conditioned under the influence of the alternate infusate. Electroencephalographic (EEG) activity was sampled on inspirations before and during odor presentations. During vehicle infusion a transient alteration in the pattern of activity was acquired that occurred during the second and third inspirations following presentation of the reinforced odor. The acquisition did not occur when propranolol was infused. No significant pattern changes occurred with unreinforced odors in either condition. There was no local anesthetic effect of the racemic mixture of propranolol found for any type of electric activity, including antidromic spike activity observed in an independent control group. Intrabulbar norepinephrine injection (100 microM, 10 microL) resulted in an amplitude increase of the bulbar 40-80-Hz EEG and a potentiation of the transient spatial pattern change to a novel odor, when compared with those observed during vehicle infusion. It is concluded that norepinephrine released under centrifugal control may act to prevent or delay habituation that otherwise occurs rapidly to unreinforced odors.     

Generalization of visuomotor adaptation depends on the spatial characteristic of visual workspace

The present study aims to address a novel aspect of visuomotor adaptation and its generalization. It is based on the assumption that the spatial structure of the distal action space is crucial for generalization. In the experiments, the distal action spaces could manifest either a symmetric or parallel structure. The imposed visuomotor rotations in the adaptation and the following generalization were either the same or opposing each other. In the generalization phase, motor bias resulting from prior adaptation was observed, and it turned out to substantially depend on the property of the workspace. In Experiment 1 with a parallel workspace, preceding adaptation to the same rotation was more advantageous than adaptation to an opposing rotation. This observation was reversed in Experiment 2 with the symmetrical workspace: prior adaptation to an opposing rotation was more advantageous for the generalization than prior adaptation to the same rotation. Mechanisms possibly underlying the observed influence of the workspace configuration were discussed.     

Optokinetic nystagmus in albino rats depends on stimulus pattern

Summary Ocular responses to optokinetic stimulation were reexamined in adult albino rats of two different strains. Eye movements were measured in head-restrained animals using the search coil method. In contrast to some previous results, the albino rats showed optokinetic nystagmus, and some of them made responses comparable to those previously recorded from pigmented rats. However, the type of stimulus pattern used to elicit optokinetic nystagmus proved to be crucial for albino rats. The deficit is attributed to abnormalities in the albino rat's visual sensory apparatus. Inverted optokinetic nystagmus was elicited in albino rats by restricting the optokinetic stimulation to the anterior visual field of both eyes. The same phenomenon has been observed previously in albino rabbits and mice, and has been suggested to be due to the abnormally small number of uncrossed optic nerve fibers in albinos.     

CB1受体通过钾离子通道介导外周镇痛作用

目的:探究大麻素1型受体(CB1受体)在外周的镇痛机制。方法:建立坐骨神经慢性压迫性损伤(CCI)小鼠模型,测量机械触诱发痛和热敏痛阈值观察痛行为变化,采用Western blot检测CB1受体的动态变化,记录坐骨神经单纤维放电频率以探究CB1受体激活是否受到钾通道的调节。结果:伴随着疼痛阈值的降低,小鼠坐骨神经损伤区CB1受体表达升高。外周损伤区注射CB1受体特异性激动剂HU210具有显著的镇痛作用,但预先20 min注射CB1受体特异性拮抗剂AM281或钾通道非特异性阻断剂四乙铵(TEA)之后再注射HU210,其镇痛作用消失。在损伤区灌流槽中加入HU210能够明显使起步点自发电的频率降低,但是提前加入AM281或TEA均能阻碍这个作用。结论:CB1受体在外周的镇痛作用是通过钾通道介导的。     

Neutrophil role in pulmonary paracoccidioidomycosis depends on the resistance pattern of hosts

The immunoprotective and immunomodulatory role of neutrophils during pulmonary infection of resistant (A/J) and susceptible (B10.A) mice to Paracoccidioides brasiliensis was investigated. First, comparative studies about early cellular influx to the lungs demonstrated higher numbers of neutrophils in susceptible rather than in resistant mice. Neutrophil depletion resulted in decreased survival times of susceptible but not resistant mice. In both mouse strains, depletion led to increased fungal burdens at Week 1 of infection; however, only susceptible mice remained with increased pulmonary fungal loads and presented a dramatic fungal dissemination to liver and spleen. At Week 1 of infection, treated and untreated B10.A and A/J mice were negative for delayed-type hypersensitivity (DTH) reactions, which remained negative for the susceptible strain. In contrast, from the second week onward, control and neutrophil-depleted, resistant mice became positive for DTH reactions. In B10.A mice, neutrophil depletion resulted in increased levels of interleukin (IL)-12 and IL-4 in the lungs, high levels of hepatic cytokines, and increased synthesis of T helper cell type 1 (Th1)- and Th2-regulated antibodies [immunoglobulin G1 (IgG1), IgA, and IgG3]. In neutrophil-depleted A/J mice, high levels of pulmonary IL-12 and granulocyte macrophage-colony stimulating factor were concomitant to diminished levels of hepatic cytokines and increased amounts of Th1-regulated isotypes (IgG2a, IgG2b, and IgG3). Differently from primary infection, neutrophil depletion did not alter immunoprotection in secondary paracoccidioidomycosis. As a whole, our data showed that the genetic patterns of hosts exert an important influence on the immunoprotective and immunoregulatory functions of neutrophils, which appear to be essential in situations devoid of cell-mediated immunity.     

The dynamics of signaling at the histaminergic photoreceptor synapse of arthropods

Histamine, a ubiquitous aminergic messenger throughout the body, also serves as a neurotransmitter in both vertebrates and invertebrates. In particular, the photoreceptors of adult arthropods use histamine, modulating its release to signal increases and decreases in light intensity. Strong evidence from various arthropod species indicates that histamine is synthesized and stored in photoreceptors, undergoes Ca-dependent release, inhibits postsynaptic interneurons by gating Cl channels, and is then recycled. In Drosophila, the synthetic enzyme, histidine decarboxylase, and the subunits of the histamine-gated chloride channel have been cloned. Possible histamine transporters at synaptic vesicles and for reuptake remain elusive. Indeed, the mechanisms that remove histamine from the synaptic cleft, and that help terminate histamine's action, are unexpectedly complex, their details remaining unresolved. A major pathway in Drosophila, and possibly other arthropod species, is by conjugation of histamine to beta-alanine to form carcinine in adjacent glia. This conjugate then returns to the photoreceptors where it is hydrolysed to liberate histamine, which is then loaded into synaptic vesicles. Evidence from other species suggests that direct reuptake of histamine into the photoreceptors may also occur. Light depolarizes the photoreceptors, causing histamine release and postsynaptic inhibition; dimming hyperpolarizes the photoreceptors, causing a decrease in histamine release and an "off" response in the postsynaptic cell. Further pursuit of histamine's action at these highly specialized synapses should lead to an understanding of how they signal minute changes in presynaptic membrane potential, how they reliably extract signals from noise, and how they adapt to a wide range of presynaptic membrane potentials.     

In the immune synapse,ZAP-70 controls T cell polarization and recruitment of signaling proteins but not formation of the synaptic pattern

Recognition by T cells of their ligands at the surface of antigen-presenting cells (APCs) leads to T cell activation, polarization of the T cell toward the APC, and formation of an immune synapse. Using ZAP-70-deficient T cells expressing zeta-GFP, we show that ZAP-70 signaling drives the TCR-dependent reorientation of the microtubule-organizing center thus leading to relocation of a zeta-GFP(+) intracellular compartment close to the APC. ZAP-70 is also necessary to supply the synapse with the signaling molecules PKC-theta and LAT. In contrast, ZAP-70 is not required for clustering of zeta-GFP and CD2 or exclusion of CD45 and CD43 from the synapse. These data show that ZAP-70-dependent signaling is required for formation of a functional immune synapse.     

Visual map development depends on the temporal pattern of binocular activity in mice

Binocular competition is thought to drive eye-specific segregation in the developing visual system, potentially through Hebbian synaptic learning rules that are sensitive to correlations in afferent activity. Altering retinal activity can disrupt eye-specific segregation, but little is known about the temporal features of binocular activity that modulate visual map development. We used optogenetic techniques to directly manipulate retinal activity in vivo and identified a critical period before eye opening in mice when specific binocular features of retinal activity drive visual map development. Synchronous activation of both eyes disrupted segregation, whereas asynchronous stimulation enhanced segregation. The optogenetic stimulus applied was spatially homogenous; accordingly, retinotopy of ipsilateral projections was markedly perturbed, but contralateral retinotopy was unaffected or even improved. These results provide direct evidence that the synchrony and precise temporal pattern of binocular retinal activity during a critical period in development regulates eye-specific segregation and retinotopy in the developing visual system.     

肌萎缩蛋白参与淋巴细胞的活化及免疫突触的形成

目的：探讨在神经肌接头中发挥重要作用的膜表面糖化蛋白-肌萎缩蛋白是否参与免疫突触的形成，进而影响淋巴细胞的活化。方法：首先通过RT-PCR和FACS分别从mRNA水平和蛋白水平观察肌萎缩蛋白在各种免疫细胞中的表达，并经过共聚焦显微镜观察其是否参与免疫突触的形成，应用构建的反义质粒，研究其是否影响淋巴细胞的抗原特异性和非特异性活化。结果：肌萎缩蛋白广泛表达于T细胞、B细胞、不成熟DC、成熟DC及巨噬细胞中，且参与了免疫突触的形成。当淋巴细胞活化后其表达含量无明显上升，但其表达被下调后，不管是对特异抗原引起的淋巴细胞活化还是对非特异抗原引起的淋巴细胞活化都具有显著的抑制作用。结论：组成性表达于各种免疫细胞中的肌萎缩蛋白参与了免疫突触的形成，并影响了抗原特异性和抗原非特异性的淋巴细胞的活化。     

Age-related HMG-CoA reductase deregulation depends on ROS-induced p38 activation

BACKGROUND: It seems to be clear that hepatic age-related HMG-CoA reductase total activation is connected to a rise of reactive oxygen species (ROS). However, the mechanism by which ROS achieve this effect is unknown. Thus, in this work, we have performed a study of HMG-CoAR by analyzing the enzymes involved in its short-term regulation, namely, AMP-activated kinase (AMPK) and protein phosphatase 2A (PP2A). METHODS AND MATERIALS: In the liver of aged rats and in H(2)O(2)-stimulated HepG2 cells the ROS content, the HMG-CoA reductase activation state, its regulatory enzymes and the p38 downstream pathway involved in reductase deregulation, have been studied. RESULTS AND CONCLUSIONS: Our data show that the hepatic HMG-CoAR is completely dephosphorylated in the liver of old rat being the PP2A increased association with HMG-CoAR the main responsible. On the other hand, the age-related greater association between PP2A and HMG-CoAR results to be due to an increase in ROS that is present during aging and has already been demonstrated to influence HMG-CoAR activation state. Moreover, H(2)O(2)-stimulated HepG2 cell line shows that the ROS effect on the HMG-CoAR dephosphorylation is mediated by the activation of p38/MAPK pathway.     

Semaphorin 3E-Plexin-D1 signaling controls pathway-specific synapse formation in the striatum

The proper formation of synaptic connectivity in the mammalian brain is critical for complex behavior. In the striatum, balanced excitatory synaptic transmission from multiple sources onto two classes of principal neurons is required for coordinated and voluntary motor control. Here we show that the interaction between the secreted semaphorin 3E (Sema3E) and its receptor Plexin-D1 is a critical determinant of synaptic specificity in cortico-thalamo-striatal circuits in mice. We find that Sema3e (encoding Sema3E) is highly expressed in thalamostriatal projection neurons, whereas in the striatum Plxnd1 (encoding Plexin-D1) is selectively expressed in direct-pathway medium spiny neurons (MSNs). Despite physical intermingling of the MSNs, genetic ablation of Plxnd1 or Sema3e results in functional and anatomical rearrangement of thalamostriatal synapses specifically in direct-pathway MSNs without effects on corticostriatal synapses. Thus, our results demonstrate that Sema3E and Plexin-D1 specify the degree of glutamatergic connectivity between a specific source and target in the complex circuitry of the basal ganglia.     

Rabbit P300-like potential depends on cortical muscarinic receptor activation

Novel stimuli trigger a positive brain potential P300 or P3a in mammalian animals, which is considered to represent an orienting response. Drugs systemically administered showed that acetylcholine is involved in the generation of P3. However, it is not known in which structure acetylcholine interacts with other neuronal substances for P3 generation. In this study, we injected scopolamine, an acetylcholine antagonist, into the parietal cortex. After the injection the amplitude of P3 from the parietal electrode decreased, while P3 recorded from neighbouring cortex was preserved. The peak latency of it did not show any significant change after the injection. P3 did not show any significant change after injecting normal saline into the same area. The parietal cortex is an essential structure for local P3 generation Different cerebral cortical regions respond to novel stimuli in parallel, and muscarinic receptor activation is necessary for processing the information of novelty detection.     

The effect of the time pattern of presynaptic impulses on the transfer of information across an inhibitory synapse

The effects of different time patterns in presynaptic spike trains on the transmission of information across an inhibitory synapse is examined in the muscle receptor organs of the crayfish abdomen. With regular input, the system would be strongly affected by phaselocking (Perkel et al. 1964), and it is shown that a similar phenomenon would occur during closedloop inhibitory feedback. The conditions under which different degrees of phaselocking occur is studied in simple models of the system, and the model predictions is compared with experimental observations of pre- and postsynaptic spike trains. The results suggest that phaselocking is uncommon during the normal operation of these sense organs, due to the special design of its neuronal elements, which promote irregular time patterns of impulse firing in both receptors and inhibitory neurons.     

Endothelial nitric oxide synthase regulates T cell receptor signaling at the immunological synapse

The role of nitric oxide (NO) in T cells remains controversial, and the origin and localization of endogenous NO and whether it regulates lymphocyte activation are unclear. We show here that, within minutes of binding to antigen, T cells produce NO via endothelial nitric oxide synthase (eNOS). This process required increased intracellular Ca2+ and phosphoinositide3-kinase activity. By using an eNOS-green fluorescent fusion protein and fluorescent probes to detect NO, we show that eNOS translocates with the Golgi apparatus to the immune synapse of T helper cells engaged with antigen-presenting cells (APC), where it was fully activated. Overexpression of eNOS prevented the central coalescence of CD3 at the T cell-APC contact site, which was accompanied by increased phosphorylation of CD3zeta chain, ZAP-70, and extracellular signal-regulated kinases and increased IFN-gamma synthesis, but reduced production of IL-2. Therefore, eNOS-derived NO selectively potentiates T cell receptor signaling to antigen at the immunological synapse.