Baro-activated neurons with pulse-modulated activity in the rat caudal ventrolateral medulla express GAD67 mRNA

GABAergic neurons in the caudal ventrolateral medulla (CVLM) are believed to mediate the sympathetic baroreceptor reflex by inhibiting presympathetic neurons in the rostral ventrolateral medulla (RVLM). Accordingly, some CVLM neurons are activated by increased arterial pressure (AP; baro-activated), have activity strongly modulated by the AP pulse (pulse-modulated), and can be antidromically activated from the RVLM. This study examined whether baro-activated, pulse-modulated CVLM neurons are indeed GABAergic and examined their structures. We recorded extracellularly from 19 baro-activated, pulse-modulated CVLM neurons in chloralose-anesthetized rats. Most of these cells (13/19) were silenced by decreasing AP with nitroprusside, but some (6/19) remained active at low AP levels. They were also excited by phenyl biguanide (17/17) but inhibited by noxious tail pinch (8/11). Twelve baro-activated cells were filled with biotinamide and examined for expression of GAD67 mRNA. Because adjacent vagal motor neurons are also activated by increased AP, we examined choline acetyltransferase (ChAT) immunoreactivity. Most baro-activated cells (9/12) expressed high levels of GAD67 mRNA, the rest (3/12) displayed lower levels of GAD67 mRNA, but none showed ChAT immunoreactivity. In contrast, adjacent baro-inhibited CVLM cells had no GAD67 mRNA (n = 5) but were instead tyrosine hydroxylase immunoreactive (n = 7). Reconstruction of baro-activated CVLM neurons revealed axons that projected dorsomedially and rostrally with several axon collaterals. These data demonstrate the existence of GABAergic CVLM neurons with the physiological characteristics expected of interneurons that mediate the sympathetic baroreceptor reflex. In addition, baro-activated GABAergic CVLM neurons appear to integrate several types of inputs and provide inhibition to multiple targets.     

Group I metabotropic glutamate receptors on second-order baroreceptor neurons are tonically activated and induce a Na+-Ca2+ exchange current

The nucleus tractus solitarius (NTS) is essential for coordinating baroreflex control of blood pressure. The baroreceptor sensory fibers make glutamatergic synapses onto second-order NTS neurons. Glutamate spillover activates Group II and III presynaptic metabotropic glutamate receptors (mGluRs) on the baroreceptor central terminals to inhibit synaptic transmission, but the role of postsynaptic mGluRs is less understood. We used whole cell patch-clamping in anatomically identified second-order baroreceptor neurons in a brain stem slice to test whether Group I, II, and III mGluRs had postsynaptic effects at this first central synapse in the baroreceptor afferent pathway. The Group I agonist DHPG induced a depolarization and spiking that was mimicked by endogenous glutamate. Group I mGluR blockade prevented the depolarization and slightly hyperpolarized the neurons, suggesting a small tonic Group I mGluR activation. The DHPG-induced inward current consisted of voltage-dependent and -independent components; the former was blocked by TEA and the latter was blocked by replacing extracellular NaCl with LiCl or Tris-HCl. The DHPG current was potentiated in a Ca2+-free external solution and was diminished by intracellular dialysis with BAPTA and by perfusion with Na+-Ca2+ exchanger blockers, KB-R7943 or 3',4'-dichlorobenzamil. Intracellular dialysis with GDPbetaS or heparin and perfusion with the PLC inhibitor U-73122 or the Ca2+-calmodulin inhibitor W-7 significantly decreased the DHPG current. The data suggest that Group I mGluRs on baroreceptor neurons are functional; are activated by endogenous glutamate; and activate a Na+-Ca2+ exchanger through G-protein, PLC, IP3, and Ca2+-calmodulin mechanisms to excite the cell, thus providing postsynaptic mechanisms to enhance or prolong baroreceptor signal transmission.     

大鼠脑干5-羟色胺能和儿茶酚胺能神经元向孤束核的投射——荧光金标记结合免疫荧光技术研究

应用荧光金逆行追踪和免疫荧光技术相结合的方法,对投射至大鼠孤束核的５－羟色胺能和儿茶酚胺能神经纤维的脑干来源进行了研究。结果证明,将荧光金注入一侧孤束核的中尾段,逆标神经元分布于脑干下行抑制系统的大部分核团。结合５－羟色胺和酪氨酸羟化酶免疫荧光组织化学技术研究发现：荧光金／５－ＨＴ 双重反应阳性神经元分布于中脑导水管周围灰质的腹外侧区、中缝背核、脑桥被盖网状核、脑桥尾侧网状核、中缝桥核、中缝正中核、中缝大核、巨细胞网状核α部、中缝隐核和中缝苍白核等核团,其中中央灰质腹外侧区、中缝大核、巨细胞网状核α部、中缝隐核、中缝苍白核等处的荧光金／５－ＨＴ 双重反应阳性神经元数量占脑干向孤束核投射的５－ＨＴ 阳性神经元总数的近７０％ （６９．９１％ ）;荧光金／酪氨酸羟化酶双重反应阳性神经元主要分布于脑干中脑中央灰质腹外侧区、Ａ７、蓝斑及蓝斑下核（Ａ６）、Ａ５、巨细胞网状核α部和Ａ１ 等核团,其中中央灰质腹外侧区、Ａ５、巨细胞网状核α部和Ａ１ 内的荧光金／酪氨酸羟化酶神经元数量占脑干向孤束核投射的酪氨酸羟化酶阳性神经元总数的８８．１７％ 。本研究提示,大鼠脑干下行抑制系统形成了至ＮＴＳ中尾段的以中脑中央灰质腹外侧区及中缝大核、?     

大鼠孤束核内儿茶酚胺能神经元接受面口部深层组织伤害性信息并向臂旁核投射的形态学研究

为了探讨孤束核(NTS)内儿茶酚胺能神经元是否与面口部深层组织的伤害性信息有关并向臂旁核投射,本研究运用荧光金(FG))逆行追踪,福尔马林刺激咬肌和免疫荧光技术相结合的三重标记方法,在荧光显微镜下观察了大鼠NTS内酪氨酸羟化酶(TH)阳性并表达FOS蛋白的神经元向臂旁核的投射。将2％FG注入一侧臂旁外侧核后,向同侧咬肌内注射2％福尔马林溶液,并行TH和FOS免疫荧光组织化学染色,荧光显微镜下在同侧NTS内的连合、内侧、中间内侧和腹侧亚核中可见重叠分布的FG、FOS、TH单标神经元以及FG／TH、FOS／TH、FOS／FG双标和FG／FOS／TH三标神经元。FG／TH和FOS／TH双标神经元分别占同侧NTS内TH阳性神经元总数的28.6％和34.8％;FOS／FG双标神经元占同侧FG逆标神经元总数的26.4％;FG／FOS／TH三标神经元分别占同侧TH阳性神经元和FG逆标神经元总数的23.7％和8.4％。本结果提示大鼠NTS中的部分儿茶酚胺能神经元接受面口部深层组织的伤害性信息并向臂旁外侧核传递。     

中脑导水管周围灰质、中缝背核、中缝大核和巨细胞网状核α部向孤束核的定位投射

本文用荧光金逆行追踪技术对大鼠下行抑制系统的中脑导水管周围灰质、中缝背核、中缝大核和巨细胞网状核a部向孤束核的投射进行了研究．将荧光金分别注入到孤束核的吻段、中段和尾段后，上述核团内出现的逆行标记神经元分布如下：（1）在冠状切面上，中脑导水管周围灰质内的荧光金标记细胞群集存在；在吻尾方向上呈柱状分布．三个实验组中，除吻段注射组的标记细胞数量少于其它2组外．在分布上完全一致。腹外侧区的标记细胞数量最多，但从尾侧到吻侧逐渐减少；背内侧区的标记细胞数量较少，以中、吻段较多；背外侧区的标记细胞出现于中脑导水管周围灰质的中、尾段，尾段最多，吻段内未见标记细胞．所有实验动物的中脑导水管周围灰质的内侧区均未出现标记细胞．（2）中缝背核内的标记细胞，多数位于其吻段的背侧都与收侧部的移行部，并且以注射区在孤束核的吻段者标记细胞较多；中缝背核的中尾段标记细胞量少，且散在于背外侧部，以注射区在孤束核的中段者标记细胞较多．（3）中缝大核内的标记细胞以核的尾段较多，吻段较少；巨细胞同状核a部内的标记细胞在吻尾方向上分布均匀。此两核团内的标记细胞数量以注射区在孤束核的中、尾段者较多。（4）上述脑区内标记细胞的数量均为注射区的同侧多于对侧。本研     

Group I metabotropic glutamate receptors prevent endothelial programmed cell death independent from MAP kinase p38 activation in rat

Activation of Group I metabotropic glutamate receptors (mGluRs) prevents neuronal programmed cell death (PCD), but the role of these receptors in the vascular endothelial cell (EC) system has not been defined. Since ECs are principal targets for ischemic free radical injury, we examined whether the mGluR system could modulate vascular PCD. Activation of the Group I mGluR system, but not antagonism, addressed two distinct pathways of PCD by preventing the destruction of genomic DNA and maintaining EC membrane asymmetry. The induction of nitric oxide (NO)-induced PCD in ECs paralleled the specific activation of the MAP kinase p38 pathway, but the vascular protection conferred by the Group I mGluR system appears to rely on more downstream cellular pathways. We provide initial evidence for Group I mGluRs to prevent NO-induced vascular injury and offer new directions for vascular disease treatment.     

Modulation of synaptic transmission from primary afferents to spinal substantia gelatinosa neurons by group III mGluRs in GAD65-EGFP transgenic mice

Group III metabotropic glutamate receptors (mGluRs) are involved in nociceptive transmission in the spinal cord. However, the cellular mechanism underlying the modulation of synaptic transmission from nociceptive primary afferents to dorsal horn neurons by group III mGluRs has yet to be explored. In this study, we used transgenic mice expressing enhanced green fluorescent protein (EGFP) under the control of the glutamate decarboxylase (GAD) 65 promoter to identify specific subpopulations of GABAergic inhibitory interneurons. By GABA immunolabeling, we confirmed the majority of GAD65-EGFP-expressing neurons were GABAergic. Because GAD65-EGFP-expressing neurons have not been examined in detail before, we first investigated the physiological properties of GAD65-EGFP- and non-EGFP-expressing neurons in substantia gelatinosa (SG) of the spinal dorsal horn. Membrane properties, such as the resting membrane potential, membrane capacitance, action potential threshold, and action potential height, differed significantly between these two groups of neurons. Most EGFP-expressing neurons displayed a tonic firing pattern (73% of recorded neurons) and received monosynaptic Aδ and/or C primary afferent inputs (85% of recorded neurons). In contrast, we observed a delayed firing pattern in 53% of non-EGFP-expressing neurons. After identifying the physiological properties of EGFP-expressing neurons, we tested the effects of group III mGluRs on synaptic transmission pharmacologically. A group III mGluR agonist, L-AP4, attenuated Aδ fiber-evoked synaptic transmission but did not affect C fiber-evoked synaptic transmission to EGFP-expressing neurons. Similar primary afferent-specific inhibition by L-AP4 was also observed in non-EGFP-expressing neurons. Moreover, Aδ fiber-evoked synaptic transmission was suppressed by a selective mGluR7 agonist, AMN082. These results suggest that modulation of the synaptic transmission from primary afferents to SG neurons by group III mGluR agonist is specific to the type of nociceptive primary afferents but not to the type of target neurons.     

大鼠延髓背角Ⅱ层神经元向臂旁区、延髓尾侧腹外侧区和脊髓的投射

将逆行追踪剂荧光金分别注入大鼠一侧臂旁区、延髓尾侧腹外侧区和颈髓第四节段 ,观察到延髓背角浅层 ( 、 层 )向上述部位均有投射 , 层外侧部的投射神经元多于 层内侧部。臂旁区接受双侧延髓背角浅层的投射 ,但以同侧为主 ;延髓尾侧腹外侧区和第 4颈髓接受同侧延髓背角浅层神经元的投射但延髓背角浅层向第 4颈髓投射的神经元数量较少。结合免疫荧光组织化学研究表明 , 层向臂旁区和延髓尾侧腹外侧区投射的神经元部分呈 calbindin-D2 8k样阳性 ,而未见呈 parvalbumin样阳性者。向第 4颈髓投射的 层神经元数量很少 ,未见有呈 calbindin-D2 8K和 parvalbumin样阳性者。本研究结果进一步支持 层有传出投射的观点 ,也提示 层的 calbindin-D2 8K样和 parvalbumin样阳性神经元可能分别属于不同的细胞亚群。     

Systemic cholecystokinin differentially affects baro-activated GABAergic neurons in rat caudal ventrolateral medulla

Cholecystokinin (CCK) is released after a meal to promote digestion and satiety. Circulating CCK inhibits splanchnic sympathetic nerve activity (sSNA), which may contribute to postprandial increases in mesenteric blood flow. The CCK-induced sympathoinhibition occurs by activation of vagal afferent nerves and inhibition of a subset of presympathetic rostral ventrolateral medullary (RVLM) neurons. The present study sought to determine whether the caudal ventrolateral medulla (CVLM) may also play a role in the CCK-induced changes in sSNA. Rats were anesthetized with chloralose, artificially ventilated, paralyzed, and prepared for recording arterial pressure (AP), heart rate (HR), sSNA, and activity of individual CVLM neurons. Injection of CCK-8 (8-10 microg/kg, iv) decreased sSNA, AP, and HR. Most baro-activated CVLM neurons were excited by CCK (n = 25, 3.4-fold increase), whereas other baro-activated CVLM neurons were not affected (n = 7) or were inhibited (n = 3). A subset of baro-activated CVLM neurons that were activated (n = 8) or unaffected (n = 2) was confirmed to be GABAergic by the presence of GAD67 mRNA. Bilateral inhibition of the CVLM by microinjections of muscimol reversed the decreases in sSNA and AP to a prominent sympathoactivation and increase in AP (n = 18). These data suggest that systemic injection of CCK leads to the activation of most baro-activated GABAergic CVLM neurons and that the CVLM is essential for the production of CCK-induced inhibition of sSNA. The differential responses of baro-activated GABAergic CVLM neurons to CCK may contribute to the diverse responses of presympathetic RVLM neurons and sympathetic outflows observed with systemic CCK.     

Activation of metabotropic glutamate receptors inhibits high-voltage-gated calcium channel currents of chicken nucleus magnocellularis neurons

Using whole cell patch-clamp recordings, we pharmacologically characterized the voltage-gated Ca2+ channel (VGCC) currents of chicken nucleus magnocellularis (NM) neurons using barium as the charge carrier. NM neurons possessed both low- and high-voltage-activated Ca2+ channel currents (HVA I(Ba2+)). The N-type channel blocker (omega-conotoxin-GVIA) inhibited more than half of the total HVA I(Ba2+), whereas blockers of L- and P/Q-type channels each inhibited a small fraction of the current. Metabotropic glutamate receptor (mGluR)-mediated modulation of the HVA I(Ba2+) was examined by bath application of glutamate (100 microM), which inhibited the HVA I(Ba2+) by an average of 16%. The inhibitory effect was dose dependent and was partially blocked by omega-conotoxin-GVIA, indicating that mGluRs modulate N and other type HVA I(Ba2+). The nonspecific mGluR agonist, (1S,3R)-1-aminocyclopentane-1,3-dicarbosylic acid (1S,3R-ACPD), mimicked the inhibitory effect of glutamate on HVA I(Ba2+). Group I-III mGluR agonists showed inhibition of the HVA current with the most potent being the group III agonist L(+)-2-amino-4-phosphonobutyric acid. 1S,3R-ACPD (200 microM) had no effect on K+ or Na+ currents. The firing properties of NM neurons were also not altered by 1S,3R-ACPD. We propose that the inhibition of VGCC currents by mGluRs limits depolarization-induced Ca2+ entry into these highly active NM neurons and regulates their Ca2+ homeostasis.     

Collateral damage and compensatory changes after injection of a toxin targeting neurons with the neurokinin-1 receptor in the nucleus tractus solitarii of rat

Injection into the nucleus tractus solitarii (NTS) of toxins that target substance P (SP) receptors ablates neurons that express neurokinin-1 (NK1) receptors, attenuates baroreflexes, and results in increased lability of arterial pressure. We and others have shown that the toxin leads to loss of neurons containing SP receptors and loss of GABAergic neurons in the NTS; but given that neither type neuron is thought to be integral to baroreflex transmission in NTS, mechanisms responsible for the cardiovascular changes remained unclear. Because NK1 receptors colocalize with N-methyl-d-aspartate (NMDA) receptors and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in NTS and because glutamate transmission may be integral to baroreflex transmission in the NTS we hypothesized that the toxic lesions may interrupt mechanisms for glutamate transmission. Interruption of those mechanisms could be responsible for the cardiovascular effects. We tested the hypothesis by performing fluorescent immunohistochemistry, confocal microscopy and image analysis after injecting stabilized SP-SAP (SSP-SAP) unilaterally into the NTS. We assessed changes in immunoreactivity (IR) of NMDA receptor subunit 1 (NMDAR1), AMPA receptor subunit 2 (GluR2), and 3 types of vesicular glutamate transporters (VGluT) as well as IR of gamma-aminobutyric acid receptors type b (GABAb), neuronal nitric oxide synthase (nNOS), tyrosine hydroxylase (TH), and protein gene product 9.5 (PGP 9.5), a neuronal marker, in the NTS. When compared to that of the same section of the un-injected NTS, IR decreased significantly in the injected side for NMDAR1 (p<0.01), GluR2 (p<0.01), VGluT3 (p<0.01), GABAb (p<0.001), and PGP9.5 (p<0.001). In contrast, IR for VGluT1 (p<0.001), VGluT2 (p<0.001), nNOS (p<0.001), and TH (p<0.001) increased significantly. We conclude that pathologic effects following ablation of neurons with NK1 receptors in NTS may result from interruption of neurotransmission through other neurochemical systems associated with NK1 receptors-containing neurons.     

Inhibitory effects of Group I metabotropic glutamate receptors antagonists on the expression of NMDA receptor NR1 subunit in morphine tolerant rats

N-Methyl-d-aspartate receptor (NMDAR) and Group I metabotropic glutamate receptors (mGluRs) are involved in the process of morphine tolerance. Previous studies have shown that Group I mGluRs can modulate NMDAR functions in the central nervous system. The aim of the present study was to examine the influence of Group I mGluRs antagonists on the expression of NMDA receptor NR1 subunit (NR1) in the rat spinal cord. Morphine tolerance was induced in rats by repeated administration of 10 μg morphine (intrathecal, i.t.) twice a day for 7 consecutive days. Tail flick test was used to assess the effect of Group I mGluRs antagonist, AIDA ((RS)-1-Aminoindan-1,5 dicarboxylic acid) or mGluR5 antagonist, MPEP (2-methyl-6-(phenylethynyl)pyridine) on morphine antinociceptive tolerance. The expression of NR1 was measured by immunofluorescence and Western blot. Behavioral tests revealed that both AIDA and MPEP attenuated the development of morphine tolerance. The expression of NR1 was upregulated in the dorsal horn of spinal cord after chronic morphine treatment. AIDA or MPEP co-administered with morphine attenuated morphine induced upregulation of NR1. These findings suggest that the development of morphine tolerance partly prevented by Group I mGluRs antagonists may due to its inhibitory effect on the expression of NR1 subunit.     

Prenatal ozone exposure abolishes stress activation of Fos and tyrosine hydroxylase in the nucleus tractus solitarius of adult rat

Ozone (O₃) is widely distributed in the environment, with high levels of air pollution. However, very few studies have documented the effects on postnatal development of O₃ during pregnancy. The long-term effects of prenatal O₃ exposure in rats (0.5 ppm 12 h/day from embryonic day E5 to E20) were evaluated in the adult nucleus tractus solitarius (NTS) regulating respiratory control. Neuronal response was assessed by Fos protein immunolabeling (Fos-IR), and catecholaminergic neuron involvement by tyrosine hydroxylase (TH) labeling (TH-IR). Adult offspring were analyzed at baseline and following immobilization stress (one hour, plus two hours’ recovery); immunolabeling was observed by confocal microscopy. Prenatal O₃ increased the baseline TH gray level per cell (p < 0.001). In contrast, the number of Fos-IR cells, Fos-IR/TH-IR colabeled cells and proportion of TH double-labeled with Fos remained unchanged. After stress, the TH gray level (p < 0.001), number of Fos-IR cells (p < 0.001) and of colabeled Fos-IR/TH-IR cells (p < 0.05) and percentage of colabeled Fos-IR/TH-IR neurons against TH-IR cells (p < 0.05) increased in the control group. In prenatal-O₃ rats, immobilization stress abolished these increases and reduced the TH gray level (p < 0.05), indicating that prenatal O₃ led to loss of adult NTS reactivity to stress. We conclude that long-lasting sequelae were detected in the offspring beyond the prenatal O₃ exposure. Prenatal O₃ left a print on the NTS, revealed by stress. Disruption of neuronal plasticity to new challenge might be suggested.     

Group I metabotropic glutamate receptors: implications for brain diseases.

Glutamate is the major excitatory neurotransmitter in the brain and plays a unique role in a variety of central nervous system (CNS) functions. The discovery of the metabotropic receptors (mGluRs), a family of G-protein coupled receptors than can be activated by glutamate, has led to an impressive number of studies in recent years aimed at understanding their biochemical, physiological and pharmacological characteristics. The eight mGluRs now known are divided into three groups according to their sequence homology, signal transduction mechanisms, and agonist selectivity. Group I mGluRs include mGluR1 and mGluR5, which are linked to the activation of phospholipase C; Groups II and III include all others and are negatively coupled to adenylyl cyclases. The availability in recent years of agents selective for Group I mGluRs has made possible the study of the physiological roles of these receptors in the CNS. In addition to mediating glutamatergic neurotransmission, Group I mGluRs can modulate other neurotransmitter receptors, including GABA and the ionotropic glutamate receptors. Group I mGluRs are involved in many CNS functions and may participate in a variety of disorders such as pain, epilepsy, ischemia, and chronic neurodegenerative diseases. This class of receptor may provide important pharmacological therapeutic targets and elucidating its functions will be relevant to develop new treatments for neurological and psychiatric disorders in which glutamatergic neurotransmission is abnormally regulated. In this review anatomical, physiological and pharmacological results are presented with a special emphasis on the role of Group I mGluRs in functional and pathological processes.     

Right atrial stretch activates neurons in autonomic brain regions that project to the rostral ventrolateral medulla in the rat

Activation of the cardiac mechanoreceptors results in changes in sympathetic nerve activity and plays an important role in the responses elicited by elevated blood volume. Stimulation of the reflex influences several key autonomic regions, namely the paraventricular nucleus (PVN), the nucleus of the tractus solitarius (NTS) and the caudal ventrolateral medulla (CVLM). Neurons in these regions project directly to the rostral ventrolateral medulla (RVLM), a critical region in the generation of sympathetic vasomotor tone. The aim of the present experiments was to determine whether neurons in the PVN, NTS and CVLM that are activated by cardiac mechanoreceptor stimulation also project to the RVLM. Animals were prepared, under general anesthesia, by microinjection of a retrogradely transported tracer into the pressor region of the RVLM, and the placement of a balloon-tipped cannula at the junction of the right atrium and the superior vena cava. On the experimental day, in conscious rats, the balloon was inflated to stimulate cardiac mechanoreceptors (n = 9), or left uninflated (control, n = 8). Compared with controls, there was a significantly increased number of Fos-immunoreactive neurons (a marker of activation) in both the PVN (2.5-fold) and NTS (two-fold), but this was not seen in the CVLM. Compared with controls, a significant number of the neurons in the PVN (8%) and NTS (4.0%) that projected to the RVLM were activated. The data suggest that subgroups of RVLM-projecting neurons located in the PVN and NTS are involved in the central reflex pathway activated by cardiac mechanoreceptor stimulation.     

Regulation of phosphorylation of NMDA receptor NR1 subunits in the rat neostriatum by group I metabotropic glutamate receptors in vivo

Group I metabotropic glutamate receptors (mGluRs) are Gαq-protein-coupled receptors and are densely expressed in medium-sized spiny projection neurons of the neostriatum. Among different subtypes of glutamate receptors, group I mGluRs have been demonstrated to actively interact with the ionotropic glutamate receptor N-methyl-d-aspartate (NMDA) subtypes for regulating various forms of cellular activities and synaptic plasticity. In this study, the possible role of group I mGluRs in regulating serine phosphorylation of NMDA receptor NR1 subunits in the neostriatum was investigated in vivo. We found in chronically cannulated rats that injection of the group I mGluR agonist 3,5-dihydroxyphenylglycine (DHPG) into the dorsal striatum (caudate putamen) significantly increased phosphorylation of the two serine residues (serine 896 and serine 897) on the intracellular C-terminus of the NR1. The increase in NR1 phosphorylation was dose-dependent and DHPG had no effect on basal levels of NR1 proteins. Intrastriatal infusion of the group I mGluR antagonist N-phenyl-7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxamide (PHCCC) significantly attenuated the DHPG-stimulated NR1 phosphorylation. Pretreatment with the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP) also produced the same effect. These data suggest that group I mGluRs, likely mGluR5 subtypes, possess the ability to upregulate protein phosphorylation of NMDA receptor NR1 subunits in striatal neurons in vivo.     

Activation of metabotropic glutamate receptor 1 inhibits glutamatergic transmission in the substantia nigra pars reticulata

The substantia nigra pars reticulata is a primary output nucleus of the basal ganglia motor circuit and is controlled by a fine balance between excitatory and inhibitory inputs. The major excitatory input to GABAergic neurons in the substantia nigra arises from glutamatergic neurons in the subthalamic nucleus, whereas inhibitory inputs arise mainly from the striatum and the globus pallidus. Anatomical studies revealed that metabotropic glutamate receptors (mGluRs) are highly expressed throughout the basal ganglia. Interestingly, mRNA for group I mGluRs are abundant in neurons of the subthalamic nucleus and the substantia nigra pars reticulata. Thus, it is possible that group I mGluRs play a role in the modulation of glutamatergic synaptic transmission at excitatory subthalamonigral synapses. To test this hypothesis, we investigated the effects of group I mGluR activation on excitatory synaptic transmission in putative GABAergic neurons in the substantia nigra pars reticulata using the whole cell patch clamp recording approach in slices of rat midbrain. We report that activation of group I mGluRs by the selective agonist (R,S)-3,5-dihydroxyphenylglycine (100 microM) decreases synaptic transmission at excitatory synapses in the substantia nigra pars reticulata. This effect is selectively mediated by presynaptic activation of the group I mGluR subtype, mGluR1. Consistent with these data, electron microscopic immunocytochemical studies demonstrate the localization of mGluR1a at presynaptic sites in the rat substantia nigra pars reticulata.From this finding that group I mGluRs modulate the major excitatory inputs to GABAergic neurons in the substantia nigra pars reticulata we suggest that these receptors may play an important role in basal ganglia functions. Studying this effect, therefore, provides new insights into the modulatory role of glutamate in basal ganglia output nuclei in physiological and pathophysiological conditions.     

A unilateral 6-hydroxydopamine lesion decreases the expression of metabotropic glutamate receptors in rat substantia nigra

Loss of dopaminergic neurons in the substantia nigra pars compacta (SNc) in Parkinson's disease (PD) leads to augmentation of glutamatergic activity in the subthalamic nucleus (STN). Moreover, antagonizing excitotoxicity has yielded mostly symptomatic improvements in experimental animals of PD. Therefore, we used immunocytochemistry to examine the effect of unilateral 6-hydroxydopamine lesions of SNc on the expression of metabotropic glutamate receptors (mGluR1a, 2/3, 5, 4, 8) and tyrosine hydroxylase (TH). 6-Hydroxydopamine causes a fall in the number of mGluRs and TH in the lesioned lateral substantia nigra. Pharmacological activation of group II or III mGluRs or blockade of group I mGluRs for 1 week significantly increased the expression of the same group receptors. The alteration in the receptor expression may be a compensatory mechanism developed after mGluRs ligands neuroprotective treatment.     

大鼠孤束核内含calbindin D-28K的内脏伤害性神经元向终纹床核的投射—荧光金标记结合免疫荧光技术研究

既往的研究证明孤束核和终纹床核参与内脏伤害性信息的传递和调控。Calbindin D-2 8K是钙结合蛋白家族的成员 ,为神经细胞特别是投射神经元的选择性标记物。应用荧光金逆行追踪和免疫荧光技术相结合的方法 ,对给予内脏伤害性刺激后大鼠孤束核内 FOS的表达并显示 Calbindin D-2 8K免疫阳性的神经元向终纹床核的投射进行了研究。结果显示 :将荧光金注入一侧终纹床核外侧部后 ,孤束核中尾段内双侧出现荧光金逆行标记细胞 ,注射区同侧占优势 :孤束核的相同平面可观察到双侧等量分布的免疫反应阳性的 Calbindin D-2 8K和 FOS细胞 :三种阳性细胞的分布有明显的重叠现象。在其重叠分布区可见荧光金 /Calbindin D-2 8K、FOS/Calbindin D-2 8K、荧光金 /FOS双重阳性以及荧光金 /Calbindin D-2 8K/FOS三重阳性细胞。除 FOS/Cal-bindin D-2 8K双重阳性细胞为双侧分布外 ,荧光金 /Calbindin D-2 8K、荧光金 /FOS双重阳性以及荧光金 /Calbindin D-2 8K/F OS三重阳性细胞的出现均以注射区同侧为主。荧光金 /Calbindin D-2 8K、F OS/Calbindin D-2 8K双重阳性和荧光金 /Calbindin D-2 8K/F OS三重阳性神经元占孤束核内 Calbindin D-2 8K免疫阳性神经元总数的百分比分别为 2 .79%、15 .3 %和 2 .5 6% ;荧光金/Calbindin     

Cellular localization of metabotropic glutamate receptors in cortical tubers and subependymal giant cell tumors of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder associated with cortical malformations (cortical tubers) and the development of glial tumors (subependymal giant-cell tumors, SGCTs). Expression of metabotropic glutamate receptor (mGluR) subtypes is developmentally regulated and several studies suggest an involvement of mGluR-mediated glutamate signaling in the regulation of proliferation and survival of neural stem-progenitor cells, as well as in the control of tumor growth. In the present study, we have investigated the expression and cell-specific distribution of group I (mGluR1, mGluR5), group II (mGluR2/3) and group III (mGluR4 and mGluR8) mGluR subtypes in human TSC specimens of both cortical tubers and SGCTs, using immunocytochemistry. Strong group I mGluR immunoreactivity (IR) was observed in the large majority of TSC specimens in dysplastic neurons and in giant cells within cortical tubers, as well as in tumor cells within SGCTs. In particular mGluR5 appeared to be most frequently expressed, whereas mGluR1alpha was detected in a subpopulation of neurons and giant cells. Cells expressing mGluR1alpha and mGluR5, demonstrate IR for phospho-S6 ribosomal protein (PS6), which is a marker of the mammalian target of rapamycin (mTOR) pathway activation. Group II and particularly group III mGluR IR was less frequently observed than group I mGluRs in dysplastic neurons and giant cells of tubers and tumor cells of SGCTs. Reactive astrocytes were mainly stained with mGluR5 and mGluR2/3. These findings expand our knowledge concerning the cellular phenotype in cortical tubers and in SGCTs and highlight the role of group I mGluRs as important mediators of glutamate signaling in TSC brain lesions. Individual mGluR subtypes may represent potential pharmacological targets for the treatment of the neurological manifestations associated with TSC brain lesions.