Differential Effects of Chemical Sympathectomy on Expression and Activity of Tyrosine Hydroxylase and Levels of Catecholamines and DOPA in Peripheral Tissues of Rats

Tyrosine hydroxylase (TH) mRNA and activity and concentrations of 3,4-dihydroxyphenylalanine (DOPA) and catecholamines were examined as markers of sympathetic innervation and catecholamine synthesis in peripheral tissues of sympathectomized and intact rats. Chemical sympathectomy with 6-hydroxydopamine (6-OHDA) markedly decreased norepinephrine and to a generally lesser extent TH activities and dopamine in most peripheral tissues (stomach, lung, testis, duodenum, pancreas, salivary gland, spleen, heart, kidney, thymus). Superior cervical ganglia, adrenals and descending aorta were unaffected and vas deferens showed a large 92% decrease in norepinephrine, but only a small 38% decrease in TH activity after 6-OHDA. Presence of chromaffin cells or neuronal cell bodies in these latter tissues, indicated by consistent expression of TH mRNA, explained the relative resistance of these tissues to 6-OHDA. Stomach also showed consistent expression of TH mRNA before, but not after 6-OHDA, suggesting that catecholamine synthesizing cells in gastric tissue are sensitive to the toxic effects of 6-OHDA. Tissue concentrations of DOPA were mainly unaffected by 6-OHDA, indicating that much of the DOPA in peripheral tissues is synthesized independently of local TH or sympathetic innervation. The differential effects of chemical sympathectomy on tissue catecholamines, DOPA, TH mRNA and TH activity demonstrate that these variables are not simple markers of sympathetic innervation or catecholamine synthesis. Other factors, including presence of neuronal cell bodies, parenchymal chromaffin cells, non-neuronal sites of catecholamine synthesis and alternative sources of tissue DOPA, must also be considered when tissue catecholamines, DOPA and TH are examined as markers of sympathetic innervation and local catecholamine synthesis.     

Differential involvement of central and peripheral norepinephrine in the central lipopolysaccharide-induced interleukin-6 responses in mice

Intracerebroventricular injection of lipopolysaccharide (LPS) induces a marked increase in circulating interleukin (IL)-6 levels and in IL-6 mRNA expression in brain and peripheral organs. Recently, it was reported that intraperitoneal administration of alpha-adrenoceptor antagonists inhibits centrally injected LPS-induced increases in plasma IL-6 levels, suggesting the involvement of the norepinephrine (NE) system in the central LPS-induced IL-6 response. However, the localization (either central or peripheral) of NE involvement in the central LPS-induced IL-6 response has not been characterized. In the present study, mice were pretreated with 6-hydroxydopamine (6-OHDA) administered intracerebroventricularly or intraperitoneally to deplete central or peripheral stores of NE, respectively. Intracerebroventricular LPS (50 ng/mouse) markedly increased plasma IL-6 levels and IL-6 mRNA expression in choroid plexus, hypothalamus, pituitary, adrenals, heart, liver, spleen, and lymph nodes, but with minimal effect in lung, kidney, and testis, as revealed by RT-PCR. Pretreatment with intracerebroventricular 6-OHDA (50 microg/mouse) decreased the LPS-induced plasma IL-6 levels by 39% and the LPS-induced IL-6 mRNA expression in liver, spleen, and lymph nodes, but not in choroid plexus, hypothalamus, pituitary, adrenals, and heart. Pretreatment with intraperitoneal 6-OHDA (100 mg/kg) decreased the LPS-induced plasma IL-6 levels by 36% and the LPS-induced IL-6 mRNA expression in all the peripheral organs displaying increased IL-6 mRNA. Central LPS-induced increase in plasma corticosterone levels was decreased slightly by central but not by peripheral NE depletion. These results suggest that central NE and peripheral NE are differentially involved in the central LPS-induced IL-6 mRNA expression in peripheral organs.     

Central catecholamine depletion inhibits peripheral lymphocyte responsiveness in spleen and blood

Experimental and clinical evidence has demonstrated extensive communication between the CNS and the immune system. To analyse the role of central catecholamines in modulating peripheral immune functions, we injected the neurotoxin 6-hydroxydopamine (6-OHDA) i.c.v. in rats. This treatment significantly reduced brain catecholamine content 2, 4 and 7 days after injection, and in the periphery splenic catecholamine levels were reduced 4 days after treatment. Central catecholamine depletion induced an inhibition of splenic and blood lymphocyte proliferation and splenic cytokine production and expression (interleukin-2 and interferon-gamma) 7 days after injection. In addition, central treatment with 6-OHDA reduced the percentage of spleen and peripheral blood natural killer (CD161 +) cells, and T-cytotoxic (CD8 +) cells in peripheral blood. The reduction in splenocyte proliferation was not associated with a glucocorticoid alteration but was completely abolished by prior peripheral sympathectomy. These data demonstrate a crucial role of central and peripheral catecholamines in modulating immune function.     

Increased vulnerability of dopaminergic neurons in MPTP-lesioned interleukin-6 deficient mice

To test the hypothesis that neuroinflammation contributes to dopaminergic neuron death in the MPTP-lesioned mouse, we compared nigrostriatal degeneration in interleukin (IL)-6 (+/+) with IL-6 (-/-) mice. In the absence of IL-6, a single injection of MPTP (30 mg/kg) resulted in significantly greater striatal dopamine depletion than that measured in IL-6 (+/+) mice. The observed dopamine depletion was MPTP dose dependent. This loss of striatal dopamine and a significantly greater loss of TH+ cells in the substantia nigra pars compacta in IL-6 (-/-) mice as compared with control IL-6 (+/+) mice, suggest that IL-6 is neuroprotective in the MPTP-lesioned nigrostriatal system. Co-localization experiments identified striatal astrocytes as the source of IL-6 in IL-6 (+/+) mice at 1 and 7 days postinjection of MPTP. The increased sensitivity of dopaminergic neurons to neurotoxicant in the absence of IL-6, is compatible with a neuroprotective activity of IL-6 in the injured nigrostriatal system.     

Intranigral infusion of interleukin-1beta activates astrocytes and protects from subsequent 6-hydroxydopamine neurotoxicity

Activation of glial cells is a prevalent response to neuronal damage in brain disease and ageing, with potential neuroprotective and neurotoxic consequences. We were interested in studying the role of glial activation on dopaminergic neurons of the substantia nigra in an animal model of Parkinson's disease. Thus, we evaluated the effect of a pre-existing glial activation on the dopaminergic neuronal death induced by striatal infusion of 6-hydroxydopamine. We established a model of local glial activation by stereotaxic infusion of interleukin-1beta in the substantia nigra of adult rats. Interleukin-1beta (20 ng) induced a marked activation of astrocytes at days 2, 5 and 10, revealed by heat-shock protein 27 and glial fibrillary acid protein immunohistochemistry, but did not affect the microglial markers OX-42 and heat-shock proteins 32 or 47. Intranigral infusion of interleukin-1beta 5 days before a striatal injection of 6-hydroxydopamine significantly protected nigral dopaminergic cell bodies, but not striatal terminals from the 6-hydroxydopamine lesion. Also, in the animals pre-treated with interleukin-1beta, a significant prevention of 6-hydroxydopamine-induced reduction of adjusting steps, but not of 6-hydroxydopamine-induced amphetamine rotations, were observed. These data show the characterization of a novel model of local astroglial activation in the substantia nigra and support the hypothesis of a neuroprotective role of activated astrocytes in Parkinson's disease.     

中枢白细胞介素-1在应激反应中的作用

白细胞介素-1（interleukin-1,IL-1）系统分子广泛分布于中枢神经系统。中枢IL-1具有极其丰富的生物学功能,作为经典炎性细胞因子,在多种生理、病理生理过程中起重要作用。近几年来,中枢IL-1的应激介质作用备受关注。本文综述了中枢IL-1在应激反应中作用的最新进展,包括应激对中枢IL-1系统的影响,中枢IL-1对应激反应的启动和介导作用;参与中枢IL-1-应激介导作用的神经环路和细胞信号转导通路,以及中枢IL-1对应激时脑高级功能和行为反应的影响。     

Hypermetabolism in mice caused by the central action of an unliganded thyroid hormone receptor alpha1

Thyroid hormone, via its nuclear receptors TRalpha and TRbeta, controls metabolism by acting locally in peripheral tissues and centrally by regulating sympathetic signaling. We have defined aporeceptor regulation of metabolism by using mice heterozygous for a mutant TRalpha1 with low affinity to T3. The animals were hypermetabolic, showing strongly reduced fat depots, hyperphagia and resistance to diet-induced obesity accompanied by induction of genes involved in glucose handling and fatty acid metabolism in liver and adipose tissues. Increased lipid mobilization and beta-oxidation occurred in adipose tissues, whereas blockade of sympathetic signaling to brown adipose tissue normalized the metabolic phenotype despite a continued perturbed hormone signaling in this cell type. The results define a novel and important role for the TRalpha1 aporeceptor in governing metabolic homeostasis. Furthermore, the data demonstrate that a nuclear hormone receptor affecting sympathetic signaling can override its autonomous effects in peripheral tissues.     

Increased fibrillar beta-amyloid in response to human clq injections into hippocampus and cortex of APP+PS1 transgenic mice

Human C1q when injected directly into hippocampus and cortex of doubly transgenic APP+PS1 mice results in the increase of Congo red-positive fibrillar deposits. Although there was no significant change in overall area stained for A total, qualitatively it appeared that there was less diffuse A in C1q-treated mice versus vehicle. There was no apparent change in astroglial or microglial activation caused by injection of C1q with respect to vehicle injections. These effects of C1q were only found in 50% BUB/BnJ mice, a strain with higher serum complement activity than other mouse lines. These in vivo data were consistent with the effects of C1q to increase fibrillogenesis of A in vitro. In conclusion, complement protein C1q, believed to be involved in the pathogenesis of Alzheimer's disease in humans, can cause increased fibrillogenesis in the APP+PS1 mouse model of amyloid deposition.     

Differential effects of hydrocortisone on sympathetic and hemodynamic responses to sympathoexcitatory manoeuvres in men

Aim of the present study was to investigate the influence of hydrocortisone on muscle sympathetic nerve activity (MSNA) and hemodynamic parameters during different sympathoexcitatory manoeuvres in humans. The study focuses on the interaction of the hypothalamo-pituitary-adrenal system and the sympathetic nervous system. Hydrocortisone 100 mg or placebo was administered intravenously to eight young healthy subjects in a double-blind crossover design. After 6 h, blood pressure, heart rate and MSNA from the peroneal nerve were recorded at rest, during an arithmetic stress task, an apnea and a cold pressor test. Hydrocortisone treatment increased serum cortisol levels to the upper physiological range and suppressed basal levels of adrenocorticotropin. During mental stress, MSNA, heart rate and blood pressure levels were elevated independently of hydrocortisone pre-treatment. However, hydrocortisone induced a sustained increase in basal heart rate throughout the whole experiment. A stronger increase in diastolic blood pressure was observed during apnea and cold pressor test in the hydrocortisone experiments. MSNA or plasma catecholamines at rest or during the manoeuvres were not affected by hydrocortisone. The observed hydrocortisone effects may be due to an increased responsiveness of adrenergic receptors towards catecholamines or a central modulation of the baroreflex involving parasympathetic mechanisms. Further studies are needed to confirm that the increase in MSNA during mental stress does not depend on a concomitant activation of the hypothalamo-pituitary-adrenal system.     

Relationship between microglial activation and dopaminergic neuronal loss in the substantia nigra: a time course study in a 6-hydroxydopamine model of Parkinson's disease

Cellular interactions between activated microglia and degenerating neurons in in vivo models of Parkinson's disease are not well defined. This time course study assesses the dynamics of morphological and immunophenotypic properties of activated microglia in a 6-hydroxydopamine (6-OHDA) model of Parkinson's disease. Neurodegeneration in the substantia nigra pars compacta (SNc) was induced by unilateral injection of 6-OHDA into the medial forebrain bundle. Activated microglia, identified using monoclonal antibodies: clone of antibody that detects major histocompatibility complex (MHC) class II antigens (OX6) for MHC class II, clone of antibody that detects cell surface antigen-cluster of differentiation 11b – anti-complement receptor 3, a marker for complement receptor 3 and CD 68 for phagocytic activity. Activation of microglia in the lesioned SNc was rapid with cells possessing amoeboid or ramified morphology appeared on day 1, whilst antibody clone that detects macrophage-myeloid associated antigen immunoreactivity was observed at day 3 post-lesion when there was no apparent loss of tyrosine hydroxylase (TH)+ve dopaminergic (DA) SNc neurons. Thereafter, OX6 and antibody clone that detects macrophage-myeloid associated antigen activated microglia selectively adhered to degenerating axons, dendrites and apoptotic (caspase 3+ve) DA neurons in the SNc were observed at day 7. This was followed by progressive loss of TH+ve SNc neurons, with the peak of TH+ve cell loss (51%) being observed at day 9. This study suggests that activation of microglia precedes DA neuronal cell loss and neurons undergoing degeneration may be phagocytosed prematurely by phagocytic microglia.     

Expression of human FE65 in amyloid precursor protein transgenic mice is associated with a reduction in beta-amyloid load

FE65 is an adaptor protein that interacts with the cytoplasmic tail of the amyloid precursor protein (APP). In cultured non-neuronal cells, the formation of the FE65-APP complex is a key element for the modulation of APP processing, signalling and beta-amyloid (Abeta) production. The functions of FE65 in vivo, including its role in the metabolism of neuronal APP, remain to be investigated. In this study, transgenic mice expressing human FE65 were generated and crossbred with APP transgenic mice, known to develop Abeta deposits at 6 months of age. Compared with APP mice, APP/FE65 double transgenic mice exhibited a lower Abeta accumulation in the cerebral cortex as demonstrated by immunohistochemistry and immunoassay, and a lower level of APP-CTFs. The reduced accumulation of Abeta in APP/FE65 double transgenics, compared with APP mice, could be linked to the low Abeta42 level observed at 4 months of age and to the lower APP-CTFs levels. The present work provides evidence that FE65 plays a role in the regulation of APP processing in an in vivo model.     

6-hydroxydopamine increases the hydroxylation and nitration of phenylalanine in vivo: implication of peroxynitrite formation

In the present study, we investigated the effect of the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) on hydroxyl free radical and peroxynitrite formation in vivo using D-phenylalanine as a novel mechanistic probe. In vivo microdialysis was carried out in the striatum of freely moving male Wistar rats. The microdialysis probes were perfused with artificial cerebrospinal fluid containing 5 mM D-phenylalanine (flow rate 2 microL/min). After obtaining a stable baseline 6-OHDA was delivered into the striatum via reverse microdialysis for 60 min. HPLC measurements of the effluent were performed using photodiode array detection for determination of phenylalanine derived o-tyrosine and m-tyrosine (as hydroxylation markers) as well as of nitrotyrosine and nitrophenylalanine (as nitration markers). The basal levels of the hydroxylation derived products of phenylalanine were approximately 100-fold higher than those of the nitration derived products. 6-OHDA (0.1, 1, 10 mM) significantly increased o- and m-tyrosine up to nine- and 13-fold, respectively, whereas levels of 3-nitrotyrosine and 4-nitrophenylalanine were significantly increased up to 422- and 358-fold, respectively. The results demonstrate that phenylalanine is a sensitive in vivo marker for 6-OHDA-induced hydroxylation and nitration reactions which are clearly concentration dependent. We conclude that peroxynitrite formation is involved in 6-OHDA-induced neurochemical effects.     

A Low Sympathoadrenal Activity is Associated with Body Weight Gain and Development of Central Adiposity in Pima Indian Men

TATARANNI P ANTONIO JAMES B YOUNG, CLIFTON BOGARDUS, ERIC RAVUSSIN. A low sympathoadrenal activity is associated with body weight gain and development of central adiposity in Pima Indian men. To investigate the possible role of impaired sympathetic nervous system and/or adrenal medullary function in the etiology of human obesity, we studied 64 Pima Indian men (28 ± 6 years, 101 ± 25 kg, 34 ± 9% body fat, mean ± SD) in whom sympathoadrenal function was estimated at baseline by measurements of 24-hour urinary norepinephrine (NE) and epinephrine (Epi) excretion rates under weight-maintenance conditions. Body weight, body composition (hydrodensitometry), and body fat distribution (waist-to-thigh circumference ratio, W/T) were measured at baseline and follow-up. Follow-up data were available on 44 subjects who gained on average 8.4 ± 9.5 kg over 3.3 ± 2.1 years. In these subjects, baseline NE excretion rate, adjusted for its determinants (i.e., fat free mass, fat mass, and W/T), correlated negatively with bodyweight gain (r=?0.38; p=0.009). Baseline Epi excretion rate correlated negatively with changes in W/T (r=?0.44; p=0.003). In conclusion, our data show for the first time that a low sympathetic nervous system activity is associated with body weight gain in humans. Also, a low activity of the adrenal medulla is associated with the development of central adiposity.     

Increased Cerebral Glucose-6-Phosphate Dehydrogenase Activity in Alzheimer''s Disease May Reflect Oxidative Stress

The activities of the hexose monophosphate pathway enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were measured at autopsy in control and Alzheimer's disease brains. Enzyme activities did not vary between different areas of brain and were unaltered by age. In Alzheimer's disease, the activities of both enzymes were increased, the glucose-6-phosphate dehydrogenase activity being almost double the activity of normal controls. We propose that this increased enzyme activity is a response to elevated brain peroxide metabolism.     

In vivo characterization of somatodendritic dopamine release in the substantia nigra of 6-hydroxydopamine-lesioned rats

We investigated the effect of an injection of 6-hydroxydopamine (6-OHDA) into the rat medial forebrain bundle (MFB) on the degeneration and the function of the dopaminergic cell bodies in the substantia nigra (SN) 3 and 5 weeks after lesioning. After injection of 6-OHDA into the MFB a complete loss of dopamine content was apparent in the striatum 3 weeks after lesioning. In the SN the amount of tyrosine hydroxylase-immunoreactive dopamine cells decreased gradually, with a near-complete lesion (> 90%) obtained only after 5 weeks, indicating that neurodegeneration of the nigral cells was still ongoing when total dopamine denervation of the striatum had already been achieved. Baseline dialysate and extracellular dopamine levels in the SN, as determined by in vivo microdialysis, were not altered by the lesion. A combination of compensatory changes of the remaining neurones and dopamine originating from the ventral tegmental area may maintain extracellular dopamine at near-normal levels. In both intact and lesioned rats, the somatodendritic release was about 60% tetrodotoxin (TTX) dependent. Possibly two pools contribute to the basal dopamine levels in the SN: a fast sodium channel-dependent portion and a TTX-insensitive one originating from diffusion of dopamine. Amphetamine-evoked dopamine release and release after injection of the selective dopamine reuptake blocker GBR 12909 were attenuated after a near-complete denervation of the SN (5 weeks after lesioning). So, despite a 90% dopamine cell loss in the SN 5 weeks after an MFB lesion, extracellular dopamine levels in the SN are kept at near-normal levels. However, the response to a pharmacological challenge is severely disrupted.     

A stimulatory effect by nerve growth factor on the regrowth of adrenergic nerve fibres in the mouse peripheral tissues after chemical sympathectomy with 6-hydroxydopamine

Summary Systemically administered Nerve Growth Factor (NGF) had a strong stimulating effect on the regeneration of fully developed adrenergic neurons in the peripheral tissues of the mouse after axotomy induced by 6-hydroxydopamine. The NGF stimulation was investigated at 9 and 21 days after the 6-hydroxydopamine injection, and was observed fluorescence histochemically as an increase in number, length, and thickness of the outgrowing adrenergic fibre bundles, in the extent and abundance of the terminal ramifications of the regrowing fibres, and in their fluorescence intensity. This increase in the regrowth of the lesioned adrenergic axons was paralleled by strong and significant increases in the recovery of endogenous noradrenaline in several peripheral tissues. The present findings demonstrate a sensitivity of fully developed adrenergic neurons to NGF during axonal regeneration, and it is suggested that NGF might play a normal physiological role in this process.     

金属硫蛋白-3研究进展

金属硫蛋白－3（MT－3）是近年来发现的一种脑特异性金属硫蛋白。本文综述了其在分布、蛋白结构及基因调控方面的特点;着重介绍了其在中枢神经系统中的功能及结构与功能关系的研究进展;总结了国外对其与老年痴呆症的可能关系的研究。     

Serofendic acid prevents 6-hydroxydopamine-induced nigral neurodegeneration and drug-induced rotational asymmetry in hemi-parkinsonian rats

Serofendic acid was recently identified as a neuroprotective factor from fetal calf serum. This study was designed to evaluate the neuroprotective effects of an intranigral microinjection of serofendic acid based on behavioral, neurochemical and histochemical studies in hemi-parkinsonian rats using 6-hydroxydopamine (6-OHDA). Rats were injected with 6-OHDA in the presence or absence of serofendic acid, or were treated with serofendic acid on the same lateral side, at 12, 24 or 72 h after 6-OHDA lesion. Intranigral injection of 6-OHDA alone induced a massive loss of tyrosine hydroxylase (TH)-immunopositive neurons in the substantia nigra pars compacta (SNpc). Either simultaneous or 12 h post-administration of serofendic acid significantly prevented both dopaminergic neurodegeneration and drug-induced rotational asymmetry. Immunoreactivities for oxidative stress markers, such as 3-nitrotyrosine (3-NT) and 4-hydroxy-2-nonenal (4-HNE), were markedly detected in the SNpc of rats injected with 6-OHDA alone. These immunoreactivities were markedly suppressed by the co-administration of serofendic acid, similar to the results in vehicle-treated control rats. In addition, serofendic acid inhibited 6-OHDA-induced alpha-synuclein expression and glial activation in the SNpc. These results suggest that serofendic acid protects against 6-OHDA-induced SNpc dopaminergic neurodegeneration in a rat model of Parkinson's disease.     

Broad DNA repair responses in neural injury are associated with activation of the IL-6 pathway in cholesterol-fed rabbits

The importance of DNA repair in the pathogenic mechanism of Alzheimer's Disease (AD) is still poorly understood. Here, we report that a broad range of responses by DNA repair proteins plays a critical role in the regulation of inflammatory response in rabbits fed with cholesterol-rich diet, a model system for AD. We found accumulation of oxodG DNA adduct in the brain of rabbits fed with cholesterol-enriched diets compared to control diets, which subsequently induced a broad range of DNA repair protein activities. Also, the hippocampus was identified as the primary site of oxidative DNA damage and elevated OGG1 activity. In addition, a physical interaction between XPB and OGG1 may account for a potential mechanism involving these DNA repair responses. DNA repair proteins also impact activation of various signaling cascades, including Src in response to cholesterol oxidation. Furthermore, OGG1 deficient mice showed no IL-6 activation as seen in wt mice but a drastic increase of TNF-α, a pro-inflammatory cytokine. Thus, OGG1 may be associated with cytokine production induced by high cholesterol levels, impacting neurodegeneration. Together, our studies suggest that critical DNA repair proteins are associated with development of AD, and may serve as potential targets for the treatment of AD.