Peripheral inflammation increases the damage in animal models of nigrostriatal dopaminergic neurodegeneration: possible implication in Parkinson's disease incidence.

Inflammatory processes described in Parkinson's disease (PD) and its animal models appear to be important in the progression of the pathogenesis, or even a triggering factor. Here we review that peripheral inflammation enhances the degeneration of the nigrostriatal dopaminergic system induced by different insults; different peripheral inflammations have been used, such as IL-1ß and the ulcerative colitis model, as well as insults to the dopaminergic system such as 6-hydroxydopamine or lipopolysaccharide. In all cases, an increased loss of dopaminergic neurons was described; inflammation in the substantia nigra increased, displaying a great activation of microglia along with an increase in the production of cytokines such as IL-1ß and TNF-α. Increased permeability or disruption of the BBB, with overexpression of the ICAM-1 adhesion molecule and infiltration of circulating monocytes into the substantia nigra, is also involved, since the depletion of circulating monocytes prevents the effects of peripheral inflammation. Data are reviewed in relation to epidemiological studies of PD.

Inflammatory Animal Model for Parkinson's Disease: The Intranigral Injection of LPS Induced the Inflammatory Process along with the Selective Degeneration of Nigrostriatal Dopaminergic Neurons.

We have developed an animal model of degeneration of the nigrostriatal dopaminergic neurons, the neuronal system involved in Parkinson's disease (PD). The implication of neuroinflammation on this disease was originally established in 1988, when the presence of activated microglia in the substantia nigra (SN) of parkinsonians was reported by McGeer et al. Neuroinflammation could be involved in the progression of the disease or even has more direct implications. We injected 2 µg of the potent proinflammatory compound lipopolysaccharide (LPS) in different areas of the CNS, finding that SN displayed the highest inflammatory response and that dopaminergic (body) neurons showed a special and specific sensitivity to this process with the induction of selective dopaminergic degeneration. Neurodegeneration is induced by inflammation since it is prevented by anti-inflammatory compounds. The special sensitivity of dopaminergic neurons seems to be related to the endogenous dopaminergic content, since it is overcome by dopamine depletion. Compounds that activate microglia or induce inflammation have similar effects to LPS. This model suggest that inflammation is an important component of the degeneration of the nigrostriatal dopaminergic system, probably also in PD. Anti-inflammatory treatments could be useful to prevent or slow down the rate of dopaminergic degeneration in this disease.

Stress increases vulnerability to inflammation in the rat prefrontal cortex.

Inflammation could be involved in some neurodegenerative disorders that accompany signs of inflammation. However, because sensitivity to inflammation is not equal in all brain structures, a direct relationship is not clear. Our aim was to test whether some physiological circumstances, such as stress, could enhance susceptibility to inflammation in the prefrontal cortex (PFC), which shows a relative resistance to inflammation. PFC is important in many brain functions and is a target for some neurodegenerative diseases. We induced an inflammatory process by a single intracortical injection of 2 microg of lipopolysaccharide (LPS), a potent proinflammogen, in nonstressed and stressed rats. We evaluated the effect of our treatment on inflammatory markers, neuronal populations, BDNF expression, and behavior of several mitogen-activated protein (MAP) kinases and the transcription factor cAMP response element-binding protein. Stress strengthens the changes induced by LPS injection: microglial activation and proliferation with an increase in the levels of the proinflammatory cytokine tumor necrosis factor-alpha; loss of cells such as astroglia, seen as loss of glial fibrillary acidic protein immunoreactivity, and neurons, studied by neuronal-specific nuclear protein immunohistochemistry and GAD67 and NMDA receptor 1A mRNAs expression by in situ hybridization. A significant increase in the BDNF mRNA expression and modifications in the levels of MAP kinase phosphorylation were also found. In addition, we observed a protective effect from RU486 [mifepristone (11beta-[p-(dimethylamino)phenyl]-17beta-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one)], a potent inhibitor of the glucocorticoid receptor activation. All of these data show a synergistic effect between inflammation and stress, which could explain the relationship described between stress and some neurodegenerative pathologies.

Blood-brain barrier disruption highly induces aquaporin-4 mRNA and protein in perivascular and parenchymal astrocytes: protective effect by estradiol treatment in ovariectomized animals.

Strong evidence involves aquaporin-4 (AQP4) in the physiopathology of brain edema. Two major points remain unsolved: (1) the capacity of perivascular glial cells to regulate AQP4 in response to disruption of the blood-brain barrier (BBB); and (2) the potential beneficial role of AQP4 in the clearance of brain edema. We used intraparenchymal injection of lipopolysaccharide (LPS) as an efficient model to induce BBB disruption. This was monitored by IgG extravasation and AQP4 was studied at the mRNA and protein level. The first signs of BBB disruption coincided with strong induction of AQP4 mRNA in perivascular glial cells. At the early phase, estradiol treatment highly prevented the LPS-induced disruption of the BBB and the induction of AQP4. Efficient clearance of vasogenic edema is supposed to occur once BBB is restored. This phase coincided with high induction of AQP4 mRNA in parenchymal reactive astrocytes and perivascular glial processes. High levels of AQP4 mRNA may be beneficial under these conditions. Our data may clarify why estradiol treatment reduces mortality in conditions typically associated with edema formation, like stroke.

Inflammatory process as a determinant factor for the degeneration of substantia nigra dopaminergic neurons.

The specific degeneration of dopaminergic neurons in the substantia nigra (SN) is a pathological hallmark of Parkinson's disease (PD). Although the cause of chronic nigral cell death in PD and its underlying mechanisms remain elusive, substantial involvement of inflammatory events has been postulated since inflammatory features have been described in parkinsonians CNS tissue. We have developed an animal model of dopaminergic neurons degeneration by the single intranigral injection of lipopolysaccharide (LPS), an inflammatory compound. This single injection produced the induction of inflammatory process with the activation of microglia along with the specific degeneration of dopaminergic neurons in the SN without affecting neither other neurotransmitter systems nor other structures of the CNS. Dexamethasone, a potent anti-inflammatory drug preventing many of the features characterizing pro-inflammatory glial activation, prevented the loss of dopaminergic cells. We also discuss other inductors of inflammatory process in relationship to the dopaminergic degeneration in the SN.

The degenerative effect of a single intranigral injection of LPS on the dopaminergic system is prevented by dexamethasone, and not mimicked by rh-TNF-alpha, IL-1beta and IFN-gamma.

It is becoming widely accepted that the inflammatory response is involved in neurodegenerative disease. In this context, we have developed an animal model of dopaminergic system degeneration by the intranigral injection of lipopolysaccharide (LPS), a potent inductor of inflammation. To address the importance of the inflammatory response in the LPS-induced degeneration of nigral dopaminergic neurones, we carried out two different kinds of studies: (i) the possible protective effect of an anti-inflammatory compound, and (ii) the effect of the intranigral injection of inflammatory cytokines (TNF-alpha, IL-1beta and IFN-gamma) on dopaminergic neurones viability. Present results show that dexamethasone, a potent anti-inflammatory drug that interferes with many of the features characterizing pro-inflammatory glial activation, prevented the loss of catecholamine content, Tyrosine hydroxylase (TH) activity and TH immunostaining induced by LPS-injection and also the bulk activation of microglia/macrophages. Surprisingly, injection of the pro-inflammatory cytokines failed to reproduce the LPS effect. Taken together, our results suggest that inflammatory response is implicated in LPS-induced neurodegeneration. This damage may be due, at least in part, to a cascade of events independent of that described for TNF-alpha/IL-1 beta/IFN-gamma.

The single intranigral injection of LPS as a new model for studying the selective effects of inflammatory reactions on dopaminergic system.

We have injected lipopolysaccharide (LPS) into the nigrostriatal pathway of rats in order to address the role of inflammation in Parkinson's disease (PD). LPS induced a strong macrophage/microglial reaction in Substantia nigra (SN), with a characteristic clustering of macrophage cells around blood-vessels. The SN was far more sensitive than the striatum to the inflammatory stimulus. Moreover, only the dopaminergic neurons of the SN were affected, with no detectable damage to either the GABAergic or the serotoninergic neurons. The damage to the DA neurons in the SN was permanent, as observed 1 year postinjection. Unlike the direct death of dopaminergic neurons caused by agents as MPP(+) or 6-OHDA, LPS seems to cause indirect death due to inflammatory reaction. Therefore, we suggest that the injection of a single dose of LPS within the SN is an interesting model for studying the selective effects of inflammatory reaction on dopaminergic system and also potentially useful for studying PD.

Lipopolysaccharide intranigral injection induces inflammatory reaction and damage in nigrostriatal dopaminergic system.

The pathogenesis of Parkinson's disease is still poorly understood. To address the hypothesis that immune-mediated events, such as microglial activation, may be involved in the dopaminergic neurodegeneration, we have studied the effect that intranigral injection of the immunostimulant lipopolysaccharide has on monoaminergic neurotransmitters in rats. Activation of microglial cells, visualized by immunohistochemistry with a specific monoclonal antibody, was already obvious 2 days after injection. In relation to the biochemical parameters studied, we found a significant decrease of dopamine levels in both the substantia nigra and striatum up to at least 21 days after intranigral injection of lipopolysaccharide. This result was supported by the decrease in tyrosine hydroxylase activity and the loss of tyrosine hydroxylase-positive neuronal bodies, shown by immunohistochemistry. These alterations of the dopaminergic system did not reverse during the interval studied (21 days); conversely, the serotoninergic system suffered only transient damage. In addition, we found that the neurotoxic effect of lipopolysaccharide was not mediated by nitric oxide. Based on our results we suggest that the nigrostriatal dopaminergic system is susceptible to damage by inflammatory events and that these may be implicated in neurodegeneration processes such as Parkinson's disease.

Low selenium diet increases the dopamine turnover in prefrontal cortex of the rat.

It has been proposed that interaction of catecholamines and indoleamines with free radicals may result in the formation of endogenous neurotoxins. In order to better understand the mechanisms involved in neurodegenerative disorders showing evidence of oxidative stress, we have studied the basal concentrations and the turnover rates of dopamine, noradrenaline, serotonin and their metabolites in the prefrontal cortex of rats that were fed on control or low selenium diets. Nutritional deficit of selenium decreases the brain antioxidant protection in experimental conditions by the decrease in glutathione peroxidase activity. The dopamine and serotonin turnover increased and noradrenaline and 5-hydroxy-3-indoleacetic acid turnover decreased compared to experimental control animals. The increase of dopamine turnover in experimental rats was accompanied by an increase in tyrosine hydroxylase activity. These results suggest that the decrease of brain protection against oxidative damage could induce brain damage by disturbing the turnover rate of some monoamines.

The effect of experimental ischaemia and excitatory amino acid agonists on the GABA and serotonin immunoreactivities in the rabbit retina.

The aim of the described experiments was to use immunohistochemistry to visualize the release of GABA from specific retinal amacrine cells following ischaemia and to establish the involvement of defined glutamatergic receptors. In initial experiments, rabbit retinas were exposed in vitro to excitatory amino acid agonists alone or in combination with a putative antagonist, or in physiological solution lacking oxygen and glucose, or in solution containing potassium cyanide for 45 min at 37 degrees C. The nature of the GABA immunoreactivity was then examined by immunohistochemistry. In other in vitro experiments, retinas were first allowed to accumulate exogenous serotonin before exposing the tissues to the combinations as described. These tissues were then processed immunohistochemically for the localization of serotonin. In yet other experiments, the intraocular pressure of a rabbit's eye was raised to about 110 mmHg for 60 min and a reperfusion time of 45 min allowed before dissecting the retina and processing for the localization of GABA immunoreactivity. The other eye served as a control. Of the excitatory amino acid agonists tested, only N-methyl-D-aspartate, kainate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid caused a change in the GABA immunoreactivity. The N-methyl-D-aspartate effect was specifically antagonized by dizocilpine maleate, dextromethorphan and memantine, and was characterized by a reduction in the number of GABA-immunoreactive perikarya. The GABA "staining" in the inner plexiform layer also appeared as four clear bands. The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid- and kainate-induced effects were both antagonized by 6-cyano-2,3-dihydroxy-7-nitroquinoxaline-2,3-dione and partially by kynurenic acid at the concentrations used. Here, the amount of GABA-positive perikarya was greatly reduced and three immunoreactive bands appeared in the inner plexiform layer. However, for low concentrations of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid four GABA-immunoreactive bands could be identified in the inner plexiform layer. The normal GABA immunoreactivity of the inner plexiform layer also appeared to be in defined bands in retinas which received an ischaemic insult either by reducing the availability of glucose and oxygen, exposing the tissue to potassium cyanide or raising the intraocular pressure of an eye. In these cases the number of GABA-positive perikarya was also reduced. Only alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and kainate of the excitatory amino acid agonists tested caused a release of serotonin and this process was antagonized by 6-cyano-2,3-dihydroxy-7-nitroquinoxaline-2,3-dione and partially by kynurenic acid.(ABSTRACT TRUNCATED AT 400 WORDS)

Versatilidad de la cardioplejía anterógrada/retrógrada en cirugía cardiaca / Versality of antegrade and retrograde cardioplegia in heart surgery

Desde marzo de 1990 hasta marzo de 1992, se operaron 80 pacientes de corazón por diversas patologías. Se usó como medida de protección miocárdica la combinación de las vías anterógrada por la raíz aórtica y la retrógrada por el seno venoso coronario (SVC) para el paso de la solución cardiopléjica. La cánula de retroplejía fue introducida al SVC de dos maneras: en 67 pacientes se canuló vía transatrial (método ciego) con cánula única para el retorno venoso; a los 13 restantes se les canuló bajo visión directa por atriotomía derecha con canulación bicava para el retorno venoso total. Los procedimientos quirúrgicos realizados fueron variados y prolongados en la mayoría y sólo se usó cardioplejía cristaloide fría a 4 grados centígrados con potasio, excepto en un paciente con daño ventricular severo en el cual, por ser cirugía de rescate, se administró cardioplejía sanguínea caliente. No se presentaron complicaciones en lo tocante a la canulación del SVC (bloqueo A-V, ruptura del seno venoso), no hubo dificultades técnicas para canular el SVC ni para el paso de la solución cardiopléjica que fue monitorizado en forma continua manteniendo una presión en el SVC por debajo de los 40 mm Hg. La mortalidad hospitalaria (30 días de postoperatorio) fue de 3.75 por ciento (3 casos): por sepsis en 2 casos y uno por accidente vascular cerebral. La mayoría de los pacientes no recibieron inotrópicos para sostén ventricular en el postoperatorio inmediato y sólo algunos recibieron dabutamina o dopamina para mantener la función renal. Concluimos, con base en este estudio, que la cardioplejía combinada anterógrada/retrógrada puede ser aplicada en forma rutinaria en la mayoría de los pacientes que son sometidos a cirugía de corazón abierto

Ageing and monoamine turnover in the lateral geniculate nucleus and visual cortex of the rat.

The effects of ageing on the turnover of dopamine, noradrenaline and serotonin in the lateral geniculate nucleus and the visual cortex were evaluated, using high performance liquid chromatography (HPLC) with electrochemical detection. Compared to adult animals, aged rats showed more changes in the visual cortex than in the lateral geniculate nucleus, with dopamine turnover decreased in both structures and noradrenaline turnover unaltered. Changes in serotonin turnover were witnessed only in the visual cortex. A decrease in the monoamine oxidase-A to -B ratio was also observed with increased age for both the lateral geniculate nucleus and visual cortex.

NADPH diaphorase localization and nitric oxide synthetase activity in the retina and anterior uvea of the rabbit eye.

The distribution of the enzyme nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase was examined histochemically in the retina, iris, ciliary processes, cornea and conjunctiva of the rabbit eye. The epithelial cells of the ciliary process, iris, conjunctiva and, to a lesser extent, the cornea all showed intense staining. In the retina, staining for NADPH diaphorase was intense in the inner segments of the photoreceptors and a sparsely distributed population of amacrine cells. In addition, another population of amacrine cells, some presumed ganglion cells as well as a number of horizontal cells, stained less intensely for the enzyme. The retina, ciliary processes and, as a comparison, the cerebellum of the rabbit all contain nitric oxide synthetase (NOS) activity, as each tissue can metabolize citrulline from arginine. This process is Ca2+ dependent and is reduced by the NOS inhibitor, NG-monomethyl-L-arginine. The presence of NOS activity in the ciliary processes and the localization of NADPH diaphorase in the ciliary epithelial cells are of significance as they suggest that the ciliary epithelial cells may contain NOS which would imply a role for nitric oxide in aqueous humour production.

Effects of a short period of vitamin E-deficient diet in the turnover of different neurotransmitters in substantia nigra and striatum of the rat.

Measurement of turnover of dopamine, noradrenaline and serotonin and their metabolites was assessed in striatum and substantia nigra of adult female rats that were fed control or vitamin E-deficient diets over 15 days. The levels and turnover of dopamine increased and the levels of serotonin decreased in both structures whereas serotonin turnover decreased only in striatum. No change was found in the turnover rate of noradrenaline between control and experimental animals. However, the most striking result was the increase of dopamine turnover found in substantia nigra. This dopamine increase was accompanied by an increase in 3-methoxytyramine turnover which seems to indicate an increase in dopamine release after vitamin E deficiency. The present study indicates that the nigrostriatal dopamine neurons are susceptible to the deficiency of vitamin E. Moreover, these data suggest that substantia nigra may be more susceptible to damage from vitamin E deficiency than striatum.

Changes in neurotransmitter levels associated with the deficiency of some essential amino acids in the diet.

The contents of dopamine (DA) and serotonin (5-HT) and their metabolites were measured in rat substantia nigra and corpus striatum following dietary changes, including restriction of protein content (low-protein diet; LPD) and the contents of several large neutral amino acids (isoleucine, leucine, methionine, phenylalanine, tryptophan and valine) for 25 d. The LPD produced an increase in the concentration of tyrosine (TYR) in the two regions of the brain studied. This effect was also observed with all amino acid deficiencies studied except for valine in the substantia nigra, tryptophan in the striatum and phenylalanine in both regions. Likewise, the concentration of 5-hydroxyindoleacetic acid (5-HIAA), the main metabolite of 5-HT, increased in the substantia nigra but not in the striatum after LPD, as well as with all the amino acid deficiencies studied, with the exception of tryptophan deficiency. In this case there was a dramatic effect on all components of the serotoninergic system, with decreases in the concentration of tryptophan (TRP; precursor), 5-HT and 5-HIAA. This behaviour clearly shows an interrelationship between precursor (TRP) availability and 5-HT synthesis and metabolism. With valine deficiency, dopaminergic and serotoninergic systems demonstrated opposite effects in the substantia nigra and the corpus striatum, and the behaviour of the two monoamines was also opposite within each structure. The significance of these changes is discussed.

The influence of age on neurotransmitter turnover in the rat's superior colliculus.

Measurements of the turnover of dopamine, noradrenaline and serotonin and their metabolites have been performed in the superior colliculus of adult and aged rats. The turnover of dopamine, noradrenaline and their metabolites after pargyline treatment was significantly lower in aged rats than in adults. On the contrary, the synthesis rate of serotonin (measured by accumulation of 5-hydroxytryptophan after decarboxylase blockade) and the turnover rate of serotonin (after pargyline treatment) did not change during aging. These findings suggest that aging has a different effect on catecholamines and serotonin turnover in the superior colliculus of the aged rats.

Effects of neonatal bilateral eye enucleation on postnatal development of the monoamines in posterior thalamus of the rat.

Levels of dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (serotonin, 5-HT) and their metabolites, and the activities of tyrosine hydroxylase (TH), tryptophan hydroxylase (TPH) and monoamine oxidase A and B (MAO-A and MAO-B) have been determined in the rat posterior thalamus after enucleation during postnatal development. DA and 5-HT turnover rate have been measured as 3,4-dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) accumulation rates after central decarboxylase inhibition by 3-hydroxybenzylhydrazine (NSD-1015). The major changes were an increase in noradrenergic and serotoninergic metabolism in enucleated animals compared with control animals. A decrease of the MAO-A to MAO-B ratio during postnatal development was found.

Effects of enucleation on postnatal development of catecholamines and serotonin metabolism in the superior colliculus of the rat.

We have measured the level of catecholamines and serotonin and their principal metabolites, and the activities of tyrosine hydroxylase, tryptophan hydroxylase and monoamine oxidase-A and -B in the rat superior colliculus during postnatal development after bilateral removal of the eyes. The visual deprivation has different effects on the catecholamines and serotonin metabolism. The major changes in both amines were at day 15. Tyrosine hydroxylase and tryptophan hydroxylase activities increased during postnatal development but this increase was higher in enucleated compared with controls. An increase of the MAO-B to MAO-A ratio during postnatal development was found. The significance of these changes has been discussed.

Neonatal enucleation alters catecholamine and serotonin metabolism in the lateral geniculate and visual cortex in developing rats.

Levels of dopamine, noradrenaline and serotonin and of their metabolites along with tryptophan hydroxylase, tyrosine hydroxylase and monoamine oxidase A and B activities have been determined in lateral geniculate (LG) and visual cortex (VC) after enucleation during postnatal development. Lateral geniculate showed more changes in serotonin metabolism than visual cortex, whereas the most significant change in visual cortex was in noradrenaline metabolism. Both monoamines underwent a general decrease at day 15. An increase of the MAO-B to MAO-A ratio during postnatal development was found.