L-citrulline immunostaining identifies nitric oxide production sites within neurons

Localization of nitric oxide-producing hemocytes in Aedes and Culex mosquitoes infected with bacteria

Mosquitoes are significant vectors of various pathogens. Unlike vertebrates, insects rely solely on innate immunity. Hemocytes play a crucial role in the cellular part of the innate immune system. The gaseous radical nitric oxide (NO) produced by hemocytes acts against pathogens and also functions as a versatile transmitter in both the immune and nervous systems, utilizing cyclic guanosine monophosphate (cGMP) as a second messenger. This study conducted a parallel comparison of NO synthase (NOS) expression and NO production in hemocytes during Escherichia coli K12 infection in four vector species: Aedes aegypti, Aedes albopictus, Culex pipiens molestus, and Culex pipiens quinquefasciatus. Increased NOS expression by NADPH diaphorase (NADPHd) staining and NO production by immunofluorescence against the by-product L-citrulline were observed in infected mosquito hemocytes distributed throughout the abdomens. NADPHd activity and citrulline labeling were particularly found in periostial hemocytes near the heart, but also on the ventral nerve chord (VNC). Pericardial cells of Ae. aegypti and Cx. p. molestus showed increased citrulline immunofluorescence, suggesting their involvement in the immune response. Oenocytes displayed strong NADPHd and citrulline labeling independent of infection status. This comparative study, consistent with findings in other species, suggests a widespread phenomenon of NO's role in hemocyte responses during E. coli infection. Found differences within and between genera highlight the importance of species-specific investigations.

Medium-Chain Fatty Acids Rescue Motor Function and Neuromuscular Junction Degeneration in a Drosophila Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterised by progressive degeneration of the motor neurones. An expanded GGGGCC (G4C2) hexanucleotide repeat in C9orf72 is the most common genetic cause of ALS and frontotemporal dementia (FTD); therefore, the resulting disease is known as C9ALS/FTD. Here, we employ a Drosophila melanogaster model of C9ALS/FTD (C9 model) to investigate a role for specific medium-chain fatty acids (MCFAs) in reversing pathogenic outcomes. Drosophila larvae overexpressing the ALS-associated dipeptide repeats (DPRs) in the nervous system exhibit reduced motor function and neuromuscular junction (NMJ) defects. We show that two MCFAs, nonanoic acid (NA) and 4-methyloctanoic acid (4-MOA), can ameliorate impaired motor function in C9 larvae and improve NMJ degeneration, although their mechanisms of action are not identical. NA modified postsynaptic glutamate receptor density, whereas 4-MOA restored defects in the presynaptic vesicular release. We also demonstrate the effects of NA and 4-MOA on metabolism in C9 larvae and implicate various metabolic pathways as dysregulated in our ALS model. Our findings pave the way to identifying novel therapeutic targets and potential treatments for ALS.

NO Synthesis in Immune-Challenged Locust Hemocytes and Potential Signaling to the CNS

Simple Summary

Insects, in the same way as vertebrates, are exposed to a broad variety of pathogens but lack their adaptive immune system. Relying on their innate immune system, they respond to pathogens by phagocytosis, melanization, and the synthesis of antimicrobial or cytotoxic compounds. In this study, we evaluated the production of the cytotoxic gaseous radical nitric oxide (NO) in hemocytes, the immune cells of the model insect Locusta migratoria in response to various immune stimuli. Both sessile and circulating hemocytes responded to gram-negative Escherichia coli and gram-positive Streptococcus suis injection with a strong increase in NO production. In contrast, the gram-positive bacterium Staphylococcus aureus elicited only a minor response. In addition, bacteria were encapsulated by hemocytes. Since NO is an important neurotransmitter, NO-producing hemocytes were tested on the locust central nervous system (CNS) in an embryo culture model. CNS neurons responded with a distinct increase in production of the second messenger, cGMP. This is indicative of the influence of the immune response on the CNS. Our findings show that NO production in hemocytes and capsule formation need complex stimuli and contribute to the understanding of neuroimmune interactions in insects.

Abstract

Similar to vertebrates, insects are exposed to a broad variety of pathogens. The innate insect immune system provides several response mechanisms such as phagocytosis, melanization, and the synthesis of antimicrobial or cytotoxic compounds. The cytotoxic nitric oxide (NO), which is also a neurotransmitter, is involved in the response to bacterial infections in various insects but has rarely been shown to be actually produced in hemocytes. We quantified the NO production in hemocytes of Locusta migratoria challenged with diverse immune stimuli by immunolabeling the by-product of NO synthesis, citrulline. Whereas in untreated adult locusts less than 5% of circulating hemocytes were citrulline-positive, the proportion rose to over 40% after 24 hours post injection of heat-inactivated bacteria. Hemocytes surrounded and melanized bacteria in locust nymphs by forming capsules. Such sessile hemocytes also produced NO. As in other insect species, activated hemocytes were found dorsally, close to the heart. In addition, we frequently observed citrulline-positive hemocytes and capsules near the ventral nerve cord. Neurites in the CNS of sterile locust embryos responded with elevation of the second messenger cGMP after contact with purified adult NO-producing hemocytes as revealed by immunofluorescence. We suggest that hemocytes can mediate a response in the CNS of an infected animal via the NO/cGMP signaling pathway.

In human brain ornithine transcarbamylase (OTC) immunoreactivity is strongly expressed in a small number of nitrergic neurons

There is recent evidence for ornithine transcarbamylase (OTC) expression in adult human brain. We decided to immunocytochemically map OTC throughout brain, and to further characterize OTC-immunopositive neurons. By using double immunolabeling technique for OTC and neuronal nitric oxide synthase (nNOS) OTC protein expression was revealed in a small subset of nitrergic (nNOS) neurons. Since citrulline (the reaction product of OTC) enhances the bioavailability of L-arginine, the substrate of nNOS, it is conceivable that OTC activity supports NO production in nitrergic neurons.

The Effects of Blast Exposure on Protein Deimination in the Brain

Oxidative stress and calcium excitotoxicity are hallmarks of traumatic brain injury (TBI). While these early disruptions may be corrected over a relatively short period of time, long-lasting consequences of TBI including impaired cognition and mood imbalances can persist for years, even in the absence of any evidence of overt injury based on neuroimaging. This investigation examined the possibility that disordered protein deimination occurs as a result of TBI and may thus contribute to the long-term pathologies of TBI. Protein deimination is a calcium-activated, posttranslational modification implicated in the autoimmune diseases rheumatoid arthritis and multiple sclerosis, where aberrant deimination creates antigenic epitopes that elicit an autoimmune attack. The present study utilized proteomic analyses to show that blast TBI alters the deimination status of proteins in the porcine cerebral cortex. The affected proteins represent a small subset of the entire brain proteome and include glial fibrillary acidic protein and vimentin, proteins reported to be involved in autoimmune-based pathologies. The data also indicate that blast injury is associated with an increase in immunoglobulins in the brain, possibly representing autoantibodies directed against novel protein epitopes. These findings indicate that aberrant protein deimination is a biomarker for blast TBI and may therefore underlie chronic neuropathologies of head injury.

Protein Citrullination: A Proposed Mechanism for Pathology in Traumatic Brain Injury

Protein citrullination is a calcium-driven post-translational modification proposed to play a causative role in the neurodegenerative disorders of Alzheimer’s disease, multiple sclerosis (MS), and prion disease. Citrullination can result in the formation of antigenic epitopes that underlie pathogenic autoimmune responses. This phenomenon, which is best understood in rheumatoid arthritis, may play a role in the chronic dysfunction following traumatic brain injury (TBI). Despite substantial evidence of aberrations in calcium signaling following TBI, there is little understanding of how TBI alters citrullination in the brain. The present investigation addressed this gap by examining the effects of TBI on the distribution of protein citrullination and on the specific cell types involved. Immunofluorescence revealed that controlled cortical impact in rats profoundly up-­regulated protein citrullination in the cerebral cortex, external capsule, and hippocampus. This response was exclusively seen in astrocytes; no such effects were observed on the status of protein citrullination in neurons, oligodendrocytes or microglia. Further, proteomic analyses demonstrated that the effects of TBI on citrullination were confined to a relatively small subset of neural proteins. Proteins most notably affected were those also reported to be citrullinated in other disorders, including prion disease and MS. In vivo findings were extended in an in vitro model of simulated TBI employing normal human astrocytes. Pharmacologically induced calcium excitotoxicity was shown to activate the citrullination and breakdown of glial fibrillary acidic protein, producing a novel candidate TBI biomarker and potential target for autoimmune recognition. In summary, these findings demonstrate that the effects of TBI on protein citrullination are selective with respect to brain region, cell type, and proteins modified, and may contribute to a role for autoimmune dysfunction in chronic pathology following TBI.

Topographical distribution and morphology of NADPH-diaphorase-stained neurons in the human claustrum

We studied the topographical distribution and morphological characteristics of NADPH-diaphorase-positive neurons and fibers in the human claustrum. These neurons were seen to be heterogeneously distributed throughout the claustrum. Taking into account the size and shape of stained perikarya as well as dendritic and axonal characteristics, Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd)-positive neurons were categorized by diameter into three types: large, medium and small. Large neurons ranged from 25 to 35 μm in diameter and typically displayed elliptical or multipolar cell bodies. Medium neurons ranged from 20 to 25 μm in diameter and displayed multipolar, bipolar and irregular cell bodies. Small neurons ranged from 14 to 20 μm in diameter and most often displayed oval or elliptical cell bodies. Based on dendritic characteristics, these neurons were divided into spiny and aspiny subtypes. Our findings reveal two populations of NADPHd-positive neurons in the human claustrum-one comprised of large and medium cells consistent with a projection neuron phenotype, the other represented by small cells resembling the interneuron phenotype as defined by previous Golgi impregnation studies.

Homology of insect corpora allata and vertebrate adenohypophysis?

Animal species of various phyla possess neuroendocrine glands whose hormonal products regulate developmental and physiological mechanisms and directly impact behavior. Two examples, the corpora allata of insects and the vertebrate adenohypophysis have previously been regarded as analogous tissues that evolved independently from diffuse epidermal nerve nets of early metazoans. More recent developmental and functional studies accumulated evidence suggesting that the bilaterian nervous systems including its modern parts (e.g. pallium or cortex and mushroom bodies) and its neuroendocrine appendages (that are considered to be more ancient structures) possess a single evolutionary origin. The corpora allata of insects and the vertebrate adenohypophysis share a number of characteristics in respect of morphology, control of hormone release by RFamides, metabolites produced by closely related cytochrome P450 enzymes and gene expression during embryonic development. This review incorporates latest findings into an extensive description of similarities between insect corpora allata and vertebrate adenohypophysis that should encourage further studies about the onto- and phylogenetic origin of these neuroendocrine glands.

NO-dependent protective effect of VEGF against excitotoxicity on layer VI of the developing cerebral cortex

In industrialized countries, cerebral palsy affects 2.5‰ of preterm and term infants. At a neurochemical level, the massive release of glutamate constitutes a major process leading to excitotoxicity and neonatal brain lesions. Previous studies, conducted in the laboratory, revealed that, in (δ/δ)VEGF(A) transgenic mice, glutamate-induced brain lesions are exacerbated suggesting that VEGF(A) could play a protective action against excitotoxicity. Using a model of cultured cortical brain slices, the aim of the study was to characterize the central effects of VEGF against glutamate-induced excitotoxicity in neonates. Exposure of brain slices to glutamate induced a strong increase of necrotic cell death in the deep cortical layer VI and a decrease of apoptotic death in superficial layers II-IV. When administered alone, a 6-h treatment with VEGF(A) had no effect on both apoptotic and necrotic deaths. In contrast, VEGF(A) abolished the glutamate-induced necrosis observed in layer VI. While MEK and PI3-K inhibitors had no effect on the protective action of VEGF(A), L-NAME, a pan inhibitor of NOS, abrogated the effect of VEGF(A) and exacerbated the excitotoxic action of glutamate. Calcimetry experiments performed on brain slices revealed that VEGF(A) reduced the massive calcium influx induced by glutamate in layer VI and this effect was blocked by L-NAME. Neuroprotective effect of VEGF(A) was also blocked by LNIO and NPLA, two inhibitors of constitutive NOS, while AGH, an iNOS inhibitor, had no effect. Nitrite measurements, electron paramagnetic resonance spectroscopy and immunohistochemistry indicated that glutamate was a potent inducer of NO production via activation of nNOS in the cortical layer VI. In vivo administration of nNOS siRNA promoted excitotoxicity and mimicked the effects of L-NAME, LNIO and NPLA. A short-term glutamate treatment increased nNOS Ser1412 phosphorylation, while a long-term exposure inhibited nNOS/NR2B protein-protein interactions. Altogether, these findings indicate that, in deep cortical layers of mice neonates, glutamate stimulates nNOS activity. Contrasting with mature brain, NO production induced by high concentrations of glutamate is neuroprotective and is required for the anti-necrotic effect of VEGF(A).

Neurochemical architecture of the central complex related to its function in the control of grasshopper acoustic communication

The central complex selects and coordinates the species- and situation-specific song production in acoustically communicating grasshoppers. Control of sound production is mediated by several neurotransmitters and modulators, their receptors and intracellular signaling pathways. It has previously been shown that muscarinic cholinergic excitation in the central complex promotes sound production whereas both GABA and nitric oxide/cyclic GMP signaling suppress its performance. The present immunocytochemical and pharmacological study investigates the question whether GABA and nitric oxide mediate inhibition of sound production independently. Muscarinic ACh receptors are expressed by columnar output neurons of the central complex that innervate the lower division of the central body and terminate in the lateral accessory lobes. GABAergic tangential neurons that innervate the lower division of the central body arborize in close proximity of columnar neurons and thus may directly inhibit these central complex output neurons. A subset of these GABAergic tangential neurons accumulates cyclic GMP following the release of nitric oxide from neurites in the upper division of the central body. While sound production stimulated by muscarine injection into the central complex is suppressed by co-application of sodium nitroprusside, picrotoxin-stimulated singing was not affected by co-application of this nitric oxide donor, indicating that nitric oxide mediated inhibition requires functional GABA signaling. Hence, grasshopper sound production is controlled by processing of information in the lower division of the central body which is subject to modulation by nitric oxide released from neurons in the upper division.

Effect of an hyperbaric nitrogen narcotic ambience on arginine and citrulline levels, the precursor and co-product of nitric oxide, in rat striatum

Previous studies performed in the laboratory have shown that nitrogen narcosis induces a decrease in striatal glutamate and dopamine levels. Although we stimulated the N-methyl-D-aspartate (NMDA) receptor, an important glutamate receptor required for motor and locomotor activity managed by the striatum, and demonstrated that the receptor was effective when exposed to nitrogen at 3MPa, it was not possible to return the striatal glutamate level to its base values. We conclude that it was the striatopetal neurons of the glutamatergic pathways that were mainly affected in this hyperbaric syndrome, without understanding the principal reasons. Hence we sought to establish what happens in the vicinity of the plasma membrane, downstream the NMDA-Receptor, and we used the hypothesis that there could be neuronal nitric oxide synthase (nNOS) disturbances. A microdialysis study was performed in rat striatum in order to analyse levels of citrulline, the NO co-product, and arginine, the NO precursor. Those both NO metabolites were detectable with an HPLC coupled to a fluorimetric detector. Exposure to pressurized nitrogen induced a reduction in citrulline (-18.9%) and arginine (-10.4%) levels. Under the control normobaric conditions, the striatal NMDA infusion enhanced the citrulline level (+85.6%), whereas under 3 MPa of nitrogen, the same NMDA infusion did not change the citrulline level which remains equivalent to that of the baseline. The level of arginine increased (+45.7%) under normobaric conditions but a decrease occurred in pressurized nitrogen (-51.6%). Retrodialysis with Saclofen and KCl in the prefrontal cortex under normobaric conditions led to an increase in striatal levels of citrulline (+30.5%) and a decrease in arginine levels (-67.4%). There was no significant difference when nitrogen at 3MPa was added. To conclude, the synthesis of citrulline/NO is reduced in nitrogen narcosis while it seems possible to activate it artificially by infusion. We have suggested that the low glutamate levels recorded in nitrogen narcosis induced these dopamine and NO reductions in the striatum.

Nitric oxide/cGMP signaling in the corpora allata of female grasshoppers

The corpora allata (CA) of various insects express enzymes with fixation resistant NADPHdiaphorase activity. In female grasshoppers, juvenile hormone (JH) released from the CA is necessary to establish reproductive readiness, including sound production. Previous studies demonstrated that female sound production is also promoted by systemic inhibition of nitric oxide (NO) formation. In addition, allatotropin and allatostatin expressing central brain neurons were located in close vicinity of NO generating cells. It was therefore speculated that NO signaling may contribute to the control of juvenile hormone release from the CA. This study demonstrates the presence of NO/cGMP signaling in the CA of female Chorthippus biguttulus. CA parenchymal cells exhibit NADPHdiaphorase activity, express anti NOS immunoreactivity and accumulate citrulline, which is generated as a byproduct of NO generation. Varicose terminals from brain neurons in the dorsal pars intercerebralis and pars lateralis that accumulate cGMP upon stimulation with NO donors serve as intrinsic targets of NO in the CA. Both accumulation of citrulline and cyclic GMP were inhibited by the NOS inhibitor aminoguanidine, suggesting that NO in CA is produced by NOS. These results suggest that NO is a retrograde transmitter that provides feedback to projection neurons controlling JH production. Combined immunostainings and backfill experiments detected CA cells with processes extending into the CC and the protocerebrum that expressed immunoreactivity against the pan-neural marker anti-HRP. Allatostatin and allatotropin immunopositive brain neurons do not express NOS but subpopulations accumulate cGMP upon NO-formation. Direct innervation of CA by these peptidergic neurons was not observed.

Nitric oxide as a regulator of neuronal motility and regeneration in the locust embryo

Nitric oxide (NO) is known as a gaseous messenger in the nervous system. It plays a role in synaptic plasticity, but also in development and regeneration of nervous systems. We have studied the function of NO and its signaling cascade via cyclic GMP in the locust embryo. Its developing nervous system is well suited for pharmacological manipulations in tissue culture. The components of this signaling pathway are localized by histochemical and immunofluorescence techniques. We have analyzed cellular mechanisms of NO action in three examples: 1. in the peripheral nervous system during antennal pioneer axon outgrowth, 2. in the enteric nervous system during migration of neurons forming the midgut nerve plexus, and 3. in the central nervous system during axonal regeneration of serotonergic neurons after axotomy. In each case, internally released NO or NO-induced cGMP synthesis act as permissive signals for the developmental process. Carbon monoxide (CO), as a second gaseous messenger, modulates enteric neuron migration antagonistic to NO.

NO/cGMP signalling: L: -citrulline and cGMP immunostaining in the central complex of the desert locust Schistocerca gregaria

Nitric oxide (NO) is a gaseous messenger molecule formed during conversion of L: -arginine into L: -citrulline by the enzyme NO synthase (NOS), which belongs to a group of NADPH diaphorases. Because of its gaseous diffusion properties, NO differs from classical neurotransmitters in that it is not restricted to synaptic terminals. In target cells, NO activates soluble guanylyl cyclase leading to an increase in cGMP levels. In insects, this NO/cGMP-signalling pathway is involved in development, memory formation and processing of visual, olfactory and mechanosensory information. We have analysed the distribution of putative NO donor and target cells in the central complex, a brain area involved in sky-compass orientation, of the locust Schistocerca gregaria by immunostaining for L: -citrulline and cGMP. Six types of citrulline-immunostained neurons have been identified including a bilateral pair of hitherto undescribed neurons that connect the lateral accessory lobes with areas anterior to the medial lobes of the mushroom bodies. Three-dimensional reconstructions have revealed the connectivity pattern of a set of 18 immunostained pontine neurons of the central body. All these neurons appear to be a subset of previously mapped NADPH-diaphorase-positive neurons of the central complex. At least three types of central-complex neurons show cGMP immunostaining including a system of novel columnar neurons connecting the upper division of the central body and the lateral triangle of the lateral accessory lobe. Our results provide the morphological basis for further studies of the function of the labelled neurons and new insights into NO/cGMP signalling.

Suppression of grasshopper sound production by nitric oxide-releasing neurons of the central complex

The central complex of acridid grasshoppers integrates sensory information pertinent to reproduction-related acoustic communication. Activation of nitric oxide (NO)/cyclic GMP-signaling by injection of NO donors into the central complex of restrained Chorthippus biguttulus females suppresses muscarine-stimulated sound production. In contrast, sound production is released by aminoguanidine (AG)-mediated inhibition of nitric oxide synthase (NOS) in the central body, suggesting a basal release of NO that suppresses singing in this situation. Using anti-citrulline immunocytochemistry to detect recent NO production, subtypes of columnar neurons with somata located in the pars intercerebralis and tangential neurons with somata in the ventro-median protocerebrum were distinctly labeled. Their arborizations in the central body upper division overlap with expression patterns for NOS and with the site of injection where NO donors suppress sound production. Systemic application of AG increases the responsiveness of unrestrained females to male calling songs. Identical treatment with the NOS inhibitor that increased male song-stimulated sound production in females induced a marked reduction of citrulline accumulation in central complex columnar and tangential neurons. We conclude that behavioral situations that are unfavorable for sound production (like being restrained) activate NOS-expressing central body neurons to release NO and elevate the behavioral threshold for sound production in female grasshoppers.

Dopamine D1 receptor-dependent regulation of extracellular citrulline level in the rat nucleus accumbens during conditioned fear response

Nucleus accumbens (N.Acc) contains a subclass of nitric oxide (NO)-generating interneurons that are presumably regulated by the dopamine input. Receptor mechanisms underlying dopamine-NO interaction in the N.Acc are poorly understood. In the current study, we used in vivo microdialysis combined with high-performance liquid chromatography to examine participation of dopamine D1 receptors in regulation of extracellular levels of citrulline (an NO co-product) in the medial N.Acc of Sprague-Dawley rats during both pharmacological challenge and a conditioned fear response. The intraaccumbal infusion of the D1 receptor agonist SKF-38393 (100-500 microM) increased dose-dependently the local dialysate citrulline levels. The SKF-38393-induced increase in extracellular citrulline was prevented by intraaccumbal infusions of 500 microM 7-nitroindazole, a neuronal NO synthase inhibitor. In behavioral microdialysis experiment, the accumbal levels of extracellular citrulline markedly increased in rats given a mild footshock paired with tone. The presentation of the tone previously paired with footshock (the conditioned fear response) produced a "conditioned" rise of extracellular citrulline levels in the N.Acc which was attenuated by intraaccumbal infusion of 100 microM SCH-23390, a dopamine D1 receptor antagonist, and prevented by intraaccumbal infusion of 500 microM 7-nitroindazole. The results suggest that in the N.Acc, the dopamine D1 receptors might regulate the neuronal NO synthase activity; this dopamine-dependent mechanism seems to participate in activation of the neuronal NO synthase and probably NO formation in this brain area during the conditioned fear response.

Coupling of neuronal nitric oxide synthase to NMDA receptors via postsynaptic density-95 depends on estrogen and contributes to the central control of adult female reproduction

Considerable research has been devoted to the understanding of how nitric oxide (NO) influences brain function. Few studies, however, have addressed how its production is physiologically regulated. Here, we report that protein-protein interactions between neuronal NO synthase (nNOS) and glutamate NMDA receptors via the scaffolding protein postsynaptic density-95 (PSD-95) in the hypothalamic preoptic region of adult female rats is sensitive to cyclic estrogen fluctuation. Coimmunoprecipitation experiments were used to assess the physical association between nNOS and NMDA receptor NR2B subunit in the preoptic region of the hypothalamus. We found that nNOS strongly interacts with NR2B at the onset of the preovulatory surge at proestrus (when estrogen levels are highest) compared with basal-stage diestrous rats. Consistently, estrogen treatment of gonadectomized female rats also increases nNOS/NR2B complex formation. Moreover, endogenous fluctuations in estrogen levels during the estrous cycle coincide with changes in the physical association of nNOS to PSD-95 and the magnitude of NO release in the preoptic region. Finally, temporary and local in vivo suppression of PSD-95 synthesis by using antisense oligodeoxynucleotides leads to inhibition of nNOS activity in the preoptic region and disrupted estrous cyclicity, a process requiring coordinated activation of neurons containing gonadotropin-releasing hormone (the neuropeptide controlling reproductive function). In conclusion, our findings identify a novel steroid-mediated molecular mechanism that enables the adult mammalian brain to control NO release under physiological conditions.

Vestibular neurons in the rat contain imidazoleacetic acid-ribotide, a putative neurotransmitter involved in blood pressure regulation

A substantial body of research has led to the recognition that the vestibular system participates in blood pressure modulation during active movements and changes in posture, and that this modulation is effected at least partly by the caudal vestibular nuclei. The I-4 isomer of imidazoleacetic acid-ribotide (IAA-RP) is a putative neurotransmitter/modulator that is thought to be an endogenous regulator of general sympathetic drive, particularly systemic blood pressure. The present study employed immunofluorescence and light and electron microscopic immunocytochemistry to visualize IAA-RP in the vestibular nuclei of adult male rats. The results demonstrate IAA-RP immunolabeling of subpopulations of vestibular neurons in the descending nucleus and the caudal half of the medial nucleus, with scattered immunostained vestibular neurons also present more rostrally. On the basis of double immunofluorescence staining for IAA-RP and calbindin, many of these ribotide-immunoreactive neurons appear to be innervated by cerebellar Purkinje cell afferents. Ultrastructural observations in the caudal vestibular nuclei confirm the IAA-RP immunolocalization in cell bodies and dendritic processes, and in some myelinated axons and presynaptic boutons. The regional distribution of IAA-RP immunoreactivity corresponds to the location of vestibular neurons involved in autonomic functions. The presence of IAA-RP in those neurons suggests that they participate specifically in vestibulo-autonomic regulation of blood pressure. The localization of immunostain in processes and terminals suggests that vestibulo-autonomic activity is subject to local feedback control. Overall, the observations offer a chemoanatomic basis for understanding the vestibular side effects commonly experienced by patients treated with clonidine and other imidazoline-related drugs.

Extracellular citrulline levels in the nucleus accumbens during the acquisition and extinction of a classical conditioned reflex with pain reinforcement

Studies on Sprague-Dawley rats using in vivo microdialysis and HPLC showed that the acquisition and performance of a classical conditioned reflex with pain reinforcement was accompanied by increases in the concentrations of citrulline (a side product of nitric oxide formation) and arginine (the substrate of NO synthase) in the intercellular space of the nucleus accumbens. During extinction of the reflex, there was a decrease in the elevation of extracellular citrulline in this brain structure, which correlated with the extent of extinction of the reflex. Recovery of the reflex led to increases in arginine and citrulline levels in the nucleus accumbens. These data suggest that there is an increase in nitric oxide production in the nucleus accumbens during the acquisition and performance of a classical conditioned reflex with pain reinforcement, which decreases as the reflex is extinguished and recovers with recovery of the reflex.

Neuronal nitric oxide synthase immunopositive neurons in cat vestibular complex: a light and electron microscopic study

Nitric oxide is a unique neurotransmitter, which participates in many physiological and pathological processes in the organism. Nevertheless, there are little data about the neuronal nitric oxide synthase immunoreactivity (nNOS-ir) in the vestibular complex of a cat. In this respect, the aims of this study were to: (1) demonstrate nNOS-ir in the neurons and fibers, from all major and accessory vestibular nuclei; (2) describe their light microscopic morphology and distribution; (3) investigate and analyze the ultrastructure of the NOS I-immunopositive neurons, fibers, and synaptic boutons. For demonstration of the nNOS-ir, the peroxidase-antiperoxidase-diaminobenzidin method was applied. Immunopositive for nNOS neurons and fibers were present in all major and accessory vestibular nuclei. On the light microscope level, the immunopositive neurons were different in shape and size. According to the latter, they were divided into four groups--small (with diameter less than 15 microm), medium-sized (with diameter from 15 to 30 microm), large type I (with diameter from 30 to 40 microm), and large type II (with diameter greater than 40 microm). On the electron microscope level, the immunoproduct was observed in neurons, dendrites, and terminal boutons. According to the ultrastructural features, the neurons were divided into three groups--small (with diameter less than 15 microm), medium-sized (with diameter from 15 to 30 microm), and large (with diameter greater than 30 microm). At least two types of nNOS-ir synaptic boutons were easily distinguished. As a conclusion, we hope that this study will contribute to a better understanding of the functioning of the vestibular complex in cat and that some of the data presented could be extrapolated to other mammals, including human.

Effects of local infusions of apomorphine on the extracellular citrulline level in the striatum: Involvement of D1 and D2 dopamine receptors

Studies using vital microdialysis and high-performance liquid chromatography showed that local infusion of the NO synthase inhibitor N-nitro-L-arginine (1 mM) into the striatum decreased, while infusion of the dopamine receptor agonist apomorphine (100 microM) increased the level of citrulline (a side product of nitric oxide synthesis) in the intercellular space of this structure in Sprague-Dawley rats. The increase in the citrulline level induced by infusions of apomorphine was completely prevented by local infusions of N-nitro-L-arginine (1 mM) and raclopride (10 microm), a dopamine D2 receptor blocker, but not by infusion of SCH-23390 (50 microm), a dopamine D1 receptor blocker. These data suggest that the increase in extracellular citrulline in the striatum induced by dopaminergic stimulation results from local increases in NO synthase activity and that this effect involves D2, but not D1 dopamine receptors.

Testosterone induction of male-typical sexual behavior is associated with increased preoptic NADPH diaphorase and citrulline production in female whiptail lizards

In rodents, male-typical copulatory behavior is generally dependent on gonadal sex steroids such as testosterone, and it is thought that the mechanism by which the hormone gates the behavior involves the gaseous neurotransmitter nitric oxide. According to one model, testosterone induces an up-regulation of nitric oxide synthase (NOS) in the preoptic area, increasing nitric oxide synthesis following exposure to a sexual stimulus. Nitric oxide in turn, possibly through its effect on catecholamine turnover, influences the way the stimulus is processed and enables the appropriate copulatory behavioral response. In whiptail lizards (genus Cnemidophorus), administration of male-typical levels of testosterone to females induces the display of male-like copulatory responses to receptive females, and we hypothesized that this radical change in behavioral phenotype would be accompanied by a large change in the expression of NOS in the preoptic area. As well as comparing NOS expression using NADPH diaphorase histochemistry between testosterone-treated females and controls, we examined citrulline immunoreactivity (a marker of recent nitric oxide production) in the two groups, following a sexual stimulus and following a nonsexual stimulus. Substantially more NADPH diaphorase-stained cells were observed in the testosterone-treated animals. Citrulline immunoreactivity was greater in testosterone-implanted animals than in blank-implanted animals, but only following exposure to a sexual stimulus. This is the first demonstration that not only is NOS up-regulated by testosterone, but NOS thus up-regulated is activated during male-typical copulatory behavior.

Effects of N-methyl-d-aspartate on extracellular citrulline level in the rat nucleus accumbens

In vivo microdialysis combined with high-performance liquid chromatography and electrochemical detection was used to study effects of intraaccumbal infusion of N-methyl-D-aspartate (NMDA) on the content of extracellular citrulline (a nitric oxide co-product) in the medial nucleus accumbens of Sprague-Dawley rats. The intraaccumbal NMDA infusion (10-1000 microM) dose-dependently increased the local dialysate citrulline levels (193+/-7% and 258+/-7% versus basal for the 100 and 1000 microM, respectively). The NMDA-induced increase of extracellular citrulline was completely prevented by intraaccumbal infusions through the dialysis probe both of 50 microM dizocilpine maleate (an NMDA antagonist) and of 0.5 mM N-nitro-L-arginine (a nitric oxide synthase inhibitor). Local infusion of N-nitro-L-arginine (0.5 mM) slightly decreased basal citrulline levels in the nucleus accumbens throughout the entire period of the infusion, whereas dizocilpine maleate (50 microM) had no long-lasting effect. These results suggest that NMDA receptor stimulation of the medial nucleus accumbens might cause a local nitric oxide synthase activation resulting in nitric oxide production in this brain area.

The anatomy of the vestibular nuclei

The vestibular portion of the eighth cranial nerve informs the brain about the linear and angular movements of the head in space and the position of the head with respect to gravity. The termination sites of these eighth nerve afferents define the territory of the vestibular nuclei in the brainstem. (There is also a subset of afferents that project directly to the cerebellum.) This chapter reviews the anatomical organization of the vestibular nuclei, and the anatomy of the pathways from the nuclei to various target areas in the brain. The cytoarchitectonics of the vestibular brainstem are discussed, since these features have been used to distinguish the individual nuclei. The neurochemical phenotype of vestibular neurons and pathways are also summarized because the chemical anatomy of the system contributes to its signal-processing capabilities. Similarly, the morphologic features of short-axon local circuit neurons and long-axon cells with extrinsic projections are described in detail, since these structural attributes of the neurons are critical to their functional potential. Finally, the composition and hodology of the afferent and efferent pathways of the vestibular nuclei are discussed. In sum, this chapter reviews the morphology, chemoanatomy, connectivity, and synaptology of the vestibular nuclei.

The physiology and pathophysiology of nitric oxide in the brain

Nitric oxide (NO) is a molecule with pleiotropic effects in different tissues. NO is synthesized by NO synthases (NOS), a family with four major types: endothelial, neuronal, inducible and mitochondrial. They can be found in almost all the tissues and they can even co-exist in the same tissue. NO is a well-known vasorelaxant agent, but it works as a neurotransmitter when produced by neurons and is also involved in defense functions when it is produced by immune and glial cells. NO is thermodynamically unstable and tends to react with other molecules, resulting in the oxidation, nitrosylation or nitration of proteins, with the concomitant effects on many cellular mechanisms. NO intracellular signaling involves the activation of guanylate cyclase but it also interacts with MAPKs, apoptosis-related proteins, and mitochondrial respiratory chain or anti-proliferative molecules. It also plays a role in post-translational modification of proteins and protein degradation by the proteasome. However, under pathophysiological conditions NO has damaging effects. In disorders involving oxidative stress, such as Alzheimer's disease, stroke and Parkinson's disease, NO increases cell damage through the formation of highly reactive peroxynitrite. The paradox of beneficial and damaging effects of NO will be discussed in this review.

A role for nitric oxide in sensory-induced neurogenesis in an adult insect brain

In the adult cricket, neurogenesis occurs in the mushroom bodies, the main integrative structures of the insect brain. Mushroom body neuroblast proliferation is modulated in response to environmental stimuli. However, the mechanisms underlying these effects remain unspecified. In the present study, we demonstrate that electrical stimulation of the antennal nerve mimics the effects of olfactory activation and increases mushroom body neurogenesis. The putative role of nitric oxide (NO) in this activity-regulated neurogenesis was then explored. In vivo and in vitro experiments demonstrate that NO synthase inhibition decreases, and NO donor application stimulates neuroblast proliferation. NADPH-d activity, anti-L-citrulline immunoreactivity, as well as in situ hybridization with a probe specific for Acheta NO synthase were used to localize NO-producing cells. Combining these three approaches we clearly establish that mushroom body interneurons synthesize NO. Furthermore, we demonstrate that experimental interventions known to upregulate neuroblast proliferation modulate NO production: rearing crickets in an enriched sensory environment induces an upregulation of Acheta NO synthase mRNA, and unilateral electrical stimulation of the antennal nerve results in increased L-citrulline immunoreactivity in the corresponding mushroom body. The present study demonstrates that neural activity modulates progenitor cell proliferation and regulates NO production in brain structures where neurogenesis occurs in the adult insect. Our results also demonstrate the stimulatory effect of NO on mushroom body neuroblast proliferation. Altogether, these data strongly suggest a key role for NO in environmentally induced neurogenesis.

Light microscopical study of nitric oxide synthase I-positive neurons, including fibres in the vestibular nuclear complex of the cat

Nitric oxide is a gaseous neurotransmitter that is synthesized by the enzyme nitric oxide synthase I (NOS I). At present, little is known of NOS I-positive neurons in the vestibular nuclear complex of the cat (VNCc). The aim of the present study was to examine the morphology, distribution patterns and interconnections of NOS I-positive neurons, including fibres in the VNCc. Five adult cats were used as experimental animals. All cats were anaesthetized and perfused transcardially. Brains were removed, postfixed, cut on a freezing microtome and stained in three different ways. Every third section was treated with the Nissl method, other sections were stained either histochemically for NADPH diaphorase or immunohistochemically for NOS I. The atlas of Berman (1928) was used for orientation in the morphometric study. NOS I-positive neurons and fibres were found in all parts of VNCc: medial vestibular nucleus (MVN); lateral vestibular nucleus (LVN); superior vestibular nucleus (SVN); inferior vestibular nucleus (IVN); X, Y, Z groups and Cajal's nucleus. The NOS I-positive neurons were classified according to their size (small, medium-sized, large neurons type I and type II) and their shape (oval, fusiform, triangular, pear-shaped, multipolar and irregular). In every nucleus, a specific neuronal population was observed. In SVN, a large number of interconnections between NOS I-positive neurons were identified. In MVN, chain-like rolls of small neurons were found. Tiny interconnections between MVN and mesencephalic reticular formation were present. Our data provide information on the morphology, distribution patterns and interconnections of NOS I-positive neurons in the VNCc and can be extrapolated to other mammals.

Nitric oxide increases the spontaneous firing rate of rat medial vestibular nucleus neurons in vitro via a cyclic GMP-mediated PKG-independent mechanism

The effects of nitric oxide (NO) on the discharge rate of medial vestibular nucleus neurons (MVNn) were investigated in rat brainstem slices. The NO-donor sodium nitroprusside (SNP, 200 microM) caused a marked enhancement (+36.7%) of MVNn spontaneous firing rate, which was prevented by the NO-scavenger, carboxy-PTIO (300 microM). The SNP effects were not modified (+37.4%) by synaptic uncoupling, suggesting that NO influences intrinsic membrane properties of MVNn rather than the synaptic input they receive. The excitatory action of SNP was virtually abolished by slice pretreatment with the soluble guanylyl cyclase inhibitor, ODQ (10 microM), and it was mimicked (+33.1%) by the cGMP analogue 8-Br-cGMP (400 microM). Protein kinase G (PKG) and cAMP/protein kinase A (PKA) were both excluded as downstream effectors of the NO/cGMP-induced excitation. However, the cyclic nucleotide-gated (CNG) channel blockers, L-cis-diltiazem (LCD, 100 microM) and Sp-8-Br-PET-cGMPS (100 microM), significantly reduced the firing rate increase produced by 8-Br-cGMP. Moreover, LCD alone decreased spontaneous MVNn firing (-19.7%), suggesting that putative CNG channels may contribute to the tonic control of resting MVNn discharge. 8-Br-cAMP (1 mM) also elicited excitatory effects in MVNn (+40.8%), which occluded those induced by 8-Br-cGMP, indicating that the two nucleotides share a common target. Finally, nested-polymerase chain reaction assay revealed the expression of CNG channel alpha subunit transcript in MVNn. Our data provide the first demonstration that NO/cGMP signalling modulates MVNn spontaneous firing through a mechanism that is independent of PKG or PKA and probably involves activation of CNG channels.

L-Citrulline Immunoreactivity Reveals Nitric Oxide Production in the Electromotor and Electrosensory Systems of the Weakly Electric Fish, Apteronotus leptorhynchus

Weakly electric fish produce electric organ discharges (EODs) used for electrolocation and communication. In the brown ghost knifefish, Apteronotus leptorhynchus, several neuron types in brain regions that control the EOD or process electrosensory information express nitric oxide synthase (NOS). The present study used immunoreactivity for L-citrulline, a byproduct of the production of nitric oxide (NO) by NOS, to assess NO production in NOS-expressing neurons. A polyclonal antibody against L-citrulline produced specific labeling in most neuronal populations previously identified to express NOS. Specifically, several cell types that precisely encode temporal information and/or fire at high frequencies, including spherical cells in the electrosensory lateral line lobe, giant cells in layer VI of the dorsal torus semicircularis, and pacemaker and relay cells in the pacemaker nucleus, were strongly immunoreactive for L-citrulline. This suggests that these neurons produced high levels of NO. Notably, electromotor neurons, which also strongly express NOS, were not immunoreactive for L-citrulline, suggesting that NOS did not produce high levels of NO in these neurons. No apparent differences in L-citrulline distribution or intensity were observed between socially isolated fish and fish exposed to playback stimuli simulating the presence of a conspecific. This suggests that social stimulation by electrocommunication signals is not necessary for high levels of NO production in many NOS-positive neurons. Future studies focusing on regulation of NO production in these systems, and the effects of NO on electrosensory processing and electromotor pattern generation will help elucidate the function of NO signaling pathways in this system.

Prolonged exposure to intermittent alcohol vapors decreases the ACTH as well as hypothalamic nitric oxide and cytokine responses to endotoxemia

BACKGROUND

Prolonged exposure to alcohol blunts the response of the hypothalamic-pituitary-adrenal (HPA) axis to various stressors, including the systemic injection of a lipopolysaccharide (LPS). We previously showed that decreased synthesis of the hypothalamic peptides corticotropin-releasing factor (CRF) and vasopressin (VP) played a central role in this phenomenon. However, the mechanisms that lead to decreased hypothalamic neuronal activity have not been identified. In the present work, we tested the hypothesis that alcohol decreased signals that are elicited by LPS and that stimulate hypothalamic CRF and VP synthesis, namely nitric oxide (NO) and the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6).

METHODS

Adult male rats were exposed to intermittent (5 hr/day) alcohol vapors for 5 days. Control animals were kept in comparable chambers but not exposed to the vapors. On day 6, the animals received an injection of LPS through permanent indwelling intravenous cannulae. The dependent variables were plasma ACTH levels measured by IRMA (immunoradiometric assay); pituitary and hypothalamic TNF-alpha and IL-6 mRNA levels measured by RNase protection assay; basal activity of neuronal NO synthase measured by conversion of [14C]arginine to [14C]citrulline, the constitutive enzyme that synthesizes NO and modulates the influence of this gas on LPS-induced HPA axis activity; and basal and LPS-induced levels of citrulline (an index of NO formation) in the hypothalamus, measured by immunocytochemistry.

RESULTS

After injection with LPS, rats that were pretreated with alcohol exhibited a significantly (p < 0.01) decreased release of ACTH, compared with controls. There was no difference in basal NO synthase activity or hypothalamic citrulline levels. In contrast, LPS-induced hypothalamic citrulline levels were significantly (p < 0.01) lower in alcohol-exposed rats, as were pituitary TNF-alpha and IL-6 transcripts. In the hypothalamus, the TNF-alpha but not IL-6 response to LPS was also reduced.

CONCLUSIONS

These results indicate that prolonged exposure to alcohol decreases the ACTH, hypothalamic NO and TNF-alpha, and pituitary TNF-alpha and IL-6 responses to LPS. This suggests that altered NO and proinflammatory cytokine levels in the brain may modulate the inhibitory influence exerted by alcohol on the HPA axis response to endotoxemia.

Nitric Oxide Synthase in Acute Alteration of Nitric Oxide Levels after Subarachnoid Hemorrhage

OBJECTIVE

Subarachnoid hemorrhage (SAH) is associated with acute decreases and subsequent recovery of cerebral nitric oxide (NO) levels, but the mechanisms of these alterations are not known. In this study, we measured NO synthase (NOS) protein and kinetics to determine its involvement in the alterations of cerebral NO levels after SAH.

METHODS

The endovascular rat model of SAH was used. The number of NOS-1 (neuronal) and NOS-2 (inducible)-positive cells (0-96 h) was determined by counting immunoreactive cells in 8-microm cryostat sections. The tissue content of active NOS and its kinetic parameters were studied with an enzymatic l-citrulline assay.

RESULTS

The number of NOS-1-positive cells increased between 1 and 3 hours after SAH, decreased to and below control values at 6 and 72 hours after SAH, and increased to control values 96 hours after SAH. The number of NOS-2-positive cells increased 1 hour after SAH, decreased to control values at 24 hours, and increased above control values 96 hours after SAH. The Michaelis-Menten kinetic parameters (V(max), K(m), slope) of NOS remained unchanged at 10 and 90 minutes after SAH.

CONCLUSION

NOS-1 and -2 proteins undergo a triphasic alteration after SAH, whereas the amount of active NOS and its kinetic parameters remain unchanged during the first 90 minutes after SAH. Depletion of NOS is not involved in the acute alterations of cerebral NO levels after SAH.

Evidence of nuclear localization of neuronal nitric oxide synthase in cultured astrocytes of rats

With immunocytochemistry, we have observed the nuclear localization of neuronal nitric oxide synthase (nNOS) in cultured cerebral cortical astrocytes of rats. During the early six days in the subcultures of these cells, nNOS-immunoreactivity was mainly distributed in the cytoplasm. However, nNOS-immunoreactivity was mainly distributed in the nucleus at day 7, and this nuclear localization lasted about ten hours. Meanwhile, inducible nitric oxide synthase expression was significantly inhibited in these cells. Thereafter, nNOS-immunoreactivity was mainly distributed in the cytoplasm again. By confocal microscopy and western blot analysis, the phenomenon of nNOS nuclear localization was further confirmed; and the activity of nNOS in nuclear protein extracts from astrocytes of day 7-subculture could be detected using electron spin resonance (ESR) technique. These results may represent a new pathway of nitric oxide/nNOS participating in inducible nitric oxide synthase gene transcription regulation.

Oxidative injury to the endoplasmic reticulum in mouse brains after transient focal ischemia

Oxidative damage to the endoplasmic reticulum (ER) could be involved in ischemic neuronal cell death because this organelle is susceptible to reactive oxygen species. Using wild-type mice and copper/zinc-superoxide dismutase (SOD1) transgenic mice, we induced focal cerebral ischemia and compared neuronal degeneration and ER stress, that is, phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha) and RNA-dependent protein kinase-like ER eIF2alpha kinase (PERK). We found that neurons with severe and prolonged phosphorylation of eIF2alpha and PERK underwent later degeneration, and that this was partially prevented by SOD1 overexpression. Signals for superoxide production and phospho-PERK were colocalized, which further indicates a pivotal role for superoxide in ER damage. We investigated the molecular mechanisms of oxidative ER stress and found that detachment of glucose-regulated protein 78 from PERK was the key step. We conclude that ER damage is involved in oxidative neuronal injury in the brain after ischemia/reperfusion.

Comparison between the influence of shocks and endotoxemia on the activation of brain cells that contain nitric oxide

We sought to identify the brain circuitry that underlies the stimulatory role of nitric oxide (NO) role on the hypothalamic-pituitary-adrenal (HPA) axis. Specifically, we determined whether electrofootshocks (60 min) or the intravenous administration of lipopolysaccharide (LPS, 100 microg/kg)-activated neurocircuitries that express either neuronal NO synthase (nNOS), a constitutive enzyme responsible for NO formation, or L-citrulline, an amino acid that is produced in equimolar amounts with NO. Shocks significantly increased the number of cells showing Fos immunoreactivity (ir) in the paraventricular nucleus (PVN) of the hypothalamus, the lateral hypothalamus (LH), amygdaloid complex (AD) and thalamus (TH), and to a lesser extent, in the hippocampus (HP), caudate putamen (CP) and frontal cortex (FC). However, shocks did not alter the number of nNOS-positive cells nor increased citrulline signals in these brain regions. LPS significantly upregulated the number of cells with fos-like ir in the PVN, LH, AD, TH, HP, CP and FC, but only increased the number of cells positive for citrulline in the PVN, 87% of which co-expressed Fos. Thus, while shocks did not alter nNOS gene expression or citrulline levels in the brain regions studied, LPS significantly increased the number of PVN cells expressing citrulline without concomitant changes in other brain areas. Endotoxemia also upregulated significantly more PVN cells that co-expressed Fos and nNOS, compared to shocks. As NO stimulates the PVN circuitries that participate in shocks- and LPS-induced ACTH release, the lack of changes in nNOS or citrulline levels due to shocks suggests that, in this model, constitutively formed NO may modulate HPA axis activity in the absence of changes in its synthesis.

Further characterisation of particulate neuronal nitric oxide synthase in rat small intestine

Neuronal NO-synthase (nNOS) was investigated in rat longitudinal muscle/myenteric plexus (LM/MP) tissue at the cellular and subcellular level. Using preparations and double immune staining and light and electron microscopy, we concluded that, in these preparations, nNOS is only present in neuronal cells. However, in spite of numerous attempts to morphologically identify the NOS-containing subcellular structure, no firm conclusions were possible. Consequently, the problem was approached by biochemical methods including gradient centrifugation followed by analysis of the fractions. Using a protocol involving gentle homogenisation of the tissue, we found that about 10% of the nNOS immune reactivity was particle-bound confirming previous results (Biochem. Pharmacol. 60 (2000) 145). However, applying a different protocol including strong homogenisation, we now demonstrated that about 50% of the immune reactive nNOS was sedimentable. The results suggested that particulate nNOS is associated with one single subcellular structure, which is different from the plasma membrane, rough and smooth endoplasmic reticulum, mitochondria and lysosomes. The equilibrium sedimentation characteristics of the nNOS containing particles corresponded partly to those containing vasoactive intestinal polypeptide (VIP) or synaptobrevin. Application of non-equilibrium centrifugation conditions, however, demonstrated that almost no co-localisation occurred. We conclude that, in the LM/MP tissue, nNOS is about 50% particle-bound in a subcellular structure, which is different from the VIP-containing particle and from synaptobrevin-containing exocytotic particles.

Oxidative damage to the endoplasmic reticulum is implicated in ischemic neuronal cell death

The endoplasmic reticulum (ER), which plays important roles in apoptosis, is susceptible to oxidative stress. Because reactive oxygen species (ROS) are robustly produced in the ischemic brain, ER damage by ROS may be implicated in ischemic neuronal cell death. We induced global brain ischemia on wild-type and copper/zinc superoxide dismutase (SOD1) transgenic rats and compared ER stress and neuronal damage. Phosphorylated forms of eukaryotic initiation factor 2 alpha (eIF2 alpha) and RNA-dependent protein kinase-like ER eIF2 alpha kinase (PERK), both of which play active roles in apoptosis, were increased in hippocampal CA1 neurons after ischemia but to a lesser degree in the transgenic animals. This finding, together with the finding that the transgenic animals showed decreased neuronal degeneration, indicates that oxidative ER damage is involved in ischemic neuronal cell death. To elucidate the mechanisms of ER damage by ROS, we analyzed glucose-regulated protein 78 (GRP78) binding with PERK and oxidative ER protein modification. The proteins were oxidatively modified and stagnated in the ER lumen, and GRP78 was detached from PERK by ischemia, all of which were attenuated by SOD1 overexpression. We propose that ROS attack and modify ER proteins and elicit ER stress response, which results in neuronal cell death.

Immunohistochemical localization of citrullinated proteins in adult rat brain

By using hybridoma technology, an IgM monoclonal antibody (F95) against multiple citrullinated synthetic and natural peptides was recently developed and used to stain immunohistochemically subsets of astrocytes and myelin basic protein (MBP) from selected regions of human brain (Nicholas and Whitaker [2002] Glia 37:328-336). With this antibody, the present study provides a more detailed localization of citrullinated epitopes in the central nervous system (CNS) by examining immunohistochemical staining patterns for F95 in the normal adult rat brain. Thus, immunohistochemical labeling for citrullinated epitopes was seen in white matter areas consistent with myelin staining; however, in general, it was more prominent and uniform in the caudal CNS (spinal cord, medulla oblongata, pons, and cerebellum) than in more rostral areas. F95 staining was also seen in cells and fibers often intimately associated with blood vessels and/or ventricular surfaces. By using dual-color immunofluorescence, the vast majority of this latter staining was colocalized within a subset of astrocytes also immunoreactive for glial fibrillary acidic protein (GFAP). By using Western blot analysis of rat brain proteins, multiple GFAP- and MBP-immunoreactive proteins and peptide fragments were seen, and many of them were also reactive with the F95 antibody. Thus, the present study not only demonstrates that citrullinated epitopes in normal rat brain are most concentrated in subsets of myelin and astrocytes but also provides evidence that GFAP, like MBP, may be present as multiple citrullinated isoforms.