Developmental profile of NTPDase activity in synaptic plasma membranes isolated from rat cerebral cortex

Participation of ecto-5'-nucleotidase in the inflammatory response in an adult zebrafish (Danio rerio) model

The ecto-5'-nucleotidase is an important source of adenosine in the extracellular medium. Adenosine modulation appears early in evolution and performs several biological functions, including a role as an anti-inflammatory molecule. Here, we evaluate the activity and mRNA expression of ecto-5'-nucleotidase in response to lipopolysaccharide (LPS) using zebrafish as a model. Adult zebrafish were injected with LPS (10 μg/g). White blood cell differential counts, inflammatory markers, and ecto-5'-nucleotidase activity and expression in the encephalon, kidney, heart, and intestine were evaluated at 2, 12, and 24 h post-injection (hpi). At 2 hpi of LPS, an increase in neutrophils and monocytes in peripheral blood was observed, which was accompanied by increased tnf-α expression in the heart, kidney, and encephalon, and increased cox-2 expression in the intestine and kidney. At 12 hpi, monocytes remained elevated in the peripheral blood, while tnf-α expression was also increased in the intestine. At 24 hpi, the white blood cell differential count no longer differed from that of the control, whereas tnf-α expression remained elevated in the encephalon but reduced in the kidney compared with the controls. AMP hydrolysis in LPS-treated animals was increased in the heart at 24 hpi [72 %; p = 0.029] without affecting ecto-5'-nucleotidase gene expression. These data indicate that, in most tissues studied, inflammation does not affect ecto-5'-nucleotidase activity, whereas in the heart, a delayed increase in ecto-5'-nucleotidase activity could be related to tissue repair.

Lambda-cyhalothrin exposure alters purine nucleotide hydrolysis and nucleotidase gene expression pattern in platelets and liver of rats

Lambda-cyhalothrin (LCT) is a broad-spectrum pesticide widely used in agriculture throughout the world. This pesticide is considered a potential contaminant of surface and underground water as well as food, posing a risk to ecosystems and humans. In this sense, we decided to evaluate the activity of enzymes belonging to the purinergic system, which is linked with regulation of extracellular nucleotides and nucleosides, such as adenosine triphosphate (ATP) and adenosine (Ado) molecules involved in the regulation of inflammatory response. However, there are no data concerning the effects of LCT exposure on the purinergic system, where extracellular nucleotides act as signaling molecules. The aim of this study was to evaluate nucleotide hydrolysis by E-NTPDase (ecto-nucleoside triphosphate diphosphohydrolase), Ecto-NPP (ecto-nucleotide pyrophosphatase/phosphodiesterase), ecto-5'-nucleotidase and ecto-adenosine deaminase (E-ADA) in platelets and liver of adult rats on days 7, 30, 45 and 60 after daily gavage with 6.2 and 31.1 mg/kg bw of LCT. Gene expression patterns of NTPDases1-3 and 5'-nucleotidase were also determined in those tissues. In parallel, lambda-cyhalothrin metabolites [3-(2-chloro-3,3,3- trifluoroprop-1-enyl)-2,2-dimethyl-cyclopropane carboxylic acid (CFMP), 4-hydroxyphenoxybenzoic acid (4-OH-3-PBA), and 3-phenoxybenzoic acid (3-PBA)] were measured in plasma. Results showed that exposure rats to LCT caused a significant increase in the assessed enzymes activities. Gene expression pattern of ectonucleotidases further revealed a significant increase in E-NTPDase1, E-NTPDase2, and E-NTPDase3 mRNA levels after LCT administration at all times. A dose-dependent increase in LCT metabolite levels was also observed but there no significant variations in levels from weeks to week, suggesting steady-steady equilibrium. Correlation analyses revealed that LCT metabolites in the liver and plasma were positively correlated with the adenine nucleotides hydrolyzing enzyme, E-ADA and E-NPP activities in platelets and liver of rats exposed to lambda-cyhalothin. Our results show that LCT and its metabolites may affect purinergic enzymatic cascade and cause alterations in energy metabolism.

Complex regulation of ecto-5'-nucleotidase/CD73 and A2AR-mediated adenosine signaling at neurovascular unit: A link between acute and chronic neuroinflammation

The review summarizes available data regarding the complex regulation of CD73 at the neurovascular unit (NVU) during neuroinflammation. Based on available data we propose the biphasic pattern of CD73 regulation at NVU, with an early attenuation and a postponed up-regulation of CD73 activity. Transient attenuation of CD73 activity on leukocyte/vascular endothelium and leukocyte/astrocyte surface, required for the initiation of a neuroinflammatory response, may be effectuated either by catalytic inhibition of CD73 and/or by shedding of the CD73 molecule from the cell surface, while postponed induction of CD73 is effectuated by transcriptional up-regulation of Nt5e and posttranslational modifications. Neuroinflammatory conditions are also associated with significant enhancement and gain-of-function of A_2AR-mediated adenosine signaling. However, in contrast to the temporary prevalence of A_2AR over A₁R signaling during an acute inflammatory response, prolonged induction of A_2AR and resulting perpetual CD73/A_2AR coupling may be a contributing factors in the transition between acute and chronic neuroinflammation. Thus, pharmacological targeting of the CD73/A_2AR axis may attenuate inflammatory response and ameliorate neurological deficits in chronic neuroinflammatory conditions.

Role of Ectonucleotidases in Synapse Formation During Brain Development: Physiological and Pathological Implications

BACKGROUND

Extracellular adenine nucleotides and nucleosides, such as ATP and adenosine, are among the most recently identified and least investigated diffusible signaling factors that contribute to the structural and functional remodeling of the brain, both during embryonic and postnatal development. Their levels in the extracellular milieu are tightly controlled by various ectonucleotidases: ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPP), alkaline phosphatases (AP), ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) and ecto-5'- nucleotidase (eN).

METHODS

Studies related to the expression patterns of ectonucleotidases and their known features during brain development are reviewed, highlighting involvement of these enzymes in synapse formation and maturation in physiological as well as in pathological states.

RESULTS

During brain development and in adulthood all ectonucleotidases have diverse expression pattern, cell specific localization and function. NPPs are expressed at early embryonic days, but the expression of NPP3 is reduced and restricted to ependymal area in adult brain. NTPDase2 is dominant ectonucleotidase existing in the progenitor cells as well as main astrocytic NTPDase in the adult brain, while NTPDase3 is fully expressed after third postnatal week, almost exclusively on varicose fibers. Specific brain AP is functionally associated with synapse formation and this enzyme is sufficient for adenosine production during neurite growth and peak of synaptogenesis. eN is transiently associated with synapses during synaptogenesis, however in adult brain it is more glial than neuronal enzyme.

CONCLUSION

Control of extracellular adenine nucleotide levels by ectonucleotidases are important for understanding the role of purinergic signaling in developing tissues and potential targets in developmental disorders such as autism.

Purinergic signalling during development and ageing

Extracellular purines and pyrimidines play major roles during embryogenesis, organogenesis, postnatal development and ageing in vertebrates, including humans. Pluripotent stem cells can differentiate into three primary germ layers of the embryo but may also be involved in plasticity and repair of the adult brain. These cells express the molecular components necessary for purinergic signalling, and their developmental fates can be manipulated via this signalling pathway. Functional P1, P2Y and P2X receptor subtypes and ectonucleotidases are involved in the development of different organ systems, including heart, blood vessels, skeletal muscle, urinary bladder, central and peripheral neurons, retina, inner ear, gut, lung and vas deferens. The importance of purinergic signalling in the ageing process is suggested by changes in expression of A1 and A2 receptors in old rat brains and reduction of P2X receptor expression in ageing mouse brain. By contrast, in the periphery, increases in expression of P2X3 and P2X4 receptors are seen in bladder and pancreas.

Adenosine triphosphate-induced photoreceptor death and retinal remodeling in rats

Many common causes of blindness involve the death of retinal photoreceptors, followed by progressive inner retinal cell remodeling. For an inducible model of retinal degeneration to be useful, it must recapitulate these changes. Intravitreal administration of adenosine triphosphate (ATP) has recently been found to induce acute photoreceptor death. The aim of this study was to characterize the chronic effects of ATP on retinal integrity. Five-week-old, dark agouti rats were administered 50 mM ATP into the vitreous of one eye and saline into the other. Vision was assessed using the electroretinogram and optokinetic response and retinal morphology investigated via histology. ATP caused significant loss of visual function within 1 day and loss of 50% of the photoreceptors within 1 week. At 3 months, 80% of photoreceptor nuclei were lost, and total photoreceptor loss occurred by 6 months. The degeneration and remodeling were similar to those found in heritable retinal dystrophies and age-related macular degeneration and included inner retinal neuronal loss, migration, and formation of new synapses; Müller cell gliosis, migration, and scarring; blood vessel loss; and retinal pigment epithelium migration. In addition, extreme degeneration and remodeling events, such as neuronal and glial migration outside the neural retina and proliferative changes in glial cells, were observed. These extreme changes were also observed in the 2-year-old P23H rhodopsin transgenic rat model of retinitis pigmentosa. This ATP-induced model of retinal degeneration may provide a valuable tool for developing pharmaceutical therapies or for testing electronic implants aimed at restoring vision.

Proline-induced changes in acetylcholinesterase activity and gene expression in zebrafish brain: reversal by antipsychotic drugs

Hyperprolinemia is an inherited disorder of proline metabolism and hyperprolinemic patients can present neurological manifestations, such as seizures, cognitive dysfunctions, and schizoaffective disorders. However, the mechanisms related to these symptoms are still unclear. In the present study, we evaluated the in vivo and in vitro effects of proline on acetylcholinesterase (AChE) activity and gene expression in the zebrafish brain. For the in vivo studies, animals were exposed at two proline concentrations (1.5 and 3.0mM) during 1h or 7 days (short- or long-term treatments, respectively). For the in vitro assays, different proline concentrations (ranging from 3.0 to 1000 μM) were tested. Long-term proline exposures significantly increased AChE activity for both treated groups when compared to the control (34% and 39%). Moreover, the proline-induced increase on AChE activity was completely reverted by acute administration of antipsychotic drugs (haloperidol and sulpiride), as well as the changes induced in ache expression. When assessed in vitro, proline did not promote significant changes in AChE activity. Altogether, these data indicate that the enzyme responsible for the control of acetylcholine levels might be altered after proline exposure in the adult zebrafish. These findings contribute for better understanding of the pathophysiology of hyperprolinemia and might reinforce the use of the zebrafish as a complementary vertebrate model for studying inborn errors of amino acid metabolism.

Morphine treatment alters nucleotidase activities in rat blood serum

Morphine has been widely used in neonatal pain management. However, this treatment may produce adaptive changes in several physiologic systems. Our laboratory has demonstrated that morphine treatment in neonate rats alters nucleoside triphosphate diphosphohydrolase (NTPDase) activity and gene expression in central nervous system structures. Considering the relationship between the opioid and purinergic systems, our aim was to verify whether treatment with morphine from postnatal days 8 (P8) through 14 (P14) at a dose of 5 μg per day alters NTPDase and 5′-nucleotidase activities in rat serum over the short, medium, and long terms. After the in vivo assay, the morphine group showed increased hydrolysis of all nucleotides at P30, and a decrease in adenosine 5′-diphosphate hydrolysis at P60. Moreover, we found that nucleotidase activities change with age; adenosine 5′-triphosphate hydrolysis activity was lower at P16, and adenosine 5′-monophosphate hydrolysis activity was higher at P60. These changes are very important because these enzymes are the main regulators of blood nucleotide levels and, consequently, nucleotide signaling. Our findings showed that in vivo morphine treatment alters nucleotide hydrolysis in rat blood serum, suggesting that purine homeostasis can be influenced by opioid treatment during the neonatal period.

Long-term proline exposure alters nucleotide catabolism and ectonucleotidase gene expression in zebrafish brain

Hyperprolinemia is an inherited disorder of proline metabolism and hyperprolinemic patients can present neurological manifestations, such as seizures cognitive dysfunctions, and psychotic disorders. However, the underlying mechanisms of these symptoms are still unclear. Since adenine nucleotides play crucial roles in neurotransmission and neuromodulation, we evaluated the in vivo and in vitro effects of proline on ectonucleotidase activities and gene expression in zebrafish brain. For the in vivo studies, animals were exposed at two proline concentrations (1.5 and 3.0 mM) during 1 h or 7 days (short- or long-term treatments, respectively). For the in vitro assays, different proline concentrations (ranging from 3.0 to 1000 μM) were tested. Short-term proline exposure did not promote significant changes on the ectonucleotidase activities and gene expression. Long-term proline exposure significantly increased ATP catabolism in both concentrations tested (14 % and 22 %, respectively), whereas ADP and AMP hydrolysis were increased only at 3.0 mM proline (21 % and 17 %, respectively) when compared to control. Moreover, the relative gene expression of enpd3 increased in both treated groups after long-term proline, whereas enptd1 increased only at 3.0 mM proline. Proline in vitro did not promote significant changes on ectonucleotidase activities. Altogether, these data indicate that the enzymes responsible for the control of extracellular nucleotides levels might be altered after proline exposure in zebrafish, contributing to better understand the pathophysiology of this disease. Moreover, such findings might facilitate the use of the zebrafish as a complementary vertebrate model for studying inborn errors of amino acid metabolism.

Long-term methionine exposure induces memory impairment on inhibitory avoidance task and alters acetylcholinesterase activity and expression in zebrafish (Danio rerio)

Hypermethioninemic patients exhibit a variable degree of neurological dysfunction. However, the mechanisms involved in these alterations have not been completely clarified. Cholinergic system has been implicated in many physiological processes, including cognitive performances, as learning, and memory. Parameters of cholinergic signaling have already been characterized in zebrafish brain. Since zebrafish is a small freshwater teleost which is a vertebrate model for modeling behavioral and functional parameters related to human pathogenesis and for clinical treatment screenings, in the present study we investigated the effects of short- and long-term methionine exposure on cognitive impairment, AChE activity and gene expression in zebrafish. For the studies, animals were exposed at two methionine concentrations (1.5 and 3.0 mM) during 1 h or 7 days (short- or long-term treatments, respectively). We observed a significant increase in AChE activity of zebrafish brain membranes after long-term methionine exposure at 3.0 mM. However, AChE gene expression decreased significantly in both concentrations tested after 7 days of treatment, suggesting that post-translational events are involved in the enhancement of AChE activity. Methionine treatment induces memory deficit in zebrafish after long-term exposure to this amino acid, which could be related, at least in part, with cognitive impairment observed in hypermethioninemia. Therefore, the results here presented raise a new perspective to use the zebrafish as a complementary vertebrate model for studying inborn errors of metabolism, which may help to better understand the pathophysiology of this disease.

Endotoxin-induced effects on nucleotide catabolism in mouse kidney

Extracellular adenosine 5'-triphosphate (ATP) acts as a proinflammatory mediator. Adenosine, the final product of ATP breakdown, is an anti-inflammatory compound, acting mainly on adenosine A(2A) receptors. Considering that the kidney is an organ strongly affected during systemic inflammatory responses and that ectonucleotidases are responsible for the control of extracellular nucleotide and nucleoside levels, we examined the endotoxin-induced effects on ectonucleotidases in kidney membranes of mice, and whether CGS-21680 hydrochloride (3-[4-[2-[[6-amino-9-[(2R,3R,4S,5S)-5-(ethylcarbamoyl)-3,4-dihydroxy-oxolan-2-yl]purin-2-yl]amino]ethyl]phenyl]propanoic acid), a selective adenosine A(2A) receptor agonist, antagonizes the lipopolysaccharide (LPS)-induced effects on nucleotide catabolism in kidney. Animals were injected intraperitoneally with 12 mg/kg LPS and/or 0.5mg/kg CGS-21680 or saline. Nucleotidase activities were determined in kidney membrane preparations and ATP metabolism was measured by high performance liquid chromatography (HPLC) assay. Analysis of ectonucleotidase expression was carried out by semi-quantitative semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Exposure to endotoxemia promoted an increase in ATP and p-Nitrophenyl thymidine 5'-monophosphate (p-Nph-5'-TMP) hydrolysis, and a decrease in adenosine 5'-monophosphate (AMP) hydrolysis. CGS-21680 treatment failed to reverse these changes. HPLC analysis indicated a decrease in extracellular ATP and adenosine levels in groups treated with LPS and LPS plus CGS-21680. The expression pattern of ectonucleotidases revealed an increase in Entpd3, Enpp2, and Enpp3 mRNA levels after LPS injection. These findings indicate that nucleotide and nucleoside availability in mouse kidney is altered at different stages of endotoxemia, in order to protect the integrity of this organ when exposed to systemic inflammation.

Chronic mild hyperhomocysteinemia alters ectonucleotidase activities and gene expression of ecto-5'-nucleotidase/CD73 in rat lymphocytes

Since mild hyperhomocysteinemia is a risk factor for cardiovascular and cerebral diseases and extracellular nucleotides/nucleosides, which are controlled by the enzymatic action of ectonucleotidases, can induce an immune response, in the present study, we investigated the effect of chronic mild hyperhomocysteinemia on ectonucleotidase activities and expression in lymphocytes from mesenteric lymph nodes and serum of adult rats. For the chronic chemically induced mild hyperhomocysteinemia, Hcy (0.03 μmol/g of body weight) or saline (control) were administered subcutaneously from the 30th to the 60th day of life. Results showed that homocysteine significantly decreased ATP, ADP, and AMP hydrolysis in lymphocytes of adult rats. E-NTPDases transcriptions were not affected, while the ecto-5'-nucleotidase transcription was significantly decreased in mesenteric lymph nodes of hyperhomocysteinemic rats. ATP, ADP, and AMP hydrolysis were not affected by homocysteine in rat serum. Our findings suggest that Hcy in levels similar to considered risk factor to development of vascular diseases modulates the ectonucleotidases, which could lead to a pro-inflammatory status.

Profile of nucleotide catabolism and ectonucleotidase expression from the hippocampi of neonatal rats after caffeine exposure

Nucleotides and nucleosides play an important role in neurodevelopment acting through specific receptors. Ectonucleotidases are the major enzymes involved in controlling the availability of purinergic receptors ligands. ATP is co-released with several neurotransmitters and is the most important source of extracellular adenosine by catabolism exerted by ectonucleotidases. The main ectonucleotidases are named NTPDases (1-8) and 5'-nucleotidase. Adenosine is a powerful modulator of neurotransmitter release. Caffeine blocks adenosine receptor activity as well as adenosine-mediated neuromodulation. Considering the susceptibility of the immature brain to caffeine and the need for correct purinergic signaling during fetal development, we have analyzed the effects of caffeine exposure during gestational and lactational periods on nucleotide degradation and ectonucleotidase expression from the hippocampi of 7-, 14- and 21-days-old rats. Nucleotides hydrolysis was assessed by colorimetric determination of inorganic phosphate released. Ectonucleotidases expression was performed by RT-PCR. ATP and ADP hydrolysis displayed parallel age-dependent decreases in both control and caffeine-treated groups. AMP hydrolysis increased with caffeine treatment in 7-days-old rats (75%); although there was no significant difference in AMP hydrolysis between control (non caffeine-treated) rats and 14- or 21-days caffeine-treated rats. ADP hydrolysis was not affected by caffeine treatment. Caffeine treatment in 7- and 14-days-old rats decreased ATP hydrolysis when compared to the control group (19% and 60% decrease, respectively), but 21-days-treated rats showed an increase in ATP hydrolysis (39%). Expression levels of NTPDase 1 and 5 decreased in hippocampi of caffeine-treated rats. The expression of 5'-nucleotidase was not affected after caffeine exposure. The changes observed in nucleotide hydrolysis and ectonucleotidases expression could promote subtle effects on normal neural development considering the neuromodulatory role of adenosine.

Dynamic changes in the expression pattern of ecto-5'-nucleotidase in the rat model of cortical stab injury

Traumatic injury induces massive release of ATP in the extracellular space, where it influences numerous aspects of neuronal, astrocytic, and microglial responses to injury by activating P2X and P2Y receptors. The extracellular ATP actions are controlled by the ectonucleotidase enzyme pathway, which hydrolyses ATP to adenosine at all neuronal and nonneuronal cell types. Adenosine activates its P1 receptors, which have important neuroprotective roles. The rate-limiting enzyme in the ectonucleotidase pathway is ecto-5'-nucleotidase (e-5NT), which catalyzes the final step of dephosphorylation of AMP to adenosine. The aim of the present study was to characterize the expression pattern and cellular distribution of e-5NT in the perilesioned cortex at 4 hr and 1, 2, 7, and 15 days after unilateral cortical stab injury (CSI). Immunoblot and immunohistochemical studies showed that overall e-5NT expression was lower 4 hr and 1 day postinjury and then gradually increased above the control levels. Double-immunofluorescence studies further showed in control tissue the presence of the enzyme in the membranes surrounding neuronal somata and apical dendrites and less frequently in astrocytes. CSI caused a rapid (after 4 hr) and irreversible loss of the enzyme from neurons, accounting for a decrease in the overall enzyme expression. This was accompanied with a gradual increase in e-5NT-positive astrocytes, accounting for up-regulation of the enzyme levels in the injured area. Thus, CSI induced dynamic changes in the expression pattern of e-5NT that modify the ATP/adenosine ratio and the extent of P1 and P2 receptors activation and, therefore, outcome of the pathological processes after CSI.

Adenosine A(2A) receptor agonist (CGS-21680) prevents endotoxin-induced effects on nucleotidase activities in mouse lymphocytes

Adenosine 5'-triphosphate (ATP) released during inflammation presents proinflammatory properties. Adenosine, produced by catabolism of ATP, is an anti-inflammatory compound. Considering the role of ATP and adenosine in inflammation and the importance of ectonucleotidases in the maintenance of their extracellular levels, we investigated the effect of a selective agonist of the adenosine A(2A) receptor (CGS-21680) on ectonucleotidase activities and gene expression patterns in lymphocytes from mice submitted to an endotoxemia model. Animals were injected intraperitoneally with 12mg/kg Lipopolyssacharide (LPS) and/or 0.5mg/kg CGS-21680 or saline. Nucleotidase activities were determined in lymphocytes from mesenteric lymph nodes and analysis of ectonucleotidase expression was carried out by a semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay. Exposure to endotoxemia promoted an increase in nucleotide hydrolysis. When CGS-21680 was administered concomitantly with LPS, this increase was prevented for ATP, adenosine 5'-monophosphate (AMP), and p-Nitrophenyl thymidine 5'-monophosphate (p-Nph-5'-TMP) hydrolysis. However, when CGS-21680 was administered 24h after LPS injection, the increase was not reversed. The expression pattern of ectonucleotidases was not altered between LPS and LPS plus CGS-21680 groups, indicating that the transcriptional control was not involved on the effect exerted for CGS-21680. These results showed an enhancement of extracellular nucleotide catabolism in lymphocytes after induction of endotoxemia, which was prevented, but not reversed by CGS-21680 administration. These findings suggest that the control of nucleotide and nucleoside levels exerted by CGS-21680 could contribute to the modulation of the inflammatory process promoted by adenosine A(2A) agonists.

Neonatal morphine exposure alters E-NTPDase activity and gene expression pattern in spinal cord and cerebral cortex of rats

The neonate opioid system has been frequently investigated, and studies have shown that exposure to drugs in early life can have implications for nervous system development. It has been proposed that adenosine is involved in opioid antinociception, and ATP is involved in central and peripheral mechanisms of nociception. Extracellular nucleotides can be hydrolyzed by E-NTPDases and ecto-5'nucleotidase, which present the functions of removing ATP and generating adenosine. In this study, we evaluated ATP, ADP, and AMP hydrolysis in synaptosomes from spinal cord and cerebral cortex of rats at postnatal day 16 after repeated morphine exposure in early life (postnatal day 8 to 14). Additionally, we evaluated E-NTPDase (1, 2 and 3) and ecto-5'nucleotidase gene expression by semi-quantitative RT-PCR analysis. We observed an increase in ATP hydrolysis in the cerebral cortex, and a decrease in ADP hydrolysis in spinal cord. Expression levels of E-NTPDase 1 decreased in cerebral cortex and increased in spinal cord. Our findings highlight the importance of the purinergic system in young rats submitted to repeated morphine exposure by showing that in the neonatal period such exposure is capable of affecting the control system for nucleotide levels, which can promote changes in modulation or transmission of painful stimuli.

Early temporal changes in ecto-nucleotidase activity after cortical stab injury in rat

During a variety of insults to the brain adenine nucleotides are released in large quantities from damaged cells, triggering multiple cellular responses to injury. Here, we evaluated changes in extracellular ATP, ADP and AMP hydrolysis at different times (0-24 hours) after unilateral cortical stab injury (CSI) in adult rats. Results demonstrated that 24 hours following CSI, ATP and ADP hydrolyzing activities were not significantly altered in injured cortex. Based on calculated V (ATP)/V (ADP) ratio it was concluded that ATP/ADP hydrolysis was primarily catalyzed by NTPDase1 enzyme form. In contrast, AMP hydrolysis, catalyzed by 5'-nucleotidase, was significantly reduced at least 4 hours following CSI. Kinetic analysis and Lineweaver-Burk transformation of the enzyme velocities obtained over the range of AMP concentrations (0.05-1.50 mM) revealed that inhibition of 5'-nucleotidase activity after CSI was of the uncompetitive type. Taken together our data suggest that injured tissue has reduced potential for extracellular metabolism of adenine nucleotides in early stages after CSI.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Immunolocalization of ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) in the rat forebrain

Immunohistochemical study was performed to determine distribution of ecto-nucleotide pyrophosphatase/phosphodiesterase1 (NPP1) in adult rat forebrain. The study revealed widespread distribution of NPP1 in rat forebrain, yet with regional differences in the expression pattern and abundance. Strong NPP1 immunoreaction was detected in pyramidal cell layer of cerebral cortex and hippocampus, and in the midline regions of hypothalamus and thalamus. In many immunopositive forebrain areas, NPP1 was mainly localized at neuronal cell bodies. However, prominent immunoreaction was also detected at ependymal cells, tanycytes, endothelial cells of the capillaries and cells of the choroid plexus, suggesting that NPP1 could be involved in some highly specialized transport process.

Apyrase and 5'-nucleotidase activities in synaptosomes from the cerebral cortex of rats experimentally demyelinated with ethidium bromide and treated with interferon-beta

Apyrase and 5'-nucleotidase activities were analyzed in an ethidium bromide (EB) demyelinating model associated with interferon-beta (IFN-beta). The animals were divided in groups: I, control (saline); II, saline and IFN-beta; III, EB and IV, EB and IFN-beta. After 7, 15 and 30 days the animals (n = 5) were sacrificed and the cerebral cortex was removed for synaptosome preparation and enzymatic assays. Apyrase activity using ATP as substrate increased in groups II, III and IV (P < 0.001) after 7 days and in groups III and IV (P < 0.001) after 15 days. Using ADP as substrate, an activation of this enzyme was observed in group III (P < 0.05) after seven and 15 days. The 5'-nucleotidase activity increased in group III (P < 0.05) after 7 days and in groups II, III and IV (P < 0.001) after 15 days. After 30 days treatment, no significant alteration was observed in enzyme activities. Results showed that apyrase and 5'-nucleotidase activities are altered in demyelination events and that IFN-beta was able to regulate the adenine nucleotide hydrolysis.