5′-Nucleotidase in the Nervous System

Convective-diffusive mass transfer of agonist and the intracellular calcium response of endothelial cell

Endothelial cell layer regulates several crucial physiological processes of the vascular system. The mechanism of the response of this cell layer to the flow of surrounding fluid is still largely unclear. In the present article, a comparison of the available experimental results for the intracellular calcium ion concentration and theoretical results for the extra-cellular ATP concentration obtained using a convective-diffusive mass transfer model, has been made which supports the mass transfer model for the endothelial cell response to the fluid flow. The experimental results are in excellent agreement with the calculated values assuming the effect of ATP concentration alone.

Immunohistological Determination of Ecto-nucleoside Triphosphate Diphosphohydrolase1 (NTPDase1) and 5′-nucleotidase in Rat Hippocampus Reveals Overlapping Distribution

Distribution of two enzymes involved in the ectonucleotidase enzyme chain, ecto-nucleoside triphosphate diphosphohydrolase1 (NTPDase1) and ecto-5'-nucleotidase, was assessed by immunohistochemistry in the rat hippocampus. Obtained results have shown co-expression of the enzymes in the hippocampal region, as well as wide and strikingly similar cellular distribution. Both enzymes were expressed at the surface of pyramidal neurons in the CA1 and CA2 sections, while cells in the CA3 section were faintly stained. The granule cell layer of the dentate gyrus was moderately stained for NTPDase1, as well as for ecto-5'-nucleotidase. Glial association for ecto-5'-nucleotidase was also observed, and fiber tracts were intensively stained for both enzymes. This is the first comparative study of NTPDase1 and ecto-5'-nucleotidase distribution in the rat hippocampus. Obtained results suggest that the broad overlapping distribution of these enzymes in neurons and glial cells reflects the functional importance of ectonucleotidase actions in the nervous system.

A CUB-serine protease in the olfactory organ of the spiny lobster Panulirus argus

csp, a gene encoding a protein with high sequence identity to trypsinlike serine protease and CUB domains, was identified from a cDNA library from the olfactory organ (antennular lateral flagellum) of the spiny lobster Panulirus argus. The full-length cDNA sequence of csp is 1801 bp, encoding a protein of 50.25 kD, with three domains: signal peptide, trypsinlike serine protease, and CUB (named for a class of compounds including Complement subcomponents Clr/Cls, Uegf, and Bone morphogenic protein-1). RT-PCR, Northern blots, and immunoblots showed that csp is predominantly expressed in the lateral flagellum and eyestalk. Immunocytochemistry showed that Csp is present in olfactory (aesthetasc) sensilla around auxiliary cells (glia that surround the inner dendrites of olfactory receptor neurons, ORNs) and ORN outer dendrites. We propose that Csp is expressed and secreted by auxiliary cells, associates with ORN cell membranes or extracellular matrix via the CUB domain, and has trypsinlike activity. In the eyestalk, Csp is associated with cells surrounding axons between neuropils of the eyestalk ganglia. Possible functions in the olfactory organ and eyestalk are discussed. To our knowledge, this is the first report from any olfactory system of a gene encoding a protein with serine protease and CUB domains.

5'-Nucleotidase activity of mossy fibers in the dentate gyrus of normal and epileptic rats

Sprouting of mossy fibers in the hippocampus of rats that underwent limbic epileptogenesis by amygdala kindling or kainate injection was studied at the light microscopic and ultrastructural levels by cytochemical demonstration of the enzyme 5'-nucleotidase. This adenosine-producing ectoenzyme has previously been shown to characterize malleable terminals during brain development and lesion-induced synaptogenesis, but to be otherwise associated with glial membranes. At the light microscopic level, kainate-treated but not control or kindled rats showed 5'-nucleotidase activity in the CA3 region and in the inner molecular layer of the dentate gyrus. At the ultrastructural level, in control animals, the synapses of the molecular and granular layers were enzyme negative. Only some mossy fiber boutons of the dentate hilus exhibited 5'-nucleotidase activity. In epileptic rats, synaptic labeling within the hilus appeared more intense. Moreover, 5'-nucleotidase-containing terminals within the inner molecular layer, presumably ectopic mossy fiber boutons, were found in both kindled and kainate-treated rats. It is concluded that, in both the normal and epileptic hippocampus, 5'-nucleotidase is associated with axons capable of a plastic sprouting response. The synaptic enzyme may attenuate the glutamatergic transmission of mossy fibers, in particular of the aberrant mossy fibers in epileptic rats, by producing the inhibitory neuromodulator adenosine. Alternatively, 5'-nucleotidase may influence synapse formation by its putative non-enzymatic, adhesive functions.

Expression of purine metabolism-related enzymes by microglial cells in the developing rat brain

The nucleoside triphosphatase (NTPase), nucleoside diphosphatase (NDPase), 5'-nucleotidase (5'-Nase), and purine nucleoside phosphorylase (PNPase) activity has been examined in the cerebral cortex, subcortical white matter, and hippocampus from embryonic day (E)16 to postnatal day (P)18. Microglia display all four purine-related enzymatic activities, but the expression of these enzymatic activities differed depending on the distinct microglial typologies observed during brain development. We have identified three main morphologic typologies during the process of microglial differentiation: ameboid microglia (parenchymatic precursors), primitive ramified microglia (intermediate forms), and resting microglia (differentiated cells). Ameboid microglia, which were encountered from E16 to P12, displayed the four enzymatic activities. However, some ameboid microglial cells lacked 5'-Nase activity in gray matter, and some were PNPase-negative in both gray and white matter. Primitive ramified microglia were already observed in the embryonic period but mostly distributed during the first 2 postnatal weeks. These cells expressed NTPase, NDPase, 5'-Nase, and PNPase. Similar to ameboid microglia, we found primitive ramified microglia lacking the 5'-Nase and PNPase activities. Resting microglia, which were mostly distinguishable from the third postnatal week, expressed NTPase and NDPase, but they lacked or displayed very low levels of 5'-Nase activity, and only a subpopulation of resting microglia was PNPase-positive. Apart from cells of the microglial lineage, GFAP-positive astrocytes and radial glia cells were also labeled by the PNPase histochemistry. As shown by our results, the differentiation process from cell precursors into mature microglia is accompanied by changes in the expression of purine-related enzymes. We suggest that the enzymatic profile and levels of the different purine-related enzymes may depend not only on the differentiation stage but also on the nature of the cells. The use of purine-related histoenzymatic techniques as a microglial markers and the possible involvement of microglia in the control of extracellular purine levels during development are also discussed.

Immature chemodifferentiation of Purkinje cell synapses revealed by 5'-nucleotidase ecto-enzyme activity in the cerebellum of the reeler mouse

During postnatal development of the rodent cerebellum, a transient enzyme activity of ecto-5'-nucleotidase has been shown in the asymmetrical synapses of Purkinje cells. The alterations of the afferent circuitry and microenvironment of the ectopic Purkinje cells present in the cerebellum of the reeler mutant mouse could enlighten parameters that influence the synaptic 5'-nucleotidase activity of these cells. Ecto-enzyme cytochemistry reveals intense 5'-nucleotidase activity in 43% of synapses of the Purkinje cells throughout the cortex and the core of the reeler cerebellar vermis, although the molecular layer displays large areas with less than 1% of labelled synapses. However, enzymatic labelling is found in considerably more Purkinje cells synapses (73%) throughout the granular layer and the subcortical mass. Climbing fiber synapses of monoinnervated Purkinje cells are labelled by 5'-nucleotidase activity in the molecular layer, as well as asymmetrical synapses made on the subjacent ectopic Purkinje cells by the multiple climbing fibers and by the heterologous afferences. The non-innervated dendritic spines of these cells are also labelled, suggesting that 5'-nucleotidase activity at postsynaptic sites of reeler Purkinje cells does not depend on the presynaptic innervation. Rather, 5'-nucleotidase enzyme activity is enhanced at theses sites when the Purkinje cells have not achieved chemodifferentiation but have conserved immature wiring, i.e., low parallel fiber and multiple climbing fiber inputs.

Focal cerebral ischemia enhances glial expression of ecto-5'-nucleotidase

The effect of ischemia on the reactive expression of ecto-5'-nucleotidase in rat brain was studied 6 h and 1, 2 and 7 days after permanent middle cerebral artery occlusion (MCAO). The distribution of 5'-nucleotidase in the infarcted brain was compared to markers for astrocytes (glial fibrillary acidic protein (GFAP)) and microglia (complement receptor type 3, antibody OX42) using histological staining or immunohistochemistry. 5'-Nucleotidase could be associated with reactive astrocytes by immunohistochemistry and with reactive microglia by enzyme histochemistry. In the untreated control 5'-nucleotidase was associated with astrocytes only in the hippocampus and the submeningeal space. After ischemia the enzyme was expressed on reactive astrocytes in the tissue surrounding the volume of infarction. Individual reactive astrocytes were observed 6 h after MCAO and the astrocytic expression became continuously enhanced during the following days. An enzyme histochemical analysis of 5'-nucleotidase activity revealed a postischemic increase in reaction product around the infarcted tissue. Seven days after MCAO a discrete band (0.2-0.4 mm) of reaction product characterized the rim of the infarcted area. This band of activity of 5'-nucleotidase colocalized with a band of immunoreactivity for OX42, indicative of an intense accumulation of 5'-nucleotidase expressing microglia. Our results suggest that ischemia following permanent MCAO results in an upregulation of the capacity for the hydrolysis of nucleotides within the tissue adjacent to the infarcted volume. Nucleotides released from the damaged cells can be hydrolyzed and the adenosine eventually formed may exert neuroprotective functions limiting the extent of damage.

5'-nucleotidase enzyme cytochemistry as a tool for revealing activated glial cells and malleable synapses in CNS development and regeneration

The demonstration of 5'-nucleotidase in neural tissue is achieved at both the light and electron microscopic levels by means of an enzyme cytochemical lead method, which is specific, sensitive and fast. By its activity this adenosine-producing ecto-enzyme (EC 3.1.3.5) outlines cellular surface membranes at the ultrastructural level. It is classically known as a marker of myelin and of astrocytes as well as (activated) microglial cells in the mature nervous system. In recent years, we discovered that 5'-nucleotidase is transiently active within synaptic clefts under conditions of development and regeneration. The enzyme is also seen at terminals in the mature retina and olfactory bulb, where spontaneous synaptic turnover occurs at adulthood. Thus, 5'-nucleotidase cytochemistry is useful in revealing sites of glial reactions and synaptic plasticity in CNS development and repair. It is assumed that the molecule affects terminal formation and cell motility due to dual functions in adenosine production and cell adhesion. Finally, at the light microscopic level, 5'-nucleotidase activity displays a dense neuropil staining which identifies topographic sub-units of certain parts of the nervous system, such as the striosomes of the basal ganglia, ocular dominance columns of the visual cortex and parasagittal bands of the cerebellum.

Development of 5'-nucleotidase staining in the olfactory bulbs of normal and naris-occluded rats

The distribution of the adenosine-producing ecto-enzyme 5'-nucleotidase was investigated histochemically in the developing rat olfactory bulb. Rat pups underwent either unilateral surgical occlusion of the right external naris or sham surgery on postnatal day 1. At 10, 20, or 30 days postpartum, horizontal sections of the olfactory bulb were reacted histochemically to reveal the locus and intensity of 5'-nucleotidase activity. Relative staining levels were determined by optical densitometry in standardized bulb regions. A marked, age-related increase in staining density was observed. Reaction product was found primarily in neuropil areas. The P10 and P20 control animals did not exhibit right/left differences in bulb staining; however, some laterality was observed in P30 animals. Inter-glomerular and regional variations were observed throughout the developmental period, including (1) differences between neighboring glomeruli; (2) a gradient in the dorsal-ventral axis of the bulb; and (3) a higher staining density in the medial-caudal portion of the bulb. In subjects with occluded nares, asymmetries in right/left bulb 5'-nucleotidase staining patterns were detected throughout development. Bulbs ipsilateral to the blocked nares exhibited increased staining density, suggesting that the procedure enhanced enzymatic activity. Understanding these variations in 5'-nucleotidase staining may be important for a complete understanding of the mechanisms of olfactory bulb maturation and may give insight into the possible role of this enzyme in synaptic malleability during nervous system development and regeneration.

Biochemistry, localization and functional roles of ecto-nucleotidases in the nervous system

Nucleotides such as ATP, ADP, UTP or the diadenosine polyphosphates and possibly even NAD+ are extracellular signaling substances in the brain and in other tissues. Enzymes located on the cell surface catalyze the hydrolysis of these compounds and thus limit their spatio-temporal activity. As a final hydrolysis product they generate the nucleoside and phosphate. The paper discusses the biochemical properties, cellular localization and functional properties of surface-located enzymes that hydrolyse nucleotides released from nervous tissue. This is preceded by a brief discussion of nucleotide receptors, cellular storage and mechanisms of nucleotide release. In nervous tissue nucleoside 5'-triphosphates are hydrolysed by ecto-ATP-diphosphohydrolase and possibly in addition also by ecto-nucleoside triphosphatase and ecto-nucleoside diphosphatase. The molecular identity of the ATP-diphosphohydrolase has now been revealed. The hydrolysis of nucleoside 5'-monophosphates is catalysed by 5'-nucleotidase whose biochemical properties and molecular structure have been studied in detail. Little is known about the molecular properties of the diadenosine polyphosphatases. Surface located enzymes for the extracellular hydrolysis of NAD+ and also ecto-protein kinases are discussed briefly. The cellular localization of the ecto-nucleotidases is only partly defined. Whereas in adult mammalian brain activity for hydrolysis of ATP and ADP may be associated with nerve cells or glial cells 5'-nucleotidase appears to have a preferential glial allocation in the adult mammal. The extracellular hydrolysis of the nucleotides is of functional importance not only during synaptic transmission where it functions in signal elimination. It plays a crucial role also for the survival and differentiation of neural cells in vitro and presumably during neuronal development in vivo.

5'-nucleotidase activity as a synaptic marker of parasagittal compartmentation in the mouse cerebellum

In the molecular layer of the mouse cerebellum, the histochemical activity of the adenosine-producing ectoenzyme 5'-nucleotidase discloses a parasagittal pattern of alternating enzyme-rich and enzyme-poor bands. In the rat, 5'-nucleotidase activity transiently labels cerebellar synapses during postnatal development and shifts later on towards an exclusive glial location in the molecular layer. We therefore asked whether different ultrastructural expression of 5'-nucleotidase would account for the light microscopic pattern seen in the adult mouse cerebellum. Using an enzyme cytochemical method, we localized 5'-nucleotidase activity on the glial cells and at the main types of asymmetrical synapses in the developing and mature cerebellum of the mouse. The percentage of labelled synapses increased until adulthood within the 5'-nucleotidase-positive bands. Here, the vast majority (86%) of the synapses were labelled against only 27% within the negative bands in the adult. Thus, 5'-nucleotidase appears as a marker of glia and of Purkinje cell synapses across cerebellar compartments. Changes in purinergic neuromodulation and/or cell adhesion mediated by 5'-nucleotidase across bands might participate in the functional differentiation of the cerebellar parasagittal subsets.

Purinergic inhibition of neurotransmitter release in the central nervous system

Neurotransmitter release and the role of adenosine in its regulation has been investigated for more than twenty years, and it is now widely accepted that adenosine tonically inhibits the release of excitatory neurotransmitters. This effect of adenosine is operated by an A1 adenosine receptor. Since activation of this receptor could inhibit Ca2+ conductance, increase K+ conductance, inhibit adenylate cyclase or phospholipase C, it is not clear if there is only one mechanism or several mechanisms operated by adenosine to inhibit neurotransmitter release, and in that case, what is the relative importance of each mechanism. The mechanism by which adenosine inhibits evoked synchronous transmitter release might be different from that used by the nucleoside to inhibit spontaneous asynchronous release. In some systems adenosine triphosphate per se acts like adenosine and inhibits neurotransmitter release. However, in most cases the inhibitory effect of this adenine nucleotide depends upon its hydrolysis into adenosine by a cascade of ectoenzymes, the last step being mediated by ecto-5'-nucleotidase.

Species-specific patterns of glycoprotein expression in the developing rodent caudoputamen: association of 5'-nucleotidase activity with dopamine islands and striosomes in rat, but with extrastriosomal matrix in mouse

The glycoprotein 5'-nucleotidase is a cell surface phosphatase and represents a new marker for striosomes in the adult rat caudoputamen. We report here on its developmental expression in the rat and mouse striatum, and show an unexpected converse 5'-nucleotidase chemoarchitecture of the caudoputamen in these closely related species. In the rat, 5'-nucleotidase activity was first visible as neuropil staining in tyrosine hydroxylase-positive dopamine islands of the midstriatum on postnatal day 1, and by the end of the first postnatal week, 5'-nucleotidase-positive dopamine islands also appeared rostrally. This compartmental pattern persisted thereafter, so that in adult animals, in all but the caudal caudoputamen, zones of enhanced 5'-nucleotidase staining were restricted to calbindin-D28k-poor striosomes. Weak 5'-nucleotidase activity also emerged in the matrix. In striking contrast, in the mouse striatum, enhanced 5'-nucleotidase activity was preferentially associated with extrastriosomal tissue. Enzymatic reaction first appeared on embryonic day 18, and developed over the first postnatal week into a mosaic pattern in which the matrix was stained but the dopamine islands were unstained. The matrix staining itself was heterogeneous. After the second postnatal week, most of the caudoputamen was stained, and in adult mice only rostral striosomes expressed low 5'-nucleotidase activity. We conclude that in rats, 5'-nucleotidase represents one of the few substances that maintains a preferential dopamine island/striosome distribution during striatal development. In mice, 5'-nucleotidase activity is expressed preferentially in the matrix during development, and its compartmental pattern is gradually lost with maturation, except very rostrally. These findings do not suggest an instructive role of the enzyme in striatal compartment formation in either species, but do suggest the possibility that 5'-nucleotidase contributes to the differentiation of striatal compartments during development.

Cytochemical redistribution of 5'-nucleotidase in the developing cat visual cortex

The adenosine-producing ectoenzyme 5'-nucleotidase has recently been shown to undergo a marked redistribution during development of the cat visual cortex and to be involved in the remodelling of ocular dominance columns (Schoen et al., J. Comp. Neurol., 296, 379-392, 1990). Using an enzyme-cytochemical technique, we now investigate the developmental redistribution of 5'-nucleotidase activity in area 17 of kittens at the ultrastructural level. Between postnatal days 35 and 42, when 5'-nucleotidase is concentrated in layer IV, enzyme reaction product occupies the clefts of asymmetrical synapses within the neuropil. During later development (9th and 13th postnatal weeks), when 5'-nucleotidase spreads over all cortical laminae, the enzyme disappears from its synaptic localization and becomes increasingly associated with astrocytic membranes. The transient appearance of 5'-nucleotidase at synapses parallels the time-course and laminar profile of the synaptic remodelling which takes place during the critical period of visual cortex development. This suggests that synapse-bound 5'-nucleotidase activity plays a role in synaptic malleability, whereas its later association with glial profiles is likely to reflect other functions of the enzyme.

5'-nucleotidase: a new marker for striosomal organization in the rat caudoputamen

The distribution of the adenosine-producing ectoenzyme 5'-nucleotidase was studied by means of a histochemical lead technique in the caudoputamen of normal adult rats and of rats in which injections either of 6-hydroxydopamine in the medial forebrain bundle or of ibotenic acid in the caudoputamen had been made 1-3 weeks previously. The patterns of striatal 5'-nucleotidase activity in these animals were compared in serial sections to the patterns of calbindin-D28k immunoreactivity and of 3H-naloxone ligand binding, which respectively mark the known matrix and striosome (patch) compartments of the caudoputamen. In the normal rats, 5'-nucleotidase activity was differentially concentrated in striosomes, where it produced a dense staining of the neuropil. The enzymatic staining followed a striosomal distribution in all but the caudal caudoputamen. Within the striatal matrix, 5'-nucleotidase staining also observed a lateromedial density gradient. Depletion of the dopamine-containing nigrostriatal innervation of the caudoputamen with 6-hydroxydopamine did not alter the striosomal selectivity of 5'-nucleotidase activity. Destruction of intrastriatal neurons by ibotenic acid led to a strongly 5'-nucleotidase-positive gliosis within the resulting necrotic region. Elsewhere in the caudoputamen, the enzyme's striosomal distribution was not detectably altered. We conclude that 5'-nucleotidase histochemistry provides an advantageous tool for detecting the striosomal architecture of the rat's caudoputamen. Moreover, 5'-nucleotidase is prominently associated with glial membranes in the central nervous system, so that the concentration of this enzyme in striosomes could mark these as sites of selective glial populations within striatum. These properties and actions of 5'-nucleotidase in purinergic neurotransmission and in neuroadhesion may contribute to the specialized functions of striosomes and matrix.

Ecto-5'-nucleotidase is associated with cholinergic nerve terminals in the hippocampus but not in the cerebral cortex of the rat

The extracellular catabolism of exogenously added AMP was studied in immunopurified cholinergic nerve terminals and in slices of the hippocampus and cerebral cortex of the rat. AMP (10 microM) was catabolized into adenosine and inosine in hippocampal cholinergic nerve terminals and in hippocampal slices, as well as in cortical slices. IMP formation from extracellular AMP was not detected. alpha, beta-Methylene ADP (100 microM) inhibited almost completely the extracellular catabolism of AMP in these preparations. The relative rate of catabolism of AMP was greater in hippocampal slices than in cortical slices. AMP was virtually not catabolized when added to immunopurified cortical cholinergic nerve terminals, although ATP could be catabolized extracellularly under identical conditions. The comparison of the relative rates of catabolism of exogenously added AMP, calculated from the amount of AMP catabolized after 5 min, in hippocampal cholinergic nerve terminals and in hippocampal slices revealed a nearly 50-fold enrichment in the specific activity of ecto-5'-nucleotidase upon immunopurification of the cholinergic nerve terminals from the hippocampus. The results suggest that there is a regional variation in the subcellular distribution of ecto-5'-nucleotidase activity in the rat brain, the ecto-5'-nucleotidase in the hippocampus being closely associated with the cholinergic nerve terminals, whereas in the cerebral cortex ecto-5'-nucleotidase activity seems to be located preferentially outside the cholinergic nerve terminals.

Adenosine 5'-monophosphate transport across the membrane of synaptosomes and myelin

Synaptosome-enriched preparations from rat and guinea pig brain tissue vigorously accumulated [3H]-adenosine 5'-monophosphate ([3H]AMP). When the accumulation of [3H]AMP was determined using incubation periods of 30 s or less, high concentrations of adenosine, dipyridamole and soluflazine did not inhibit the accumulation of label appreciably. The accumulation of [3H]AMP was saturable, temperature-dependent, osmotic-sensitive and exhibited structural specificity. Based on the kinetics of uptake by different subcellular fractions, and the inhibitory effects of other nucleotides, the uptake of AMP appeared to be mediated by three saturable systems with Kt values of approximately 0.2, 6, and 100 microM. The transport system with the highest affinity for AMP was selectively inhibited by guanosine 5'-monophosphate, and its Vmax was several fold higher in a myelin-enriched fraction than in synaptosome-enriched fractions. The transport system with the Kt approximately 6 microM was selectively inhibited by alpha, beta-methylene adenosine diphosphate, and its Vmax was several times higher in a fraction enriched in high-density synaptosomes than in fractions enriched in low-density synaptosomes or myelin. Both of these transport systems were potently inhibited by ATP and ADP. Nucleotides that were either weak or inactive as inhibitors of AMP transport included 3'-AMP, cyclic AMP, guanosine 5'-diphosphate, and the 5'-mononucleotides of cytosine, inosine, and uridine. GTP consistently enhanced uptake at concentrations greater than or equal to 1 microM. The transport of AMP was not Na(+)-dependent and was not inhibited by membrane depolarization. This transport system may mediate the release of AMP for subsequent conversion to adenosine extracellularly.

Adenosine receptors in post-mortem human brain

1. Adenosine A2-like binding sites were characterized in post-mortem human brain membranes by examining several compounds for their ability to displace [3H]-CGS 21680 (2[p-(2 carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamido adenosine) binding. 2. Two A2-like binding sites were identified in the striatum. 3. The more abundant striatal site was similar to the A2a receptor previously described in rat striatum, both in its pharmacological profile and striatal localization. 4. The less abundant striatal site had a pharmacological profile similar to that of the binding site characterized in the other brain regions examined. This was intermediate in character between A1 and A2 and may represent another adenosine receptor subtype. 5. The co-purification of [3H]-CGS 21680 binding during immunoisolation of human striatal cholinergic membranes was used to assess the possible cholinergic localization of A2-like binding sites in the human striatum. Only the more abundant striatal site co-purified with cholinergic membranes. This suggests that this A2a-like site is present on cholinergic neurones in the human striatum.

5'-Nucleotidase immunoreactivity of perineuronal microglia responding to rat facial nerve axotomy

The ecto-enzyme 5'-nucleotidase was localized immunocytochemically in the axotomized rat facial nucleus. As revealed by the monoclonal antibody 5N4-2,5'-nucleotidase immunoreactivity markedly increased on perineuronal microglia during the first week following axotomy, and gradually disappeared from these cells by the end of the third post-operative week. Interestingly, parenchymal microglia were not or only weakly stained. These findings indicate that 5'-nucleotidase 5N4-2-immunoreactivity may serve as a marker for perineuronal microglia, a population of satellite glial cells that appear to be actively engaged in lesion-induced synaptic changes during regeneration.

Metabolism of extracellular adenine nucleotides by cultured rat brain astrocytes

Intact astrocytes cultured from newborn rat cerebral cortex rapidly converted extracellular ATP to ADP. The ATPase responsible was apparently not saturated, even at 750 microM ATP. In contrast, the conversion of ADP to AMP was slow, and the reaction was limiting for the subsequent dephosphorylation process. Adenosine formation was the only fate for AMP. The reaction was catalyzed by 5'-nucleotidase with an apparent Km of 55 microM for AMP and appeared to be inhibited by high concentrations of ATP and ADP. Astrocytes were able to take up adenosine with an apparent Km value of 45 microM. Uptake was inhibited by dipyridamole but not by anti-5'-nucleotidase IgG. The results support the proposal that astrocytes play a role in modulating synaptic events involving ATP and adenosine.

Soluble 5'-nucleotidase activities in rat brain

5'-Nucleotidase activity was assayed in 105,000-g supernatants from rat brain by following conversion of [3H]AMP into adenosine. The effect of ATP on this process was complex and suggested the presence of at least two soluble 5'-nucleotidase activities: one inhibited by ATP and another activated by ATP. The relative proportions of these activities differed considerably among brain regions. Activity changes induced by hypothyroidism also suggested that these activities may be regulated independently. These findings may have consequences for the regional regulation of adenosine formation in the brain.

Ocular dominance plasticity and developmental changes of 5'-nucleotidase distributions in the kitten visual cortex

The distribution of the adenosine-producing ecto-enzyme 5'-nucleotidase was investigated histochemically in the visual cortex of normally reared and monocularly deprived kittens and cats. In normally reared kittens aged between 11 to 44 days, 5'-nucleotidase activity formed a band of intense neuropil staining throughout cortical layer IV of areas 17 and 18. The other layers were almost devoid of reaction product. Between the 4th and 6th week, this band had a patchy appearance in area 17, the center-to-center spacing of 5'-nucleotidase patches being approximately 1 mm. Monocular enucleation accentuated these patches of enhanced 5'-nucleotidase activity or made them reappear at developmental stages at which they had normally faded. Simultaneous visualization of ocular dominance columns by transneuronal transport of intraocularly injected 3H-proline showed that the patches of enhanced 5'-nucleotidase activity coincided with the territories of afferents from the intact eye. With increasing age and normal visual development, the patches disappeared and 5'-nucleotidase activity spread to the supra- and infragranular layers. The adult pattern was characterized by dense staining of all cortical laminae in both areas 17 and 18 and was established at about 8 weeks of age. At approximately 7 weeks of age, when the patches in layer IV had disappeared in the course of normal development, monocular enucleation caused a reappearance of the discontinuous pattern of 5'-nucleotidase activity in layer IV. These results reveal a close relation between the distribution of 5'-nucleotidase and the time course of the developmental phase during which the visual cortex is susceptible to experience-dependent alterations. As suggested by the correlation between sites of enzyme activity and eye dominance columns, the expression of 5'-nucleotidase patches in layer IV appears to be associated with the remodelling of ocular dominance territories that occurs both in normal development and after manipulation of afferent retinal input. Thus, 5'-nucleotidase is likely to serve a function in activity-dependent modifications of cortical circuitry. Moreover, 5'-nucleotidase activity is the only endogenous marker known to date that exhibits a columnar pattern in cat visual cortex.

ATP release, adenosine formation, and modulation of dynorphin and glutamic acid release by adenosine analogues in rat hippocampal mossy fiber synaptosomes

Using a hippocampal subcellular fraction enriched in mossy fiber synaptosomes, evidence was obtained indicating that adenosine derived from a presynaptic pool of ATP may modulate the release of prodynorphin-derived peptides. and glutamic acid from mossy fiber terminals. Synaptosomal ATP was released in a Ca2+-dependent manner by K+-induced depolarization. The rapid hydrolysis of extracellular [14C]ATP in the presence of intact mossy fiber synaptosomes resulted in the production of [14C]adenosine. Micromolar concentrations of a stable adenosine analogue, 2-chloroadenosine, inhibited the K+-stimulated release of both dynorphin B and dynorphin A(1-8). 2-Chloroadenosine failed to suppress the evoked release of glutamic acid, measured in these same superfusates, unless the mossy fiber synaptosomes were pretreated with D-aspartic acid to deplete the cytosolic, Ca2+-independent, pool of this acidic amino acid. In synaptosomes pretreated in this manner, release of the remaining Ca2+-dependent pool of glutamic acid was significantly inhibited by NiCl2, 2-chloroadenosine, 5'-N-ethylcarboxamidoadenosine, cyclohexyladenosine, and R(-)-N6(2-phenylisopropyl)adenosine, but not by ATP. 2-Chloroadenosine-induced inhibition was reversed when the external CaCl2 concentration was raised from 1.8 mM to 6 mM. 8-Phenyltheophylline, an adenosine receptor antagonist, effectively blocked the inhibitory effects of 2-chloroadenosine on mossy fiber synaptosomes and significantly enhanced the K+-evoked release of both glutamic acid and dynorphin A(1-8) when added alone to the superfusion medium. These results support the proposition that depolarized hippocampal mossy fiber synaptosomes release endogenous ATP and are capable of forming adenosine from extracellular ATP, and that endogenous adenosine may act at a presynaptic site to inhibit the further release of glutamic acid and the prodynorphin-derived peptides.

5'-Nucleotidase activity in the pineal organ of the pike. An electron-microscopic study

To date, it is still unknown whether the metabolism of purine nucleotides and nucleosides plays an important role in the pineal organ of lower vertebrates. We have therefore investigated the sites of 5'-nucleotidase activity in the pineal organ of the pike (Esox lucius L.). Various ultracytochemical procedures were used. An intense ecto-5'-nucleotidase activity was characteristic of the entire plasma membrane of the phototransducers (cone-like and modified photoreceptor elements) and the interstitial cells, with exception of the portions facing the basal lamina of the pericapillary spaces. Additionally, intracellular sites of activity were also visualized in the inner segment and the pedicle of the phototransducers. Most of the intracellular deposits were apparently cytosolic and only few seemed to be associated with the membrane of the clear "synaptic" vesicles of the pedicle. Phagocytotic cells in the pineal lumen also showed a strong enzymatic activity on the outer surface of their plasmalemma (in ectoposition). This was apparently not the case for the cell types of the tissues surrounding the pineal vesicle. The present study emphasizes the importance of the occurrence and metabolism of purine nucleotides and nucleosides in a photoreceptive pineal organ.

ATP release from affinity-purified rat cholinergic nerve terminals

Cholinergic nerve terminals were affinity purified from rat caudate nucleus. On stimulation with both 22.6 mM KCl and 50 microM veratridine, ATP was released in a Ca2+-dependent manner. The molar ratio of released acetylcholine to ATP (9:1) was closer to that found in isolated cholinergic vesicles (7:1) than whole terminals (3:1). Extracellular [14C]ATP was rapidly metabolized by these terminals to adenosine and inosine via ectonucleotidases. The terminals had a saturable, high-affinity uptake mechanism for adenosine (Km = 16.6 microM). Veratridine stimulation also caused the Ca2+-dependent release of nucleosides in a dipyridamole-sensitive manner. Both theophylline treatment and inhibition of extracellular ATP breakdown resulted in increased ATP and nucleoside release. Extracellular adenosine was shown to inhibit acetylcholine release, probably via the A1 receptor. The role of extracellular purines at the cholinergic nerve terminal is discussed.

Light and electron microscopical immunocytochemistry of 5'-nucleotidase in rat cerebellum

5'-Nucleotidase in nervous tissue has so far not been localised at the ultrastructural level using immunocytochemical techniques. We have now applied monoclonal antibodies and a polyclonal antiserum raised against this ecto-enzyme and describe the distribution of 5'-nucleotidase antigenicity in rat cerebellum both at the light and electron microscopic levels. Within all cerebellar layers, 5'-nucleotidase immunoreactivity was found on plasma membranes of glial elements, i.e. Bergmann glial cell processes crossing the molecular layer, astrocytic end-feet around blood vessels and glial cell extensions surrounding single Purkinje cells. In the granular layer, 5'-nucleotidase immunoreactivity was present on glial membranes interposed between granule cells. Neuronal cells or processes were devoid of immunoreactivity. The immunocytochemical results were compared with conventional 5'-nucleotidase histochemistry. Both techniques showed the same ecto-localisation of the enzyme and favour the view of 5'-nucleotidase being predominantly situated at glial plasma membranes.