Persistent increase in ecto‑5'‑nucleotidase activity from encephala of adult zebrafish exposed to ethanol during early development

Prenatal alcohol exposure causes alterations to the brain and can lead to numerous cognitive and behavioral outcomes. Long-lasting effects of early ethanol exposure have been registered in glutamatergic and dopaminergic systems. The purinergic system has been registered as an additional target of ethanol exposure. The objective of this research was to evaluate if the ecto‑5'‑nucleotidase and adenosine deaminase activities and gene expression of adult zebrafish exposed to 1% ethanol during early development could be part of the long-lasting targets of ethanol. Zebrafish embryos were exposed to 1% ethanol in two distinct developmental phases: gastrula/segmentation (5-24 h post-fertilization) or pharyngula (24-48 h post-fertilization). At the end of three months, after checking for morphological outcomes, the evaluation of enzymatic activity and gene expression was performed. Exposure to ethanol did not promote gross morphological defects; however, a significant decrease in the body length was observed (17% in the gastrula and 22% in the pharyngula stage, p < 0.0001). Ethanol exposure during the gastrula/segmentation stage promoted an increase in ecto‑5'‑nucleotidase activity (39.5%) when compared to the control/saline group (p < 0.0001). The ecto‑5'‑nucleotidase gene expression and the deamination of adenosine exerted by ecto and cytosolic adenosine deaminase were not affected by exposure to ethanol in both developmental stages. HPLC experiments did not identify differences in adenosine concentration on the whole encephala of adult animals exposed to ethanol during the gastrula stage or on control animals (p > 0.05). Although the mechanism underlying these findings requires further investigation, these results indicate that ethanol exposure during restricted periods of brain development can have long-term consequences on ecto‑5'‑nucleotidase activity, which could have an impact on subtle sequels of ethanol early exposure.

Contributions from extracellular sources of adenosine to the ethanol toxicity in zebrafish larvae

The effects of ethanol exposure on extracellular adenosine sources in zebrafish were evaluated. In the acute treatment, the embryos were exposed to 2% ethanol on day 1 post-fertilization (dpf). In the chronic treatment, the exposure was continued for 2h/day up to 6 dpf. Ecto-5'-nucleotidase activity was assessed by colorimetric method and gene expression determined by RT-qPCR in 7 dpf zebrafish. Body length, ocular distance and surface area of the eyes were registered in animals acutely exposed to ethanol and pretreated with AOPCP (5-500 nM), an ecto-5'-nucleotidase inhibitor, or dipyridamole (10-100 μM), a blocker of nucleoside transport. Both ethanol exposures promoted increased ecto-5'-nucleotidase activity, impaired locomotion and morphology. Ecto-5'-nucleotidase expression was not affected. AOPCP promoted mild prevention of morphological defects caused by acute treatment, while dipyridamole worsened these defects. Early ethanol exposure altered adenosinergic tonus, especially through nucleoside transporters, contributing to morphological defects produced by ethanol in zebrafish.

Enhanced survival of lethally irradiated adenosine A3 receptor knockout mice. A role for hematopoietic growth factors?

Adenosine A3 receptor knockout (A3AR KO) mice and their wild-type (WT) counterparts were compared from the point of view of their abilities to survive exposures to lethal doses of γ-radiation belonging to the range of radiation doses inducing the bone marrow acute radiation syndrome. Parameters of cumulative 30-day survival (experiment using a midlethal radiation dose) or cumulative 11-day survival (experiment using an absolutely lethal radiation dose), and of mean survival time were evaluated. The values of A3AR KO mice always reflected their higher survival in comparison with WT ones, the P values being above the limit for statistical significance after the midlethal radiation dose and standing for statistical significance after the absolutely lethal radiation dose. This finding was considered surprising, taking into account the previously obtained findings on defects in numbers and functional properties of peripheral blood cells in A3AR KO mice. Therefore, previous hematological analyses of A3AR KO mice were supplemented in the present studies with determination of serum levels of the granulocyte colony-stimulating factor, erythropoietin, and thrombopoietin. Though distinct differences in these parameters were observed between A3AR KO and WT mice, none of them could explain the relatively high postirradiation survival of A3AR KO mice. Further studies on these mice comprising also those on other than hemopoietic tissues and organs can help to clarify their relative radioresistance.

Lack of adenosine A3 receptors causes defects in mouse peripheral blood parameters

The role of the adenosine A3 receptor in hematopoiesis was studied using adenosine A3 receptor knockout (A3AR KO) mice. Hematological parameters of peripheral blood and femoral bone marrow of irradiated and untreated A3AR KO mice and their wild-type (WT) counterparts were investigated. Irradiation of the mice served as a defined hematopoiesis-damaging means enabling us to evaluate contingent differences in the pattern of experimentally induced hematopoietic suppression between the A3AR KO mice and WT mice. Defects were observed in the counts and/or functional parameters of blood cells in the A3AR KO mice. These defects include statistically significantly lower values of blood neutrophil and monocyte counts, as well as those of mean erythrocyte volume, mean erythrocyte hemoglobin, blood platelet counts, mean platelet volume, and plateletcrit, and can be considered to bear evidence of the lack of a positive role played by the adenosine A3 receptor in the hematopoietic system. Statistically significantly increased values of the bone marrow parameters studied in A3AR KO mice (femoral bone marrow cellularity, granulocyte/macrophage progenitor cells, and erythrocyte progenitor cells) can probably be explained by compensatory mechanisms attempting to offset the disorders in the function of blood elements in these mice. The pattern of the radiation-induced hematopoietic suppression was very similar in A3AR KO mice and their WT counterparts.

Distribution of purinergic P2X receptors in the equine digit, cervical spinal cord and dorsal root ganglia

Purinergic pathways are considered important in pain transmission, and P2X receptors are a key part of this system which has received little attention in the horse. The aim of this study was to identify and characterise the distribution of P2X receptor subtypes in the equine digit and associated vasculature and nervous tissue, including peripheral nerves, dorsal root ganglia and cervical spinal cord, using PCR, Western blot analysis and immunohistochemistry. mRNA signal for most of the tested P2X receptor subunits (P2X1-5, 7) was detected in all sampled equine tissues, whereas P2X6 receptor subunit was predominantly expressed in the dorsal root ganglia and spinal cord. Western blot analysis validated the specificity of P2X1-3, 7 antibodies, and these were used in immunohistochemistry studies. P2X1-3, 7 receptor subunits were found in smooth muscle cells in the palmar digital artery and vein with the exception of the P2X3 subunit that was present only in the vein. However, endothelial cells in the palmar digital artery and vein were positive only for P2X2 and P2X3 receptor subunits. Neurons and nerve fibres in the peripheral and central nervous system were positive for P2X1-3 receptor subunits, whereas glial cells were positive for P2X7 and P2X1 and 2 receptor subunits. This previously unreported distribution of P2X subtypes may suggest important tissue specific roles in physiological and pathological processes.

Ecto-nucleotidase activities in spinal cord of rats changes as function of age

An increase in ADP hydrolysis was observed in spinal cord synaptosomal fractions of 2-month-old Wistar male rats, when compared to other ages (1, 4 and 6 months of age), while no change in ATPase activity was observed. Conversely, in female rats, whilst no change in ADPase activity was observed in the spinal cord synaptosomal fraction, ATPase activity diminished with age, in 1-6-month-old animals. 5'-Nucleotidase activity was higher in the 4-month-old male and female rats in relation to 1 and 2-month-old animals. In the female rats, this activity continued to increase at least until 6 months of age. In conclusion, adenine nucleotides hydrolysis in synaptosomes from rat spinal cord is influenced by age and by gender. Since both ATP and adenosine may act as neuromodulators in the spinal cord, influencing several processes such as nociception, the regulation of ATP-metabolizing enzymes in spinal cord is probably important for the normal function of this tissue at different ages.

The extracellular ATP receptor, cP2Y(1), inhibits cartilage formation in micromass cultures of chick limb mesenchyme

We have investigated the function of the G protein-coupled receptor for extracellular ATP, chick P2Y(1) (cP2Y(1)) during development of the chick limb. cP2Y(1) is strongly expressed in undifferentiated limb mesenchyme cells but appears to be lost from cells as they differentiate, raising the possibility that the function of this receptor may be to inhibit cell differentiation. This pattern of expression was particularly striking surrounding areas of cartilage formation. We tested whether cP2Y(1) was able to regulate cartilage formation by using an in-vitro micromass model of chondrogenesis. Because limb cells in micromass culture lose expression of cP2Y(1), we have used a gain-of-function approach to demonstrate that cP2Y(1) expression can inhibit cartilage differentiation. We also demonstrate that early limb mesenchyme cells release ATP into the extracellular medium and have mechanisms to breakdown extracellular ATP. These results suggest that extracellular ATP, signaling through cP2Y(1), can modulate the differentiation of limb mesenchyme cells in vitro, and the expression pattern of cP2Y(1) suggests that this type of signaling could play a similar role in ovo.

Age-related changes in the localization of P2X (nucleotide) receptors in the rat adrenal gland

Observation of the changes in the occurrence and distribution of nucleotide (P2X) receptors in the adrenal gland during development and ageing, and correlation with the changes in adrenal status at similar stages may give morphological insights into the functions of purine nucleotides in the gland. Age-related changes in the localization of all seven subtypes of the P2X receptor in the adrenal gland of rat were therefore investigated immunohistochemically. In the adrenal glands of prenatal rats, immunoreactivity to P2X receptor subtypes was not observed. In glands of the postnatal rat at the developmental stages studied, only immunoreactivity for the P2X(5) receptor subtype was observed. A small number of faintly P2X(5)-immunoreactive chromaffin cells were found in the adrenal glands of 1-day-old rats; the frequency of localization and intensity of staining of immunoreactive cells had increased by day 4 and was further increased at day 7. P2X(5) immunoreactivity was not observed in the adrenal glands from 14- and 21-day-old rats. At 8 weeks of age, immunoreactivity with a specific distribution for each of the seven receptor subtypes was observed. Except for the P2X(4) receptor, adrenal glands at 24 months showed a similar pattern of immunoreactivity for the receptor subtypes as that observed at 8 weeks. Immunoreactivity for P2X(4) was first observed in the adrenal cortical cells of the zona reticularis at 8 weeks, but was absent in 24-month-old rats. However, several P2X(4)-immunoreactive chromaffin cells appeared at 24 months. Such immunoreactive cells were not seen in rats of any of the other ages studied. It was concluded that the greater expression of P2X(5) receptor at an early developmental stage and of P2X(4) in ageing might reflect functional roles for purines in cellular proliferation and/or differentiation, and in cellular degeneration, respectively, in adrenal glands of rat.

Involvement of P2 purinoceptors in the regulation of DNA synthesis in the neural retina of chick embryo

The activation of P2 purinoceptors induces Ca2+ mobilization in the early embryonic chick neural retina. This purinergic Ca2+ response declines parallel with the decrease in mitotic activity during retinal development. To investigate the role of P2 purinoceptors in the regulation of retinal cell proliferation, we studied the effects of the P2 purinoceptor antagonists suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), and of the agonist ATP on DNA synthesis in retinal organ cultures from embryonic day 3 (E3) chick. Suramin inhibited [3H]-thymidine incorporation in a dose-dependent manner (IC50: approximately 70 microM). PPADS also reduced [3H]-thymidine incorporation with maximum inhibition of 46% at 100 microM. Exogenous ATP enhanced [3H]-thymidine incorporation in a dose-dependent manner to maximally 200% of control (EC50: approximately 70 microM). In dissociated retinal cultures from E7 chick, both antagonists showed similar inhibitory effects on [3H]-thymidine incorporation without affecting cell viability. In line with these observations, the presence of extracellular ATP was demonstrated both in vitro and in vivo. In the medium of E3 retinal organ cultures, the concentration of ATP increased 25-fold within 1 h of incubation and this concentration was kept for at least 24 h. In the chick amniotic fluid, the ATP concentration was nearly 3 microM at E3 and declined to 0.15 microM at E7. The results indicate that P2 purinoceptors activated by autocrine or paracrine release of ATP are involved in the regulation of DNA synthesis in the neural retina at early embryonic stages.

A2B adenosine and P2Y2 receptors stimulate mitogen-activated protein kinase in human embryonic kidney-293 cells. cross-talk between cyclic AMP and protein kinase c pathways

Mitogen-activated protein kinase (MAPK) cascades underlie long-term mitogenic, morphogenic, and secretory activities of purinergic receptors. In HEK-293 cells, N-ethylcarboxamidoadenosine (NECA) activates endogenous A2BARs that signal through Gs and Gq/11. UTP activates P2Y2 receptors and signals only through Gq/11. The MAPK isoforms, extracellular-signal regulated kinase 1/2 (ERK), are activated by NECA and UTP. H-89 blocks ERK activation by forskolin, but weakly affects the response to NECA or UTP. ERK activation by NECA or UTP is unaffected by a tyrosine kinase inhibitor (genistein), attenuated by a phospholipase C inhibitor (U73122), and is abolished by a MEK inhibitor (PD098059) or dominant negative Ras. Inhibition of protein kinase C (PKC) by GF 109203X failed to block ERK activation by NECA or UTP, however, another PKC inhibitor, Ro 31-8220, which unlike GF 109203X, can block the zeta-isoform, and prevents UTP- but not NECA-induced ERK activation. In the presence of forskolin, Ro 31-8220 loses its ability to block UTP-stimulated ERK activation. PKA has opposing effects on B-Raf and c-Raf-1, both of which are found in HEK-293 cells. The data are explained by a model in which ERK activity is modulated by differential effects of PKC zeta and PKA on Raf isoforms.