Conformational flexibility of the agonist binding jaw of the human P2X3 receptor is a prerequisite for channel opening.

BACKGROUND AND PURPOSE: It is assumed that ATP induces closure of the binding jaw of ligand-gated P2X receptors, which eventually results in the opening of the membrane channel and the flux of cations. Immobilization by cysteine mutagenesis of the binding jaw inhibited ATP-induced current responses, but did not allow discrimination between disturbances of binding, gating, subunit assembly or trafficking to the plasma membrane. EXPERIMENTAL APPROACH: A molecular model of the pain-relevant human (h)P2X3 receptor was used to identify amino acid pairs, which were located at the lips of the binding jaw and did not participate in agonist binding but strongly approached each other even in the absence of ATP. KEY RESULTS: A series of cysteine double mutant hP2X3 receptors, expressed in HEK293 cells or Xenopus laevis oocytes, exhibited depressed current responses to α,ß-methylene ATP (α,ß-meATP) due to the formation of spontaneous inter-subunit disulfide bonds. Reducing these bonds with dithiothreitol reversed the blockade of the α,ß-meATP transmembrane current. Amino-reactive fluorescence labelling of the His-tagged hP2X3 receptor and its mutants expressed in HEK293 or X. laevis oocytes demonstrated the formation of inter-subunit cross links in cysteine double mutants and, in addition, confirmed their correct trimeric assembly and cell surface expression. CONCLUSIONS AND IMPLICATIONS: In conclusion, spontaneous tightening of the binding jaw of the hP2X3 receptor by inter-subunit cross-linking of cysteine residues substituted at positions not directly involved in agonist binding inhibited agonist-evoked currents without interfering with binding, subunit assembly or trafficking.

Phosphodiesterase 2 inhibitors promote axonal outgrowth in organotypic slice co-cultures.

The development of appropriate models assessing the potential of substances for regeneration of neuronal circuits is of great importance. Here, we present procedures to analyze effects of substances on fiber outgrowth based on organotypic slice co-cultures of the nigrostriatal dopaminergic system in combination with biocytin tracing and tyrosine hydroxylase labeling and subsequent automated image quantification. Selected phosphodiesterase inhibitors (PDE-Is) were studied to identify their potential growth-promoting capacities. Immunohistochemical methods were used to visualize developing fibers in the border region between ventral tegmental area/substantia nigra co-cultivated with the striatum as well as the cellular expression of PDE2A and PDE10. The quantification shows a significant increase of fiber density in the border region induced by PDE2-Is (BAY60-7550; ND7001), comparable with the potential of the nerve growth factor and in contrast to PDE10-I (MP-10). Analysis of tyrosine hydroxylase-positive fibers indicated a significant increase after treatment with BAY60-7550 and nerve growth factor in relation to dimethyl sulfoxide. Additionally, a dose-dependent increase of intracellular cGMP levels in response to the applied PDE2-Is in PDE2-transfected HEK293 cells was found. In summary, our findings show that PDE2-Is are able to significantly promote axonal outgrowth in organotypic slice co-cultures, which are a suitable model to assess growth-related effects in neuro(re)generation.

Electrophysiological classification of P2X7 receptors in rat cultured neocortical astroglia.

BACKGROUND AND PURPOSE: P2X7 receptors are ATP-gated cation channels mediating important functions in microglial cells, such as the release of cytokines and phagocytosis. Electrophysiological evidence that these receptors also occur in CNS astroglia is rare and rather incomplete. EXPERIMENTAL APPROACH: We used whole-cell patch-clamp recordings to search for P2X7 receptors in astroglial-neuronal co-cultures prepared from the cerebral cortex of rats. KEY RESULTS: All the astroglial cells investigated responded to ATP with membrane currents, reversing around 0 mV. These currents could be also detected in isolated outside-out patch vesicles. The results of the experiments with the P2X [alpha,beta-methylene ATP and 2'-3'-O-(4-benzoyl) ATP] and P2Y receptor agonists [adenosine 5'-O-(2-thiodiphosphate), uridine 5'-diphosphate, uridine 5'-triphosphate (UTP) and UDP-glucose] suggested the involvement of P2X receptors in this response. The potentiation of ATP responses in a low divalent cation or alkaline bath, but not by ivermectin, made it likely that a P2X7 receptor is operational. Blockade of the ATP effect by the P2X7 antagonists Brilliant Blue G, calmidazolium and oxidized ATP corroborated this assumption. CONCLUSIONS AND IMPLICATIONS: Rat cultured cortical astroglia possesses functional P2X7 receptors. It is suggested that astrocytic P2X7 receptors respond to high local ATP concentrations during neuronal injury.

Increase of intracellular Ca2+ by P2X and P2Y receptor-subtypes in cultured cortical astroglia of the rat.

Astrocytes express purinergic receptors that are involved in glial-neuronal cell communication. Experiments were conducted to characterize the expression of functional P2X/P2Y nucleotide receptors in glial cells of mixed cortical cell cultures of the rat. The vast majority of these cells was immunopositive for glial fibrillary acidic protein (GFAP) and was considered therefore astrocyte-like; for the sake of simplicity they were termed "astroglia" throughout. Astroglia expressed predominantly P2X(4,6,7) as well as P2Y(1,2) receptor-subtypes. Less intensive immunostaining was also found for P2X(5) and P2Y(4,6,13,14) receptors. Pressure application of ATP and a range of agonists selective for certain P2X or P2Y receptor-subtypes caused a concentration-dependent increase of intracellular Ca(2+) ([Ca(2+)](i)). Of the agonists tested, only the P2X(1,3) receptor-selective alpha,beta-methylene ATP was ineffective. Experiments with Ca(2+)-free solution and cyclopiazonic acid, an inhibitor of the endoplasmic Ca(2+)-ATPase, indicated that the [Ca(2+)](i) response to most nucleotides, except for ATP and 2',3'-O-(benzoyl-4-benzoyl)-ATP, was due primarily to the release of Ca(2+) from intracellular stores. A Gprotein-mediated release of Ca(2+) is the typical signaling mechanism of various P2Y receptor-subtypes, whose presence was confirmed also by cross-desensitization experiments and by using selective antagonists. Thus, our results provide direct evidence that astroglia in mixed cortical cell cultures express functional P2Y (P2Y(1,2,6,14) and probably also P2Y(4)) receptors. Several unidentified P2X receptors, including P2X(7), may also be present, although they appear to only moderately participate in the regulation of [Ca(2+)](i). The rise of [Ca(2+)](i) is due in this case to the transmembrane flux of Ca(2+) via the P2X receptor-channel. In conclusion, P2Y rather than P2X receptor-subtypes are involved in modulating [Ca(2+)](i) of cultured astroglia and thereby may play an important role in cell-to-cell signaling.

Women's health in menopause with a focus on hypertension.

In menopause transition many women have vasomotor symptoms which may affect their normal daily activities. With the decline in oestrogen levels, risk factors for coronary heart disease (CHD) become more apparent, especially hypertension. The onset of hypertension can cause a variety of complaints that are often attributed to the menopause. Risk factor identification is poorly managed in middle-aged women and should be the first step in the evaluation and treatment of women with perimenopausal symptoms. In women at low risk for CHD, there is still a window of opportunity for safe hormone prescription in the first years proximal to menopause. (Neth Heart J 2009;17:68-72.).

P2 receptor-mediated stimulation of the PI3-K/Akt-pathway in vivo.

ATP acts as a growth factor as well as a toxic agent by stimulating P2 receptors. The P2 receptor-activated signaling cascades mediating cellular growth and cell survival after injury are only incompletely understood. Therefore, the aim of the present study was to identify the role of the phosphoinositide 3 kinase (PI3-K/Akt) and the mitogen-activated protein kinase/extracellular signal regulated protein kinase (MAPK/ERK) pathways in P2Y receptor-mediated astrogliosis after traumatic injury and after microinfusion of ADP beta S (P2Y(1,12,13) receptor agonist) into the rat nucleus accumbens (NAc). Mechanical damage and even more the concomitant treatment with ADP beta S, enhanced P2Y(1) receptor-expression in the NAc, which could be reduced by pretreatment with the P2X/Y receptor antagonist PPADS. Quantitative Western blot analysis indicated a significant increase in phosphorylated (p)Akt and pERK1/2 2 h after ADP beta S-microinjection. Pretreatment with PPADS or wortmannin abolished the up-regulation of pAkt by injury alone or ADP beta S-treatment. The ADP beta S-enhanced expression of the early apoptosis marker active caspase 3 was reduced by PPADS and PD98059, but not by wortmannin. Multiple immunofluorescence labeling indicated a time-dependent expression of pAkt and pMAPK on astrocytes and neurons and additionally the colocalization of pAkt, pMAPK, and active caspase 3 with the P2Y(1) receptor especially at astrocytes. In conclusion, the data show for the first time the involvement of PI3-K/Akt-pathway in processes of injury-induced astroglial proliferation and anti-apoptosis via activation of P2Y(1) receptors in vivo, suggesting specific roles of P2 receptors in glial cell pathophysiology in neurodegenerative diseases.

Effects of fulvestrant alone or combined with different steroids in human breast cancer cells in vitro.

OBJECTIVES: Fulvestrant is an estrogen receptor (ER) antagonist that binds, blocks and degrades the estrogen receptor and is currently used in adjuvant treatment in postmenopausal women with ER-positive breast cancer as an alternative for tamoxifen. As an antagonist, it may induce or aggravate climacteric symptoms. In order to alleviate these symptoms, one could consider hormone therapy. The objective of this study was to analyze the effect of fulvestrant alone or in combination with different steroids in human breast cancer cells in vitro, and to demonstrate whether these steroids will compromise the efficacy of fulvestrant in ER-positive breast cancer cells. METHODS: We performed experiments in vitro with various hormone therapy preparations (estradiol (E2), dihydrodydrogesterone (DHD) and tibolone) at a concentration of 10(-6) mol/l alone or combined with fulvestrant in different breast cancer cell lines, ER-positive and ER-negative. After an incubation of 144 h, proliferation and apoptosis were measured. The first was measured by quantification of the expression of cyclin D1 mRNA, the latter by the Nicoletti fragmentation assay. RESULTS: This in vitro study revealed clear differences in results when various hormone therapy preparations, alone or combined with fulvestrant, are added to ER-positive and ER-negative breast cancer cell lines. CONCLUSIONS: Our study demonstrated that fulvestrant, an ER antagonist used in the treatment of ER-positive breast cancer, combined with E2 and DHD or in combination with tibolone, is not compromised in its efficacy in inducing apoptosis in ER-positive breast cancer cell lines in vitro.

Tibolone and low-dose continuous combined hormone treatment: vaginal bleeding pattern, efficacy and tolerability.

OBJECTIVES: The primary objective was to compare the vaginal bleeding pattern during administration of tibolone and low-dose continuous combined estradiol plus norethisterone acetate (E2/NETA). The secondary objectives were efficacy on vasomotor symptoms and vaginal atrophy. DESIGN: A randomised, double-blind, double-dummy, group comparative intervention trial. SETTING: Multicentre study executed in 32 centres in 7 European countries. SAMPLE: Five hundred and seventy-two healthy symptomatic postmenopausal women, aged 45-65 years. METHODS: Participants were randomised to receive 2.5 mg tibolone or 1 mg 17beta estradiol plus 0.5 mg norethisterone acetate (E2/NETA) daily for 48 weeks. MAIN OUTCOME MEASURES: Prevalence of vaginal bleeding, hot flushes and adverse events. RESULTS: The incidence of bleeding was significantly lower in the tibolone group during the first 3 months of treatment (18.3 versus 33.1%; P < 0.001) when compared with the E2/NETA group. This effect on the bleeding pattern was sustained throughout the study, although reaching statistical significance again only in 7-9 months of treatment (11 versus 19%; P < 0.05). In both treatment groups, vasomotor symptoms and vaginal atrophy were significantly reduced to a similar extent when compared with baseline. The prevalence of breast pain/tenderness was significantly lower with tibolone compared with E2/NETA (3.2 versus 9.8%; P < 0.001). CONCLUSION: Tibolone reduces menopausal symptoms to a similar extent as conventional low-dose continuous combined hormone therapy but causes significant less vaginal bleeding in the first 3 months of treatment. This constitutes an important argument for woman adherence to therapy.

P2 receptor expression in the dopaminergic system of the rat brain during development.

Extracellular ATP facilitates the release of dopamine via P2 receptor activation in parts of the mesolimbic system. To characterize P2X/Y receptor subtypes in the developing dopaminergic system, their expression in organotypic slice co-cultures including the ventral tegmental area/substantia nigra (VTA/SN) complex and the prefrontal cortex (PFC) was studied in comparison to the receptor expression in 3-5 day-old and adult rats. Reverse transcriptase-polymerase chain reaction (RT-PCR) with specific primers for the P2X(1,2,3,4,6,7) and P2Y(1) receptors in the tissue extracts of organotypic co-cultures revealed the presence of the P2X and P2Y receptor mRNAs investigated. Multiple immunofluorescence labeling of the P2X/Y receptor protein indicated differences in the regional expression in the organotypic co-cultures after 10 days of cultivation (VTA/SN, P2X(1,2,3,4,6,7), P2Y(1,6,12); PFC, P2X(1,3,4,6,7), P2Y(1,2,4,6,12)). At postnatal days 3-5, an immunofluorescence mostly comparable to that of adult rats was observed (VTA/SN and PFC: P2X(1,2,3,4,6,7), P2Y(1,2,4,6,12)). There was one important exception: the P2X(7) receptor immunocytochemistry was not found in adult tissue, suggesting a potential role of this receptor in the development. Only few P2 receptors (e.g. P2X(1), P2Y(1)) were expressed at fibers interconnecting the dopaminergic VTA/SN with the PFC in the organotypic co-cultures. The treatment of the cultures with the ATP analogues 2-methylthio-ATP and alpha,beta-methylene-ATP induced an increase in axonal outgrowth and fiber density, which could be inhibited by pre-treatment with the P2X/Y receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid. The co-localization of the dopamine-(D1) receptor with the P2X(1) receptor in organotypic slice cultures was evident. In the PFC of the co-cultures, and that of young but not adult rats, a number of tyrosine hydroxylase (TH)-positive cells also possessed P2Y(1)-immunoreactivity (IR). Additionally, a strong P2Y(1)-IR was observed on astrocytes. The present results show a time-, region- and cell type-dependent in vitro and in vivo expression pattern of different P2 receptor subtypes in the dopaminergic system indicating the involvement of ATP and its receptors in neuronal development and growth.

Involvement of P2X and P2Y receptors in microglial activation in vivo.

Microglial cells are the primary immune effector cells in the brain. Extracellular ATP, e.g., released after brain injury, may initiate microglial activation via stimulation of purinergic receptors. In the rat nucleus accumbens (NAc), the involvement of P2X and P2Y receptors in the generation of microglial reaction in vivo was investigated. A stab wound in the NAc increased immunoreactivity (IR) for P2X(1,2,4,7) and P2Y(1,2,4,6,12) receptors on microglial cells when visualized with confocal laser scanning microscopy. A prominent immunolabeling of P2X(7) receptors with antibodies directed against the ecto- or endodomain was found on Griffonia simplicifolia isolectin-B4-positive cells. Additionally, the P2X(7) receptor was colocalized with active caspase 3 but not with the anti-apoptotic marker pAkt. Four days after local application of the agonists alpha,betameATP, ADPbetaS, 2MeSATP, and BzATP, an increase in OX 42- and G. simplicifolia isolectin-IR was observed around the stab wound, quantified both densitometrically and by counting the number of ramified and activated microglial cells, whereas UTPgammaS appeared to be ineffective. The P2 receptor antagonists PPADS and BBG decreased the injury-induced increase of these IRs when given alone and in addition inhibited the agonist effects. Further, the intra-accumbally applied P2X(7) receptor agonist BzATP induced an increase in the number of caspase-3-positive cells. These results indicate that ATP, acting via different P2X and P2Y receptors, is a signaling molecule in microglial cell activation after injury in vivo. The up-regulation of P2X(7)-IR after injury suggests that this receptor is involved in apoptotic rather than proliferative effects.

Differential effects of bisphosphonates on breast cancer cell lines.

Bisphosphonates may induce direct anti-tumor effects in breast cancer cells in vitro. In this study, six bisphosphonates were administered to three breast cancer cell lines. Cell proliferation was measured by quantification of the expression of Cyclin D1 mRNA. Apoptosis was determined by flow cytometry of a DNA fragmentation assay. We demonstrated that bisphosphonates have direct effects on cell proliferation and apoptosis in different breast cancer cell lines. However, not all bisphosphonates act equally on breast cancer cells in vitro. Zoledronate seems to be the most potent of the six bisphosphonates. This in vitro study showed that bisphosphonates possess promising anti-tumor potential.

Neuroprotective effects of the P2 receptor antagonist PPADS on focal cerebral ischaemia-induced injury in rats.

After acute injury of the central nervous system extracellular adenosine 5'-triphosphate (ATP) can reach high concentrations as a result of cell damage and subsequent increase in membrane permeability. Released ATP may act as a toxic agent, which causes cellular degeneration and death, mediated through P2X and P2Y receptors. Mechanisms underlying the various effects of purinoceptor modulators in models of cerebral damage are still uncertain. In the present study the effect of P2 receptor inhibition after permanent middle cerebral artery occlusion (MCAO) in spontaneously hypertensive rats was investigated. Rats received either the non-selective P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) or artificial cerebrospinal fluid (ACSF) as control by the intracerebroventricular route. First, these treatments were administered 10 min before MCAO and subsequently twice daily for 1 or 7 days after MCAO. The functional recovery of motor and cognitive deficits was tested at an elevated T-labyrinth. The PPADS-treated group showed a significant reduction of paresis-induced sideslips compared with ACSF-treated animals. Infarct volume was reduced in the PPADS group in comparison with the ACSF group. A significant decrease in intermediately and profoundly injured cells in favour of intact cells in the PPADS group was revealed by quantification of celestine blue/acid fuchsin-stained cells in the peri-infarct area. The data provide further evidence for the involvement of P2 receptors in the pathophysiology of cerebral ischaemia in vivo. The inhibition of P2 receptors at least partially reduces functional and morphological deficits after an acute cerebral ischaemic event.

Increased polysialic acid neural cell adhesion molecule expression in human hippocampus of heroin addicts.

Chronic exposure to heroin is known to cause cognitive deficits. However, little is known about the underlying molecular mechanisms. It has been suggested that opiate-induced neurotoxicity as well as impaired plasticity and regeneration may be relevant. One of the target regions where regeneration still can be observed in the adult brain is the hippocampus. Since polysialic acid neural cell adhesion molecule is regarded as one of the key players involved in plasticity and regeneration of neural tissue, we analyzed polysialic acid neural cell adhesion molecule expression in the fascia dentate hilus of the human hippocampus of 29 lethally intoxicated heroin addicts and matched controls. Immunohistochemistry with an antibody directed against polysialic acid neural cell adhesion molecule revealed its expression in differently sized cells which could be identified as neurons and glial cells. We observed an increase in the percentage of polysialic acid neural cell adhesion molecule positive neurons in hippocampal hilus of heroin addicts compared with controls (P = 0.001).Interestingly, we also observed polysialic acid neural cell adhesion molecule expression in glial cells as evidenced by double immunofluorescence with glial fibrillary acidic protein and polysialic acid neural cell adhesion molecule using confocal laser scanning microscopy. The fraction of polysialic acid neural cell adhesion molecule positive glial cells was also higher in heroin addicts compared with controls (P = 0.009). In addition, within the group of addicts morphine blood concentrations showed a positive correlation with the percentage of polysialic acid neural cell adhesion molecule positive neurons (P = 0.04; r = 0.547). In conclusion, we observed an increase in polysialic acid neural cell adhesion molecule positive neurons and glial cells in hippocampi of heroin addicts. This might reflect an attempt to repair cell damage due to heroin exposure.

Apoptosis and proliferation in breast cancer cells, cultured in vitro: effects of SERMs.

OBJECTIVE: Selective estrogen receptor modulators (SERMs) decrease the risk of developing breast cancer. As an antagonistic effect, SERMs may aggravate or induce climacteric symptoms. Hormone therapy (HT) would be able to alleviate these symptoms. The present in vitro study tries to elucidate the effects of several HT preparations combined with SERMs on estrogen receptor-positive (ER +) (i.e. MCF-7 and T-47D) and -negative (ER-) (i.e. MDA-MB-231) human breast cancer cells in vitro. METHODS: We performed experiments with various HT preparations (estradiol (E2)/E2 + progesterone/E2 + dihydrodydrogesterone /E2 + norethisterone acetate/E2 + medroxyprogesterone acetate/tibolone) in the concentration of 10(-6) mol/l together with SERMs (raloxifene or tamoxifen) added to different breast cancer cell lines in vitro. After an incubation period of 144 h, proliferation and apoptosis were measured. The first was measured by quantification of the expression of cyclin D1 mRNA, the latter by the Nicoletti method. RESULTS: This in vitro study clearly demonstrates differences in results if various HT preparations, combined with SERMs, are added to ER + and ER- breast cancer cell lines. CONCLUSIONS: Adding estradiol/progestogens in combination with a SERM to estrogen receptor-positive breast cancer cell lines does not obligatorily lead to proliferation of tumor cells. Not all progestogens act equally.

Hyperbaric and normobaric reoxygenation of hypoxic rat brain slices--impact on purine nucleotides and cell viability.

Hyperbaric oxygen treatment has been suggested as able to reduce hypoxia induced neuronal damage. The aim of the study was to compare the impact of different reoxygenation strategies on early metabolical (purine nucleotide content determined by HPLC) and morphological changes (index of cell injury after celestine blue/acid fuchsin staining) of hypoxically damaged rat neocortical brain slices. For this purpose slices (300 microm and 900 microm) were subjected to either 5 or 30 min of hypoxia by gassing the incubation medium with nitrogen. During the following reoxygenation period treatment groups were administered either 100% oxygen (O) or room air (A) at normobaric (1 atm absolute, NB-O; NB-A) or hyperbaric (2.5 atm absolute, HB-O; HB-A) conditions. After 5 min of hypoxia, both HB-O and NB-O led to a complete nucleotide status restoration (ATP/ADP; GTP/GDP) in 300 microm slices. However, reoxygenation after 30 min of hypoxia was less effective, irrespective of the oxygen pressure. Furthermore, administering hyperbaric room air resulted in no significant posthypoxic nucleotide recovery. In 900 microm slices, both control incubation as well as 30 min of hypoxia resulted in significantly lower trinucleotide and higher dinucleotide levels compared to 300 microm slices. While there was no significant difference between HB-O and NB-O on the nucleotide status, morphological evaluation revealed a better recovery of the index of cell injury (profoundly injured/intact cell-ratio) in the HB-O group. Conclusively, the posthypoxic recovery of metabolical characteristics was dependent on the duration of hypoxia and slice thickness, but not on the reoxygenation pressure. A clear restorative effect on purine nucleotides was found only in early-administered HB-O as well as NB-O in contrast to room air treated slices. However, these pressure independent metabolic changes were morphologically accompanied by a significantly improved index of cell injury, indicating a possible neuroprotective role of HB-O in early posthypoxic reoxygenation.

4-Epidoxycycline: an alternative to doxycycline to control gene expression in conditional mouse models.

Since the pioneering work by Gossen and Bujard in 1992 demonstrating the usefulness of the Escherichia coli derived tet resistance operon for regulating gene expression a large collection of doxycycline-controlled transgenic mice has been established. Gene switching in eukaryotic tissue culture cells or mice requires administration of tetracycline, anhydrotetracycline or doxycycline to efficiently inactivate the transactivator protein tTA (TET-OFF system) or alternatively to activate the reverse transactivator protein rtTA (TET-ON system). However, the antibiotic activity of doxycycline can create an imbalance of the intestinal flora, resulting in diarrhoea and in a smaller number of animals in colitis. Previous studies reported that 4-epidoxycycline (4-ED), a hepatic metabolite of doxycycline, does not function as an antibiotic in mice. This gave us the idea that 4-ED might be useful for controlling gene expression in mice without the unwanted antibiotic side effect. To study the applicability of 4-ED for control of gene expression we used cell lines expressing the oncogene HER2 under control of tTA (TET-OFF) as well as rtTA (TET-ON). 4-ED and doxycycline were similarly efficient in switching on or -off HER2 expression. In vivo we used a conditional mouse model that allows switching off HER2 in tumor tissue. We show that (i) doxycycline, 7.5mg/ml in drinking water (used as a positive control), (ii) 4-ED, 7.5mg/ml in drinking water, (iii) 4-ED, 10mg/kg body weight, s.c., and (iv) anhydrotetracycline, 10mg/kg, s.c. (used as a second positive control), were similarly efficient. Using mice with tumor volumes of 1.6cm(3) all four schedules led to a tumor remission of more than 95% within 7 days. In conclusion, 4-ED is similarly efficient as doxycycline to control gene expression in vitro and in mice. Since 4-ED lacks the antibiotic activity of doxycycline it may help to avoid adverse side effects and selection of resistant bacteria.

P2Y receptor expression on astrocytes in the nucleus accumbens of rats.

The expression of purinoceptor (P2)Y-subtypes on astrocytes in vivo under physiological conditions and after stab wound injury was investigated. Reverse transcriptase-polymerase chain reaction with specific primers for the receptor-subtypes P2Y1,2,4,6,12 in tissue extracts of the nucleus accumbens of untreated rats revealed the presence of all P2Y receptor mRNAs investigated. Double immunofluorescence visualized with laser scanning microscopy indicated the expression of the P2Y1,4 receptors on glial fibrillary acidic protein (GFAP)-labeled astrocytes under physiological conditions. After stab wound injury the additional expression of the P2Y2 and P2Y6 receptors, and an up-regulation of the P2Y1,4 receptor-labeling on astrocytic cell bodies and/or processes was observed. Astrocytes of cortical, in contrast to accumbal areas exhibited P2Y1,2,4,6 receptor-immunoreactivity (IR) under control conditions, which was up-regulated after stab would injury. Labeling for the P2Y12 receptor was not observed on GFAP-positive cortical and accumbal astrocytes under any of the conditions used. For the first time, the co-localization of different P2 receptor-subtypes (e.g. P2Y1 and P2X3) on the same astrocyte was shown immunocytochemically. The up-regulation of P2Y1 receptor-IR on astrocytes and non-glial cells after mechanical injury could be facilitated by microinfusion of the P2Y1,12,13 receptor agonist adenosine 5'-O-(2-thiodiphosphate) (ADPbetaS). Proliferative changes after ADPbetaS-microinjection were characterized by means of double-staining with antibodies against GFAP and 5-bromo-2'-deoxyuridine. The non-selective P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid, the P2Y1 receptor antagonist N6-methyl-2'-deoxyadenosine 3',5'-bisphosphate and the P2Y1 receptor-antibody itself inhibited the agonist-induced effects. The data indicate the region-specific presence of P2Y receptors on astrocytes in vivo and their up-regulation after injury as well as the co-localization of P2X and P2Y receptor-subtypes on the same astrocyte. The dominant role of P2Y1 receptors in proliferation and the additional stimulation of non-P2Y1 receptors has been demonstrated in vivo suggesting the involvement of this receptor-type in the gliotic response under physiological and pathological conditions.