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B B Fredholm

Publications and source records attributed to B B Fredholm.

At least 19 recordsLinked to original sources
PubMed1995

Adenosine A2A receptors stimulate acetylcholine release from nerve terminals of the rat hippocampus.

The nature of the adenosine receptors involved in the enhancement of acetylcholine release in the hippocampus was studied. The A2A agonist, CGS 21680, increased the veratridine-evoked release of [3H]acetylcholine from hippocampal synaptosomes. This presynaptic effect of CGS 21680 was greater at 3-30 nM than at 100 nM. The excitatory effect of CGS 21680 was antagonised by the A2 antagonist, DMPX (10 microM), and by the A2A antagonist, CSC (200 nM), but not by the A1 antagonist, DPCPX (20 nM). We also found co-expression of A2A and choline acetyltransferase mRNAs in the nucleus of the diagonal band and the medial septum, where the cholinergic cell bodies that project into the hippocampus are located. These results indicate that A2A adenosine receptors are present in cholinergic nerve terminals in the hippocampus and that activation of these receptors enhances acetylcholine release.

Acetylcholine↗
PubMed1995

[Growth factors--clarification of their mechanism].

Every cell possesses a complex network of proteins that regulate its fundamental life processes. Growth factors act on specific cell surface receptors that activate these proteins, thereby regulating cell division, cell differentiation, or apoptosis. A cascade of protein phosphorylation reactions, ultimately resulting in the activation of gene transcription, is a common feature. Many of the proteins involved in the actions of growth factors have mutated variants that act as oncogenes. Although our knowledge of the mechanisms involved in growth factor action and in the development of malignancy is rapidly expanding, the route toward its utilisation in new therapeutic approaches will be long and arduous.

Cell Cycle Proteins↗
PubMed1995

Activation of adenosine A1 and bradykinin receptors increases protein kinase C and phospholipase D activity in smooth muscle cells.

Since adenosine A1 receptors activate phospholipase C (PLC) in DDT1 MF-2 smooth muscle cells we have examined whether phospholipase D (PLD) and protein kinase C (PKC) activities are also increased. The formation of diacylglycerol was also measured. PKC activity was determined by measuring the phosphorylation of two peptide substrates after rapidly permeabilizing the cells. PLD activity was determined by measuring the formation of phosphatidylethanol. N6-cyclopentyladenosine, a selective adenosine A1 receptor agonist (100 nM) and bradykinin (1 microM) both stimulated the formation of diacylglycerol. The activation was biphasic with a rapid, transient increase (within 1 min) followed by a second increase. N6-cyclopentyladenosine increased the activity of PKC (EC50 5.6 nM) and PLD (EC50 18.7 nM). This was blocked by treatment of cells with pertussis toxin or the adenosine A1 receptor selective antagonist, 8-cyclopentyl-1,3-dipropylxanthine. Ki values (3 nM for PKC; 0.1 nM for PLD) were consistent with responses mediated via adenosine A1 receptors. Bradykinin (1 microM) also increased PKC and PLD activity, but these responses were insensitive to pertussis toxin treatment. The activation of PKC by N6-cyclopentyladenosine or bradykinin was transient, reaching a maximum at 1-2 min, and was preceded by increases in the formation of diacylglycerol. When adenosine A1 and bradykinin receptors were activated simultaneously, a synergistic activation of PKC was seen. There was no synergistic effect on PLD activity. In summary, the present study shows that activation of adenosine receptors of the A1 subtype increases PKC and PLD activity. Simultaneous activation of adenosine A1 and bradykinin receptors causes a synergistic increase in PKC.

Amino Acid Sequence↗
PubMed1995

Activation of phospholipase C and phospholipase D by stimulation of adenosine A1, bradykinin or P2U receptors does not correlate well with protein kinase C activation.

Activation of adenosine A1-, bradykinin- or P2U-receptors on DDT1 MF-2 smooth muscle cells all increased the formation of inositol 1,4,5-trisphosphate and the mobilization of intracellular calcium. All three types of agents could increase [Ca2+]i in the same cell. Activation of the P2U receptor with ATP or UTP produced larger responses than activation of bradykinin- and adenosine A1-receptors, with bradykinin and N6-cyclopentyladenosine. When agonist-stimulated levels of diacylglycerol were determined, all agonists caused biphasic changes of similar magnitudes. If anything, ATP and UTP tended to give larger increases in the second phase of stimulation. Phospholipase D, measured as the formation of phosphatidylethanol in cells labeled with [3H]palmitic acid and activated in the presence of ethanol, was activated similarly as phospholipase C, i.e. ATP or UTP caused the largest increase in phosphatidylethanol formation, followed by N6-cyclopentyladenosine and bradykinin which caused weaker responses. Activation of PLD by P2U receptors was pertussis toxin insensitive. The activation of PLD by the agonists was only weakly affected by a PKC inhibitor, Ro 31-7549 (3-[1-(3-aminopropanyl)-3- indolyl]-4-(1-methyl-3-indolyl)-1H-pyrrole-2,5-dione). In contrast, ATP or UTP did not activate protein kinase C, determined in a permeabilized cell assay using two specific protein kinase C substrates, whereas N6-cyclopentyladenosine and bradykinin caused a substantial activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Further characterization of the binding of the adenosine receptor agonist [3H]CGS 21680 to rat brain using autoradiography.

2-[p-(2-carboxyethyl)-phenylethylamino]-5'-N-ethylcarboxamidoadeno sine (CGS 21680) is considered a selective ligand for adenosine A2A receptors, which are known to be enriched in striatum and olfactory tubercle. We have investigated the characteristics of [3H]CGS 21680 binding in several brain regions using quantitative autoradiography. In agreement with previous data the radioligand was found to label the caudate-putamen, accumbens nucleus, olfactory tubercle and globus pallidus, but also many other structures, e.g. cerebral and cerebellar cortex, hippocampus, thalamus and some brainstem nuclei, were labelled. Cortical and striatal binding of [3H]CGS 21680 was unaltered by high concentrations of the adenosine transport inhibitor dipyridamole or the phosphodiesterase inhibitor rolipram but was displaced by 1,3-diethyl-8-phenylxanthine, the A2 selective adenosine antagonist CP 66,713, and the A2A selective agonist SHA 118. These three agents were approximately equipotent in striatum, cortex and hippocampus. The A2 selective agonist CV 1808 was a 4-5 times more potent displacer in cortex and hippocampus than in the striatum. [3H]CGS 21680 binding was strongly magnesium-dependent in all the studied brain regions, in contrast to the binding of adenosine A1 agonists. The binding of [3H]CGS 21680 to cerebral cortex and hippocampus, but not the binding to striatum, was displaced by the adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine in nanomolar concentrations. The present study provides evidence that in cerebral cortex and hippocampus, most of the [3H]CGS 21680 binds to a receptor site that is distinct from the striatal A2A receptor and the classical adenosine A1 receptor and may represent a hitherto unrecognized binding site.

Adenosine↗
PubMed1995

Involvement of adenosine deaminase and adenosine kinase in regulating extracellular adenosine concentration in rat hippocampal slices.

In this study the relative importance of adenosine deaminase and adenosine kinase in regulating extracellular adenosine concentration was investigated in rat hippocampal slices labelled with [3H]-adenine. The release of [3H]-purines evoked by electrical stimulation or energy depletion (oxygen and glucose deprivation) was measured and, using high-performance liquid chromatography (HPLC), the proportion of [3H]-label in the form of [3H]-adenosine, [3H]-inosine and [3H]-hypoxanthine was determined. In addition, endogenous purine release was measured by HPLC with UV detection. 10 microM 5-iodotubericidin (5-IT), an inhibitor of adenosine kinase, significantly increased endogenous adenosine release and altered the pattern of [3H]-purine release by increasing the proportion released as [3H]-adenosine, under basal conditions and after electrical stimulation or energy depletion. 5 microM erythro-9-(2-hydroxy-3-nonyl) adenosine (EHNA), an inhibitor of adenosine deaminase, also increased endogenous adenosine release and altered the pattern of [3H]-purine release evoked by energy depletion by decreasing the proportion of [3H]-label released as [3H]-hypoxanthine and [3H]-inosine, whilst approximately doubling that of [3H]-adenosine. In contrast, adenosine release was not altered by EHNA under basal conditions or electrical stimulation. It is concluded that under conditions which provide adequate oxygen and glucose, adenosine kinase plays a much greater role than adenosine deaminase in regulating the extracellular concentration of adenosine. However, adenosine deaminase becomes important in regulating extracellular adenosine concentration when adenosine formation is increased by energy depletion.

Adenine↗
PubMed1995

Astra Award Lecture. Adenosine, adenosine receptors and the actions of caffeine.

Of the known biochemical actions of caffeine, only inhibition of adenosine receptors occurs at concentrations achieved during normal human consumption of the drug. Under normal physiological conditions, adenosine is present in sufficient concentrations to activate A1 and A2a receptors. Via actions on A1 receptors, adenosine decreases neuronal firing and the release of neurotransmitters. The exact mechanisms are not known, but several possibilities are discussed. Via actions on A2a receptors, adenosine--and hence caffeine--can influence dopaminergic neurotransmission. Caffeine can induce rapid changes in gene expression and, somewhat later, marked adaptive changes. These include antiepileptic and neuroprotective changes. Thus, caffeine has a number of central effects directly or indirectly related to adenosine receptors. Some of these are potentially useful, and drug development based on the actions of caffeine should be interesting.

Adenosine↗
PubMed1995

Purinoceptors in the nervous system.

The purine nucleoside adenosine and the purine nucleotide ATP play different roles in the nervous system. Adenosine acts on a family of G protein coupled receptors, collectively called adenosine receptors or P1 purinoceptors. Four members of this family have been cloned and pharmacologically characterized: A1, A2A, A2B and A3. Their distribution, pharmacology and biological roles are briefly discussed. In particular, the evidence that adenosine acting at A1 receptors regulates the release of several neurotransmitters and that adenosine acting at A2A receptors modulates dopaminergic transmission is summarized. ATP acts on receptors called P2 purinoceptors, which appear to fall into at least two main families--G protein coupled receptors and intrinsic ion channels. Their subclassification is becoming clearer as receptors are cloned and new selective agonists and/or antagonists are becoming available. There is an interesting potential for development of drugs targeted at purines or their receptors.

Adenosine↗
PubMed1995

Effect of different xanthines and phosphodiesterase inhibitors on c-fos expression in rat striatum.

It has previously been shown that caffeine, in a dose-dependent manner, increases the expression of the protooncogene c-fos in the rat brain, predominantly in the caudate-putamen and tuberculum olfactorium. In this study we examined the effect of related xanthines and of selective phosphodiesterase inhibitors on c-fos expression. The effect of caffeine (75 mg kg-1) was mimicked by 3-isobutyl-1-methyl xanthine (IBMX) (25 mg kg-1) and theophylline (100 mg kg-1) but not by 8-p-sulfophenyltheophylline (10 mg kg-1), enprofylline, theobromine or paraxanthine (each at 100 mg kg-1). Moreover, the cyclic AMP-selective phosphodiesterase inhibitors rolipram (10 or 20 mg kg-1) and SQ 20,006 (25 mg kg-1) and the cyclic GMP-selective phosphodiesterase inhibitor zaprinast (10 mg kg-1) failed to induce c-fos in striatum, but caused a clear-cut induction in the overlying cerebral cortex. Thus, c-fos is induced in rat striatum following administration of caffeine and other xanthines that (provided they enter the brain) block adenosine receptors, suggesting an involvement of central adenosine receptors. Inhibition of cyclic nucleotide phosphodiesterase does not appear to play any important role in c-fos induction by the xanthines.

1-Methyl-3-isobutylxanthine↗
PubMed1995

The effect of long term caffeine treatment on hypoxic-ischemic brain damage in the neonate.

There is considerable concern over the widespread use of caffeine during and after pregnancy. We have therefore examined the effect of perinatal caffeine use on the vulnerability of the immature brain to hypoxic ischemia (HI). Rat pups were exposed to caffeine during the first 7 d after birth by addition of a low or a high dose (0.3 or 0.8 g/L) of caffeine to the drinking water of their dams. At 7 d the pups were exposed to unilateral carotid occlusion+exposure to 7.70% oxygen for 100 min. The extent of HI brain damage was evaluated 2 wk after the insult. The effects of caffeine on A1 and A2a receptors, A1 mRNA and A2a mRNA, were examined by receptor autoradiography and in situ hybridization. Caffeine, theobromine, theophylline, and paraxanthine were analyzed in plasma of separate animals. Exposure to caffeine reduced HI brain damage from 40.3 +/- 3.2% in controls to 29.8 +/- 4.0% (p < 0.05) in low dose and 33.7 +/- 3.9% (NS) in the high dose group. The A1 receptor density measured as [3H]-1,3-dipropyl-8-cyclopentyl xanthine ([3H]-DPCPX) binding was not significantly affected after low dose caffeine but increased in the brain of rat pups in the high dose group. The A2a receptor density measured as [3H]-2[p-(2-carbonylethyl)-phenethylamino]-5'-N- ethylcarboxamidoadenosine ([3H]-CGS 21680) binding and the expression of A1 mRNA and A2a mRNA were not altered by caffeine treatment. In conclusion, low dose caffeine exposure (plasma levels corresponding to umbilical cord plasma in newborns of coffee-consuming mothers) reduced HI brain damage by 30% in 7-d-old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Biphasic changes in locomotor behavior and in expression of mRNA for NGFI-A and NGFI-B in rat striatum following acute caffeine administration.

The time course of expression of mRNA for NGFI-A and NGFI-B after a single intraperitoneal injection of saline or caffeine was examined using in situ hybridization. Administration of a high dose of caffeine (100 mg/kg) decreased locomotor behavior and increased NGFI-A and NGFI-B mRNA in the entire striatum. A lower dose of caffeine (50 mg/kg) caused a weak enhancement of both messages, which was confined to the lateral part of caudate-putamen. This dose increased horizontal, but not vertical, movement. In rats treated with the lowest dose of caffeine (25 mg/kg), the expression of both investigated genes tended to be lower than for saline-treated rats and both horizontal and vertical locomotor activity increased markedly. The reduction in the number of labeled neurons seemed to occur predominantly in enkephalin-containing neurons, which coexpress adenosine A2A receptors and dopamine D2 receptors. The decrease of mRNA for NGFI-A, NGFI-B, and jun B caused by caffeine (25 mg/kg) could be mimicked by the D2 agonist quinpirole (1 and 3 mg/kg). Moreover, caffeine could significantly decrease the expression seen following treatment with the D2 antagonist raclopride (2 mg/kg). In addition, in the parietal cortex, 25 mg/kg of caffeine caused a significant elevation of both examined immediate early genes. Thus, biphasic changes in locomotion induced by caffeine are paralleled by biphasic changes in mRNA for NGFI-A, NGFI-B, and jun B. The results also provide additional support for a functionally important interaction between adenosine and dopamine D2 receptors.

Animals↗
PubMed1995

Increased expression of c-jun, junB, AP-1, and preproenkephalin mRNA in rat striatum following a single injection of caffeine.

The effect of a single injection of caffeine on the expression of c-fos, c-jun, junB, and junD, on activator protein 1 (AP-1) and on the levels of preproenkephalin mRNA in rat striatum was studied. Male rats were given caffeine (25 mg/kg, 50 mg/kg, or 100 mg/kg, i.p.) and sacrificed at different times (0.5, 1, 2, 4, or 8 hr) after administration. By using in situ hybridization of adjacent sections we found a rapid, transient, and dose-dependent increase of c-fos, c-jun, and junB by caffeine in striatum, especially in the lateral part. The induction peaked after 1 hr, but persisted for 2 hr, and in the case of junB for 4 hr. No induction of junD was found. A strong induction of junB, a weak induction of c-fos and c-jun, but not of junD, was seen in nucleus accumbens. Furthermore, by using gel shift assay we found an induction of AP-1 by caffeine (100 mg/kg) in striatum, which peaked 2 hr after administration and was clearly increased after 4 hr. c-Fos, c-Jun, and JunB proteins were components of the AP-1. There was also a dose-dependent induction of preproenkephalin mRNA, which was most pronounced in the lateral and caudal part of striatum; the level peaked 4 hr after injection and was still significantly increased after 8 hr. In a complementary study we could not find increased binding to the AP-1-like site in the 5'-flanking sequence of proenkephalin following caffeine treatment. The data show that a single dose of caffeine induces a temporally and spatially characteristic pattern of c-fos, c-jun, and junB induction, followed by changes in AP-1 and preproenkephalin mRNA. Thus, a single dose of caffeine causes changes in gene transcription in the brain that may be related to the adaptive changes that occur after caffeine administration. However, a direct causal link between the immediate early genes and enkephalin could not be proven.

Analysis of Variance↗
PubMed1994

[The 1994 Nobel Prize: discovery and significance of G-proteins].

Exactly how a cell responds to a hormone or transmitter substance depends on at least three factors: which type of receptors the cell has, which G-proteins are present and which amplifying system exists in precisely that cell. This means that the number of possible signalling pathways becomes extremely great. Here lies the most important aspect of the discoveries that have been rewarded with this year's Nobel prize. The translation of a message from an extracellular signal to an altered cellular function demands reoperation between a cascade of different proteins. One cell has one certain structure, another contains quite different components. In this manner, a limited number of signals and signal-transmitting molecules may be combined to produce extremely varied signalling pathways. Life is characterized by simplicity in design and colossal variation in form. The G-proteins' role in signal transmission in the cell is a shining example of this principle of variations on a theme that achieve the diversity necessary to maintain life.

Animals↗
PubMed1994

Propentofylline enhancement of the actions of adenosine on neutrophil leukocytes.

In agreement with previous results, activation of adenosine A2 receptors was found to inhibit the exocytotic release of elastase and the oxidative burst induced by formyl-MetLeuPhe (fMLP) in human neutrophils. The adenosine analogue 5'-N-ethylcarboxamidoadenosine (NECA) was more potent than adenosine (IC50 14 vs 64 nM). The effects of adenosine and NECA were not influenced by the A1-adenosine receptor selective antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 300 nM), but were abolished by the non-selective adenosine receptor antagonist 9-chloro-2-(2-furanyl)-5,6-dihydro-[1,2,4]-triazolo[1,5]quinazolin -5-imine monomethanesulfonate (CGS 15943; 10 microM). Propentofylline per se caused a concentration-dependent inhibition of H2O2 production. At 100 microM propentofylline significantly enhanced the effect of adenosine, but not that of NECA. This effect of propentofylline was shared by the known uptake inhibitor dipyridamole. Neither adenosine nor propentofylline altered fMLP-induced inositol-(1,4,5)-trisphosphate (IP3) formation. The results demonstrate that propentofylline can counteract neutrophil activation, at least partly by enhancing the action of adenosine through blocking its removal, and that the effect is exerted at a step after the initial receptor events.

Adenosine↗
PubMed1994

A2a/D2 receptor interactions are not observed in COS-7 cells transiently transfected with dopamine D2 and adenosine A2a receptor cDNA.

The rat D2 receptor and the dog A2a receptor subcloned into the pXM vector were transiently transfected into COS-7 cells using the DEAE-dextran method. The transfected cells expressed approx. 200 fmol D2 receptors/mg protein and approx. 5 pmol/mg protein of the A2a receptor as judged by binding experiments with [3H]raclopride [or[3H]-N-propyl-apomorphine (NPA)] and [3H]-CGS 21680, respectively. The high affinity KD values were 0.43 and 19 nM for D2 and A2a receptors, respectively, in agreement with results obtained from other cells and tissues. The non-selective adenosine receptor agonist NECA stimulated cAMP accumulation both in non-transfected and transfected COS-7 cells with only a slight difference in potency, suggesting that most of the stimulation is due to activation of A2b receptors known to be present on virtually every cell. The two A2a selective agonists CGS 21680 and CV-1808 were essentially inactive in transfected COS-7 cells, but were very active in PC-12 cells known to possess functional A2a receptors. Dopamine did not decrease cAMP accumulation in the transfected COS-7 cells. CGS 21680 (30 nM) did not affect the binding characteristics of D2 receptors in the co-transfected COS-7 cells in contrast to the increased KH, KL and RH values found previously in rat striatal membranes after CGS 21680 treatment. The present findings indicate that transiently transfected A2a and D2 receptors in COS-7 cells have normal binding properties, but couple poorly to adenylyl cyclase, despite the presence of Gs protein and adenylyl cyclase in these cells. Our results also demonstrate that the previously reported interactions between A2a receptors and D2 receptors do not occur when only the receptor proteins are expressed in COS-7 cells, suggesting that the two receptor molecules do not interact directly to influence binding characteristics.

Adenosine↗