Increased incidence and analysis of emperipolesis in megakaryocytes of the mouse mutant gunmetal

Mutant gunmetal (gm/gm) mice exhibit prolonged bleeding, platelet granule defects, abnormal megakaryocyte demarcation membranes, and thrombocytopenia. The number of megakaryocytes in gm/gm mice is increased substantially. Also, the percentage of gm/gm megakaryocytes exhibiting emperipolesis is increased. However, the number of emperipolesed cells per megakaryocyte is not. EC are of several hematopoietic lineages, with a slight skew to granulocytes, and include mature, primitive, and degenerating cells. No significant differences in the types of emperipolesed cells were observed between mutant mice and their normal gm/+ or +/+ counterparts. The increased incidence of emperipolesis in gm/gm megakaryocytes is controlled by the megakaryocyte genotype, not systemic factors. A significant practical finding of these studies was the demonstration that increased emperipolesis results in a significant "right shift" in megakaryocyte ploidy determined by flow cytometry.

Survival and lung pathology of mouse models of Hermansky-Pudlak syndrome and Chediak-Higashi syndrome

Hermansky-Pudlak Syndrome (HPS), a recessively inherited disease in humans, affects the biosynthesis/processing of the related intracellular organelles: lysosomes, melanosomes, and platelet dense granules. The disease is multigenic in both humans and mice where 14 separate genes have been demonstrated to be causative. Patients often die prematurely with severe lung abnormalities. Patients with the related Chediak-Higashi Syndrome (CHS) likewise have significantly reduced life spans. Long-term survival and lung histomorphology were analyzed in a pilot experiment involving several genetically defined singly and doubly mutant mouse HPS mutants and the beige CHS mutant to determine whether these parameters are altered in the mouse models. The mutants differed widely in both longevity and lung architecture. Mice doubly homozygous for the pale ear and ruby eye or for the muted and pearl genes had the shortest life spans with none surviving the two-year experimental duration. Life spans were similarly severely reduced in the beige and gunmetal mutants. Intermediate life spans were apparent in the pearl, pallid, and cocoa mutants whereas minimal effects were noted in ruby eye, muted, light ear, and cocoa mutants. Enlarged air spaces were noted in histologic sections of lungs of several of the mutants. For the most part, the severity of lung abnormalities was inversely proportional to the long-term survival of these various mutants, suggesting that lung pathology may contribute to mortality, as has been suggested for human HPS patients.

Regulation of plasminogen activator inhibitor-1 mRNA accumulation by basic fibroblast growth factor and transforming growth factor-beta1 in cultured rat astrocytes

The effects of transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) were examined on the accumulation of plasminogen activator inhibitor-1 (PAI-1) mRNA in astrocytes in vitro. Both cytokines stimulated PAI-1 mRNA expression transiently with a maximal fivefold (bFGF) and 30-fold (TGF-beta1) at 4 h, decreasing to basal levels within 32 h. EC50 values were 1.4 nM for bFGF and 6.7 pM for TGF-beta1 on PAI-1 mRNA accumulation. A twofold increase in content of tPA mRNA was observed with bFGF but not with TGF-beta1. The action of TGF-beta1 on PAI-1 mRNA was inhibited by cycloheximide, indicating a requirement for de novo protein synthesis. In contrast, cycloheximide potentiated the action of bFGF. Nuclear run-on assays showed that bFGF, but not TGF-beta1, stimulated astrocytic PAI-1 gene transcription. Thus, TGF-beta1 predominantly uses posttranscriptional mechanisms to raise the level of PAI-1 mRNA in astrocytes, whereas bFGF acts at both the transcriptional and posttranscriptional levels. The data reveal differences in the mechanisms underlying the regulation of PAI-1 mRNA levels by TGF-beta1 in astrocytes compared with other cells. The action of TGF-beta1 and bFGF on the plasminogen activator system in astrocytes might be involved in the cellular events accompanying glial activation following injury of the CNS.

Cultured astrocytes express functional receptors for galanin

The neuropeptides galanin and calcitonin gene-related peptide (CGRP) are strongly up-regulated in motoneurons following axotomy. Earlier reports have suggested that peptides might be released from injured neurons to recruit surrounding glia. In this study, the effects of galanin and CGRP on cultured rat astrocytes were investigated using the expression of immediate early genes as a model for receptor-mediated transcriptional activation. Galanin was found to induce c-fos, junB, and Tis11 mRNA in cultured astrocytes, providing evidence for the presence of functional galanin receptors on neuroglial cells. In contrast, CGRP only led to the induction of c-fos and junB mRNA. Cholecystokinin (CCK-8) and substance P, which are also up-regulated in select motoneuron populations following axotomy, fail to induce immediate early genes in astrocytes, indicating specificity of neuropeptides in their ability to stimulate glial cells. The differential induction of immediate early gene expression by galanin and CGRP in astrocytes points to differences in intracellular signal transduction mechanisms. Whereas CGRP was found to stimulate the accumulation of cyclic AMP by 10- to 20-fold, galanin had no effect on basal cyclic AMP content. The effect of CGRP on cyclic AMP accumulation was completely reversed by the CGRP receptor antagonist, CGRP(8-37). These results suggest roles for galanin and CGRP in the transcriptional activation of astrocytes.

Stimulation of P2Y-purinoceptors on astrocytes results in immediate early gene expression and potentiation of neuropeptide action

The action of adenosine-5'-O-(2-thiodiphosphate), a non-hydrolysable purine analogue and potent P2Y1-purinoceptor agonist, was studied on immediate early gene expression in rat astrocyte cultures. A rapid and transient increase in c-fos, junB, c-jun and Tis11 messenger RNA was observed in cultured astrocytes after treatment with adenosine-5'-O-(2-thiodiphosphate). Maximal induction of immediate early gene expression was obtained within 30 min of stimulation and c-fos was the most sensitive indicator of P2Y-purinoceptor activation. Calcitonin gene-related peptide has also been shown to be a potent inducer of c-fos messenger RNA in cultured astroglial cells. The combined stimulation of astrocytes with calcitonin gene-related peptide and adenosine-5'-O-(2-thiodiphosphate) resulted in the potentiated expression of c-fos messenger RNA. The superinduction of immediate early gene expression by calcitonin gene-related peptide and extracellular ATP in cultured astrocytes might result from intracellular signal transduction cross-talk, since adenosine-5'-O-(2-thiodiphosphate) was found to increase calcitonin gene-related peptide-induced cyclic AMP accumulation by 35%. Phorbol 12-myristate 13-acetate also increased calcitonin gene-related peptide-evoked cyclic AMP accumulation and led to the induction of immediate early gene expression, suggesting that protein kinase C might be at least in part involved in purinergic cross-talk. Our results demonstrate synergistic roles for extracellular ATP and calcitonin gene-related peptide in the transcriptional activation of astroglial cells.

Induction of urokinase-type plasminogen activator in rat facial nucleus by axotomy of the facial nerve

The response of plasminogen activator activity in the CNS to peripheral nerve axotomy was examined in vivo. After transection of the rat facial nerve, a transient increase in plasminogen activator activity was observed in the facial nucleus on the operated side with maximal activity 3-5 days after lesion. This activity was inhibited by the urokinase-specific inhibitor amiloride but not by antibodies against tissue plasminogen activator. The molecular mass of the induced form of plasminogen activator was estimated to be approximately 48 kDa. An in vitro assay of plasminogen hydrolysis also demonstrated an increase in amiloride-sensitive plasminogen activator activity in facial nerve extracts following facial nerve axotomy. These data indicate that the plasminogen activator activity induced in the facial nucleus following axotomy of facial motoneurons is of the urokinase type. It is suggested that the urokinase-type plasminogen activator might play a role in the events accompanying injury and regeneration in the facial nucleus following motoneuron lesion.

Molecular markers near the mouse brachymorphic (bm) gene, which affects connective tissues and bleeding time

Several inherited skeletal/connective tissue defects are associated with hemorrhagic disorders in humans. Accordingly, three mouse mutants (brachymorphic [bm], hemimelic extra toes [Hx], and ulnaless [Ul]), with inherited skeletal abnormalities, were analyzed for hemorrhagic tendencies. All three had prolonged bleeding times. Platelet numbers, size, and function, as well as common soluble plasma clotting factors, were not measurably affected. To further define the bm mutation, its chromosomal location relative to 19 other molecular markers was determined to a high resolution in a large interspecific backcross. Several microsatellite markers were found to be very closely linked to bm and should provide useful entry points for the eventual identification of this gene by positional/candidate cloning techniques. These results suggest that inherited skeletal abnormalities and bleeding tendencies are associated more frequently in both humans and animal models than is commonly recognized. Identification of these genes may reveal novel relationships between osteogenesis and hemostasis.

Inherited prolonged bleeding time and platelet storage pool deficiency in the subtle gray (sut) mouse

A high proportion of mouse mutants with diluted pigmentation have severely prolonged bleeding times due to platelet storage pool deficiency. The deficiency is associated with concomitant abnormalities in platelet dense granules and coat pigment granules. The coat color of the subtle gray (sut) mouse is diluted to a relatively minor degree. Analysis of platelet serotonin concentration established that this dense granule component similarly is reduced a relatively small amount in this mutant. The subtle gray mouse thus allowed a test of the hypothesis that relatively small changes in platelet dense granule contents may cause discernible increases in bleeding times. Bleeding times of mutant mice were significantly prolonged (3.4-fold) in comparison with those in normal sut/+ controls. These bleeding times were significantly reduced in comparison with other mouse pigment dilution mutants with more severe storage pool deficiency. These results establish the subtle gray mouse as an appropriate animal model for mild storage pool deficiency and human Hermansky-Pudlak syndrome. They indicate, together with related experiments, that bleeding times are highly sensitive to concentrations of platelet dense granule components such as serotonin.

Calcitonin gene-related peptide and ATP induce immediate early gene expression in cultured rat microglial cells

Factors affecting gene expression in microglial cells were investigated using the induction of immediate early genes in cultured microglia as a model. In particular, the actions of calcitonin gene-related peptide (CGRP) and ATP, both of which have been proposed as signalling molecules in the activation of glial cells, were evaluated using Northern blotting and in situ hybridization methods. In the presence of CGRP, c-fos and junB mRNAs accumulated in microglial cultures, whereas no significant change in c-jun and TIS11 mRNAs occurred. A similar pattern of immediate early gene activation was obtained when adenylate cyclase was stimulated with forskolin. CGRP also stimulated cyclic AMP accumulation with a half-maximal effect in the range 2-5 nM, suggesting a possible role for cyclic AMP as a mediator of the effects of CGRP on gene expression. In contrast to the selective induction of c-fos and junB by CGRP and forskolin, ATP led to the accumulation of all four immediate early genes studied, i.e., c-fos, junB, c-jun, and TIS11. Similar results were obtained when protein kinase C was stimulated with phorbol ester indicating that the induction of immediate early gene expression by ATP and CGRP involves different intracellular mechanisms. The action of ATP was mimicked by ADP and the poorly hydrolyzable analogues, ADP beta S and 2-methylthio ATP, but not by beta, gamma-methylene ATP, AMP, or adenosine, indicating that the receptor mediating the actions of ATP on microglial gene expression is probably of the P2Y-purinoreceptor type. The results suggest roles for CGRP and ATP as transcriptional activators in microglial cells.

Astrocytes and microglia as potential targets for calcitonin gene related peptide in the central nervous system

Injury of peripheral motoneurons leads to the activation of astrocytes and microglia in the vicinity of the damaged neurons in the central nervous system. It has been proposed that neuropeptides such as the calcitonin gene related peptide (CGRP), which show an increased expression in motoneurons following axotomy, play a role as signalling molecules mediating the interactions between the damaged neurons and surrounding glial cells. Evidence supporting this hypothesis is provided by in vitro investigations of the actions of neuropeptides on glial cells. CGRP induces activation of both astrocytes and microglia at the transcriptional level, as seen by the stimulation of mRNA for the immediate early gene, c-fos, in these cells in culture. In addition to its stimulation of immediate early gene expression, treatment of astrocyte cultures with CGRP stimulated release of the tissue plasminogen activator and led to the accumulation of mRNAs for tissue plasminogen activator and the plasminogen activator inhibitor 1. These components of the plasminogen activator system, which has been implicated in processes of tissue remodelling, are upregulated in astrocytes in the facial nucleus in vivo after facial nerve axotomy. The data suggest a role for CGRP as a mediator of glial cell activation following motoneuron injury.

Inherited thrombocytopenia caused by reduced platelet production in mice with the gunmetal pigment gene mutation

Hereditary macrothrombocytopenia and prolonged bleeding times are associated with the recessive mouse pigment dilution gene gunmetal (gm). Other platelet abnormalities include a mild storage pool deficiency and abnormal expression of two low-molecular-weight guanosine triphosphate binding proteins. These studies were designed to further elucidate the cause of the macrothrombocytopenia. The life span of gunmetal mouse platelets was not significantly different from normal. However, rates of platelet synthesis, measured by sulfate incorporation, were decreased to 25% of normal values. Bone marrow transplantation of normal marrow cells corrected the thrombocytopenia. Furthermore, direct morphologic analysis of mature mutant marrow megakaryocytes by transmission electron microscopy showed reductions in the normal cytoplasmic demarcation membrane system, areas of abnormal membrane complexes, and an increased incidence of emperipolesis. Mutant platelets were relatively more heterogeneous in size and contained unusual elongated and striated inclusions. Mutant megakaryocyte numbers were increased threefold to fivefold over normal numbers in marrow and spleen. Thus, the efficiency of platelet production from gunmetal megakaryocytes is reduced by an order of magnitude. Mutant marrow had a greater proportion of 32N and a smaller proportion of 8N megakaryocytes. Collectively, the results indicate that the gunmetal gene acts intrinsically in megakaryocytes and that an abnormality in this gene causes significant qualitative and quantitative effects on platelet production.

von Willebrand disease in the RIIIS/J mouse is caused by a defect outside of the von Willebrand factor gene

An animal model for human type I von Willebrand disease (vWD) has been previously described in the inbred mouse strain RIIIS/J. Murine vWD is characterized by a prolonged bleeding time, normal von Willebrand factor (vWF) multimer distribution, autosomal dominant inheritance, and proportionately decreased plasma vWF antigen, ristocetin cofactor, and factor VIII (FVIII) activities. To study the molecular genetics of murine vWD, a portion of the vWF gene surrounding exon 28 was cloned, sequenced, and used to develop two informative DNA sequence polymorphisms for rapid genotyping by DNA polymerase chain reaction. RIIIS/J mice were crossed with PWK/Ph mice, an inbred line of Mus musculus musculus, and the F1 progeny backcrossed to the parental PWK/Ph strain. vWF antigen levels in F1 mice were not significantly different from the parental RIIIS/J strain but were markedly decreased compared with the parental PWK/Ph mice. Genetic linkage analysis of 104 backcross progeny showed no correlation between vWF antigen level and vWF genotype. These data indicate that murine vWD is caused by a defect at a novel genetic locus, distinct from the murine vWF gene. The distribution of vWF antigen levels among backcross progeny suggests the presence of one major dominant vWD gene in the RIIIS/J mouse with possible modifying contributions from one or more additional minor loci. These observations may provide new insights into the molecular basis and variable expressivity of human vWD.

Inherited abnormalities in platelet organelles and platelet formation and associated altered expression of low molecular weight guanosine triphosphate-binding proteins in the mouse pigment mutant gunmetal

Gunmetal (gm/gm) is a recessively inherited mouse pigment dilution mutant that has high mortality and poor reproductive rates. In these studies, several hematologic defects were found associated with the mutation, including prolonged bleeding times, together with thrombocytopenia and increased platelet size. A unique feature is the presence of simultaneous abnormalities in two platelet organelles, dense granules and alpha-granules. The dense granule component serotonin is present at about half the normal concentration, as are visible dense granules. Three alpha-granule components (fibrinogen, platelet factor 4, and von Willebrand factor) are also significantly reduced. Thus, in several respects the gunmetal mutant resembles the human gray platelet syndrome. A novel abnormality in expression of low molecular weight guanosine triphosphate (GTP)-binding proteins occurs in platelets of gunmetal. In Western blot assays, two additional GTP-binding proteins of 28.5 and 25 Kd were detected. The abnormal expression of GTP-binding proteins is, like the hematologic defects, genetically recessive and is tissue specific. Liver, kidney, brain, spleen, macrophages, and neutrophils have normal GTP-binding protein expression. The additional GTP-binding proteins are soluble. The data indicate that platelet formation and platelet organelle biogenesis are under common genetic control and that abnormal regulation of GTP-binding proteins may affect one or both processes.

Platelet storage pool deficiency associated with inherited abnormalities of the inner ear in the mouse pigment mutants muted and mocha

Several inherited human syndromes have combined platelet, auditory, and/or pigment abnormalities. In the mouse the pallid pigment mutant has abnormalities of the otoliths of the inner ear together with a bleeding abnormality caused by platelet storage pool deficiency (SPD). To determine if this association is common, two other mouse pigment mutants, muted and mocha, which are known to have inner ear abnormalities, were examined for hematologic abnormalities. Both mutants had prolonged bleeding times accompanied by abnormalities of dense granules as determined by whole mount electron microscopy of platelets and by labeling platelets with mepacrine. When mutant platelets were treated with collagen, there was minimal secretion of adenosine triphosphate and aggregation was reduced. Lysosomal enzyme secretion in response to thrombin treatment was partially reduced in muted platelets and markedly reduced in mocha platelets. Similar reductions in constitutive lysosomal enzyme secretion from kidney proximal tubule cells were noted in the two mutants. These studies show that several mutations that cause pigment dilution and platelet SPD are associated with abnormalities of the inner ear. Also, these mutants, like previously described mouse pigment mutants, are models for human Hermansky-Pudlak syndrome and provide additional examples of single genes that simultaneously affect melanosomes, lysosomes, and platelet dense granules.

The action of calcitonin gene-related peptide on astrocyte morphology and cyclic AMP accumulation in astrocyte cultures from neonatal rat brain

The actions of calcitonin gene-related peptide (CGRP) were investigated on 9- to 14-day-old astrocyte cultures obtained from the cerebra of 1- to 2-day-old rats. The morphological appearance of the cells was monitored by immunofluorescent staining of glial fibrillary acidic protein (GFAP), and the concentration of adenosine 3',5'-monophosphate (cyclic AMP) was measured in the cultures using radioimmunoassay. CGRP induced a morphological change in cultured astrocytes from rat brain. Flat, polygonal cells positive for GFAP became multipolar with many processes. In addition, CGRP stimulated the accumulation of cyclic AMP by up to 30-fold, half maximal stimulation being obtained at CGRP concentrations in the range 100-300 nM. These data provide evidence for the presence of functional CGRP receptors on astrocytes and suggest a role for CGRP as an intercellular messenger controlling the state of differentiation and activation of astroglial cells.

Sandy: a new mouse model for platelet storage pool deficiency

Sandy (sdy) is a mouse mutant with diluted pigmentation which recently arose in the DBA/2J strain. Genetic tests indicate it is caused by an autosomal recessive mutation on mouse Chromosome 13 near the cr and Xt genetic loci. This mutation is different genetically and hematologically from previously described mouse pigment mutations with storage pool deficiency (SPD). The sandy mutant has diluted pigmentation in both eyes and fur, is fully viable and has prolonged bleeding times. Platelet serotonin levels are extremely low although ATP dependent acidification activity of platelet organelles appears normal. Also, platelet dense granules are extremely reduced in number when analysed by electron microscopy of unfixed platelets. Platelets have abnormal uptake and flashing of the fluorescent dye mepacrine. Secretion of lysosomal enzymes from kidney and from thrombin-stimulated platelets is depressed 2- and 3-fold, and ceroid pigment is present in kidney. Sandy platelets have a reduced rate of aggregation induced by collagen. The sandy mutant has an unusually severe dense granule defect and thus may be an appropriate model for cases of human Hermansky-Pudlak syndrome with similarly extreme types of SPD. It represents the tenth example of a mouse mutant with simultaneous defects in melanosomes, lysosomes and/or platelet dense granules.

Autoradiographic localization of adenosine A1 receptors in brainstem of fetal sheep

Quantitative autoradiographic techniques were used to localize adenosine A1 receptors at the light microscopic level with the antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine [( 3H]DPCPX) in the brainstem of fetal sheep. Since adenosine has been proposed as a neuromodulator, which effects the depression of fetal breathing movements during hypoxia, attention was directed to respiratory neuronal areas. The highest density of A1 receptors in respiratory related groups was found in an area of the rostral ventrolateral medulla, which is ventral to the facial nucleus, caudal to the superior olive and lateral to the rostral inferior olive. Intermediate densities were seen in the medial and lateral parabrachial nuclei. Adenosine A1 receptor density was low in the areas of the nucleus of the solitary tract and the nucleus ambiguous. These data suggest that moderate hypoxia in the fetus may depress respiration by withdrawing a tonic stimulus at the level of the ventral lateral medullary chemoreceptors.

Modulation of A1 adenosine receptor function in rat brain by the polyamine, spermine

Studies on factors modulating the binding of agonist ligands to A1 adenosine receptors in rat forebrain membranes revealed that the reduction of [3H]cyclohexyladenosine [( 3H]CHA) binding, observed after removing Mg2+ by pretreatment with ethylene-dinitrilo-tetraacetic acid (EDTA), was restored by the polyamine, spermine (1mM). Parallel electrophysiological experiments performed on rat hippocampal slices in Mg(2+)-free medium indicated that spermine also led to a recovery of the depressive effect of 1 microM adenosine on stimulus train-evoked neuronal Ca2+ influx. These observations suggest that the polyamine, spermine is, like Mg2+, able to control the physiological adenosine-mediated modulation of synaptic transmission by changing the affinity state of A1 receptors.

The RIIIS/J inbred mouse strain as a model for von Willebrand disease

Mice of the RIIIS/J inbred strain have prolonged bleeding times (greater than 15 minutes) after experimental injury when compared with normal C57BL/6J mice (1.8 minutes) and other strains of mice. The prolonged bleeding time was accompanied by normal platelet counts. Platelet aggregation with collagen and agglutination with ristocetin were not significantly altered in RIIIS/J mice. Also, platelets from RIIIS/J mice had normal serotonin content and normal numbers of dense granules by electron microscopy. Thus, the bleeding abnormality is not due to platelet storage pool deficiency as has been found in several other mouse mutants. The activated partial thromboplastin time (APTT) which plasma from RIIIS/J mice was prolonged compared with normal mice, and factor VIII:C activity and von Willebrand antigen levels were one half to one third that of normal mouse plasma. Factor XI activity was also significantly deficient (levels at 42% to 64% of normal). Plasma of RIIIS/J mice contained the full complement of multimers of von Willebrand factor, although each multimer was lower in concentration compared with that in normal mice. Platelet alpha-granule von Willebrand antigen levels were similar to those of normal mice. The prolonged bleeding time of RIIIS/J mice was corrected by treatment with desmopressin. Heterozygous C57BL/6J x RIIIS/J F1 animals had low plasma von Willebrand antigen levels like the RIIIS/J parent and had variable bleeding times. Inheritance of the bleeding tendency was as an incomplete dominant, autosomal trait. These data indicate the RIIIS/J strain is a suitable animal model for type IA von Willebrand disease.

Effects of mixed chimeric bone marrow repopulation on platelet storage pool-associated bleeding defects in mouse mutants

We have previously shown mouse platelet storage pool deficiency (SPD) to be associated with lesions at eight different genetic loci, each of which is sufficient to produce murine SPD. We have also shown that normal bleeding times and normal platelet functions are restored when mice with SPD are transplanted with marrow from normal mice. Conversely, when normal mice are transplanted with mutant marrow, they present symptoms of SPD. In order to determine the amount of normal platelets needed to prevent the prolonged bleeding times associated with SPD, we established stable mixed chimeric mice by transplanting various ratios of normal and mutant marrow into lethally irradiated host animals. The proportion of normal input marrow correlated well with the proportion of normal peripheral red blood cells and platelets determined in chimerae 100 days after transplantation using direct morphology and electrophoretic variants of glucose phosphate isomerase to identify normal and mutant cell populations. The proportions of normal input marrow were also reflected in the proportions of platelets with normal and mutant platelet morphology in the chimerae. This confirms that the platelet abnormality in SPD is intrinsic to the stem cell population from which the platelets are derived. When bleeding times were determined in the mixed chimeric mice, a surprisingly high percentage of normal platelets (greater than 50% and sometimes greater than 75%) were needed to stop bleeding. These results suggest that the mutant platelets in the mixed chimeric mice may interfere with normal platelet aggregation patterns. They also raise some important considerations in devising treatment for SPD. Bleeding episodes in human SPD are normally treated by platelet transfusion. The results suggest that, at least in some cases, transfusions may not be effective. Also, in future gene therapy of this disease, it is like that a functional gene will have to be present in greater than 50% of stem cells for therapy to be effective.

Both A1 and A2a purine receptors regulate striatal acetylcholine release

The receptors responsible for the adenosine-mediated control of acetylcholine release from immunoaffinity-purified rat striatal cholinergic nerve terminals have been characterized. The relative affinities of three analogues for the inhibitory receptor were (R)-phenylisopropyladenosine greater than cyclohexyladenosine greater than N-ethylcarboxamidoadenosine (NECA), with binding being dependent of the presence of Mg2+ and inhibited by 5'-guanylylimidodiphosphate [Gpp(NH)p] and adenosine receptor antagonists. Adenosine A1 receptor agonists inhibited forskolin-stimulated cholinergic adenylate cyclase activity, with an IC50 of 0.5 nM for (R)-phenylisopropyladenosine and 500 nM for (S)-phenylisopropyladenosine. A1 agonists inhibited acetylcholine release at concentrations approximately 10% of those required to inhibit the cholinergic adenylate cyclase. High concentrations (1 microM) of adenosine A1 agonists were less effective in inhibiting both adenylate cyclase and acetylcholine release, due to the presence of a lower affinity stimulatory A2 receptor. Blockade of the A1 receptor with 8-cyclopentyl-1,3-dipropylxanthine revealed a half-maximal stimulation by NECA of the adenylate cyclase at 10 nM, and of acetylcholine release at approximately 100 nM. NECA-stimulated adenylate cyclase activity copurified with choline acetyltransferase in the preparation of the cholinergic nerve terminals, suggesting that the striatal A2 receptor is localized to cholinergic neurones. The possible role of feedback inhibitory and stimulatory receptors on cholinergic nerve terminals is discussed.

Radiation inactivation analysis of the A1 adenosine receptor of rat brain. Decrease in radiation inactivation size in the presence of guanine nucleotide

Radiation inactivation analysis of the binding of the A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine to rat brain membranes yielded a radiation inactivation size of 58 kDa. In the presence of GTP gamma S this was reduced to 33 kDa, in good agreement with the size of the ligand-binding subunit detected after photoaffinity labelling. The data indicate that the structural association of A1 adenosine receptors with G-protein components is altered in situ in the presence of guanine nucleotides.

The cellular localization of adenosine receptors in rat neostriatum

Using quantitative autoradiography of ligand binding sites combined with lesions of specific neuronal pathways, the cellular locations of A1 and A2 adenosine receptors, as well as a third binding site for the adenosine receptor ligand, [3H]N-ethylcarboxamidoadenosine, and a nucleoside transporter were investigated in rat neostriatum. Intrastriatal kainic acid administration resulted in the loss of 50% of A1 adenosine receptors and virtually abolished ligand binding to A2 receptors. A small reduction in [3H]cyclohexyladenosine binding to striatal A1 receptors was found after lesioning the corticostriatal input. A2 receptor sites were unaffected by this treatment. Destruction of dopaminergic neurons using 6-hydroxydopamine or the raphestriatal serotoninergic input using 5,7-dihydroxytryptamine affected neither A1 nor A2 binding sites. These results indicate the localization of both A1 and A2 adenosine receptors on neurons intrinsic to the neostriatum and probably postsynaptic to the dopaminergic input. In addition, a binding site for [3H]N-ethylcarboxamidoadenosine which is not affected by the adenosine receptor agonist, R-phenylisopropyladenosine, was also partly abolished after kainic acid injection. In contrast, no significant change in the binding of the nucleoside transporter ligand, [3H]nitrobenzylthioinosine, was observed after any lesions, indicating the widespread association of this site with various cell types.

Effect of carbamazepine on stimulus-evoked Ca2+ fluxes in rat hippocampal slices and its interaction with A1-adenosine receptors

In rat hippocampal slices superfused with a medium lacking Mg2+ ions, CA1 neurons generated burst discharges which were sensitive to blockade by 2-amino-5-phosphonovaleric acid (APV) and antagonized by 20-50 microM carbamazepine (CBZ). Decreases of [Ca2+]o (delta Ca), evoked by repetitive synaptic activation, were reduced in the presence of CBZ by 20-50%, associated with a reduced membrane depolarization. CBZ also abolished an APV-sensitive increase of delta Ca in the synaptic area elicited by theophylline. CBZ inhibited binding of the A1-adenosine receptor antagonist, [3H]8-cyclopentyl-1,3-dipropylxanthine [( 3H]DPCPX), in a dose-dependent manner. The displacement curve was shifted to the left in the presence of guanine nucleotide, suggesting that CBZ acts as an antagonist at A1-receptors. It is concluded that CBZ exerts its electrophysiological actions in the hippocampus at a site beyond the ligand recognition moiety.

Cocoa: a new mouse model for platelet storage pool deficiency

We describe genetic, haematological and biochemical properties of a new mouse pigment mutant, cocoa (coa). Cocoa is a recessive mutation located on the centromeric end of chromosome 3 near the Car-2 locus. The mutation causes increased bleeding time accompanied by symptoms of platelet storage pool deficiency (SPD), including decreased platelet serotonin and decreased visibility of dense granules as analysed by electron microscopy of unfixed platelets. Dense granules were visible in normal numbers when platelets were incubated with the fluorescent dye, mepacrine. The intragranular environment, however, was abnormal as indicated by decreased flashing of mepacrine-loaded dense granules after exposure to ultraviolet light. Unlike the previously described seven mouse pigment mutations with SPD in which pigment granules, platelet dense granules and lysosomes are affected, the cocoa mutant had normal secretion of lysosomal enzymes from kidney proximal tubule cells and platelets. The cocoa mutation thus represents an example of a single gene which simultaneously affects melanosomes and platelet dense granules but probably does not affect lysosomes. The results indicate that melanosomes and platelet dense granules share steps in synthesis and/or processing. Cocoa may be a model for cases of human Hermansky-Pudlak syndrome in which functions of melanosomes and platelet dense granules, but not lysosomes, are involved.

8-Cyclopentyl-1,3-dipropylxanthine (DPCPX)--a selective high affinity antagonist radioligand for A1 adenosine receptors

The properties of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) as an antagonist ligand for A1 adenosine receptors were examined and compared with other radioligands for this receptor. DPCPX competitively antagonized both the inhibition of adenylate cyclase activity via A1 adenosine receptors and the stimulation via A2 adenosine receptors. The Ki-values of this antagonism were 0.45 nM at the A1 receptor of rat fat cells, and 330 nM at the A2 receptor of human platelets, giving a more than 700-fold A1-selectivity. A similar A1-selectivity was determined in radioligand binding studies. Even at high concentrations, DPCPX did not significantly inhibit the soluble cAMP-phosphodiesterase activity of human platelets. [3H]DPCPX (105 Ci/mmol) bound in a saturable manner with high affinity to A1 receptors in membranes of bovine brain and heart, and rat brain and fat cells (KD-values 50-190 pM). Its nonspecific binding was about 1% of total at KD, except in bovine myocardial membranes (about 10%). Binding studies with bovine myocardial membranes allowed the analysis of both the high and low agonist affinity states of this receptor in a tissue with low receptor density. The binding properties of [3H]DPCPX appear superior to those of other agonist and antagonist radioligands for the A1 receptor.

Immature dense granules in platelets from mice with platelet storage pool disease

Mepacrine uptake into platelets and bone marrow megakaryocytes was analyzed to further characterize the dense granule defects in a group of seven mouse pigment mutants that have characteristics of platelet storage pool disease (SPD). In contrast to our previous studies using electron microscopy, this method revealed that all mutants had normal numbers of dense granules. However, total mepacrine uptake in all mutant platelets was significantly diminished to less than 50% of normal uptake. Also, the flashing phenomenon observed when normal dense granules are irradiated with ultraviolet light was either greatly diminished or absent when platelets of individual mutants were similarly irradiated. Therefore the principal defect in the mutant platelets is an inability to accumulate dense granule contents rather than an absence of the granules. Mepacrine uptake into megakaryocytes was indistinguishable in normal and mutant mice. This indicates the mutant dense granule defects appear either very late in megakaryocyte development or early in platelet formation in correlation with development of the mature dense granule. By standard transmission electron microscopy we have not been able to detect gross structural or subcellular abnormalities in either platelets or megakaryocytes of mutant mice. It appears all seven mutants produce immature or functionally abnormal dense granules.

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.

Heterogeneity of binding sites for N-ethylcarboxamido[3H]adenosine in rat brain: effects of N-ethylmaleimide

Binding sites for N-ethylcarboxamido[3H]adenosine (NECA) in rat brain membranes and cryostat sections were examined in relation to their sensitivities to displacement by unlabeled NECA and R(-)-phenylisopropyladenosine (R-PIA). In membrane fractions from cerebral cortex, cerebellum, hippocampus and striatum, nanomolar concentrations of these adenosine receptor agonists displaced [3H]NECA such that R-PIA was more effective than NECA, consistent with the presence of an A1-adenosine receptor. At concentrations of displacing agent higher than 1 microM, R-PIA was unable to displace [3H]NECA further in cerebral cortex, cerebellum and hippocampus. In striatum, a second R-PIA-sensitive component of [3H]NECA binding was evident which was more sensitive to NECA than to R-PIA, i.e. it showed the characteristics of an A2-adenosine receptor. In striatum, however, R-PIA was also unable to displace [3H]NECA binding completely. Similar results were obtained in quantitative autoradiographic studies. Preincubation of cryostat sections with N-ethylmaleimide (NEM) abolished both the A1- and R-PIA-insensitive binding components such that both NECA and R-PIA were able to displace [3H]NECA binding completely. The remaining sites showed IC50 values of 0.13 and 3.68 microM for NECA and R-PIA, respectively. These A2-like [3H]NECA binding sites had a highly specific distribution in the brain, being concentrated in the striatum, nucleus accumbens and olfactory tubercle. The results indicate the presence in brain tissue of at least 3 classes of [3H]NECA binding sites, an A1-site, an A2-site and a third, unidentified R-PIA-insensitive site.

Autoradiographic evidence for multiple CNS binding sites for adenosine derivatives

The binding of the adenosine analogues, 5'-N-ethylcarboxamido[3H]adenosine and N6-cyclohexyl[3H]adenosine, to the rat brain was examined utilizing light-microscopic autoradiographic techniques. While associated with many of the same structures, binding sites for these compounds showed distinct differences in both their patterns of distribution and their capacities to be inhibited by the adenosine analogue, R-phenylisopropyladenosine. Previous studies have shown that, at nanomolar concentrations, cyclohexyladenosine and R-phenylisopropyladenosine bind rather exclusively to the A1 type of adenosine receptors. In contrast, 5'-N-ethylcarboxamidoadenosine has almost equal affinity for A1 and A2 sites. Taking advantage of these characteristics, non-A1 binding sites were resolved by examining 5'-N-ethylcarboxamidoadenosine binding in the presence of micromolar concentrations of unlabeled R-phenylisopropyladenosine. The autoradiographically demonstrated distribution of R-phenylisopropyladenosine-insensitive 5'-N-ethylcarboxamidoadenosine binding sites differed significantly from that of the cyclohexyladenosine binding sites. Such non-A1 binding sites were concentrated in the striatum, nucleus accumbens, medial geniculate, olfactory tubercle, amygdala and certain thalamic nuclei. In contrast to the distribution of A1 adenosine receptor sites, R-phenylisopropyladenosine-insensitive 5'-N-ethylcarboxamidoadenosine binding was only low to moderate in the hippocampus, cerebellum and superior colliculus, regions which are strongly positive for cyclohexyladenosine binding. The present study provides the first autoradiographic evidence for multiple adenosine binding sites in the brain by demonstrating that the adenosine analogue 5'-N-ethylcarboxamidoadenosine can bind to a site or sites distinct from the A1 adenosine receptor site. The 5'-N-ethylcarboxamidoadenosine binding site which is not displaced by low concentrations of R-phenylisopropyladenosine may correspond to an A2 adenosine receptor site and/or an as yet uncharacterized type of adenosine receptor.

The distribution of adenosine A1 receptors and 5'-nucleotidase in the hippocampal formation of several mammalian species

The distributions of adenosine A1 receptors, as demonstrated by 3H-cyclohexyladenosine (3H-CHA) binding, and the adenosine-producing enzyme 5'-nucleotidase were examined in the hippocampal formation of the rat, mouse, gerbil, cat, hamster, rabbit, and guinea pig. The enzyme and binding sites were restricted to subregions and often individual layers of this structure. The distribution of 3H-CHA binding was consistent among the species with the strata radiatum and oriens of fields CA1 and CA3 exhibiting the highest levels of binding. A distinct band of 3H-CHA binding was observed in the stratum moleculare of the dentate gyrus; and in most species, this band was restricted to the inner one-third of the stratum moleculare (i.e., proximal to the stratum granulosum). The strata pyramidale, granulosum, and lucidum were in general only weakly positive for 3H-CHA binding. The binding to the stratum lacunosum/moleculare (or the distinct strata lacunosum and moleculare in the rabbit and cat) was moderate. In contrast to the relative consistency of the patterns of 3H-CHA binding in these species, 5'-nucleotidase exhibited wide variations in both the absolute amount of activity and its localization. In all species, the strata granulosum and pyramidale appeared devoid of 5'-nucleotidase activity. The only clear exception to this rule was the CA3 region of the cat where activity was seen between the cell bodies of stratum pyramidale. The strata radiatum and oriens of CA1 were strongly positive in the rat and hamster but only low to moderately stained in the other species examined.(ABSTRACT TRUNCATED AT 250 WORDS)

1,3-Dipropyl-8-cyclopentylxanthine (DPCPX) inhibition of [3H]N-ethylcarboxamidoadenosine (NECA) binding allows the visualization of putative non-A1 adenosine receptors

The binding of the adenosine receptor agonists, [3H]N-ethylcarboxamidoadenosine (NECA) and [3H]cyclohexyladenosine (CHA) to membrane preparations and to cryostat sections of the rat brain was examined. The xanthine derivative, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) was ca. 500-fold more effective at A1 than at A2 sites. [3H]CHA binding to A1 adenosine receptors was virtually eliminated by the inclusion of DPCPX (50 nM), while [3H]NECA binding was only partially inhibited. The pattern of DPCPX-insensitive [3H]NECA binding sites was strikingly different from that of A1 receptors and is believed to represent an association with A2 type adenosine receptors and perhaps another or several, previously undescribed non-A1 sites.

Properties of binding sites for [3H]cyclohexyladenosine in the hippocampus and other regions of rat brain: a quantitative autoradiographic study

The properties of binding sites for the adenosine receptor ligand, [3H]cyclohexyladenosine ([3H]CHA), were investigated in rat brain using quantitative autoradiography. Scatchard analysis of the binding data showed that there were no significant differences between Kd values for [3H]CHA in any of the regions investigated. The highest concentrations of [3H]CHA binding sites were found in the cerebellum (molecular layer) and the stratum oriens and stratum radiatum of the hippocampus (CAI region). Displacement curves obtained using N-ethylcarboxamidoadenosine (NECA) and the R- and S-diastereoisomers of phenylisopropyl adenosine (PIA) showed the [3H]CHA binding sites to have the pharmacological properties of A1-adenosine receptors, i.e. the order of potency for these derivatives was R-PIA greater than NECA greater than S-PIA, in all regions tested. Further, [3H]CHA binding was in all cases attenuated by the guanosine triphosphate derivative, beta, gamma-imidoguanosine triphosphate. These results indicate that [3H]CHA binding sites throughout the central nervous system have the properties of A1-adenosine receptors and that these are in all regions associated with guanine nucleotide regulatory proteins.

Tubuloglomerular feedback-mediated decreases in glomerular pressure in Munich-Wistar rats

These experiments were performed to evaluate directly measured glomerular capillary pressure and single nephron glomerular filtration rate (SNGFR) tubuloglomerular feedback responses in Munich-Wistar rats during increased distal flow rate achieved by infusing an isotonic electrolyte solution into unblocked late proximal tubules. Arterial pressure averaged 114 +/- 2 mmHg and proximal tubule pressure was 14 +/- 1 mmHg. In eight tubules, control SNGFR based on distal tubular fluid collections averaged 22 +/- 3 nl/min, decreased to 15 +/- 2.3 nl/min when 10-12 nl/min of perfusate was infused into the late proximal tubule, and further decreased to 9 +/- 1.7 nl/min at an infusion of 20-24 nl/min. In 22 tubules, control glomerular capillary pressure was 55 +/- 1.6 mmHg, decreased to 43 +/- 2.5 mmHg with addition of perfusate into a late proximal tubule at a rate of 24 nl/min, and returned to 53 +/- 3.1 mmHg when perfusion was stopped. In eight nephrons, glomerular capillary pressure was shown to be responsive to smaller increments in the late proximal infusion rate and was reduced by 4 +/- 0.5 and 7 +/- 1.1 mmHg at the intermediate rates of 10 and 15 nl/min, respectively. These results demonstrate that glomerular pressure decreases during increased distal delivery even when the tubule is not blocked. They are consistent with the hypothesis that increases in afferent arteriolar resistance are primarily responsible for feedback-mediated reductions in glomerular filtration rate.

Subcellular localization of 5'-nucleotidase in rat brain

The subcellular distribution of the ectoenzyme, 5'-nucleotidase, in cerebral cortex and cerebellum of the rat was studied both biochemically and cytochemically. The fractions were characterized biochemically by marker enzymes. The localization of 5'-nucleotidase activity was also investigated cytochemically in the myelin, synaptosomal, mitochondrial, and microsomal fractions. Biochemically 5'-nucleotidase was found to be enriched in the membrane-containing fractions, i.e., myelin, synaptosomal, and microsomal fractions. Cytochemistry showed the reaction product in the myelin fraction to be associated with myelin profiles. In the synaptosomal fraction reaction product could occasionally be seen at synaptosomal membranes, although it could not be attributed unequivocally to the synaptosome itself, since in positions with reaction product unidentifiable membrane structures could always be seen attached. Mitochondria were virtually without any reaction product. In the microsomal fraction 5'-nucleotidase activity was associated with unidentifiable membrane structures. It is concluded that 5'-nucleotidase is associated with myelin profiles and that the high activity found in the synaptosomal fraction is probably not associated with nerve ending plasma membranes.

Adenosine receptor density and the depression of evoked neuronal activity in the rat hippocampus in vitro

The relationship between the heterogeneous distribution of A-1 adenosine receptors and the capacity of adenosine to depress neuronal activity was examined in the rat hippocampus. Utilizing autoradiographic techniques, the distribution of A-1 adenosine receptors was assessed by the binding of [3H]cyclohexyladenosine ([3H]CHA) to cryostat sections of rat brain. The apical dendritic region of CA1 showed a differential distribution of adenosine receptors between the stratum radiatum and stratum lacunosum/moleculare. The physiological relevance of this binding difference was studied in the hippocampal slice by examining the capacity of adenosine to depress evoked potentials in these two strata. It was observed that the receptor differences correlated with differential sensitivities to adenosine modulation of the evoked potentials. These data suggest that receptor density, as shown by binding techniques, may provide not only a qualitative but also a quantitative map of the sites of adenosine action.

Regulation of the strength of adenosine modulation in the hippocampus by a differential distribution of the density of A1 receptors

Correlative studies examining: (1) the binding of [3H]cyclohexyladenosine to A1 adenosine receptor sites, and (2) the depressive action of adenosine on evoked activity, were performed in the hippocampal formation. A greater number of A1 sites was observed in the dorsal versus ventral aspect of the hippocampus, and a larger depression of evoked potentials by adenosine was obtained in the dorsal aspect. These observations suggest that a differential density of A1 receptors might control the magnitude of modulatory action by adenosine on hippocampal circuitry.

Adenosine metabolism in a rat hippocampal slice preparation: incorporation into S-adenosylhomocysteine

The incorporation of [14C]adenosine into various metabolites was studied in a hippocampal slice preparation in order to assess the extent of adenosine metabolism via synthesis of S-adenosylhomocysteine, a potent inhibitor of transmethylation reactions. Highest incorporation of 14C occurred into nucleotides, with only a few percent being recovered in inosine + hypoxanthine, S-adenosylhomocysteine, and the free adenosine pool. Labeling of S-adenosylhomocysteine did not significantly increase with higher concentrations of added adenosine despite greater accumulation of free [14C]adenosine in the tissue. Addition of L-homocysteine significantly increased the labelling of S-adenosylhomocysteine. The results indicate that S-adenosylhomocysteine synthesis is a minor pathway of adenosine metabolism in brain tissue under steady-state conditions. Further, changes in adenosine concentration, without a concomitant change in L-homocysteine availability, are unlikely to lead to a significant accumulation of S-adenosylhomocysteine. S-Adenosylhomocysteine is therefore not likely to play a significant role in mediating the biological effects of adenosine in the CNS via inhibition of transmethylations.

5'-Nucleotidase activity in human astrocytomas

Human astrocytomas contain 5'-nucleotidase as shown using histochemical, cytochemical and biochemical techniques. 5'-Nucleotidase activity was revealed by electron microscopy to be associated with the outer surface of the plasma membrane of astrocytoma cells. The results confirm and extend previous reports of the localisation of 5'-nucleotidase in normal astrocytes in situ. Biochemical assay of 5'-nucleotidase activity in 35 tumours showed it to be clearly higher in malignant (anaplastic astrocytomas and glioblastomas) than in benign astrocytomas.

An A1-adenosine receptor, characterized by [3H] cyclohexyladenosine binding, mediates the depression of evoked potentials in a rat hippocampal slice preparation

In slices of rat hippocampus, adenosine and several adenosine derivatives depressed evoked neuronal responses to afferent stimulation. The nanomolar potency of adenosine derivatives and their relative effectiveness indicate that the depression of evoked potentials is mediated via an A1-adenosine receptor. A remarkable similarity was found between the relative potencies of nucleoside derivatives with respect to their electrophysiological effects and to their inhibition of high affinity [3H] cyclohexyladenosine ([3H]CHA) binding to rat brain membranes. We conclude that the [3H] CHA binding site in rat brain membranes represents a physiological receptor of the A1-type.