Radioimagers as an alternative to film autoradiography for in situ quantitative analysis of 125I-ligand receptor binding and pharmacological studies

RGD peptides grafting onto poly(ethylene terephthalate) with well controlled densities

The aim of this study was to graft RGD peptides with well controlled densities onto poly(ethylene terephthalate) (PET) film surfaces. Biomimetic modifications were performed by means of a four-step reaction procedure: surface modification in order to create -COOH groups onto polymer surface, coupling agent grafting and finally immobilization of peptides. The originality of this work is to evaluate several grafted densities peptides. Toluidine blue and high-resolution mu-imager (using [(3)H]-Lys) were used to evaluate densities. Moreover, mu-imager has exhibited the stability of peptides grafted onto the surface when treated under harsh conditions. Benefits of the as-proposed method were related to the different concentrations of peptides grafted onto the surface as well as the capacity of RGD peptide to interact with integrin receptors.

Endogenous oxidized indoles share inhibitory potency against [3H]isatin binding in rat brain

Isatin is an endogenous oxidized indole that influences a range of processes in vivo and in vitro. It has a distinct and discontinuous distribution in the brain and [3H]isatin binding sites are widely distributed in rat brain sections. The highest labelling is found in hypothalamic nuclei and in the cortex, hippocampus, and cerebellum (Crumeyrolle-Arias et al., 2003). However, the properties of most isatin binding sites and their physiological ligands remain unknown. In the present study the effects of three endogenous oxidized indoles (oxindole, 5-hyxdoxyoxindole, and isatin) on [3H]isatin binding were investigated in rat brain sections. In most regions cold isatin (0.2 mM) significantly reduced [3H]isatin binding. In addition to isatin, the other endogenous oxidized indoles, 5-hydroxyoxindole and oxindole were effective in displacing [3H]isatin. Total irreversible inhibition of monoamine oxidases caused inhibition of specific [3H]isatin binding in 7 of 10 brain region studied. This was accompanied by altered sensitivity of [3H]isatin binding to these indoles, including regions where a decrease of specific binding was not detected. The combinations of the three oxidized indoles produced two clear effects: augmentation (potentiation) and attenuation (blockade) of inhibitory activity compared with the independent effects of these compounds. The different effects of oxidized indoles and their combinations (isatin + 5-hydroxyoxindole and isatin + oxindole) in various brain regions therefore suggest an interaction of [(3H]isatin with different and multiple isatin-binding sites, which exhibit different sensitivity to endogenous oxidizing indoles.

Competitive displacement binding assay on rat brain sections and using a beta-imager: application to mu-opioid ligands

A new approach of competitive displacement binding assay using brain sections and a beta-imager is presented to estimate binding parameters such as affinity and selectivity of new compounds or to characterize receptor families or subtypes of receptors in small brain regions. This method includes a preliminary saturation assay intended to define the optimal concentration of displaceable radio-labeled ligand followed by the determination of displacement constants (IC(50) and K(i)) in cerebral regions rich in studied receptor. The technique application was demonstrated in seven rat brain structures, using displacement of the selective tritiated mu-opioid ligand [(3)H]-DAMGO by six opioid ligands: a specific agonist (DAMGO), less specific agonists (morphine, remifentanil), a non-specific antagonist with good affinity for mu receptors (naloxone) and ligands specific of other opioid subtypes (naltrindole, U50.488). Radioactivity counts were collected during 48 h. The assay-validation was performed by measuring intra- and inter-assay variation on determinations and by comparing presently obtained K(i) values with data from recognised methodologies. Both prove the accuracy of the proposed method.

Natriuretic peptide interaction with [3H]isatin binding sites in rat brain

Isatin is an endogenous indole, which has a distinct and discontinuous distribution in the brain and exhibits a wide range of physiological and pharmacological effects. In the present study, we have demonstrated that atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) inhibited [3H]isatin binding to rat brain sections and isolated membrane fractions. Isatin itself antagonised not only natriuretic peptide receptor type A (NPR-A) (ANP-stimulation of guanylyl cyclase) but also NPR-C (ANP and CNP mediated inhibition of adenylyl cyclase) signalling. These results suggest that some [3H]isatin binding in the brain may be to NPR-A and NPR-C. Competitive interactions between isatin and natriuretic peptides and their receptors give a possible explanation of the known anxiogenic effect of low doses of isatin, interacting at NPR-A, and the sedative effects of higher doses, antagonising respectively the anxiolytic effect of ANP and the anxiogenic effect of CNP.

Localization of [3H]nicotine, [3H]cytisine, [3H]epibatidine, and [125I]alpha-bungarotoxin binding sites in the brain of Macaca mulatta

We determined the localization of [(3)H]nicotine, [(3)H]cytisine, [(3)H]epibatidine, and [(125)I]alpha-bungarotoxin binding sites in the brain of rhesus monkey by means of receptor autoradiography. The labelings by [(3)H]nicotine, [(3)H]cytisine, and [(3)H]epibatidine were highly concordant, except for epibatidine. Layer IV of some cortical areas, most thalamic nuclei, and presubiculum displayed high levels of labeling for the three ligands. Moderate levels of binding were detected in the subiculum, the septum, and the mesencephalon. Low levels were present in layers I-II and VI of the cortex, the cornu Ammonis, the dentate gyrus, and the amygdala. In addition, the level of epibatidine labeling was very high in the epithalamic nuclei and the interpeduncular nucleus, whereas labeling by nicotine and cytisine was very weak in the same regions. The distribution of [(125)I]alpha-bungarotoxin binding differed from the binding of the three agonists. The labeling was dense in layer I of most cortical areas, dentate gyrus, stratum lacunosum-moleculare of CA1 field, several thalamic nuclei, and medial habenula. A moderate labeling was found in layers V and VI of the prefrontal and frontal cortices, layer IV of primary visual cortex, amygdala, septum, hypothalamus, and some mesencenphalic nuclei. A weak signal was also detected in subiculum, claustrum, stratum oriens, and stratum lucidum of cornu Ammonis and also in some mesencephalic nuclei. The distribution of nicotine, cytisine, and epibatidine bindings corresponds broadly to the patterns observed in rodents, with the marked exception of the epithalamus. However, in monkey, those distributions match the distribution of alpha2 messenger RNA, rather than that of alpha4 transcripts as it exists in rodent brains. The distribution of the binding sites for alpha-bungarotoxin is larger in the brain of rhesus monkeys than in rodent brain, suggesting a more important role of alpha7 receptors in primates.

In situ imaging of specific binding of [3H]isatin in rat brain

Isatin is an endogenous indole that influences a range of processes both in vivo and in vitro. It has a distinct and discontinuous distribution in the brain, as well as in other mammalian tissues and body fluids. However, the distribution of isatin binding sites in the brain is not known. Using a real-time beta-imager we have investigated the distribution of [3H]isatin-specific binding in rat brain sections. The highest labeling was found in hypothalamic nuclei and in the cortex, hippocampus, and cerebellum. Administration of the mechanism based monoamine oxidase inhibitor, pargyline, reduced but did not abolish the specific binding of [3H]isatin in the rat brain. The distribution became cortex, cerebellum, hypothalamus > hippocampus > brain stem > thalamus approximately striatum.

Fate of Entamoeba histolytica during establishment of amoebic liver abscess analyzed by quantitative radioimaging and histology

The protozoan parasite Entamoeba histolytica is the causative agent of amoebiasis, a human disease characterized by dysentery and liver abscess. The physiopathology of hepatic lesions can be satisfactorily reproduced in the hamster animal model by the administration of trophozoites through the portal vein route. Hamsters were infected with radioactively labeled amoebas for analysis of liver abscess establishment and progression. The radioimaging of material from parasite origin and quantification of the number inflammation foci, with or without amoebas, described here provides the first detailed assessment of trophozoite survival and death during liver infection by E. histolytica. The massive death of trophozoites observed in the first hours postinfection correlates with the presence of a majority of inflammatory foci without parasites. A critical point for success of infection is reached after 12 h when the lowest number of trophozoites is observed. The process then enters a commitment phase during which parasites multiply and the size of the infection foci increases fast. The liver shows extensive areas of dead hepatocytes that are surrounded by a peripheral layer of parasites facing inflammatory cells leading to acute inflammation. Our results show that the host response promotes massive parasite death but also suggest also that this is a major contributor to the establishment of inflammation during development of liver abscess.

Distribution, cellular localization and functional role of CCR2 chemokine receptors in adult rat brain

Recent studies demonstrated that the chemokine monocyte chemoattractant protein-1 (MCP-1)/CCL2 and its receptor, CCR2, play important roles in various brain diseases. In this study, using quantitative autoradiography, we studied the pharmacological properties of [125l]MCP-1/CCL2 binding in rat brain and we clearly showed the distribution of CCR2 receptors in cerebral cortex, nucleus accumbens, striatum, amygdala, thalamus, hypothalamus, hippocampus, substantia nigra, mammillary bodies and raphe nuclei. Moreover, using double fluorescent immunohistochemistry, we showed that CCR2 receptors were constitutively expressed on neurons and astrocytes. Using RT-PCR methods, we demonstrated that CCR2 mRNA is present in various brain areas described above. Four hours after an acute intraperitoneal lipopolysaccharide injection, we showed that MCP-1/CCL2 binding was up-regulated in several brain structures; this effect took place on both CCR2B labelled neurons and astrocytes and to a lesser extent on activated microglia. To explore neurobiological function of CCR2, actimetric study was carried out. After intracerebroventricular injections of MCP-1/CCL2, we showed that motor activity was markedly decreased. Our results provide the first evidence for constitutive CCR2 receptor expression with precise neuroanatomical and cellular localizations in the brain, and its regulation during an inflammatory process, suggesting that MCP-1/CCL2 and CCR2 play important physiological and pathophysiological role(s) in the CNS.

Characterization and visualization of [125I] stromal cell-derived factor-1alpha binding to CXCR4 receptors in rat brain and human neuroblastoma cells

Stromal cell-Derived Factor-1 (SDF-1alpha), binds to the seven-transmembrane G protein-coupled CXCR4 receptor and modulates cell migration, differentiation, and proliferation. CXCR4 has been reported to be expressed in various tissues including brain. Moreover, CXCR4 has recently been shown to be one of the coreceptors for HIV-1 infection which could be implicated in HIV encephalitis. In the present study, the binding properties and autoradiographic distribution of [125I]SDF-1alpha binding to CXCR4 were characterized in the adult rat brain. SDF-1alpha binding and CXCR4 coupling system were also studied in human neuroblastoma cell line SK-N-SH. The binding of [125I]SDF-1alpha on rat brain sections was specific, time-dependent and reversible. The highest densities of CXCR4 were detected in the choroid plexus of the lateral and the dorsal third ventricle. Lower densities of [125I]SDF-1alpha binding sites were observed in various brain regions including cerebral cortex, anterior olfactory nuclei, hippocampal formation, thalamic nuclei, blood vessels and pituitary gland. In the choroid plexus, the IC(50) and K(d) of [125I]SDF-1alpha binding were respectively 0.6 nM and 0. 36 nM. Similar IC(50) values were obtained in other brain structures. A CXCR4 antagonist, bicyclam, competed with SDF-1alpha binding (30% inhibition at 10(-6) M). In SK-N-SH cells, [125I]SDF-1alpha bound to CXCR4 with a K(d) of 5.0 nM and a maximal binding capacity of 460 fmol/mg of protein. SDF-1alpha induced a rapid and transient intracellular calcium increase in SK-N-SH cells. These findings suggest that CXCR4 is highly expressed in some brain structures and have a regulatory role in the nervous system. The significance of this expression in the brain parenchyma and more specifically in the choroid plexus remains to be clarified in the normal as well as in the infected brain.

A new gene involved in X-linked mental retardation identified by analysis of an X;2 balanced translocation

X-linked forms of mental retardation (MR) affect approximately 1 in 600 males and are likely to be highly heterogeneous. They can be categorized into syndromic (MRXS) and nonspecific (MRX) forms. In MRX forms, affected patients have no distinctive clinical or biochemical features. At least five MRX genes have been identified by positional cloning, but each accounts for only 0.5%-1.0% of MRX cases. Here we show that the gene TM4SF2 at Xp11.4 is inactivated by the X breakpoint of an X;2 balanced translocation in a patient with MR. Further investigation led to identification of TM4SF2 mutations in 2 of 33 other MRX families. RNA in situ hybridization showed that TM4SF2 is highly expressed in the central nervous system, including the cerebral cortex and hippocampus. TM4SF2 encodes a member of the tetraspanin family of proteins, which are known to contribute in molecular complexes including beta-1 integrins. We speculate that through this interaction, TM4SF2 might have a role in the control of neurite outgrowth.

A new member of the IL-1 receptor family highly expressed in hippocampus and involved in X-linked mental retardation

We demonstrate here the importance of interleukin signalling pathways in cognitive function and the normal physiology of the CNS. Thorough investigation of an MRX critical region in Xp22.1-21.3 enabled us to identify a new gene expressed in brain that is responsible for a non-specific form of X-linked mental retardation. This gene encodes a 696 amino acid protein that has homology to IL-1 receptor accessory proteins. Non-overlapping deletions and a nonsense mutation in this gene were identified in patients with cognitive impairment only. Its high level of expression in post-natal brain structures involved in the hippocampal memory system suggests a specialized role for this new gene in the physiological processes underlying memory and learning abilities.

A new high resolution radioimager for the quantitative analysis of radiolabelled molecules in tissue section

We present a high-speed, high-resolution imager of beta particles. It is devoted to be used in autoradiography experiments such as receptor binding or in situ hybridization experiments, either instead of, or in complement with autoradiographic film and emulsions. It allows the user to locate and perform quantitative analyses of (3H, 14C, 35S, 33P, 32P, 125I) labelled molecules with a 15 microm spatial resolution on a 0.9 x 1.3 cm2 sensitive area. Combining recent techniques (specific scintillator thin sheets and intensified charge-coupled device (CCD)) this imager offers a wide dynamic range and real-time acquisition.

Radio-imaging for quantitative autoradiography in biology

We present here an overview of new in vitro and ex vivo radio-imaging systems developed to overcome the limitations of films and emulsions currently used in histological autoradiography experiments. The shortcomings of films for quantitative studies are first introduced. Principles and performances of each family of imagers are discussed and illustrated in various biological contexts. Finally, perspectives of development including nonradioactive labeling techniques are briefly presented.

Mapping of 5-HT-moduline binding sites in guinea-pig brain by film and digital autoradiography

5-HT-moduline is a cerebral tetrapeptide [Leu-Ser-Ala-Leu] that was recently isolated from bovine brain tissue and shown to interact specifically with 5-HT1B receptors, particularly in rodents. The pharmacological properties of 5-HT1B receptors in rodents are different from those in other species. In order to better understand the role of this peptide in non-rodent species, we determined the distribution of 5-HT-moduline binding sites in guinea-pig brain using both the film autoradiography and digital autoradiography with a newly developed high resolution beta-imaging techniques. We found that 5-HT-moduline binding sites were expressed in various brain regions. Quantitative analysis showed that densities of binding sites were similar to those observed previously in rat brain. Regions with the highest labelling included cortex, septum, hippocampus and some regions of basal ganglia. Our results extend previous data and show that 5-HT-moduline interacts with the two forms of 5-HT1B receptors that are distinct pharmacologically. By this interaction, 5-HT-moduline may play an important role in regulating the functional activity of 5-HT1B receptors, thereby contributes to the pathophysiology of serotonergic transmission.

Interleukin-1 receptor defect in autoimmune NZB mouse brain

Interleukin-1 receptors (IL-1R type I and II) have been characterized in murine nervous structures (hippocampus and frontal cortex), in vascular structures (vessels, choroid plexus), and in the anterior pituitary. Because interleukin-1 (IL-1), injected or induced in the brain, is a powerful regulator of the stress axis and immune functions, it was of interest to investigate IL-1Rs and IL-1 in autoimmune mice. In control mice, bacterial lipopolysaccharide (LPS), administered i.p. or i.c.v., induces a sharp decrease in available brain IL-1 receptors, in spite of a moderate increase in mRNAs for both receptor types. This is concomitant with an increase in IL-1 alpha, beta, and ra mRNA. Ligand production clearly overcomes receptor turnover. In autoimmune mice (NZB and NZB/NZW F1), a strong defect in IL-1R (type I) is demonstrated in the dentate gyrus. This tissue-specific defect cannot be explained by increased occupancy by endogeneous ligands as for LPS-treated mice. The transmission of the defect is Mendelian and suggests the involvement of a single gene. However patterns of IL-1R mRNAs (evaluated by RT-PCR) are similar in NZB and in controls, suggesting a translational or post-translational abnormality. The contribution of this genetic disorder in the development of autoimmunity remains to be clarified. Because the brain IL-1 system sends inhibitory signals towards immune functions, this lack of functional IL-1 binding sites might participate in the disregulations observed in NZB autoimmune mice.