Development of chiral N-alkylcarbamates as new leads for potent and selective H3-receptor antagonists: synthesis, capillary electrophoresis, and in vitro and oral in vivo activity

Novel carbamates as derivatives of 3-(1H-imidazol-4-yl)propanol with an N-alkyl chain were prepared as histamine H3-receptor antagonists. Branching of the N-alkyl side chain with methyl groups led to chiral compounds which were synthesized stereospecifically by a Mitsunobu protocol adapted Gabriel synthesis. The optical purity of some of the chiral compounds was determined (ee > 95%) by capillary electrophoresis (CE). The investigated compounds showed pronounced to high antagonist activity (Ki values of 4.1-316 nM) in a functional test for histamine H3 receptors on rat cerebral cortex synaptosomes. Similar H3-receptor antagonist activities were observed in a peripheral model on guinea pig ileum. No stereoselective discrimination for the H3 receptor for the chiral antagonists was found with the in vitro assays. All compounds were also screened for central H3-receptor antagonist activity in vivo in mice after po administration. Most compounds were potent agents of the H3-receptor-mediated enhancement of brain Ntau-methylhistamine levels. The enantiomers of the N-2-heptylcarbamate showed a stereoselective differentiation in their pharmacological effect in vivo (ED50 of 0.39 mg/kg for the (S)-derivative vs 1.5 mg/kg for the (R)-derivative) most probably caused by differences in pharmacokinetic parameters. H1- and H2-receptor activities were determined for some of the novel carbamates, demonstrating that they have a highly selective action at the histamine H3 receptor.

Ciproxifan and chemically related compounds are highly potent and selective histamine H3-receptor antagonists

We determined the affinities of five newly synthesized histamine H3-receptor antagonists in an H3-receptor binding assay and their potencies in a functional H3-receptor model. Furthermore, we determined their potencies in a histamine H2- and H1-receptor model. The compounds differ from histamine in that the ethylamine side chain is replaced by an aryl-substituted propyloxy chain and they differ from one another by varying substituents of the aryl rest. Iodoproxyfan, a highly potent and selective antagonist at H3 receptors, is structurally related to these five compounds. The specific binding of [3H]-Nalpha-methylhistamine to rat brain cortex membranes was monophasically displaced by each of the five compounds at pKi values ranging from 8.24 to 9.27. Inhibition by histamine of the electrically evoked tritium overflow from mouse brain cortex slices preincubated with [3H]noradrenaline was antagonized by all compounds and the concentration-response curve was shifted to the right with apparent pA2 values ranging from 7.78 to 9.39. The five compounds under study possess negligible potencies at histamine H2 and H1 receptors studied in the guinea-pig right atrium and ileum, respectively (pD'2 or pKp values < or = 5.2). The present paper shows that the five compounds under study possess high affinities and potencies at histamine H3 receptors, four out of the five compounds in this respect being equipotent with iodoproxyfan. Like iodoproxyfan, the five compounds show an at least 1000-fold selectivity for H3 as compared to H2 and H1 receptors.

Migratory flight strategies of Levant sparrowhawks: time or energy minimization?

Diurnal and nocturnal flight paths of 364 Levant sparrowhawks, Accipiter brevipes, were recorded by radar and used to analyse migratory strategies. Soaring-gliding was the predominant flight strategy during the day when thermals were available. Also during the day, and at night, flapping-gliding flight was used. Levant sparrowhawks flew at similar altitudes as other migrating raptors in Israel during the day; however, they showed different diurnal patterns, using flapping flight at high altitudes soon after sunrise and late in the afternoon. Migratory directions were strongly concentrated on a south-southwest-north-northeast axis in spring and autumn, whereby birds compensated for lateral drift. Soaring-gliding birds maximized cross-country airspeed according to optimal flight theory and, thus, minimized time needed per distance. In flapping-gliding flight, they adjusted their airspeed with respect to the wind to fly at the maximum range speed, suggesting that they minimized energy consumption per distance. Calculations based on aerodynamic flight theory showed that the optimal migratory strategy of a Levant sparrowhawk with respect to time and energy depends on feeding conditions en route: in poor conditions, both time and energy are minimized by a pure soaring-gliding flight strategy. If food is available en route, soaring-gliding flight should be combined with flapping flight when no thermals are available, as this will minimize time spent on migration. The evidence for both strategies is discussed. Copyright 1998 The Association for the Study of Animal Behaviour.

Neurochemical and behavioral effects of ciproxifan, a potent histamine H3-receptor antagonist

Ciproxifan, i.e., cyclopropyl-(4-(3-1H-imidazol-4-yl)propyloxy) phenyl) ketone, belongs to a novel chemical series of histamine H3-receptor antagonists. In vitro, it behaved as a competitive antagonist at the H3 autoreceptor controlling [3H]histamine release from synaptosomes and displayed similar Ki values (0.5-1.9 nM) at the H3 receptor controlling the electrically-induced contraction of guinea pig ileum or at the brain H3 receptor labeled with [125I]iodoproxyfan. Ciproxifan displayed at least 3-orders of magnitude lower potency at various aminergic receptors studied in functional or binding tests. In vivo, measurement of drug plasma levels, using a novel radioreceptor assay in mice receiving ciproxifan p.o. or i.v., led to an oral bioavailability ratio of 62%. Oral administration of ciproxifan to mice enhanced by approximately 100% histamine turnover rate and steady state level of tele-methylhistamine with an ED50 of 0.14 mg/kg. Ciproxifan reversed the H3-receptor agonist induced enhancement of water consumption in rats with and ID50 of 0.09 +/- 0.04 mg/kg, i.p. In cats, ciproxifan (0.15-2 mg/kg, p.o.) induced marked signs of neocortical electroencephalogram activation manifested by enhanced fast-rhythms density and an almost total waking state. In rats, ciproxifan enhanced attention as evaluated in the five-choice task performed using a short stimulus duration. Ciproxifan appears to be an orally bioavailable, extremely potent and selective H3-receptor antagonist whose vigilance- and attention-promoting effects are promising for therapeutic applications in aging disorders.

4-Alkynylphenyl imidazolylpropyl ethers as selective histamine H3-receptor antagonists with high oral central nervous system activity

In search for potent and therapeutically useful H3-receptor antagonists, we prepared novel 4-alkynylphenyl ether derivatives of 3-(1H-imidazol-4-yl)propanol in a convenient synthetic route. All compounds were tested for in vitro and in vivo H3-receptor antagonist activity as well as for H3-receptor selectivity versus H1- and H2-receptors. The presented 4-alkynylphenyl ethers are highly potent and selective H3 antagonists showing oral activity and improved brain penetration. Particularly 4-ethynylphenyl 3-(1H-imidazol-4-yl)propyl ether (14a) displays striking in vitro and in vivo activity with a -log Ki value of 8.6 and an ED50 value of 0.12 mg/kg. At present 14a is the most potent H3-receptor antagonist in vivo and may therefore be a potential drug for the therapy of H3-receptor-dependent diseases of the central nervous system (CNS).

General construction pattern of histamine H3-receptor antagonists: change of a paradigm

Novel omega-phenyl substituted and unsubstituted alkyl and alkenyl imidazole derivatives were prepared and tested for their antagonist activity in vitro and in vivo at histamine H3-receptors. Some compounds showed high in vitro and in vivo H3-receptor activity despite their structure bearing no polar moiety in the centre of the molecule which is a common structural feature of all other antagonists known. Quite probably there are further in vivo effects for some compounds resulting from other receptor interactions.

Development of a binding site model for histamine H3-receptor agonists

On the basis of molecular modelling studies the structural and conformational requirements for receptor affinity and activity of histamine H3-receptor agonists were studied. It was shown that the known H3-receptor agonists can be fitted accurately into a common pharmacophoric pattern. Using the YAK pseudoreceptor approach an amino acid model for the H3-receptor agonist binding site was generated which reflects binding properties and biological data of the investigated agonists. The postulated binding site model was validated by predicting biological data for four structures not considered in model construction. The amino acid positions of the pseudoreceptor were found to be in good agreement with calculated GRID interaction fields for the investigated histamine H3-receptor agonists.

Correlation of the expansion segments in mammalian rRNA with the fine structure of the 80 S ribosome; a cryoelectron microscopic reconstruction of the rabbit reticulocyte ribosome at 21 A resolution

Samples of 80 S ribosomes from rabbit reticulocytes were subjected to electron cryomicroscopy combined with angular reconstitution. A three-dimensional reconstruction at 21 A resolution was obtained, which was compared with the corresponding (previously published) reconstruction of Escherichia coli 70 S ribosomes carrying tRNAs at the A and P sites. In the region of the intersubunit cavity, the principal features observed in the 70 S ribosome (such as the L1 protuberance, the central protuberance and A site finger in the large subunit) could all be clearly identified in the 80 S particle. On the other hand, significant additional features were observed in the 80 S ribosomes on the solvent sides and lower regions of both subunits. In the case of the small (40 S) subunit, the most prominent additions are two extensions at the base of the particle. By comparing the secondary structure of the rabbit 18 S rRNA with our model for the three-dimensional arrangement of E. coli 16 S rRNA, these two extensions could be correlated with the rabbit expansion segments (each totalling ca 170 bases) in the regions of helix 21, and of helices 8, 9 and 44, respectively. A similar comparison of the secondary structures of mammalian 28 S rRNA and E. coli 23 S rRNA, combined with preliminary modelling studies on the 23 S rRNA within the 50 S subunit, enabled the additional features in the 60 S subunit to be sub-divided into five groups. The first (corresponding to a total of ca 335 extra bases in helices 45, 98 and 101) is located on the solvent side of the 60 S subunit, close to the L7/L12 area. The second (820 bases in helices 25 and 38) is centrally placed on the solvent side of the subunit, whereas the third group (totaling 225 bases in helices 18/19, 27/29, 52 and 54) lies towards the L1 side of the subunit. The fourth feature (80 bases in helices 78 and 79) lies within or close to the L1 protuberance itself, and the fifth (560 bases in helix 63) is located underneath the L1 protuberance on the interface side of the 60 S subunit.

Development of FUB 181, a selective histamine H3-receptor antagonist of high oral in vivo potency with 4-(omega-(arylalkyloxy)alkyl)-1H-imidazole structure

A series of 4-(omega-(arylalkyloxy)alkyl)-1H-imidazoles and related sulphur-containing compounds have been prepared and evaluated for their histamine H3-autoreceptor antagonist in vitro potency in an assay on synaptosomes of rat cerebral cortex. In addition, the in vivo potency has been determined from the changes in N tau-methylhistamine levels in brain after p.o. administration to mice. Compounds with different alkyl chains and various aryl moities have been synthesized and tested to explore structure-activity relationships. Within this series of novel antagonists, (1H-imid-azol-4-yl)methyl and 2-(1H-imidazol-4-yl)ethyl ether derivatives showed low to moderate H3-receptor antagonist potency, whereas the corresponding allyl and propyl derivatives were compounds with high antagonist in vitro potency. Corresponding thioether or sulphoxide derivatives also showed antagonists activity. Additionally, some ether derivatives possessed high in vivo potency as well. The most active ether derivatives under in vivo conditions were 4-(3-(3-(4-fluorophenyl)propyloxy)propyl)-1H-imidazole (11b) and the corresponding chloro compound 11c (FUB 181) with ED50 values of 0.76 and 0.80 mg/kg, respectively. On the other hand, all compounds tested showed weak activity at histamine H1 or H2 receptors. Furthermore, the most promising ether FUB 181 exhibited low activity at adrenergic alpha 1, beta 1/2, serotonergic 5-HT2A, 5-HT3, and muscarinic M3 receptors. Time-course investigations of FUB 181 in mice showed a rapid mode of action with the highest value 3 h after p.o. application. Thus, FUB 181 appears to block histamine H3 receptors potently and selectively.

Effects of intracerebroventricularly infused histamine and selective H1, H2 and H3 agonists on food and water intake and urine flow in Wistar rats

The actions of intracerebroventricularly-infused histamine and selective histamine H1, H2 and H3 receptor agonists on food and water intake and urine flow were studied in rats. It was found that 100-800 nmoles of histamine significantly suppressed feeding. The H1 agonist 2-(3- trifluoromethylphenyl)histamine (FMPH) decreased food intake, whereas the H2 agonist dimaprit was without effect. Histamine- and FMPH-induced suppressions of feeding were attenuated by blockade of H1 but not by H2 receptors. The results clearly demonstrate that activation of brain H1 receptors decreases food intake. In subsequent studies, we found that both metoprine and thioperamide, which increase histaminergic activity through different mechanisms, also reduced food intake. This finding indicates that the brain histaminergic system is associated with feeding behavior. The same is true with body water homeostasis. Histamine caused a long-lasting diuresis. Also dimaprit and metoprine increased urine flow and the blockade of H2 receptors abolished the diuretic responses to histamine and dimaprit. On the other hand, the H3 agonist (R)-alpha-methylhistamine elicited drinking and this effect could be prevented by thioperamide pretreatment. The results imply that activation of H3 receptors predominantly provokes drinking, whereas central H2 receptors mediate the diuretic effect of histamine.

Improvement by FUB 181, a novel histamine H3-receptor antagonist, of learning and memory in the elevated plus-maze test in mice

Effects of FUB 181 [3-(4-chlorophenyl)propyl-3-(1H-imidazol-4-yl)propyl ether], a novel histamine H3-receptor antagonist, on a scopolamine-induced learning deficit in the elevated plus-maze test were studied in mice. FUB 181 alone (2.5 and 5 mg/kg, i.p.) ameliorated the scopolamine-induced learning deficit in mice. This effect was antagonized by BP 2.94 (10 mg/kg, i.p.), a prodrug of (R)-alpha-methylhistamine (histamine H3-receptor agonist), and by ketotifen (4 mg/kg, i.p.), a histamine H1-receptor antagonist, both penetrating the blood-brain barrier. However, the ameliorating effect of FUB 181 (2.5 mg/kg) was not antagonized by either terfenadine (10 mg/kg, i.p.), a histamine H1-receptor antagonist with poor penetration of the blood-brain barrier, or zolantidine (20 mg/kg, i.p.), a centrally effective histamine H2-receptor antagonist. In a biochemical study, FUB 181 had no significant effect on either acetylcholine or choline level in mice brain at the doses tested. These findings suggest that FUB 181 increases the release of histamine by blocking presynaptic histamine H3 autoreceptors, and that released histamine in turn activates postsynaptic H1 and H2 receptors, predominantly histamine H1 receptors, and in this fashion improves learning and memory in mice. Our findings also suggest that the histaminergic system may play an important role in learning and memory, and that FUB 181 may be a clinical candidate for the therapy of dementia.

The 80S rat liver ribosome at 25 A resolution by electron cryomicroscopy and angular reconstitution

BACKGROUND

The ribosome is central to protein synthesis in all living organisms. Single-particle electron cryomicroscopy has recently led to the determination of three-dimensional structures of bacterial ribosomes to approximately 20 A, which have since revolutionised our understanding of ribosomal function. The structure we present here of the 80S rat liver ribosome leads the way to similar progress for mammalian ribosomes.

RESULTS

Among the new details revealed by our 25 A structure of the 80S rat liver ribosome are channels within the subunits, a large 'flat ribosomal surface' (FRS) on the outer surface of the large subunit and structural extensions of the mammalian compared to the bacterial ribosome. The main large subunit channel in both the bacterial and the mammalian species starts at the peptidyl transferase centre, below the central protuberance, and ends in the FRS, at the lower back of the large subunit. Structurally, the channels of both species can be directly superimposed.

CONCLUSIONS

The mammalian structural extensions--none of which trespass the FRS--can be interpreted in terms of rRNA inserts and additional protein content over that of bacterial ribosomes. The main large subunit channel, which ends at the FRS, is the best candidate for the exit channel for proteins targeted for the endoplasmic reticulum.

Visualization of elongation factor Tu on the Escherichia coli ribosome

The delivery of a specific amino acid to the translating ribosome is fundamental to protein synthesis. The binding of aminoacyl-transfer RNA to the ribosome is catalysed by the elongation factor Tu (EF-Tu). The elongation factor, the aminoacyl-tRNA and GTP form a stable 'ternary' complex that binds to the ribosome. We have used electron cryomicroscopy and angular reconstitution to visualize directly the kirromycin-stalled ternary complex in the A site of the 70S ribosome of Escherichia coli. Electron cryomicroscopy had previously given detailed ribosomal structures at 25 and 23 A resolution, and was used to determine the position of tRNAs on the ribosome. In particular, the structures of pre-translocational (tRNAs in A and P sites) and post-translocational ribosomes (P and E sites occupied) were both visualized at a resolution of approximately 20 A. Our three-dimensional reconstruction at 18 A resolution shows the ternary complex spanning the inter-subunit space with the acceptor domain of the tRNA reaching into the decoding centre. Domain 1 (the G domain) of the EF-Tu is bound both to the L7/L12 stalk and to the 50S body underneath the stalk, whereas domain 2 is oriented towards the S12 region on the 30S subunit.

A new model for the three-dimensional folding of Escherichia coli 16 S ribosomal RNA. III. The topography of the functional centre

We describe the locations of sites within the 3D model for the 16 S rRNA (described in two accompanying papers) that are implicated in ribosomal function. The relevant experimental data originate from many laboratories and include sites of foot-printing, cross-linking or mutagenesis for various functional ligands. A number of the sites were themselves used as constraints in building the 16 S model. (1) The foot-print sites for A site tRNA are all clustered around the anticodon stem-loop of the tRNA; there is no "allosteric" site. (2) The foot-print sites for P site tRNA that are essential for P site binding are similarly clustered around the P site anticodon stem-loop. The foot-print sites in 16 S rRNA helices 23 and 24 are, however, remote from the P site tRNA. (3) Cross-link sites from specific nucleotides within the anticodon loops of A or P site-bound tRNA are mostly in agreement with the model, whereas those from nucleotides in the elbow region of the tRNA (which also exhibit extensive cross-linking to the 50 S subunit) are more widely spread. Again, cross-links to helix 23 are remote from the tRNAs. (4) The corresponding cross-links from E site tRNA are predominantly in helix 23, and these agree with the model. Electron microscopy data are presented, suggestive of substantial conformational changes in this region of the ribosome. (5) Foot-prints for IF-3 in helices 23 and 24 are at a position with close contact to the 50 S subunit. (6) Foot-prints from IF-1 form a cluster around the anticodon stem-loop of A site tRNA, as do also the sites on 16 S rRNA that have been implicated in termination. (7) Foot-print sites and mutations relating to streptomycin form a compact group on one side of the A site anticodon loop, with the corresponding sites for spectinomycin on the other side. (8) Site-specific cross-links from mRNA (which were instrumental in constructing the 16 S model) fit well both in the upstream and downstream regions of the mRNA, and indicate that the incoming mRNA passes through the well-defined "hole" at the head-body junction of the 30 S subunit.

Search for novel leads for histamine H3-receptor antagonists: oxygen-containing derivatives

This study was performed in order to develop new leads for antagonists of the histamine H3-receptor subtype. omega-(1 H-Imidazol-4-yl)alkyl derivatives with ester, ketone or alcohol functionality in the side chain were synthesized and tested concerning their H3-receptor antagonist activity on synaptosomes of rat cerebral cortex. The novel compounds, which possess no nitrogen-containing polar group in the side chain of the imidazole moiety, presented moderate to high antagonist potency in vitro. In this series 3-(1 H-imidazol-4-yl)propyl-3-cyclopentylpropanoate (4) was the most potent compound in vitro with -log Ki = 8.5. Unfortunately, no central antagonist H3-receptor activity was detectable for ester derivatives in the in vitro H3-receptor assay based upon measurement of brain N tau-methylhistamine levels after p.o. administration to mice. Some of these novel antagonists are useful tools for investigations on ligand-receptor interaction because of their distinct receptor activities. On the other hand, the ketone derivative 1-(1 H-imidazol-4-yl)-7-phenyl-4-heptanone (9) in vitro presented an ED50-value of 3.5 +/- 1.5 mg/kg p.o. thus proving to be a new lead for further drug investigations. The most potent compounds in vitro and in vivo also showed high H3-receptor selectivity when tested at other histamine receptor subtypes.

Search for novel leads for histamine H3-receptor antagonists: amine derivatives

In search for novel leads for histamine H3-receptor antagonists a number of amine derivatives of different (1 H-imidazol-4-yl)anilines and omega-(1 H-imidazol-4-yl)alkanamines were prepared. Pharmacological in vitro H3-receptor investigations of the prepared urea, amide, inverse amide, thioamide, and thiourea derivatives on synaptosomes of rat cerebral cortex proved that the aniline derivatives are inactive at H3-receptors, whereas derivatives of the omega-(1 H-imidazol-4-yl)-alkanamines showed moderate to good activity. Some compounds are active in the nanomolar concentration range. The most potent compounds in this series are the thioamide derivative 7 and the urea derivatives 11, 12 of 3-(1 H-imidazol-4-yl) propanamine. Therefore, the urea derivatives were tested in vitro on isolated organs of the guinea pig for their activity on the other two histamine receptor subtypes proving their high selectivity. In vivo studies of the effects of the urea derivatives 11 and 12 on brain Nt-methylhistamine levels, a test of central H3-receptor activity after peroral application to mice, showed no detectable activity. Thus, the urea type antagonists are useful potent and selective H3-receptor tools for in vitro studies and for investigations of ligand-receptor interactions.

Bioavailability, antinociceptive and antiinflammatory properties of BP 2-94, a histamine H3 receptor agonist prodrug

(R)alpha-Methylhistamine [(R)alpha-MeHA], a potent and selective histamine H3 receptor agonist in vitro and in vivo in rodents, was found to display comparatively low plasma level in healthy human volunteers, attributable to an extensive methylation of the drug's imidazole ring by histamine-N-methyltransferase. To limit this inactivation process, BP 2-94, ie., (R)-(-)-2-[[N-[1-(1H-imidazol-4-yl)-2-propyl]imino]phenylmethyl] phenol, was selected as a prodrug. A sensitive radioimmunoassay was developed to study the generation of (R)alpha-MeHA slowly released from BP 2-94 in vitro and in vivo by chemical hydrolysis. In mice after oral administration of BP 2-94 high levels of both prodrug and (R)alpha-MeHA were detected in plasma and various tissues except in the brain. In humans receiving 0.1 mmol BP 2-94 orally, plasma levels of (R)alpha-MeHA-like immunoreactivity decayed with a t(1/2) more than 24 hr, the area under the curve being two orders of magnitude higher than after oral administration of (R)alpha-MeHA. BP 2-94 displayed antiinflammatory and antinociceptive properties in rodents, related to the H3 receptor stimulation. It dose-dependently inhibited capsaicin-induced plasma protein extravasation in many rat tissues with ED50s of 0.6 to 14 micromol/kg p.o., and maximal reductions by 35 to 87%. BP 2-94 also reduced zymosan-induced paw swelling in mice with an ED50 of 1 micromol/kg p.o. and showed marked activity in the phenylbenzoquinone-induced writhing (ED50 = 0.03 micromol/kg, p.o.) or formalin tests in mice, but not in the hot plate jump test. From its pharmacokinetics and pharmacological profile BP 2-94 appears to be a promising novel therapeutic agent in disorders such as asthma, migraine or a variety of inflammatory diseases and pain associated with these disorders.

Urinary tract infections in girls: the cost-effectiveness of currently recommended investigative routines

Current recommendations for the universal investigation of urinary tract infection (UTI) in children by ultrasonography, voiding cystourethrography, and dimercaptosuccinic acid renal scan (and sometimes intravenous pyelography as well) are not based on any convincing evidence as to the necessity or effectiveness of such a routine. Over 8% of all girls will have a UTI during childhood. About 87 individuals in a million will develop end-stage renal disease (ESRD) by the age of 60 years, caused in about 9% by pyelonephritis (PN) or reflux nephropathy. From these statistics, the maximal risk of a first diagnosed UTI progressing to ESRD is approximately 1:10,000. The risk of developing hypertension following a first UTI in childhood, without eventual evolution to ESRD, appears to be very small. The cost of the widely recommended routine imaging procedures ranges from U.S. $355 in Britain to U.S. $1,090 in the United States. The minimal cost of preventing a single progression to ESRD by early diagnosis of underlying pathology-if this were possible in all cases-would range between U.S. $5 million in Britain and U.S. $15 million in the United States. Since in many instances progressive renal damage can not be prevented, the true cost is considerably higher. Lower UTI in girls is a very common and, in most cases, benign finding in primary-care practice. It is suggested that girls with afebrile UTI, presenting with lower urinary tract symptoms alone, need not undergo any imaging procedures, but should be followed with urine examinations and cultures at the time of febrile illness. The recommended investigative routines should be reserved for UTI in infants and in girls with fever or other symptoms suggesting PN, and for proven recurrent UTI. Such a regimen will allow a marked saving in terms of costs and in terms of unnecessary radiation, psychological stress to children, and stress, inconvenience, and time loss to parents. There is no evidence that this approach will compromise the course or final outcome of this very common condition.

Novel Colloidal Interactions in Anisotropic Fluids

Small water droplets dispersed in a nematic liquid crystal exhibit a novel class of colloidal interactions, arising from the orientational elastic energy of the anisotropic host fluid. These interactions include a short-range repulsion and a long-range dipolar attraction, and they lead to the formation of anisotropic chainlike structures by the colloidal particles. The repulsive interaction can lead to novel mechanisms for colloid stabilization.

Binding of histamine H3-receptor antagonists to hematopoietic progenitor cells. Evidence for a histamine transporter unrelated to histamine H3 receptors

Hematopoietic progenitor cells can take up histamine or release IL-3-induced histamine through a bi-directional transport system that is blocked by H3-receptor antagonists. In the present study we demonstrate a correlation between the affinity of various H3-receptor antagonists and their potency as inhibitors of histamine uptake. All compounds that blocked histamine uptake also inhibited IL-3-induced histamine release. Yet, classical H3 receptors are not involved in this biological activity, since highly specific histamine H3-receptor agonists neither alter histamine uptake nor affect the release of endogenous histamine synthesized in response to IL-3. Furthermore, the inhibitory effect of H3-receptor antagonists on histamine uptake was not reversed by the agonists. Unlike H3-receptor antagonists, the agonists did not displace the binding of the labeled antagonist iodoproxyfan.

Quantitation of T2' anisotropic effects on magnetic resonance bone mineral density measurement

In this paper, the authors quantitate the anisotropy of susceptibility effects in an uniaxial trabecular bone model and show its relevance to clinical MR bone mineral density measurements. A physical model is described that quantitates the anisotropic MR behavior of uniaxial trabecular bone. To test the model; a phantom of parallel polyethylene filaments was scanned every 15 degrees between 0 degrees and 90 degrees with respect to the system's main magnetic field (B0). The distal radial metaphysis of a healthy female volunteer was scanned in orthogonal projections. The signal from each phantom image and each radial image was separated in a pixel-wise fashion into R2 and R2' maps. As predicted, R2' relaxation showed anisotropic behavior and changed according to sin2 (theta), confirming that columnar structures parallel with B0 will cause no MR susceptibility effects. Scans of the distal radius showed that R2' relaxation was twice as great with the forearm perpendicular to B0 as when it was parallel to it, demonstrating different contributions from struts and columns. For both phantom and radial bone scans, R2 relaxation was isotropic and did not change with object orientation.

Dopaminergic and serotonergic neurotransmission systems are differentially involved in auditory cortex learning: a long-term microdialysis study of metabolites

Auditory cortex has been shown to be a site of widespread neuronal learning processes even in the context of simple auditory conditioning behavior. In view of their presumed role in determining behavioral and motivational relevance of incoming information we investigated whether the dopaminergic and serotonergic systems are involved in auditory cortex learning. Using a chronic brain microdialysis technique over 4 days, samples from auditory cortex were obtained before, during, and after daily footshock avoidance training simultaneously from trained gerbils and passive control animals or pseudotrained animals. Because of detection limits of dopamine and serotonin in auditory cortex, the response profiles of extracellular homovanillic acid as the metabolite of the dopaminergic system and of 5-hydroxyindoleacetic acid as the metabolite of the serotonergic system were determined from consecutive dialysis samples each day. The response of the dopaminergic system appeared to reflect the initial formation of the behaviorally relevant association exclusively during the first training day, whereas the serotonergic response appeared to correlate with the stress level of animals.