Thrombin receptor on the placental syncytiotrophoblastic plasma membrane

Summary Purified placental syncytiotrophoblastic membrane has been used in a radioreceptor assay to study the binding of tritium radiolabeled human thrombin. Binding was found to be saturable at higher membrane concentrations when using a fixed amount of ligand and showed a hyperbola analogous to enzyme-substrate binding. A Scatchard plot was linear and revealed homogeneous binding sites with a high-affinity constant K_a=3×10¹⁰ M⁻¹ and capacity of 3.05×10¹¹ sites/mg of membrane protein. This high-affinity compares well with chick and embryo cell thrombin receptor which has homogeneous sites and high-affinity in contrast to platelet thrombin receptor which exhibits multiple binding sites and cooperative effects as previously noted. A thrombin receptor on the placenta might serve to mobilize thrombin into placental tissue leading to conversion of fibrinogen into fibrin, fibrinoid necrosis being so common in certain placentae. A receptor-mediated transplacental passage of thrombin into the fetal circulation is also proposed.     

Role of the pineal gland in the regulation of prostatic androgen receptors in pubertal and mature rats

The effects of exposure to continuous light, continuous darkness, and administration of melatonin on prostatic androgen receptors in relation to pubertal development in rats were examined. Darkness produced dissimilar results between the pubertal and adult groups. Whereas the prostate weight in the pubertal group remained unaltered, it increased in the adult group. In the pubertal group exposed to darkness, plasma melatonin increased significantly, and androgen receptors declined, whereas in the adult group these receptors rose significantly with a simultaneous increment of melatonin concentration in plasma. Exposure to continuous light did not produce any effective alterations in the parameters examined. The afternoon melatonin administration showed trends similar to those seen in animals exposed to darkness. The results indicate that exposure to darkness or administration of melatonin both have age-dependent effects on prostatic androgen receptors. Exposure to darkness may interfere with the process of sexual maturation in the pubertal animal as a result of increased melatonin production.     

Significance of testing platelet functions in vitro

Abstract. Platelets respond through discrete receptors to a number of physiological agonists and foreign surfaces with a sequence of measurable responses: shape change, aggregation, secretion and arachidonate liberation. Three secretory responses are distinguished: exocytosis of substances from (1) dense granules, (2) α-granules and (3) lysosomes. Free arachidonate, liberated from phospholipids by phospholi-pase A₂, is rapidly converted (by oxygenation) to prostaglandins and thromboxanes which, together with secreted ADP and close cell contact, will cause further platelet activation through ‘positive feedback’ (autocrine stimulation). Some agonists are classified as ‘weak’ (ADP, vasopressin, platelet-activating factor [PAF], serotonin) because they depend on autocrine stimulation to promote the full sequence of responses, while others are ‘strong’ agonists (thrombin, collagen) and activate all responses directly without autocrine stimulation. Adrenaline, long thought to be a platelet agonist per se, most probably acts by amplifying the activation brought about by other, proper, agonists. Such synergistic interaction among agonists is very typical for platelet activation and most likely takes place in vivo. Shape change, aggregation and secretion(s) may be tested by flow cytometry or electron microscopy in vitro under conditions that probably reflect the in vivo situation. However, the aggregation response to weak agonists in vitro is dependent on the extracellular [Ca²⁺], with biphasic aggregation at the low [Ca²⁺] present when citrate is used as anticoagulant (or in suspension of washed platelets) but not at the physiological [Ca²⁺] present in platelet-rich plasma from heparinized blood.     

Critical evaluation of the ‘heated-hand-technique’ for obtaining ‘arterialized’ venous blood: incomplete arterialization and alterations in glucagon responses

Summary. In order to test the degree of ‘arterialization’ and the occurrence of arterio-(or capillary-) venous differences in glucose concentrations for commonly used blood sampling sites (including the retrogradely cannulated dorsal hand vein with application of dry heat to this hand/arm – the ‘heated-hand-technique’), oxygen partial pressure (oxygen saturation) and plasma glucose was determined in blood drawn from different venous sites before and after an oral glucose load (75 g). Experiments with and without heating (hot air 68°C) were compared in nine healthy volunteers. Basal pO₂ (and oxygen saturation) increased in the order cubital fossa vein < superficial forearm vein < dorsal hand vein. Heating raised pO₂ by ?20 mmHg; P=0.008) and oxygen saturation (P= 0.008–0.02) at all sites, including those on the contralateral arm. Capillary-venous glucose differences after the glucose challenge were significantly related to the sampling site (P< 0.0001). They were reduced by ?50% in response to heat exposure (P=0.008–0.011) and could be correlated to pO₂-values (r=0.92; P= 0.01). The lowest capillary-venous glucose concentration difference was measured with the ‘heated-hand-technique’ (0.4 ± 0.1 mmol l^-1). Heating did not alter integrated incremental glucose (capillary values), insulin, and C-peptide-responses and late, counter-regulatory responses (120–240 min after glucose) of Cortisol, growth hormone, and adrenalin. However, the late glucagon response was enhanced (P=0.011) by heating, concomitant with a significantly reduced ‘reactive’ decrement in glucose concentrations. In conclusion, the ‘heated-hand-technique’ provides blood more similar to arterial blood that can be obtained from other venous sampling sites. However, significant residual differences in pO₂ and glucose concentrations remain. In addition, altered counter-regulatory hormone responses may occur with heating.     

Binding of Dipyridamole to Human Platelets and to α1 Acid Glycoprotein and its Significance for the Inhibition of Adenosine Uptake

The interactions of dipyridamole with α₁ acid glycoprotein of plasma and with human platelets are related to inhibition of adenosine uptake by platelets. Binding studies by equilibrium gel filtration suggested that 1 mol of dipyridamole binds per mol of α₁ acid glycoprotein with a dissociation constant of 1.6 μM. Platelets contain two populations of binding sites, one with high and another with lower affinity for the drug. The binding of dipyridamole to the high-affinity sites follows a Michaelis-Menten binding pattern with a dissociation constant of 0.04 μM. Approximately 2 × 10⁴ dipyridamole molecules are bound at the high-affinity sites of each platelet. The lower affinity sites bind the drug with a dissociation constant of 4 μM. In the presence of α₁ acid glycoprotein of plasma, the binding of dipyridamole to human platelets is inhibited. Correspondingly, the dipyridamole inhibition of adenosine uptake by platelets is reduced 1,000-fold by purified α₁ acid glycoprotein. The binding of dipyridamole to human platelets was found to be essential for its inhibition of adenosine uptake by platelets. Dipyridamole decreases the incorporation of [¹⁴C]adenosine radioactivity in platelet nucleotides and reduces the [¹⁴C]-ATP to [¹⁴C]ADP ratio. Purified α₁ acid glycoprotein reverses these effects of dipyridamole on adenosine metabolism of platelets in a concentration-dependent manner. An equilibrium of dipyridamole binding to α₁ acid glycoprotein and to platelets is proposed.     

CB₁-independent mechanisms of Δ⁹-THCV, AM251 and SR141716 (rimonabant)

What is known and Objective: The potential beneficial therapeutic effects of cannabinoid CB₁ receptor antagonists or partial agonists have driven drug discovery and development efforts and have led to clinical candidates. It is generally assumed that these compounds are CB₁‘selective’ and produce their effects exclusively via CB₁ receptors. Methods: A literature search was conducted of preclinical publications containing information about non‐CB₁ receptor pharmacology of these agents. The information was summarized and evaluated from the perspective of contribution to a fuller understanding of this aspect of these compounds. Results and Discussion: A number of recent studies have revealed that these compounds have CB₁‐independent pharmacological actions. We highlight the evidence regarding effects produced in cells lacking CB₁ receptors, effects on neuronal membranes from CB₁ receptor‐deficient mutant KO ‘knockout’ mice and affinity for μ‐opioid receptors. What is new and Conclusion: CB₁‘selective’ antagonists and partial agonists have been studied for their anorexigenic and other potential therapeutic uses. An awareness of CB₁‐independent mechanism(s) of these agents might contribute to a better understanding of the pharmacologic and toxicologic profiles of these agents.     

Identification of functional GRP-preferring bombesin receptors on human melanoma cells

Bombesin was originally isolated from amphibian skin, wherease its mammalian counterpart, gastrin-releasing peptide (GRP), was first identified in the nervous system of the gastrointestinal tract. Whether GRP is present in the human skin is not known. Bombesin-like peptides are also known to modulate growth. We therefore investigated whether human melanoma cell lines express functional GRP-preferring bombesin receptors and whether they alter growth or other specific cellular functions of these tumour cells. GRP receptor mRNA was found in HBL, D-10, Me-28 and A375-6 cell lines, but only A375-6 cells express a large number of high-affinity binding sites for [¹²⁵I]-[Tyr⁴] bombesin (K_d 0.31 ± 0.04 nmol L^?1, 3880 ± 429 binding sites per cell). Bombesin dose-dependently increased cytosolic calcium, but did not alter interleukin (IL) 1β-induced reduction of cell viability or IL-6 secretion, both A375-6-specific cell functions. Growth of A375-6 cells was not altered by bombesin or the specific GRP receptor antagonist BIM26226 as measured by [³H]-thymidine incorporation or methylene blue assay, whereas insulin alone or in combination with other potential growth factors dose-dependently stimulated growth of these cells. The newly characterized GRP-preferring bombesin receptors on highly malignant human melanoma cells could initiate studies of growth effects on solid tumours or in vivo scanning using radiolabelled tracers.     

Ramelteon: a review of its therapeutic potential in sleep disorders

Ramelteon is a tricyclic synthetic analog of melatonin that acts specifically on MT₁ and MT₂ melatonin receptors. Ramelteon’s half-life is longer than that of melatonin, being metabolized in the body to four main metabolites, M-I, M-II, M-III, and M-IV. M-II has an affinity to MT₁ and MT₂ of about one-tenth of the parent compound, but its concentration in the circulation exceeds that of ramelteon by more than an order of magnitude. Ramelteon is effective in decreasing latency to persistent sleep and increasing total sleep time in freely moving monkeys. A number of clinical studies have been undertaken to study the efficacy of ramelteon in subjects with chronic insomnia. In almost all of these studies, ramelteon, in various doses of 4, 8, or 16 mg most commonly, significantly reduced sleep latency and increased sleep duration. Its primary action in sleep promotion is not a generalized gamma-aminobutyric (GABA)-ergic central nervous system depression, but rather it acts as a melatonergic agonist in the suprachiasmatic nucleus (and at other central nervous system sites), from where downstream processes, including GABA-ergic effects, are controlled via the hypothalamic sleep switch. Unlike other commonly prescribed hypnotic drugs, ramelteon is not associated with next morning hangover effects or reductions in alertness, nor has it been shown to cause withdrawal symptoms. The adverse symptoms reported with ramelteon are mild. All long-term investigations that have been carried out support the conclusion that ramelteon is a well tolerated and effective drug for the treatment of insomnia.     

Binding properties of antagonists to Cannabinoid receptors in intact cells

The implication of the cannabinoid receptor 1 (CB₁ receptor) in several pathophysiological states has sparked the development of selective antagonists. Here we compare binding of the antagonists [³H]‐AZ12491187, [³H]‐taranabant and [³H]‐rimonabant to intact human embryonic kidney cells stably expressing recombinant human CB₁ receptors (CB1r cells). Unlabelled ligands decreased the total binding of the three radioligands with closely the same order of potency: i.e. AZ12288553 ～ AZ12491187 ～ taranabant > rimonabant. Nondisplaceable (i.e. nonspecific) binding to the CB1r cells was the same as total binding to the wells containing untransfected cells and it was more pronounced for [³H]‐AZ12491187 and [³H]‐rimonabant than for [³H]‐taranabant. [³H]‐Rimonabant and (to a lesser extent) [³H]‐AZ12491187 were also prone to bind nonspecifically to the walls of the wells. Compared to the other radioligands, [³H]‐rimonabant displayed lower potency for the CB₁ receptors in saturation binding studies and faster association and dissociation in kinetic experiments. When dissociated, the three radioligands also showed prominent rebinding to the cells in medium only. This could be relieved by the presence of excess of unlabelled ligand and of bovine serum albumin (BSA) but a combination thereof was most efficient. The long ‘residence time’ of AZ12491187 at the CB₁ receptor (because of slow dissociation and prominent rebinding) and its pronounced incorporation into the membranes of the cells could contribute to long‐lasting in vivo CB₁ receptor blockade.     

Jet lag,circadian rhythm sleep disturbances,and depression: the role of melatonin and its analogs

Traveling through several time zones results in a constellation of symptoms known as jet lag. These include reduced alertness, daytime fatigue, loss of appetite, reduced cognitive skills, and disruption of the sleep/wake cycle. In susceptible air travel passengers, jet lag may exacerbate affective illness and result in psychiatric morbidity. Dysregulation of circadian rhythms and melatonin secretion represent the common underlying factor in jet lag and other circadian disorders. Recent studies have established the effectiveness of strategically timed administration of melatonin and appropriate timed exposure to environmental schedules including light in counteracting the dysregulation (chronobiologic actions). With the introduction of melatonergic agonists such as ramelteon and tasimelteon, which have both a stronger affinity for MT₁ and MT₂ melatonin receptors and a longer half-life, new therapeutic options now exist for treating the sleep disturbances associated with jet lag. The melatonin analogs are unique inasmuch as they can also enhance daytime alertness. The recently introduced melatonergic antidepressant agomelatine, which has established its supremacy over other antidepressants in having a significant chronobiologic activity, represents a good choice for treating depressive symptoms that are associated with jet lag.     

Coleoptera in litter of dry sclerophyll eucalypt forest and the effects of low-intensity prescribed fire on their activity and composition in west-central Victoria

Surface-active Coleoptera (beetles) were monitored in dry sclerophyll mixed eucalypt forest of west-central Victoria near Daylesford, and the effects of a one-off low-intensity prescribed fire applied during spring (15 October 1985) or autumn (25 March 1987) were assessed on families and species between 19 March 1985 and 28 February 1989. The study was based on 27 550 adult specimens, ranging in length from 0.5 mm to 22.0 mm and representing 30 families and 109 species, of which 78 species (71.6%) are undescribed. The most commonly trapped ‘major’ families were the Staphylinidae (predominantly predators), followed by the Nitidulidae and Leiodidae (both decomposers/fungus feeders). The specimens were contained in 3 140 pitfall trap samples taken from two sites burnt in spring, two sites burnt in autumn and one ‘control’ site, all adjacent to each other within an 80.5 ha study area. This is the first Australian study that has examined in detail the effects of prescribed fire on both families and species of the Coleoptera within litter of native forest.

A high level of stability in activity was evident among coleopteran populations over the 4-year study period when fire was absent. The same was observed at the two sites burnt in autumn (fire intensity = 176 kW m^?1). Both fires had no effect on family or species richness. However, the spring fire (256 kW m^?1) at one study site temporarily boosted activity of the ‘major’ family Staphylinidae after early autumn of the second post-fire year, and induced a short burst in activity of species Thalycrodes pulchrum (Nitidulidae) during the first post-fire winter, and among Leiodidae during the first postfire spring. At both spring-burnt sites, the pool of the 19 less commonly trapped ‘minor’ families incurred an immediate post-fire upsurge lasting until early summer 1986. As these positive responses at the spring-burnt sites were associated with a 4.41 ha^?1 lower fine fuel load (humus, litter, twigs of < 6mm diameter) during the first post-fire year compared with the autumn-burnt sites, it is possible that they reflect enhanced trapping efficiency and not increased population levels. Until this question is resolved, it appears preferable to apply any necessary one-off prescribed fire for reducing fuel loads on the forest floor during autumn rather than spring to minimise possible short-term impacts on surface-active Coleoptera.     

Calculation algorithms alter the breath‐by‐breath gas exchange values when abrupt changes in ventilation occur

The automatic metabolic units calculate breath‐by‐breath gas exchange from the expiratory data only, applying an algorithm (‘expiration‐only’ algorithm) that neglects the changes in the lung gas stores. These last are theoretically taken into account by a recently proposed algorithm, based on an alternative view of the respiratory cycle (‘alternative respiratory cycle’ algorithm). The performance of the two algorithms was investigated where changes in the lung gas stores were induced by abrupt increases in ventilation above the physiological demand. Oxygen, carbon dioxide fractions and ventilatory flow were recorded at the mouth in 15 healthy subjects during quiet breathing and during 20‐s hyperventilation manoeuvres performed at 5‐min intervals in resting conditions. Oxygen uptakes and carbon dioxide exhalations were calculated throughout the acquisition periods by the two algorithms. Average ventilation amounted to 6·1 ± 1·4 l min^?1 during quiet breathing and increased to 41·8 ± 27·2 l min^?1 during the manoeuvres (P<0·01). During quiet breathing, the two algorithms provided overlapping gas exchange data and noise. Conversely, during hyperventilation, the ‘alternative respiratory cycle’ algorithm provided significantly lower gas exchange data as compared to the values yielded by the ‘expiration‐only’ algorithm. For the first breath of hyperventilation, the average values provided by the two algorithms amounted to 0·37 ± 0·34 l min^?1 versus 0·96 ± 0·73 l min^?1 for O₂ uptake and 0·45 ± 0·36 l min^?1 versus 0·80 ± 0·58 l min^?1 for exhaled CO₂ (P<0·001 for both). When abrupt increases in ventilation occurred, such as those arising from a deep breath, the ‘alternative respiratory cycle’ algorithm was able to halve the artefactual gas exchange values as compared to the ‘expiration‐only’ approach.     

Development of the Demotivating Beliefs Inventory and Test of the Cognitive Triad of Amotivation

Recent cognitive models of negative symptoms in psychosis posit that amotivation relevant beliefs are reflected in the cognitive triad of negative beliefs concerning the self, others and the future. The aim of this study was to test the proposed three-factor structure of putative ‘demotivating beliefs’ and to ascertain the strength of their association with self-reported amotivation. We combined existing scales assessing ‘demotivating beliefs’ to the Demotivating Beliefs Inventory. This scale was used for exploratory and confirmatory factor analyses as well as latent regression analyses with amotivation in two independent community (n₁?=?98; n₂?=?347) and one clinical sample (n?=?36). We found a three-factor structure with satisfying model fit (‘selfdefeating beliefs’, ‘social indifference beliefs’ and ‘low-expectancy-of-pleasure beliefs’). Each factor showed moderate associations with amotivation (β-coefficients from 0.34 to 0.43; R²?=?.30). Our results support the validity of the cognitive triad and its benefit as a framework to analyze demotivating beliefs.     

Defects of β2-adrenergic signal transduction in chronic lymphocytic leukaemia: relationship to disease progression

The second messenger 3′:5′-cyclic adenosine monophosphate (cAMP) inhibits the proliferation of human B lymphocytes. In lymphoid malignancies, cAMP levels or the number of β₂-adrenergic receptors seem to be decreased. In order to explore this phenomenon further, the function of the β₂-adrenergic receptor complex was examined in mononuclear leucocytes (MNLs) from patients with B-cell chronic lymphocytic leukaemia (CLL). Peripheral blood MNLs from 25 CLL patients (16 male, nine female; aged 62 ± 9 years) and 10 healthy volunteers (seven male, three female; aged 47 ± 19 years) were used. The binding characteristics of β₂-adrenergic receptors (β₂-AR) on MNLs were determined by radioligand binding assays with [¹²⁵I]-cyanopindolol ([¹²⁵I]-CYP). The number of high-affinity binding sites for [¹²⁵I]-CYP was significantly lower in CLL patients (313 ± 300 sites per cell; mean ± SD) than in control subjects (1479 ± 1268 sites per cell). Moreover, the density of β₂-AR decreased with disease progression, from Binet stage A (371 ± 236, n = 13) to B (236 ± 136, n = 7) and C (141 ± 59, n = 5) (P < 0.05; Kruskal–Wallis analysis). Functional analyses of the β₂-AR complex were performed by measuring the cellular cAMP content of MNLs in response to different stimulators. The cAMP production of MNLs upon isoprenaline stimulation (ISO; 10 min, 10^?4 mol L^?1) was slightly lower in CLL patients (12.5 ± 7.04 pmol 10^?6 cells) than in control subjects (15.91 ± 10.08 pmol 10^?6 cells), and decreased with CLL progression (stage A 14 ± 7; stage B 13.66 ± 3.91; stage C 3.07 ± 0.79 pmol 10^?6 cells). In contrast, cAMP accumulation in response to cholera toxin (CHO; 10^?4 g ml^?1, 120 min) was not different in control subjects (70.07 ± 31.30 pmol 10^?6 cells) and CLL patients (stage A 95.24 ± 123.07 , stage B 70.76 ± 57.37, stage C 33.21 ± 33.73 pmol 10^?6 cells). When stimulated with forskolin (100 μmol L^?1, 15 min), control MNLs produced about ten-fold more cAMP than CLL MNLs (188.56 ± 92.53 vs. 17.88 ± 10.32 pmol 10^?6 cells); this response was not stage dependent. Taken together, the results show that the β₂-AR transmembrane signalling is impaired in CLL patients. The correlation of some β₂-AR signalling defects with disease progression suggests that they may contribute to the disease progression of CLL patients.     

Effects of in vitro adult platelet transfusions on neonatal hemostasis

Summary. Background: Thrombocytopenia is frequent among neonates, and 20–25% of affected infants are treated with platelet transfusions. These are frequently given for mild thrombocytopenia (platelets: 50–100 × 10⁹ L^?1), largely because of the known hyporeactivity of neonatal platelets. In tests of primary hemostasis, however, neonates have shorter bleeding and closure times (CTs) than adults. This has been attributed to their higher hematocrits, higher von Willebrand factor (VWF) concentrations, and predominance of longer VWF polymers. Objective: To determine whether the ‘transfusion’ of adult (relatively hyperreactive) platelets into neonatal blood results in a hypercoagulable profile. Methods: Cord blood (CB) and adult peripheral blood (PB) were separated (with a modified buffy coat method) to generate miniaturized platelet concentrates (PCs) and thrombocytopenic blood. PB‐derived and CB‐derived PCs (n = 7 per group) were then ‘transfused’in vitro into thrombocytopenic CB and PB. The effects of autologous vs. allogeneic (developmentally mismatched) ‘transfusions’ were evaluated with whole blood aggregometry, a platelet function analyzer (PFA‐100), and thromboelastography (TEG). Results: Adult platelets aggregated significantly better than neonatal platelets in response to thrombin receptor‐activating peptide, ADP, and collagen, regardless of the blood into which they were transfused. The ‘transfusion’ of adult platelets into thrombocytopenic CB resulted in shorter CTs‐EPI (PFA‐100) and higher clot strength and firmness (TEG) than ‘transfusion’ of neonatal autologous platelets. Conclusions: In vitro‘transfusion’ of adult platelets into neonatal blood results in shorter CTs than ‘transfusion’ with neonatal platelets. Our findings should raise awareness of the differences between the neonatal and adult hemostatic system and the potential ‘developmental mismatch’ associated with platelet transfusions for neonatal hemostasis.     

ICOS-dependent extrafollicular helper T cells elicit IgG production via IL-21 in systemic autoimmunity

The role of specialized follicular helper T (T_FH) cells in the germinal center has become well recognized, but it is less clear how effector T cells govern the extrafollicular response, the dominant pathway of high-affinity, isotype-switched autoantibody production in the MRL/MpJ-Fas^lpr (MRL^lpr) mouse model of lupus. MRL^lpr mice lacking the Icos gene have impaired extrafollicular differentiation of immunoglobulin (Ig) G⁺ plasma cells accompanied by defects in CXC chemokine receptor (CXCR) 4 expression, interleukin (IL) 21 secretion, and B cell helper function in CD4 T cells. These phenotypes reflect the selective loss of a population of T cells marked by down-regulation of P-selectin glycoprotein ligand 1 (PSGL-1; also known as CD162). PSGL-1^lo T cells from MRL^lpr mice express CXCR4, localize to extrafollicular sites, and uniquely mediate IgG production through IL-21 and CD40L. In other autoimmune strains, PSGL-1^lo T cells are also abundant but may exhibit either a follicular or extrafollicular phenotype. Our findings define an anatomically distinct extrafollicular population of cells that regulates plasma cell differentiation in chronic autoimmunity, indicating that specialized humoral effector T cells akin to T_FH cells can occur outside the follicle.     

Non‐competitive interaction between raclopride and spiperone on human D2L‐receptors in intact Chinese hamster ovary cells

We recently investigated the binding properties of the antagonists [³H]‐raclopride and [³H]‐spiperone to intact Chinese hamster ovary cells expressing recombinant human D_2long‐dopamine receptors (CHO‐D_2L cells). Compared with saturation binding with [³H]‐raclopride, raclopride reduced [³H]‐spiperone binding with to low potency in competition binding experiments. The present findings illustrate the ability of spiperone to inhibit [³H]‐raclopride binding non‐competitively. While raclopride only decreases the apparent K_D of [³H]‐raclopride in saturation binding experiments, spiperone only decreases the number of sites to which [³H]‐raclopride binds with high affinity. Also, while the IC₅₀ of raclopride depends on the concentration of [³H]‐raclopride in competition experiments, this is not the case for spiperone. Kinetic studies reveal that the binding of raclopride at its high affinity sites does not affect the association of subsequently added [³H]‐spiperone nor the rebinding of freshly dissociated [³H]‐spiperone to the same or surrounding receptors. Yet, spiperone does not affect the dissociation rate of [³H]‐raclopride and raclopride does not affect the (genuine) dissociation rate of [³H]‐spiperone. The easiest way to interpret the present findings in molecular terms is to assume that D_2L‐receptors or their dimeric complexes possess two distinct binding sites: one with high affinity/accessibility for [³H]‐raclopride and the other one with high affinity/accessibility for [³H]‐spiperone. The ability of bound spiperone to inhibit high affinity raclopride binding while the reverse is not the case suggests for the occurrence of non‐reciprocal allosteric interactions. These new findings could point at the occurrence of allosteric interactions between different classes of D₂‐receptor antagonists.     

HER2 as a target for breast cancer therapy

Importance of the field: Differential levels of HER2 expression in normal versus HER2-overexpressing breast carcinomas, together with the demonstration of a key role for HER2 in tumor progression, make HER2 an ideal target for specific therapeutic approaches.

Areas covered in this review: This review considers the clinical value of trastuzumab and lapatinib, the two HER2-targeted therapies approved for clinical practice. References were chosen by searching the PubMed and MEDLINE datasets using as search term: ‘HER2’, in association with ‘prognosis’, ‘response’, ‘trastuzumab’, ‘lapatinib’ and ‘resistance’.

What the reader will gain: This review deals with HER2 as a target for breast carcinoma treatment, focusing on anti-HER2 therapies used in clinical practice, their merits and shortcomings.

Take home message: The benefit of anti-HER2 therapies demonstrated in clinical trials indicates that HER2 is, to date, one of the most promising molecules for targeted therapy. Nevertheless, since tumor cells utilizing alternative growth signaling pathways through transmembrane receptors as well as intracellular signaling transduction molecules can bypass HER2 blockade, a future ambitious aim is the successful combination of anti-HER2 strategies with drugs directed to molecules that contribute to anti-HER2 resistance.     

A possible significant role of zinc and GPR39 zinc sensing receptor in Alzheimer disease and epilepsy

Zinc the essential trace element, plays a significant role in the brain development and in the proper brain functions at every stage of life. Misbalance of zinc (Zn²⁺) ions in the central nervous system is involved in the pathogenesis of numerous neurodegenerative disorders such as Alzheimer's disease, Depression, and Epilepsy. In brain, Zn²⁺ has been identified as a ligand, capable of activating and inhibiting the receptors including the NMDA-type glutamate receptors (NMDARs), GABA_A receptors, nicotinic acetylcholine receptors (nAChRs), glycine receptors (glyR) and serotonin receptors (5-HT3). Recently GPR39 has been identified as a zinc-specific receptor, widely expressed in brain tissues including the frontal cortex, amygdala, and hippocampus. GPR39, when binding with Zn²⁺ has shown promising therapeutic potentials. This review presents current knowledge regarding the role of GPR39 zinc sensing receptor in brain, with a focus on Alzheimer’s disease and Epilepsy. Although the results are encouraging, further research is needed to clarify zinc and GPR39 role in the treatment of Alzheimer's disease and Epilepsy.