Increasing the number of 5-HT(1A)-receptors in cortex and hippocampus does not induce mnemonic deficits in mice.

Even though the role of the serotonin1A (5-HT(1A))-receptor for cognitive processes is undisputed, the exact involvement of pre- and postsynaptic sites remains unexplained. Recently, we introduced a mouse line overexpressing the 5-HT(1A)-receptor in the hippocampus and cortex. In this study we investigated in comparison to wild-type mice their cognitive abilities using the Morris water-maze task and inhibitory avoidance test. Acute effects of pre- and posttraining administered 8-OH-DPAT (0.03-0.3 mg/kg i.p.) were examined in the inhibitory avoidance test. Additionally, habituation learning was studied in the hole-board test. Transgenic mice showed no overall learning deficit. Spatial learning and memory revealed in the Morris water-maze task was comparable to wild-type mice, and both genotypes habituated to the hole-board arena in a similar manner. Comparing the performance of both genotypes in the inhibitory avoidance test, cognitive functions of transgenic mice seemed to be slightly impaired. When 8-OH-DPAT was administered pretraining an amnesic effect was produced only in transgenic mice and only at the highest dose (0.3 mg/kg). Posttraining administered 0.3 mg/kg 8-OH-DPAT did not affect the performance of both genotypes. Overall, the cortical and hippocampal overexpression of the 5-HT(1A)-receptor had no major effect on cognitive functions in mice, suggesting that changes in the 5-HT(1A)-receptor density are not necessarily accompanied with alterations of learning and memory processes.

The pharmacological rationale behind polypharmacy in heart failure.

The treatment of heart failure (HF) commonly requires a complex pharmacological regimen. Currently HF polypharmacy consists of drugs that target different factors for disease progression, such as altered hemodynamics and elevated neurohumoral factors. Even though a significant improvement of HF has been achieved by combination treatment with regard to morbidity and mortality rate, the increasing numbers and daily doses of drugs bare the risk of potential and sometimes unavoidable drug interactions. Furthermore, comorbidities can be a complication of polypharmacy treatment in HF patients. A pharmacological rationale behind polypharmacy in HF will be discussed on the basis of current treatment recommendations by the American Heart Association and the European Society of Cardiology. Finally, difficulties in polypharmacy regarding the major adverse drug effects and interactions will be outlined. Heart Fail Monitor 2008;6(1):20-27.

Mice over-expressing the 5-HT(1A) receptor in cortex and dentate gyrus display exaggerated locomotor and hypothermic response to 8-OH-DPAT.

The serotonin 1A (5-HT(1A)) receptor is one of the best described receptor subtypes of the serotonergic system. Due to the complex distribution pattern, the pre- and postsynaptic localisation, the impact on various monoamines, as well as the influence on a wide range of physiological functions, the contribution of 5-HT(1A) receptors to behavioural outcomes is difficult to define. In this study, we present a new transgenic mouse model with a prominent over-expression of the 5-HT(1A) receptor in the outer cortical layers (I-III) and the dentate gyrus. Behavioural studies revealed a slight decrease in baseline motor activity of homozygous mice during the open field test. Moreover, core body temperature of male transgenic mice was significantly lower than that of wild-type mice. Pharmacological studies with the 5-HT(1A) receptor agonist 8-OH-DPAT (0.1-2.5 mg/kg, i.p.) revealed an exaggerated drug response in mutant mice. 8-OH-DPAT led to a drastic decrease in motor activity in the open field and elevated plus maze test. This significant effect on motor activity became more apparent by investigating the serotonergic syndrome induced by 8-OH-DPAT. Concentration as low as 0.5 mg/kg 8-OH-DPAT caused immobility in transgenic mice for 30 min, head weaving behaviour, and backward walking, whereas in wild-type animals, typical behaviours of the serotonin syndrome were first observed at concentrations of 1.5 mg/kg and more. In addition, the 8-OH-DPAT induced hypothermia was more pronounced in mutant mice than in wild-type animals. Therefore, these genetically modified mice represent a promising model for further investigations of the role of 5-HT(1A) receptors.

Regulation of transport of the angiotensin AT2 receptor by a novel membrane-associated Golgi protein.

OBJECTIVE: Synthesis and maturation of G protein-coupled receptors are complex events that require an intricate combination of processes including protein folding, posttranslational modifications, and transport through distinct cellular compartments. Little is known concerning the regulation of G protein-coupled receptor transport from the endoplasmic reticulum to the cell surface. METHODS AND RESULTS: Here we show that the cytoplasmatic carboxy-terminal of the angiotensin AT2 receptor (AT2R) acts independently as an endoplasmic reticulum-export signal. Using a yeast two-hybrid system, we identified a Golgi membrane-associated protein termed ATBP50 (for AT2R binding protein of 50 kDa) that binds to this motif. We also cloned ATBP60 and ATBP135 encoded by the same gene as ATBP50 that mapped to chromosomes 8p21.3. Downregulation of ATBP50 using siRNA leads to retention of AT2R in inner compartments, reduced cell surface expression, and decreased antiproliferative effects of the receptor. CONCLUSIONS: Our results indicate that ATBP50 regulates the transport of the AT2R to cell membrane by binding to a specific motif within its cytoplasmic carboxy-terminal and thereby enabling the antiproliferative effects of the receptor.

Reduced anxiety-related behaviour in transgenic mice overexpressing serotonin 1A receptors.

Serotonergic neurons play a major role in the modulation of emotion and behaviour. Especially knockout studies have revealed a role for the serotonin(1A) (5-HT(1A)) receptor in anxiety related behaviour. Mutant animals exhibit enhanced anxiety-like responses, possibly resulting from impaired autoinhibitory control of midbrain serotonergic neurons. To further elucidate the role of the 5-HT(1A) receptors in affective behaviour, a complementary approach has been used and transgenic mice overexpressing this receptor subtype have been generated. The expression of the active 5-HT(1A) receptor protein as indicated by autoradiography was transiently increased during early postnatal development (P1.5) as compared to wild-type mice. Within the next 2 weeks, the increase in receptor binding vanished and was also not apparent in adult animals indicating adaptive changes in the regulation of 5-HT(1A) receptor expression. Although no evidence for increased receptor binding in the brains of adult homozygous mice was found by autoradiography, typical phenotypic changes indicative of 5-HT(1A) receptor overactivity were apparent. Transgenic mice revealed a reduced molar ratio of 5-hydroxyindoleacetic acid to serotonin in several brain areas and elevated serotonin values in the hippocampus and striatum. Moreover, anxiety-like behaviour was decreased in male and female transgenic mice and body temperature was lowered in male transgenic mice in comparison with heterozygous and wild-type mice. These findings further underline the pivotal role of 5-HT(1A) receptors in the homeostasis of anxiety-like behaviour and the crucial importance of stimulation of the 5-HT(1A) receptor during the early postnatal development for normal anxiety-like behaviour throughout life.

Analysis of the murine 5-HT receptor gene promoter in vitro and in vivo.

The expression level of the 5-HT(1A) receptor gene (htr1a) in the central nervous system (CNS) is implicated in the aetiology and treatment of anxiety disorders and depression. Previous studies of the murine htr1a have revealed that its proximal promoter is GC rich and TATA-less. Several functional transcription factor binding sites, including MAZ and SP1 recognition sequences, have been identified. To further analyse the promoter of this receptor gene, additional upstream sequence information extending to -5.5 kb of the murine htr1a was generated and promoter fragments extending to -20 kb were analysed for activity in cell culture and transgenic animals. Promoter fragments greater than 4.5 kb in length were active in 5-HT(1A) receptor mRNA positive cells and inactive in 5-HT(1A) receptor mRNA negative cells. Smaller fragments were not able to confer this specificity. In agreement, using additive transgenesis to drive LacZ expression in vivo, CNS specific reporter gene expression was found with these longer constructs. Transgene expression in the 4.5- and 20-kb mouse lines resembled the endogenous htr1a expression pattern, whereas the 5.5-kb mouse lines surprisingly revealed strongly reduced expression. None of the three constructs was prone to confer ectopic expression, however, variation of expression between the transgenic lines was observed. Using colocalization studies we analysed the degree of concurrence of transgenic and endogenous htr1a expression brought about by these three different constructs. The highest degrees of colocalization were observed in mice harbouring the 20-kb construct, suggesting a large promoter fragment is required to faithfully direct transgene expression in a 5-HT(1A) receptor like pattern.

Regulation and function of somatostatin receptors.

This review summarizes the latest advances that have been made to elucidate the somatostatinergic system in respect to somatostatin receptor evolution, the development of receptor agonists/antagonists, receptor regulation, signal transduction, effects on cell proliferation, receptor-receptor or receptor-protein interactions and receptor function.

Vasoactive peptides, their receptors and drug development.

Vasoactive peptides with vasoconstrictor properties play an important role in many physiological and pathological conditions. The peptides act via specific receptors, most of them belonging to the group of seven transmembrane G-protein coupled receptors. These receptors have become important targets for drugs developed to inhibit vasoconstrictor actions. Alternatively, compounds which inhibit enzymes generating vasoactive peptides have also been demonstrated to represent valuable therapeutic tools. This review will first describe the properties and distribution of two very potent vasoconstrictors, angiotensin II and endothelin. It will further focus on their receptors and on new drugs, which act as antagonists for these receptors. In addition, the properties of indirectly acting drugs like angiotensin-converting enzyme inhibitors and--in analogy--endothelin-converting enzyme inhibitors will be presented.

High-frequency stimulation of the subthalamic nucleus enhances striatal dopamine release and metabolism in rats.

High-frequency stimulation of the subthalamic nucleus is believed to exert its main effects via the basal ganglia output structures. Previously, we have shown a concomitant increase in striatal dopamine (DA) metabolites in normal and 6-hydroxydopamine-lesioned rats. The present study was designed to determine whether this increase in striatal DA metabolites reflects enhanced intraneuronal DA turnover or, alternatively, is due to increased DA release with subsequent rapid and efficient reuptake and/or metabolism. Thus, high-frequency stimulation of the subthalamic nucleus was performed in normal rats after inhibition of DA reuptake, metabolism or DA depletion. Extracellular levels of striatal DA and its metabolites were assessed using microdialysis. Our data suggest that subthalamic high-frequency stimulation increases striatal DA release and activates independent striatal DA metabolism. Since such changes could be triggered by modification of either the activity or the gene expression of the rate-limiting enzyme tyrosine hydroxylase, an activity assay and RT-PCR of striatal and nigral samples were performed. Subthalamic stimulation increased striatal tyrosine hydroxylase activity without affecting gene expression. We, therefore, conclude that the application of subthalamic high-frequency stimulation could partially compensate for the DA deficit by inducing increased striatal DA release and metabolism.