Neurotoxicity of Anhydroecgonine Methyl Ester, a Crack Cocaine Pyrolysis Product

Smoking crack cocaine involves the inhalation of cocaine and its pyrolysis product, anhydroecgonine methyl ester (AEME). Although there is evidence that cocaine is neurotoxic, the neurotoxicity of AEME has never been evaluated. AEME seems to have cholinergic agonist properties in the cardiovascular system; however, there are no reports on its effects in the central nervous system. The aim of this study was to investigate the neurotoxicity of AEME and its possible cholinergic effects in rat primary hippocampal cell cultures that were exposed to different concentrations of AEME, cocaine, and a cocaineAEME combination. We also evaluated the involvement of muscarinic cholinergic receptors in the neuronal death induced by these treatments using concomitant incubation of the cells with atropine. Neuronal injury was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays. The results of the viability assays showed that AEME is a neurotoxic agent that has greater neurotoxic potential than cocaine after 24 and 48 h of exposure. We also showed that incubation for 48 h with a combination of both compounds in equipotent concentrations had an additive neurotoxic effect. Although both substances decreased cell viability in the MTT assay, only cocaine increased LDH release. Caspase-3 activity was increased after 3 and 6 h of incubation with 1mM cocaine and after 6 h of 0.1 and 1.0mM AEME exposure. Atropine prevented the AEME-induced neurotoxicity, which suggests that muscarinic cholinergic receptors are involved in AEME's effects. In addition, binding experiments confirmed that AEME has an affinity for muscarinic cholinergic receptors. Nevertheless, atropine was not able to prevent the neurotoxicity produced by cocaine and the cocaineAEME combination, suggesting that these treatments activated other neuronal death pathways. Our results suggest a higher risk for neurotoxicity after smoking crack cocaine than after cocaine use alone.

Regulation of neurogenesis and gliogenesis of retinoic acid-induced P19 embryonal carcinoma cells by P2X2 and P2X7 receptors studied by RNA interference

Embryonic carcinoma cells are widely used models for studying the mechanisms of proliferation and differentiation occurring during early embryogenesis. We have now investigated how down-regulation of P2X2 and P2X7 receptor expression by RNA interference (RNAi) affects neural differentiation and phenotype specification of P19 embryonal carcinoma cells. Wild-type P19 embryonal carcinoma cells or cells stably expressing shRNAs targeting P2X2 or P2X7 receptor expression were induced to differentiate into neurons and glial cells in the presence of retinoic acid. Silencing of P2X2 receptor expression along differentiation promoted cell proliferation and an increase in the percentage of cells expressing glial-specific GFAP, while the presence of beta-3 tubulin-positive cells diminished at the same time. Proliferation induction in the presence of stable anti-P2X2 receptor RNAi points at a mechanism where glial proliferation is favored over growth arrest of progenitor cells which would allow neuronal maturation. Differently from the P2X2 receptor, inhibition of P2X7 receptor expression during neural differentiation of P19 cells resulted in a decrease in cell proliferation and GFAP expression, suggesting the need of functional P2X7 receptors for the progress of gliogenesis. The results obtained in this study indicate the importance of purinergic signaling for cell fate determination during neural differentiation, with P2X2 and P2X7 receptors promoting neurogenesis and gliogenesis, respectively. The shRNAs down-regulating P2X2 or P2X7 receptor gene expression, developed during this work, present useful tools for studying mechanisms of neural differentiation in other stem cell models. (C) 2012 ISDN. Published by Elsevier Ltd. All rights reserved.

PTTG expression in different experimental and human prolactinomas in relation to dopaminergic control of lactotropes

Abstract Background Pituitary tumor transforming gene (pttg) is a novel oncogene that is expressed at higher level in most of the tumors analyzed to date compared to normal tissues. Nevertheless, its expression in prolactinomas and its relation with the pituitary dopamine receptor 2 (D2R) are not well defined. We sought to determine the pituitary level of pttg in three different experimental models of prolactinomas with altered dopaminergic control of the pituitary: the dopaminergic D2R knockout female mouse, the estrogen-treated rat, and the senescent female rat. These three models shared the characteristics of increased pituitary weight, hyperprolactinemia, lactotrope hyperplasia and reduced or absent dopaminergic action at the pituitary level. We also studied samples from human macroprolactinomas, which were characterized as responsive or resistant to dopamine agonist therapy. Results When compared to female wild-type mice, pituitaries from female D2R knockout mice had decreased PTTG concentration, while no difference in pttg mRNA level was found. In senescent rats no difference in pituitary PTTG protein expression was found when compared to young rats. But, in young female rats treated with a synthetic estrogen (Diethylstylbestrol, 20 mg) PTTG protein expression was enhanced (P = 0.029). Therefore, in the three experimental models of prolactinomas, pituitary size was increased and there was hyperprolactinemia, but PTTG levels followed different patterns. Patients with macroprolactinomas were divided in those in which dopaminergic therapy normalized or failed to normalize prolactin levels (responsive and resistant, respectively). When pituitary pttg mRNA level was analyzed in these macroprolactinomas, no differences were found. We next analyzed estrogen action at the pituitary by measuring pituitary estrogen receptor α levels. The D2R knockout female mice have low estrogen levels and in accordance, pituitary estrogen receptors were increased (P = 0.047). On the other hand, in senescent rats estrogen levels were slightly though not significantly higher, and estrogen receptors were similar between groups. The estrogen-treated rats had high pharmacological levels of the synthetic estrogen, and estrogen receptors were markedly lower than in controls (P < 0.0001). Finally, in patients with dopamine resistant or responsive prolactinomas no significant differences in estrogen receptor α levels were found. Therefore, pituitary PTTG was increased only if estrogen action was increased, which correlated with a decrease in pituitary estrogen receptor level. Conclusion We conclude that PTTG does not correlate with prolactin levels or tumor size in animal models of prolactinoma, and its pituitary content is not related to a decrease in dopaminergic control of the lactotrope, but may be influenced by estrogen action at the pituitary level. Therefore it is increased only in prolactinomas generated by estrogen treatment, and not in prolactinomas arising from deficient dopamine control, or in dopamine resistant compared with dopamine responsive human prolactinomas. These results are important in the search for reliable prognostic indicators for patients with pituitary adenomas which will make tumor-specific therapy possible, and help to elucidate the poorly understood phenomenon of pituitary tumorigenesis.

Untersuchung neuer hochwirksamer neuroprotektiver Antioxidantien in experimentellen Modellen der Parkinsonschen Krankheit

Bei der Parkinsonschen Krankheit kommt es zu einer selektiven Degeneration der dopaminergen Neurone in der Substantia nigra pars compacta. Die Rolle des oxidativen Stresses in der Pathogenese dieser Erkrankung konnte an post mortem Untersuchungen der Parkinson-Patienten, wie auch an zahlreichen in vitro und in vivo Modellen bestätigt werden. Die Anwendung von Antioxidantien wurde als therapeutische Strategie der Parkinsonschen Krankheit vorgeschlagen. In dieser Hinsicht wurden bereits antioxidative Substanzen in klinischen Studien evaluiert. Klinische Studien mit Antioxidantien haben jedoch bislang nur wenig überzeugende Ergebnisse erbracht, mit Ausnahme des Einsatzes des Ubichinons (Coenzym Q). Eine kritische Analyse der klinischen Studien lässt zusammenfassen, dass auf Seiten der verwendeten Antioxidantien noch massiver Optimierungsbedarf besteht. Für einen erfolgreichen therapeutischen Einsatz von Antioxidantien bei dieser Krankheit sind folgende Eigenschaften der Substanzen von höchster Bedeutung: i) maximale neuroprotektive Aktivität bei geringen Dosen; ii) geringe Nebenwirkungen; iii) eine hohe Blut-Hirn-Schrankengängigkeit.In dieser Arbeit wurde das neuroprotektive Potential von drei Bisarylimin-basierten antioxidativen Strukturen (Phenothiazin, Iminostilben und Phenoxazin) in in vitro und in vivo Parkinson-Modellsystemen evaluiert. Beide experimentellen Modelle basieren auf der Wirkung der mitochondrialen Komplex I Inhibitoren 1-Methyl-4-Phenylpyridin (MPP+) und Rotenon, welche pathophysiologische Charakteristika der Parkinsonschen Krankheit reproduzieren. Unsere in vitro Untersuchungen an primären Neuronen des Mittelhirns und der klonalen SH-SY5Y-Neuroblastomazelllinie konnten zeigen, dass die Komplex I Inhibition krankheitsspezifische zelluläre Merkmale induziert, wie die Abnahme der antioxidativen Verteidigungskapazität und Verlust des mitochondrialen Membranpotentials. Zusätzlich kommt es in primären Neuronen des Mittelhirns zur selektiven Degeneration dopaminerger Neurone, welche in der Parkinsonschen Erkrankung besonders betroffen sind. Ko-Inkubation der in vitro Modelle mit Phenothiazin, Iminostilben und Phenoxazin in niedrigen Konzentrationen (50 nM) halten die pathologischen Prozesse fast vollständig auf. In vivo Untersuchungen am MPP+- und Rotenon-basierten Caenorhabditis elegans (C. elegans) Modell bestätigen das neuroprotektive Potential der Bisarylimine. Hierfür wurde eine transgene C. elegans Linie mithilfe einer dopaminerg spezifischen DsRed2- (Variante des rot fluoreszierenden Proteins von Discosoma sp.)-Expression und pan-neuronaler CFP- (cyan fluoreszierendes Protein)-Expression zur Visualisierung der dopaminergen Neuronenpopulation in Kontrast zum Gesamtnervensystem erstellt. Behandlung des C. elegans mit MPP+ und Rotenon im larvalen und adulten Stadium führt zu einer selektiven Degeneration dopaminerger Neurone, sowie zum Entwicklungsarrest der larvalen Population. Die dopaminerge Neurodegeneration, wie auch weitere phänotypische Merkmale des C. elegans Modells, können durch Phenothiazin, Iminostilben und Phenoxazin in niedrigen Konzentrationen (500 nM) komplett verhindert werden. Ein systemischer Vergleich aromatischer Bisarylimine mit bekannten, gut charakterisierten Antioxidantien, wie α-Tocopherol (Vitamin E), Epigallocatechingallat und β-Catechin, zeigt, dass effektive Konzentrationen für Phenothiazin, Iminostilben und Phenoxazin um Zehnerpotenzen niedriger liegen im Vergleich zu natürlichen Antioxidantien. Der Wirkungsmechanismus der Bisarylimine konnte in biochemischen und in vitro Analysen, sowie in Verhaltensuntersuchungen an C. elegans von der Wirkungsweise strukturell ähnlicher, neuroleptisch wirkender Phenothiazin-Derivate differenziert werden. Die Analyse des dopaminerg-gesteuerten Verhaltens (Beweglichkeit) in C. elegans konnte verdeutlichen, dass antioxidative und Dopaminrezeptor-bindende Eigenschaften der Bisaryliminstrukturen sich gegenseitig ausschließen. Diese qualitativen Merkmale unterscheiden Bisarylimine fundamental von klinisch angewandten Neuroleptika (Phenothiazin-Derivate), welche als Dopaminrezeptor-Antagonisten zur Behandlung psychischer Erkrankungen klinisch eingesetzt werden.Aromatische Bisarylimine (Phenothiazin, Iminostilben und Phenoxazin) besitzen günstige strukturelle Eigenschaften zur antioxidativ-basierter Neuroprotektion. Durch die Anwesenheit der antioxidativ wirkenden, nicht-substituierten Iminogruppe unterscheiden sich Bisarylimine grundlegend von neuroleptisch-wirkenden Phenothiazin-Derivaten. Wichtige strukturelle Voraussetzungen eines erfolgreichen antioxidativen Neuropharmakons, wie eine hohe Radikalisierbarkeit, die stabile Radikalform und der lipophile Charakter des aromatischen Ringsystems, werden in der Bisaryliminstruktur erfüllt. Antioxidative Bisarylimine könnten in der Therapie der Parkinsonschen Krankheit als eine effektive neuroprotektiv-therapeutische Strategie weiter entwickelt werden.

Functional characterisation of in vitro synthesised G-protein coupled receptors in polymersomes

Membrane proteins play an indispensable role in physiological processes. It is, therefore, not surprising that many diseases are based on the malfunction of membrane proteins. Hence membrane proteins and especially G-protein coupled receptors(GPCRs)- the largest subfamily- have become an important drug target. Due to their high selectivity and sensitivity membrane proteins are also feasible for the detection of small quantities of substances with biosensors. Despite this widespread interest in GPCRs due to their importance as drug targets and biosensors there is still a lack of knowledge of structure, function and endogenous ligands for quiet a few of the previously identified receptors.rnBottlenecks in over-expression, purification, reconstitution and handling of membrane proteins arise due to their hydrophobic nature. Therefore the production of reasonable amounts of functional membrane proteins for structural and functional studies is still challenging. Also the limited stability of lipid based membrane systems hampers their application as platforms forrnscreening applications and biosensors.rnIn recent years the in vitro protein synthesis became a promising alternative to gain better yields for expression of membrane proteins in bio-mimetic membrane systems. These expression systems are based on cell extracts. Therefore cellular effects on protein expression are reduced. The open nature of the cell-free expression systems easily allows for the adjustment of reactionrnconditions for the protein of interest. The cell-free expression in the presence of bio-mimetic membrane systems allows the direct incorporation of the membrane proteins and therefore skips the time-consuming purification and reconstitution processes. Amphiphilic block-copolymers emerged as promising alternative for the less stable lipid-based membrane systems. They, likernlipids, form membraneous structures in aqueous solutions but exhibit increased mechanical and chemical stability.rnThe aim of this work was the generation of a GPCR-functionalised membrane system by combining both promising alternatives: in vitro synthesis and polymeric membrane systems. This novel platform should be feasible for the characterisation of the incorporated GPCR. Immunodetection of Dopamine receptor 1 and 2 expressed in diblock- and triblock-polymersomes demonstrated the successful in vitro expression of GPCRs in polymeric membranes. Antibodyrnbinding studies suggested a favoured orientation of dopamine receptors in triblockpolymersomes.rnA dopamine-replacement assay on DRD2-functionalised immobilised triblockpolymersomes confirmed functionality of the receptor in the polymersomes. The altered binding curve suggests an effect of the altered hydrophobic environment presented by the polymer membrane on protein activity.

Role of somatostatins in gastroenteropancreatic neuroendocrine tumor development and therapy

The incidence and prevalence of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) have increased in the past 20 years. GEP-NETs are heterogeneous tumors, in terms of clinical and biological features, that originate from the pancreas or the intestinal tract. Some GEP-NETs grow very slowly, some grow rapidly and do not cause symptoms, and others cause hormone hypersecretion and associated symptoms. Most GEP-NETs overexpress receptors for somatostatins. Somatostatins inhibit the release of many hormones and other secretory proteins; their effects are mediated by G protein-coupled receptors that are expressed in a tissue-specific manner. Most GEP-NETs overexpress the somatostatin receptor SSTR2; somatostatin analogues are the best therapeutic option for functional neuroendocrine tumors because they reduce hormone-related symptoms and also have antitumor effects. Long-acting formulations of somatostatin analogues stabilize tumor growth over long periods. The development of radioactive analogues for imaging and peptide receptor radiotherapy has improved the management of GEP-NETs. Peptide receptor radiotherapy has significant antitumor effects, increasing overall survival times of patients with tumors that express a high density of SSTRs, particularly SSTR2 and SSTR5. The multi-receptor somatostatin analogue SOM230 (pasireotide) and chimeric molecules that bind SSTR2 and the dopamine receptor D2 are also being developed to treat patients with GEP-NETs. Combinations of radioactive labeled and unlabeled somatostatin analogues and therapeutics that inhibit other signaling pathways, such as mammalian target of rapamycin (mTOR) and vascular endothelial growth factor, might be the most effective therapeutics for GEP-NETs.

The status of olfactory function and the striatal dopaminergic system in drug-induced parkinsonism

Olfactory impairment has been reported in drug-induced parkinsonism (DIP), but the relationship between dopaminergic dysfunction and smell deficits in DIP patients has not been characterized. To this end, we studied 16 DIP patients and 13 patients affected by Parkinson's disease (PD) using the "Sniffin' Sticks" test and [(123)I] FP-CIT SPECT (single-photon emission computed tomography). DIP patients were divided based on normal (n = 9) and abnormal (n = 7) putamen dopamine transporter binding. Nineteen healthy age- and sex-matched subjects served as controls of smell function. Patients with DIP and pathological putamen uptake had abnormal olfactory function. In this group of patients, olfactory TDI scores (odor threshold, discrimination and identification) correlated significantly with putamen uptake values, as observed in PD patients. By contrast, DIP patients with normal putamen uptake showed odor functions-with the exception of the threshold subtest-similar to control subjects. In this group of patients, no significant correlation was observed between olfactory TDI scores and putamen uptake values. The results of our study suggest that the presence of smell deficits in DIP patients might be more associated with dopaminergic loss rather than with a drug-mediated dopamine receptor blockade. These preliminary results might have prognostic and therapeutic implications, as abnormalities in these individuals may be suggestive of an underlying PD-like neurodegenerative process.

[The treatment of orthostatic hypotension with metoclopramide]

The dopamine receptor antagonist metoclopramide (paspertin, primpéran, gastrosil, meclopran, gastro-timelets), used as monotherapy or in combination with an inhibitor of the cyclooxygenase enzyme, affords good results in orthostatic hypotension due to insufficiency of the sympathetic nervous system. The mechanism of action in these cases is unclear but is assumed to be elevation of vascular tone in the splanchnic vessels. A case is discussed which documents the effectiveness of metoclopramide therapy in orthostatic hypotension, even in absence of signs of autonomic dysfunction.

Locomotor velocity and striatal adaptive gene expression changes of the direct and indirect pathways in Parkinsonian rats

BACKGROUND In Parkinson's disease (PD), bradykinesia, or slowness of movement, only appears after a large striatal dopamine depletion. Compensatory mechanisms probably play a role in this delayed appearance of symptoms. OBJECTIVE Our hypothesis is that the striatal direct and indirect pathways participate in these compensatory mechanisms. METHODS We used the unilateral 6-hydroxydopamine (6-OHDA) rat model of PD and control animals. Four weeks after the lesion, the spontaneous locomotor activity of the rats was measured and then the animals were killed and their brain extracted. We quantified the mRNA expression of markers of the striatal direct and indirect pathways as well as the nigral expression of dopamine transporter (DAT) and tyrosine hydroxylase (TH) mRNA. We also carried out an immunohistochemistry for the striatal TH protein expression. RESULTS As expected, the unilateral 6-OHDA rats presented a tendency to an ipsilateral head turning and a low locomotor velocity. In 6-OHDA rats only, we observed a significant and positive correlation between locomotor velocity and both D1-class dopamine receptor (D1R) (direct pathway) and enkephalin (ENK) (indirect pathway) mRNA in the lesioned striatum, as well as between D1R and ENK mRNA. CONCLUSIONS Our results demonstrate a strong relationship between both direct and indirect pathways and spontaneous locomotor activity in the parkinsonian rat model. We suggest a synergy between both pathways which could play a role in compensatory mechanisms and may contribute to the delayed appearance of bradykinesia in PD.

Cellular mechanisms of operant and classical conditioning

The ability to associate a predictive stimulus with a subsequent salient event (i.e., classical conditioning) and the ability to associate an expressed behavior with the consequences (i.e., operant conditioning) allow for a predictive understanding of a changing environment. Although they are operationally distinct, there has been considerable debate whether at some fundamental level classical and operant conditioning are mechanistically distinct or similar. Feeding behavior of Aplysia (i.e., biting) was chosen as the model system and was successfully conditioned with appetitive forms of both operant and classical conditioning. The neuronal circuitry responsible for feeding is well understood and is suitable for cellular analyses, thus providing for a mechanistic comparison between these two forms of associative learning. ^ Neuron B51 is part of the feeding circuitry of Aplysia and is critical for the expression of ingestive behaviors. B51 also is a locus of plasticity following both operant and classical conditioning. Both in vivo and in vitro operant conditioning increased the input resistance and the excitability of B51. No pairing-specific changes in the input resistance were observed following both in vivo and in vitro classical conditioning. However, classical conditioning decreased the excitability of B51. Thus, both operant and classical conditioning modified the threshold level for activation of neuron B51, but in opposite directions, revealing key differences in the cellular mechanisms underlying these two forms of associative learning. ^ Next, the cellular mechanisms underlying operant conditioning were investigated in more detail using a single-cell analogue. The single-cell analogue successfully recapitulated the previous in vivo and in vitro operant conditioning results by increasing the input resistance and the excitability of B51. Both PKA and PKC were necessary for operant conditioning. Dopamine appears to be the transmitter mediating the reinforcement signal in this form of conditioning. A D1 dopamine receptor antibody revealed that the D1receptor localizes to the axon hillock, which is also the region that gives the strongest response when iontophoresing dopamine. ^ The studies presented herein, thus, provide for a greater understanding of the mechanisms underlying both of these forms of associative learning and demonstrate that they likely operate through distinct cellular mechanisms. ^

Receptors induce chemotaxis by releasing the βγ subunit of Gi, not by activating Gq or Gs

Many chemoattractants cause chemotaxis of leukocytes by stimulating a structurally distinct class of G protein-coupled receptors. To identify receptor functions required for chemotaxis, we studied chemotaxis in HEK293 cells transfected with receptors for nonchemokine ligands or for interleukin 8 (IL-8), a classical chemokine. In gradients of the appropriate agonist, three nonchemokine Gi-coupled receptors (the D2 dopamine receptor and opioid μ and δ receptors) mediated chemotaxis; the β2-adrenoreceptor and the M3-muscarinic receptor, which couple respectively to Gs and Gq, did not mediate chemotaxis. A mutation deleting 31 C-terminal amino acids from the IL-8 receptor type B quantitatively impaired chemotaxis and agonist-induced receptor internalization, but not inhibition of adenylyl cyclase or stimulation of mitogen-activated protein kinase. To probe the possible relation between receptor internalization and chemotaxis, we used two agonists of the μ-opioid receptor. Morphine and etorphine elicited quantitatively similar chemotaxis, but only etorphine induced receptor internalization. Overexpression of two βγ sequestering proteins (βARK-ct and αt) prevented IL-8 receptor type B-mediated chemotaxis but did not affect inhibition of adenylyl cyclase by IL-8. We conclude that: (i) Nonchemokine Gi-coupled receptors can mediate chemotaxis. (ii) Gi activation is necessary but probably not sufficient for chemotaxis. (iii) Chemotaxis does not require receptor internalization. (iv) Chemotaxis requires the release of free βγ subunits.

Altered brain neurotransmitter receptors in transgenic mice expressing a portion of an abnormal human Huntington disease gene

Loss of neurotransmitter receptors, especially glutamate and dopamine receptors, is one of the pathologic hallmarks of brains of patients with Huntington disease (HD). Transgenic mice that express exon 1 of an abnormal human HD gene (line R6/2) develop neurologic symptoms at 9–11 weeks of age through an unknown mechanism. Analysis of glutamate receptors (GluRs) in symptomatic 12-week-old R6/2 mice revealed decreases compared with age-matched littermate controls in the type 1 metabotropic GluR (mGluR1), mGluR2, mGluR3, but not the mGluR5 subtype of G protein-linked mGluR, as determined by [3H]glutamate receptor binding, protein immunoblotting, and in situ hybridization. Ionotropic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and kainate receptors were also decreased, while N-methyl-d-aspartic acid receptors were not different compared with controls. Other neurotransmitter receptors known to be affected in HD were also decreased in R6/2 mice, including dopamine and muscarinic cholinergic, but not γ-aminobutyric acid receptors. D1-like and D2-like dopamine receptor binding was drastically reduced to one-third of control in the brains of 8- and 12-week-old R6/2 mice. In situ hybridization indicated that mGluR and D1 dopamine receptor mRNA were altered as early as 4 weeks of age, long prior to the onset of clinical symptoms. Thus, altered expression of neurotransmitter receptors precedes clinical symptoms in R6/2 mice and may contribute to subsequent pathology.

Hyperactivity and impaired response habituation in hyperdopaminergic mice

Abnormal dopaminergic transmission is implicated in schizophrenia, attention deficit hyperactivity disorder, and drug addiction. In an attempt to model aspects of these disorders, we have generated hyperdopaminergic mutant mice by reducing expression of the dopamine transporter (DAT) to 10% of wild-type levels (DAT knockdown). Fast-scan cyclic voltammetry and in vivo microdialysis revealed that released dopamine was cleared at a slow rate in knockdown mice, which resulted in a higher extracellular dopamine concentration. Unlike the DAT knockout mice, the DAT knockdown mice do not display a growth retardation phenotype. They have normal home cage activity but display hyperactivity and impaired response habituation in novel environments. In addition, we show that both the indirect dopamine receptor agonist amphetamine and the direct agonists apomorphine and quinpirole inhibit locomotor activity in the DAT knockdown mice, leading to the hypothesis that a shift in the balance between dopamine auto and heteroreceptor function may contribute to the therapeutic effect of psychostimulants in attention deficit hyperactivity disorder.

Systemic apomorphine alters HPA axis responses to interleukin-1 beta adminstration but not sound stress

Apomorphine is a dopamine receptor agonist that was recently licensed for the treatment of erectile dysfunction. However, although sexual activity can be stressful, there has been little investigation into whether treatments for erectile dysfunction affect stress responses. We have examined whether a single dose of apomorphine, sufficient to produce penile erections (50 mug/kg, i.a.), can alter basal or stress-induced plasma ACTH levels, or activity of central pathways thought to control the hypothalamic-pituitary-adrenal axis in rats. An immune challenge (interleukin-1beta, 1 mug/kg, i.a.) was used as a physical stressor while sound stress (100 dB white noise, 30 min) was used as a psychological stressor. Intravascular administration of apomorphine had no effect on basal ACTH levels but did substantially increase the number of Fos-positive amygdala and nucleus tractus solitarius catecholamine cells. Administration of apomorphine prior to immune challenge augmented the normal ACTH response to this stressor at 90 min and there was a corresponding increase in the number of Fos-positive paraventricular nucleus corticotropin-releasing factor cells, paraventricular nucleus oxytocin cells and nucleus tractus solitarius catecholamine cells. However, apomorphine treatment did not alter ACTH or Fos responses to sound stress. These data suggest that erection-inducing levels of apomorphine interfere with hypothalamic-pituitary-adrenal axis inhibitory feedback mechanisms in response to a physical stressor, but have no effect on the response to a psychological stressor. Consequently, it is likely that apomorphine acts on a hypothalamic-pituitary-adrenal axis control pathway that is unique to physical stressors. A candidate for this site of action is the nucleus tractus solitarius catecholamine cell population and, in particular, A2 noradrenergic neurons. (C) 2003 Elsevier Science Ltd. All rights reserved.

A Biocultural Examination of Student Learning Behaviors in Large Undergraduate Lectures

Thesis (Ph.D.)--University of Washington, 2016-08