Pyrene-Appended Boronic Acids on Graphene Foam Electrodes Provide Quantum Capacitance-Based Molecular Sensors for Lactate

Molecular recognition and sensing can be coupled to interfacial capacitance changes on graphene foam surfaces linked to double layer effects and coupled to enhanced quantum capacitance. 3D graphene foam film electrodes (Gii-Sens; thickness approximately 40 μm; roughness factor approximately 100) immersed in aqueous buffer media exhibit an order of magnitude jump in electrochemical capacitance upon adsorption of a charged molecular receptor based on pyrene-appended boronic acids (here, 4-borono-1-(pyren-2-ylmethyl)pyridin-1-ium bromide, or abbreviated T1). This pyrene-appended pyridinium boronic acid receptor is employed here as a molecular receptor for lactate. In the presence of lactate and at pH 4.0 (after pH optimization), the electrochemical capacitance (determined by impedance spectroscopy) doubles again. Lactic acid binding is expressed with a Hillian binding constant (Klactate = 75 mol-1 dm3 and α = 0.8 in aqueous buffer, Klactate = 460 mol-1 dm3 and α = 0.8 in artificial sweat, and Klactate = 340 mol-1 dm3 and α = 0.65 in human serum). The result is a selective molecular probe response for lactic acid with LoD = 1.3, 1.4, and 1.8 mM in aqueous buffer media (pH 4.0), in artificial sweat (adjusted to pH 4.7), and in human serum (pH adjusted to 4.0), respectively. The role of the pyrene-appended boronic acid is discussed based on the double layer structure and quantum capacitance changes. In the future, this new type of molecular capacitance sensor could provide selective enzyme-free analysis without analyte consumption for a wider range of analytes and complex environments.

Tuning and Coupling Irreversible Electroosmotic Water Flow in Ionic Diodes: Methylation of an Intrinsically Microporous Polyamine (PIM-EA-TB)

Molecularly rigid polymers with internal charges (positive charges induced by amine methylation) allow electroosmotic water flow to be tuned by adjusting the charge density (the degree of methylation). Here, a microporous polyamine (PIM-EA-TB) is methylated to give a molecularly rigid anion conductor. The electroosmotic drag coefficient (the number of water molecules transported per anion) is shown to increase with a lower degree of methylation. Net water transport (without charge flow) in a coupled anionic diode circuit is demonstrated based on combining low and high electroosmotic drag coefficient materials. The AC-electricity-driven net process offers water transport (or transport of other neutral species, e.g., drugs) with net zero ion transport and without driver electrode side reactions.

Understanding Transient Ionic Diode Currents and Impedance Responses for Aquivion-Coated Microholes

Ionic diode based devices or circuits can be applied, for example, in electroosmotic pumps or in desalination processes. Aquivion ionomer coated asymmetrically over a Teflon film (5 μm thickness) with a laser-drilled microhole (approximately 10 μm diameter) gives a cationic diode with a rectification ratio of typically 10-20 (measured in 0.01 M NaCl with ±0.3 V applied bias). Steady state voltammetry, chronoamperometry, and electrochemical impedance spectroscopy data are employed to characterize the ionic diode performance parameters. Next, a COMSOL 6.0 finite element model is employed to quantitatively assess/compare transient phenomena and to extract mechanistic information by comparison with experimental data. The experimental diode time constant and diode switching process associated with a distorted semicircle (with a typical diode switching frequency of 10 Hz) in the Nyquist plot are reproduced by computer simulation and rationalized in terms of microhole diffusion-migration times. Fundamental understanding and modeling of the ionic diode switching process can be exploited in the rational/optimized design of new improved devices.

Nanophase-photocatalysis: loading, storing, and release of H2O2 using graphitic carbon nitride

A blue light mediated photochemical process using solid graphitic carbon nitride (g-C₃N₄) in ambient air/isopropanol vapour is suggested to be linked to "nanophase" water inclusions and is shown to produce approx. 50 μmol H₂O₂ per gram of g-C₃N₄, which can be stored in the solid g-C₃N₄ for later release for applications, for example, in disinfection or anti-bacterial surfaces.

Effects of g-C3N4 Heterogenization into Intrinsically Microporous Polymers on the Photocatalytic Generation of Hydrogen Peroxide

Graphitic carbon nitride (g-C₃N₄) is known to photogenerate hydrogen peroxide in the presence of hole quenchers in aqueous environments. Here, the g-C₃N₄ photocatalyst is embedded into a host polymer of intrinsic microporosity (PIM-1) to provide recoverable heterogenized photocatalysts without loss of activity. Different types of g-C₃N₄ (including Pt@g-C₃N₄, Pd@g-C₃N₄, and Au@g-C₃N₄) and different quenchers are investigated. Exploratory experiments yield data that suggest binding of the quencher either (i) directly by adsorption onto the g-C₃N₄ (as shown for α-glucose) or (ii) indirectly by absorption into the microporous polymer host environment (as shown for Triton X-100) enhances the overall photochemical H₂O₂ production process. The amphiphilic molecule Triton X-100 is shown to interact only weakly with g-C₃N₄ but strongly with PIM-1, resulting in accumulation and enhanced H₂O₂ production due to the microporous polymer host.

Polymer indicator displacement assay: electrochemical glucose monitoring based on boronic acid receptors and graphene foam competitively binding with poly-nordihydroguaiaretic acid

A poly-nordihydroguaiaretic acid film is employed as a voltammetric indicator for bound/unbound boronic acid sites to report on glucose and fructose concentration.

TiO2 nanocrystal rods on titanium microwires: growth, vacuum annealing, and photoelectrochemical oxygen evolution

Titania nanocrystal rods grown hydrothermally onto titanium microwire are mechanically robust and photoelectrochemically active.

Hydrogen Peroxide Versus Hydrogen Generation at Bipolar Pd/Au Nano-catalysts Grown into an Intrinsically Microporous Polyamine (PIM-EA-TB)

Binding of PdCl42− into the polymer of intrinsic microporosity PIM-EA-TB (on a Nylon mesh substrate) followed by borohydride reduction leads to uncapped Pd(0) nano-catalysts with typically 3.2 ± 0.2 nm diameter embedded within the microporous polymer host structure. Spontaneous reaction of Pd(0) with formic acid and oxygen is shown to result in the competing formation of (i) hydrogen peroxide (at low formic acid concentration in air; with optimum H2O2 yield at 2 mM HCOOH), (ii) water, or (iii) hydrogen (at higher formic acid concentration or under argon). Next, a spontaneous electroless gold deposition process is employed to attach gold (typically 10- to 35-nm diameter) to the nano-palladium in PIM-EA-TB to give an order of magnitude enhanced production of H2O2 with high yields even at higher HCOOH concentration (suppressing hydrogen evolution). Pd and Au work hand-in-hand as bipolar electrocatalysts. A Clark probe method is developed to assess the catalyst efficiency (based on competing oxygen removal and hydrogen production) and a mass spectrometry method is developed to monitor/optimise the rate of production of hydrogen peroxide. Heterogenised Pd/Au@PIM-EA-TB catalysts are effective and allow easy catalyst recovery and reuse for hydrogen peroxide production.

Graphical abstract

Defect-Engineered β-MnO2-δ Precursors Control the Structure-Property Relationships in High-Voltage Spinel LiMn1.5Ni0.5O4-δ

This study examines the role of defects in structure-property relationships in spinel LiMn_1.5Ni_0.5O₄ (LMNO) cathode materials, especially in terms of Mn³⁺ content, degree of disorder, and impurity phase, without the use of the traditional high-temperature annealing (≥700 °C used for making disordered LMNO). Two different phases of LMNO (i.e., highly P4₃32-ordered and highly Fd3̅m-disordered) have been prepared from two different β-MnO_2-δ precursors obtained from an argon-rich atmosphere (β-MnO_2-δ (Ar)) and a hydrogen-rich atmosphere [β-MnO_2-δ (H₂)]. The LMNO samples and their corresponding β-MnO_2-δ precursors are thoroughly characterized using different techniques including high-resolution transmission electron microscopy, field-emission scanning electron microscopy, Raman spectroscopy, powder neutron diffraction, X-ray photoelectron spectroscopy, synchrotron X-ray diffraction, X-ray absorption near-edge spectroscopy, and electrochemistry. LMNO from β-MnO_2-δ (H₂) exhibits higher defects (oxygen vacancy content) than the one from the β-MnO_2-δ (Ar). For the first time, defective β-MnO_2-δ has been adopted as precursors for LMNO cathode materials with controlled oxygen vacancy, disordered phase, Mn³⁺ content, and impurity contents without the need for conventional methods of doping with metal ions, high synthetic temperature, use of organic compounds, postannealing, microwave, or modification of the temperature-cooling profiles. The results show that the oxygen vacancy changes concurrently with the degree of disorder and Mn³⁺ content, and the best electrochemical performance is only obtained at 850 °C for LMNO-(Ar). The findings in this work present unique opportunities that allow the use of β-MnO_2-δ as viable precursors for manipulating the structure-property relationships in LMNO spinel materials for potential development of high-performance high-voltage lithium-ion batteries.

Photo-Chlorine Production with Hydrothermally Grown and Vacuum-Annealed Nanocrystalline Rutile

Photo-generated high-energy surface states can help to produce chlorine in aqueous environments. Here, aligned rutile (TiO2) nanocrystal arrays are grown onto fluorine-doped tin oxide (FTO) substrates and activated either by hydrothermal Sr/Ba surface doping and/or by vacuum-annealing. With vacuum-annealing, highly photoactive films are obtained with photocurrents of typically 8 mA cm−2 at 1.0 V vs. SCE in 1 M KCl (LED illumination with λ = 385 nm and approx. 100 mW cm−2). Photoelectrochemical chlorine production is demonstrated at proof-of-concept scale in 4 M NaCl and suggested to be linked mainly to the production of Ti(III) surface species by vacuum-annealing, as detected by post-catalysis XPS, rather than to Sr/Ba doping at the rutile surface. The vacuum-annealing treatment is proposed to beneficially affect (i) bulk semiconductor TiO2 nanocrystal properties and electron harvesting, (ii) surface TiO2 reactivity towards chloride adsorption and oxidation, and (iii) FTO substrate performance.

Indirect (hydrogen-driven) electrodeposition of porous silver onto a palladium membrane

Hydrogen permeation through a pure palladium film (25 μm thickness, optically dense) is employed to trigger electron transfer (hydrogen-driven) reactions at the external palladium | aqueous electrolyte interface of a two-compartment electrochemical cell. Two systems are investigated to demonstrate feasibility for (i) indirect hydrogen-mediated silver electrodeposition with externally applied potential and (ii) indirect hydrogen-mediated silver electrodeposition driven by external formic acid decomposition. In both cases, porous metal deposits form as observed by optical and electron microscopies. Processes are self-limited as metal deposition blocks the palladium surface and thereby slows down further hydrogen permeation. The proposed methods could be employed for a wider range of metals, and they could provide an alternative (non-electrochemical or indirect) procedure for metal removal or metal recovery processes or for indirect metal sensing.

Extraction of hydrophobic analytes from organic solution into a titanate 2D-nanosheet host: Electroanalytical perspectives

Titanate nanosheets (single layer, typically 200 nm lateral size) deposited from aqueous colloidal solution onto electrode surfaces form lamellar hosts that bind redox active molecular redox probes. Here, hydrophobic redox systems such as anthraquinone, 1-amino-anthraquinone, deca-methylferrocene, 5,10,15,20-tetraphenyl-21H,23H-porphine manganese (III) chloride (TPPMnCl), and α-tocopherol are shown to bind directly from cyclopentanone solution (and from other types of organic solvents) into the titanate nanosheet film. For anthraquinone derivatives, stable voltammetric responses are observed in aqueous media consistent with 2-electron 2-proton reduction, however, independent of the pH of the outside solution phase environments. For decamethylferrocene a gradual decay of the voltammetric response is observed, but for TPPMnCl a more stable voltammetric signal is seen when immersed in chloride containing (NaCl) electrolyte. α-Tocopherol exhibits chemically irreversible oxidation and is detected with 1 mM–20 mM linear range and approximately 10⁻³ M concentration limit of detection. All redox processes exhibit an increase in current with increasing titanate film thickness and with increasing external electrolyte concentration. This and other observations suggest that important factors are analyte concentration and mobility within the titanate host, as well as ion exchange between titanate nanosheets and the outside electrolyte phase to maintain electroneutrality during voltammetric experiments. The lamellar titanate (with embedded tetrabutyl-ammonium cations) behaves like a hydrophobic host (for hydrophobic redox systems) similar to hydrophobic organic microphase systems. Potential for analytical applications is discussed.

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Extraction of hydrophobic guest molecules (e.g. vitamin E) from organic solvents into titanate nanosheet deposits.

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Redox processes at the electrode.|titanate interface coupled to ion exchange at the titanate|aqueous electrolyte interface

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Transport phenomena in 2D-titanate nanosheet deposits disected into a redox layer and an ion transport layer.

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Suppression of pH effects due to un-buffered conditions within the titanate nanosheet environment.

Pdxdc1 modulates prepulse inhibition of acoustic startle in the mouse

Current antipsychotic medications used to treat schizophrenia all target the dopamine D2 receptor. Although these drugs have serious side effects and limited efficacy, no novel molecular targets for schizophrenia treatment have been successfully translated into new medications. To identify novel potential treatment targets for schizophrenia, we searched for previously unknown molecular modulators of acoustic prepulse inhibition (PPI), a schizophrenia endophenotype, in the mouse. We examined six inbred mouse strains that have a range of PPI, and used microarrays to determine which mRNA levels correlated with PPI across these mouse strains. We examined several brain regions involved in PPI and schizophrenia: hippocampus, striatum, and brainstem, found a number of transcripts that showed good correlation with PPI level, and confirmed this with real-time quantitative PCR. We then selected one candidate gene for further study, Pdxdc1 (pyridoxal-dependent decarboxylase domain containing 1), because it is a putative enzyme that could metabolize catecholamine neurotransmitters, and thus might be a feasible target for new medications. We determined that Pdxdc1 mRNA and protein are both strongly expressed in the hippocampus and levels of Pdxdc1 are inversely correlated with PPI across the six mouse strains. Using shRNA packaged in a lentiviral vector, we suppressed Pdxdc1 protein levels in the hippocampus and increased PPI by 70%. Our results suggest that Pdxdc1 may regulate PPI and could be a good target for further investigation as a potential treatment for schizophrenia.

The adrenergic α2 antagonist atipamezole alters the behavioural effects of pramipexole and increases pramipexole concentration in blood plasma

Pramipexole is a dopaminergic agonist used in Parkinson's disease treatment. It is thought to exert its therapeutic and side effects through actions on dopamine D3 receptors. In a recent study, we found that at doses occupying D3 but not D2 receptors pramipexole reduced locomotion and operant responding for primary and conditioned reinforcement. These effects, however, were not blocked by a D3 receptor antagonist and were present in D3 knockout mice, suggesting non-D3 receptor mechanisms. Among the next highest affinity binding sites of pramipexole are adrenergic α2 receptors. Here we explored α2 receptor involvement in the behavioural effects of pramipexole. We found that the α2 antagonist atipamezole, which was itself behaviourally silent, counteracted pramipexole's reduction of locomotion, but not operant responding for water or a conditioned reinforcer. The resulting behavioural profile was similar to that of a higher dose of pramipexole, leading to the hypothesize that atipamezole mediates its behavioural effects by increasing pramipexole effective dose. In support of this hypothesis, we found that atipamezole increased pramipexole concentration in blood plasma. This is not likely due to an effect on drug metabolism since pramipexole is not known to undergo metabolic transformation. Future work should examine two alternative hypotheses; that pramipexole plasma concentration is elevated as the result of 1) competition with atipamezole for renal excretion, or 2) atipamezole blockade of peripheral α2 binding sites, thereby preventing pramipexole distribution to α2-rich tissues. The suggestion of adrenergic effects of pramipexole is important in light of recent interest in adrenergic pathophysiology in Parkinson's disease.

Low dose pramipexole causes D3 receptor-independent reduction of locomotion and responding for a conditioned reinforcer

Pramipexole is a clinically important dopamine receptor agonist with reported selectivity for dopamine D3 receptors over other dopaminergic and non-dopaminergic sites. Many of its behavioural effects are therefore attributed to D3 receptor activity. Here we relate pramipexole's ex vivo D2 and D3 receptor binding (measured using [(3)H]-(+)-PHNO binding experiments) to its effects on locomotion and operant responding for primary and conditioned reinforcers. We show that pramipexole has inhibitory behavioural effects on all three behaviours at doses that occupy D3 but not D2 receptor. However, these effects are 1) not inhibited by a D3 selective dose of the antagonist SB-277011-A, and 2) present in D3 receptor knockout mice. These results suggest that a pharmacological mechanism other than D3 receptor activity must be responsible for these behavioural effects. Finally, our receptor binding results also suggest that these behavioural effects are independent of D2 receptor activity. However, firmer conclusions regarding D2 involvement would be aided by further pharmacological or receptor knock-out experiments. The implications of our findings for the understanding of pramipexole's behavioural and clinical effects are discussed.

Evaluation of chemically diverse 5-HT₂c receptor agonists on behaviours motivated by food and nicotine and on side effect profiles

RATIONALE

Selective 5-HT2C receptor agonists, such as lorcaserin, are being developed for the treatment of obesity. Studies suggest that they may also have therapeutic potential for addictive behaviours including nicotine dependence, although few drugs of this class have been evaluated.

OBJECTIVES

The primary aim was to evaluate the highly selective 5-HT2C agonist, CP-809101, against food-motivated (operant FR5 and progressive ratio schedules, palatability-induced feeding) and nicotine-motivated (intravenous self-administration, drug discrimination) behaviours in rats and to compare with equivalent findings for the structurally distinct 5-HT2C receptor agonists lorcaserin and Ro 60-0175. The secondary aims were to evaluate the side effect profiles of lorcaserin and CP-809101 and to determine the plasma levels of lorcaserin at a dose (1 mg/kg) that reduces both food and nicotine reinforcement for comparison to plasma concentrations reported in human trials.

RESULTS

CP-809101 (0.3-3 mg/kg SC) reduced responding for both nicotine and food and blocked the discriminative stimulus properties of nicotine in a similar manner to lorcaserin and Ro 60-0175. Behaviours such as hypolocomotion, chewing and ptosis became evident following both CP-809101 and lorcaserin administration at higher doses. Plasma levels of lorcaserin were of similar range to those reported in obesity trials.

CONCLUSIONS

These studies support the utility of 5-HT2C agonists as a therapeutic approach to treat nicotine dependence. Plasma exposure levels after acute lorcaserin treatment suggest that equivalent dosages could be used to evaluate these drugs in obesity and smoking cessation trials. Finally, there may be differences in the side effect profiles between lorcaserin and CP-809101, raising the possibility for tolerability differences amongst 5-HT2C agonists.

Cannabidiol, a non-psychotropic component of cannabis, attenuates vomiting and nausea-like behaviour via indirect agonism of 5-HT(1A) somatodendritic autoreceptors in the dorsal raphe nucleus

BACKGROUND AND PURPOSE

To evaluate the hypothesis that activation of somatodendritic 5-HT(1A) autoreceptors in the dorsal raphe nucleus (DRN) produces the anti-emetic/anti-nausea effects of cannabidiol (CBD), a primary non-psychoactive cannabinoid found in cannabis.

EXPERIMENTAL APPROACH

The potential of systemic and intra-DRN administration of 5-HT(1A) receptor antagonists, WAY100135 or WAY100635, to prevent the anti-emetic effect of CBD in shrews (Suncus murinus) and the anti-nausea-like effects of CBD (conditioned gaping) in rats were evaluated. Also, the ability of intra-DRN administration of CBD to produce anti-nausea-like effects (and reversal by systemic WAY100635) was assessed. In vitro studies evaluated the potential of CBD to directly target 5-HT(1A) receptors and to modify the ability of the 5-HT(1A) agonist, 8-OH-DPAT, to stimulate [(35) S]GTPγS binding in rat brainstem membranes.

KEY RESULTS

CBD suppressed nicotine-, lithium chloride (LiCl)- and cisplatin (20 mg·kg(-1) , but not 40 mg·kg(-1) )-induced vomiting in the S. murinus and LiCl-induced conditioned gaping in rats. Anti-emetic and anti-nausea-like effects of CBD were suppressed by WAY100135 and the latter by WAY100635. When administered to the DRN: (i) WAY100635 reversed anti-nausea-like effects of systemic CBD, and (ii) CBD suppressed nausea-like effects, an effect that was reversed by systemic WAY100635. CBD also displayed significant potency (in a bell-shaped dose-response curve) at enhancing the ability of 8-OH-DPAT to stimulate [(35) S]GTPγS binding to rat brainstem membranes in vitro. Systemically administered CBD and 8-OH-DPAT synergistically suppressed LiCl-induced conditioned gaping.

CONCLUSIONS AND IMPLICATIONS

These results suggest that CBD produced its anti-emetic/anti-nausea effects by indirect activation of the somatodendritic 5-HT(1A) autoreceptors in the DRN.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

The pharmacist's contribution to clinicians' ward rounds: analysis by the stages in the drug use process

Hospital pharmacists are increasingly becoming an integral part of the clinical team, with many pharmacists now attending clinicians' ward rounds. This exploratory study observed five pharmacists attending ward rounds in hospitals in South East England, each on two or three occasions. The pharmacists volunteered to take part in the study and consent was obtained from the clinicians in charge. Each round was observed, tape recorded and transcribed. The verbal contributions of each member of the team to the discussions of drugs were analysed and categorised using the stages of the drug use process.

The rounds involved 109 patients and there were 269 separate conversations involving medication. Of these, 135 were patient-specific drug discussions where therapy was reviewed; the pharmacists made proposals to start, stop or alter therapy in nearly half of these discussions. There was no review of therapy in 38 per cent of patients in the study, ranging from 0 per cent on a medical round, to 75 per cent on a surgical round. The pharmacists were particularly involved in selecting the most appropriate dose, stopping drug therapy, and monitoring drugs. The clinicians were more involved in initiating drug therapy. All doctors questioned expressed their satisfaction with the pharmacists and their contribution to the ward rounds.

Enhanced dopamine function in DISC1-L100P mutant mice: implications for schizophrenia

Significant advances have been made in understanding the role of disrupted-in-schizophrenia-1 (DISC1) in the brain and accumulating findings suggest the possible implication of DISC1 in the regulation of dopamine (DA) function. A mutation in the second exon of DISC1 at L100P leads to the development of schizophrenia-related behavior in mutant mice (DISC1-L100P). We investigated here the role of DA in the expression of schizophrenia-related endophenotypes in the DISC1-L100P genetic mouse model. The mutated DISC1 resulted in facilitation of the psychostimulant effect of amphetamine in DISC1-L100P mutant mice assessed in the open field and prepulse inhibition (PPI) tests. Biochemical studies detected a 2.1-fold increase in the proportion of striatal D receptors without significant changes in DA release in vivo in the striatum of DISC1-L100P mutants in response to the low dose of amphetamine. The D(2) receptor antagonist haloperidol reversed the hyperactivity, PPI and latent inhibition (LI) deficits and blocked the psychostimulant effect of amphetamine in DISC1-L100P mutants. Taken together, our findings show the role of DISC1 in D(2) -related pathophysiological mechanism of schizophrenia, linking DISC1 with well-established DA hypothesis of schizophrenia.

The amphetamine-induced sensitized state as a model of schizophrenia

Schizophrenia is a serious psychiatric disorder which impacts a broad range of cognitive, behavioural and emotional domains. In animals, exposure to an intermittent, escalating dose regimen of amphetamine induces a sensitized state that appears to share a number of behavioural and neurochemical similarities with schizophrenia. In humans repeated exposure to amphetamine, or other psychomotor stimulants, can induce sensitization as well as psychosis. The following paper evaluates the evidence for the amphetamine-induced sensitized state as an animal model of schizophrenia, focussing separately on the positive, cognitive and negative symptoms associated with this disease. Current evidence supports the use of amphetamine sensitization as a model of the positive symptoms observed in schizophrenia. Additionally, there is increasing evidence for long-lasting cognitive deficits in sensitized animals, especially in the area of attention and/or cognitive flexibility. Other areas of cognition, such as long-term memory, appear to be unaltered in sensitized animals. Finally, little evidence currently exists to either support or refute the use of amphetamine sensitization as a model of negative symptoms. It is concluded that amphetamine sensitization likely impacts behaviour by altering the functioning of mesolimbic dopamine systems and prefrontal cortical function and can serve as a model of certain domains of schizophrenia.

Early life tactile stimulation changes adult rat responsiveness to amphetamine

Previously, we have found that total maternal deprivation of rat pups, achieved through artificial rearing, leads to a number of behavioral and neurophysiological changes, suggesting a change in the dopamine system. The purpose of this study was to further investigate possible changes in the functioning of dopamine systems, associated with artificial rearing, by examining the locomotor stimulant effects of the dopamine releaser amphetamine and the dopamine reuptake inhibitor methylphenidate. Rats were mother-reared or artificially reared. Some of those artificially reared rats were provided with either a maximum level (artificially reared maximal stimulation) or a minimal level of maternal licking-like tactile stimulation (artificially reared minimal stimulation). In adulthood, rats' locomotion was measured after an injection of d-amphetamine (0, 0.25, 0.5 and 1.0 mg/kg) or methylphenidate (0, 2, 5 and 10 mg/kg). Locomotor activity in response to a novel environment was enhanced in artificially reared rats, although this effect habituated over three daily 1-h sessions. Both amphetamine and methylphenidate dose dependently increased locomotor activity. The effect of amphetamine, but not methylphenidate was greatly enhanced in artificially reared minimally stimulated rats. The enhancement of the effect of amphetamine by artificial rearing was not apparent in artificially reared maximal stimulation rats.

Effects of injections of 8-hydroxy-2-(di-n-propylamino)tetralin or muscimol in the median raphe nucleus on c-fos mRNA in the rat brain

Inhibition of the median raphe nucleus (MRN) by the local injection of 5-HT(1A) or GABA(A) receptor agonists produces strong activational effects on feeding, drinking and locomotor activity. Using an animal model of relapse, we have shown that intra-MRN injection of the 5-HT(1A) autoreceptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) reinstates alcohol seeking in rats. The circuitry underlying the behavioral effects of intra-MRN injection of these drugs is not known. In order to identify the brain areas that may be involved, we measured levels of mRNA of the immediate early gene c-fos in discrete nuclei of the rat brain following intra-MRN infusions of these drugs. Male Wistar rats received intra-MRN infusions of 8-OH-DPAT (1 mug), muscimol (25 ng) or saline vehicle immediately prior to placement in locomotor activity chambers. Thirty minutes later, they were decapitated, and their brains processed for in situ hybridization of c-fos mRNA. In agreement with previous reports, injections of 8-OH-DPAT or muscimol into the MRN resulted in large increases in locomotor activity. Intra-MRN injections of these drugs increased c-fos in a number of brain nuclei previously shown to be involved in the rewarding effects of drugs of abuse in a regionally specific manner. Both drugs significantly increased the expression of c-fos mRNA in the medial frontal cortex, nucleus accumbens, lateral septum, dorsal bed nucleus of the stria terminalis and ventral tegmental area. In the ventral hippocampus, only 8-OH-DPAT increased c-fos, while in the basolateral nucleus of the amygdala and locus coeruleus, it was increased only by muscimol. These results are discussed in terms of the projections of the MRN and the pathways involved in relapse to alcohol and drug seeking.

Automated flow injection analyzer with on-line solid-phase extraction and chemiluminescence detection for the determination of dodecylamine in diesel fuels

This paper describes the development of a portable, automated flow injection-chemiluminescence (FI-CL) analyzer incorporating on-line solid-phase extraction (SPE) for the determination of dodecylamine (detergent) in diesel fuels. The method is based on the peroxyoxalate/sulforhodamine 101 chemiluminescence reaction, with SPE required to remove indigenous compounds within the diesel fuel matrix that interfere with the CL response. The automated analyzer achieved a detection limit of 2.9 mg L(-1) and a linear range of 2.9-50 mg L(-1), which was suitable for determinations of dodecylamine at levels typically present in fully formulated diesel fuels (40 mg L(-1)). Analyses of base fuels from five different sources demonstrated that an automated FI-CL-SPE system could provide a portable instrument for monitoring the presence/absence of dodecylamine in diesel fuels.

The role of corticotropin-releasing factor in the median raphe nucleus in relapse to alcohol

Using an animal model of drug relapse, we found that intermittent footshock stress reinstates alcohol seeking, an effect attenuated by the 5-HT reuptake blocker fluoxetine and by corticotropin-releasing factor (CRF) receptor antagonists. Here we studied the role of the 5-HT cell body region of the median raphe nucleus (MRN) and CRF receptors in this site in reinstatement of alcohol seeking. Rats were given alcohol in a two-bottle choice procedure (water vs alcohol) for 25 d and were then trained for 1 hr/d to press a lever for alcohol (12% w/v) for 23-30 d. Subsequently, lever pressing for alcohol was extinguished by terminating drug delivery for 5-9 d. Tests for reinstatement of alcohol seeking were then performed under extinction conditions. Intra-MRN infusions of 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin] (a 5-HT1A agonist that decreases 5-HT cell firing and release) reinstated alcohol seeking. Reinstatement of alcohol seeking also was observed after intra-MRN infusions of low doses of CRF (3-10 ng), which mimicked the effect of ventricular infusions of higher doses of the peptide (300-1000 ng). Finally, intra-MRN infusions of the CRF receptor antagonist d-Phe CRF (50 ng) blocked the effect of intermittent footshock (10 min) on reinstatement. These data suggest that an interaction between CRF and 5-HT neurons within the MRN is involved in footshock stress-induced reinstatement of alcohol seeking.

Pre-exposure to (+/-)3,4-methylenedioxy-methamphetamine (MDMA) facilitates acquisition of intravenous cocaine self-administration in rats

Pre-exposure to (+/-)3,4-methylenedioxymeth-amphetamine (MDMA) elevates locomotor activity and extracellular dopamine levels in the nucleus accumbens following a cocaine challenge. The present study determined whether MDMA-induced sensitization to the effects of cocaine could be demonstrated in rats self-administering cocaine. Three groups of rats were treated with saline (Sal), 5 mg/kg MDMA (once per day for 10 days; MDMA-5) or 20 mg/kg MDMA (twice per day for 4 days; MDMA-20). Subsequently, spontaneous acquisition of cocaine self-administration was measured in 12 daily 2-h sessions. During these test sessions, two response levers were present. Responses on one lever delivered infusions of 0.1 mg of cocaine; responses on the other lever had no programmed consequences. Group Sal showed a weak preference for the active lever; whereas, group MDMA-20 exhibited a stronger active lever preference. By day 12, the MDMA-20 group earned approximately twice the number of cocaine infusions as those in group SAL. At this time point, more than twice as many rats in group MDMA-20 were taking a minimum of 10 infusions per session, as compared to group Sal. Rats in group MDMA-5 did not seem to differ from group Sal in terms of lever discrimination, number of cocaine infusions, and percentage of rats obtaining a criterion of 10 infusions. These results indicate that pre-exposure to a high dose of MDMA may facilitate acquisition of cocaine self-administration. This dosing regimen of MDMA is likely to release DA and to be neurotoxic to 5-HT neurons. Either or both of these mechanisms could contribute to the ability of MDMA to facilitate cocaine self-administration.

The adenosine A2A agonist CGS 21680 reverses the reduction in prepulse inhibition of the acoustic startle response induced by phencyclidine, but not by apomorphine and amphetamine

Systemic administration of the selective adenosine A2A agonist CGS 21680, at the highest dose tested (0.5 mg/kg), selectively reversed the reduction in prepulse inhibition (PPI) of the acoustic startle response induced by the NMDA antagonist phencyclidine (PCP), but not by the dopaminergic agonists apomorphine and amphetamine. CGS 21680 by itself was without effect on PPI, but did reduce the amplitude of the startle response. PCP also reduced startle amplitude, but there was no additive or synergistic effect between PCP and CGS 21680 on the startle response. CGS 21680 (0.5 mg/kg) blocked the locomotor activating effect of amphetamine, but this may have been secondary to a reduction in spontaneous locomotion induced by this compound. Taken together, these results indicate that stimulation of adenosine A2A receptors produce no consequence on dopamine agonist-induced disruption in PPI, but regulate the inhibitory effect of NMDA receptor blockade on PPI. This finding raises the possibility that adenosine A2A agonists possess antipsychotic-like properties.

Reduced brain serotonin activity disrupts prepulse inhibition of the acoustic startle reflex. Effects of 5,7-dihydroxytryptamine and p-chlorophenylalanine

These experiments examined the impact of extensive depletions of forebrain 5-hydroxytryptamine (5-HT; serotonin) levels on prepulse inhibition (PPI) of the acoustic startle reflex in rats. In Experiment 1, injection of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) into the dorsal and median raphe nuclei disrupted PPI. This deficit was observed beginning 2 days after lesioning and was still apparent 8 weeks later. Basal startle reactivity was not altered. The 5-HT(1A) receptor agonist 8-OH-DPAT (0.1 mg/kg) and the dopamine receptor agonist apomorphine (1mg/kg) also disrupted PPI; the effect of 8-OH-DPAT, but not apomorphine, was potentiated in 5-HT-depleted rats. Basal startle reactivity was enhanced by 8-OH-DPAT in sham-lesioned rats but not in 5,7-DHT-lesioned rats. In Experiment 2, a second method for depleting 5-HT was used. The tryptophan hydroxylase inhibitor p-chlorophenylalanine (PCPA) also disrupted PPI without altering basal startle reactivity. Again, 8-OH-DPAT disrupted PPI in control animals; this effect was not altered in PCPA-treated rats but the increase in basal startle reactivity induced by 8-OH-DPAT was not observed in PCPA-treated rats. Taken together with the results of previous experiments involving drugs that enhance 5-HT neurotransmission it appears that both increases and decreases in 5-HT activity disrupt PPI.

Extracellular amino acid profiles in the paraventricular nucleus of the rat hypothalamus are influenced by diet composition

One possible mechanism by which food consumption signals feeding centers is through the resulting changes in amino acid profiles in the brain. In this study we examined the effect of voluntary consumption of a 50% protein diet or a 0% protein (carbohydrate) diet on extracellular amino acid profiles in the hypothalamic paraventricular nucleus (PVN) of freely moving rats from 1800 to 2100 h. Dialysates were continuously collected via microdialysis probes inserted in the PVN at 1500 h. Extracellular concentrations of isoleucine, leucine, methionine, tyrosine and valine were elevated within the first or second 20 min following the start of the 50% protein diet (P<0.05). The ratio of tryptophan to the total branched-chain amino acids (BCAA) in extracellular fluid increased following consumption of the carbohydrate diet (P<0.05), but decreased after the protein diet. An elevated ratio of tyrosine to BCAA was observed at the end of the measurement following the protein-free meal. It is concluded that amino acid concentrations in extracellular fluid of the PVN change rapidly after food consumption and that the changes are influenced by dietary composition.

Differences in cardiac procedures among patients in metropolitan and non-metropolitan hospitals in New South Wales after acute myocardial infarction and angina

An observational cohort study examined the difference in use of cardiac procedures during and after hospital admission for acute chest pain in 47 metropolitan or non-metropolitan hospitals across New South Wales (NSW). There were 3836 patients, represented by 4151 admissions to hospital after acute myocardial infarction (AMI), unstable angina or other angina. Follow up at 22 months was completed on 1695 patients. Patients admitted to metropolitan hospitals had higher rates of most cardiac procedures while in-patients than did patients in non-metropolitan hospitals. Odds ratios (95% confidence intervals) for the use of exercise stress tests, echocardiograms, nuclear studies and coronary angiography were 3.30 (1.38, 7.90), 9.34 (4.07, 21.44), 4.87 (2.08, 11.39) and 68.64 (17.29, 272.49), respectively, for patients with AMI and 1.93 (0.91, 4.12), 5.60 (1.60, 19.57), 3.51 (1.48, 8.33) and 38.57 (9.36, 158.94), respectively, for patients with unstable angina. Rates were similar between hospital types during the 22 months after discharge. The appropriateness of this large variation in resource use between metropolitan and non-metropolitan hospitals requires examination.

Studies to investigate the role of 5-HT(2C) receptors on cocaine- and food-maintained behavior

The present series of studies were designed to investigate the 5-HT(2C) receptor agonist Ro 60-0175 on cocaine- and food-maintained behavior in the rat. Ro 60-0175 (0.1-3 mg/kg, s.c.) reduced cocaine (15 mg/kg, i.p.)-induced hyperactivity. This inhibitory effect of Ro 60-0175 (1 mg/kg, s.c.) was completely blocked by pretreatment with the selective 5-HT(2C) antagonist SB 242,084 (0.5 mg/kg, i.p.). In further studies, Ro 60-0175 (1-3 mg/kg, s.c.) reduced responding for both food (45-mg Noyes pellet) and cocaine (0.25 mg/infusion) maintained under identical schedules of reinforcement (fixed ratio (5), time out 1 min, 60-min duration). The effect on food-maintained responding was blocked by SB 242,084 (0.5 mg/kg, i.p.). Ro 60-0175 (0.3-3 mg/kg, s.c.) also reduced the breakpoint for cocaine self-administration under a progressive ratio schedule of reinforcement. After a period of extinction training, where cocaine solution was substituted with saline, an acute priming injection of cocaine (15 mg/kg, i.p.) but not Ro 60-0175 (1 mg/kg, s.c.) reinstated cocaine responding. In this model of relapse, Ro 60-0175 (1-3 mg/kg, s.c.) pretreatment attenuated the priming effect of acute cocaine injection. In a final series of studies to examine the cataleptogenic properties of Ro 60-0175, very mild indices of catalepsy were observed at the 3 mg/kg dose only. These catalepsy scores were significantly lower than that produced by haloperidol (0. 5 mg/kg, s.c.). In further tests of motor function using the Rotarod, deficits were again seen at the 3 mg/kg dose, but not at lower doses. Taken together, these studies suggest that, in addition to reducing food intake, 5-HT(2C) receptor agonists reduce cocaine-reinforced behavior. This would be consistent with electrophysiological and biochemical evidence suggesting an important modulatory influence of 5-HT(2C) receptor activation on mesolimbic dopamine function.

The rewarding properties of neuropeptide Y in perifornical hypothalamus vs. nucleus accumbens

There is a high coexistence of substance abuse in humans with eating disorders. One theory offered to account for this fact is that a common biochemical substrate may exist that mediates both processes. Brain neuropeptide Y (NPY) is one neurochemical system that might contribute to these separate, yet related, problems. To clarify the role of NPY in mediating reward processes and the possible interaction between reward and feeding, the present study examined the effects of injecting NPY bilaterally into the perifornical hypothalamus (PFH) vs. the nucleus accumbens (NAC) on intake of preferred vs. non-preferred food types, as well as on conditioned place preference (CPP) learning. NPY (24, 78, 156 and 235 pmol/side) stimulated intake of both regular powdered chow and sucrose when injected into the PFH, but not the NAC. A CPP that was negatively correlated with food intake occurred with the low (24 pmol/side) dose of NPY in the PFH, while a CPP that was not correlated with food intake was produced with the same dose in the NAC. The extent of the CPPs produced by NPY injection in both brain sites mirrored that produced by peripheral injection of amphetamine (2.5 mg/kg). These results indicate that NPY elicits reward-related behavior, but not feeding, from the NAC, and both behaviors from the PFH. However, the feeding effect derived from the PFH appears to overshadow a rewarding effect derived from this site. Considered together, these findings suggest that altered NPY functioning in both brain regions may contribute to some of the pathophysiological processes observed in eating disordered patients who have additional proclivities for substance abuse.

Modification of dopamine D(1) receptor knockout phenotype in mice lacking both dopamine D(1) and D(3) receptors

Experimental evidence suggests that dopamine D(1) and D(3) receptors may interact in an opposing or synergistic fashion. To investigate interactions between both receptors in behaviour, we have used dopamine D(1) and D(3) receptor knockout mice to generate mice lacking both receptors. D(1)(-/-)D(3)(-/-) mice were viable, fertile and showed no gross morphological abnormalities. In an open field, they exhibited lower activity than wild-type, D(1)(-/-) and D(3)(-/-) mice. D(1)(-/-)D(3)(-/-) mice performed equally poorly in the rotarod and Morris water maze tasks as their D(1)(-/-) littermates. Basal locomotor activity and anxiety-like behaviour were normal in D(1)(-/-)D(3)(-/-) mice. Combined deletion of both receptors abolished the exploratory hyperactivity and anxiolytic-like behaviour of dopamine D(3) receptor mutant phenotype and further attenuated the low exploratory phenotype of D(1)(-/-) mice. These results imply an interaction of both receptors in the expression of exploratory behaviour in a novel environment, and the need for the presence of intact dopamine D(1) receptor for the expression of certain behaviours manifested in dopamine D(3) receptor mutant phenotype. In addition, dopamine D(1) receptor, but not dopamine D(3) receptor, is involved in the ability to perform on the rotarod and spatial learning.

Subchronic fluoxetine treatment induces a transient potentiation of amphetamine-induced hyperlocomotion: possible pharmacokinetic interaction

The results of the present study show that 5 days of systemic treatment with fluoxetine (5 mg/kg) resulted in an augmented locomotor response to amphetamine (0.5 mg/kg). This augmented response to amphetamine was observed 24 and 48 h, but not 5 days, after the cessation of fluoxetine treatment. Subchronic fluoxetine treatment also produced an increase in the brain concentration of amphetamine when rats were challenged with amphetamine 48 h, but not 5 days, after the cessation of fluoxetine treatment. Thus, the effect of subchronic fluoxetine in augmenting amphetamine-induced hyperactivity was consistent with the effect of subchronic fluoxetine in augmenting the amphetamine concentration in the brain. This pattern of results indicates that subchronic fluoxetine potentiates the response to amphetamine within a limited time-window, and that this potentiating effect is likely to be due to the reduced metabolism of amphetamine via the inhibition of cytochrome P450 by fluoxetine and/or its metabolite norfluoxetine.

Antipsychoticlike effects of amoxapine, without catalepsy, using the prepulse inhibition of the acoustic startle reflex test in rats

BACKGROUND

The dibenzoxazepine amoxapine was introduced as an antidepressant but has shown antipsychoticlike activity in a number of animal screening tests. A recent positron emission tomography study showed a 5-HT(2)/D(2) receptor occupancy profile of amoxapine that is very similar to that of established atypical antipsychotics. Schizophrenics display deficits in sensory gating mechanisms, such as prepulse inhibition (PPI) of the acoustic startle reflex. A similar deficit can be produced by dopamine (DA) and by 5-HT(2A/C) receptor agonists in rats. Antipsychotic compounds reverse this effect.

METHODS

Effects of amoxapine on apomorphine- or 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI)-induced disruption of PPI were studied in adult male Sprague-Dawley rats. The extrapyramidal side effect (EPS) liability of amoxapine was assessed using the inclined grid catalepsy (CAT) test. Statistical analyses were performed by analysis of variance (ANOVA) for fully repeated measures (PPI) and by the Kruskal-Wallis one-way ANOVA by ranks (CAT).

RESULTS

Apomorphine (0.5 mg/kg) produced a significant reduction in PPI compared with the case of rats in the saline control group. Pretreatment with amoxapine (10 mg/kg) significantly attenuated the apomorphine-induced disruption of PPI. DOI (0.5 mg/kg) significantly reduced PPI compared with saline controls. Pretreatment with amoxapine (5 or 10 mg/kg) produced a significant attenuation of the DOI-induced disruption of PPI. Amoxapine by itself did not alter PPI. Amoxapine (5 or 10 mg/kg) did not produce CAT.

CONCLUSIONS

The DA D(2)/5-HT(2) receptor antagonist amoxapine produced an antipsychoticlike reversal of both apomorphine- and DOI-induced disruption of PPI. Furthermore, the same doses of amoxapine that reversed disruption of PPI did not produce CAT. The results confirm and lend further support to the results of previous studies on amoxapine, suggesting that amoxapine might possess antipsychotic activity with little propensity for producing EPS.

Dietary protein content affects the profiles of extracellular amino acids in the medial preoptic area of freely moving rats

This study examined the effect of protein consumption on extracellular amino acid concentrations in the medial preoptic area (MPOA) of rats. Rats were given free access to diets containing 0, 25 or 50 % protein for 3-h duration, starting from the onset of dark cycle (1800 h). The microdialysis probe was implanted into the MPOA at 1500 h. Dialysates were collected every 20 min from 1700 h to 2100 h. Amino acid concentrations in dialysate samples were determined by reverse phase-HPLC. Extracellular amino acid concentrations in the MPOA were elevated by protein consumption within 20 to 40 min following the start of the meal. The 50 % protein diet resulted in increased (p<0.05) alanine, glutamine, isoleucine, leucine, methionine, tyrosine and valine concentrations, when compared with both baseline and the 0% protein diet. When the 25 % protein diet was fed, amino acid concentrations in the MPOA were between those after the 0 and 50% protein diets. The ratio of tryptophan to the total branched-chain amino acids in extracellular fluid was highest after the 0% protein diet and increased with time. We conclude that extracellular amino acid profiles in the MPOA are affected by dietary protein content.

Selective destruction of brain serotonin neurons by 5,7-dihydroxytryptamine increases responding for a conditioned reward

RATIONALE

Previously, we have shown that increasing 5-hydroxytryptamine (5-HT) activity attenuates responding for conditioned reward (CR), and the response potentiating effect of d-amphetamine on this behaviour.

OBJECTIVES

The present experiments examined the effects of reducing 5-HT function on responding for CR.

METHODS

In experiment 1, thirsty rats were trained to associate a CS+ with water delivery. The neurotoxin 5,7-DHT was then injected into the dorsal and median raphe nuclei. Subsequently, rats were treated with intraaccumbens d-amphetamine (1, 3, 10 micrograms) or saline and given access to two levers. One lever delivered the CS+ (now termed a CR), while the other was inactive. In experiment 2, the lesion was carried out prior to conditioning, and approach behaviour to the water magazine was measured during CS+ periods. Subsequently, rats were allowed to respond for the CS. In experiment 3, non-deprived rats learned to associate a CS+ with 10% sucrose; these animals also experienced a CS- which was not paired with sucrose. During a test phase responses on the two levers delivered either the CS+ or the CS-.

RESULTS

5,7-DHT substantially reduced 5-HT levels in striatum and hippocampus. In experiment 1, responding for the CR was enhanced by both d-amphetamine and 5-HT depletion in an additive fashion. In experiments 2 and 3, the discriminative control over behaviour exerted by the CS+ was not affected by 5-HT depletion. However, compared to control animals 5-HT-depleted rats showed higher levels of operant responding for the CR.

CONCLUSIONS

Serotonin depletion selectively enhances responding for CR. Although 5-HT depletion did not potentiate the effects of d-amphetamine, it is suggested that CRs activate the mesolimbic dopamine system, and that removal of an inhibitory influence of 5-HT on the activity of this system results in increased responding for CR in 5,7-DHT-treated rats.