Functional potencies of dopamine agonists and antagonists at human dopamine D₂ and D₃ receptors

We measured the functional agonist potencies of dopamine agonists including antiparkinson drugs, and functional antagonist potencies of antipsychotics at human dopamine D(2) and D(3) receptors. In vitro pharmacological assessment included inhibition of forskolin-stimulated cAMP accumulation and the reversal of dopamine-induced inhibition in clonal Chinese hamster ovary cells expressing low and high densities of human dopamine D(2L) and D(2S) receptors (hD(2L)-Low, hD(2L)-High, hD(2S)-Low and hD(2S)-High, respectively) and human dopamine D(3) Ser-9 and D(3) Gly-9 receptors (hD(3)-Ser-9 and hD(3)-Gly-9, respectively). Cabergoline, bromocriptine, pergolide, (±)-7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT), talipexole, pramipexole, R-(+)-trans-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-olhydrochloride (PD128907) and ropinirole behaved as dopamine D(2) and D(3) receptor full agonists and showed higher potencies in hD(2L)-High and hD(2S)-High compared to hD(2L)-Low and hD(2S)-Low. In hD(3)-Ser-9 and hD(3)-Gly-9 compared to hD(2L)-Low and hD(2S)-Low, dopamine, ropinirole, PD128907, and pramipexole potencies were clearly higher; talipexole and 7-OH-DPAT showed slightly higher potencies; pergolide showed slightly lower potency; and, cabergoline and bromocriptine potencies were lower. Aripiprazole acted as an antagonist in hD(2L)-Low; a low intrinsic activity partial agonist in hD(2S)-Low; a moderate partial agonist in hD(3)-Ser-9 and hD(3)-Gly-9; a robust partial agonist in hD(2L)-High; and a full agonist in hD(2S)-High. Amisulpride, sulpiride and perphenazine behaved as preferential antagonists; and chlorpromazine and asenapine behaved as modest preferential antagonists; whereas fluphenazine, haloperidol, and blonanserin behaved as non-preferential antagonists in hD(2S)-Low and hD(2S)-High compared to hD(3)-Ser-9 and hD(3)-Gly-9. These findings may help to elucidate the basis of therapeutic benefit observed with these drugs, with varying mechanisms of action, in the treatment of Parkinson's disease, depression and schizophrenia.     

Differential actions of dopamine agonists and antagonists on the γ-butyrolactone-induced increase in mouse brain dopamine

-Butyrolactone (GBL) increased the dopamine concentration in the forebrain of the mouse. Apomorphine dose-dependently antagonized the GBL effect, while piribedil was less effective. Haloperidol prevented the antagonism of GBL by apomorphine but pimozide was ineffective in blocking apomorphine. After chronic treatment with haloperidol or pimozide, there was no alteration of the maximum GBL-induced increase in dopamine nor was there any significant change in the antagonism by apomorphine, although a trend toward increased sensitivity to apomorphine was noted in the group withdrawn from haloperidol. These results suggest that in the mouse, haloperidol is a more effective antagonist of presynaptic dopamine autoreceptors than pimozide, while apomorphine is a better presynaptic agonist than piribedil.     

Blockade of dopamine D₃ but not D₂ receptors reverses the novel object discrimination impairment produced by post-weaning social isolation: implications for schizophrenia and its treatment

Dopamine D? receptors are densely expressed in mesolimbic projection areas, and selective antagonists enhance cognition, consistent with their potential therapeutic use in the treatment of schizophrenia. This study examines the effect of dopamine D? vs. D? receptor antagonists on the cognitive impairment and hyperactivity produced by social isolation of rat pups, in a neurodevelopmental model of certain deficits of schizophrenia. Three separate groups of male Lister hooded rats were group-housed or isolation-reared from weaning. Six weeks later rats received either vehicle or the dopamine D? selective antagonist, S33084 (0.04 and 0.16 mg/kg), the preferential D? antagonist, S33138 (0.16 and 0.63 mg/kg) or the preferential D? antagonist, L-741,626 (0.63 mg/kg) s.c. 30 min prior to recording; horizontal locomotor activity in a novel arena for 60 min and, the following day, novel object discrimination using a 2-h inter-trial interval. Isolation rearing induced locomotor hyperactivity in a novel arena and impaired novel object discrimination compared to that in group-housed littermates. Both S33084 and S33138 restored novel object discrimination deficits in isolation-reared rats without affecting discrimination in group-housed controls. By contrast, L-741,626 impaired novel object discrimination in group-housed rats, without affecting impairment in isolates. S33084 (0.16 mg/kg), S33138 and, less markedly, L741,626 reduced the locomotor hyperactivity in isolates without attenuating activity in group-housed controls. Selective blockade of dopamine D? receptors reverses the visual recognition memory deficit and hyperactivity produced by isolation rearing. These data support further investigation of the potential use of dopamine D? receptor antagonists to treat schizophrenia.     

A Dopamine D1 Receptor-Dependent ��-Arrestin Signaling Complex Potentially Regulates Morphine-Induced Psychomotor Activation but not Reward in Mice

Morphine is a widely used analgesic in humans that is associated with multiple untoward effects, such as addiction and physical dependence. In rodent models, morphine also induces locomotor activity. These effects likely involve functionally selective mechanisms. Indeed, G protein-coupled receptor desensitization and adaptor protein β-arrestin 2 (βarr2) through its interaction with the μ-opioid receptor regulates the analgesic but not the rewarding properties of morphine. However, βarr2 is also required for morphine-induced locomotor activity in mice, but the exact cellular and molecular mechanisms that mediate this arrestin-dependent behavior are not understood. In this study, we show that βarr2 is required for morphine-induced locomotor activity in a dopamine D1 receptor (D1R)-dependent manner and that a βarr2/phospho-ERK (βarr2/pERK) signaling complex may mediate this behavior. Systemic administration of SL327, an MEK inhibitor, inhibits morphine-induced locomotion in wild-type mice in a dose-dependent manner. Acute morphine administration to mice promotes the formation of a βarr2/pERK signaling complex. Morphine-induced locomotor activity and formation of the βarr2/pERK signaling complex is blunted in D1R knockout (D1-KO) mice and is presumably independent of D2 dopamine receptors. However, D1Rs are not required for morphine-induced reward as D1-KO mice show the same conditioned place preference for morphine as do control mice. Taken together, these results suggest a potential role for a D1R-dependent βarr2/pERK signaling complex in selectively mediating the locomotor-stimulating but not the rewarding properties of morphine.     

Uptake inhibitors do not change the effect of imidazoline α2-adrenoceptor agonists on transmitter release evoked by single pulse stimulation in mouse vas deferens

Summary The present study was undertaken to compare the presynaptic interaction of neuronal noradrenaline uptake inhibitors with imidazoline and phenylethylamine ₂adrenoceptor agonists under two different conditions: at low and high noradrenaline concentrations in the biophase.Isolated mouse vasa deferentia were stimulated with trains of 7 pulses given at 0.2 Hz and the inhibition by the ₂-adrenoceptor agonists clonidine, -methylnoradrenaline, and UK-14,304 of twitch responses was measured in the absence and in the presence of either cocaine (12 mol/l) or desipramine (40 nmol/l). The effects were determined for the first (equivalent to single pulse stimulation) and the last stimulus of each train. Both uptake inhibitors antagonized the presynaptic inhibitory effects of imidazolines (clonidine and UK-14,304) on the last twitch; the effects on the first twitch remained unchanged. In contrast, the uptake inhibitors potentiated the inhibitory effect of the phenylethylamine (-methylnoradrenaline) on both the first and the last twitches.These results support the view that the concentration of noradrenaline in the biophase plays a decisive role in the inhibition by a₂-adrenoceptor agonists of the electrically evoked release of noradrenaline. Agonists that are not substrates of neuronal uptake (i.e., clonidine, UK-14,304) become less effective when noradrenaline is present in the biophase while substrates of neuronal uptake (i. e., -methylnoradrenaline) do not. The results argue against the hypothesis that uptake inhibitors interact directly with presynaptic ₂-adrenoceptors or act at some link between uptake and receptor sites. Send offprint requests to S. Guimarães at the above address     

Tramadol antinociception is potentiated by clonidine through α₂-adrenergic and I₂-imidazoline but not by endothelin ET(A) receptors in mice

Tramadol is a centrally acting analgesic that acts via μ-opioid agonism and by blocking the neuronal uptake of norepinephrine and serotonin. Clonidine potentiates the antinociceptive effects of tramadol; however the receptors involved in this potentiation have not been studied. Endothelin ET(A) receptor antagonists potentiate antinociceptive effects of morphine and oxycodone; however the effects of endothelin ET(A) receptor antagonists on tramadol antinociception have not been evaluated. This study was conducted to determine the effect of clonidine on tramadol antinociception; the role of opioid, α?-adrenergic and I?-imidazoline receptors in clonidine potentiation of tramadol antinociception; and the effect of endothelin ET(A) receptor antagonists in modulating tramadol antinociception. Antinociceptive (tail-flick and hot-plate) latencies were measured in male Swiss Webster mice treated with tramadol; clonidine plus tramadol; or antagonists plus tramadol. Mice were pretreated with naloxone (opioid antagonist), yohimbine (α?-adrenoceptor antagonist), idazoxan (α?-adrenoceptor/I?-imidazoline antagonist), BMS182874 or BQ123 (endothelin ET(A) receptor antagonists) to study the involvement of these receptors. Tramadol produced a dose dependent increase in antinociceptive latencies. Tramadol antinociception was partially blocked by naloxone but not by yohimbine or idazoxan. Clonidine potentiated tramadol antinociception; potentiation was blocked by naloxone, yohimbine and idazoxan. Idazoxan produced a more pronounced blockade of potentiation than yohimbine. BMS182874 or BQ123 had no effect on tramadol antinociception, indicating that endothelin ET(A) receptors are not involved in tramadol antinociception in mice. Results demonstrate the involvement of opioid but not α?-adrenergic/I?-imidazoline receptors in tramadol antinociception and that opioid, α?-adrenergic and I?-imidazoline receptors are involved in clonidine potentiation of tramadol antinociception.     

The α₁-, but not α₂-, adrenoceptor in the nucleus accumbens plays an inhibitory role upon the accumbal noradrenaline and dopamine efflux of freely moving rats

In vivo microdialysis was used to analyse the role of the α(1)- and α(2)-adrenoceptor subtypes in the regulation of noradrenaline and dopamine efflux in the nucleus accumbens of freely moving rats. Intra-accumbal infusion of α(1)-adrenoceptor agonist methoxamine (24pmol) failed to alter the noradrenaline efflux, but decreased the dopamine efflux. The intra-accumbal infusion of α(1)-adrenoceptor antagonist prazosin (6, 600 and 6000pmol) produced a dose-related increase and decrease of the noradrenaline and dopamine efflux, respectively. An ineffective dose of prazosin (6pmol) counteracted the methoxamine (24pmol)-induced decrease of dopamine efflux. The prazosin (6000pmol)-induced increase of noradrenaline efflux, but not the decrease of dopamine efflux, was suppressed by the co-administration of an ineffective dose of methoxamine (0.024pmol). Neither the α(2)-adrenoceptor agonist clonidine (300pmol) and UK 14,304 (300pmol) nor the α(2)-adrenoceptor antagonist RX 821002 (0.6, 3, 600 and 6000pmol) significantly affected the accumbal noradrenaline and dopamine efflux. The doses mentioned are the total amount of drug over the 60-min infusion period. The present results show that (1) accumbal α(1)-adrenoceptors which are presynaptically located on noradrenergic nerve terminals inhibit the accumbal noradrenaline efflux, increasing thereby the accumbal dopamine efflux, (2) accumbal α(1)-adrenoceptors which are postsynaptically located on dopaminergic nerve terminals inhibit the accumbal dopamine efflux, and (3) accumbal α(2)-adrenoceptors play no major role in the regulation of accumbal efflux of noradrenaline and dopamine.     

Dopamine on D2-like receptors “reboosts” dopamine D1-like receptor-mediated behavioural activation in rats licking for a isotonic NaCl solution

Rationale

We recently suggested that dopamine on D1-like receptors is involved in the activation of goal-directed responses and the level of response activation is “reboosted” on the basis of an evaluation process involving D2-like receptors assessing “response efficacy”. A main piece of evidence in support of this hypothesis was the observation of an “extinction mimicry” effect in the time course of licking bursts after dopamine D2-like receptor blockade in rats licking for sucrose.

Objectives

The aim of this study was to determine whether the pattern of licking observed with sucrose as a reward could be reproduced in rats licking for a different reward (0.9 % NaCl).

Materials and methods

We investigated the effects of the dopamine D1-like receptor antagonist SCH 23390 (0.01–0.04 mg/kg) and of the dopamine D2-like receptor antagonist raclopride (0.025–0.25 mg/kg) on the microstructure of licking for a 0.9 % NaCl solution in 12-h water-deprived rats in 30-min sessions.

Results

As previously observed with sucrose as a reward, raclopride reduced the size of licking bursts and produced on the burst number time course an “extinction mimicry” effect, while SCH 23390 reduced licking exclusively by reducing burst number.

Conclusions

These results are consistent with the proposed hypothesis and provide support to the use of the study of licking microstructure as a valid model not only for the investigation of the mechanisms governing ingestive behaviour but also for the investigation of the mechanisms underlying behavioural activation and the related evaluation processes.     

Hetero-oligomerization between adenosine A₁ and thromboxane A₂ receptors and cellular signal transduction on stimulation with high and low concentrations of agonists for both receptors

Growing evidence indicates that G protein-coupled receptors can form homo- and hetero-oligomers to diversify signal transduction. However, the molecular mechanisms and physiological significance of G protein-coupled receptor-oligomers are not fully understood. Both ADOR1 (adenosine A(1) receptor) and TBXA2R (thromboxane A(2) receptor α; TPα receptor), members of the G protein-coupled receptor family, act on astrocytes and renal mesangial cells, suggesting certain functional correlations. In this study, we explored the possibility that adenosine A(1) and TPα receptors form hetero-oligomers with novel pharmacological profiles. We showed that these receptors hetero-oligomerize by conducting coimmunoprecipitation and bioluminescence resonance energy transfer (BRET(2)) assays in adenosine A(1) receptor and TPα receptor-cotransfected HEK293T cells. Furthermore, coexpression of the receptors affected signal transduction including the accumulation of cyclic AMP and phosphorylation of extracellular signal-regulated kinase-1 and -2 was significantly increased by high and low concentrations of adenosine A(1) receptor agonist and TPα agonists, respectively. Our study provides evidence of hetero-oligomerization between adenosine A(1) and TPα receptors for the first time, and suggests that this oligomerization affects signal transduction responding to different concentrations of receptor agonists.     

Selective dopamine antagonist pretreatment on the antiparkinsonian effects of benzazepine D1 dopamine agonists in rodent and primate models of parkinson's disease — the differential effects of D1 dopamine antagonists in the primate

In rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the medial forebrain bundle, pretreatment with the D₁ DA antagonists, SCH 23390 (7-chloro-8-hydroxy-2,3,4,5-tetrahydro-3-methyl-1-phenyl-1H-3-benzazepine) and A66359 (1-[2-bromo-4, 5-dimethoxybenzyl]-7-hydroxy-6-methoxy-2-methyl-1,2,3,4 tetrahydroisoquinoline), but not the D₂ DA antagonist raclopride inhibited the contralateral circling induced by the benzazepine D₁ DA agonists SKF 38393 (7-H, 3-H analogue of SCH 23390), SKF 80723 (7-H, 3-H, 6-Br analogue) and SKF 83959 (7-H, 6-Cl, 3-CH₃ analogue). In MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) treated common marmosets, administration of SKF 80723 and SKF 83959 increased locomotor activity and reversed the motor disability. Grooming and oral activities were also increased. Pretreatment with SCH 23390 and A66359 inhibited all the behavioural changes induced by both D₁ DA agonists. In general, higher doses of A66359 and more especially SCH 23390 were needed to inhibit SKF 83959 and SKF 80723 induced increases in oral activity and grooming than locomotor activity. Raclopride pretreatment did not affect SKF 83959 and SKF 80723 induced oral activity and grooming, though it reduced the duration of the locomotor changes induced by the D₁ DA agonists. These findings demonstrate that the behavioural effects of benzazepine D₁ DA agonists in the 6-OHDA lesioned rat and MPTP-treated marmoset are mediated by D₁ DA receptor sites, although in the primate, stimulation of D₂ DA receptors by endogenous DA may be necessary in facilitating the antiparkinsonian effects of D₁ DA agonists. The differential sensitivities of locomotor/motor disability and oral/grooming behaviours to antagonism by D₁ DA antagonists may indicate the involvement of multiple D₁ DA receptor subtypes in mediating benzazepine D₁ DA agonist induced behaviours in the MPTP-treated marmoset.     

Nicotine potentiation of brain stimulation reward reversed by DHβE and SCH 23390, but not by eticlopride, LY 314582 or MPEP in rats

RATIONALE: Systemic nicotine administration increases dopamine and glutamate levels in reward-related brain areas. Nicotine-induced increases of dopamine in the nucleus accumbens are in part mediated by glutamatergic projections to the ventral tegmental area dopamine neurons. OBJECTIVES: To assess the effects of actions at acetylcholine, dopamine, presynaptic (mGluR(2/3)) and postsynaptic (mGluR(5)) metabotropic glutamate receptors (mGluRs) on the potentiation of brain stimulation reward induced by systemically administered nicotine (0.125-0.5 mg/kg; free base) in rats. METHODS: A discrete-trial current-threshold s stimulation reward procedure (electrodes placed in the posterior lateral hypothalamus) was used to assess the effects of DH beta E (0.5-5 mg/kg), an acetylcholine nicotinic receptor antagonist, SCH 23390 (1.25-5 microg/kg), a dopamine D(1) receptor antagonist, eticlopride (2.5-20 microg/kg), a dopamine D(2) receptor antagonist, LY 314582 (1-20 mg/kg), an mGluR(2/3) agonist, and MPEP (1-9 mg/kg), an mGluR(5) antagonist, on the reward potentiating effects of nicotine (0.25 mg/kg). RESULTS: DH beta E had no effect on reward thresholds when administered alone, but dose-dependently reversed the nicotine-induced potentiation of brain stimulation reward. SCH 23390 (5 microg/kg) elevated thresholds when administered alone, and reversed the nicotine-induced potentiation of brain stimulation reward even at a dose (2.5 microg/kg) that had no effect on reward thresholds. Eticlopride (10-20 microg/kg), LY 314582 (10-20 mg/kg) and MPEP (9 mg/kg) elevated thresholds when administered alone but had no effect on the nicotine-induced potentiation of brain stimulation reward. CONCLUSIONS: These results indicate that nicotinic and dopamine D(1) receptors are involved in the nicotine-induced potentiation of brain stimulation reward, while actions at dopamine D(2), mGlu(2/3) and mGlu(5) receptors did not modulate this effect of nicotine.     

Hydrogen sulphide protects mouse pancreatic β-cells from cell death induced by oxidative stress, but not by endoplasmic reticulum stress

BACKGROUND AND PURPOSE

Hydrogen sulphide (H₂S), a potentially toxic gas, is also involved in the neuroprotection, neuromodulation, cardioprotection, vasodilatation and the regulation of inflammatory response and insulin secretion. We have recently reported that H₂S suppresses pancreatic β-cell apoptosis induced by long-term exposure to high glucose. Here we examined the protective effects of sodium hydrosulphide (NaHS), an H₂S donor, on various types of β-cell damage.

EXPERIMENTAL APPROACH

Isolated islets from mice or the mouse insulinoma MIN6 cells were cultured with palmitate, cytokines (a mixture of tumour necrosis factor-α, interferon-γ and interleukin-1β), hydrogen peroxide, thapsigargin or tunicamycin with or without NaHS. We examined DNA fragmentation, caspase-3 and -7 activities and reactive oxygen species (ROS) production in the treated cells thereafter. Apoptotic cell death in isolated islets was also assessed by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) method.

KEY RESULTS

NaHS suppressed DNA fragmentation and the activities of caspase-3 and -7 induced by palmitate, the cytokines or hydrogen peroxide. In contrast, NaHS failed to protect islets and MIN6 cells from apoptosis induced by thapsigargin and tunicamycin, both of which cause endoplasmic reticulum stress. NaHS suppressed ROS production induced by cytokines or hydrogen peroxide but it had no effect on ROS production in thapsigargin-treated cells. NaHS increased Akt phosphorylation in MIN6 cells treated with cytokines but not in cells treated with thapsigargin. Treatment with NaHS decreased TUNEL-positive cells in cytokine-exposed islets.

CONCLUSIONS AND IMPLICATIONS

H₂S may prevent pancreatic β-cells from cell apoptosis via an anti-oxidative mechanism and the activation of Akt signalling.     

Sertindole, a potent antagonist at dopamine D₂ receptors, induces autophagy by increasing reactive oxygen species in SH-SY5Y neuroblastoma cells

Autophagy is associated with cell survival and cell death. Autophagy is implicated in the pathophysiology of various human diseases. In order to identify autophagy regulatory molecules, we screened a chemical drug library in SH-SY5Y cells and selected Sertindole as a potent autophagy inducer. Sertindole was developed as an antipsychotic drug for Schizophrenia. Sertindole treatment highly induced the formation of autophagosomes as well as LC3 conversion. Subsequently, Sertindole-induced autophagy was efficiently suppressed by down regulation of ATG5. Sertindole also increased reactive oxygen species (ROS) production, which contributes to autophagy-associated cell death in neuroblastoma cells. ROS scavengers such as N-acetylcysteine and Trolox suppressed not only ROS generation but also autophagy activation by Sertindole. These results suggest Sertindole induces autophagy and autophagy-associated cell death by ROS production in neuroblastoma cells.     

Do men outperform women in smoking cessation trials? Maybe,but not by much

Using data from 4 smoking cessation trials conducted from 1988 to 2000, the authors investigated whether men are more successful than women in quitting smoking. Odds ratios indicated that the abstinence rates were not significantly different for men and women. Thus, there may be little value to diverting research funds from efforts to develop more effective treatments for both men and women to efforts to explain a very small gender effect associated with existing treatments. However, it may be appropriate to make gender comparisons for new therapies for nicotine dependence. The authors recommend against analyses of gender differences in studies that do not account for gender in their research designs.     

Repeated but not acute treatment with ∆9-tetrahydrocannabinol disrupts prepulse inhibition of the acoustic startle: Reversal by the dopamine D2/3 receptor antagonist haloperidol

Cannabis produces cognitive dysfunctions that resemble those of schizophrenia; yet the neurobiological substrate of this similarity remains unclear. Schizophrenia patients show deficits in prepulse inhibition (PPI) of the acoustic startle reflex (ASR), an operational measure of the information-processing abnormalities that may underlie the cognitive and positive symptoms of the disease. However, the effect of cannabis on PPI remains poorly understood, as data are often contradictory. Here, we investigated the effect of acute and repeated treatment with ∆⁹-tetrahydrocannabinol (THC), the main psychoactive constituent of cannabis, on PPI in rats, and the role of dopamine D_2/3-receptor blockade in this effect. PPI and ASR were sequentially measured after the first and the last dose of a 21-days treatment with THC (1 mg/kg/day) or vehicle and at 1-week following discontinuation of treatment. The effect of haloperidol (0.1 mg/kg) on THC-induced PPI alteration was also evaluated. Chronic, but not acute, THC treatment produced significant reductions in PPI that were normalized back to control values within one-week of THC discontinuation. The THC-induced gating deficits were observed in the absence of ASR change and were reversed by the D_2/3-receptor antagonist haloperidol. Chronic THC exposure induced PPI disruptions that emerged only following repeated administrations, suggesting that time-dependent neuroadaptations within the DA mesolimbic system are involved in the disruptive effects of THC on sensorimotor gating. These gating deficits were transient and appeared to be dependent on an overactivity of D_2/3-receptor-mediated dopamine signaling, highlighting a potential role for D_2/3-receptors in the propsychotic action of THC.     

β-Amyloid exacerbates inflammation in astrocytes lacking fatty acid amide hydrolase through a mechanism involving PPAR-α, PPAR-γ and TRPV1, but not CB₁ or CB₂ receptors

BACKGROUND AND PURPOSE

The endocannabinoid system may regulate glial cell functions and their responses to pathological stimuli, specifically, Alzheimer''s disease. One experimental approach is the enhancement of endocannabinoid tone by blocking the activity of degradative enzymes, such as fatty acid amide hydrolase (FAAH).

EXPERIMENTAL APPROACH

We examined the role of FAAH in the response of astrocytes to the pathologic form of β-amyloid (Aβ). Astrocytes from wild-type mice (WT) and from mice lacking FAAH (FAAH-KO) were incubated with Aβ for 8, 24 and 48 h, and their inflammatory responses were quantified by elisa, western-blotting and real-time quantitative-PCR.

KEY RESULTS

FAAH-KO astrocytes were significantly more responsive to Aβ than WT astrocytes, as shown by the higher production of pro-inflammatory cytokines. Expression of COX-2, inducible NOS and TNF-α was also increased in Aβ-exposed KO astrocytes compared with that in WTs. These effects were accompanied by a differential pattern of activation of signalling cascades involved in mediating inflammatory responses, such as ERK1/2, p38MAPK and NFκ B. PPAR-α and PPAR-γ as well as transient receptor potential vanilloid-1 (TRPV1), but not cannabinoid CB₁ or CB₂ receptors, mediate some of the differential changes observed in Aβ-exposed FAAH-KO astrocytes. The pharmacological blockade of FAAH did not render astrocytes more sensitive to Aβ. In contrast, exogenous addition of several acylethanolamides (anandamide, palmitoylethanolamide and oleoylethanolamide) induced an antiinflammatory response.

CONCLUSIONS

The genetic deletion of FAAH in astrocytes exacerbated their inflammatory phenotype against Aβ in a process involving PPAR-α, PPAR-γ and TRPV1 receptors.     

Comparison of D₂ dopamine receptor occupancy after oral administration of quetiapine fumarate immediate-release and extended-release formulations in healthy subjects

Quetiapine is an established drug for treatment of schizophrenia, bipolar disorder, and major depressive disorder. While initially manufactured as an immediate-release (IR) formulation, an extended-release (XR) formulation has recently been introduced. Pharmacokinetic studies show that quetiapine XR provides a lower peak and more stable plasma concentration than the IR formulation. This study investigated if the pharmacokinetic differences translate into different time curves for central D? dopamine receptor occupancy. Eleven control subjects were examined with positron emission tomography (PET) and the radioligand [11C]raclopride. Eight subjects underwent all of the scheduled PET measurements. After baseline examination, quetiapine XR was administered once-daily for 8 d titrated to 300 mg/d on days 5-8, followed by 300 mg/d quetiapine IR on days 9-12. PET measurements were repeated after the last doses of quetiapine XR and IR at predicted times of peak and trough plasma concentrations. Striatal D? receptor occupancy was calculated using the simplified reference tissue model. Peak D? receptor occupancy was significantly higher with quetiapine IR than XR in all subjects (50 ± 4% and 32 ± 11%, respectively), consistent with lower peak plasma concentrations for the XR formulation. Trough D? receptor occupancy was similarly low for both formulations (IR 7 ± 7%, XR 8 ± 6%). The lower peak receptor occupancy associated with quetiapine XR may explain observed pharmacodynamic differences between the formulations. Assuming that our findings in control subjects are valid for patients with schizophrenia, the study supports the view that quetiapine, like the prototype atypical antipsychotic clozapine, may show antipsychotic effect at lower D? receptor occupancy than typical antipsychotics.