Oral and Palmitate Paliperidone Long-Acting Injectable Formulations' Use in Schizophrenia Spectrum Disorders: A Retrospective Cohort Study from the First Episode Psychosis Intervention Program (CRUPEP).

BACKGROUND: Long-acting injectable antipsychotics (LAIs) may be a suitable therapeutic option for those patients in earlier stages of psychosis to avoid relapses and disease progression. Despite that, there is a lack of evidence in the literature regarding the use of LAIs in this profile of patients. METHODS: This is a retrospective cohort analysis to assess the efficacy, tolerability, and pattern of use of palmitate paliperidone long-acting injectable (PPLAI) formulations (1- and 3-month doses) compared to oral paliperidone/risperidone in patients with a nonaffective first episode of psychosis (FEP) over 12 months of follow-up. Relevant sociodemographic and clinical information were assessed, as well as main clinical scales: Positive and Negative Syndrome Scale, Personal and Social Performance Scale, and Clinical Global Impression Scale Improvement and Severity measures. RESULTS: The study included 48 patients, 16 per arm, who were aged 20-50 years and had an FEP. Significant improvements were registered for all treatment groups. Despite that, patients receiving PPLAI 1- and 3-month formulations obtained greater improvements than those in the oral group in the main domains assessed (P < .001). We found no statistically significant differences in hospitalizations between groups. Side effects were presented in 24% of patients. A trend towards reducing antipsychotic doses was observed in 43.8% of patients to achieve the minimum effective dose and avoid the occurrence of side effects. CONCLUSIONS: To our knowledge, this is the first study assessing the use of palmitate paliperidone long-acting formulations versus oral risperidone or paliperidone in FEP. Treatment with PPLAI formulations seems to be an effective therapeutic choice at earlier stages of the disease.

Brain RGS4 and RGS10 protein expression in schizophrenia and depression. Effect of drug treatment.

RATIONALE: Regulator of G-protein signaling (RGS) proteins, RGS4 and RGS10, may be involved in the pathophysiology of schizophrenia. RGS4 has attracted special interest since the reports of genetic association between SNPs in RGS4 and schizophrenia. However, there is no information about the subcellular distribution of RGS4 and RGS10 proteins in psychiatric disorders. OBJECTIVES: Plasma membrane RGS4 and cytosolic RGS10 protein immunoreactivity in prefrontal cortex from schizophrenic subjects (n = 25), non-diagnosed suicides (n = 13), and control subjects (n = 35), matched by age, gender, and postmortem delay, was analyzed by western blot. A second group of depressed subjects (n = 25) and control subjects (n = 25) was evaluated. The effect of the antipsychotic or antidepressant treatments was also assessed. RESULTS: No significant differences in plasma membrane RGS4 and cytosolic RGS10 protein expression were observed between schizophrenic subjects, non-diagnosed suicides, and control subjects. However, RGS4 immunoreactivity was significantly higher (Δ = 33 ± 10 %, p < 0.05) in the antipsychotic-treated subgroup (n = 12) than in the antipsychotic-free subgroup (n = 13). Immunodensities of plasma membrane RGS4 and cytosolic RGS10 proteins did not differ between depressed and matched control subjects. CONCLUSIONS: Expression of RGS4 and RGS10 proteins at their predominant subcellular location was studied in the postmortem brain of subjects with psychiatric disorders. The results suggest unaltered membrane RGS4 and cytosolic RGS10 proteins levels in schizophrenia and major depression. Antipsychotic treatment seems to increase membrane RGS4 immunoreactivity. Further studies are needed to elucidate RGS4 and RGS10 functional status.

The inverse agonist effect of rimonabant on G protein activation is not mediated by the cannabinoid CB1 receptor: evidence from postmortem human brain.

Rimonabant (SR141716) was the first potent and selective cannabinoid CB1 receptor antagonist synthesized. Several data support that rimonabant behaves as an inverse agonist. Moreover, there is evidence suggesting that this inverse agonism may be CB1 receptor-independent. The aim of the present study was to elucidate whether the effect of rimonabant over G protein activation in postmortem human brain is CB1 dependent or independent. [(35)S]GTPγS binding assays and antibody-capture [(35)S]GTPγS scintillation proximity assays (SPA) were performed in human and mice brain. [(3)H]SR141716 binding characteristics were also studied. Rimonabant concentration-dependently decreased basal [(35)S]GTPγS binding to human cortical membranes. This effect did not change in the presence of either the CB1 receptor agonist WIN 55,212-2, the CB1 receptor neutral antagonist O-2050, or the CB1 allosteric modulator Org 27569. [(35)S]GTPγS binding assays performed in CB1 knockout mice brains revealed that rimonabant inhibited the [(35)S]GTPγS binding in the same manner as it did in wild-type mice. The SPA combined with the use of specific antibody-capture of G(α) specific subunits showed that rimonabant produces its inverse agonist effect through G(i3), G(o) and G(z) subtypes. This effect was not inhibited by the CB1 receptor antagonist O-2050. Finally, [(3)H]SR141716 binding assays in human cortical membranes demonstrated that rimonabant recognizes an additional binding site other than the CB1 receptor orthosteric binding site recognized by O-2050. This study provides new data demonstrating that at least the inverse agonist effect observed with >1µM concentrations of rimonabant in [(35)S]GTPγS binding assays is not mediated by the CB1 receptor in human brain.

Molecular adaptations of apoptotic pathways and signaling partners in the cerebral cortex of human cocaine addicts and cocaine-treated rats.

Cocaine induces apoptotic effects in cultured cells and in the developing brain, but the aberrant activation of cell death in the adult brain remains inconclusive, especially in humans. This postmortem human brain study examined the status of canonical apoptotic pathways, signaling partners, and the cleavage of poly(ADP-ribose) polymerase-1 (PARP-1), a sensor of DNA damage, in prefrontal cortex (PFC) of a small but well-characterized cohort of cocaine abusers (n=10). For comparison, the chosen targets were also quantified in the cerebral cortex of cocaine-treated rats. In the PFC of cocaine abusers, FS7-associated cell surface antigen (Fas) receptor aggregates and Fas-associated death domain (FADD) adaptor were reduced (-26% and -66%, respectively) as well as the content of mitochondrial cytochrome c (-61%). In the same brain samples of cocaine abusers, the proteolytic cleavage of PARP-1 was increased (+39%). Nuclear PARP-1 degradation, possibly a consequence of increased mitochondrial oxidative stress, involved the activation of apoptosis-inducing factor (AIF) and not that of caspase-3. In the PFC of cocaine abusers, several signaling molecules associated with cocaine/dopamine and/or apoptotic pathways were not significantly altered, with the exception of anti-apoptotic truncated DARPP-32 (t-DARPP), a truncated isoform of dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32), whose content was decreased (-28%). Chronic exposure to cocaine in rats, including withdrawal for 3 days, did not alter Fas-FADD receptor complex, cytochrome c, caspase-3/fragments, AIF, PARP-1 cleavage, and associated signaling in the cerebral cortex. Chronic cocaine and abstinence, however, increased the content of t-DARPP (+39% and +47%) in rat brain cortex. The major findings indicate that cocaine addiction in humans is not associated with abnormal activation of extrinsic and intrinsic apoptotic pathways in PFC. The downregulation of Fas-FADD receptor complex and cytochrome c could reflect the induction of contraregulatory adaptations or non-apoptotic (neuroplastic) actions induced by the psychostimulant. The enhanced degradation of nuclear PARP-1, a hallmark of apoptosis, indicates the possibility of aberrant cell death.

Phosphorylation of FADD (Fas-associated death domain protein) at serine 194 is increased in the prefrontal cortex of opiate abusers: relation to mitogen activated protein kinase, phosphoprotein enriched in astrocytes of 15 kDa, and Akt signaling pathways involved in neuroplasticity.

Fas-associated protein with death domain (FADD) is a multifunctional protein that can induce both apoptotic and non-apoptotic actions. Recently, FADD was found downregulated in the prefrontal cortex of opiate abusers, which suggested an attenuation of Fas death signals in human addicts. Phosphorylation of FADD (Ser194) has been reported to regulate its non-apoptotic activity, which might include the induction of neuroplastic effects in the brain. This postmortem brain study examined the status of phosphorylated (p)-Ser194 FADD and signaling pathways involved in neuroplasticity in the prefrontal cortex (BA 9) of short-term (ST) and long-term (LT) heroin or methadone abusers. In these subjects, the content of monomeric p-FADD was significantly increased when compared with that in age-, gender-, and postmortem delay-matched controls (all addicts: 65%, n=26; ST abuse: 51%; n=11; LT abuse: 75%, n=15). Oligomeric p-FADD forms were modestly increased (11%-23%). At the subcellular level, opiate addiction upregulated the expression of monomeric p-FADD in the nucleus (110%) and that of p-oligomers in the cytosol (66%). In LT opiate addicts (but not ST abusers), a pronounced downregulation of p-extracellular signal-regulated kinase (ERK)1/2 (52%) and p-c-Jun NH(2)-terminal protein kinase (JNK)1/2 (51%), but not p-p38 mitogen-activated protein kinase (MAPK), was quantified in the prefrontal cortex (total homogenate and subcellular compartments). Similarly, the signaling pathway mediated by p-phosphoprotein enriched in astrocytes of 15 kDa (PEA-15) protein and its phosphorylating kinase p-Akt1 was also downregulated in cortical homogenate (43% and 41%, respectively) and cytosolic preparations of chronic opiate addicts. The results indicate that opiate addiction in humans is associated with an altered balance between p-Ser194 FADD (increased) and total FADD (decreased) in brain, which may favor its neuroplastic actions. The interaction between p-FADD (upregulated) and neuronal pathways (downregulated) could play a relevant role in mediating specific forms of structural and behavioral neuroplasticity.

[Imidazoline I(2) receptors as a possible marker for malignancy in human glial cell tumours]. / Los receptores para imidazolinas I(2) como posible marcador de malignidad en tumores gliales humanos.

AIM: To present the experimental data that support the hypothesis that the imidazoline I(2) receptors may be assessed as a biological marker to establish diagnosis and grade of human gliomas. DEVELOPMENT: Gliomas constitute the most important group of brain neoplasm in humans. In these tumours accurate histopathologic diagnosis is a first crucial prerequisite for patient treatment. However, current grading schemes are still limited by subjective histologic criteria. Therefore, the search for new molecular and biological markers of gliomas represents a crucial step. In this context, it has been reported a significant increase in I(2) density in human gliomas when compared with normal brain tissue and other intracranial non-glial tumours. Moreover, this increase seems to fit well with the degree of malignancy in human gliomas. Thus, in glioblastomas multiformes the I(2) density is 1.4 times higher than in anaplastic astrocytomas and 2.2 higher than in low-grade astrocytomas. CONCLUSIONS: The present results demonstrate that the measurement of the I(2) density by positron emission tomography techniques could be used in the future for grading and prognosis of human gliomas. This could avoid the current need for tumour biopsies in order to obtain a histopathologic diagnosis.

Characterization of CB1 cannabinoid receptor immunoreactivity in postmortem human brain homogenates.

The CB1 cannabinoid receptor (CB1) is the predominant type of cannabinoid receptor in the CNS, in which it displays a unique anatomical distribution and is present at higher densities than most other known seven transmembrane domain receptors. Nevertheless, as with almost all seven transmembrane domain receptors, the tertiary and quaternary structure of this receptor is still unknown. Studies of CB1 in rat cerebral tissue are scarce, and even less is known regarding the expression of CB1 in the human brain. Thus, the aim of the present work was to characterize CB1 expression in membranes from postmortem human brain using specific antisera raised against this protein. Western blot analysis of P1 and P2 fractions, and crude plasma membrane preparations from the prefrontal cortex showed that CB1 migrated as a 60 kDa monomer under reducing conditions. These data were confirmed by blotting experiments carried out with human U373MG astrocytoma cells as a positive control for CB1 expression and wild-type CHO cells as negative control. In addition, when proteins were solubilized in the absence of dithiothreitol, the anti-human CB1 antiserum detected a new band migrating at around 120 kDa corresponding in size to a putative CB1 dimer. This band was sensitive to reducing agents (50 mM dithiothreitol) and showed sodium dodecylsulphate stability, suggesting the existence of disulfide-linked CB1 dimers in the membrane preparations. Important differences in the anatomical distribution of CB1 were observed with regard to that described previously in monkey and rat; in the human brain, CB1 levels were higher in cortex and caudate than in the cerebellum.

Aminopeptidase activity in the postmortem brain of human heroin addicts.

Several studies have reported that the chronic administration of opioids induces changes in the biosynthesis of endogenous opioid peptides or their precursors in specific brain regions of the adult central nervous system. However, little is known about the catabolic regulation of opioid peptides and its contribution to neuroadaptative changes underlying drug addiction. In the present study, we have analyzed the activity of two enkephalin-degrading enzymes (puromycin-sensitive aminopeptidase or PSA and aminopeptidase N or APN) and two functionally different, soluble aminopeptidases (aminopeptidase B and aspartyl-aminopeptidase) in postmortem samples of prefrontal cortex and caudate nucleus of eight human heroin addict brains and eight matched-controls. Enzyme activities were fluorimetrically measured using beta-naphthylamide derivatives. An increase in the activity of soluble PSA in the prefrontal cortex of heroin abusers was observed (heroin addict group: 51,452+/-3892 UAP/mg protein versus control group: 42,003+/-2597 UAP/mg protein; P<0.05), while the activity of the other peptidases in both brain regions remained unaltered. This result agrees with previous findings in morphine-tolerant rats, and indicates that soluble PSA may be involved in neurobiological processes which underlie heroin addiction.

Imidazoline I(2) receptor density increases with the malignancy of human gliomas.

BACKGROUND: Current glioma grading schemes are limited by subjective histological criteria. Imidazoline I(2) receptors are principally expressed on glial cells. OBJECTIVE: To investigate the feasibility of using the measurement of imidazoline I(2) receptor expression to differentiate glial tumours from other types of brain tumours and for grading the different gliomas. METHODS: The specific binding of [(3)H]idazoxan to imidazoline I(2) receptors was measured in homogenates from human gliomas of different grades. RESULTS: The density of imidazoline I(2) receptors was significantly greater in the three types of malignant glial tumours than in postmortem control brain or non-glial tumours. The increase in density correlated with the malignancy grade of the gliomas. No significant differences in affinity values were observed. CONCLUSION: These results suggest that the density of imidazoline I(2) receptors may be a useful radioligand parameter for the differentiation of glial tumours from other types of brain tumours and for grading the different gliomas.

Effects of chronic tramadol on pre- and post-synaptic measures of monoamine function.

The atypical analgesic tramadol has strong structural similarities to the antidepressant venlafaxine and is a mixed noradrenaline (NA) and serotonin (5-HT) uptake inhibitor. Because tramadol has been found active in the forced swim test, a common predictor of antidepressant efficacy, we therefore examined the effects of chronic tramadol on various pre- and post-synaptic monoamine measures. Male Wistar rats (150-200 g) received tramadol (20 mg/kg i.p.) or vehicle for 21 days and were sacrificed 24 h after the last dose. Quantitative autoradiography revealed that specific frontocortical [3H]dihydroalprenolol and [3H]ketanserin binding was lower in the chronic tramadol group than controls (beta: 37+/-8 and 217+/-56 fmol/mg; 5-HT2A: 23+/-3 and 44+/-7 fmol/mg, respectively, p < 0.05). Chronic tramadol had no effect on the magnitude of electrically stimulated noradrenaline (NA) efflux or uptake in locus coeruleus (LC) slices. Although dexmedetomidine (10 nM) decreased LC NA efflux equally (by approximately 60%) in chronic tramadol and vehicle groups, desipramine (50 nM) increased LC NA efflux more in vehicle (to 164+/-7%) than tramadol-treated rats (144+/-6%; p < 0.05). Chronic tramadol had no effect on dorsal raphé (DRN) or median raphé (MRN) 5-HT efflux. However, 5-HT uptake in tramadol-treated rats was slower (p < 0.05) in MRN and nearly so (p = 0.055) in DRN. The selective 5-HT1A agonist 8-OH-DPAT reduced 5-HT efflux in both DRN and MRN. Its effect in DRN was greater in rats given chronic tramadol than in vehicle controls (54+/-2 versus 32+/-6% reduction in 5-HT efflux, respectively). In conclusion, we suggest that tramadol has many of the pre- and postsynaptic neurochemical features of a conventional antidepressant, as might be predicted from its pharmacology.

Differential [(3)H]idazoxan and [(3)H]2-(2-benzofuranyl)-2-imidazoline (2-BFI) binding to imidazoline I(2) receptors in human postmortem frontal cortex.

[(3)H]2-(2-benzofuranyl)-2-imidazoline (2-BFI) and [(3)H]idazoxan are the most used tools to characterise imidazoline I(2) receptors. We evaluated the binding of both radioligands to human postmortem frontal cortex membranes. Saturation binding analyses revealed that [(3)H]idazoxan (in the presence of 2 microM efaroxan to avoid radioligand binding to alpha(2)-adrenoceptors and imidazoline I(1) receptors) and [(3)H]2-BFI bound with high affinity to an apparent single population of sites. However, in competition studies whereas [(3)H]idazoxan (10 nM) binding was displaced monophasically by idazoxan and 2-BFI, both drugs displayed biphasic curves for [(3)H]2-BFI (1 nM). The proportion of the low-affinity binding site increased from 17% to 25% when 10 nM [(3)H]2-BFI was displaced by idazoxan. Amiloride inhibited [(3)H]2-BFI (10 nM) binding with low affinity and in a monophasic way. These data indicate that [(3)H]2-BFI recognises in human postmortem brain membranes a second binding site different from the imidazoline I(2) receptors labelled by [(3)H]idazoxan.

Regulation of phospholipase Cbeta activity by muscarinic acetylcholine and 5-HT(2) receptors in crude and synaptosomal membranes from human cerebral cortex.

Stimulation of phospholipase Cbeta by receptor agonists and G proteins has been characterized in crude cerebral membrane preparations, but little is known about their presynaptic localizations and little information is currently available for human brain tissue. The characteristics of phosphoplipase C transmembrane signaling were studied in crude and synaptosomal plasma membranes from postmortem human prefrontal cortex by measuring the hydrolysis of exogenous [(3)H]phosphatidylinositol4,5bisphosphate(PIP(2)) and the immunoreactive levels of phospholipase C (PLC) and G(alphaq/11) proteins. Regulation of PLC activity by Ca(2+) and the 5-HT(2) receptor agonist 5-methyltryptamine, but not by guanosine 5'-O-[3-thiotriphosphate] and the muscarinic acetylcholine receptor agonist carbachol were different between crude and synaptosomal membranes. KCl (20 mM) stimulation was absent in both preparations. Levels of G(alphaq/11)-protein subunits differed between preparations. The functional inhibition carried out with pirenzepine in crude membranes in order to reverse the carbachol-induced PLC stimulation indicates the existence of a component (53%) of the response that is activated by the M(1) muscarinic acetylcholine receptor subtype, and another component (47%) probably mediated by the M(3) muscarinic acetylcholine receptor subtype. In synaptosomal plasma membranes an increased inhibition of carbachol-induced PLC activation through M(1) was found. The PLC activation by 5-methyltryptamine (ketanserin-sensitive in crude membranes) was absent in synaptosomal plasma membranes suggesting the lack of activity mediated by 5-HT(2)-serotonin receptors.

I2-Imidazoline receptors and monoamine oxidase B enzyme sites in human brain: covariation with age.

An association between monoamino oxidase B enzyme (MAO-B) sites and I(2)-imidazoline receptors (I(2)-IR) has been established in human brain on the basis of correlational studies of radiolabelled binding sites. Because both MAO-B and I(2)-IR densities increase with aging, the age at death could be partially involved in the observed correlations. The evaluation of two independent but similar datasets demonstrated that the linear correlation between MAO-B and I(2)-IR densities dropped from 0.70 (P=0.02) and 0.41 (P=0.14) in the crude analyses to the negligible values of 0.07 (P=0.84) and 0.09 (P=0.75) when the age at death was controlled for in the statistical analyses. The results lead to conclude, contrary to former interpretations, that there is not any statistical association linking both MAO-B catalytic unit sites and I(2)-IR densities in the human brain.

Spatiotemporal interaction of alpha(2) autoreceptors and noradrenaline transporters in the rat locus coeruleus: implications for volume transmission.

We investigated the roles of alpha(2) autoreceptors and noradrenaline (NA) transporters on NA efflux and uptake in the rat locus coeruleus after electrical stimulation. NA efflux was evoked by various trains (50 pulses, 10-500 Hz) and measured by fast cyclic voltammetry. NA efflux and uptake half-time (t(1/2)) were stimulus-dependent, ranging from 43 +/- 3 nM and 2.45 +/- 0.21 s, respectively, with 500-Hz stimuli to 127 +/- 11 nM and 4.41 +/- 0.34 s, respectively, with 100-Hz trains. Based on these data, we calculate that each transporter removes 0.19 NA molecules from the extracellular space every second, a velocity compatible more with transporter-than channel-mode conduction. Dexmedetomidine (10 nM) decreased NA efflux by approximately 30% on stimulations of < or =1 s in duration. BRL 44408 (1 microM) increased NA efflux on stimuli of > or =2 s (by up to 92 +/- 16%). Desipramine (50 nM) increased NA efflux on stimuli of > or =1 s (by 113 +/- 24%) but slowed NA uptake on all stimuli. When given together, the effects of desipramine and BRL 44408 were additive at stimuli of >or =1 s but showed potentiation on shorter trains. There was a significant time delay for the elevation of NA efflux by blockade of uptake (0.79 s) or autoreceptors (1.14 s), suggesting that both are located extrasynaptically and that NA must diffuse through the extracellular space to these structures. We suggest that released NA may interact with alpha(2) autoreceptors and NA transporters as far as 10 microm from the release sites, an action compatible with a volume transmission role of NA in the locus coeruleus.

Propofol decreases stimulated dopamine release in the rat nucleus accumbens by a mechanism independent of dopamine D2, GABAA and NMDA receptors.

Although propofol (2,6-di-isopropylphenol) is a popular i.v. general anaesthetic, it has been suggested to have abuse potential. As many drugs of abuse act preferentially via release of dopamine in the limbic system, we investigated the action of propofol on stimulated dopamine release in the rat nucleus accumbens. Nucleus accumbens slices were superfused (1.6 ml min-1) with artificial cerebrospinal fluid at 32 degrees C. Dopamine release was evoked by electrical stimulation (10 pulses, 0.1 ms, 10 mA, 10 Hz, every 10 min) and monitored by fast cyclic voltammetry. Propofol 100 mumol litre-1 reduced stimulated dopamine release over the 2 h after administration, relative to intralipid controls, to mean 30 (SEM 2)% (P < 0.01). The dopamine D2 receptor antagonist metoclopramide 0.3 mumol litre-1 increased dopamine release but did not block the effect of propofol (38 (3)%). The selective GABAA antagonist bicuculline 24 mumol litre-1 also failed to antagonize the action of propofol (45 (3)%). The NMDA receptor antagonist dextromethorphan 10 mumol litre-1 decreased dopamine release to 57 (6)% (P < 0.01) but failed to block the inhibitory effect of propofol (46 (6)%). Although propofol has been reported to bind to D2, GABAA and NMDA receptors, failure of metoclopramide and bicuculline to block its effects suggests that an agonist action at D2 or GABAA receptors does not mediate the effects of propofol on dopamine release in the rat nucleus accumbens. The lack of effect of dextromethorphan makes an NMDA receptor antagonist action unlikely.

Effects of dizocilpine (MK 801) on noradrenaline, serotonin and dopamine release and uptake.

In the present study, we examined the actions of the NMDA antagonist dizocilpine (MK801) on electrically evoked release and uptake of noradrenaline (NA) in the locus coeruleus (LC), serotonin (5-HT) in the dorsal raphe nucleus (DRN) and dopamine (DA) in the nucleus accumbens (NAc), measured by fast cyclic voltammetry (FCV) in rat brain slices. Dizocilpine (10 microM) significantly increased NA (to 248 +/- 15%) and 5-HT release (to 184 +/- 29%) and slowed monoamine uptake in the LC (t1/2 = 853 +/- 129%) and the DRN (t1/2 = 387 +/- 70%), respectively. However, dizocilpine had no effect on DA release or uptake in NAc. Actions on monoamines are thus likely and should be considered in the interpretation of data regarding dizocilpine.

Differential modulation of alpha2-adrenoceptor subtypes in rat kidney by chronic desipramine treatment.

The profile of [3H]RX821002 (2-methoxy idazoxan) binding to alpha2-adrenoceptor subtypes in rat kidney membranes was evaluated in controls and after chronic treatment with desipramine (10 mg/kg, i.p., every 12 h, 7 days) or clorgyline (2 mg/kg, i.p., every 24 h, 21 days). [3H]RX821002 recognized with high affinity (Kd=1.5+/-0.2 nM in controls) a single and saturable population of binding sites (Bmax=57+/-5 fmol/mg protein in controls). The competitions by (-)-adrenaline, the alpha2B-adrenoceptor selective drug ARC239 (2-[2-[4-(o-methoxyphenyl)-piperazin-1-yl]-ethyl]-4,4-dimethyl-1,3 (2H,4H)-isoquinolindione) and the alpha2A-adrenoceptor selective drug BRL44408 (2-[2H-(1-methyl-1,3-dihydroisoindole)methyl]-4,5-dihydroimidaz ole) suggested the existence of both alpha2A- and alpha2B-adrenoceptors together with a non-adrenoceptor binding site. After chronic desipramine but not after chronic clorgyline treatments, the density (Bmax) of alpha2-adrenoceptors was increased (46%). In the presence of ARC239 (50 nM), the density of alpha2A-adrenoceptors increased (44%) in the desipramine-treated group without changes in the clorgyline-treated group. Conversely, in the presence of BRL44408 (100 nM), the density of alpha2B-adrenoceptors was not affected by the treatments. The selective upregulation of the alpha2A-adrenoceptor subtype following chronic desipramine administration is compatible with a differential location and function of the alpha2-adrenoceptor subtypes in the rat kidney.

Alpha2A- but not alpha2B/C-adrenoceptors modulate noradrenaline release in rat locus coeruleus: voltammetric data.

In this study, we used subtype-selective antagonists to determine the subtype of alpha2-adrenoceptor controlling noradrenaline release in rat locus coeruleus. Noradrenaline release was measured in locus coeruleus slices using fast cyclic voltammetry at carbon fibre microelectrodes. On long stimulation trains (40 pulses, 20 Hz), the alpha2A-adrenoceptor selective antagonist BRL 44408 (2-[2H-(1-methyl-1,3-dihydroisoindole) methyl]-4,5-dihydroimidazole) at 100 nM and 1 microM significantly increased stimulated noradrenaline release, whereas the alpha2B/C-selective antagonist ARC 239 (2-[2[4-(o-methoxyphenyl)piperazin-1-yl] ethyl]-4,4dimethyl-1,3-(2H,4H)-isoquinolinedione) at 50 and 500 nM had no effect. On short stimuli (20 pulses, 200 Hz), the non-specific alpha2-adrenoceptor agonist dexmedetomidine (10 nM) significantly decreased noradrenaline release, an effect reversed by BRL 44408 (1 microM) but not by ARC 239 (500 nM). These data demonstrate that autoreceptor control of noradrenaline release in the locus coeruleus is mediated by alpha2A but not alpha2B/C-adrenoceptors.

Effects of tramadol stereoisomers on norepinephrine efflux and uptake in the rat locus coeruleus measured by real time voltammetry.

Despite its structural similarity to codeine, tramadol is an unusual analgesic whose antinociceptive efficacy is not solely a result of opioid actions but also of its apparent capacity to block monoamine uptake. Tramadol is a mixture of stereoisomers. In this study, we have examined the actions of racemic, (+)- and (-)-tramadol, in addition to O-desmethyltramadol (the main human metabolite), on electrically evoked norepinephrine efflux and uptake in the locus coeruleus brain slice, measured by fast cyclic voltammetry. Racemic tramadol and its (+)- and (-)-enantiomers (all at 5 mumol litre-1) significantly increased stimulated norepinephrine efflux (P < 0.01) by mean 66 (SEM 10)%, 57 (7)% and 64 (13)%, respectively. However, only (-)-tramadol blocked norepinephrine reuptake (P < 0.01), increasing the reuptake half-time to 499 (63)% of pre-drug values. The metabolite O-desmethyl tramadol was inactive at the concentration tested (5 mumol litre-1). In the case of (-)-tramadol, the effect on norepinephrine efflux was directly proportional to, but significantly smaller than, the effect on norepinephrine uptake (P < 0.01). This appeared to be a result of compensatory alpha 2A autoreceptor tone as the selective alpha 2A autoreceptor antagonist BRL 44408 (1 mumol litre-1) eliminated this difference when its own effects on norepinephrine reuptake were taken into account. The efficacy of (-)-tramadol on norepinephrine uptake, at clinically relevant concentrations, may contribute to its antinociceptive efficacy.