Effects of striatal lesions with kainic acid on morphine-induced “catatonia” and increase of striatal dopamine turnover

Summary The influence of striatal lesions (head of the caudate nucleus) with kainic acid on catatonia and on the increase of the dopamine metabolite DOPAC in the striatum after systemic morphine administration was measured in rats. These lesions strongly prevented the morphine-induced muscular rigidity, measured as activity in the electromyogram (EMG) of the gastrocnemius-soleus muscle of non-anesthesized animals. On the other hand, the decrease of locomotion (akinesia) measured using an Animex Activity Meter and an acitivity wheel, was not prevented or reduced. The lesions did not influence the inhibitory effect of morphine on the activation of flexor -motoneurones, either. These results suggest that the head of the caudate nucleus plays an important role in mediating morphine rigidity, but not akinesia or inhibition of the activation of flexor -motoneurones. Opioid-induced catatonia ought to be regarded as a mixture both of rigidity and of akinesia.Morphine led to a rapid decrease, followed by a slow increase of striatal DOPAC concentration. Lesions induced by kainic acid slightly inhibited the decrease and markedly enhanced the increase of DOPAC. Accordingly, an intact nigro-striato-nigral loop is not necessary for the increase of striatal dopamine turnover, observed after morphine administration. The different sites of action, which are likely to mediate all these effects of morphine, are discussed.     

Psychomotor stimulation by dopamine D₁-like but not D₂-like agonists in most mouse strains

Many neurological and psychiatric disorders are treated with dopamine modulators. Studies in mice may reveal genetic factors underlying those disorders or responsiveness to various treatments, and species and strain differences both complicate the use of mice and provide valuable tools. We evaluated psychomotor effects of the dopamine D?-like agonist R-6-Br-APB and the dopamine D?-like agonist quinelorane using a locomotor activity procedure in 15 mouse strains (inbred 129S1/SvImJ, 129S6/SvEvTac, 129X1/SvJ, A/J, BALB/cByJ, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/EiJ, DBA/2J, FVB/NJ, SJL/J, SPRET/EiJ, outbred Swiss Webster, and CD-1) and Sprague-Dawley rats, using groups of both females and males. Both D? and D? stimulation produced hyperactivity in the rats, and surprisingly, only two mouse strains were similar in that regard (C3H/HeJ, SPRET/EiJ). In contrast, the majority of mouse strains exhibited hyperactivity only with D? stimulation, whereas D? stimulation had no effect or decreased activity. BALB substrains, A/J and FVB/NJ mice showed only decreased activity after either D? or D? stimulation. CAST/EiJ mice exhibited hyperactivity exclusively with D? stimulation. Sex differences were observed but no systematic trend emerged: For example, of the five strains in which a main factor of sex was identified for the stimulant effects of the D? agonist, responsiveness was greatest in females in three of those strains and in males in two of those strains. These results should aid in the selection of mouse strains for future studies in which D? or D? responsiveness is a necessary consideration in the experimental design.     

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.     

Ketoconazole-associated preferential increase in dopamine D2 receptor occupancy in striatum compared to pituitary in vivo: role for drug transporters?

Membrane transporters such as P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are efflux pumps that remove drugs from the brain back to the peripheral blood compartment, serving as a functional component of the blood-brain barrier (BBB). We report here that coadministration of the P-gp and BCRP inhibitor ketoconazole with risperidone may preferentially increase D2 receptor occupancy in the striatum compared to pituitary. Four male patients with schizophrenia or schizoaffective disorder who had received at least 4 prior injections of the long-acting risperidone at a stable dose of 25 to 50 mg participated in this positron emission tomography study. Multiple-dose ketoconazole coadministration reduced the P-gp activity as shown by fexofenadine oral challenge. Importantly, we found a strong statistical trend in this sample of 4 subjects who consistently showed a decrease in striatal fluorine 18 (F)-fallypride binding (an indication of increased D2 receptor occupancy) after ketoconazole coadministration (P = 0.057), whereas the pituitary (a region that lies outside the BBB) F-fallypride binding did not change (P = 0.99). These observations warrant further research with selective drug transporter inhibitors. We suggest that in neuroimaging studies, the pituitary drug occupancy can serve as a useful new "positive control" to evaluate whether drug occupancy is preferentially increased in brain regions that fall inside the BBB after cotreatment with P-gp and BCRP inhibitors. This is a noteworthy study design consideration regarding the future clinical testing of novel adjunct interventions aimed at modulating membrane transporter function at the BBB, with the goal of augmenting drug access into the brain compartment, particularly in treatment-resistant psychiatric illness.     

Octanoic acid prevents reduction of striatal dopamine in the MPTP mouse model of Parkinson’s disease

Background

Parkinson’s disease (PD) is a progressive neurodegenerative process leading to the loss of dopaminergic neurons and their projections. 1-methyl-4-phenol-1,2,5,6-tetrahydropyridine (MPTP) toxicity is a well-recognized animal model of PD. It is suggested that the impairment of mitochondrial function in the substantia nigra plays an important role in both the onset and the progression of PD.Octanoic acid (C8), a fatty acid that is the main constituent of the medium-chain triglyceride ketogenic diet, increases the metabolic activity of mitochondria; hence, it seemed interesting to investigate whether C8 exhibits neuroprotective effects in the MPTP model of PD and whether it affects mitochondria function in the striatum.

The effect of the dopamine agonist pergolide on tyrosine hydroxylase activity in rat striatal and limbic miniprisms in vitro: A model for the dopamine autoreceptor?

Summary A method for the assay of tyrosine hydroxylase activity in rat striatal and limbic (nucleus accumbens + olfactory tubercle) brain miniprisms is described. The dopamine agonists apomorphine (1 mol/l) and pergolide (0.01–100 mol/l) inhibited the tyrosine hydroxylase activity in both regions. The inhibition produced by 1 mol/l pergolide was antagonised partially in striatal miniprisms and completely in limbic miniprisms by 1 mol/l haloperidol. The dopamine D₂-selective antagonist raclopride, at concentrations up to 300 nmol/l, did not antagonise the inhibition produced by pergolide in striatal miniprisms, but appeared partially to antagonise the inhibition in limbic miniprisms. It is concluded that whilst pergolide potently inhibits tyrosine hydroxylase activity in striatal and limbic miniprisms, the inhibition is of doubtful value as a predictive model of dopamine autoreceptor function in striatal miniprisms, but may be useful when limbic miniprisms are used.     

Binding of 3H-spiperone and 3H-(−)-sulpiride to dopamine D2 receptors in rat striatal membranes: methodological considerations and demonstration of the identical nature of the binding sites for the two ligands

Summary In order to test the hypothesis emerging from the literature that ³H-sulpiride and ³H-spiperone might label different subclasses of dopamine D2 receptors in the brain, the binding properties of the two ligands were compared under optimized conditions. ³H-sulpiride was found to show a very fast rate of dissociation from the receptor. Furthermore, with this ligand, an apparently specific binding to glass fiber filters was observed. A centrifugation assay was therefore used for the characterization of ³H-sulpiride binding. The binding of ³H-spiperone was measured in a way which prevented its attachment to sites other than D2 receptors. Under these conditions, the two ligands were found to label identical dopaminergic recognition sites (D2 receptors) according to the following criteria: ³H-sulpiride and ³H-spiperone both labelled only one single site with a comparable density. Identical changes in the receptor number for both ligands were found in the tissue from animals with nigrostriatal 6-hydroxydopamine lesions. The potencies of various dopamine agonists and antagonists in displacing ³H-sulpiride or ³H-spiperone from their binding sites showed a highly significant one to one correlation. Finally, the binding of both ligands could be inactivated by pretreatment of the membranes with N-ethylmaleimide, with or without Na⁺-ions being present. This inactivation followed exactly the same kinetics for both radioligands. Thus, no indication supporting the hypothesis that ³H-sulpiride and ³H-spiperone might label different subsets of dopamine D2 receptors in the rat brain could be found.Abbreviations 6,7-ADTN 2-Amino-6,7-Dihydroxy-1,2,3,4-Tetrahydronaphthalene - NEM N-Ethyl-maleimide - 5HT Serotonin - 6-OHDA 6-hydroxydopamine Send offprint requests to S. Urwyler at the above address     

β(2)-Adrenoceptors increase translocation of GLUT4 via GPCR kinase sites in the receptor C-terminal tail

BACKGROUND AND PURPOSE

β-Adrenoceptor stimulation induces glucose uptake in several insulin-sensitive tissues by poorly understood mechanisms.

EXPERIMENTAL APPROACH

We used a model system in CHO-K1 cells expressing the human β₂-adrenoceptor and glucose transporter 4 (GLUT4) to investigate the signalling mechanisms involved.

KEY RESULTS

In CHO-K1 cells, there was no response to β-adrenoceptor agonists. The introduction of β₂-adrenoceptors and GLUT4 into these cells caused increased glucose uptake in response to β-adrenoceptor agonists. GLUT4 translocation occurred in response to insulin and β₂-adrenoceptor stimulation, although the key insulin signalling intermediate PKB was not phosphorylated in response to β₂-adrenoceptor stimulation. Truncation of the C-terminus of the β₂-adrenoceptor at position 349 to remove known phosphorylation sites for GPCR kinases (GRKs) or at position 344 to remove an additional PKA site together with the GRK phosphorylation sites did not significantly affect cAMP accumulation but decreased β₂-adrenoceptor-stimulated glucose uptake. Furthermore, inhibition of GRK by transfection of the βARKct construct inhibited β₂-adrenoceptor-mediated glucose uptake and GLUT4 translocation, and overexpression of a kinase-dead GRK2 mutant (GRK2 K220R) also inhibited GLUT4 translocation. Introducing β₂-adrenoceptors lacking phosphorylation sites for GRK or PKA demonstrated that the GRK sites, but not the PKA sites, were necessary for GLUT4 translocation.

CONCLUSIONS AND IMPLICATIONS

Glucose uptake in response to activation of β₂-adrenoceptors involves translocation of GLUT4 in this model system. The mechanism is dependent on the C-terminus of the β₂-adrenoceptor, requires GRK phosphorylation sites, and involves a signalling pathway distinct from that stimulated by insulin.     

123I-β-CIT SPECT demonstrates increased presynaptic dopamine transporter binding sites in basal ganglia in vivo in schizophrenia

Rationale The dopamine hypothesis for schizophrenia postulates overactivity of dopamine transmission in the basal ganglia. Most effective antipsychotic drugs block postsynaptic dopamine receptors, but in-vivo imaging studies have not been able to show changes in these receptors in drug-naive schizophrenics.Objectives The presynaptic dopamine transporter (DAT) is thought to be an important regulator of synaptic dopamine concentration. We have used SPECT with ¹²³I--CIT, which has a high affinity for DAT, in order to further examine the dopamine hypothesis for schizophrenia.Methods Six patients with chronic schizophrenia treated with classic dopamine D₂-receptor blocking neuroleptics were investigated. The number of DAT binding sites in the basal ganglia was calculated and compared with five healthy volunteers and ten parkinsonian patients.Results The schizophrenic patients showed a 36–63% increase in DAT binding sites compared with the volunteers, whereas the parkinsonian patients showed a 57–96% decrease. The differences between the groups were highly significant (even after correction for different age composition within the groups).Conclusions There was an increased number of DAT binding sites in the schizophrenic patients treated with dopamine D₂-receptor blocking neuroleptics. This fits well with several recent reports that have shown increased volumes of basal ganglia in this patient category. It thus appears that there is an increased number of presynaptic dopamine releasing nerve terminals in the basal ganglia, possibly as a biological adaptation to counteract the postsynaptic dopamine D₂-receptor blockade.     

β-Endorphin-induced locomotor stimulation and reinforcement are associated with an increase in dopamine release in the nucleus accumbens

In vivo microdialysis was used to compare the effects of β-endorphin upon dopamine (DA) release in the nucleus accumbens (NAC) of anesthetized versus freely moving rats, and to examine the role of the the mesolimbic DA system in mediating both the motoric and secondary reinforcing effects of this peptide. Microdialysis probes were inserted into the NAC and perfusates were analyzed for DA and its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), using a reversed phase HPLC system with electrochemical detection for separation and quantification. Intracerebroventricular (ICV) administration of β-endorphin (2.5 and 5.0 µg) increased DA release and metabolites in both freely moving and anesthetized rats. This effect was of greater magnitude and duration in freely moving rats and was accompanied by stimulation of locomotor activity. The 5 µg dose also functioned as a secondary reinforcer in a conditioned place preference paradigm. A higher dose of β-endorphin (7.5 µg) stimulated DA release and metabolites in anesthetized rats but failed to affect these parameters in freely moving rats. At this dose, catalepsy and a loss of the reinforcing effects of this peptide were observed. These data demonstrate marked differences in the effects of β-endorphin upon DA release in the awake versus anesthetized rat. Further, the finding that the reinforcing and locomotor stimulating effects of β-endorphin only occur at those doses which stimulate DA release suggest that this action is critical for the expression of both behavioral effects.     

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.     

Investigations of the roles of dihydropyridine and ω-conotoxin-sensitive calcium channels in mediating depolarisation-evoked endogenous dopamine release from striatal slices

Summary The relative roles of L- and N-type voltage-sensitive calcium channels (VSCC) in mediating endogenous dopamine release have been investigated by examining the effects of the dihydropyridine (DHP) agonist BAY K 8644 and the antagonist PN 200-110, as well as the VSCC-blocking peptide -conotoxin GVIA, on depolarisationevoked dopamine release from superfused rat striatal slices. Dopamine release evoked by electrical field stimulation was virtually unaffected by either of the DHP drugs, but release evoked by raising the K⁺ concentration to 25 mmol/l was significantly increased by BAY K 8644 and reduced stereospeciflcally by PN 200-110. Quantitative differences between electrically-evoked and K⁺-evoked dopamine release with respect to their dependence on extracellular calcium concentration were also observed, with electrically-evoked release requiring higher calcium concentrations. The adenylate cyclase activator forskolin itself increased dopamine release, but did not appear to influence the effectiveness of either DHP drug in altering dopamine release. In contrast to the relatively small effects of the DHP drugs, -conotoxin produced a major reduction in electrically-evoked dopamine release as well as a substantial decrease in K⁺-evoked release. Since -conotoxin is thought to block both L- and N-type neuronal VSCC whereas DHP drugs affect only L-type VSCC, these findings suggest that electrically-evoked dopamine release is mediated mainly by calcium influx through N-type VSCC, accounting for the reported lack of effect of many organic calcium antagonists on this process. In contrast, K⁺-evoked dopamine release appears to involve both L- and N-type VSCC, and can occur at lower extracellular calcium concentrations.Abbreviations DHP 1,4-dihydropyridine - HPLC high-performance liquid chromatography - VSCC voltage-sensitive calcium channels Send offprint requests to H. Herdon at the above address     

“5-HT1R” or 5-HT1D sites? Evidence for 5-HT 1D binding sites in rabbit brain

Summary Radioligand binding studies were performed in membranes of rabbit whole brain and striatum using the novel iodinated radioligand for 5-hydroxytryptamine 5-HT_1B and 5-HT_1D sites, Serotonin-5-O-Carboxymethyl-Glycyl[¹²⁵I]Tyrosinamide ([¹²⁵I]GTI).[¹²⁵I]GTI labelled a finite number of high affinity sites in rabbit brain membranes, B_max = 191 +- 47 fmol/mg protein, pK_D (-log mol/1) = 8.50 +- 0.13, n = 5. The pharmacological profile of [¹⁵²I]GTI binding was fully comparable to that reported previously in human and other brain preparations known to possess 5-HT_1D sites (using either [³H]5-HT or [¹²⁵I]GTI) and displayed a characteristic rank order of affinity: 5-carboxamidotryptamine > 5-HT = dihydroergotamine _> ergotamine _ sumatriptan >_ CGS 12066 >- metergoline > yohimbine >_ methysergide > ICYP > 8-OH-DPAT >_ CP 93129 > (-)pindolol > ketanserin > isamoltane > mesulergine > corynanthine > buspirone > MDL 72222.Autoradiographic studies were performed on rabbit brain slices using [³H]5-HT in the presence of 100 nmol/1 8-OH-DPAT and mesulergine (in order to mask 5-HT_1A and 5-HT_1c binding sites) and [¹²⁵I]CYP (iodocyanopindolol) in the presence of µmol/I isoprenaline and 100 nmol/l 8-OH-DPAT (in order to mask adrenoceptor and 5-HT_1A binding sites). There was no detectable specific binding of [¹²⁵I]CYP through the brain, thus excluding the presence of 5-HT_1B sites in rabbit brain. By contrast, [³H]5-HT labelled a high density of sites in globus pallidus, substantia nigra and superior colliculus. Other regions displaying labelling include the striatum, the dentate gyrus of the hippocampus and the periaqueductal grey matter. This pattern of distribution is compatible with that reported for 5-HT_1D sites in other species.The present data strongly suggest that rabbit brain has recognition sites with the pharmacological profile and distribution characteristic of the 5-HT_1D recognition site. These findings are in agreement with results obtained by Limberger et al. (1991), suggesting the terminal 5-HT autoreceptor of the rabbit brain to belong to the 5-HT_1D subtype. Except for limited species variations (see Bruinvels et al. 1992), the pharmacology of these sites does not justify an addition to the existing nomenclature (5-HT_1R), in contrast to what has been proposed by Xiong and Nelson (1989). The rabbit represents another laboratory species in which 5-HT_1D receptor mediated effects could be studied. Correspondence to D. Hoyer at the above address     

Does amphetamine preferentially increase the extracellular concentration of dopamine in the mesolimbic system of freely moving rats?

It was suggested recently that a fundamental property of drugs that are rewarding, and thus have a high potential for abuse, is that they preferentially increase the extracellular concentration of dopamine (DA) in mesolimbic structures. This hypothesis was tested here by use of microdialysis in freely moving rats to determine the effects of systemic d-amphetamine administration on the extracellular concentration of DA in the so-called "limbic" (nucleus accumbens) and "motor" (dorsolateral caudate nucleus) subdivisions of the striatal complex. Amphetamine (2.03, 4.07, or 8.14 mumols/kg) greatly increased the extracellular concentration of DA in both structures, but there was no evidence of a preferential effect in the nucleus accumbens. The two higher doses of amphetamine actually increased extracellular DA to a greater extent in the dorsolateral caudate, but there was no significant regional difference if the data were expressed as a percent of baseline. These data do not support the hypothesis that drugs of abuse preferentially increase the extracellular concentration of DA in mesolimbic structures, although other ways in which amphetamine may selectively influence mesolimbic DA activity are discussed.     

Effect of the κ opioid agonist R-84760 on cocaine-induced increases in striatal dopamine levels and cocaine-induced place preference in C57BL/6J mice

Rationale While the effects of several kappa opioid receptor agonists on cocaine-induced reward have been studied, such effects of R-84760, a novel non-peptidic, potent and selective kappa opioid agonist that has been studied in humans, are not yet known.Objective To study the effects of R-84760 on basal levels of dopamine, cocaine-induced increases in dopamine levels, cocaine-induced conditioned place preference and locomotor activity in mice.Methods In the first experiment, R-84760 was administered i.p. (0, 0.01, 0.05 or 0.1 mg/kg) to C57BL/6J mice. Its effect on basal dopamine levels in the caudate putamen was measured with in vivo microdialysis. In the second experiment, the effect of pretreatment with 0.1 mg/kg R-84760 on cocaine-induced increases in dopamine levels was studied. The third experiment examined the effect of R-84760 (0.1 mg/kg) on the development of cocaine-induced conditioned place preference and locomotor activity in the conditioning chamber.Results R-84760 decreased dopamine levels in a dose-dependent manner. The highest dose of R-84760 (0.1 mg/kg, i.p.) significantly decreased dopamine levels relative to vehicle, an effect completely blocked by pre-injection with 10 mg/kg of the kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI). The same dose of R-84760 blocked cocaine-induced increases in dopamine levels, cocaine-induced conditioned place preference and attenuated cocaine-induced locomotor response.Conclusion These findings suggest that R-84760 decreases dopamine levels in the caudate putamen through kappa-opioid receptors. The inhibitory effect of R-84760 on striatal dopamine may contribute to its blockade of cocaine-induced increases in dopamine levels, cocaine-induced conditioned place preference and the associated increases in locomotor activity.     

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.     

AC927, a σ receptor ligand, blocks methamphetamine-induced release of dopamine and generation of reactive oxygen species in NG108-15 cells

Methamphetamine is a highly addictive psychostimulant drug of abuse that causes neurotoxicity with high or repeated dosing. Earlier studies demonstrated the ability of the selective σ receptor ligand N-phenethylpiperidine oxalate (AC927) to attenuate the neurotoxic effects of methamphetamine in vivo. However, the precise mechanisms through which AC927 conveys its protective effects remain to be determined. With the use of differentiated NG108-15 cells as a model system, the effects of methamphetamine on neurotoxic endpoints and mediators such as apoptosis, necrosis, generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), and dopamine release were examined in the absence and presence of AC927. Methamphetamine at physiologically relevant micromolar concentrations caused apoptosis in NG108-15 cells. At higher concentrations of methamphetamine, necrotic cell death was observed. At earlier time points, methamphetamine caused ROS/RNS generation, which was detected with the fluorigenic substrate 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescin diacetate, acetyl ester, in a concentration- and time-dependent manner. N-Acetylcysteine, catalase, and l-N(G)-monomethyl arginine citrate inhibited the ROS/RNS fluorescence signal induced by methamphetamine, which suggests the formation of hydrogen peroxide and RNS. Exposure to methamphetamine also stimulated the release of dopamine from NG108-15 cells into the culture medium. AC927 attenuated methamphetamine-induced apoptosis, necrosis, ROS/RNS generation, and dopamine release in NG108-15 cells. Together, the data suggest that modulation of σ receptors can mitigate methamphetamine-induced cytotoxicity, ROS/RNS generation, and dopamine release in cultured cells.     

Imaging the high-affinity state of the dopamine D2 receptor in vivo: Fact or fiction?

Positron Emission Tomography (PET) has been used for more than three decades to image and quantify dopamine D2 receptors (D2R) in vivo with antagonist radioligands but in the recent years agonist radioligands have also been employed. In vitro competition studies have demonstrated that agonists bind to both a high and a low-affinity state of the D2Rs, of which the high affinity state reflects receptors that are coupled to G-proteins and the low-affinity state reflects receptors uncoupled from G-proteins. In contrast, antagonists bind with uniform affinity to the total pool of receptors. Results of these studies led to the proposal that D2Rs exist in high and low-affinity states for agonists in vivo and sparked the development and use of agonist radioligands for PET imaging with the primary purpose of measuring the proportion of receptors in the high-affinity (activating) state. Although several lines of research support the presence of high and low-affinity states of D2Rs and their detection by in vivo imaging paradigms, a growing body of controversial data has now called this into question. These include both in vivo and ex vivo studies of anesthesia effects, rodent models with increased proportions of high-affinity state D2Rs as well as the molecular evidence for stable receptor-G-protein complexes. In this commentary we review these data and discuss the evidence for the in vivo existence of D2Rs configured in high and low-affinity states and whether or not the high-affinity state of the D2R can, in fact, be imaged in vivo with agonist radioligands.     

2D and 3D QSAR analyses to predict favorable substitution sites in anilino-monoindolylmaleimides acting as PKC��II selective inhibitors

Diabetic cardiomyopathy (DCM) is a clinical condition, diagnosed when ventricular dysfunction develops in diabetic patients without coronary atherosclerosis and hypertension. Intensive studies on pathogenesis of DCM show PKCβII as one of the mediators, responsible for developing DCM. 2D-QSAR (HQSAR) and 3D-QSAR (CoMSIA) studies were performed on a dataset of 42 anilino-monoindolylmaleimides acting as PKCβII selective inhibitors. Among the different alignment strategies used for CoMSIA study FlexS was found to be the best alignment method. Conformational search was performed for a few molecules to obtain the best model. CoMSIA analysis gave information about sites of favorable substitutions and steered us to assume that alkyl amine substitution on the pharmacophore would be a favorable substituent for improving the biological activity. From HQSAR studies we could extrapolate the presence of tertiary acceptor group may probably be responsible for increase in the activity whereas occurrence of cyclic ring structures would lead to decrease in the activity.