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Background:The α-syn Origin site and Connectome model (SOC) proposes that α-synucleinopathies can be divided into two categories: the asymmetrical brain-first, and more symmetrical body-first Lewy body disease. We have hypothesized that most patients with dementia with Lewy bodies (DLB) belong to the body-first subtype, whereas patients with Parkinson’s disease (PD) more often belong to the brain-first subtype.Objective:To compare asymmetry of striatal dopaminergic dysfunction in DLB and PD patients using [18F]-FE-PE2I positron emission tomography (PET).Methods:We analyzed [18F]-FE-PE2I PET data from 29 DLB patients and 76 PD patients who were identified retrospectively during a 5-year period at Dept. of Neurology, Aarhus University Hospital. Additionally, imaging data from 34 healthy controls was used for age-correction and visual comparison.Results:PD patients showed significantly more asymmetry in specific binding ratios between the most and least affected putamen (p Conclusion:Patients with DLB show significantly more symmetric striatal degeneration on average compared to PD patients. These results support the hypothesis that DLB patients may be more likely to conform to the body-first subtype characterized by a symmetrical spread of pathology, whereas PD patients may be more likely to conform to the brain-first subtype with more lateralized initial propagation of pathology.

Dopamine supports locomotor control and higher brain functions such as motivation and learning. Consistently, dopaminergic dysfunction is involved in a spectrum of neurological and neuropsychiatric diseases. Detailed data on dopamine dynamics is needed to understand how dopamine signals translate into cellular and behavioral responses, and to uncover pathological disturbances in dopamine-related diseases. Genetically encoded fluorescent dopamine sensors have recently enabled unprecedented monitoring of dopamine dynamics in vivo. However, these sensors' utility for in vitro and ex vivo assays remains unexplored. Here, we present a blueprint for making dopamine sniffer cells for multimodal dopamine detection. We generated sniffer cell lines with inducible expression of seven different dopamine sensors and perform a head-to-head comparison of sensor properties to guide users in sensor selection. In proof-of-principle experiments, we apply the sniffer cells to record endogenous dopamine release from cultured neurons and striatal slices, and for determining tissue dopamine content. Furthermore, we use the sniffer cells to measure dopamine uptake and release via the dopamine transporter as a radiotracer free, high-throughput alternative to electrochemical- and radiotracer-based assays. Importantly, the sniffer cell framework can readily be applied to the growing list of genetically encoded fluorescent neurotransmitter sensors., Communications Biology, 5, ISSN:2399-3642

The striatum receives dense dopaminergic projections, making it a key region of the dopaminergic system. Its dysfunction has been implicated in various conditions including Parkinson's disease (PD) and substance use disorder. However, the investigation of dopamine-specific functioning in humans is problematic as current MRI approaches are unable to differentiate between dopaminergic and other projections. Here, we demonstrate that 'connectopic mapping' - a novel approach for characterizing fine-grained, overlapping modes of functional connectivity - can be used to map dopaminergic projections in striatum. We applied connectopic mapping to resting-state functional MRI data of the Human Connectome Project (population cohort; N = 839) and selected the second-order striatal connectivity mode for further analyses. We first validated its specificity to dopaminergic projections by demonstrating a high spatial correlation (r = 0.884) with dopamine transporter availability - a marker of dopaminergic projections - derived from DaT SPECT scans of 209 healthy controls. Next, we obtained the subject-specific second-order modes from 20 controls and 39 PD patients scanned under placebo and under dopamine replacement therapy (L-DOPA), and show that our proposed dopaminergic marker tracks PD diagnosis, symptom severity, and sensitivity to L-DOPA. Finally, across 30 daily alcohol users and 38 daily smokers, we establish strong associations with self-reported alcohol and nicotine use. Our findings provide evidence that the second-order mode of functional connectivity in striatum maps onto dopaminergic projections, tracks inter-individual differences in PD symptom severity and L-DOPA sensitivity, and exhibits strong associations with levels of nicotine and alcohol use, thereby offering a new biomarker for dopamine-related (dys)function in the human brain., Research funding partners Abbvie, Avid Radiopharmaceuticals, Biogen Idec, BioLegend, Bristol- Myers Squibb, Eli Lilly & Co., F Hoffman-La Roche, Ltd., GE Healthcare, Genentech, GlaxoSmithKline, Lundbeck, Merck, MesoScale Discovery, Piramal, Pfizer, Sanofi Genzyme, Servier, Takeda, Teva, and UCB.

BACKGROUND: A wide range of neuropsychiatric disorders, from schizophrenia to drug addiction, involve abnormalities in both the mesolimbic dopamine system and the cortical salience network. Both systems play a key role in the detection of behaviorally relevant environmental stimuli. Although anatomical overlap exists, the functional relationship between these systems remains unknown. Preclinical research has suggested that the firing of mesolimbic dopamine neurons may activate nodes of the salience network, but in vivo human research is required given the species-specific nature of this network.METHODS: We employed positron emission tomography to measure both dopamine release capacity (using the D2/3 receptor ligand 11C-PHNO, n = 23) and dopamine synthesis capacity (using 18F-DOPA, n = 21) within the ventral striatum. Resting-state functional magnetic resonance imaging was also undertaken in the same individuals to investigate salience network functional connectivity. A graph theoretical approach was used to characterize the relationship between dopamine measures and network connectivity.RESULTS: Dopamine synthesis capacity was associated with greater salience network connectivity, and this relationship was particularly apparent for brain regions that act as information-processing hubs. In contrast, dopamine release capacity was associated with weaker salience network connectivity. There was no relationship between dopamine measures and visual and sensorimotor networks, indicating specificity of the findings.CONCLUSIONS: Our findings demonstrate a close relationship between the salience network and mesolimbic dopamine system, and they are relevant to neuropsychiatric illnesses in which aberrant functioning of both systems has been observed.

Invertebrate and vertebrate nervous systems generate different types of dopaminergic neurons in distinct parts of the brain. We have taken a genetic approach to understand how the four functionally related, but lineally unrelated, classes of dopaminergic neurons of the nematode Caenorhabditis elegans, located in distinct parts of its nervous system, are specified. We have identified several genes involved in the generation of a specific dopaminergic neuron type that is generated from the so-called postdeirid lineage, called PDE. Apart from classic proneural genes and components of the mediator complex, we identified a novel, previously uncharacterized zinc finger transcription factor, ztf-6 Loss of ztf-6 has distinct effects in different dopamine neuron-producing neuronal lineages. In the postdeirid lineage, ztf-6 is required for proper cell division patterns and the proper distribution of a critical cell fate determinant, the POP-1/TCF-like transcription factor.

Invertebrate and vertebrate nervous systems generate different types of dopaminergic neurons in distinct parts of the brain. We have taken a genetic approach to understand how the four functionally related, but lineally unrelated, classes of dopaminergic neurons of the nematode Caenorhabditis elegans, located in distinct parts of its nervous system, are specified. We have identified several genes involved in the generation of a specific dopaminergic neuron type that is generated from the so-called postdeirid lineage, called PDE. Apart from classic proneural genes and components of the mediator complex, we identified a novel, previously uncharacterized zinc finger transcription factor, ztf-6. Loss of ztf-6 has distinct effects in different dopamine neuron-producing neuronal lineages. In the postdeirid lineage, ztf-6 is required for proper cell division patterns and the proper distribution of a critical cell fate determinant, the POP-1/TCF-like transcription factor.

Prenatal alcohol exposure causes alterations to the brain and can lead to numerous cognitive and behavioral outcomes. Long-lasting effects of early ethanol exposure have been registered in glutamatergic and dopaminergic systems. The purinergic system has been registered as an additional target of ethanol exposure. The objective of this research was to evaluate if the ecto‑5'‑nucleotidase and adenosine deaminase activities and gene expression of adult zebrafish exposed to 1% ethanol during early development could be part of the long-lasting targets of ethanol. Zebrafish embryos were exposed to 1% ethanol in two distinct developmental phases: gastrula/segmentation (5-24 h post-fertilization) or pharyngula (24-48 h post-fertilization). At the end of three months, after checking for morphological outcomes, the evaluation of enzymatic activity and gene expression was performed. Exposure to ethanol did not promote gross morphological defects; however, a significant decrease in the body length was observed (17% in the gastrula and 22% in the pharyngula stage, p 0.05). Although the mechanism underlying these findings requires further investigation, these results indicate that ethanol exposure during restricted periods of brain development can have long-term consequences on ecto‑5'‑nucleotidase activity, which could have an impact on subtle sequels of ethanol early exposure.

Invertebrate and vertebrate nervous systems generate different types of dopaminergic neurons in distinct parts of the brain. We have taken a genetic approach to understand how the four functionally related, but lineally unrelated, classes of dopaminergic neurons of the nematode Caenorhabditis elegans, located in distinct parts of its nervous system, are specified. We have identified several genes involved in the generation of a specific dopaminergic neuron type that is generated from the so-called postdeirid lineage, called PDE. Apart from classic proneural genes and components of the mediator complex, we identified a novel, previously uncharacterized zinc finger transcription factor, ztf-6 Loss of ztf-6 has distinct effects in different dopamine neuron-producing neuronal lineages. In the postdeirid lineage, ztf-6 is required for proper cell division patterns and the proper distribution of a critical cell fate determinant, the POP-1/TCF-like transcription factor.

Neurons in the periaqueductal gray (PAG) modulate threat responses and nociception. Activity in the ventral tegmental area (VTA) on the other hand can cause reinforcement and aversion. While in many situations these behaviors are related, the anatomical substrate of a crosstalk between the PAG and VTA remains poorly understood. Here we describe the anatomical and electrophysiological organization of the VTA-projecting PAG neurons. Using rabies-based, cell type-specific retrograde tracing, we observed that PAG to VTA projection neurons are evenly distributed along the rostro-caudal axis of the PAG, but concentrated in its posterior and ventrolateral segments. Optogenetic projection targeting demonstrated that the PAG-to-VTA pathway is predominantly excitatory and targets similar proportions of Ih-expressing VTA DA and GABA neurons. Taken together, these results set the framework for functional analysis of the interplay between PAG and VTA in the regulation of reward and aversion.

Low testosterone (T) in men, especially its free fraction, has been associated with loss of energy. In accordance, orchidectomy (ORX) in rodents results in decreased physical activity. Still, the mechanisms through which T stimulates activity remain mostly obscure. Here, we studied voluntary wheel running behavior in three different mouse models of androgen deficiency: ORX, androgen receptor (AR) knock-out (ARKO) and sex hormone binding globulin (SHBG)-transgenic mice, a novel mouse model of "low free T". Our results clearly show a fast and dramatic action of T stimulating wheel running, which is not explained by its action on muscle, as evidenced by neuromuscular studies and in a muscle-specific conditional ARKO mouse model. The action of T occurs via its free fraction, as shown by the results in SHBG-transgenic mice, and it implies both androgenic and estrogenic pathways. Both gene expression and functional studies indicate that T modulates the in vivo sensitivity to dopamine (DA) agonists. Furthermore, the restoration of wheel running by T is inhibited by treatment with DA antagonists. These findings reveal that the free fraction of T, both via AR and indirectly through aromatization into estrogens, stimulates physical activity behavior in male mice by acting on central DA pathways. ispartof: Scientific Reports vol:8 issue:1 pages:957- ispartof: location:England status: published

Despite the numerous benefits of microwave applications in our daily life, microwaves were associated with diverse neurological complaints such as headaches and impaired sleep patterns, and changes in the electroencephalogram (EEG). To which extent microwaves influence the brain function remains unclear. This exploratory study assessed the behavior and neurochemistry in mice immediately or 4 weeks after a 6-day exposure to low-intensity 10-GHz microwaves with an amplitude modulation (AM) of 2 or 8 Hz. These modulation frequencies of 2 and 8 Hz are situated within the delta and theta-alpha frequency bands in the EEG spectrum and are associated with sleep and active behavior, respectively. During these experiments, the specific absorbance rate was 0.3 W/kg increasing the brain temperature with 0.23 °C. For the first time, exposing mice to 8-Hz AM significantly reduced locomotor activity in an open field immediately after exposure which normalized after 4 weeks. This in contrast to 2-Hz AM which didn't induce significant changes in locomotor activity immediately and 4 weeks after exposure. Despite this difference in motor behavior, no significant changes in striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels and DOPAC/DA turnover nor in cortical glutamate (GLU) concentrations were detected. In all cases, no effects on motor coordination on a rotarod, spatial working memory, anxiety nor depressive-like behavior were observed. The outcome of this study indicates that exposing mice to low-intensity 8-Hz AM microwaves can alter the locomotor activity in contrast to 2-Hz AM which did not affect the tested behaviors.

In recent years concern has risen about the increasing prevalence of Autism Spectrum Disorders (ASD). Accumulating evidence shows that exposure to neurotoxic compounds is related to ASD. Neurotransmitters might play a key role, as research has indicated a connection between neurotoxic compounds, neurotransmitters and ASD. In the current review a literature overview with respect to neurotoxic exposure and the effects on neurotransmitter systems is presented. The aim was to identify mechanisms and related factors which together might result in ASD. The literature reported in the current review supports the hypothesis that exposure to neurotoxic compounds can lead to alterations in the GABAergic, glutamatergic, serotonergic and dopaminergic system which have been related to ASD in previous work. However, in several studies findings were reported that are not supportive of this hypothesis. Other factors also might be related, possibly altering the mechanisms at work, such as time and length of exposure as well as dose of the compound. Future research should focus on identifying the pathway through which these factors interact with exposure to neurotoxic compounds making use of human studies.

A progressive loss of dopamine neurons in the substantia nigra (SN) is considered the main feature of idiopathic Parkinson's disease (PD). Recent neuropathological evidence however suggests that the axons of the nigrostriatal dopaminergic system are the earliest target of α-synuclein accumulation in PD, thus the principal site for vulnerability. Whether this applies to in vivo PD, and also to the mesolimbic system has not been investigated yet. We used [11C]FeCIT PET to measure presynaptic dopamine transporter (DAT) activity in both nigrostriatal and mesolimbic systems, in 36 early PD patients (mean disease duration in months ± SD 21.8 ± 10.7) and 14 healthy controls similar for age. We also performed anatomically-driven partial correlation analysis to evaluate possible changes in the connectivity within both the dopamine networks at an early clinical phase. In the nigrostriatal system, we found a severe DAT reduction in the afferents to the dorsal putamen (DPU) (η2 = 0.84), whereas the SN was the less affected region (η2 = 0.31). DAT activity in the ventral tegmental area (VTA) and the ventral striatum (VST) were also reduced in the patient group, but to a lesser degree (VST η2 = 0.71 and VTA η2 = 0.31). In the PD patients compared to the controls, there was a marked decrease in dopamine network connectivity between SN and DPU nodes, supporting the significant derangement in the nigrostriatal pathway. These results suggest that neurodegeneration in the dopamine pathways is initially more prominent in the afferent axons and more severe in the nigrostriatal system. Considering PD as a disconnection syndrome starting from the axons, it would justify neuroprotective interventions even if patients have already manifested clinical symptoms., Highlights • In vivo study of mesolimbic and nigrostriatal dopamine systems in early iPD • Evidence for a severe axonal damage with relative sparing of SN • Evidence for a moderate damage of the mesolimbic pathway in early iPD • Significant reduction of molecular connectivity between nigrostriatal nodes • Justification for neuroprotective interventions in early-iPD phase

The retention of episodic-like memory is enhanced, in humans and animals, when something novel happens shortly before or after encoding. Using an everyday memory task in mice, we sought the neurons mediating this dopamine-dependent novelty effect, previously thought to originate exclusively from the tyrosine-hydroxylase-expressing (TH+) neurons in the ventral tegmental area. Here we report that neuronal firing in the locus coeruleus is especially sensitive to environmental novelty, locus coeruleus TH+ neurons project more profusely than ventral tegmental area TH+ neurons to the hippocampus, optogenetic activation of locus coeruleus TH+ neurons mimics the novelty effect, and this novelty-associated memory enhancement is unaffected by ventral tegmental area inactivation. Surprisingly, two effects of locus coeruleus TH+ photoactivation are sensitive to hippocampal D1/D5 receptor blockade and resistant to adrenoceptor blockade: memory enhancement and long-lasting potentiation of synaptic transmission in CA1 ex vivo. Thus, locus coeruleus TH+ neurons can mediate post-encoding memory enhancement in a manner consistent with possible co-release of dopamine in the hippocampus., The study was funded by the European Research Council (G.F., R.G.M.M.: ERC-2010-AdG-268800-NEUROSCHEMA), UK Medical Research Council (A.J.D., R.G.M.M.), the European Commission’s 7th Framework 2011 ICT Programme for Future Emerging Technologies (A.J.D., R.G.M.M.: 600725-GRIDMAP), Department Veterans Affairs, National Institutes of Health grant 5R01MH080297 (R.W.G.), and NIDA-T32-DA7290 Basic Science Training Program in Drug Abuse (principal investigator A. Eisch (A.S.)). The Instituto de Neurociencias at Alicante is ‘Centre of Excellence Severo Ochoa’.

Intercalated cells (ITCs) of the amygdala are clusters of GABAergic cells that surround the basolateral complex of the amygdala (BLA). Growing evidence suggests that ITCs are required for the expression of fear extinction. The main intercalated nucleus (Im) is the largest of the ITC clusters and could also be important for emotional processing. We used whole-cell recordings from Im neurons in acute slices of mouse amygdala. We found that these neurons were medium-sized spiny projection cells. Their passive and active membrane responses were consistent with those previously reported in other ITC clusters. The axon of Im neurons was, in many cases, cut at the slice boundaries, suggesting long-range projections. Axonal branches could be detected in several amygdala nuclei where they made functional synapses. We also functionally studied Im cell inputs. Excitatory postsynaptic currents (eEPSCs) were evoked by the stimulation of the Im, intermediate capsula (IC), external capsula (EC) or BLA, when GABAergic transmission was pharmacologically blocked. An occlusion test indicated that fibres recruited by stimulating Im and IC, or Im and EC were distinct. These eEPSCs had both NMDA and AMPA receptor components. Inhibitory postsynaptic currents (eIPSCs) were evoked after the stimulation of the Im, the EC and the BLA, when glutamatergic transmission was pharmacologically blocked. Furthermore, dopamine reversibly hyperpolarised, and decreased the firing frequency and the input resistance of Im cells via dopamine type 1 receptor. Our data suggest that the Im is functionally connected to other amygdala nuclei and is under neuromodulatory influence. We propose that the Im serves as key neuronal substrate of fear extinction. © 2011 The Authors. Journal compilation © 2011 The Physiological Society.

Haploinsufficiency of SHANK3, encoding the synapse scaffolding protein SHANK3, leads to a highly penetrant form of autism spectrum disorder. How SHANK3 insufficiency affects specific neural circuits and how this is related to specific symptoms remains elusive. Here we used shRNA to model Shank3 insufficiency in the ventral tegmental area of mice. We identified dopamine (DA) and GABA cell-type-specific changes in excitatory synapse transmission that converge to reduce DA neuron activity and generate behavioral deficits, including impaired social preference. Administration of a positive allosteric modulator of the type 1 metabotropic glutamate receptors mGluR1 during the first postnatal week restored DA neuron excitatory synapse transmission and partially rescued the social preference defects, while optogenetic DA neuron stimulation was sufficient to enhance social preference. Collectively, these data reveal the contribution of impaired ventral tegmental area function to social behaviors and identify mGluR1 modulation during postnatal development as a potential treatment strategy.

Numerous studies have shown the neuroprotective and regenerative benefits of glial cell line-derived neurotrophic factor (GDNF) in animal models of PD. Brain delivery of GDNF can, however, be associated with limiting side-effects in both primates and PD patients, rendering the duration of delivery a critical factor. In the present study, the effects of transient vs. sustained GDNF delivery by encapsulated cells were evaluated in a bilateral animal model, closely mimicking advanced PD. One week following bilateral striatal 6- hydroxydopamine injections in rats, capsules loaded with human fibroblasts genetically engineered to release GDNF were bilaterally implanted in the striatum. GDNF delivery resulted in a significant improvement of movement initiation and swimming performance in the lesioned animals, associated with striatal reinnervation of dopaminergic fibers. To test the sustainability of the behavioral improvement, GDNF-secreting capsules were withdrawn in a subgroup of animals, 7 weeks post-implantation. Strikingly, both the behavioral and morphological improvements were maintained until the sacrifice of the animals 6 weeks post-GDNF withdrawal. The sustained cellular and behavioral benefits after GDNF washout suggest the need for temporary delivery of the trophic factor in PD. Retrievable encapsulated cells represent an attractive delivery tool to achieve this purpose.

Many theories of human sexual behavior assume that sexual stimuli obtain arousing properties through associative learning processes. It is widely accepted that classical conditioning contributes to the etiology of both normal and maladaptive human behaviors. Despite the hypothesized importance of basic learning processes in sexual behavior, research on classical conditioning of the sexual response in humans is scarce. In the present paper, animal studies and studies in humans on the role of pavlovian conditioning on sexual responses are reviewed. Animal research shows robust, direct effects of conditioning processes on partner- and place preference. On the contrast, the empirical research with humans in this area is limited and earlier studies within this field are plagued by methodological confounds. Although recent experimental demonstrations of human sexual conditioning are neither numerous nor robust, sexual arousal showed to be conditionable in both men and women. The present paper serves to highlight the major empirical findings and to renew the insight in how stimuli can acquire sexually arousing value. Hereby also related neurobiological processes in reward learning are discussed. Finally, the connections between animal and human research on the conditionability of sexual responses are discussed, and suggestions for future directions in human research are given.

The synaptic plasticity and memory hypothesis asserts that activity-dependent synaptic plasticity is induced at appropriate synapses during memory formation and is both necessary and sufficient for the encoding and trace storage of the type of memory mediated by the brain area in which it is observed. Criteria for establishing the necessity and sufficiency of such plasticity in mediating trace storage have been identified and are here reviewed in relation to new work using some of the diverse techniques of contemporary neuroscience. Evidence derived using optical imaging, molecular-genetic and optogenetic techniques in conjunction with appropriate behavioural analyses continues to offer support for the idea that changing the strength of connections between neurons is one of the major mechanisms by which engrams are stored in the brain.

Maladaptive dopaminergic mediation of reward processing in humans is thought to underlie multiple neuropsychiatric disorders, including addiction, Parkinson's disease, and schizophrenia. Mechanisms responsible for the development of such disorders may depend on individual differences in neural signaling within large-scale cortico-subcortical circuitry. Using a combination of functional neuroimaging and pharmacological challenges in healthy volunteers, we identified opposing dopamine agonistic and antagonistic neuromodulatory effects on distributed functional interactions between specific subcortical regions and corresponding neocortical "resting-state" networks, known to be involved in distinct aspects of cognition and reward processing. We found that, relative to a placebo, levodopa and haloperidol challenges, respectively, increased or decreased the functional connectivity between (1) the midbrain and a "default mode" network, (2) the right caudate and a right-lateralized frontoparietal network, and (3) the ventral striatum and a fronto-insular network. Further, we found drug-specific associations between brain circuitry reactivity to dopamine modulation and individual differences in trait impulsivity, revealing dissociable drug-personality interaction effects across distinct dopamine-dependent cortico-subcortical networks. Our findings identify possible systems underlying pathogenesis and treatment efficacy in disorders of dopamine deficiency.

Benzodiazepines are widely used clinically to treat anxiety and insomnia. They also induce muscle relaxation, control epileptic seizures, and can produce amnesia. Moreover, benzodiazepines are often abused after chronic clinical treatment and also for recreational purposes. Within weeks, tolerance to the pharmacological effects can develop as a sign of dependence. In vulnerable individuals with compulsive drug use, addiction will be diagnosed. Here we review recent observations from animal models regarding the cellular and molecular basis that might underlie the addictive properties of benzodiazepines. These data reveal how benzodiazepines, acting through specific GABA(A) receptor subtypes, activate midbrain dopamine neurons, and how this could hijack the mesolimbic reward system. Such findings have important implications for the future design of benzodiazepines with reduced or even absent addiction liability.

Using positron emission tomography in isoflurane-anaesthetised cat, we recently demonstrated that the effect of D-amphetamine (AMPH) was greater on the binding potential (BP(ND)) of the agonist dopamine D2/D3 radiotracer (+)-4-[(11)C]propyl-3,4,4a,5,6,10b-hexahydro-2H-naphtho[1,2-b][1, 4]oxazin-9-ol ([(11)C]-(+)-PHNO) than on that of the antagonist [(11)C]-raclopride, a finding that we were unable to replicate in conscious rat. Herein we tested whether isoflurane differentially affects the AMPH sensitivity of [(11)C]-(+)-PHNO and [(3)H]-raclopride.Conscious or isoflurane-anaesthetised rats pretreated intravenously (i.v.) with saline or 4 mg/kg AMPH were co-injected i.v. with [(11)C]-(+)-PHNO/[(3)H]-raclopride or [(3)H]-(+)-PHNO/[(11)C]-(-)-N-propyl-norapomorphine ([(11)C]-(-)-NPA) and euthanised 2, 10, 20, 30, 40 or 60 min following [(11)C]-(+)-PHNO/[(3)H]-raclopride or 60 min following [(3)H]-(+)-PHNO/[(11)C]-(-)-NPA. Striatal binding at 60 min, estimated by the specific binding ratio (SBR) and the binding potential with respect to non-displaceable binding (BP(ND)) for pseudodynamic data, was calculated using the simplified reference tissue model.Isoflurane increased [(11)C]-(+)-PHNO, [(3)H]-(+)-PHNO and [(11)C]-(-)-NPA SBR (mean ± SD) by 80 ± 30%, 170 ± 50% and 120 ± 40%, and doubled the effect of AMPH on the SBR of these radiotracers to -61 ± 9%, -69 ± 12% and -60 ± 12%, respectively. Neither effect was seen for [(3)H]-raclopride SBR. Similar results were observed for [(11)C]-(+)-PHNO and [(3)H]-raclopride BP(ND).Isoflurane differentially increases the binding and AMPH sensitivity of [(11)C]-(+)-PHNO and [(11)C]-(-)-NPA relative to [(3)H]-raclopride, suggesting that agonist radiotracers will prove no more effective for imaging dopaminergic activity in human than antagonist radiotracers.

Experience-dependent changes in synaptic strength, or synaptic plasticity, may underlie many learning processes. In the reward circuit for example, synaptic plasticity may serve as a cellular substrate for goal-directed behaviors. Addictive drugs, through a surge of dopamine released from neurons of the ventral tegmental area, induce widespread synaptic adaptations within this neuronal circuit. Such drug-evoked synaptic plasticity may constitute an early cellular mechanism eventually causing compulsive drug-seeking behavior in some drug users. In the present review we will discuss how different classes of addictive drugs cause an increase of dopamine release and describe their effects on synapses within the mesolimbic dopamine system. We will emphasize the early synaptic changes in the ventral tegmental area common to all additive drugs and go on to show how these adaptations may reorganize neuronal circuits, eventually leading to behaviors that define addiction.

Background: Addictive drugs have in common that they cause surges in dopamine (DA) concentration in the mesolimbic reward system and elicit synaptic plasticity in DA neurons of the ventral tegmental area (VTA). Cocaine for example drives insertion of GluA2-lacking AMPA receptors (AMPARs) at glutamatergic synapes in DA neurons. However it remains elusive which molecular target of cocaine drives such AMPAR redistribution and whether other addictive drugs (morphine and nicotine) cause similar changes through their effects on the mesolimbic DA system. Methodology / Principal Findings: We used in vitro electrophysiological techniques in wild-type and transgenic mice to observe the modulation of excitatory inputs onto DA neurons by addictive drugs. To observe AMPAR redistribution, postembedding immunohistochemistry for GluA2 AMPAR subunit was combined with electron microscopy. We also used a double-floxed AAV virus expressing channelrhodopsin together with a DAT Cre mouse line to selectively express ChR2 in VTA DA neurons. We find that in mice where the effect of cocaine on the dopamine transporter (DAT) is specifically blocked, AMPAR redistribution was absent following administration of the drug. Furthermore, addictive drugs known to increase dopamine levels cause a similar AMPAR redistribution. Finally, activating DA VTA neurons optogenetically is sufficient to drive insertion of GluA2-lacking AMPARs, mimicking the changes observed after a single injection of morphine, nicotine or cocaine. Conclusions / Significance: We propose the mesolimbic dopamine system as a point of convergence at which addictive drugs can alter neural circuits. We also show that direct activation of DA neurons is sufficient to drive AMPAR redistribution, which may be a mechanism associated with early steps of non-substance related addictions.

The Flinders Sensitive Line (FSL) rat model of depression exhibits some behavioral, neurochemical, and pharmacological features that have been reported in depressed patients and has been very effective in screening antidepressants. Major factor that determines the effectiveness and toxicity of a drug is the drug metabolizing capacity of the liver. Therefore, in order to discriminate possible differentiation in the hepatic drug metabolism between FSL rats and Sprague-Dawley (SD) controls, their hepatic metabolic profile was investigated in this study. The data showed decreased glutathione (GSH) content and glutathione S-transferase (GST) activity and lower expression of certain major CYP enzymes, including the CYP2B1, CYP2C11 and CYP2D1 in FSL rats compared to SD controls. In contrast, p-nitrophenol hydroxylase (PNP), 7-ethoxyresorufin-O-dealkylase (EROD) and 16alpha-testosterone hydroxylase activities were higher in FSL rats. Interestingly, the wide spread environmental pollutant benzo(alpha)pyrene (B(alpha)P) induced CYP1A1, CYP1A2, CYP2B1/2 and ALDH3c at a lesser extend in FSL than in SD rats, whereas the antidepressant mirtazapine (MIRT) up-regulated CYP1A1/2, CYP2C11, CYP2D1, CYP2E1 and CYP3A1/2, mainly, in FSL rats. The drug also further increased ALDH3c whereas suppressed GSH content in B(alpha)P-exposed FSL rats. In conclusion, several key enzymes of the hepatic biotransformation machinery are differentially expressed in FSL than in SD rats, a condition that may influence the outcome of drug therapy. The MIRT-induced up-regulation of several drug-metabolizing enzymes indicates the critical role of antidepressant treatment that should be always taken into account in the designing of treatment and interpretation of insufficient pharmacotherapy or drug toxicity. Prog Neuropsychopharmacol Biol Psychiatry

In peripheral tissues, dopamine is released from neuronal cells and is synthesized within specific parenchyma. Dopamine released from sympathetic nerves predominantly contributes to plasma dopamine levels. Despite growing evidence for peripheral source and action of dopamine and the widespread expression of dopamine receptors in peripheral tissues, most studies have focused on functions of dopamine in the central nervous system. Symptoms of several brain disorders, including schizophrenia, Parkinson's disease, attention-deficit hyperactivity disorder, and depression, are alleviated by pharmacological modulation of dopamine transmission. Regarding systemic disorders, the role of dopamine is still poorly understood. Here we describe the pioneering and recent evidence for functional roles of peripheral dopamine. Peripheral and central dopamine systems are sensitive to environmental stress, such as a high-fat diet, suggesting a basis of covariance of peripheral and central actions of dopaminergic agents. Given the extended use of such medications, it is crucial to better understand the integrated effects of dopamine in the whole organism. Delineation of peripheral and central dopaminergic mechanisms would facilitate targeted and safer use of drugs modulating dopamine action. We discuss the increasing evidence for a link between peripheral dopamine and obesity. This review also describes the recently uncovered protective actions of dopamine on energy metabolism and proliferation in tumoral cells.

Aims This study investigated the role of the cannabinoid CB1 receptor agonist, WIN 55,212-2, on motor activity. Subsequently, the effects of a low, stimulatory dose of WIN 55,212-2 and cocaine, as a positive control, were evaluated using a conditioned place preference (CPP) procedure. Upon completion of CPP, in rats that had been treated with WIN 55,212-2, dopaminergic status and spontaneous and d -amphetamine-induced motor activity were assessed. Main methods Sprague–Dawley rats were evaluated for habituated motor activity following WIN 55,212-2 (0, 0.1, 0.3, 1 mg/kg, i.p.) administration. A stimulatory dose of WIN 55,212-2 (0.1 mg/kg, i.p.) and cocaine (20 mg/kg, i.p.) was selected to assess CPP behaviour. Upon completion of CPP, in one group, tissue levels of dopamine and its metabolites were measured in distinct brain regions (dorsal striatum, nucleus accumbens, prefrontal cortex, amygdala, hippocampus) using High Performance Liquid Chromatography with electrochemical detection. In another group, spontaneous and d -amphetamine-induced motor activity was evaluated in an open-field apparatus. Key findings The lowest dose of WIN 55,212-2 increased motor activity but did not produce CPP. As expected, cocaine induced clear CPP. Dopaminergic status was increased in a region-specific way and motor activity was enhanced following a challenge of d -amphetamine in rats that had been administered with WIN 55,212-2 during conditioning. Significance A stimulatory effect of WIN 55,212-2 on motor activity was not accompanied by place preference. Upon completion of the CPP procedure, this dose was found to induce region-specific hyperdopaminergia along with a greater sensitivity to a subsequent challenge dose of d -amphetamine.

Children have an amazing facility to learn, and our society does everything to encourage this. Learning is good and it is difficult to conceive that too much could have a negative impact. However, this is just what recent theories on addiction suggest; addictive substances promote the learning of drug-related behaviors such that they become exclusive. As a consequence drug-use becomes compulsive and continues despite negative consequences, a defining feature of addiction. This theory has its roots in the assumption that dopamine released by the neurons of the midbrain represents a strong learning signal.

The aim of this study was to investigate the effect of benzo(alpha)pyrene (B(alpha)P), a representative polycyclic aromatic hydrocarbon (PAH), on dopaminergic activity in brain. (B(alpha)P) altered dopaminergic activity in discrete regions of the rat brain, including the hippocampus, hypothalamus, caudate putamen and nucleus accumbens. Specifically, B(alpha)P increased DA levels in the hippocampus and DA turnover in the caudate putamen. In addition, B(alpha)P suppressed DA levels in the caudate putamen and DA turnover in the nucleus accumbens. B(alpha)P also altered the effect of several dopaminergic agents, L-DOPA, sulpiride and bromocriptine, on DA activity. In particular, B(alpha)P enhanced the L-DOPA-induced increase in the DA turnover ratio in the caudate putamen and increased DA levels in the nucleus accumbens. B(alpha)P also reversed the sulpiride-induced increase of DA turnover in the nucleus accumbens and the bromocriptine-induced increase of DA turnover in the hippocampus. In addition, DA turnover was increased by B(alpha)P in the nucleus accumbens and caudate putamen and DA levels were suppressed in the nucleus accumbens of bromocriptine treated rats, though the drug alone had no effect. These changes indicate that exposure to B(alpha)P and related compounds may affect dopaminergic function in discrete brain regions that are implicated in cognitive functions, psychosis, depression and Parkinson's disease, and may possibly interfere with their pharmacological intervention. Neurotoxicology

The role of prefrontal cortical dopamine (DA) in the modulation of working memory functions is well documented, but substantial evidence indicates that the locus ceruleus noradrenergic system also modulates working memory via actions within the prefrontal cortex (PFC). This study shows that PFC noradrenaline (NA) and DA dialysate levels phasically increase when rats perform correctly in a delayed alternation task in a T-maze, a test of spatial working memory. However, NA levels were markedly enhanced in animals trained to alternate compared with rats that acquired the spatial information about the location of food in the maze but were untrained to make a choice to obtain the reward. In contrast, PFC DA elevations occurred independently of whether the animal had acquired the trial-specific information for correct task execution. The contribution of anticipatory responses to catecholamine efflux was also evaluated by exposing rats to an environment signaling the presence of the reward in the successive alternation task. No conditioned NA efflux was observed in either group. In contrast, in both groups, DA efflux increased in the anticipatory phase of the test to the same levels of those reached during the task. These data provide the first direct evidence for a selective activation of PFC NA transmission during a spatial working memory task. We propose that, in the working memory task, DA is primarily associated with reward expectancy, whereas NA is involved in the active maintenance of the information about a goal and the rules to achieve it.

In vivo microdialysis combined with high performance liquid chromatography (HPLC) with electrochemical detection, was used to study the effect of MK-801 (0.1 mg/kg i.p.) on extracellular concentrations of dopamine (DA) 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), norepinephrine (NE) and DOPAC/DA ratio in intact, 6-hydroxydopamine (6-OHDA)-lesioned, DSP4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzyl-amine hydrochloride)-lesioned and reserpine-treated rats. The results revealed high basal DA (0.735+/-0.05 fmol/microl), DOPAC (195.93+/-20.18 fmol/microl) and NE (0.585+/-0.01 fmol/microl), low 5-HT (0.334+/-0.032 fmol/microl) and high DOPAC/DA ratio (265.11+/-20.73) in intact cACC. 6-OHDA alone (8 microg/2 microl) depleted DA (-66%), DOPAC (-65%), and NE (-62%). On the other hand, in desipramine (DMI)-pretreated rats, 6-OHDA induced a large depletion of DA (-94%), DOPAC (-97%) and reduced DOPAC/DA ratio (-73%), but increased NE to 142% of intact and 369% of 6-OHDA-lesioned rats. DSP4 (50 mg/kg) decreased NE (-97%), DOPAC (-75%) and DOPAC/DA ratio (-69%). Reserpine (5 mg/kg s.c.) significantly decreased DOPAC (-84%), DOPAC/DA ratio (-81%), 5-HT (-69%) and NE (-86%), but nonsignificantly increased DA. In the intact rats, MK-801 did not change DA, but increased DOPAC and DOPAC/DA ratio. In 6-OHDA-lesioned rats, MK-801 increased DA, whereas in 6-OHDA+DMI rats MK-801 additionally increased DOPAC and DOPAC/DA ratio. DSP4 and reserpine reduced the ability of MK-801 to increase DOPAC and DOPAC/DA ratio. MK-801 did not change NE concentration in dialysates collected from intact rats, but increased that from 6-OHDA+DMI-lesioned rats. In DSP4-lesioned and reserpine-treated rats, MK-801 increased NE but to a level lower than that observed in the intact rats. These results suggest that systemic administration of a low dose of MK-801, which induces profound locomotor stimulation without stereotypy, increases DOPAC and DOPAC/DA ratio in the cACC of intact rats, whereas it additionally increases the depleted DA and NE concentrations especially in 6-OHDA-lesioned rats pretreated with DMI.

A multicenter study is under way to investigate the efficacy of allografting of embryonic mesencephalic neurons in a pig model of Parkinson's disease. We have first established that a stable parkinsonian syndrome can be established by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication of adult male Göttingen minipigs. We are now using positron emission tomography (PET) methods for testing the physiological responses to MPTP intoxication and the time course of the response to several treatment strategies. We now report preliminary results obtained in 11 pigs employed in the initial phase of the study; the completed study shall ultimately include 30 pigs. Animals were randomly assigned to one of five groups: 1) Control, 2) MPTP intoxication, 3) MPTP intoxication followed by allograft, 4) MPTP intoxication followed by allograft with immunosuppression, and 5) MPTP intoxication followed by allograft with immunosuppression and co-grafting of immortalized HiB5 cells, which had been manipulated to secrete glia cell line-derived neurotrophic factor (GDNF) (≈2 ng GDNF/h/105 cells). MPTP was administered (1 mg/kg/day, SC) for 7–10 days until the pigs had developed mild parkinsonian symptoms of muscle rigidity, hypokinesia, and impaired coordination, especially of the hind limbs. Approximately 2 weeks after the last MPTP dose, animals received a T1-weighted magnetic resonance imaging (MRI) scan, and a series of dynamic PET recordings. After the first series of PET scans, four grafts of porcine embryonic mesencephalic tissue (E28 days) were placed in each striatum of some MPTP-intoxicated pigs, using MRI-based stereotactic techniques. Immunosuppression of some animals with cyclosporin and prednisolone began just prior to surgery. Two more series of PET scans were performed at 4-month intervals after surgery. After the last scans, pigs were killed and the brains were perfused for unbiased stereological examination of cytological and histochemical markers in striatum and substantial nigra. The behavioral impairment of the animals (the “Parkinson's score”) had been evaluated throughout the 8-month period. Kinetic analysis of the first set of PET scans has indicated that the rate constant for the decarboxylation of FDOPA in catecholamine fibers was reduced by 33% in striatum of the mildly parkinsonian pigs. The rate of association of [11C]NS-2214 to catecholamine uptake sites was reduced by 62% in the same groups of pigs. No significant difference was found in the binding potential of [11C]raclopride to the dopamine D2-like receptors in striatum of the MPTP-intoxicated versus control pigs. These preliminary results are suggestive that the activity of DOPA decarboxylase may be upregulated in the partially denervated pig striatum.

Clozapine displays nanomolar affinity for cloned human D 4 -type dopamine receptors expressed in tissue culture cells. Therefore, [ 3 H]clozapine has been introduced as a radioligand for the labelling of the D 4 dopamine receptors. We found that, in membranes of postmortem human striatum, amygdala, frontal cortex and substantia nigra, neither dopamine nor the dopamine agonist apomorphine displaced the binding of [ 3 H]clozapine (5–20 nM). [ 3 H]Clozapine competition curves with clozapine and loxapine revealed the presence of two binding sites. The high-affinity site was displaced by atropine and pirenzepine with nanomolar affinity. The low-affinity site did not correspond to a serotonin, adrenergic, γ-amino butyric acid, N- methyl - d - aspartate , benzodiazepine, histamine, sigma, imidazoline receptor-binding site, or catecholamine uptake site. Our results suggest that [ 3 H]clozapine in post-mortem human brain binds to M 1 -type muscarinic cholinergic receptors and to a low-affinity binding site but is not a suitable radioligand for investigating the D 4 dopamine receptors.

Parkinson's disease (PD) is characterised by the progressive degeneration of nigrostriatal dopamine (DA) neurons resulting in the major symptoms of akinesia and rigidity. Although the primary cause of PD is still not known some features make this disorder a model for neurodegenerative diseases in general. It has been known for some time that symptomatic PD can be attributed to insults with symptoms occurring many years later such as post-encephalitic PD or PD following manganese poisoning. More recently, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) has been identified as a neurotoxin selective for melanin-containing dopaminergic neurons in humans and non-human primates. The specificity of this neurotoxin and the striking clinical similarities to idiopathic PD, seen in primates, make MPTP-induced parkinsonism the most useful animal model of a neurological disease. There are numerous theoretical possibilities to interfere with both MPTP-induced neurotoxicity and the symptomatology of PD. In recent years excitatory amino acids have gained considerable interest since they can cause excitotoxic lesion of neurons under a number of pathological conditions (Olney et al., 1989; Choi, 1988). Here we summarise the present data and provide new experimental evidence indicating that MPTP-induced degeneration of dopaminergic neurons does involve glutamate-mediated toxicity. It is concluded that glutamate-mediated excitotoxicity results in the destruction of DAergic somata in the substantia nigra. Non-competitive or competitive NMDA antagonists protect nigral neurons from MPTP-induced degeneration whereas their striatal terminals still seem to degenerate., Band hat ISBN 3-211-82542-8; Titel: Neuroprotection in neurodegeneration; hg. v. Riederer, Peter

Axonal transport of the vesicular monoamine transporter was assayed in the rat brain by in vivo binding of the specific ligand [3H]reserpine. Because of the marked localization of reserpine binding sites in dopaminergic cell bodies and nerve terminals, the dopaminergic nigrostriatal pathway was chosen for the study of the axonal transport of the monoamine carrier present in the membrane of synaptic vesicles. When labelled reserpine was injected into the substantia nigra, a delayed accumulation of radioactivity in the ipsilateral striatum was observed approximately 4 h after the injection. Similarly, injection into the right striatum was followed by a substantial accumulation of radioactivity in the ipsilateral substantia nigra, which was prevented by peripheral injection of unlabelled reserpine or tetrabenazine. This process was rapid and dependent on microtubules. In senescent rats, the amount of retrogradely transported [3H]reserpine was significantly reduced. These results demonstrate that labelled reserpine may be used to monitor in vivo fast axonal transport in central neurons.

D1 and D2 receptor densities in human substantia nigra were examined by use of the specific binding of, respectively, [3H]SCH 23390 [R(+)-7-chloro-8-hydroxy-3-[3H]methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3- benzazepine] and [3H]spiperone. A unilateral loss of striato- and pallidonigral pathways by an infarction (n = 4) had no effect on the ipsilateral nigral D2 receptors, but reduced the ipsilateral nigral D1 receptors by 48-60% compared with the intact side. These data suggest that a substantial fraction of D1 receptors in human substantia nigra is located on terminals of striato- and/or pallidonigral neurons, whereas D2 receptors are confined to intrinsic nigral cells. We also examined the effect of aging on the D1 and D2 receptors in substantia nigra obtained from 25 postmortem human brains (age range 19-88 years). The densities of both receptor types were not affected by the aging process. Since nigrostriatal dopaminergic neurons degenerate with aging, these results suggest either that the nigral D2 receptors are up-regulated in response to a progressive depletion of dopamine in the substantia nigra or that, in contrast to the rat, they are not located on dopaminergic neurons.

Dopaminergic pathways to the cerebral cortex may be involved in cognitive function. We examined the effect of aging on the D1 dopamine receptors, and their high-agonist affinity (RH) sites, in postmortem human frontal cortex (n = 32; age range, 19–88 years). With aging, there was a significant decrease in the densities of the D1 dopamine receptors, and their RH sites, in human frontal cortex. The age-related reduction of cortical dopaminergic neurotransmission might contribute to the decline in cognitive abilities of elderly persons.

By use of the radioligand [3H]spiroperidol, D2 3,4-dihydroxyphenylethylamine (dopamine) receptor binding characteristics were studied in calf globus pallidus and compared with those of neostriatum. Antagonist competition curves were monophasic and revealed similar affinities for neostriatum and globus pallidus, suggesting a uniform receptor population with one affinity state for antagonists. In both regions, competition curves with the agonist dopamine were biphasic, distinguishing a high- and low-agonist-affinity state. In neostriatum and globus pallidus, respectively, 45% and 19% of [3H]spiroperidol binding was displaced with high affinity and the remainder with low affinity. In neostriatum, the addition of 0.4 mM GTP resulted in a partial conversion from high- to low-affinity state with a remaining high-affinity component of 15%. In globus pallidus, dopamine binding was not altered by GTP. The capability of GTP to modulate agonist binding to D2 receptors appears to be dependent on their neuroanatomical localization.

Binding of 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine ([3H]GBR 12935) was studied in membrane preparations of several human brain regions. In putamen, the substituted piperazine derivates cis- and trans-flupenthixol displaced 90% of the total [3H]GBR 12935 binding. Computer-assisted analysis of the competition curves revealed a high-affinity site (30%; KiH = 54 nM) and a low-affinity site (60%; KiL = 4.5 microM). The dopamine uptake blockers mazindol and nomifensine only displaced 30% of the total [3H]GBR 12935 binding in a monophasic way. Binding of [3H]GBR 12935 to the dopamine uptake sites, i.e., that displaced by dopamine uptake blockers, corresponded to part of the binding having low affinity for flupenthixol and was only detected in putamen, nucleus caudatus, nucleus accumbens, and substantia nigra. Even after masking the high-affinity binding site for flupenthixol by including 1 microM cis-flupenthixol in the binding assays, no dopamine uptake sites could be detected in globus pallidus, amygdala, thalamus, hippocampus, and cerebral cortex. Binding of [3H]GBR 12935 to dopamine uptake sites was lost in the nucleus caudatus ipsilateral to ventral midbrain infarctions, confirming their location on nigrostriatal nerve endings. Gross unilateral lesions of the striato- and pallidonigral pathways did not affect the number of dopamine uptake sites in the ipsilateral substantia nigra, suggesting that they may reside on the soma or dendrites of nigral neurons.

High-affinity binding sites for the D 1 dopamine receptor antagonist [ 3 H]SCH 23390 were identified in membranes from human putamen, frontal cortex and calf retina. In frontal cortex binding not only occurred to D 1 but also to 5-HT 2 receptors. In retina and putamen no binding to 5-HT 2 receptors was detected. All further binding experiments in frontal cortex were carried out in the presence of 20 nM mianserin to prevent binding to 5-HT 2 receptors. In the 3 tissues, antagonist competition curves were monophasic, whereas competition curves with the agonist dopamine revealed the presence of two binding sites, one having high affinity (RH) (32% in retina, 28% in putamen, and 15% in frontal cortex) and the other having low affinity (RL). In retina, the addition of 100 μM GTP caused a full conversion of RH into RL. In contrast, in frontal cortex, RH sites were not altered by 400 μM GTP or 100 μM 5′-guanylyl-imidodiphosphate (Gpp(NH)p). In putamen, both guanine nucleotides provoked only a partial conversion of RH into RL. Dopamine (100 μM) produced a 220% and 56% increase in cAMP production in respectively retina and putamen homogenates, while no increase was observed in frontal cortex homogenate. These data may suggest that not all D 1 -receptors are coupled to the adenylate cyclase system.

The electronic properties of orthopramides, a group of selective D-2 dopamine receptor antagonists, were investigated by calculating molecular electrostatic potentials (MEP) of model compounds with the ab initio STO-3G MO method. The various substitution patterns of the aromatic ring are characterized by a positive region comprising the H-bonded 2-methoxy group and ring positions 2, 3, and 4 and a negative region comprising the CONH group, 5-substituent, and ring positions 5 and 6. The regions of positive and negative potential are separated by a "curtain" running along the longitudinal axis of the molecule. At shorter distances from the plane of the aromatic ring (1.75 and 2.0 A), this "curtain" is quite sinuous, but at greater distances (2.5 and 3.0 A) it tends toward rectilinearity. We postulate that this longitudinal separation, together with the single positive maximum and the three negative minima perceptible at 3.0 A, constitute a distance pharmacophore responsible for the recognition and proper alignment of the ligand. The more complex MEP at 1.75 and 2.0 A are equated with a contact pharmacophore. Comparison of the MEP of orthopramides and dopamine reveals some analogies and suggests a possible mode of binding of these antagonists to the D-2 receptor.

D1 dopamine receptors were identified in membranes of human nucleus caudatus, nucleus accumbens, amygdala, and globus pallidus, by the specific binding of [3H](+)-R-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-benzazepine-7 -ol [(3H]SCH 23390). In these four brain regions, dopamine/[3H]SCH 23390 competition binding curves were computer-analyzed to a two-site model, distinguishing a high- (RH) and low- (RL) affinity site for dopamine. The ability of guanine nucleotides (0.4 mM GTP or 0.1 mM 5'-guanylylimidodiphosphate) to provoke a conversion of RH into RL was different between these brain regions. In amygdala, a complete conversion was seen, whereas there was no guanine nucleotide-effect on RH in globus pallidus. In nucleus caudatus and nucleus accumbens, guanine nucleotides provoked only a partial conversion of RH into RL, suggesting that these brain regions may contain guanine nucleotide-sensitive and -insensitive receptors. Heating of the membranes at 60 degrees C for 5 min had the same effect as guanine nucleotides. The pharmacological profiles of the guanine nucleotide-sensitive and -insensitive D1 receptors were similar, suggesting that D1 receptors in human brain are heterogeneous only with respect to their effector-coupling mechanism: guanine nucleotide-sensitive receptors, which are capable of undergoing functional coupling with Gs, and guanine nucleotide-insensitive receptors, which are not.(ABSTRACT TRUNCATED AT 250 WORDS)

The distribution of dopamine D1 and D2 receptors in several human brain regions was investigated using autoradiography with the radioligands [3H]SCH 23390 and [3H]spiroperidol. The highest densities of both dopamine receptor types are seen in the nucleus caudatus, putamen and nucleus accumbens. Whereas the density of the D2 receptors is similar in the two segments of the globus pallidus, the pars medialis of the globus pallidus contains a three-fold higher concentration of D1 receptors than the pars lateralis. D1 and D2 receptors are present in the amygdala and substantia nigra. Both receptor types are absent in the cerebellum. The thalamus contains low densities of D1 receptors but no D2 receptors. Only D2 receptors are seen in the anterior lobe of the pituitary gland. The whole cerebral cortex is rich in D1 receptors, while D2 receptors, in low concentrations, are confined to the entorhinal area and cingulate cortex.