Postsynaptic Dopamine Receptors Research Articles

Unveiling the mosaic: Exploring various movement disorders in osmotic demyelination syndrome

Abstract Osmotic demyelination syndrome (ODS) is characterized by noninflammatory demyelination within the central nervous system with symmetrical lesions in the pontine and extrapontine regions, such as the caudate, putamen, midbrain, thalamus, cerebellum, and corpus callosum. Clinical manifestations of ODS can be highly variable, including encephalopathy, bradykinesia, spastic quadriparesis, rigidity, dyskinesias, tremor, choreoathetoid movements, mutism, dysarthria, dysphagia, and ophthalmoparesis. Our study included 11 patients with ODS of whom 9 were male individuals (81.81%). The mean and median ages of the patients were 46 ± 19 years and 57 years, respectively. Most patients (90.9%) had hyponatremia, while one patient (9.1%) had hypernatremia. Magnetic resonance imaging findings were observed in 81.81% (n = 9) patients at presentation. Parkinsonism was the most common manifestation observed in 10 patients (90.9%), all of whom most commonly exhibited rigidity and bradykinesia. Postural tremor was observed in four patients (36.36%), masked facies in six patients (54.54%), dystonia in four patients (36.36%), perioral dyskinesias in three patients (27.27%), and choreoathetoid movements were observed in one patient (9.09%). ODS is typically associated with rapid correction of hyponatremia, especially in patients with predisposing factors. However, in this study, gradual hyponatremia correction was performed at a rate <8 mEq/L/24 hours in three patients who later developed ODS. Individuals with ODS may exhibit symptoms of both hypokinetic and hyperkinetic movement disorders due to changes in direct and indirect pathways. Extrapontine involvement can be attributed to either presynaptic striatal dopamine transporter depletion or a deficiency of postsynaptic dopamine receptors. In this study, both hypokinetic and hyperkinetic movement disorders can be observed in ODS; however, hypokinetic movement disorders in the form of parkinsonism were more common.

Tyrosine Hydroxylase Inhibitors and Dopamine Receptor Agonists Combination Therapy for Parkinson's Disease.

There are currently no disease-modifying therapies for Parkinson's disease (PD), a progressive neurodegenerative disorder associated with dopaminergic neuronal loss. There is increasing evidence that endogenous dopamine (DA) can be a pathological factor in neurodegeneration in PD. Tyrosine hydroxylase (TH) is the key rate-limiting enzyme for DA generation. Drugs that inhibit TH, such as alpha-methyltyrosine (α-MT), have recently been shown to protect against neurodegeneration in various PD models. DA receptor agonists can activate post-synaptic DA receptors to alleviate DA-deficiency-induced PD symptoms. However, DA receptor agonists have no therapeutic effects against neurodegeneration. Thus, a combination therapy with DA receptor agonists plus TH inhibitors may be an attractive therapeutic approach. TH inhibitors can protect and promote the survival of remaining dopaminergic neurons in PD patients' brains, whereas DA receptor agonists activate post-synaptic DA receptors to alleviate PD symptoms. Additionally, other PD drugs, such as N-acetylcysteine (NAC) and anticholinergic drugs, may be used as adjunctive medications to improve therapeutic effects. This multi-drug cocktail may represent a novel strategy to protect against progressive dopaminergic neurodegeneration and alleviate PD disease progression.

Hormones and Psychosis: The Role of Estrogen in Schizophrenia

IntroductionSchizophrenia is a complex psychiatric disorder in which biological sex differences, have been extensively documented and researched. What is less well described, is what motivates these differences. Of the various proposed and explored reasons, estrogen appears to be one that has maintained some interest and promise. An increase in symptoms of schizophrenia has been observed to correspond with decreasing levels of estrogen in menopausal women, this, allied to the later symptom onset, culminated in the interest in this hormone and its role in psychotic illness.ObjectivesThe authors aim to briefly explore the current evidence on the association between estrogen and schizophrenia. Its relevance in symptom onset, protective status and eventual therapeutic applications will also be discussed.MethodsThe authors conducted a brief non-structured narrative literature review using articles published in the Medline/Pubmed, ScienceDirect and Google Scholar databases. The keywords used during the research, alone or in combination, included: sex hormones, estrogen, schizophrenia and psychiatry.The studies consulted in this work included: cross-sectional studies, cohort studies, literature reviews and clinical case reports.ResultsThe literature exploring the relationship between the sex hormone, estrogen, and schizophrenia is extensive. Various studies confirm that during periods of estrogen withdrawal, women appear more susceptible to psychotic episodes. Results also demonstred that those with low estrogen, respond poorly to anti-psychotic drugs, whereas estrogen increased the efficiency of antipsychotics. In regards to symptoms, estrogen has been demonstrated to reduce the positive and cognitive symptoms of schizophrenia in the short term, thus being proposed as an eventual complementary treatment in those suffering from the disorder. It is known that estrogen regulates important pathophysiological pathways in schizophrenia, including dopamine activity, mitochondrial function, and the stress system.One of the explanations for this beneficial effect has been proposed to be action on cerebral blood flow and glucoce metabilism, as well as sensitizing postsynaptic dopamine receptors, thus serving as a protective agent against schizophrenia.ConclusionsThe research appears to be pointing in the direction that estrogen appears to have an effect on psychosis in women, serving as a protective factor in these conditions as well as playing a significant part of the pathophysiology in schizophrenia. This influence on the pathophysiology, promises clinical pertinence, not only in a possible application so to attenuate positive and cognitive symptoms but also as a method to influence antipsychotic efficacy. Continued study in regards to the effects of sex hormones on the psychotic disorders is merited so as to further expand the tools in the mental health professional’s repertoire in the treatment of these serious mental illnesses.Disclosure of InterestNone Declared

Hyperprolactinemia as a side effect of using antipsychotics In Schizophrenic Patients

Introductions: Antipsychotics are still the mainstay of schizophrenia management. Antipsychotics are antagonistic to postsynaptic dopamine receptors in the brain. Blockade of dopamine receptors in the tuberoinfundibular pathway by antipsychotics will cause the side effect of hyperprolactinemia. Objectives: This review describes hyperprolactinemia induced by antipsychotic use and its clinical effects, monitoring, and management. Methods: reference search through Google Scholar with keywords schizophrenia, antipsychotics, prolactin, hyperprolactinemia, clinical effects of hyperprolactinemia, diagnosis of hyperprolactinemia, monitoring of hyperprolactinemia, management of hyperprolactinemia. Results: Clinicians need to take a diagnostic approach to identify the etiology of hyperprolactinemia, monitor the clinical symptoms of hyperprolactinemia during the administration of antipsychotics, and immediately carry out management according to existing strategies by considering some general principles and considerations. Conclusions: Schizophrenia is a severe mental disorder that lasts long, requiring long-term and continuous therapy. Administration of antipsychotics is still a mainstay in the management of schizophrenia. Antipsychotics are antagonists to postsynaptic dopamine receptors in the brain. The antipsychotic effect of blocking dopamine receptors not only improves the symptoms of schizophrenia but also causes side effects. The side effect when the tuberoinfundibular dopamine pathway is blocked is an increase in prolactin levels called hyperprolactinemia.

Neuroleptic-induced tardive dystonia in young patients suffering from psychosis

Tardive dystonia is one of the extrapyramidal syndromes that start after long-term use of dopamine receptor antagonists. Tardive dystonia is underdiagnosed and often misdiagnosed; some of the treatment possibilities are hardly known among psychiatrists and are notorious for being resistant to treatment. Here, we present a set of two cases who had come with neuroleptic-induced tardive dystonia, initially given oral tetrabenazine and injectable botulinum toxin, but they did not respond. They got better after treatment with the combination of oral baclofen and electroconvulsive therapy (ECT). ECT is thought to prevent the super sensitization of postsynaptic dopamine receptors that contribute to the development of tardive states. Baclofen is a presynaptic gamma-aminobutyric acid receptor agonist primarily used to treat spasticity. Both may have acted synergistically to treat the dystonia. Tardive dystonia needs to be ruled out in patients with a history of long-term antipsychotic medication use. Consultant liaison with psychiatrists will be of paramount importance in the timely management of these cases. The combination of ECT and baclofen may be an effective choice for patients of schizophrenia with tardive dystonia developed in the course of neuroleptic treatment. However, further controlled studies are needed to develop and refine the guidelines for managing it.

Tardive Dyskinesia in Older Persons Taking Antipsychotics.

Tardive dyskinesia (TD) is a hyperkinetic movement disorder caused by the use of dopamine receptor-blocking agents (DRBAs), a category of medications that includes first- and second-generation antipsychotics (APs) and agents such as metoclopramide that are used for the treatment of nausea and gastrointestinal dysmotility. While TD can affect people of all ages, older age is associated with increased risk of TD and also with the emergence of TD occurring after shorter treatment durations and lower dosages of DRBAs. TD is characterized by involuntary movements that include the face, limbs, and trunk, and is associated with increased comorbidities, social stigmatization, and impaired physical and mental health. Once present, TD tends to persist despite AP dose adjustment or discontinuation. Even with the use of US Food and Drug Administration (FDA)-approved medications for TD, symptoms may persist. Because the leading hypothesis for the pathophysiology of TD has been dysregulation of dopamine transmission due to treatment with DRBAs, APs that avoid postsynaptic dopamine receptor blockade may provide an alternative therapeutic approach for patients who require an AP. In this review, we discuss the risks, burdens, prevention, and management of TD, with a focus on older people.

Functional Characterization of the Dopaminergic Psychostimulant Sydnocarb as an Allosteric Modulator of the Human Dopamine Transporter.

The dopamine transporter (DAT) serves a critical role in controlling dopamine (DA)-mediated neurotransmission by regulating the clearance of DA from the synapse and extrasynaptic regions and thereby modulating DA action at postsynaptic DA receptors. Major drugs of abuse such as amphetamine and cocaine interact with DATs to alter their actions resulting in an enhancement in extracellular DA concentrations. We previously identified a novel allosteric site in the DAT and the related human serotonin transporter that lies outside the central orthosteric substrate- and cocaine-binding pocket. Here, we demonstrate that the dopaminergic psychostimulant sydnocarb is a ligand of this novel allosteric site. We identified the molecular determinants of the interaction between sydnocarb and DAT at the allosteric site using molecular dynamics simulations. Biochemical-substituted cysteine scanning accessibility experiments have supported the computational predictions by demonstrating the occurrence of specific interactions between sydnocarb and amino acids within the allosteric site. Functional dopamine uptake studies have further shown that sydnocarb is a noncompetitive inhibitor of DAT in accord with the involvement of a site different from the orthosteric site in binding this psychostimulant. Finally, DA uptake studies also demonstrate that sydnocarb affects the interaction of DAT with both cocaine and amphetamine. In summary, these studies further strengthen the prospect that allosteric modulation of DAT activity could have therapeutic potential.

The Interplay Between Postsynaptic Striatal D2/3 Receptor Availability, Adversity Exposure and Odd Beliefs: A [11C]-Raclopride PET Study

Between unaffected mental health and diagnosable psychiatric disorders, there is a vast continuum of functioning. The hypothesized link between striatal dopamine signaling and psychosis has guided a prolific body of research. However, it has been understudied in the context of multiple interacting factors, subclinical phenotypes, and pre-postsynaptic dynamics. This work investigated psychotic-like experiences and D2/3 dopamine postsynaptic receptor availability in the dorsal striatum, quantified by in vivo [11C]-raclopride positron emission tomography, in a sample of 24 healthy male individuals. Additional mediation and moderation effects with childhood trauma and key dopamine-regulating genes were examined. An inverse relationship between nondisplaceable binding potential and subclinical symptoms was identified. D2/3 receptor availability in the left putamen fully mediated the association between traumatic childhood experiences and odd beliefs, that is, inclinations to see meaning in randomness and unfounded interpretations. Moreover, the effect of early adversity was moderated by a DRD2 functional variant (rs1076560). The results link environmental and neurobiological influences in the striatum to the origination of psychosis spectrum symptomology, consistent with the social defeat and diathesis-stress models. Adversity exposure may affect the dopamine system as in association with biases in probabilistic reasoning, attributional style, and salience processing. The inverse relationship between D2/3 availability and symptomology may be explained by endogenous dopamine occupying the receptor, postsynaptic compensatory mechanisms, and/or altered receptor sensitivity. This may also reflect a cognitively stabilizing mechanism in non-help-seeking individuals. Future research should comprehensively characterize molecular parameters of dopamine neurotransmission along the psychosis spectrum and according to subtype profiling.

Neuroendocrine Assessment of Dopaminergic Function during Antidepressant Treatment in Major Depressed Patients.

The effects of antidepressants on dopamine (DA) receptor sensitivity in the mesolimbic–hypothalamic system have yielded contradictory results. The postsynaptic DA receptor function was evaluated by the cortisol response to apomorphine (APO; 0.75 mg SC) in 16 drug-free DSM-5 major depressed inpatients and 18 healthy hospitalized control (HC) subjects. Cortisol response to the dexamethasone suppression test (DST) was also measured. After two and four weeks of antidepressant treatment (ADT), the DST and APO test were repeated in all patients. Cortisol response to APO (∆COR) was not influenced by the hypothalamic–pituitary–adrenal (HPA) axis activity, as assessed by the DST. Pre-treatment ∆COR values did not differ significantly between patients and HCs. During ADT, ∆COR values were lower than in HCs at week 2 and 4. After four weeks of treatment, among the eight patients who had blunted ∆COR values, seven were subsequent remitters, while among the eight patients who had normal ∆COR values, seven were non-remitters. Considering the limitations of our study, the results suggest that following chronic ADT, the desensitization of postsynaptic DA receptors connected with the regulation of the HPA axis at the hypothalamic level is associated with clinical remission. These results could reflect increased DA levels in the mesolimbic pathway.

Very-Low-Dose Levodopa Therapy for Pediatric Neurological Disorders: A Preliminary Questionnaire in Japan.

Introduction: Post-synaptic dopamine receptor supersensitivity (DARSS) has been extensively researched by Dr. Masaya Segawa, who has investigated the efficacy of very-low-dose levodopa therapy (VLDT; 0.5–1 mg/kg/day). Considerable Japanese research supports the possibility that VLDT could be used to treat pediatric neurological disorders. We conducted an on-line survey in 2014 to collect real-world data on the use of VLDT to treat DARSS.Methods: A two-step survey, including a screening test and questionnaire, was posted on a private internet site that could be accessed via the VLDT Research Group home page, and 1,165 pediatric neurologists across Japan were invited to complete it.Results: A total of 25 respondents reported prescribing VLDT; 19 used VLDT to treat autism spectrum disorder, 14 for tics, 12 for speech delay, 9 for Rett syndrome, 7 for attention-deficit/hyperactivity disorder, intellectual disability, and 6 for sleep problems. Twelve respondents reported prescribing a dose of 0.5 mg/kg. Twenty-two reported that VLDT was effective for treating behavioral problems, and twenty reported a good efficacy for treating motor symptoms. Adverse events had a low incidence. Notably, respondents chose VLDT for its possible action in DARSS and for its safety. VLDT was commonly used for behavioral problems in patients younger than 5 years, and for motor symptoms in aged 5–9 years.Conclusion: VLDT could safely treat behavioral and motor symptoms in pediatric neurological disorders. In contrast, dopamine antagonists are associated with potent efficacy, but with adverse effects such as sleepiness and obesity. Further surveys should be conducted with a broader participants.

Tardive Dyskinesia: Assessing and Treating a Debilitating Side Effect of Prolonged Antipsychotic Exposure

Tardive Dyskinesia: Assessing and Treating a Debilitating Side Effect of Prolonged Antipsychotic Exposure

Altered dopaminergic firing pattern and novelty response underlie ADHD-like behavior of SorCS2-deficient mice

Attention deficit hyperactivity disorder (ADHD) is the most frequently diagnosed neurodevelopmental disorder worldwide. Affected individuals present with hyperactivity, inattention, and cognitive deficits and display a characteristic paradoxical response to drugs affecting the dopaminergic system. However, the underlying pathophysiology of ADHD and how this relates to dopaminergic transmission remains to be fully understood. Sorcs2−/− mice uniquely recapitulate symptoms reminiscent of ADHD in humans. Here, we show that lack of SorCS2 in mice results in lower sucrose intake, indicating general reward deficits. Using in-vivo recordings, we further find that dopaminergic transmission in the ventral tegmental area (VTA) is shifted towards a more regular firing pattern with marked reductions in the relative occurrence of irregular firing in Sorcs2−/− mice. This was paralleled by abnormal acute behavioral responses to dopamine receptor agonists, suggesting fundamental differences in dopaminergic circuits and indicating a perturbation in the balance between the activities of the postsynaptic dopamine receptor DRD1 and the presynaptic inhibitory autoreceptor DRD2. Interestingly, the hyperactivity and drug response of Sorcs2−/− mice were markedly affected by novelty. Taken together, our findings show how loss of a candidate ADHD-risk gene has marked effects on dopaminergic circuit function and the behavioral response to the environment.

Dopamine Oppositely Modulates State Transitions in Striosome and Matrix Direct Pathway Striatal Spiny Neurons

Corticostriatal synaptic integration is partitioned among striosome (patch) and matrix compartments of the dorsal striatum, allowing compartmentalized control of discrete aspects of behavior. Despite the significance of such organization, it's unclear how compartment-specific striatal output is dynamically achieved, particularly considering new evidence that overlap of afferents is substantial. We show that dopamine oppositely shapes responses to convergent excitatory inputs in mouse striosome and matrix striatal spiny projection neurons (SPNs). Activation of postsynaptic D1 dopamine receptors promoted the generation of long-lasting synaptically evoked "up-states" in matrix SPNs but opposed it in striosomes, which were more excitable under basal conditions. Differences in dopaminergic modulation were mediated, in part, by dendritic voltage-gated calcium channels (VGCCs): pharmacological manipulation of L-type VGCCs reversed compartment-specific responses to D1 receptor activation. These results support a novel mechanism for the selection of striatal circuit components, where fluctuating levels of dopamine shift the balance of compartment-specific striatal output.

Manganese, a Likely Cause of 'Parkinson's in Cirrhosis', a Unique Clinical Entity of Acquired Hepatocerebral Degeneration.

With idiopathic Parkinson's disease being a common entity, parkinsonism in acquired hepatocerebral degeneration (AHD) in the context of Manganese (Mn) has gained importance in recent years. An insight into the pathomechanisms behind this disease has been put forth. How can Mn as a divalent metal exert its effect in leading to chronic neurodegenerative disorder? Secondary to decreased excretion in liver cirrhosis, Mn significantly alters the striatal dopaminergic system. Management of this debilitating disease also focuses on different aspects where Mn has been involved in the pathogenesis. We have put forth the details behind Mn effects in Parkinson’s, which will be a guide for better understanding and management of this disease.A literature search was performed using PubMed as a sole database, and all the articles were peer-reviewed. The author tried to follow the PRISMA guidelines. Inclusion criteria were set for 10 years, with most studies with in the last seven years. All types of study designs were included relevant to the topic, clearly delineating the pathomechanisms of Mn in the disease and also its management. After extensive research, through the PubMed database, we found that Parkinson's disease is one of the neurological complications in advanced liver cirrhosis. Mn is an essential element behind its pathogenesis; it works at different cellular levels to promote neurotoxicity. From its influx to its effects on dopamine transporters (DAT), where it disrupts dopamine homeostasis also altering postsynaptic dopamine (D2) receptors, it disrupts mitochondria and the endoplasmic reticulum (ER) promotes oxidative stress and neuroinflammation. Misfolding of alpha-synuclein (α-Syn) is promoted on chronic exposure to Mn where α-Syn from being neuroprotective becomes neurotoxic. It also alters glutaminergic and gabaergic neurotransmission. In a nutshell, the diversity of its effect on nigrostriatal denervation is challenging. The importance of neuroimaging and various approaches to management is also discussed. AHD, an uncommon entity in advanced liver cirrhosis, needs more awareness so that it can be diagnosed earlier and better therapeutic options can be sought. Our study highlighted Mn mechanisms behind this clinical entity, putting forth grounds for a better understanding of this disease. Advanced research targeting Mn for managing this disease will be revolutionary.

Deep Brain Stimulation of the Medial Forebrain Bundle in a Rodent Model of Depression: Exploring Dopaminergic Mechanisms with Raclopride and Micro-PET

Background: Deep brain stimulation (DBS) of the medial forebrain bundle (MFB) can reverse depressive-like symptoms clinically and in experimental models of depression, but the mechanisms of action are unknown. Objectives: This study investigated the role of dopaminergic mechanisms in MFB stimulation-mediated behavior changes, in conjunction with raclopride administration and micropositron emission tomography (micro-PET). Methods: Flinders Sensitive Line (FSL) rats were allocated into 4 groups: FSL (no treatment), FSL+ (DBS), FSL.R (FSL with raclopride), and FSL.R+ (FSL with raclopride and DBS). Animals were implanted with bilateral electrodes targeting the MFB and given 11 days access to raclopride in the drinking water with or without concurrent continuous bilateral DBS over the last 10 days. Behavioral testing was conducted after stimulation. A PET scan using [¹⁸F]desmethoxyfallypride was performed to determine D2 receptor availability before and after raclopride treatment. Changes in gene expression in the nucleus accumbens and the hippocampus were assessed using quantitative polymerase chain reaction. Results: Micro-PET imaging showed that raclopride administration blocked 36% of the D2 receptor in the striatum, but the relative level of blockade was reduced/modulated by stimulation. Raclopride treatment enhanced depressive-like symptoms in several tasks, and the MFB DBS partially reversed the depressive-like phenotype. The raclopride-treated MFB DBS animals had increased levels of mRNA coding for dopamine receptor D1 and D2 suggestive of a stimulation-mediated increase in dopamine receptors. Conclusion: Data suggest that chronic and continuous MFB DBS could act via the modulation of the midbrain dopaminergic transmission, including impacting on the postsynaptic dopamine receptor profile.

Attenuated dopamine receptor signaling in nucleus accumbens core in a rat model of chemically-induced neuropathy

Neuropathy is major source of chronic pain that can be caused by mechanically or chemically induced nerve injury. Intraplantar formalin injection produces local necrosis over a two-week period and has been used to model neuropathy in rats. To determine whether neuropathy alters dopamine (DA) receptor responsiveness in mesolimbic brain regions, we examined dopamine D1-like and D2-like receptor (D1/2R) signaling and expression in male rats 14 days after bilateral intraplantar formalin injections into both rear paws. D2R-mediated G-protein activation and expression of the D2R long, but not short, isoform were reduced in nucleus accumbens (NAc) core, but not in NAc shell, caudate-putamen or ventral tegmental area of formalin- compared to saline-treated rats. In addition, D1R-stimulated adenylyl cyclase activity was also reduced in NAc core, but not in NAc shell or prefrontal cortex, of formalin-treated rats, whereas D1R expression was unaffected. Other proteins involved in dopamine neurotransmission, including dopamine uptake transporter and tyrosine hydroxylase, were unaffected by formalin treatment. In behavioral tests, the potency of a D2R agonist to suppress intracranial self-stimulation (ICSS) was decreased in formalin-treated rats, whereas D1R agonist effects were not altered. The combination of reduced D2R expression and signaling in NAc core with reduced suppression of ICSS responding by a D2R agonist suggest a reduction in D2 autoreceptor function. Altogether, these results indicate that intraplantar formalin produces attenuation of highly specific DA receptor signaling processes in NAc core of male rats and suggest the development of a neuropathy-induced allostatic state in both pre- and post-synaptic DA receptor function.

Bound, free, and total L-dopa measurement in plasma of Parkinson's disease patients.

Peaks and troughs of levodopa in plasma contribute to pulsatile postsynaptic dopamine receptor stimulation in patients with Parkinson's disease. Measurement of levodopa plasma levels mostly only considers the total levodopa plasma concentration. Objectives were to determine bound, free, and total plasma levodopa and to investigate their correlations to each other. We employed reversed-phase high-performance liquid chromatography combined with electrochemical detection. Bound levodopa was computed as difference between total and free L-dopa values. Close correlations between free and total (R = 0.93, p < 0.0001), bound and total (R = 0.91, p < 0.0001) plasma levodopa appeared. A considerable variability of levodopa concentrations occurred. The ratio between bound and free levodopa did not differ in patients with a higher and lower oral daily levodopa dosing. Free, bound, and total levodopa plasma levels are closely related. Estimation of the total levodopa level only seems to be meaningful.

Identification of a Novel Allosteric Modulator of the Human Dopamine Transporter.

The dopamine transporter (DAT) serves a pivotal role in controlling dopamine (DA)-mediated neurotransmission by clearing DA from synaptic and perisynaptic spaces and controlling its action at postsynaptic DA receptors. Major drugs of abuse such as amphetamine and cocaine interact with DAT to mediate their effects by enhancing extracellular DA concentrations. We previously identified a novel allosteric site in the related human serotonin transporter that lies outside the central substrate and inhibitor binding pocket. We used the hybrid structure based (HSB) method to screen for allosteric modulator molecules that target a similar site in DAT. We identified a compound, KM822, that was found to be a selective, noncompetitive inhibitor of DAT. We confirmed the structural determinants of KM822 allosteric binding within the allosteric site by structure/function and substituted cysteine scanning accessibility biotinylation experiments. In the in vitro cell-based assay and ex vivo in both rat striatal synaptosomal and slice preparations, KM822 was found to decrease the affinity of cocaine for DAT. The in vivo effects of KM822 on cocaine were tested on psychostimulant-associated behaviors in a planarian model where KM822 specifically inhibited the locomotion elicited by DAT-interacting stimulants amphetamine and cocaine. Overall, KM822 provides a unique opportunity as a molecular probe to examine allosteric modulation of DAT function.

The role of agonistic/antagonistic activity in the development of psychotropic effects of antipsychotics

The development of psychotic symptoms is traditionally linked to the increase of the functional activity of endogenous dopaminergic system. Antipsychotic effect of existing medications is associated with direct blockade of postsynaptic dopamine receptors. However, direct antagonistic activity is «alien» to physiological mechanisms of neurotransmission modulation, and presynaptic autoreceptor blockade mау produce a reverse (agonistic) effect, enhancing neurotransmitter release. On the other hand, anti-dopamine effect can be achieved by indirect antagonistic activity—by presynaptic dopamine depletion, which is consistent with the natural, physiological mechanisms of reducing neurotransmission. It can be assumed that modulation of presynaptic regulation is one of the promising directions for the development of antipsychotic drugs of future generations.

Role of Phospholipase C in the Dopamine D2 Signaling Pathway in the Control of Lateral Cilia in Gill of Crassostrea virginica

Lateral cell cilia of gill of Crassostrea virginica are controlled by serotonergic‐dopaminergic innervations from their ganglia. Dopamine is the neurotransmitter causing cilio‐inhibition, serotonin cilio‐excitation. Previous work of our lab showed the post‐synaptic dopamine receptors present in lateral cells are D2‐type. Dopamine D2 receptors (D2R) are G protein‐coupled metabotropic receptors. Ligand binding to D2R splits its Gi/o protein into the Gβγ and Gαi/o subunits. Gαi/o inhibits adenylyl cyclase; while Gβγ opens GIRK channels, closes L‐type Ca2+ channels and activates phospholipase C (PLC). The inhibition of adenylyl cyclase and subsequent lowering of cAMP is known to slow lateral cilia; however, the role of PLC in the signaling pathway has not been well studied with respect to control of lateral cilia. Using immunohistofluorescence, our lab visualized PLC in lateral cell. In this study we hypothesized that the PLC component of the D2 pathway also plays a role in the cilio‐inhibition. To test this we utilized PLC activators and inhibitors on excised gill to determine their effects on lateral cilia. Cilia beating rates were measured using stroboscopic microscopy. In control gill, applying a dose response of dopamine (10−6 – 10−3M) is cilio‐inhibitory, decreasing beating rates of lateral cilia to 0. Applying m‐3M3FBS (10−5 – 10−4M), a PLC activator, caused a moderate decrease in cilia beating rates. Applying U73122 (10−4M), a phosphatidylinositol 4,5‐bisphosphate specific PLC inhibitor, did not alter cilia beating rates by itself, but did effect the dose response to dopamine (10−5 – 10−3M). In the presence of the inhibitor, while the 10−5M dose of dopamine caused the expected decrease in cilia beating rates, the addition of higher doses of dopamine was unable to reduce beating rates any further. As expected, the drug D609, a PLC inhibitor but specific for phosphatidylcholine, had no effects on cilia beating rates or the actions of dopamine. The results of this study supports our hypothesis that the PLC component of the D2R signal transduction pathway plays a role in the inhibitory control of gill lateral cilia. The results show that both components of the D2R pathway, the adenylyl cyclase component and the PLC component are involved in controlling lateral cilia beating. In humans the D2R signal transduction pathway is significantly involved in the actions of antidepressants, neuroleptics, and drugs of abuse, as well as implicated in neuropsychiatric and neurodegenerative disorders. This physiology study is helpful in furthering the understanding of the pathway and should help to generate further investigations.Support or Funding InformationThis work was supported in part by grant 2R25GM06003 of the Bridge Program of NIGMS, NIH grant K12GM093854‐07A1 IRACDA Program of Rutgers University and 604060048 of PSC‐CUNY.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.