Stimulation Of Dopamine Receptors Research Articles

The Involvement of Intra-Hippocampal Dopamine Receptors in the Conditioned Place Preference Induced By Orexin Administration into the Rat Ventral Tegmental Area.

The activity of dopamine (DA)-containing neurons in the ventral tegmental area (VTA) is a key mechanism in mesolimbic reward processing that has modulatory effects on different diencephalic structures like hippocampus (HIP), and receives inhibitory feedback and excitatory feed forward control. In addition, within the hippocampus, DA receptors are mostly located in the dorsal part (CA1) and dopaminergic innervations are predominant in this sub-region. The current study aimed to examine the effect of intra-hippocampal CA1 administration of SCH23390 and Sulpiride as D1- and D2-like receptor antagonists on the acquisition of orexin-induced conditioned place preference (CPP), respectively. Cannulas were unilaterally implanted into the VTA and HIP of adult male albino Wistar rats weighing 200-250 g. For induction of CPP, orexin A (10 ng/0.3 µL saline) was daily microinjected into the VTA during a three-day conditioning phase. Thereafter, various doses of SCH23390 and Sulpiride (0.25, 1 and 4 µg) were unilaterally injected into the CA1 during this 3-day conditioning phase after intra-VTA administration. The conditioning score was then calculated. Results revealed that intra-CA1 administration of D1- and D2-like receptor antagonists during the 3-day conditioning phase attenuated the acquisition of place preference by orexin A in a dose-dependent manner. It seems the effect of D2-like receptor antagonist within the CA1 region of hippocampus on this phenomenon was found to be more considerable than that of D1-like receptor antagonist. It is concluded that orexin-induced CPP may be mediated, at least in part, by stimulation of DA receptors in the CA1.

Nucleus accumbens dopamine increases sexual motivation in sexually satiated male rats.

The influence of the main dopaminergic brain regions controlling copulation, the medial preoptic area (mPOA) and the nucleus accumbens (NAcc), on male rat sexual behavior expression has not been fully established. This work analyzes the sexual effects of dopamine (DA) receptor activation in the mPOA or the NAcc of sexually active male rats, with an intact (sexually experienced) or a reduced (sexually exhausted) sexual motivation. The non-specific DA receptor agonist apomorphine and the D2-like receptor agonist quinpirole were infused into the mPOA or the NAcc of sexually experienced or sexually exhausted male rats and their sexual behavior recorded. DA receptor activation neither in the mPOA nor in the NAcc modified the copulatory behavior of sexually experienced male rats. DA receptor stimulation in the NAcc, but not in the mPOA, reversed the characteristic sexual inhibition of sexually satiated rats, and D2-like receptors were found to participate in this effect. The optimal sexual performance of sexually experienced male rats cannot be further improved by DA receptor activation at either brain region. In sexually satiated rats, which are sexually inhibited and have a diminished sexual motivation, NAcc DA receptor stimulation appears to play a key role in their capacity to respond to a motivational significant stimulus, the receptive female, with the participation of D2-like receptors. Activation of DA receptors with the same drug, at the same dose and in the same brain region, produces different effects on copulatory behavior that depend on the animal's sexual motivational state.

Striatal dopamine deficits predict reductions in striatal functional connectivity in major depression: a concurrent 11C-raclopride positron emission tomography and functional magnetic resonance imaging investigation

Major depressive disorder (MDD) is characterized by the altered integration of reward histories and reduced responding of the striatum. We have posited that this reduced striatal activation in MDD is due to tonically decreased stimulation of striatal dopamine synapses which results in decremented propagation of information along the cortico-striatal-pallido-thalamic (CSPT) spiral. In the present investigation, we tested predictions of this formulation by conducting concurrent functional magnetic resonance imaging (fMRI) and 11C-raclopride positron emission tomography (PET) in depressed and control (CTL) participants. We scanned 16 depressed and 14 CTL participants with simultaneous fMRI and 11C-raclopride PET. We estimated raclopride binding potential (BPND), voxel-wise, and compared MDD and CTL samples with respect to BPND in the striatum. Using striatal regions that showed significant between-group BPND differences as seeds, we conducted whole-brain functional connectivity analysis using the fMRI data and identified brain regions in each group in which connectivity with striatal seed regions scaled linearly with BPND from these regions. We observed increased BPND in the ventral striatum, bilaterally, and in the right dorsal striatum in the depressed participants. Further, we found that as BPND increased in both the left ventral striatum and right dorsal striatum in MDD, connectivity with the cortical targets of these regions (default-mode network and salience network, respectively) decreased. Deficits in stimulation of striatal dopamine receptors in MDD could account in part for the failure of transfer of information up the CSPT circuit in the pathophysiology of this disorder.

Levodopa-induced dyskinesia in Parkinson disease: Current and evolving concepts.

Levodopa-induced dyskinesia is a common complication in Parkinson disease. Pathogenic mechanisms include phasic stimulation of dopamine receptors, nonphysiological levodopa-to-dopamine conversion in serotonergic neurons, hyperactivity of corticostriatal glutamatergic transmission, and overstimulation of nicotinic acetylcholine receptors on dopamine-releasing axons. Delay in initiating levodopa is no longer recommended, as dyskinesia development is a function of disease duration rather than cumulative levodopa exposure. We review current and in-development treatments for peak-dose dyskinesia but suggest that improvements in levodopa delivery alone may reduce its future prevalence. Ann Neurol 2018;84:797-811.

Role of Noradrenergic Brain Nuclei in the Regulation of Carotid Artery Blood Flow: Pharmacological Evidence from Anesthetized Pigs with Alpha-2 Adrenergic Receptor Modulator Drugs.

Cerebral hypoperfusion and degeneration of the noradrenergic locus coeruleus (LC) occur early in Alzheimer's disease (AD). Cerebral blood vessels are densely innervated by noradrenergic projections from the LC suggesting a functional role for the regulation of cerebral blood flow (CBF). Experimental LC stimulation, however, has provided no clarity as decreases or increases in CBF were reported from different experimental settings and investigators. To find out with pharmacological methods whether endogenously released norepinephrine (NE) increases or decreases carotid artery blood flow (CABF) in anesthetized pigs by investigating the effect of centrally acting alpha-2 adrenergic drugs, which increase (atipamezole) or decrease (xylazine) NE in the brain. CABF was measured by a Doppler-flow probe placed around the left carotid artery in pentobarbital anesthetized young pigs. Neither current antihypertensive drugs nor pharmacological stimulation of dopamine, histamine, serotonin or acetylcholine receptors changed CABF. The alpha-2 adrenergic-receptor agonist xylazine decreased, while the antagonist atipamezole raised CABF. This rise was abolished by a combined treatment with endothelial NO-synthase inhibitor Nω-Nitro-L-arginine methyl ester (L-NAME) and the non-selective β-receptor antagonist propranolol. Propranolol alone did not decrease CABF in contrast to L-NAME but decreased CABF after L-NAME, surprisingly. Pharmacological evidence suggests that NE released in the brain of anesthetized pigs raises CABF involving β-adrenergic mechanisms and nitric oxide. If in awake humans NE released from the LC had vasodilator effects early LC degeneration could be involved in early cerebral hypoperfusion of AD. Moreover, a cerebral adrenergic vascular innervation deficit, possibly resulting from LC degeneration, and systemic endothelial dysfunction together may act synergistically to reduce CBF.

Long-Term Follow-Up of a Phase I/II Study of ProSavin, a Lentiviral Vector Gene Therapy for Parkinson's Disease

Parkinson's disease is typically treated with oral dopamine replacement therapies. However, long-term use is complicated by motor fluctuations from intermittent stimulation of dopamine receptors and off-target effects. ProSavin, a lentiviral vector based gene therapy that delivers local and continuous dopamine, was previously shown to be well tolerated in a Phase I/II first-in-human study, with significant improvements in motor behavior from baseline at 1 year. Here, patients with Parkinson's disease from the open-label trial were followed up in the long term to assess the safety and efficacy of ProSavin after bilateral injection into the putamen. Fifteen patients who were previously treated with ProSavin have been followed for up to 5 years, with some having been seen for 8 years. Eight patients received deep brain stimulation at different time points, and their subsequent assessments continued to assess safety. Ninety-six drug-related adverse events were reported (87 mild, 6 moderate, 3 severe) of which more than half occurred in the first year. The most common drug-related events were dyskinesias (33 events, 11 patients) and on–off phenomena (22 events, 11 patients). A significant improvement in the defined “off” Unified Parkinson's Disease Rating Scale part III motor scores, compared to baseline, was seen at 2 years (mean score 29 · 2 vs. 38 · 4, n = 14, p < 0.05) and at 4 years in 8/15 patients. ProSavin continued to be safe and well tolerated in patients with Parkinson's disease. Moderate improvements in motor behavior over baseline continued to be reported in the majority of patients who could still be evaluated up to 5 years of follow-up.

Duodenale levodopa and apomorphine infusion for motor complications in advanced Parkinson's disease

Development of motor fluctuations and dyskinesia characterizes the transition from the early to the advanced Parkinson stage. Current oral therapeutic strategies aim at increasing the number of levodopa administrations and extending its benefit by the association of enzyme blockers (MAO- and COMT-inhibitors) and dopamine agonists. However, as disease progresses, mobility becomes progressively dependent on levodopa absorption and plasma bioavailability, resulting in disabling motor complications. If patients continue to experience off time with functional impact on activities of daily living after best oral medication adjustments, implementation of infusion therapies with apomorphine or levodopa, and surgical techniques should be considered. Compared with pulsatile oral therapy implementation of apomorphine and levodopa infusion determines more continuous striatal dopamine receptors stimulation resulting in significant reduction of off-time and dyskinesia, particularly peak-dose. However, long-term experience with these treatments shows that motor complications are not abolished by continuous receptor stimulation suggesting that synaptic plasticity and connectivity changes are not easily reversed once they are established. Early intervention ideally would target patients as soon as motor complications begin rather than at late stage. Preliminary evidence from early deep brain stimulation or early pump treatment suggests that this is feasible but before it is implemented in clinical practice it would require a detailed cost-benefit analysis.

Pharmaceutical interventions for weight-loss maintenance: no effect from cabergoline.

Weight regain is a major limitation to successful weight maintenance following weight loss. Observational studies suggest that stimulation of dopamine receptors in the central nervous system is associated with weight loss and inhibition of weight gain. Our objective was to test the hypothesis that dopamine agonist treatment would prevent weight regain following acute weight loss in individuals with obesity. We conducted a 2-year double blind randomised controlled trial comparing the effect of a dopamine agonist, cabergoline, with placebo on weight regain in obese individuals who had lost at least 5% of their body weight using an 800 kcal/day commercial meal replacement programme. The primary outcome measure was the difference in mean weight between the treatment and control groups over the 2-year period following randomisation. At 24 months, there was no difference in body weight between cabergoline and placebo treatment after adjustment for age, gender and baseline values (0.6 kg (95% CI: -1.5, 2.6), p = 0.58). The mean (±SD) baseline body weight of the randomised participants was 101.8 kg, the mean (±SD) weight loss with the 800 kcal/day diet was 7.1 ± 1.8 kg and the mean (±SD) weight regain at 24 months was 5.1 ± 7.5 kg. There were no significant differences in BMI, percent weight loss, waist circumference, resting energy expenditure, blood pressure or metabolic parameters at 24 months between the two groups. Treatment with the dopamine agonist cabergoline does not prevent weight regain in obese individuals following weight loss.

Apomorphine and levodopa infusion for motor fluctuations and dyskinesia in advanced Parkinson disease.

Development of motor fluctuations and dyskinesia characterizes the transition from early to advanced Parkinson disease stage. Current therapeutic strategies to manage motor complications aim at increasing the number of levodopa administrations and extending its benefit by the association of enzyme blockers and dopamine agonists. However, as disease progresses, mobility becomes progressively dependent on levodopa absorption and its plasma bioavailability, resulting in loss of independence, worse quality of life and increased caregiver burden. If patients continue to experience off-time with functional impact on activities of daily living after best medication adjustments, implementation of infusion with apomorphine or levodopa, and surgical therapies should be considered. Presence of troublesome dyskinesia would also favor the choice of an advanced treatment. Compared with pulsatile oral therapy, both apomorphine and levodopa infusion determine more continuous striatal dopamine receptors stimulation than oral levodopa resulting in significant reduction of off-time and dyskinesia, particularly peak-dose, although not in their complete resolution. This observation proves that abnormal synaptic plasticity and connectivity changes cannot be reversed once they are established. Early implementation of these therapeutic strategies ideally would target patients as soon as motor complications begin rather than at late stage of advanced Parkinson's disease (PD) before dyskinesia have manifested. Preliminary evidence from early deep brain stimulation in patients with short disease duration and modest motor complications suggests that this approach can positively impact quality of life. It is conceivable that changing our PD treatment algorithm and implementing device-aided therapies at the beginning of the advanced phase before dyskinesia has established, will provide more stable motor conditions and longer functional autonomy.

The Intersection of Central Dopamine System and Stroke: Potential Avenues Aiming at Enhancement of Motor Recovery.

Dopamine, a major neurotransmitter, plays a role in a wide range of brain sensorimotor functions. Parkinson's disease and schizophrenia are two major human neuropsychiatric disorders typically associated with dysfunctional dopamine activity levels, which can be alleviated through the druggability of the dopaminergic systems. Meanwhile, several studies suggest that optimal brain dopamine activity levels are also significantly impacted in other serious neurological conditions, notably stroke, but this has yet to be fully appreciated at both basic and clinical research levels. This is of utmost importance as there is a need for better treatments to improve recovery from stroke. Here, we discuss the state of knowledge regarding the modulation of dopaminergic systems following stroke, and the use of dopamine boosting therapies in animal stroke models to improve stroke recovery. Indeed, studies in animals and humans show stroke leads to changes in dopamine functioning. Moreover, evidence from animal stroke models suggests stimulation of dopamine receptors may be a promising therapeutic approach for enhancing motor recovery from stroke. With respect to the latter, we discuss the evidence for several possible receptor-linked mechanisms by which improved motor recovery may be mediated. One avenue of particular promise is the subtype-selective stimulation of dopamine receptors in conjunction with physical therapy. However, results from clinical trials so far have been more mixed due to a number of potential reasons including, targeting of the wrong patient populations and use of drugs which modulate a wide array of receptors. Notwithstanding these issues, it is hoped that future research endeavors will assist in the development of more refined dopaminergic therapeutic approaches to enhance stroke recovery.

Behavioral and neurochemical responses derived from dopaminergic intrastriatal grafts in hemiparkinsonian rats engaged in a novel motor task

BackgroundPutative treatments derived from in vivo stem cell transplant-derived dopamine (DA) in hemiparkinsonian rats have been assessed via DA-agonist-induced rotations involving imbalanced intra-hemispheric striatal DA receptor stimulation. However, such tests obscure the natural responses of grafts to sensory stimuli, and drug-induced plasticity can modify the circuit being tested. Thus, we propose an alternative testing strategy using a novel water tank swimming apparatus. New methodMicrodialysis was used to compare striatal DA levels when rats were: (1) in a rest-phase within a bowl-shaped apparatus, or (2) in an active forced-swim phase within a specially-equipped water tank. Resting-phase DA release levels were compared with active-phase levels obtained while rats were required to swim in the water-tank task. Behavioral variables such as asymmetric circling while swimming (rotations), front-limb strokes, and front-limb reaches were captured by a camera for analysis. Results and comparison with existing methodsTransplanted cells had a very modest effect on percentage of contralateral front-limb strokes, but did not reduce lesion-induced rotational asymmetry in the swim task. Neither striatal DA levels, nor their breakdown products, were significantly different between transplanted and sham-transplanted groups. Our new behavioral test eliminates the need for pharmacological stimulation, enabling simultaneous assessment of DA released in resting and active phases to explore graft control. ConclusionsOur new method allows for accurate assessments of stem cell therapy for PD as an alternative to “rotation” tests. Use of natural motivations to engage in sensory-driven motor tasks provides more accurate insights into ongoing graft-derived behavioral support.

Prolactin and Autoimmunity.

The great asymmetry of autoimmune diseases between genders represents one of the most enigmatic observations among the mosaic of autoimmunity. Sex hormones are believed to play a crucial role on this dimorphism. The higher prevalence of autoimmunity among women at childbearing ages, disease onset/relapses during pregnancy, and post-partum are some of the arguments that support this hypothesis. Certainly, motherhood represents one of the most remarkable challenges for the immune system, which not only has to allow for the conceptus, but also has to deal with complex endocrine alterations. Hormonal homeostasis is known to exert a crucial influence in achieving a competent and healthy immune system. Prolactin (PRL) has a bioactive function acting as a hormone and a cytokine. It interferes with immune system modulation, mainly inhibiting the negative selection of autoreactive B lymphocytes. Likewise, hyperprolactinemia has been described in relation to the pathogenesis and activity of several autoimmune disorders. Dopamine is an effective inhibitor of PRL secretion due to either a direct influence on the hypophysis or stimulation of postsynaptic dopamine receptors in the hypothalamus, arousing the release of the PRL inhibitory factor. Hence, dopamine agonists have proven to offer clinical benefits among autoimmune patients and represent a promising therapy to be explored. In this review, we attempt to provide a critical overview of the link between PRL, autoimmune diseases, and motherhood.

Infralimbic dopamine D2 receptors mediate glucocorticoid-induced facilitation of auditory fear memory extinction in rats

The infralimbic (IL) cortex of the medial prefrontal cortex plays an important role in the extinction of fear memory. Also, it has been showed that both brain glucocorticoid and dopamine receptors are involved in many processes such as fear extinction that drive learning and memory; however, the interaction of these receptors in the IL cortex remains unclear. We examined a putative interaction between the effects of glucocorticoid and dopamine receptors stimulation in the IL cortex on fear memory extinction in an auditory fear conditioning paradigm in male rats. Corticosterone (the endogenous glucocorticoid receptor ligand), or RU38486 (the synthetic glucocorticoid receptor antagonist) microinfusion into the IL cortex 10 min before test 1 attenuated auditory fear expression at tests 1–3, suggesting as an enhancement of fear extinction. The effect of corticosterone, but not RU38486 was counteracted by the dopamine D2 receptor antagonist sulpiride pre-treatment administered into the IL (at a dose that failed to alter freezing behavior on its own). In contrast, intra-IL infusion of the dopamine D1 receptor antagonist SCH23390 pre-treatment failed to alter freezing behavior. These findings provide evidence for the involvement of the IL cortex D2 receptors in CORT-induced facilitation of fear memory extinction.

Clinical Practice Guidelines for management of Sexual Disorders in Elderly.

Clinical Practice Guidelines for management of Sexual Disorders in Elderly.

Neuronal traffic signals in tardive dyskinesia: not enough “stop” in the motor striatum

Tardive dyskinesia is a disturbance in the balance between dopamine receptor stimulation and dopamine receptor blockade in the motor striatum, with hypothetically too much stimulation of supersensitive D2 receptors, resulting in "don't stop" signaling to motor output.

Reduced GO/NOGO ACC-sensitive activity in a case of Parkinson's disease with impulse control disorders

Introduction The incidence of impulse control disorders (ICDs) in Parkinson’s disease is as high as 20%. Dopamine agonists can induce alterations in those frontostriatal networks that manage reward and mediate impulse monitoring and control. Indeed, tonic stimulation of dopamine receptors may damage inhibitory control mechanisms and reward processing, while promoting compulsive repetition of behavior. The neurocognitive approach considers two measurable executive-functions from which ICDs can be detected: 1) response-inhibition, which neural substrate is located in the inferior portion of the prefrontal cortex ; 2) integration of reward/punishment contingencies in individual choices, which neural substrate is located in the orbital-prefrontal cortex. Case description A 51-year-old man with a 12-year story of Parkinson’s disease, presenting motor fluctuations, and stable on 375 mg/day of levodopa was admitted to the hospital for the ascertainment of requirements for DBS surgery (MDS-UPDRS-III OFF=56; Hoehn-Yahr=2). In 2014, the patient developed an impulse-control disorder, including compulsive intake of sugary and high-fat food, and video-games dependence. Grazing behavior and hyper-focus on in-game achievements interfered with the patient’s everyday life. During neuroimaging data acquisition, the subject was asked to perform a response-inhibition ACC-sensitive task in which the subject had to respond to GO stimuli inhibiting the response to infrequent NOGO stimuli. Results and conclusions Examination findings included the following: bilateral bradykinesia and tremor of the upper limbs. The remaining neurological examination was negative. The neuropsychiatric assessment revealed significant levels of anxiety. Although the patient exhibited a normal global cognitive profile, reaching normative scores on the screening tests, abnormalities were detected for the performance on conceptualizing and response-inhibition tasks. The MRI showed no alterations in the brain parenchyma signal. The patient showed no response-inhibition abilities as measured by the GO/NOGO task and action-monitoring deficits (error awareness). Moreover, fMRI acquisition revealed absent task-sensitive recruitment of cingulo-frontal regions for the contrast NOGO vs GO . Take-home message In our experience, fMRI response-inhibition task may be useful in PD for better characterizing the clinical profile evaluating treatment options. A frontostriatal – cingulofrontal dysfunction may reflect impairment in metacognitive-executive abilities (such as response-inhibition, action monitoring and error awareness). Interestingly, impaired response-inhibition is an example of the motor/behavioral aspect of impulse control. Its assessment is supposed to be particularly useful in the PD post-diagnostic phase, to better identify individuals at risk of developing ICDs with dopaminergic medication. Theoretical models will be more effective if they integrate fMRI and neuropsychological data according to a neurocognitive approach to Parkinson's disease and ICDs.

Molecular dynamics of conformation-specific dopamine transporter-inhibitor complexes

The recreational psychostimulant cocaine inhibits dopamine reuptake from the synapse, resulting in excessive stimulation of postsynaptic dopamine receptors in brain areas associated with reward and addiction. Cocaine binds to and stabilizes the outward- (extracellular-) facing conformation of the dopamine transporter (DAT) protein, while the low abuse potential DAT inhibitor benztropine prefers the inward- (cytoplasmic-) facing conformation. A correlation has been previously postulated between psychostimulant abuse potential and preference for the outward-facing DAT conformation. The 3β-aryltropane cocaine analogs LX10 and LX11, however, differ only in stereochemistry and share a preference for the outward-facing DAT, yet are reported to vary widely in abuse potential in an animal model. In search of the molecular basis for DAT conformation preference, complexes of cocaine, benztropine, LX10 or LX11 bound to each DAT conformation were subjected to 100ns of all-atom molecular dynamics simulation. Results were consistent with previous findings from cysteine accessibility assays used to assess an inhibitor’s DAT conformation preference. The respective 2β- and 2α-substituted phenyltropanes of LX10 and LX11 interacted with hydrophobic regions of the DAT S1 binding site that were inaccessible to cocaine. Solvent accessibility measurements also revealed subtle differences in inhibitor positioning within a given DAT conformation. This work serves to advance our understanding of the conformational selectivity of DAT inhibitors and suggests that MD may be useful in antipsychostimulant therapeutic design.

The Blue Lotus Flower (Nymphea caerulea) Resin Used in a New Type of Electronic Cigarette, the Re-Buildable Dripping Atomizer

ABSTRACTThe blue lotus flower (Nymphea caerulea) is an Egyptian water lily containing apomorphine and nuciferine. Apomorphine has been described as a psychoactive alkaloid and is a non-selective dopamine agonist primarily used to treat Parkinson’s disease as it stimulates dopamine receptors and improves motor function. Nuciferine is an alkaloid associated with dopamine receptor blockade. Today, blue lotus flower is used as a sleep aid and anxiety reliever. The rebuildable dripping atomizer (RDA) is an electronic cigarette that allows direct application of an e-liquid onto the coil in the atomizer for aerosolization, compared to a typical electronic cigarette where the e-liquid is wicked from a storage vessel to the coil. Our laboratory received a dark-brown resin material from a concerned parent. The resin had been confiscated from an adolescent who had a reported history of marijuana use. The resin was later identified as blue lotus flower (N. caerulea). This resin, together with four commercially available blue lotus products, was analyzed for content. Apomorphine was detected in two samples, and nuciferine was detected in all five samples. The confiscated resin was determined to contain no apomorphine and 4300 ng/g of nuciferine. The nuciferine resin was shown to aerosolize using aRDA electric cigarette.

Pharmacokinetics of Rytary®, An Extended-Release Capsule Formulation of Carbidopa-Levodopa.

Parkinson’s disease (PD) is a chronic progressive neurological disorder characterized by resting tremor, rigidity, bradykinesia, gait disturbance, and postural instability. Levodopa, the precursor to dopamine, coadministered with carbidopa or benserazide, aromatic amino acid decarboxylase inhibitors, is the most effective and widely used therapeutic agent in the treatment of PD. With continued levodopa treatment, a majority of patients develop motor complications such as dyskinesia and motor ‘on-off’ fluctuations, which are, in part, related to the fluctuations in plasma concentrations of levodopa. A new extended-release (ER) carbidopa–levodopa capsule product (also referred to as IPX066) was developed and approved in the US as Rytary® and in the EU as Numient®. The capsule formulation is designed to provide an initial rapid absorption of levodopa comparable to immediate-release (IR) carbidopa–levodopa, and to subsequently provide stable levodopa concentrations with reduced peak-to-trough excursions in plasma concentrations in order to reduce motor fluctuations associated with pulsatile stimulation of dopamine receptors and to minimize dyskinesia. Phase III studies of this ER carbidopa–levodopa capsule formulation in patients with PD have shown a significant reduction in ‘off’ time compared with IR carbidopa–levodopa and carbidopa–levodopa–entacapone. We present a review of the clinical pharmacokinetics and pharmacodynamics of this ER product of carbidopa–levodopa in healthy subjects and in patients with PD.Electronic supplementary materialThe online version of this article (doi:10.1007/s40262-017-0511-y) contains supplementary material, which is available to authorized users.

Chronic Cocaine Self-Administration Potentiates the Dopamine-Induced Hyperexcitability Gated by Inhibition of KCNQ/Kv7 Channels

Cocaine addiction is a chronic, unremitting brain disorder. In a rodent extinction-reinstatement model of cocaine self-administration (SA), the ability of drug-paired cues to precipitate relapse to drug-seeking requires stimulation of dopamine receptors in the prefrontal cortex (PFC) and activation of glutamatergic transmission in the PFC to the nucleus accumbens core pathway. Here, we tested the hypothesis that spike frequency adaptation (i.e., accommodation) in PFC neurons is regulated via a dopamine-mediated closure of inhibitory voltage-gated potassium channels KCNQ/Kv7 and chronic cocaine-SA causes an enduring overactivation of this mechanism. To investigate this, we prepared brain slices from animals with a history of chronic cocaine-SA, extinction training or cue-reinstatement testing and recorded glutamatergic pyramidal cells (L5) in the current clamp and voltage clamp configurations. At 24-hours after completion of operant training, all sampled cells in tissue from control (yoked-saline and yoked-cocaine) rats displayed accommodation. In contrast, in tissue from cocaine-SA rats at 24-hours after completion of operant training, 84% of cells lacked accommodation. This neuroadaptation was enduring and evident following 14d of extinction (60% cells) or re-exposure to drug predictive cues (75% cells). In similar experiments in slices from transgenic cFos-GFP rats, the adaptation was correlated with induction of cFos. In control (but not cocaine-SA) tissue, bath applied dopamine (10 micromolar) inhibited both accommodation and IKCNQ, with no further reduction in response bath application of the KCNQ channel antagonist XE-991. Furthermore, pharmacological stabilization of KCNQ channels with retigabine restored IKCNQ in slices from cocaine-SA rats and attenuated cue-induced reinstatement when microinjected into the PFC. Thus, dopamine mediated changes in inhibitory KCNQ channels may contribute to PFC hyperexcitability following cocaine-SA.