Christopher A. Lieu

A Water Extract of Mucuna pruriens Provides Long-Term Amelioration of Parkinsonism with Reduced Risk for Dyskinesias

Dopaminergic anti-parkinsonian medications, such as levodopa (LD) cause drug-induced dyskinesias (DID) in majority of patients with Parkinsons disease (PD). Mucuna pruriens, a legume extensively used in Ayurveda to treat PD, is reputed to provide anti-parkinsonian benefits without inducing DID. We compared the behavioral effects of chronic parenteral administration of a water extract of M. pruriens seed powder (MPE) alone without any additives, MPE combined with the peripheral dopa-decarboxylase inhibitor (DDCI) benserazide (MPE+BZ), LD+BZ and LD alone without BZ in the hemiparkinsonian rat model of PD. A battery of behavioral tests assessed by blinded investigators served as outcome measures in these randomized trials. In experiment 1, animals that received LD+BZ or MPE+BZ at high (6mg/kg) and medium (4mg/kg) equivalent doses demonstrated significant alleviation of parkinsonism, but, developed severe dose-dependent DID. LD+BZ at low doses (2mg/kg) did not provide significant alleviation of parkinsonism. In contrast, MPE+BZ at an equivalent low dose significantly ameliorated parkinsonism. In experiment 2, MPE without any additives (12mg/kg and 20mg/kg LD equivalent dose) alleviated parkinsonism with significantly less DID compared to LD+BZ or MPE+BZ. In experiment 3, MPE without additives administered chronically provided long-term anti-parkinsonian benefits without causing DID. In experiment 4, MPE alone provided significantly more behavioral benefit when compared to the equivalent dose of synthetic LD alone without BZ. In experiment 5, MPE alone reduced the severity of DID in animals initially primed with LD+BZ. These findings suggest that M. pruriens contains water-soluble ingredients that either have an intrinsic DDCI-like activity or mitigate the need for an add-on DDCI to ameliorate parkinsonism. These unique long-term anti-parkinsonian effects of a parenterally administered water extract of M. pruriens seed powder may provide a platform for future drug discoveries and novel treatment strategies in PD.

The interhemispheric connections of the striatum: Implications for Parkinson's disease and drug-induced dyskinesias.

Parkinsons disease (PD) is characterized by loss of nigrostriatal neurons and depletion of dopamine. This pathological feature leads to alterations to basal ganglia circuitry and subsequent motor disability. Pharmacological dopamine replacement therapy with medications such as levodopa ameliorates the symptoms of PD but can lead to motor complications known as drug-induced dyskinesias. We have recently shown that clinically hemiparkinsonian rhesus monkeys do not develop levodopa-induced dyskinesias despite chronic intermittent exposure and significant unilateral loss of nigrostriatal neurons and dopamine. It is currently unclear what mechanisms prevent the onset of dyskinesias in these animals. Based on our study and results from previous lesioning studies in both the rat and monkey models of PD, we hypothesize that one potential mechanism that may prevent the genesis of dyskinesias in these animals is interhemispheric neuromodulation. Two potential interhemispheric connections that may modulate dyskinesias are the interhemispheric nigrostriatal and corticostriatal pathways. Few investigators have examined the interhemispheric nigrostriatal and corticostriatal connections and the functional role they may play in drug-induced dyskinesias in PD. Therefore, in the following review, we assess the neuroanatomical, electrophysiological and behavioral properties of these interhemispheric connections. Future studies evaluating these interhemispheric striatal pathways and the pathophysiological changes that occur to these pathways in the dyskinetic state are warranted to further develop treatments that prevent or mitigate drug-induced dyskinesias in PD.

The effects of chronic levodopa treatments on the neuronal firing properties of the subthalamic nucleus and substantia nigra reticulata in hemiparkinsonian rhesus monkeys.

Dopamine replacement therapy with levodopa (LD) is currently the most effective pharmacological treatment for Parkinsons disease (PD), a neurodegenerative disorder characterized by dysfunction of basal ganglia electrophysiology. The effects of chronic LD treatments on the electrophysiological activity of the subthalamic nucleus (STN) and the substantia nigra reticulata (SNR) in parkinsonism are not clear. In the present study we examined the effects of chronic LD treatments on the firing rate and firing pattern of STN and SNR neurons in the stable hemiparkinsonian monkey model of PD. We also evaluated local field potentials of both nuclei before and after LD treatments. In a stable hemiparkinsonian state, STN and SNR had a mean firing rate of 42.6 ± 3.5H z (mean ± SEM) and 52.1 ± 5.7 Hz, respectively. Chronic intermittent LD exposure induced marked amelioration of parkinsonism with no apparent drug-induced motor complications. LD treatments did not significantly change the mean firing rate of STN neurons (41.3 ± 3.3 Hz) or bursting neuronal firing patterns. However, LD treatments induced a significant reduction of the mean firing rates of SNR neurons to 36.2 ± 3.3 Hz (p<0.05) and a trend toward increased burstiness. The entropy of the spike sequences from STN and SNR was unchanged by LD treatment, while there was a shift of spectral power into higher frequency bands in the LFPs. The inability of chronic LD treatments to reduce the bursty firing patterns in the STN and SNR should be further examined as a potential pathophysiological mechanism for PD symptoms that are refractory to LD treatments.

Dyskinesias Do Not Develop after Chronic Intermittent Levodopa Therapy in Clinically Hemiparkinsonian Rhesus Monkeys

The stable 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced hemiparkinsonian (HP) rhesus monkey model of Parkinsons disease (PD) has been frequently used to test preclinical experimental therapeutics targeted to treat patients with advanced PD who suffer from motor fluctuations and drug-induced dyskinesias. We retrospectively analyzed data from 17 stable HP rhesus monkeys treated long-term with chronic intermittent dosing of levodopa (LD) in an attempt to induce choreoathetoid and dystonic dyskinesias. Rhesus monkeys in stable HP state for greater than 6 months as confirmed by multiple blinded behavioral ratings and (18)F-dopa Positron Emission Tomography (PET) were treated with optimal doses of LD to provide maximal amelioration of unilateral clinical parkinsonism without any adverse effects. Thereafter, each animal was given chronic intermittent daily challenge with doses of LD up to 700 mg/day orally or with 300 mg/kg/day parenteral injections. LD treatments failed to induce choreoathetoid and dystonic dyskinesias in these animals despite chronic intermittent high dose administration. These results suggest that the stable strictly unilateral HP rhesus monkey model of PD may not be a suitable animal model to test experimental therapeutics targeted against dyskinesias, and that bilateral parkinsonian rhesus models that readily demonstrate drug-induced dyskinesias and clinically relevant motor fluctuations are more appropriate for preclinical experimental testing of therapies designed to treat patients with advanced PD.

The Antiparkinsonian and Antidyskinetic Mechanisms of Mucuna pruriens in the MPTP-Treated Nonhuman Primate

Chronic treatment with levodopa (LD) in Parkinsons disease (PD) can cause drug induced dyskinesias. Mucuna pruriens endocarp powder (MPEP) contains several compounds including natural LD and has been reported to not cause drug-induced dyskinesias. We evaluated the effects of Mucuna pruriens to determine if its underlying mechanistic actions are exclusively due to LD. We first compared MPEP with and without carbidopa (CD), and LD+CD in hemiparkinsonian (HP) monkeys. Each treatment ameliorated parkinsonism. We then compared the neuronal firing properties of the substantia nigra reticulata (SNR) and subthalamic nucleus (STN) in HP monkeys with MPEP+CD and LD+CD to evaluate basal ganglia circuitry alterations. Both treatments decreased SNR firing rate compared to HP state. However, LD+CD treatments significantly increased SNR bursting firing patterns that were not seen with MPEP+CD treatments. No significant changes were seen in STN firing properties. We then evaluated the effects of a water extract of MPEP. Oral MPWE ameliorated parkinsonism without causing drug-induced dyskinesias. The distinctive neurophysiological findings in the basal ganglia and the ability to ameliorate parkinsonism without causing dyskinesias strongly suggest that Mucuna pruriens acts through a novel mechanism that is different from that of LD.

The effect of striatal dopaminergic grafts on the neuronal activity in the substantia nigra pars reticulata and subthalamic nucleus in hemiparkinsonian rats

The electrophysiological correlates of parkinsonism in the basal ganglia have been well studied in patients with Parkinsons disease and animal models. Separately, striatal dopaminergic cell transplantation has shown promise in ameliorating parkinsonian motor symptoms. However, the effect of dopaminergic grafts on basal ganglia electrophysiology has not thoroughly been investigated. In this study, we transplanted murine foetal ventral mesencephalic cells into rats rendered hemiparkinsonian by 6-hydroxydopamine injection. Three months after transplantation, extracellular and local field potential recordings were taken under urethane anaesthesia from the substantia nigra pars reticulata and subthalamic nucleus along with cortical electroencephalograms and were compared to recordings from normal and hemiparkinsonian controls. Recordings from cortical slow-wave activity and global activation states were analysed separately. Rats with histologically confirmed xenografts showed behavioural improvement measured by counting apomorphine-induced rotations and with the extended body axis test. Firing rates in both nuclei were not significantly different between control and grafted groups. However, burst firing patterns in both nuclei in the slow-wave activity state were significantly reduced (P < 0.05) in rats with large surviving grafts, compared to hemiparkinsonian controls. The neuronal firing entropies and oscillations in both nuclei were restored to normal levels in the large-graft group. Electroencephalogram spike-triggered averages also showed normalization in the slow-wave activity state (P < 0.05). These results suggest that local continuous dopaminergic stimulation exerts a normalizing effect on the downstream parkinsonian basal ganglia firing patterns. This novel finding is relevant to future preclinical and clinical investigations of cell transplantation and the development of next-generation therapies for Parkinsons disease that ameliorate pathophysiological neural activity and provide optimal recovery of function.

Pathophysiology of Drug-Induced Dyskinesias

Christopher A. Lieu1,2, Vikram Shivkumar1, Timothy P. Gilmour1,2, Kala Venkiteswaran1,2, Mark J. Nolt1,3, Milind Deogaonkar4 and Thyagarajan Subramanian1,2 1Department of Neurology, The Pennsylvania State University College of Medicine and M.S. Hershey Medical Center, Hershey, Pennsylvania 2Department of Neural & Behavioral Sciences, The Pennsylvania State University College of Medicine and M.S. Hershey Medical Center, Hershey, Pennsylvania 3Functional Neurosurgical Services, Sentient, Inc., Hunt Valley, Maryland 4Center for Neurological Restoration, The Cleveland Clinic Foundation, Cleveland, Ohio USA

Design and implementation of a quadrature RF volume coil for in-vivo MR brain imaging of rhesus macaque monkey in a stereotaxic head frame

We describe the design and implementation of a unique coil for in-vivo rhesus macaque brain imaging in a stereotaxic device. The RF volume coil consists of a 2 turn solenoid and a saddle coil configured and fed in quadrature. Finite difference time domain method was used to design the coil. Images acquired show excellent homogeneity and SNR throughout the monkeys brain.