Experimental torticollis in the monkey produced by unilateral 6-hydroxy-dopamine brain lesions

Animal models of l-dopa-induced dyskinesia in Parkinson's disease

Understanding the biological mechanisms of l-dopa-induced motor complications is dependent on our ability to investigate these phenomena in animal models of Parkinson's disease. The most common motor complications consist in wearing-off fluctuations and abnormal involuntary movements appearing when plasma levels of l-dopa are high, commonly referred to as peak-dose l-dopa-induced dyskinesia. Parkinsonian models exhibiting these features have been well-characterized in both rodent and nonhuman primate species. The first animal models of peak-dose l-dopa-induced dyskinesia were produced in monkeys lesioned with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and treated chronically with l-dopa to elicit choreic movements and dystonic postures. Seminal studies were performed in these models using both metabolic mapping and electrophysiological techniques, providing fundamental pathophysiological insights that have stood the test of time. A decade later, it was shown possible to reproduce peak-dose l-dopa-induced dyskinesia in rats and mice rendered parkinsonian with nigrostriatal 6-hydroxydopamine lesions. When treated with l-dopa, these animals exhibit abnormal involuntary movements having both hyperkinetic and dystonic components. These models have enabled molecular- and cellular-level investigations into the mechanisms of l-dopa-induced dyskinesia. A flourishing literature using genetically engineered mice is now unraveling the role of specific genes and neural circuits in the development of l-dopa-induced motor complications. Both non-human primate and rodent models of peak-dose l-dopa-induced dyskinesia have excellent construct validity and provide valuable tools for discovering therapeutic targets and evaluating potential treatments. © 2018 International Parkinson and Movement Disorder Society.

The effects of reversible inactivation of the subthalamo-pallidal pathway on the behaviour of naive and hemiparkinsonian monkeys

This study was designed to further investigate the role of the subthalamic nucleus (STN) and globus pallidus internus (GPi) in the pathophysiology of Parkinson's disease. The prevailing theory about the pathophysiology of Parkinson's disease (PD) predicts that there is overactivity of the subthalamo-pallidal pathway. In order to inactivate that pathway, naive and hemiparkinsonian monkeys were locally administered either muscimol (to reversibly inactivate the contralateral STN) or kynurenic acid (to reduce glutamatergic activity in the contralateral GPi). Three naive and 2 hemiparkinsonian monkeys were studied. Intra-carotid MPTP was administered to produce 2 hemiparkinsonian monkeys. Injection sites of muscimol and kynurenic acid in the brain were confirmed electrophysiologically and histologically. Injections of muscimol into the STN in naive and hemiparkinsonian monkeys caused reversible contralateral dystonia, but did not alleviate Parkinsonism. Only one kynurenic acid injection into GPi partially alleviated Parkinsonism. On the basis of the results in this study, aspects of the currently accepted hypothesis of the pathophysiology of PD cannot be confirmed. However, this study reports that the STN has an important role in the production of dystonia. This experimental model of dystonia will prove suitable for further study of both the mechanisms causing dystonia as well as for possible therapeutic approaches to its treatment.

The 3R principle and the use of non-human primates in the study of neurodegenerative diseases: the case of Parkinson's disease

The aim of this paper is to offer an ethical perspective on the use of non-human primates in neurobiological studies, using the Parkinson's disease (PD) as an important case study. We refer, as theoretical framework, to the 3R principle, originally proposed by Russell and Burch [Russell, W.M.S., Burch, R.L., 1959. The Principles of Humane Experimental Technique. Universities Federation for Animal Welfare Wheathampstead, England (reprinted in 1992)]. Then, the use of non-human primates in the study of PD will be discussed in relation to the concepts of Replacement, Reduction, and Refinement. Replacement and Reduction result to be the more problematic concept to be applied, whereas Refinement offers relatively more opportunities of improvement. However, although in some cases the 3R principle shows its applicative limits, its value, as conceptual and inspirational tool remains extremely valuable. It suggests to the researchers a series of questions, both theoretical and methodological, which can have the results of improving the quality of life on the experimental models, the quality of the scientific data, and the public perception from the non-scientist community.

Animal models of focal dystonia

Animal models indicate that the abnormal movements of focal dystonia result from disordered sensorimotor integration. Sensorimotor integration involves a comparison of sensory information resulting from a movement with the sensory information expected from the movement. Unanticipated sensory signals identified by sensorimotor processing serve as signals to modify the ongoing movement or the planning for subsequent movements. Normally, this process is an effective mechanism to modify neural commands for ongoing movement or for movement planning. Animal models of the focal dystonias spasmodic torticollis, writer's cramp, and benign essential blepharospasm reveal different dysfunctions of sensorimotor integration through which dystonia can arise. Animal models of spasmodic torticollis demonstrate that modifications in a variety of regions are capable of creating abnormal head postures. These data indicate that disruption of neural signals in one structure may mutate the activity pattern of other elements of the neural circuits for movement. The animal model of writer's cramp demonstrates the importance of abnormal sensory processing in generating dystonic movements. Animal models of blepharospasm illustrate how disrupting motor adaptation can produce dystonia. Together, these models show mechanisms by which disruptions in sensorimotor integration can create dystonic movements.

Impaired visual function in focal idiopathic dystonia

Visual dysfunctions have previously been reported in Parkinson's disease and Huntington's chorea. To further characterize the pathophysiology of vision in basal ganglion diseases, we studied visual functions in focal dystonic syndromes. Colour discrimination and visual contrast perception were investigated in 37 patients with focal idiopathic dystonia (ID; 20 spasmodic torticollis, 17 blepharospasm) and in age- and sex-matched healthy volunteers using the Farnsworth-Munsell 100-hue test and stationary contrast targets (Vistech plates). The mean total error score as well as the partial scores for the 'red-green' and the 'blue-yellow' axes in the Farnsworth-Munsell 100-hue test of the patients with ID were significantly elevated as compared to controls (spasmodic torticollis mean total error score 90.9 +/- 67.6, controls: 16.6 +/- 10.2; blepharospasm mean total error score 119.4 +/- 78.6, controls: 22.7 +/- 7.9). Additionally, the spatial contrast sensitivity was impaired in patients as compared to controls. The results indicate that the visual system is affected in ID. The visual disorder may be related to an imbalance of certain neurotransmitters in the visual system of patients, e.g. in the catecholaminergic pathways.

Effects of unilateral 6-hydroxydopamine lesions on neuropeptide immunoreactivity in the basal ganglia of the common marmoset, Callithrix jacchus, a quantitative immunohistochemical analysis

Previous immunocytochemical studies in rats have indicated that striatal dopamine depletion leads to an increase in enkephalin-immunoreactivity and a decrease in substance P-immunoreactivity in the striatum. Similar studies in primates have lead to contradictory results. In the present study changes in tyrosine hydroxylase-, met-enkephalin- and substance P-immunoreactivity were determined in the basal ganglia of 6 common marmosets Callithrix jacchus following dopamine depletion by unilateral intracerebral 6-hydroxydopamine (6-OHDA) injections using three different survival times. The non-lesioned side served as an intra-individual control. Tyrosine hydroxylase immunoreactivity was strongly reduced in the entire ipsilateral striatum. Enkephalin-immunoreactivity was increased throughout the striatum. Substance P-immunoreactivity was significantly increased in only one case in the caudate nucleus and in two cases in the putamen, while in other cases either a non-significant increase or decrease was found. Therefore, the results of the present study indicate that in marmosets dopamine has a inhibiting effect on the levels of striatal enkephalin, while its effect on substance P (SP) appears to be absent.

Parkinson's disease-like effects of S-: Effects of l-Dopa

The major symptoms of Parkinson's disease (PD) are due to degeneration of the nigrostriatal pathway and depletion of dopamine (DA). Tyrosine hydroxylase (TH), norepinephrine (NE), serotonin (5-HT), and melanin pigments are also decreased and acetylcholinergic activity increased. Biochemically, increased methylation can cause the depletion of DA, NE, 5-HT, and melanin pigments and also an increase of acetylcholine; thus, increased methylation can present a biochemical picture that resembles the biochemical changes that occur in PD. During the therapy of PD with L-dopa, it is well known that L-dopa reacts avidly with S-adenosyl-L-methionine (SAM), the biologic methyl donor, to produce 3-O-methyl-dopa. Correspondingly, L-dopa has been shown to deplete the concentration of SAM, and SAM has been found to induce PD-like motor impairments in rodents; therefore, an excess of SAM-dependent methylation may be associated with Parkinsonism. To further study the effects of methylation, SAM was injected into the lateral ventricle of rats. SAM caused tremors, rigidity, abnormal posture, and dose-related hypokinesia. Doses of 9.38, 50, and 400 nM/rat caused 61.9, 73.4, and 94.8% reduction, respectively, of motor activity. A 200-mg/kg IP dose of L-dopa, given before 50 nM SAM, blocked the SAM-induced hypokinesia. SAM also caused a decrease in TH immunoreactivity, apparent degeneration of TH-containing fibers, loss of neurons, and the accumulation of phagocytic cells in the substantia nigra. These results showed that excess SAM in the brain, probably due to its ability to increase methylation, can induce symptoms that resemble some of the changes that occur in PD.

Saccadic reaction times, eye-arm coordination and spontaneous eye movements in normal and MPTP-treated monkeys

The oculomotor performance of monkeys was investigated before and after destruction of nigrostriatal dopamine neurons by MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). Stimulus-triggered saccades and their relationships to arm movements were measured in a reaction time task. Spontaneous eye movements were recorded while monkeys sat in a primate chair and looked around the laboratory without performing any task. In the reaction time task, saccades and arm movements were commonly triggered by the rapid, visible and audible opening of a small food-containing box which was located at a constant position in front of the animal at eye level. Median saccadic latencies ranged from 68 to 118 ms in intact animals. Saccades were followed by onset of electromyographic (EMG) activity in the extensor digitorum communis and the biceps brachii, the prime mover muscles for the following arm reaching movement. Latencies of stimulus-triggered saccades showed an absence of linear relationship to EMG or arm movement reaction time in intact animals (correlation coefficients of 0.15-0.56). This suggests that eye and arm movements were initiated independently from each other in this experimental situation. Treatment with MPTP resulted in 98-99.5% loss of striatal dopamine in both monkeys. This induced a 29-93% increase in saccadic latency in the reaction time task. The sequential occurrence of saccade, EMG activity and arm movement in each trial was preserved, although intervals between onset of saccades and onsets of EMGs and arm movements were prolonged by 53-173% and 33-679% respectively. Onsets of individual saccades remained uncorrelated with onsets of EMG activity or arm movement. Spontaneous eye movements were strongly reduced in frequency and amplitude after MPTP. Administration of the dopamine precursor L-Dopa increased spontaneous eye movements for less than two hours. The severe deficits in stimulus-triggered and spontaneous saccadic eye movements are oculomotor components of hypokinesia arising after MPTP-induced lesions of the nigrostriatal dopamine system in primates. The data are further evidence for a role of midbrain dopamine neurons in behavioral responsiveness and spontaneous activity.

Drug-induced dyskinesia in primates rendered hemiparkinsonian by intracarotid administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

The right common carotid artery was surgically exposed under general anaesthesia in 6 cynomolgus monkeys and MPTP (0.5-2.2 mg/kg) directly infused. This produced a hemiparkinsonian syndrome in the contralateral limbs which responded to treatment with both levodopa and apomorphine. These drugs also precipitated dose-dependent contralateral rotation which reached a peak 2 weeks after MPTP infusion. A massive depletion of large, presumably dopaminergic cells was found from the ipsilateral substantia nigra pars compacta. Three animals receiving chronic therapy with apomorphine developed choreoathetoid movements of the limbs and the face contralateral to the infusion 2 weeks after the commencement of treatment. The severity of the dyskinesia gradually increased and after 4 weeks peak-dose hemiballistic movements were seen. Levodopa and the selective D-2 and D-1 dopamine agonists LY-171555 and SKF 38393 also reversed parkinsonian features and produced contralateral rotation and peak-dose dyskinesia. This unilateral model of parkinsonism in the primate will be of value in the elucidation of the mechanisms by which chronic levodopa or dopamine agonist therapy enhance involuntary movements in parkinsonism.

Spasmodic torticollis relieved by removal of a cervical foreign body

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Differential time-course of reaction time recovery depending on variations in the amplitude of a goal-directed movement after nigrostriatal lesion in monkeys

Unilateral striatal dopamine depletion induced by 6-hydroxydopamine injections into the substantia nigra of behaving monkeys was found to increase the latency of a visually guided pointing movement performed by the contralateral forelimb. The time-course of recovery of the movement latency was faster in small displacements of the limb than in movements with larger amplitudes. The efficiency of putative compensatory mechanisms that may develop progressively in response to the striatal dopamine deficit depends on the amplitude of the movement to be initiated.

Recent physiological and pathophysiological aspects of Parkinsonian movement disorders

Deficits in the neural control of limb movements constitute a major part of Parkinsonian symptoms and are linked to a decay of dopaminergic neurotransmission. In animal models, Parkinsonian-like hypokinesia is consistently reproduced with large nigrostriatal dopamine depletions, while tremor and rigidity are less readily obtained. Lesions leading to a less than 70% striatal dopamine depletion are largely compensated by an increased activity of dopamine terminals. With more important lesions, supersensitivity of striatal non-adenylate cyclase-linked dopamine receptors occurs. Electrophysiological studies in Parkinsonian patients demonstrate increased reaction times and a reduced build-up of movement-related muscular activity underlying hypokinesia and provide circumstantial evidence for a central origin of tremor and rigidity. Single cell activity in unlesioned, behaving monkeys shows an increasingly direct relationship to movements when following the neural connections from mid-brain dopamine cells via striatum, globus pallidus, thalamus to pyramidal tract neurons of motor cortex. These data corroborate experimentally the concept that Parkinsonian hypokinesia is due to a failure of basic behavioral activating mechanisms.

Motor impairment after unilateral electrolytic lesions of the substantia nigra in baboons: behavioral data with quantitative and kinematic analysis of a pointing movement

Unilateral electrolytic lesions of the substantia nigra (SN) were carried out stereotaxically on 4 baboons which had been previously trained to perform a visually guided pointing movement. For a few days after operation, all animals exhibited a behavioral impairment affecting the contralateral body half and consisting of dystonic flexed posture and akinesia. The animals were thus unable to perform the pointing task with the contralateral hand. After a delay which depended on the extent of the SN lesion, the animals began to make the pointing movement again. Postoperative changes were then observed only on the side opposite the SN lesion. These consisted of an increase in the latency and particularly the duration of the movement without any change in the accuracy. The kinematic analysis of the hand trajectory showed that the contralateral increase in the movement duration corresponded to a regular decrease in the velocities. Study of the recovery over 120 days after SN lesion showed a progressive improvement which was faster with regard to movement duration than to movement latency. These data clearly point to the functional role of the SN in the initiation and particularly in the execution of movement. Quantitative and kinematic analysis of this pointing movement makes it possible to detect and quantify very closely the changes in movement program and execution induced by a SN lesion. This experimental model will be useful for pharmacological in vivo studies allowing a more specific assessment of the functional role of the neurotransmitters involved in SN dysfunction.

Evaluation of head motility and posture in cats with horizontal torticollis

Unilateral electrolytic lesions and injections of 6-hydroxydopamine (6-OHDA) and 5,7-dihydroxytryptamine (5,7-DHT) were made in structures and pathways linked to the striatopallidal system of cats. The effects of such lesions on horizontal head symmetry and head motility were measured in restrained cats by electrogoniometry. Analysis of electrogoniometric recordings provided (i) an index of head symmetry, (ii) net time-course patterns of head turning in degrees per minute, and (iii) time-course patterns of head motility, measured in number of head movements per minute. All lesions except the electrolytic lesion of the superior colliculus induced an enduring horizontal head asymmetry. Electrolytic, 5,7-DHT, and 6-OHDA lesions made in the medial forebrain bundle induced a nearly total head asymmetry (95 to 98%). Cats in which an electrolytic lesion was made in the substantia nigra reticulata (SNR) also displayed an important head asymmetry (80%). For all lesions except the SNR lesions the direction of the induced head asymmetry was ipsilateral. In 6-OHDA-lesion cats a marked and consistent decrease head motility was also observed. The combined evaluation of head posture and head movements indicated that according to the lesion, head symmetry and head motility are disturbed in different manners. The results further emphasized the complementary contribution of the caudate and SNR in regulation of head symmetry and indicated the advantages of the electrogoniometric method for selectively measuring head posture and movements.

Pathophysiology and pharmacotherapy of spasmodic torticollis: a review

The few existing neuropathological, neurochemical, and neuropharmacological studies have shed little light on the pathophysiology of spasmodic torticollis (ST). The relevance of experimental ST in animals and drug-induced ST in man to idiopathic ST is unclear. Most pharmacotherapeutic endeavors have focused on drugs affecting basal ganglia function. Unfortunately, problems of sample size, clinical heterogeneity of patient population, research design, objective evaluation of response, documentation of key data, and adequacy of duration of follow-up make interpretation of published results difficult. Because of the heterogeneity of ST, investigations aimed at establishing a neurotransmitter profile for each patient by observing the acute response to a test dose of drugs affecting cholinergic, dopaminergic, serotonergic, and gamma-aminobutyric acid systems may provide a more rational basis to the selection of treatment.