Neuropharmacological analysis of the compensatory-recovery processes in deficiency of the generalization function in lobectomized cats

Compensatory-recovery abilities of the cat brain were studied in free behaviour under frontal deficiency by means of parenteral pharmacological influence on dopamin-, cholin- and GABA-ergic systems. Activation of dopaminergic structures in lobectomized cats restored complex forms of generalization, and GABA-ergic system stimulation improved simple forms of generalization. Excitation of cholinergic formations deepened decompensation of generalization function.     

Pharmacoethological analysis of the effects of thyroliberin and melanostatin in a model of anxious-defensive behavior in mice

Psychotropic properties of thyroliberin and melanostatin were studied on the model of timid-defensive behaviour of mice. Oligopeptides increased defensive behaviour and timidity, and decreased intraspecies sociability. GABA deficiency and dopaminergic system blockade increased timid-defensive behaviour of mice. Mobilizing activity of peptides on the agonistic behaviour (aggression and defense) may be explained by their anxiogenic properties.     

Dose-dependent effect of mesenchymal stromal cells co-grafted with dopaminergic neurons in a Parkinson's disease rat model

A major limiting factor for cell therapy in Parkinson's disease is the poor survival and reinnervation capacity of grafted dopaminergic neurons, independently of the cell source. Mesenchymal stromal cells (MSCs) have high capability to regulate the local environment through the release of trophic, antiapoptotic and immunomodulatory factors. In this work, we investigated whether co-grafting of MSCs could improve the survival and reinnervation ability of dopaminergic precursors transplanted in animal models of Parkinson's disease. Rats with total unilateral dopaminergic denervation were grafted with a cell suspension of rat dopaminergic precursors (500,000 cells) with or without a high (200,000 cells) or low (25,000 cells) number of MSCs. Eight weeks after grafting, rats were tested for motor behaviour and sacrificed for histological analysis. Our results showed that the survival of dopaminergic neurons and graft-derived striatal dopaminergic innervation was higher in rats that received co-grafts containing a low number of MSCs than in non-co-grafted controls. However, the survival of dopaminergic neurons and graft-derived dopaminergic reinnervation was lower in rats receiving co-grafts with high number of MSCs than in non-co-grafted controls. In conclusion, co-grafting with MSCs or MSCs-derived products may constitute a useful strategy to improve dopaminergic graft survival and function. However, a tight control of MSCs density or levels of MSCs-derived products is necessary.     

Molecular mechanisms of neurodegeneration in Parkinson's disease: clues from Mendelian syndromes

The recent identification and characterization of gene products responsible for familial forms of Parkinson disease (PD) have provided significant insights into the pathogenesis of PD. Collectively, these studies point towards ubiquitin-proteasome system (UPS) dysfunction as an underlying mechanism responsible for dopaminergic cell death in PD. Emerging evidence further indicates a complex interplay between UPS derangements and other PD pathogenetic factors, all interwoven in an integrated network leading to dopaminergic cell death in PD. Taken together, these findings suggest that neuronal degeneration in PD is a result of a cascade of events, rather than a primary pathogenic event. Here, we review the clues uncovered from various Mendelian-inherited forms of PD that have helped shaped our understanding of the molecular mechanisms underlying PD pathogenesis.     

Identification of human alpha-synuclein specific single chain antibodies

Parkinson's disease (PD) is a common neurodegenerative disease of unknown etiology. Evidence suggests a role for protein misfolding in disease pathogenesis. One pathologic feature observed in dopaminergic neurons is the intracytoplasmic eosinophilic inclusions known as Lewy bodies. One component of Lewy bodies, the presynaptic protein, alpha-synuclein forms oligomers and higher order aggregates and is proposed to be involved in dopaminergic neuronal death. In an effort to discriminate between alpha-synuclein conformational forms as well as design potential disruptors of pathogenic misfolding we panned a human phage antibody library for anti-synuclein single chain antibodies (scFvs). We identified six scFvs which recognize different conformers of alpha-synuclein in both an ELISA and Western blot analysis. These scFvs may further our understanding of alpha-synuclein's role in PD.     

Elimination of the vesicular acetylcholine transporter in the striatum reveals regulation of behaviour by cholinergic-glutamatergic co-transmission

Cholinergic neurons in the striatum are thought to play major regulatory functions in motor behaviour and reward. These neurons express two vesicular transporters that can load either acetylcholine or glutamate into synaptic vesicles. Consequently cholinergic neurons can release both neurotransmitters, making it difficult to discern their individual contributions for the regulation of striatal functions. Here we have dissected the specific roles of acetylcholine release for striatal-dependent behaviour in mice by selective elimination of the vesicular acetylcholine transporter (VAChT) from striatal cholinergic neurons. Analysis of several behavioural parameters indicates that elimination of VAChT had only marginal consequences in striatum-related tasks and did not affect spontaneous locomotion, cocaine-induced hyperactivity, or its reward properties. However, dopaminergic sensitivity of medium spiny neurons (MSN) and the behavioural outputs in response to direct dopaminergic agonists were enhanced, likely due to increased expression/function of dopamine receptors in the striatum. These observations indicate that previous functions attributed to striatal cholinergic neurons in spontaneous locomotor activity and in the rewarding responses to cocaine are mediated by glutamate and not by acetylcholine release. Our experiments demonstrate how one population of neurons can use two distinct neurotransmitters to differentially regulate a given circuitry. The data also raise the possibility of using VAChT as a target to boost dopaminergic function and decrease high striatal cholinergic activity, common neurochemical alterations in individuals affected with Parkinson's disease.     

Taftsin correction of pharmacologically induced behavioral disorders in white rats

Tetrapeptide tuftsin in doses adapted to its physiological blood concentrations partially normalized locomotor activity and orientation behaviour of rats altered by drugs affecting aminergic brain systems. At the same time tuftsin had no effect when applied after the treatment by dopaminergic drugs (DTC, haloperidol, apomorphine). It can be concluded that the central effect observed in the first minutes after tuftsin administration is mediated through dopaminergic system. Elimination of some drug-induced behavioural disturbances by tuftsin opens new prospects for its therapeutic application.     

Mutant alpha-synuclein-induced degeneration is reduced by parkin in a fly model of Parkinson's disease.

Parkinson's disease (PD) patients show a characteristic loss of motor control caused by the degeneration of dopaminergic neurons. Mutations in the genes that encode alpha-synuclein and parkin have been linked to inherited forms of this disease. The parkin protein functions as a ubiquitin ligase that targets proteins for degradation. Expression of isoforms of human alpha-synuclein in the Drosophila melanogaster nervous system forms the basis of an excellent genetic model that recapitulates phenotypic and behavioural features of PD. Using this model, we analysed the effect of parkin co-expression on the climbing ability of aging flies, their life span, and their retinal degeneration. We have determined that co-expression of parkin can suppress phenotypes caused by expression of mutant alpha-synuclein. In the developing eye, parkin reduces retinal degeneration. When co-expressed in the dopaminergic neurons, the ability to climb is extended over time. If conserved in humans, we suggest that upregulation of parkin may prove a method of suppression for PD induced by mutant forms of alpha-synuclein.     

Role of brain dopamine in food reward and reinforcement

The ability of food to establish and maintain response habits and conditioned preferences depends largely on the function of brain dopamine systems. While dopaminergic transmission in the nucleus accumbens appears sufficient for some forms of reward, the role of dopamine in food reward does not appear to be restricted to this region. Dopamine plays an important role in both the ability to energize feeding and to reinforce food-seeking behaviour; the role in energizing feeding is secondary to the prerequisite role in reinforcement. Dopaminergic activation is triggered by the auditory and visual as well as the tactile, olfactory, and gustatory stimuli of foods. While dopamine plays a central role in the feeding and food-seeking of normal animals, some food rewarded learning can be seen in genetically engineered dopamine-deficient mice.     

Effect of selective monoamine oxidase A and B inhibitors on footshock induced aggression in paired rats

Effects of a selective monoamine oxidase (MAO)--A inhibitor, clorgyline, a selective MAO-B inhibitor, deprenyl, and a non-selective MAO inhibitor, nialamide, were investigated on footshock-induced aggression (FIA) in paired rats. The doses and pretreatment times of the inhibitors used were based on an earlier reported in vivo dose-response and time-course study. In addition, apomorphine, a dopaminergic receptor agonist, and beta-phenylethylamine, a preferred substrate for MAO-B, were also used to garner corroborative evidence. The results of the study indicate that selective MAO-A inhibitors are likely to attenuate FIA by augmenting central serotonergic activity, while selective MAO-B inhibitors accentuate the behaviour by facilitating dopaminergic activity. A permissive role for noradrenaline could not be delineated by the available data.     

Steric aspects of dopaminergic drugs.

There are a variety of molecule species of dopamine avaialable at physiological pH. The predominant form available at physiological pH is the phenolic ammonium salt. However, at the present time the molecular form that is optimum for producing dopaminergic activity is unknown. In attempting to delineate the conformational requirements of dopaminergic agonists, a variety of conformationally restricted analogs and complex molecules possessing a dopaminergic segment have been investigated. It appears at this time that the trans extended form of dopamine is the optimum form for binding to dopamine receptors. The rotameric forms of dopamine are also important considerations when examining a molecule for dopaminergic agonist activity. A high degree of stereospecificity has been shown in different dopaminergic systems.     

Development of vacuous chewing movements in rats: role of housing environment

The influence of stressful experiences on the development of vacuous chewing movements (VCM) was investigated in non-medicated rats. After an initial baseline period one group of rats was housed in a noisy environment while another group was housed in quiet surroundings. The development of VCM was recorded during a 16 week period. The animals subjected to uncontrollable noise developed significantly more VCM compared with the control animals. The results are consistent with the idea that stress can sentize a behaviour which is usually connected with the nigrostriatal dopaminergic system. This underscores the essential role of the housing environment as a parameter during behavioural studies of the dopaminergic system, as for example studies of VCM in neuroleptic treated rats.     

Subcellular fractionation of striatum: Sedimentation properties of dopaminergic synaptosomes

Linear sucrose density gradient centrifugation of a crude synaptosomal-mitochondrial preparation of rat striatum was performed at 82, 500g for 7.5, 15 and 30 min and 1, 4 and 20 h. After centrifugation various marker enzyme activities were measured throughout the gradients, viz. tyrosine hydroxylase (TH) and DOPA decarboxylase (DD) as markers of dopaminergic synaptosomes, lactate dehydrogenase (LDH) as a general synaptosomal marker and monoamine oxidase (MAO) as a mitochondrial marker. At all centrifugation times the distribution patterns of TH and DD activity coincided almost perfectly. Notable differences were found between the sedimentation properties of these TH/DD-containing particles and LDH-containing particles: TH and DD were symmetrically distributed in the gradient much sooner than LDH, at all centrifugation times the top of the TH and DD curves was lying deeper in the gradient than the highest LDH activity, and Th and DD became enriched in the gradients to a much greater extent than LDH. It is concluded that rat striatal dopaminergic synaptosomes form a relatively homogenous population of particles sedimenting faster into the gradients than the bulk of striatal synaptosomes does. This distinct sedimentation behaviour of the dopaminergic synaptosomes can be usefully applied for analytical purposes.     

Activation of dopaminergic system stimulates an immune response in mice with opposite type of behaviour

It was shown that activation of dopaminergic (Daergic) system induced an increase of the immune responsiveness independent of the CBA mice behaviour typeanimals without experience of victories and defeats (control), with aggression and submission. Administration of SKF-38393, a selective agonist of DA D1-receptors, resulted in enhanced immune response as tested by plaque-forming cells and rosette-forming cells number. Similar immunostimulation was observed after injection of p-chlorophenylalanine realizing its influence on the immune response through DA D2-receptors as shown by us elsewhere. It was suggested that activation of Da-ergic system produces a new neurochemical pattern (Daergic neurochemical set) which are responsible for character and intensity changes of the immune response in mice with alternative form of social behaviour.     

Catecholamines,nitrogen oxide,and resistivity to stressor lesions: effect of adaptation to hypoxia

Pronouncement of stress-induced disturbance of searching behaviour (using "open field" test) and stomach ulceration were compared for the first time with activity of the catecholamine system in hypothalamus and striatum and also with activity of the stress-limiting system of nitric oxide (NO) in the rats of two strains August and Wistar, which differ in their resistance against stress-induced cardiovascular disorders. The effect of prior adaptation to hypobaric hypoxia on these disorders was also studied. August rats appeared to be more resistant than Wistar rats against stress-induced disturbance of the searching behaviour and stomach ulceration. Results of measuring the content of catecholamines in brain structures and the content of NO stable metabolites nitrate/nitrite in plasma suggested that these differences could be due to the stress activation of the nigro-striatal dopaminergic system in August rats, which was not observed in Wistar rats, and also to the higher production of NO in August than in Wistar rats. Adaptation to hypoxia considerably restricted these stress disorders in rats of both strains. Importantly, the protective effects were associated with activation of the nigro-striatal dopaminergic system in all the animals. In the result, adapted Wistar rats, as distinct from non-adapted Wistar rats, displayed a stress activation of this system. The protective effects of adaptation were also accompanied by an increased NO synthesis. Taken together, the data suggest an important role of the responsiveness of the brain dopaminergic system and NO system in the mechanism of resistance against stress-induced disturbances.     

"Passive stabilization" of striatal extracellular dopamine across the lesion spectrum encompassing the presymptomatic phase of Parkinson's disease: a voltammetric study in the 6-OHDA-lesioned rat

Symptoms of Parkinson's disease do not present until the degeneration of nigrostriatal dopaminergic neurons is nearly complete. Maintenance of dopaminergic tone governing striatal efferents is postulated to preserve motor control during the presymptomatic phase, but the neuroadaptation responsible for normalization is not completely understood. In particular, the prevailing view that surviving dopaminergic neurons compensate by up-regulating release has been difficult to demonstrate directly. Here we investigate dopaminergic neurotransmission in the hemiparkinsonian rat using fast-scan cyclic voltammetry at carbon-fiber microelectrodes. Electrical stimulation was used to elicit extracellular dopamine levels mimicking the steady-state dynamics of tonic dopaminergic signaling. In agreement with microdialysis studies, evoked steady-state dopamine levels remained constant over the entire lesion spectrum (0 to approximately 85%) observed during the presymptomatic stage. Kinetic analysis of the voltammetric recordings demonstrated that evoked dopamine concentrations were normalized without plasticity of dopamine release and uptake, suggesting that the primary mechanisms controlling ambient levels of extracellular dopamine were not actively altered. In the present study, we formalize this neuroadaptation as "passive stabilization" . We further propose that passive stabilization is mediated by the simple physical principles of diffusion and steady state, is predicated on extrasynaptic transmission, and forms the basis for a new compensation model of preclinical parkinsonism.     

Mutant PINK1 upregulates tyrosine hydroxylase and dopamine levels,leading to vulnerability of dopaminergic neurons

PINK1 mutations cause autosomal recessive forms of Parkinson disease (PD). Previous studies suggest that the neuroprotective function of wild-type (WT) PINK1 is related to mitochondrial homeostasis. PINK1 can also localize to the cytosol; however, the cytosolic function of PINK1 has not been fully elucidated. In this study we demonstrate that the extramitochondrial PINK1 can regulate tyrosine hydroxylase (TH) expression and dopamine (DA) content in dopaminergic neurons in a PINK1 kinase activity-dependent manner. We demonstrate that overexpression of full-length (FL) WT PINK1 can downregulate TH expression and DA content in dopaminergic neurons. In contrast, overexpression of PD-linked G309D, A339T, and E231G PINK1 mutations upregulates TH and DA levels in dopaminergic neurons and increases their vulnerability to oxidative stress. Furthermore transfection of FL WT PINK1 or PINK1 fragments with the PINK1 kinase domain can inhibit TH expression, whereas kinase-dead (KD) FL PINK1 or KD PINK1 fragments upregulate TH level. Our findings highlight a potential novel function of extramitochondrial PINK1 in dopaminergic neurons. Deregulation of these functions of PINK1 may contribute to PINK1 mutation-induced dopaminergic neuron degeneration. However, deleterious effects caused by PINK1 mutations may be alleviated by iron-chelating agents and antioxidant agents with DA quinone-conjugating capacity.     

The effect of phenamine on the avoidance reaction in intact and striatectomized rats]

Various characteristics of a conditioned avoidance reaction were recorded in rats in a Y-maze. Small doses of d,l-amphetamine (0.5 mg/kg) facilitated avoidance response while large ones (5 mg/kg) worsened it. After ablation of the rostral part of the striatum, small doses of the drug had the same effect as before, but no deteriorating action of large doses was observed. The behaviour disturbance is related to the capacity of d,l-amphetamine for activating the nigro-striatal dopaminergic transmission.     

Influence of Dopaminergically Mediated Reward on Somatosensory Decision-Making

Reward-related dopaminergic influences on learning and overt behaviour are well established, but any influence on sensory decision-making is largely unknown. We used functional magnetic resonance imaging (fMRI) while participants judged electric somatosensory stimuli on one hand or other, before being rewarded for correct performance at trial end via a visual signal, at one of four anticipated financial levels. Prior to the procedure, participants received either placebo (saline), a dopamine agonist (levodopa), or an antagonist (haloperidol). Principal findings: higher anticipated reward improved tactile decisions. Visually signalled reward reactivated primary somatosensory cortex for the judged hand, more strongly for higher reward. After receiving a higher reward on one trial, somatosensory activations and decisions were enhanced on the next trial. These behavioural and neural effects were all enhanced by levodopa and attenuated by haloperidol, indicating dopaminergic dependency. Dopaminergic reward-related influences extend even to early somatosensory cortex and sensory decision-making.     

Molecular mechanisms of selective dopaminergic neuronal death in Parkinson's disease

Parkinson's disease (PD) is a progressive neurological disease caused by selective degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc). Although PD has been heavily researched, the precise etiology of nigral cell loss is still unknown and, consequently, treatment is largely symptomatic rather than preventive. There are conflicting data regarding the mode of dopaminergic cell death in PD and, hence, this remains controversial. Several mutations in specific genes have recently been linked with hereditary forms of PD. Although none of these mutations are seen in idiopathic disease cases, the elucidation of these genetic defects sheds light on the nature of idiopathic PD. It is possible that dopaminergic neurogenesis also contributes to the etiology of idiopathic PD. In addition, intracellular as well as extracellular substances found in the SNc are believed to function as damaging pathogenetic factors. These factors, and the interactions among them, might hold the secret to the underlying causes of the selective death of dopaminergic neurons in PD.