Dopaminergic neuronal degeneration and motor impairments following axon terminal lesion by instrastriatal 6-hydroxydopamine in the rat

6-Hydroxydopamine-induced nerve terminal lesion of the nigrostriatal system may provide a partial lesion model of Parkinson's disease useful for the assessment of neuroprotective treatments and behavioral recovery after therapeutic intervention. The aim of the present study was to assess the retrograde degenerative changes in the dopaminergic neurons of the substantia nigra and the associated behavioral and neurochemical consequences of intrastriatal injections of 6-hydroxydopamine in young adult rats. Four groups of rats were stereotaxically injected in the right striatum with graded doses of 6-hydroxydopamine ranging from 0 to 20 mu g. Structural and functional deficits were quantified by tyrosine hydroxylase-immunoreactive nigral cell numbers, striatal dopamine content, skilled paw use, and drug-induced rotation. The results show that striatal 6-hydroxydopamine lesions produce dose-dependent decreases in striatal dopamine levels and tyrosine hydroxylase-immunoreactive cell numbers in the ipsilateral substantia nigra, accompanied by a significant long-lasting atrophy of the remaining dopaminergic neurons. Paw reaching test scores on the side contralateral to the lesion were non-linearly correlated with dopaminergic neuronal cell loss and exhibited a clear symptomatic threshold such that impaired paw use appeared only after >50% loss of nigral dopamine neurons or a reduction of 60-80% of striatal dopamine levels. The behavioral, cellular, and neurochemical effects of the nerve terminal lesion thus bear some resemblance to the early stages of Parkinson's disease, where the severity of motor impairment is correlated with the loss of dopamine in the striatum and dopaminergic neuronal loss in the substantia nigra. Rats with intrastriatal 6-hydroxydopamine lesions thus provide a model of progressive dopamine neuron degeneration useful not only for the exploration of neuroprotective therapeutic intervention but also for the study of mechanisms of functional and structural recovery after subtotal damage of the nigrostriatal dopamine system.     

Effects of repeated administration of l-DOPA and apomorphine on circling behavior and striatal dopamine formation

We tested the circling response to l-DOPA and apomorphine administration in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra. Rats demonstrated a progressively diminished circling response when l-DOPA-carbidopa was repeatedly administered at 120 min intervals. This decreasing response was not present when apomorphine was administered under the same conditions. We also perfused l-DOPA directly into the striatum in vivo of rats with an ipsilateral 6-OHDA nigrotomy at 60 min intervals and monitored striatal dopamine levels with the technique of brain microdialysis. Dopamine formation increased from the first to the fifth trial. This may be secondary to the decrease in uptake sites which accompanies the loss of striatal dopamine nerve terminals. We postulate that the continued presence of dopamine at striatal receptor sites conditions a short-term loss of dopamine receptor sensitivity and a consequent decreased circling response. The observation that desensitization (as measured by decreasing circling) was not present following repeated apomorphine administration may be attributable to its shorter duration of action. We also perfused l-DOPA into the striatum of normal rats and noted a progressive decrease in striatal dopamine levels from the first to the fifth trial. Since this occurred following direct administration of l-DOPA into the striatum, the decrease could not be accounted for by peripheral pharmacodynamics or bioavailability of l-DOPA in the striatum. Since this decrease in dopamine formation was seen only in the normal striatum, its relevance to the diminished behavioral response is unclear.     

Reduction in enkephalin and substance P messenger RNA in the striatum of early grade Huntington's disease: a detailed cellular in situ hybridization study

The expression of enkephalin and substance P messenger RNAs was examined in the caudate-putamen of human post mortem tissue from control and Huntington's disease tissue using in situ hybridization techniques and human specific enkephalin and substance P [35S] oligonucleotides. Macroscopic and microscopic quantification of enkephalin and substance P gene expression was carried out using computer-assisted image analysis. Tissue was collected from six control cases with no sign of neurological disease and six Huntington's disease cases ranging from grades 0 to 3 as determined by neuropathological evaluation. The clinical and pathological diagnosis of Huntington's disease was confirmed unequivocally by genetic analysis of the CAG repeat length in both copies of IT15, the Huntington's disease gene. A marked reduction in both enkephalin and substance P messenger RNAs was detected in all regions of the caudate nucleus and putamen in Huntington's disease grades 2/3 when compared to controls; in the dorsal caudate few enkephalin or substance P messenger RNA-positive cells were detected. For the early grade (0/1) Huntington's disease cases, a heterogeneous reduction in both enkephalin and substance P messenger RNAs were noted; for enkephalin messenger RNA the striatal autoradiograms displayed a conspicuous patchy appearance. Detailed cellular analysis of the dorsal caudate revealed a striking reduction in the number of enkephalin and substance P messenger RNA-positive cells detected and in the intensity of hybridization signal/cell. These data suggest that both the "indirect" GABA/enkephalin and "direct" GABA/substance P pathways are perturbed very early in the course of the disease and that these early changes in chemical signalling may possibly underlie the onset of clinical symptoms.     

Pretreatment with neurokinin substance P but not with cholecystokinin-8S can alleviate functional deficits of partial nigrostriatal 6-hydroxydopamine lesion

The neuropeptide substance P (SP) has been implicated in the control of various neuro-behavioral functions including reinforcement and learning processes. It also exerts neurotrophic and regenerating effects in vitro and in vivo. A previous study indicated a potential therapeutic effect of SP in rats with partial 6-hydroxydopamine lesions of the nigrostriatal dopamine system when SP was administered after the lesion. The purpose of the present study was to determine whether prelesion treatment with SP would also interact with the effects of unilateral 6-hydroxydopamine lesion of the substantia nigra. Thus, SP (50 micrograms/kg) was administered i.p. on 8 consecutive days prior to unilateral lesion of the substantia nigra. Furthermore, we investigated the effects of prelesion treatment with cholecystokinin-8S (CCK; 1 microgram/kg), another neuropeptide, which is closely related to dopaminergic neurons, and which also can have neurotrophic and neuroprotective functions. Our results show that animals with partial neostriatal dopamine depletions (residual dopamine levels of more than 10%) did not show turning asymmetries when pretreated with SP, whereas animals pretreated with vehicle exhibited an initial ipsiversive asymmetry from which they recovered. In contrast, behavioral asymmetries were most pronounced in animals which had been pretreated with CCK. These peptide treatments did not affect the degree of neostriatal dopamine depletion; however, dihydroxyphenylacetic acid/dopamine ratios were enhanced in the neurostriatum of animals with partial dopamine damage after SP- and CCK-pretreatment, and in the ventral striatum of SP-pretreated animals. These data provide evidence that prelesion treatment with SP, but not with CCK, can alleviate functional deficits induced by a partial nigro-striatal dopamine lesion. This effect may be related to enhanced ventral striatal dopamine activity and/or to the peptide's known effects on learning, motivation, and emotion.     

Methamphetamine modulates ACh-evoked currents in Xenopus occytes expressing the rat alpha7 receptors

Growth/differentiation factor 5 (GDF5), a novel member of the transforming growth factor beta superfamily, promotes the survival of dopaminergic neurones in vitro. We present here the first evidence for a neuroprotective action of GDF5 in vivo. We investigated the effects of intracerebral administration of GDF5 on a rat model of Parkinson's disease. GDF5 was administered just above the substantia nigra and into the lateral ventricle immediately before ipsilateral injection of 6-hydroxydopamine into the medial forebrain bundle. GDF5 prevented the development of amphetamine-induced rotations and preserved the integrity of striatal dopaminergic nerve terminals, as measured by positron emission tomography. Post-mortem studies showed that GDF5 spared dopamine levels in the striatum and tyrosine hydroxylase positive neurones in the midbrain. This study suggests that GDF5 has potential for the treatment of Parkinson's disease.     

Behavioral recovery in 6-hydroxydopamine-lesioned rats by cotransduction of striatum with tyrosine hydroxylase and aromatic L-amino acid decarboxylase genes using two separate adeno-associated virus vectors

Parkinson's disease (PD) is characterized by the progressive loss of the dopaminergic neurons in the substantia nigra and a severe decrease in dopamine in the striatum. A promising approach to the gene therapy of PD is intrastriatal expression of enzymes in the biosynthetic pathway for dopamine. Tyrosine hydroxylase (TH) catalyzes the synthesis of L-dopa, which must be converted to dopamine by aromatic L-amino acid decarboxylase (AADC). Since the endogenous AADC activity in the striatum is considered to be low, coexpression of both TH and AADC in the same striatal cells would increase the dopamine production and thereby augment the therapeutic effects. In the present study, the TH gene and also the AADC gene were simultaneously transduced into rat striatal cells, using two separate adeno-associated virus (AAV) vectors, AAV-TH and AAV-AADC. Immunostaining showed that TH and AADC were coexpressed efficiently in the same striatal cells in vitro and in vivo. Moreover, cotransduction with these two AAV vectors resulted in more effective dopamine production and more remarkable behavioral recovery in 6-hydroxydopamine (6-OHDA)-lesioned rats, compared with rats receiving AAV-TH alone (p < 0.01). These findings suggest an alternative strategy for gene therapy of PD and indicate that the simultaneous transduction with two AAV vectors can extend their utility for potential gene therapy applications.     

Glial cell line-derived neurotrophic factor protects striatal calbindin-immunoreactive neurons from excitotoxic damage

The neostriatum is one of the areas with relatively high levels of glial cell line-derived neurotrophic factor (GDNF) messenger RNA expression in the developing and adult brain. GDNF expression in the neostriatum has been suggested to be involved in promoting the survival of nigral dopaminergic neurons, acting as a target-derived neurotrophic factor. However, GDNF messenger RNA expression in the striatum starts several days before dopaminergic and other afferent neurons reach the striatum, suggesting additional trophic effects of this factor on striatal neurons. In the present report, we have examined whether GDNF is able to prevent the degeneration of striatal calbindin- and parvalbumin-immunoreactive neurons in a lesion model of Huntington's disease. Fischer 344 rat 3T3 fibroblast cell line expressing high levels of GDNF (F3A-GDNF) was used to assess the protective effect of this factor, on striatal neurons, against excitotoxicity. Quinolinate (34 nmol) was injected at two different coordinates, and calbindin, parvalbumin and tyrosine hydroxylase immunoreactivity were examined seven days after lesion. Dopaminergic afferents were spared after quinolinate injection, but the number of calbindin- and parvalbumin-immunoreactive neurons was decreased. Interestingly, implantation of F3A-GDNF cells increased the density of tyrosine hydroxylase staining in the intact and also in the quinolinate-lesioned striatum. Furthermore, GDNF partially protected calbindin- but not parvalbumin-immunoreactive neurons from quinolinate excitotoxicity. Instead, mock-transfected fibroblasts did not affect any of these parameters. Our results show that GDNF specifically protects a subpopulation of striatal calbindin-immunoreactive neurons against quinolinate lesion, suggesting that GDNF administration may have a potential therapeutic application in the prevention and treatment of striatonigral degenerative disorders.     

Striatal dopamine-glutamate interactions reflected in substantia nigra reticulata firing

To gain insight into the role of striatal dopamine in basal ganglia functioning, dopaminergic drugs alone and in combination with the glutamate receptor agonist kainic acid were infused in the lateral striatum via a microdialysis probe, while single-unit recordings of substantia nigra reticulata neurons were made in chloral hydrate-anaesthetized rats. Striatal infusion of dopaminergic drugs did not significantly affect the firing rate of substantia nigra reticulata neurons, which was related to the low activity of striatal cells under basal conditions, illustrated by the lack of effect of striatal infusion of TTX on substantia nigra reticulata activity. Under glutamate-stimulated conditions, striatal infusion of d-amphetamine potentiated the inhibition of substantia nigra reticulata neurons induced by striatal kainic acid. Thus, under stimulated but not basal conditions, the modulatory role of dopamine in the striatum could be demonstrated. Dopamine potentiated the inhibitory effect of striatal kainic acid on the firing rate of the basal ganglia output neurons.     

Melatonin protects 6-OHDA-induced neuronal death of nigrostriatal dopaminergic system

In vivo neuroprotective effects of melatonin on the nigrostriatal dopaminergic system in rats unilateral 6-hydroxydopamine (6-OHDA) lesions were tested. Two weeks after lesioning the dopamine receptor agonist, apomorphine produced rotational asymmetry. In contrast, melatonin treatment significantly reduced the motor deficit following apomorphine challenge. Analysis by tyrosine hydroxylase (TH) immunocytochemistry revealed the loss of cell bodies in the substantia nigra (SN) and absence of terminals in the dorsolateral striatum ipsilaterally. Melatonin treatment also resulted in the survival of dopaminergic neurons in SN and TH-immuoreactive terminals in the dorsolateral striatum. These behavioral and histochemical results may indicate a neuroprotective action of melatonin and suggest a potential pharmacological role in the treatment of Parkinson's disease.     

Cytogenetics and molecular genetics in multiple myeloma

The striatum of the human brain has a highly differentiated neurochemical architecture visible in stains for many of the neurotransmitter-related molecules present in the striatum. The distributions for these chemical markers have never been analyzed comprehensively. We compared the distributions of multiple neurochemical markers in a serial-section analysis of the caudate nucleus, the putamen, and the ventral striatum in normal human brains. The cholinergic system was identified with choline acetyltransferase (ChAT). The organization of the cholinergic fiber system was compared with that of striatal systems expressing immunoreactivity for calbindin D28k, met-enkephalin, substance P, tyrosine hydroxylase, and parvalbumin. Each striatal region analyzed displayed a unique neurochemical organization. In the dorsal caudate nucleus, the distribution of all markers followed the classical striosome/matrix organization as previously reported. In the dorsal putamen, ChAT-staining was less intense, and striosomes were delineated primarily by unstained fiber bundles. In the ventral caudate nucleus/nucleus accumbens region, the boundaries of ChAT-stained regions were not always visible with stains for calbindin, enkephalin, and substance P. The ventral putamen displayed a similar organization, except in its lateral part, where ChAT-poor regions were often found adjacent to, rather than in register with, regions expressing low levels of the other markers (calbindin, enkephalin, substance P, and tyrosine hydroxylase). Our findings suggest that, in addition to the classical striosome-matrix organization visible in the dorsal caudate nucleus and putamen, there is further neurochemical differentiation in a large ventral part of the caudate nucleus and putamen and in the ventral striatum-nucleus accumbens proper. The more complex relationships among the different neurochemical systems in the ventral striatum may reflect the increase in size in the primate of striatal regions associated with association and limbic cortex.     

Taurine infused intrastriatally elevates, but intranigrally decreases striatal extracellular dopamine concentration in anaesthetised rats

In the present study we infused taurine (50, 150 or 450 mM, 2 microliters/min for 4h) into the dorsal striatum or into the substantia nigra via microdialysis probe and estimated the extracellular concentrations of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the dorsal striatum of anaesthetised rats. Intrastriatal infusion of taurine elevated striatal dopamine at all concentrations studied. At the 450 mM concentration taurine elevated the extracellular dopamine 10-fold, but only in the first 30 min sample after starting the taurine infusion. At 50 and 150 mM taurine elevated dopamine throughout the 4h infusion maximally up to 3-4-fold the control level. Extracellular DOPAC was increased by 150 and 450 mM taurine (up to about 150-160% of the control level), whereas at all three concentrations taurine decreased HVA to about 85% of the control; however, the decrease caused by 450 mM taurine was short-lasting. At all three concentrations taurine infused into the substantia nigra decreased the extracellular dopamine in the ipsilateral striatum to about 40-50% of the control, and increased extracellular DOPAC and HVA maximally to about 150% and 170% of the control, respectively. These results show that the effects of taurine on the concentrations of extracellular dopamine and its metabolites depend on its administration site on nigrostriatal dopaminergic neurons. It elevates the extracellular dopamine when given into the striatum, but when given into the cell body region of the nigrostriatal dopaminergic pathway it decreases the extracellular dopamine in the ipsilateral striatum.     

Melatonin increases striatal dopaminergic function in 6-OHDA-lesioned rats

The purpose of this study was to assess the in vivo effects of melatonin, as an antioxidant, on striatal dopaminergic function in rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the striatum. Compared with sham-operated controls and expressed as a ratio relative to the contralateral side, there was an increase in the lipid peroxidation product malondialdehyde (MDA, 142%) and a significant reduction in tyrosine hydroxylase (TH) enzyme activity (28%) and dopamine (DA, 32%) and its metabolite dihydroxyphenylacetic acid (DOPAC, 50%) 2 weeks after 6-OHDA injection. Melatonin treatment almost completely restored MDA levels to normal, suggesting the in vivo action of melatonin as an antioxidant. In parallel, partial, but statistically significant recovery of striatal dopaminergic function, including TH enzyme activity and DA levels, also occurred following melatonin treatment. Taken together with our previous reports showing behavioral and histochemical effects of melatonin on the nigrostriatal dopaminergic system, the present results strongly support the hypothesis that melatonin, as an antioxidant, may have beneficial effects on therapeutic approaches for the treatment of oxidative stress-induced neurodegenerative disease such as Parkinson's disease (PD).     

Iron(III) chloride injection increases nigral uric acid in guinea-pig

The present study was carried out to determine if iron chloride (FeCl3) injections into the substantia nigra of guinea-pigs produced changes in nigro-striatal uric acid levels. Two-weeks following unilateral injection of FeCl3 (185 nmol Fe3+), ipsilateral uric acid levels were increased 176% over contralateral levels in the substantia nigra. No effect on striatal uric acid levels was observed. Iron chloride injection produced a 74% depletion of dopamine levels in the ipsilateral striatum. Ipsilateral/contralateral ratios were significantly decreased for striatal dopamine and significantly increased for nigral uric acid when compared with saline-injected controls. The results of this work indicate that FeCl3 injections into the substantia nigra of guinea-pigs produce a significant, localized increase in tissue uric acid levels two weeks after treatment.     

Object-carrying by rats: Disruption by ventral mesencephalic lesions.

In 22 of 30 male Wistar rats, reliable object-carrying was elicited concurrently with self-stimulation in a shuttlebox. Unilateral electrolytic and neurotoxic 6-hydroxydopamine (6-OHDA) lesions in the vicinity of the substantia nigra in 14 of the carrier Ss disrupted object-carrying in postoperative tests. As the 6-OHDA lesions reduced ipsilateral striatal tyrosine hydroxylase levels to less than 5% of the contralateral striatum, this suggests a role for the ascending dopaminergic nigrostriatal bundle in stimulation-induced object-carrying. Shuttlebox self-stimulation was unaffected by either type of lesion, and this result is interpreted as evidence for a dissociation of the neural correlates of self-stimulation and object-carrying. Implications of this finding for S. E. Glickman and D. B. Schiff's (see record 1967-05745-001) biological theory of reinforcement are discussed. Furthermore, the ineffectiveness of substantia nigra lesions on ipsilateral hypothalamic self-stimulation implies that while the dopaminergic nigrostriatal bundle may be subserving some aspects of lateral hypothalamic self-stimulation, the role is by no means an exclusive one. (French summary) (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Localization of serotonin-4 receptors in the striatonigral pathway in rat brain

Rats were injected unilaterally with 6-hydroxydopamine either in the medial forebrain bundle or in the dorsolateral substantia nigra. Another group was injected unilaterally with kainate in the striatum. The loss of neurons was assessed by a reduction in tyrosine hydroxylase-like immunoreactivity for dopaminergic neurons, and choline acetyltransferase-like and glutamate decarboxylase-like immunoreactivities for cholinergic and GABAergic neurons, respectively. Brain sections also were analysed by autoradiography on 20 micron sections with the radio-iodinated serotonin-4 receptor antagonist [125I]SB 207710 [Brown A. M. et al. (1993) Br. J. Pharmac. 110, 10P]. Kainate injections in the striatum resulted in loss of choline acetyltransferase- and glutamate decarboxylase-like immunoreactive cell bodies in this area. There was also a decrease in glutamate decarboxylase-like immunoreactivity on the ipsilateral side in the substantia nigra and entopeduncular nucleus. These changes were accompanied by substantial (> 50%) decreases in [125I]SB 207710 binding in both the ipsilateral striatum (confined to the lesioned area) and substantia nigra, with no change in either the nucleus accumbens or the globus pallidus. There was also significant loss of [125I]SB 207710 binding in the ipsilateral entopeduncular nucleus. 6-Hydroxydopamine lesions placed either in the medial forebrain bundle or in the substantia nigra failed to decrease [125I]SB 207710 binding in any of these areas, although there was total loss of tyrosine hydroxylase-like immunoreactive terminals in the striatum and cell bodies in the nigra. We conclude that serotonin-4 receptors are present on projection neurons, both on their perikarya in the striatum and terminals in the nigra and entopeduncular nucleus. It is likely that these receptors are located on the GABAergic projection neurons and possibly on cholinergic and GABAergic interneurons. However, serotonin-4 receptors are not located on dopaminergic neurons, either on their cell bodies in the substantia nigra or terminals in the striatum.     

Neural dynamics of short and medium-term motor control effects of levodopa therapy in Parkinson's disease

A neural network model of movement control in normal and Parkinson's disease (PD) conditions is proposed to simulate the time-varying dose-response relationship underlying the effects of levodopa on movement amplitude and movement duration in PD patients. Short and long-term dynamics of cell activations and neurotransmitter mechanisms underlying the differential expression of neuropeptide messenger RNA within the basal ganglia striatum are modeled to provide a mechanistic account for the effects of levodopa medication on motor performance (e.g. the pharmacodynamics). Experimental and neural network simulation data suggest that levodopa therapy in Parkinson's disease has differential effects on cell activities, striatal neuropeptides, and motor behavior. In particular, it is shown how dopamine depletion in the striatum may modulate differentially the level of substance P and enkephalin messenger RNA in the direct and indirect basal ganglia pathways. This dissociation in the magnitude and timing of peptide expression causes an imbalance in the opponently organized basal ganglia pathways which results in Parkinsonian motor deficits. The model is validated with experimental data obtained from handwriting movements performed by PD subjects before and after medication intake. The results suggest that fine motor control analysis and network modeling of the effects of dopamine in motor control are useful tools in drug development and in the optimization of pharmacological therapy in PD patients.     

Blockade of tachykinin NK1 receptors by CP-96345 enhances dopamine release and the striatal dopamine effects of methamphetamine in rats

The nonpeptide, tachykinin NK1 receptor antagonist, CP-96345, permits the study of the physiological role of extrapyramidal substance P systems. Using microdialysis, we observed that locally applied CP-96345 (200 nM) caused a significant increase in dopamine release in the striatum as well as substantially enhancing striatal dopamine release caused by a low dose of methamphetamine (0.5 mg/kg s.c.). In addition, multiple systemic administrations of CP-96345 almost doubled the dopamine-mediated responses of the striatal neurotensin and dynorphin systems to high doses of methamphetamine (10 mg/kg/dose s.c.). Our findings suggest that the physiological role of substance P released in the striatum is to decrease the activity of the nigrostriatal dopamine pathway.