Mesencephalic dopamine neurons interfacing the shell of nucleus accumbens and the dorsolateral striatum in the rat

Parallel corticostriatonigral circuits have been proposed that separately process motor, cognitive, and emotional‐motivational information. Functional integration requires that interactions exist between neurons participating in these circuits. This makes it imperative to study the complex anatomical substrate underlying corticostriatonigral circuits. It has previously been proposed that dopaminergic neurons in the ventral mesencephalon may play a role in this circuit interaction. Therefore, we studied in rats convergence of basal ganglia circuits by depositing an anterograde neuroanatomical tracer into the ventral striatum together with a retrograde fluorescent tracer ipsilaterally in the dorsolateral striatum. In the mesencephalon, using confocal microscopy, we looked for possible appositions of anterogradely labeled fibers and retrogradely labeled neurons, “enhancing” the latter via intracellular injection of Lucifer Yellow. Tyrosine hydroxylase (TH) immunofluorescence served to identify dopaminergic neurons. In neurophysiological experiments, we combined orthodromic stimulation in the medial ventral striatum with recording from ventral mesencephalic neurons characterized by antidromic stimulation from the dorsal striatum. We observed terminal fields of anterogradely labeled fibers that overlap populations of retrogradely labeled nigrostriatal cell bodies in the substantia nigra pars compacta and lateral ventral tegmental area (VTA), with numerous close appositions between boutons of anterogradely labeled fibers and nigrostriatal, TH‐immunopositive neurons. Neurophysiological stimulation in the medial ventral striatum caused inhibition of dopaminergic nigrostriatal neurons projecting to the ventrolateral striatal territory. Responding nigrostriatal neurons were located in the medial substantia nigra and adjacent VTA. Our results strongly suggest a functional link between ventromedial, emotional‐motivational striatum, and the sensorimotor dorsal striatum via dopaminergic nigrostriatal neurons.     

Selective subregional dopamine depletions in the rat caudate-putamen following nigrostriatal lesions.

Previous work has demonstrated a complex neurochemical and neuroanatomical heterogeneity of the striatum in normal brains. The present research investigated whether the heterogeneous distribution of dopamine would be altered following unilateral injections of the neurotoxin 6-hydroxydopamine into the substantia nigra of the rat. Four weeks following injection, the nucleus accumbens and subregions of the caudate-putamen and substantia nigra were dissected and analyzed by HPLC with electrochemical detection for dopamine, 5-hydroxytryptamine, and their respective metabolites. Levels of dopamine and its metabolites in the anterodorsolateral caudate-putamen were depleted more than medial, posterior, and ventral, striatal areas in partially lesioned animals (less than 90% dopamine depletion). This resulted in an alteration of striatal heterogeneity such that a mediolateral gradient of dopamine tissue content was now superimposed on the normal rostrocaudal gradient observed in controls. Paralleling these findings, dopamine was more depleted in the lateral, as opposed to the medial, substantia nigra. These results indicate that the nigrostriatal dopamine system degenerates in a heterogeneous fashion following 6-hydroxydopamine administration. It is speculated that the differential loss of dopamine neurons observed in the nigra of Parkinson's patients may be due to a differential sensitivity to toxins within the nigra.     

Differential regulation of glutamic acid decarboxylase mRNA and tyrosine hydroxylase mRNA expression in the aged manganese-treated rats

Recent studies have implicated chronic elevated exposures to environmental agents, such as metals (e.g. manganese, Mn) and pesticides, as contributors to neurological disease. Eighteen-month-old rats received intraperitoneal injections of manganese chloride (6 mg Mn/kg/day) or equal volume of saline for 30 days in order to study the effect of manganese on the dopamine- and GABA-neurons. The structures studied were substantia nigra, striatum, ventral tegmental area, nucleus accumbens and globus pallidus. First, we studied the enzymatic activity of mitochondrial complex II succinate dehydrogenase (SDH). We found an overall decrease of SDH in the different brain areas analyzed. We then studied the mRNA levels for tyrosine hydroxylase (TH) and the dopamine transporter (DAT) by in situ hybridization. TH mRNA but not DAT mRNA was significantly induced in substantia nigra and ventral tegmental area following Mn treatment. Correspondingly, TH immunoreactivity was increased in substantia nigra and ventral tegmental area. Manganese treatment significantly decreased GAD mRNA levels in individual GABAergic neurons in globus pallidus but not in striatum. We also quantified the density of glial fibrillary acidic protein (GFAP)-labeled astrocytes and OX-42 positive cells. Reactive gliosis in response to Mn treatment occurred only in striatum and substantia nigra and the morphology of the astrocytes was different than in control animals. These results suggest that the nigrostriatal system could be specifically damaged by manganese toxicity. Thus, changes produced by manganese treatment on 18-month-old rats could play a role in the etiology of Parkinson's disease.     

Dopamine and norepinephrine levels in the nucleus accumbens, olfactory tubercle and corpus striatum following lesions in the ventral tegmentalarea.

Dopamine and norepinephrine levels were examined in 3 forebrain regions following unilateral lesions either in the ventral medial tegmental area (VMT) or in the substantia nigra. The dopamine and norepinephrine content of the nucleus accumbens, olfactory tubercle and corpus striatum were assayed ipsilaterally and contralaterally in unilaterally lesioned rats sacrificed 2, 5, 10, and 20 days after the placement of the lesions. In the nucleus accumbens and olfactory tubercle ipsilateral dopamine levels were significantly reduced below the contralateral levels at 2 days, and were decreased by 56% and 65%, respectively, 10 days after the lesion. A 30% reduction of dopamine levels occurred in corpus striatum as well, following lesions in the VMT. Lesions in the substantia nigra decreased ipsilateral dopamine levels by 68% in the corpus striatum, without affecting dopamine levels in the olfactory tubercle or nucleus accumbens. Norepinephrine levels on the side ipsilateral to the lesion did not significantly differ from contralateral levels in any of the 3 regions following lesions either in the VMT or in the substantia nigra. These results demonstrate the specificity of projection in the mesolimbic dopamine system as suggested by the original histofluorescence studies.     

Interrelationship of the distribution of neuropeptides and tyrosine hydroxylase immunoreactivity in the human substantia Nigra

The relationship in the human substantia nigra of peptidergic fibers with intrinsic dopaminergic neurons was studied in adjacent coronal sections of the mesencephalon immunohistochemically stained for enkephalin (ENK), substance P (SP), and tyrosine (TH) hydroxylase immunoreactivity. TH-positive elements are present in the substantia nigra in at least two different arrangements: 1) a dorsal tier of rather loosely arranged neurons, which is continuous medially with the ventral tegmental area and laterally with the retrorubral area, 2) a ventral tier of more closely packed neurons, clusters of which frequently form finger-like extensions deep into the pars reticulata. This ventral region contains TH-positive dendrites extending ventrally into the pars reticulata. The distribution of ENK is mainly restricted to the medial half of the ventral aspect of the substantia nigra, while SP occupies its entire rostral-caudal and medial-lateral extents. Peptide-positive fibers vary in density from dense to light. There is very little overlap between the dorsal tier of the TH-positive neurons and the ENK or SP staining. The dorsal part of the peptide-immunoreactive area extensively overlaps with the TH-positive neurons of the ventral tier of cells. The ventral part of the peptide-positive area overlaps with the pars reticulata of the substantia nigra in which the TH-positive dendrites extend. The overlap between the neuropeptide fibers and the TH-positive cells of the ventral tier is not complete, with cells found both within and outside peptide-positive fiber networks. Three patterns of overlap emerge. In dorsal regions elongated cell clusters lie partially within and partially outside the dense peptide-positive fiber networks. In the ventral regions TH-positive cells are either completely embedded within peptide fibers or clusters of cells are present in peptide-free zones. These data suggest that specific peptidergic pathways differentially innervate the substantia nigra. TH cells which lie within or outside these fibers may reflect functionally different subsystems in the striatonigral pathways in the human.     

Autoradiographic evidence for nicotine receptors on nigrostriatal and mesolimbic dopaminergic neurons

Rats received unilateral injections of 6-hydroxydopamine into the medial forebrain bundle, resulting in an ipsilateral loss of striatal dopamine and of dopaminergic perikarya. A concimitant reduction of displaceable tritiated nicotine binding was observed autoradiographically in the ipsilateral substantia nigra, ventral tegmental area, striatum, nucleus accumbens, and olfactory tubercle. Thus, nicotine receptors appear to be located on nigrostriatal and mesolimbic dopaminergic neurons at the level of perikarya and terminals.     

Neurotrophic effects of bone morphogenetic protein-7 in a rat model of Parkinson's disease

Previous studies have demonstrated that pretreatment with bone morphogenetic protein-7 (BMP7) reduces ischemic neuronal injury in vivo. Moreover, exogenous application of BMP7 increases both the number of tyrosine hydroxylase (+) cells and dopamine (DA) uptake in rat mesencephalic cell cultures. The purpose of this study was to investigate the in vivo effects of BMP7 on 6-hydroxydopamine (6-OHDA) induced lesioning of midbrain DA neurons. Adult Fischer 344 rats were anesthetized and injected with BMP7 or vehicle into the left substantia nigra, followed by local administration of 9 microg of 6-OHDA into the left medial forebrain bundle. The lesioned animals that received BMP7 pretreatment, as compared to vehicle/6-OHDA controls, had a significant reduction in methamphetamine-induced rotation 1 month after the surgery. BMP7-pretreatment partially preserved KCl-induced dopamine release in the lesioned striatum and significantly increased TH immunoreactivity in the lesioned nigra and striatum. In summary, our data suggest that BMP7 has neuroprotective and/or neuroreparative effects against 6-OHDA lesioning of the nigrostriatal DA pathway in an animal model of Parkinson's disease (PD).     

Anatomical and functional reconstruction of the nigrostriatal pathway by intranigral transplants

The main transplantation strategy in Parkinson's disease has been to place dopaminergic grafts not in their ontogenic site, the substantia nigra, but in their target area, the striatum with contrasting results. Here we have used green fluorescent protein transgenic mouse embryos as donors of ventral mesencephalic cells for transplantation into the pre-lesioned substantia nigra of an adult wild-type host. This allows distinguishing the transplanted cells and their projections from those of the host. Grafted cells integrated within the host mesencephalon and expressed the dopaminergic markers tyrosine hydroxylase, vesicular monoamine transporter 2 and dopamine transporter. Most of the dopaminergic cells within the transplant expressed the substantia nigra marker Girk2 while a lesser proportion expressed the ventral tegmental area marker calbindin. Mesencephalic transplants developed projections through the medial forebrain bundle to the striatum, increased striatal dopamine levels and restored normal behavior. Interestingly, only mesencephalic transplants were able to restore the nigrostriatal projections as dopamine neurons originating from embryonic olfactory bulb transplants send projections only in the close vicinity of the transplantation site that did not reach the striatum. Our results show for the first time the ability of intranigral foetal dopaminergic neurons grafts to restore the damaged nigrostriatal pathway in adult mice. Together with our previous findings of efficient embryonic transplantation within the pre-lesioned adult motor cortex, these results demonstrate that the adult brain is permissive to specific and long distance axonal growth. They further open new avenues in cell transplantation therapies applied for the treatment of neurodegenerative disorders such as Parkinson's disease.     

Patterns of cell and fiber vulnerability in the mesostriatal system of the mutant mouse weaver. I. Gradients and compartments.

In mice carrying the autosomal recessive gene weaver, there is a massive postnatal loss of dopamine in the caudoputamen, the target of the nigrostriatal system, with relative (though not complete) preservation of dopamine in the ventral striatum, a target of the mesolimbic system. There is concomitant death of catecholaminergic neurons in the substantia nigra, with much less cell death in the limbic midbrain area. In the study reported here, we have reexamined the mesostriatal system of weaver mice by means of tyrosine hydroxylase (TH) immunohistochemistry in order to determine the local architecture of the defect within the striatum and substantia nigra. For the dorsal striatum, the most striking finding was the appearance in the weaver caudoputamen of small pockets of especially weak immunostaining within a larger dorsal zone of generally reduced TH-positive neuropil. These pockets were identified as striosomes by calbindin28k and met-enkephalin immunohistochemistry carried out on adjacent sections. In dorsal, central, and caudal sectors of the caudoputamen, there was also more generalized depletion of TH-immunoreactive neuropil. In the mid-brains of the mutants, the patterns of loss of TH-positive neurons appeared to correspond to these distributions of reduced immunostaining in the striatum. In the substantia nigra pars compacta, ventrally situated TH-positive neurons were especially affected, suggesting preferential depletion of TH-positive neurons projecting to striosomes. In addition, there was a central sector of nearly complete loss of TH-positive neurons in the substantia nigra para compacta and a marked depletion of TH-positive neurons in cell group A8 that, together, may have accounted for the diminution of TH-positive innervation of the striatal matrix. We conclude that the effects of the weaver gene discriminate among mesostriatal subsystems not only according to the regional affiliations of these subsystems within the dorsal and ventral striatum, but also according to the preferential association of the subsystems for the striosomal and matrical compartments of the caudoputamen. The depletion of TH-positive innervation was not confined to the dorsal striatum proper. The defect extended into the adjoining nucleus accumbens, where it appeared to affect the lateral "core" division, and included also a lateral part of the olfactory tubercle. Thus, as in the dorsal striatum, the defect in the TH-positive innervation of the ventral striatum closely follows the local architecture of this striatal region. Neuronal loss in the ventral tegmental area was not evident on qualitative analysis, but at the border between lateral cell group A 10 and medial cell group A9 there was obvious loss of immunostained neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Gene therapy of Parkinson's disease using adeno-associated virus (AAV) 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 dopamine-synthesizing enzymes [tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC)]. The most appropriate gene-delivery vehicles for neurons are adeno-associated virus (AAV) vectors, which are derived from non-pathogenic virus. Therefore, TH and AADC genes were introduced into the striatum in the lesioned side using separate AAV vectors in parkinsonian rats, and the coexpression of TH and AADC resulted in better behavioral recovery compared with TH alone. Another strategy for gene therapy of PD is the protection of dopaminergic neurons in the substantia nigra using an AAV vector containing a glial cell line-derived neurotrophic factor (GDNF) gene. Combination of dopamine-supplement gene therapy and GDNF gene therapy would be a logical approach to the treatment of PD.     

Effect of intrastriatal 6-OHDA lesion on dopaminergic innervation of the rat cortex and globus pallidus

The present study examined in the rat the effect of a partial lesion of the nigrostriatal dopaminergic pathway induced by intrastriatal injection of 6-hydroxydopamine (6-OHDA), on the dopaminergic innervation of the cortex and the globus pallidus as revealed using tyrosine hydroxylase (TH) immunoreactivity. Twenty-eight days after unilateral injection of 6-OHDA into the dorsal part of the striatum, TH-positive fiber density was reduced by 41% in the dorsal and central part of the structure, and was accompanied by a retrograde loss of 33% of TH-positive neurons in the substantia nigra (SN), while the ventral tegmental area was completely spared. In the SN, TH-positive cell loss was most severe in the ventral part of the structure (-55%). In the same animals, a substantial loss of TH-positive fibers was evident in the dorsal part of the globus pallidus, and involved both thick fibers of passage and thin varicose terminal axonal branches. In the cortex, a loss of TH-positive fibers was prominent in the cingulate area, moderate in the motor area and less affected in the insular area, while the noradrenergic innervation revealed using dopamine-beta-hydroxylase immunoreactivity was preserved in all of these cortical subregions. These results demonstrate that the intrastriatal 6-OHDA lesion model in rats produces a significant loss of dopaminergic axons in extrastriatal structures including the pallidum and cortex, which may contribute to functional sequelae in this animal model of Parkinson's disease.     

Chronic levodopa is not toxic for remaining dopamine neurons,but instead promotes their recovery,in rats with moderate nigrostriatal lesions

Orally administered levodopa remains the most effective symptomatic treatment for Parkinson's disease (PD). The introduction of levodopa therapy is often delayed, however, because of the fear that it might be toxic for the remaining dopaminergic neurons and, thus, accelerate the deterioration of patients. However, in vivo evidence of levodopa toxicity is scarce. We have evaluated the effects of a 6-month oral levodoapa treatment on several dopaminergic markers, in rats with moderate or severe 6-hydroxydopamine-induced lesions of mesencephalic dopamine neurons and sham-lesioned animals. Counts of tyrosine hydroxylase (TH)-immunoreactive neurons in the substantia nigra and ventral tegmental area showed no significant difference between levodopa-treated and vehicle-treated rats. In addition, for rats of the sham-lesioned and severely lesioned groups, immunoradiolabeling for TH, the dopamine transporter (DAT), and the vesicular monoamine transporter (VMAT2) at the striatal level was not significantly defferent between rats treated with levodopa or vehicle. It was unexpected that quantification of immunoautoradiograms showed a partial recovery of all three dopaminergic markers (TH, DAT, and VMAT2) in the denervated territories of the striatum of moderately lesioned rats receiving levodopa. Furthermore, the density of TH-positive fibers observed in moderately lesioned rats was higher in those treated chronically with levodopa than in those receiving vehicle. Last, that chronic levodopa administration reversed the up-regulation of D2 dopamine receptors seen in severely lesioned rats provided evidence that levodopa reached a biologically active concentration at the basal ganglia. Our results demonstrate that a pharmacologically effective 6-month oral levodopa treatment is not toxic for remaining dopamine neurons in a rat model of PD but instead promotes the recovery of striatal innervation in rats with partial lesions.     

Topographic organization of the ventral striatal efferent projections in the rhesus monkey: An anterograde tracing study

The ventral striatum is considered to be that portion of the striatum associated with the limbic system by virtue of its afferent connections from allocortical and mesolimbic areas as well as from the amygdala. The efferent projections from this striatal region in the primate were traced by using 3H aminoacids and Phaseolus vulgaris-leucoagglutinin (PHA-L). Particular attention was paid to the topographic organization of terminal fields in the globus pallidus and substantia nigra, the projections to non-extrapyramidal areas, the relationship between projections from the nucleus accumbens and the other parts of the ventral striatum, and the comparison between ventral and dorsal striatal projections. This study demonstrates that in monkeys a circumscribed region of the globus pallidus receives topographically organized efferent fibers from the ventral striatum. The ventral striatal fibers terminate in the ventral pallidum, the subcommissural part of the globus pallidus, the rostral pole of the external segment, and the rostromedial portion of the internal segment. The more central and caudal portions of the globus pallidus do not receive this input. This striatal output appears to remain segregated from the dorsal striatal efferent projections to pallidal structures. Fibers from the ventral striatum projecting to the substantia nigra are not as confined to a specific region as those projecting to the globus pallidus. Although the densest terminal fields occur in the medial portion, numerous fibers also extend laterally to innervate the dorsal stratum of dopaminergic neurons of the substantia nigra and the retrorubral area. Furthermore, they project throughout the rostral-caudal extent of the substantia nigra. Projections from the medial part of the ventral striatum reach the more caudally located pedunculopontine tegmental nucleus. Thus unlike the above described terminals in the globus pallidus, the ventral striatum project widely throughout the substantia nigra, a fact that indicates that they may contribute to the integration between limbic and other output systems of the striatum. Finally, the ventral striatum projects to non-extrapyramidal regions including the bed nucleus of the stria terminals, the nucleus basalis magnocellularis, the lateral hypothalamus, and the medial thalamus.     

尼古丁对帕金森病大鼠纹状体GDNF和多巴胺含量的影响

目的 研究尼古丁对帕金森病（PD）大鼠纹状体脑胶质细胞源性神经营养因子(GDNF)和多巴胺（DA）含量的影响。方法 将6－羟多巴胺（6－OHDA）立体定向注射到大鼠右侧中脑腹侧背盖部（VTA）和黑质致密部（SNpc)，建立PD大鼠模型。采用生化、免疫组织化学方法观察不同剂量尼古丁对PD大鼠的作用，检测纹状体GDNF表达及DA含量的变化。结果 造模前及造模后皮下注射尼古丁的PD大鼠，纹状体GDNF表达及DA含量较PD组有明显改善（P＜0．05）。结论 尼古丁可减轻6－OHDA对黑质DA能神经元的损伤，对PD大鼠具有保护作用。     

Localization of striatal opioid gene expression,and its modulation by the mesostriatal dopamine pathway: An in situ hybridization study

In situ hybridization was used to study the macroscopic distribution and regulatory control of proenkephalin mRNA and prodynorphin mRNA in rat striatum. While proenkephalin mRNA was widely distributed throughout the striatum, levels of prodynorphin mRNA were highest in the medial and ventral portions of the striatum. Furthermore, in contrast to the results for proenkephalin mRNA, the levels of prodynorphin mRNA appeared higher in the nucleus accumbens than in the striatum. The mesostriatal dopaminergic pathway was destroyed by discrete, unilateral injection of 6-hydroxydopamine (6-OHDA) into either the substantia nigra or the neighboring ventral tegmental area (VTA). Lesions of the substantia nigra caused a dramatic ipsilateral increase in the hybridization signal for proenkephalin mRNA, but no change was observed in the hybridization signal for prodynorphin mRNA. Similar effects were seen with VTA lesions. Since destruction of the mesostriatal dopamine system elevates the levels of proenkephalin mRNA, but not of prodynorphin mRNA, in the striatal target neurons, it appears that the mesostriatal pathway exerts a tonic and selective suppression of striatal proenkephalin gene expression at the mRNA level.     

Dopaminergic sprouting in the rat striatum after partial lesion of the substantia nigra

The capacity of the dopaminergic nerve system to reinnervate the denervated adult striatum was analyzed in a model of partial 6-hydroxydopamine-induced unilateral lesion of rat substantia nigra pars compacta. Sprouting of dopaminergic fibers entering the ventrolateral part of the striatum from a narrow zone of the external capsule was detected on the lesioned side 4 and 7 months, but not 10 days, after lesioning. Ultrastructural examination of the zone of sprouting revealed hypertrophic dopaminergic fibers and growth-cone-like structures, confirming the existence of an ongoing process of spontaneous regrowth of dopaminergic fibers. The identification of the factors involved in the regrowth of dopaminergic fibers may help to orientate molecular research into new treatments for Parkinson's disease.     

Brainstem afferents to the magnocellular basal forebrain studied by axonal transport, immunohistochemistry, and electrophysiology in the rat

Brainstem afferents to the magnocellular basal forebrain were studied by using tract tracing, immunohistochemistry and extracellular recordings in the rat. WGA-HRP injections into the horizontal limb of the diagonal band (HDB) and the magnocellular preoptic area (MgPA) retrogradely labelled many neurons in the pedunculopontine and laterodorsal tegmental nuclei, dorsal raphe nucleus, and ventral tegmental area. Areas with moderate numbers of retrogradely labelled neurons included the median raphe nucleus, and area lateral to the medial longitudinal fasciculus in the pons, the locus ceruleus, and the medial parabrachial nucleus. A few labelled neurons were seen in the substantia nigra pars compacta, mesencephalic and pontine reticular formation, a midline area in the pontine central gray, lateral parabrachial nucleus, raphe magnus, prepositus hypoglossal nucleus, nucleus of the solitary tract, and ventrolateral medulla. A similar but not identical distribution of labelled neurons was seen following WGA-HRP injections into the nucleus basalis magnocellularis. The possible neurotransmitter content of some of these afferents to the HDB/MgPA was examined by combining retrograde Fluoro-Gold labelling and immunofluorescence. In the mesopontine tegmentum, many retrogradely labelled neurons were immunoreactive for choline acetyltransferase. In the dorsal raphe nucleus, some retrogradely labelled neurons were positive for serotonin and some for tyrosine hydroxylase (TH); however, the majority of retrogradely labelled neurons in this region were not immunoreactive for either marker. The ventral tegmental area, substantia nigra pars compacta, and locus ceruleus contained retrogradely labelled neurons which were also immunoreactive for TH. Of the retrogradely labelled neurons occasionally observed in the nucleus of the solitary tract, prepositus hypoglossal nucleus, and ventrolateral medulla, some were immunoreactive for either TH or phenylethanolamine-N-methyltransferase. To characterize functionally some of these brainstem afferents, extracellular recordings were made from antidromically identified cortically projecting neurons, mostly located in the HDB and MgPA. In agreement with most previous studies, about half (48%) of these neurons were spontaneously active. Electrical stimulation in the vicinity of the pedunculopontine tegmental and dorsal raphe nuclei elicited either excitatory or inhibitory responses in 21% (13/62) of the cortically projecting neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Long-term high-frequency electro-acupuncture stimulation prevents neuronal degeneration and up-regulates BDNF mRNA in the substantia nigra and ventral tegmental area following medial forebrain bundle axotomy

Electroacupuncture (EA) has been used in China for many years to treat Parkinson's disease (PD) with reportedly effective results. However, the physiological and biological mechanism behind its effectiveness is still unknown. In the present study, different frequencies of chronic EA stimulation (0, 2, 100 Hz) were tested in a partially lesioned rat model of PD which was induced by transection of the medial forebrain bundle (MFB). After 24 sessions of EA stimulation (28 days after MFB transection), dopaminergic neurons in the ventral midbrain were examined by immunohistochemical staining, and brain-derived neurotrophic factor (BDNF) mRNA levels in ventral midbrain were measured by in situ hybridization. The results show a marked decrease of dopaminergic neurons on the lesioned side of the substantia nigra (SN) comparing with the unlesioned side. Zero Hz and 2 Hz EA stimulation had no effect on the disappearance of dopaminergic neurons. However, after 100 Hz EA, about 60% of the tyrosine hydroxylase (TH)-positive neurons remained on the lesioned side of the SN. In addition, levels of BDNF mRNA in the SN and ventral tegmental area (VTA) of the lesioned side were significantly increased in the 100 Hz EA group, but unchanged in the 0 and 2 Hz groups. Our results suggest that long-term high-frequency EA is effective in halting the degeneration of dopaminergic neurons in the SN and up-regulating the levels of BDNF mRNA in the subfields of the ventral midbrain. Activation of endogenous neurotrophins by EA may be involved in the regeneration of the injured dopaminergic neurons, which may underlie the effectiveness of EA in the treatment of PD.     

Glial Cell Line-derived Neurotrophic Factor: the Lateral Cerebral Ventricle as a Site of Administration for Stimulation of the Substantia Nigra Dopamine System in Rats

The direct application of recombinant human glial cell line-derived neurotrophic factor (rhGDNF) to the deep structures of the nigrostriatum has been shown previously to augment dopamine function and inhibit loss of substantia nigra neurons in rodent models of Parkinson's disease. The present studies were designed to determine whether administration of rhGDNF into the lateral ventricle, a more clinically accessible intracranial target, is capable of augmenting dopamine function of the nigrostriatal pathway in normal rats. Single bolus intracerebroventricular (i.c.v.) injections of rhGDNF increased locomotor activity and decreased food and water consumption and body weight gain in a dose-dependent manner. rhGDNF increased concentrations of dopamine and dopamine metabolites in the substantia nigra, ventral tegmental area and hypothalamus, but had no significant effects in the striatum. rhGDNF had no effect on striatal or substantia nigral serotonin (5-HT) and 5-hydroxyindoleacetic acid levels, but these levels were significantly increased in the ventral tegmental area and hypothalamus respectively. The augmentation of the dopamine and 5-HT systems was detected 2 weeks but not 3 days or 6 weeks after rhGDNF administration. After a repeat injection of i.c.v. rhGDNF (6 weeks after the initial injection), substantia nigral dopamine, 5-HIAA and noradrenalin levels were increased. These results indicate that i.c.v. administration of rhGDNF has an influence on adult rat dopamine neurons. This route of administration may be useful for stimulating dopamine neurons in Parkinson's disease.