Development of dopamine receptor denervation supersensitivity in the neostriatum of the senescent rat

Dopamine (DA) stimulated adenylate cyclase activity and [³H]-spiroperidol specific binding were assessed in the striata from mature and old rats lesioned in the left substantia nigra with 6-hydroxydopamine (6-OHDA). Rotational behavior following the DA releasing agent, amphetamine, and the DA receptor agonist, lergotril, was also examined at 7 and 30 days, respectively, after lesioning. Results indicated that while there were rotational behavioral deficits following amphetamine in the senescent animal, none were seen with respect to lergotril. Both old and young animals showed similar degrees of contralateral rotation (with respect to the lesion) following lergotril administration. This suggested that both old and young animals showed similar development of denervation supersensitivity in the DA receptors of the lesioned striatum. Subsequent biochemical confirmation of this hypothesis was provided by findings which showed comparable relative increases in DA stimulated adenylate cyclase activity and [³H]-spiroperidol specific binding in the striata from the lesioned hemispheres of young and old rats. Additionally, high positive correlations were found between rotation and [³H]-spiroperidol specific binding, while those between DA stimulated adenylate cyclase activity and rotation were lower and dependent upon the concentration of DA used to stimulate adenylate cyclase activity (1, 5 and 100 uM). Results are discussed in terms of the specificity of the age-related deficits seen in the striatum of the senescent animal.     

Calcitriol Protection against Dopamine Loss Induced by Intracerebroventricular Administration of 6-Hydroxydopamine

Calcitriol has been implicated as an agent that has neuroprotective effects in various animal models of diseases, possibly by upregulating glial cell line-derived neurotrophic factor (GDNF). The present study examined the neuroprotective effects of calcitriol in a model of early Parkinson’s disease. Rats were treated daily with calcitriol or saline for 7 days before an intraventricular injection of 6-hydroxydopamine (6-OHDA), and then for 1 day or daily for 3½ to 4 weeks after lesioning. Evoked overflow and tissue content of dopamine (DA) were determined 3½ to 4 weeks post lesion. The 8-day calcitriol treatment did not attenuate 6-OHDA-induced decreases in evoked overflow of DA, nor did it protect against 6-OHDA-induced reductions in tissue levels of DA in the striatum or substantia nigra. However, the long-term calcitriol treatment did significantly increase evoked overflow of DA, as well as the amount of DA in the striatum, compared to saline treated animals. GDNF was significantly increased in the substantia nigra, but not in the striatum, of non-lesioned, calcitriol treated rats. These results suggest that long-term treatment with calcitriol can provide partial protection for dopaminergic neurons against the effects of intraventricularly administered 6-OHDA.     

6-Hydroxydopamine lesions of the medial prefrontal cortex of rats do not affect dopamine metabolism in the basal ganglia at short and long postsurgical intervals

Dopamine (DA) in the medial prefrontal cortex (mPFC) has been implicated in the regulation of subcortical DA function. To further characterize the potential interaction between cortical and subcortical DA systems, the short- and long-term neurochemical consequences of 6-hydroxydopamine (6-OHDA) lesions of the mPFC of rats were investigated in the mPFC and in its subcortical target structures. 4 to 5, 10 to 12 and 32 to 36 days after infusion of 6-OHDA, DA was depleted to a larger extent than noradrenaline and serotonin. No lesion-induced changes of DA and its metabolites were detected in subcortical structures. These results show that prefrontal 6-OHDA lesions produce immediate and long lasting depletions of prefrontal monoamines, especially of DA, without increasing basal DA metabolism in the striatum and nucleus accumbens.     

Neurturin Effects on Nigrostriatal Dopamine Release and Content: Comparison with GDNF

Neurturin (NTN) is a member of the glial cell line-derived neurotrophic factor (GDNF) family; and, while GDNF has been shown to increase dopamine (DA) release in normal animals, the ability of NTN to alter DA release has not been previously reported. The purpose of the present study was to determine if NTN could alter striatal DA release, and to compare the effects of NTN to GDNF. Male Fischer-344 rats were given a single injection of vehicle or 5 μg NTN or GDNF into the right substantia nigra. Three weeks later microdialysis experiments were conducted to assess striatal DA release. Basal extracellular levels of striatal DA were not affected by either NTN or GDNF. However, both NTN and GDNF led to increases in amphetamine-evoked overflow of DA from the ipsilateral striatum, and there was a trend for potassium-evoked overflow to be augmented. Postmortem tissue levels of DA were decreased by approximately 20% in the striatum, and increased by approximately 100% in the substantia nigra, on the ipsilateral side of the brain compared to the contralateral side following both NTN and GDNF injection. Thus, NTN, like GDNF, can augment striatal DA release, and the magnitude of the NTN effects are similar to those of GDNF.     

In Vivo Voltammetric Study of 6-Hydroxydopamine-Induced Neuronal Degradation

Freely moving rats were injected intraventricularly with 200 micrograms of 6-hydroxydopamine (6-OHDA) and examined for transport of this substance to the striatum, degradation of dopamine (DA) neurons, and functional recovery through microcomputer-controlled in vivo voltammetry. Approximately 6 min after the injection, 6-OHDA began to appear in the extracellular fluid of the contralateral striatum. It increased linearly and began to decrease exponentially with the termination of the injection. Two hours after the injection with 6-OHDA, a peak began to appear at the same potential as the peak of DA in the differential pulse voltammogram. It persisted for approximately 3 days. When the rats were injected intraperitoneally with L-3,4-dihydroxyphenylalanine (L-Dopa), the conversion of L-Dopa to DA was not found 1 week after the 6-OHDA injection, but was clearly recognized 5 months after the injection. When the rats were examined for behavioral changes arising from the L-Dopa injection, they were found to be clearly less hyperactive 5 months after the 6-OHDA injection than 1 week after.     

Efficacy of Brain-Derived Neurotrophic Factor and Neurotrophin-3 on Neurochemical and Behavioral Deficits Associated with Partial Nigrostriatal Dopamine Lesions

Abstract: Brain-derived neurotrophic factor (BDNF) promotes the survival of dopamine (DA) neurons, enhances expression of DA neuron characteristics, and protects these cells from 6-hydroxydopamine (6-OHDA) toxicity in vitro. We tested the ability of BDNF or neurotrophin-3 (NT-3) to exert similar protective effects in vivo during chronic delivery of 6-OHDA to the rat neostriatum. Chronic infusions of BDNF or NT-3 (12 µg/day) above the substantia nigra were started 6 days before and continued during an 8-day chronic intrastriatal infusion of 6-OHDA. In control and neurotrophin-treated animals, 6-OHDA treatment selectively depleted 50–60% of nigrostriatal DA nerve terminals but produced little if any loss of pars compacta DA cell bodies. This partial DA lesion resulted in three rotations per minute toward the lesioned hemisphere after treatment with the DA release-inducing drug d-amphetamine. Compared with supranigral infusions of vehicle, BDNF and NT-3 decreased the number of these ipsiversive rotations by 70 and 48% and increased by 20- and 10-fold, respectively, the number of contraversive rotations observed after amphetamine injection. When challenged with the DA receptor agonist apomorphine, BDNF- and NT-3-treated animals also exhibited a seven- and 3.5-fold increase in the number of contraversive rotations relative to the vehicle group, respectively. Compared with vehicle, BDNF increased striatal levels of homovanillic acid (HVA; 86%), 3,4-dihydroxyphenylacetic acid (DOPAC; 42%), and 5-hydroxyindoleacetic acid (5-HIAA; 32%) and the HVA/DA (43%) and 5-HIAA/serotonin (34%) ratios in the DA-denervated striatum. NT-3 augmented only striatal 5-HIAA levels (24%). Neither factor altered the 6-OHDA-induced decrease in striatal DA levels or high-affinity DA uptake and thus did not protect against the destruction of DA terminals and did not alter striatal D₁ or D₂ ligand binding. Choline, GABA, and glutamate uptake in the striatum were not altered by the lesion or neurotrophin treatment. Thus, BDNF and to a lesser extent NT-3 reverse rotational behavioral deficits and augment striatal DA and 5-HT metabolism in a partial DA lesion model.     

Role of high-affinity dopamine uptake and impulse activity in the appearance of extracellular dopamine in striatum after administration of exogenous L-DOPA: studies in intact and 6-hydroxydopamine-treated rats

The differential behavioral and neurochemical effects of exogenous L-DOPA in animals with intact versus dopamine (DA)-denervated striata raise questions regarding the role of DA terminals in the regulation of dopaminergic neurotransmission after administration of exogenous L-DOPA. In vivo microdialysis was used to monitor the effect of exogenous L-DOPA on extracellular DA in intact and DA-denervated striata of awake rats. In intact striatum, a small increase in extracellular DA was observed after administration of L-DOPA (50 mg/kg i.p.) but in DA-denervated striatum a much larger increase in extracellular DA was elicited. Additional experiments assessed the role of high-affinity DA uptake and impulse-dependent neurotransmitter release in the effect of exogenous L-DOPA on extracellular DA in striatum. Pretreatment with GBR-12909 (20 mg/kg i.p.), a selective DA uptake inhibitor, enhanced the ability of L-DOPA to increase extracellular DA in intact striatum. However, in DA-denervated striatum, inhibition of DA uptake did not alter the extracellular DA response to L-DOPA. Impulse-dependent neurotransmitter release was blocked by the infusion of tetrodotoxin (TTX; 1 microM), an inhibitor of fast sodium channels, through the dialysis probe. Application of TTX significantly attenuated the L-DOPA-induced increase in extracellular DA observed in striatum of intact rats pretreated with GBR-12909. In a similar manner, TTX infusion significantly attenuated the increase in extracellular DA typically observed in striatum of 6-OHDA-lesioned rats after the administration of L-DOPA. The present results indicate that DA terminals, via high-affinity uptake, play a crucial role in the clearance of extracellular DA formed from exogenous L-DOPA in intact striatum. This regulatory mechanism is absent in the DA-denervated striatum. In addition, this study has shown that DA synthesized from exogenous L-DOPA primarily is released by an impulse-dependent mechanism in both intact and DA-denervated striatum. The latter result suggests an important role for a nondopaminergic neuronal element in striatum that serves as the primary source of extracellular DA formed from exogenous L-DOPA.     

Docosahexaenoic Acid Ethyl Ester Enhances 6-Hydroxydopamine-Induced Neuronal Damage by Induction of Lipid Peroxidation in Mouse Striatum

Superoxide and hydroxyl radicals are implicated in the pathogenesis of Parkinson disease, and induction of lipid peroxidation is an important factor in progression of this disease. Docosahexaenoic acid (DHA) is a key component of the cell membrane, and its peroxidation is inducible due to the double-bond chemical structure. However, DHA has neuroprotective effects. In this study, we examined the effects of intraperitoneal injection (ipi) of DHA ethyl ester (DHA-Et) on 6-hydroxydopamine (6-OHDA)-induced dopamine (DA) reduction in the mouse striatum. DHA-Et ipi for 7 days before and 7 days after a single intracerebroventricular injection of 6-OHDA enhanced 6-OHDA-induced reduction of striatal DA level. On the other hand, ipi of DHA-Et for 7 days increased its concentration in the striatum. Co-injection of DHA-Et and 6-OHDA increased the levels of thiobarbituric acid-reactive substances (a marker of lipid peroxidation) in the striatum. Our results suggest that DHA-Et enhances 6-OHDA-induced DA depression by increasing lipid peroxidation, and that excessive use of DHA-Et may increase the susceptibility of Parkinson disease in animal model.     

Effects of 6-hydroxydopamine on primary cultures of substantia nigra: specific damage to dopamine neurons and the impact of glial cell line-derived neurotrophic factor

6-Hydroxydopamine (6-OHDA)-induced loss of dopamine (DA) neurons has served to produce an animal model of DA neuron loss in Parkinson's disease. We report here the use of 6-OHDA to produce an in vitro model of this phenomena using dissociated cultures prepared from neonatal rat mesencephalon. Cultures were exposed to 6-OHDA (40-100 microm, 15 min) in an antioxidant medium, and DA and GABA neurons evaluated by immunocytochemistry. 6-OHDA induced morphological and biochemical signs of cell death in DA neurons within 3 h, followed by loss of tyrosine hydroxylase immunoreactive neurons within 2 days. In substantia nigra (SN) cultures, DA neurons were much more affected by 6-OHDA than were GABA neurons. In contrast, DA neurons from the ventral tegmental area were only lost at higher, non-specific concentrations of 6-OHDA. The effects of 6-OHDA on nigral DA neurons were blocked by inhibitors of high affinity DA transport and by z-DEVD-fmk (150 microm), a caspase inhibitor. Glial cell line-derived neurotrophic factor (GDNF) treatment reduced TUNEL labeling 3 h after 6-OHDA exposure, but did not prevent loss of DA neurons at 48 h. Thus, 6-OHDA can selectively destroy DA neurons in post-natal cultures of SN, acting at least in part by initiating caspase-dependent apoptosis, and this effect can be attenuated early but not late by GDNF.     

Neurotoxic action of 6-hydroxydopamine on the nigrostriatal dopaminergic pathway in rats sensitized with D-amphetamine.

To determine whether behavioral sensitization produced by prolonged D-amphetamine administration affects susceptibility of nigrostriatal dopaminergic neurons to the neurotoxic actions of 6-hydroxydopamine (6-OHDA), rats were treated daily from the 23 rd day after birth for 11 consecutive days with D-amphetamine (1.0 mg/kg s.c.) or saline. On the last day of treatment, one group primed with D-amphetamine and one control group of rats were tested to confirm behavioral sensitization development. The remaining animals were additionally treated on the 34 th day (one day after the last D-amphetamine injection) with 6-OHDA HBr (300 microg in 10 microl i.c.v., salt form, half in each lateral ventricle) or its vehicle. Four weeks later the levels of dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-metoxytyramine (3-MT), as well as 5-hydroxytrypatmine (5-HT) and its metabolite 5-hydroxyindoleacteic acid (5-HIAA) were assayed in the striatum, by HPLC/ED. In rats with behavioral sensitization, 6-OHDA reduced endogenous dopamine and its metabolites content to a comparable degree in comparison to controls. This finding indicates that presumed up-regulation of the dopamine transporter in the behaviorially sensitized rats did not increase the neurotoxicity of a high dose of 6-OHDA.     

Immortalized dopamine neurons: A model to study neurotoxicity and neuroprotection

6-Hydroxydopamine (6-OHDA) causes selective degeneration of dopaminergic neurons in the rat brain and has been used to produce an animal model of Parkinsonism. Recently, a clonal line of immortalized dopamine (DA) neurons (1RB3AN27), which expresses varying levels of tyrosine hydroxylase, dopamine transporter, neuron specific enolase, and nestin, was established. These DA neurons reduce behavioral deficits in 6-OHDA-lesioned rats. The relative sensitivity of fetal and adult neurons to potential neurotoxins is not well defined. The availability of immortalized DA neurons provides a unique opportunity to compare the relative neurotoxicity of 6-OHDA in differentiated and undifferentiated DA neurons in vitro and identify neuroprotective agents. Our results showed that 6-OHDA treatment for 24 hr decreased the viability of undifferentiated and differentiated immortalized DA neurons in vitro, as determined by the MTT assay, and increased the rate of apoptosis in differentiated DA neurons. The differentiated DA neurons (IC50 = 33 microM) were about 2-fold more sensitive to 6-OHDA than undifferentiated DA neurons (IC50 = 75 microM) in cell culture. Similarly, the differentiated DA neurons were more sensitive to another neurotoxin, 1-methyl-4-phenylpyridinium (MPP+), which is commonly used to induce Parkinsonism in animal models, than were the undifferentiated DA neurons in culture. Among growth factors tested, only glial cell line-derived neurotrophic factor (GDNF) partially protected differentiated DA neurons against 6-OHDA-induced toxicity. These results suggest that undifferentiated and differentiated immortalized DA neurons can be a useful experimental model to study relative sensitivity to neurotoxins and neuroprotective agents that could have relevance to fetal and adult neurons.     

Evoked dopamine overflow is augmented in the striatum of calcitriol treated rats

Calcitriol, the active metabolite of vitamin D, has been shown to have significant effects on the brain. These actions include reducing the severity of some central nervous system lesions, possibly by upregulating trophic factors such as glial cell line-derived neurotrophic factor (GDNF). GDNF has substantial effects on the nigrostriatal dopamine (DA) system of young adult, aged and lesioned animals. Thus, the administration of calcitriol may lead to significant effects on nigrostriatal DA neuron functioning. The present experiments were designed to examine the ability of calcitriol to alter striatal DA release, and striatal and nigral tissue levels of DA. Male Fischer-344 rats were administered vehicle or calcitriol (0.3, 1.0, or 3.0 μg/kg, s.c.) once daily for eight consecutive days. Three weeks later in vivo microdialysis experiments were conducted to measure basal and stimulus evoked overflow of DA from the striatum. Basal levels of extracellular DA were not significantly affected by the calcitriol treatments. However, the 1.0 and 3.0 μg/kg doses of calcitriol led to increases in both potassium and amphetamine evoked overflow of striatal DA. Although post-mortem tissue levels of striatal DA were not altered by the calcitriol injections, nigral tissue levels of DA and its main metabolites were increased by both the 1.0 and 3.0 μg/kg doses of calcitriol. In a separate group of animals GDNF levels were augmented in the striatum and substantia nigra after eight consecutive daily injections of calcitriol. These results suggest that systemically administered calcitriol can upregulate dopaminergic release processes in the striatum and DA levels in the substantia nigra. Increases in the levels of endogenous GDNF following calcitriol treatment may in part be responsible for these changes. The ability of calcitriol to lead to augmented DA release in the striatum suggests that calcitriol may be beneficial in disease processes involving dopaminergic dysfunction.     

Effects of Zingerone [4-(4-Hydroxy-3-Methoxyphenyl)-2-Butanone] and Eugenol [2-Methoxy-4-(2-Propenyl)Phenol] on the Pathological Progress in the 6-Hydroxydopamine-Induced Parkinson’s Disease Mouse Model

Parkinson’s disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the nigrostriatal system and dopamine (DA) depletion in the striatum. The most popular therapeutic medicine for treating PD, 3-(3,4-Dihydroxyphenyl)-l-alanine (L-DOPA), has adverse effects, such as dyskinesia and disease acceleration. As superoxide (·O₂ ⁻) and hydroxyl radical (·OH) have been implicated in the pathogenesis of PD, free radical scavenging and antioxidants have attracted attention as agents to prevent disease progression. Rodents injected with 6-hydroxydopamine (6-OHDA) intracerebroventricularly are considered to be a good animal model of PD. Zingerone and eugenol, essential oils extracted from ginger and cloves, are known to have free radical scavenging and antioxidant effects. Therefore, we examined the effects of zingerone and eugenol on the behavioral problems in mouse model and on the DA concentration and antioxidant activities in the striatum after 6-OHDA administration and L-DOPA treatment. Daily oral administration of eugenol/zingerone and injection of L-DOPA intraperitoneally for 4 weeks following a single 6-OHDA injection did not improve abnormal behaviors induced by L-DOPA treatment. 6-OHDA reduced the DA level in the striatum; surprisingly, zingerone and eugenol enhanced the reduction of striatal DA and its metabolites. Zingerone decreased catalase activity, and increased glutathione peroxidase activity and the oxidized L-ascorbate level in the striatum. We previously reported that pre-treatment with zingerone or eugenol prevents 6-OHDA-induced DA depression by preventing lipid peroxidation. However, the present study shows that post-treatment with these substances enhanced the DA decrease. These substances had adverse effects dependent on the time of administration relative to model PD onset. These results suggest that we should be wary of ingesting these spice elements after the onset of PD symptoms.     

Effect of Intranigral Injection of GDNF and EGF on the Survival and Possible Differentiation Fate of Progenitors and Immature Neurons in 6-OHDA-Lesioned Rats

We investigated the survival and the possible differentiation fate of the progenitors and immature neurons in the pars compacta of the substantia nigra (SNc) by intranigral injection of a glial cell line-derived neurotropic factor (GDNF) or glial cell line-derived neurotropic factor plus epidermal growth factor (EGF + GDNF) in 6-hydroxydopamine (6-OHDA)-lesioned rats. First, we performed behavioral tests by postural asymmetry and forelimb akinesia on the rats injected with 6-OHDA in striatum at day 7, and selected the qualified model according to the results. Then, intranigral GDNF or EGF + GDNF treatment was administered in the qualified PD model rats. On day 21, behavioral tests were performed with these rats; and then the rats were sacrificed for analyses of β-tubulin isotype-III (Tuj1), nestin, glial fibrillary acidic protein (GFAP), and tyrosine hydroxylase (TH) by immunohistochemistry and Western blotting. The results indicated that GDNF could promote the survival of the progenitor cells and immature neurons in rat SNc following 6-OHDA lesion. Moreover, EGF is capable of enhancing the survival effect of GDNF on the progenitor cells and immature neurons in SNc. On day 21, rapid functional recovery from the lesion-induced behavioral asymmetries was observed in the GDNF or EGF + GDNF-treated rats, and the numbers of TH-positive neurons increased in SNc, suggesting that the rats might generate new dopaminergic neurons. Thus, our study provides the new insight that the progenitors and immature neurons in SNc of 6-OHDA-lesioned rats might be able to differentiate toward the dopaminergic neurons fate subsequent to treatment with GDNF or EGF + GDNF.     

Molecular Profiling of a 6-Hydroxydopamine Model of Parkinson’s Disease

Convection enhanced delivery of 6-hydroxydopamine (6-OHDA) to the rat striatum results in a model of Parkinson’s disease. An important feature of this unilateral model is the progressive loss of dopaminergic (DA) neurons over the course of several weeks. To improve the understanding of this model, gene expression changes in the substantia nigra, which contains the DA neuron cell bodies, and the striatum, which contains the DA neuron synaptic terminals, were examined using DNA microarrays. Samples were collected and behavior was analyzed from vehicle and toxin treated animals at 3 days, 1 week, 2 weeks and 4 weeks following 6-OHDA treatment. Tissue DA content was determined and samples from animals which exhibited a substantial depletion of striatal DA were included in the subsequent gene expression analysis. The results of the gene expression analysis indicated that 6-OHDA elicits a vigorous inflammatory response, comprised of several distinct pathways, in the striatum at the earliest time point tested. In contrast, relatively few gene expression changes were observed in the SN at the 3-day time point. In both tissues examined there was evidence for a vigorous inflammatory response at the 1- and 2-week time points, which was substantially diminished by the 4-week time point. Inflammation plays a prominent role in the 6-OHDA model of Parkinson’s disease.     

Nigral GFRα1 Infusion in Aged Rats Increases Locomotor Activity, Nigral Tyrosine Hydroxylase, and Dopamine Content in Synchronicity

Delivery of exogenous glial cell line-derived neurotrophic factor (GDNF) increases locomotor activity in rodent models of aging and Parkinson’s disease in conjunction with increased dopamine (DA) tissue content in substantia nigra (SN). Striatal GDNF infusion also increases expression of GDNF’s cognate receptor, GFRα1, and tyrosine hydroxylase (TH) ser31 phosphorylation in the SN of aged rats long after elevated GDNF is no longer detectable. In aging, expression of soluble GFRα1 in the SN decreases in association with decreased TH expression, TH ser31 phosphorylation, DA tissue content, and locomotor activity. Thus, we hypothesized that, in aged rats, replenishing soluble GFRα1 in SN could reverse these deficits and increase locomotor activity. We determined that the quantity of soluble GFRα1 in young adult rat SN is ~3.6 ng. To replenish age-related loss, which is ~30 %, we infused 1 ng soluble GFRα1 bilaterally into SN of aged male rats and observed increased locomotor activity compared to vehicle-infused rats up to 4 days following infusion, with maximal effects on day 3. Five days after infusion, however, neither locomotor activity nor nigrostriatal neurochemical measures were significantly different between groups. In a separate cohort of male rats, nigral, but not striatal, DA, TH, and TH ser31 phosphorylation were increased 3 days following unilateral infusion of 1 ng soluble GFRα1into SN. Therefore, in aged male rats, the transient increase in locomotor activity induced by replenishing age-related loss of soluble GFRα1is temporally matched with increased nigral dopaminergic function. Thus, expression of soluble GFRα1 in SN may be a key component in locomotor activity regulation through its influence over TH regulation and DA biosynthesis.     

6-羟多巴胺纹状体内注射制作大鼠帕金森病模型的研究

目的 为拓宽6-OHDA损毁多巴胺能神经元所制备大鼠帕金森病模型的应用范围,采用多位点纹状体内注入6-OHDA的途径来制备模型。方法 研究用SD大鼠,两个针道内四点定位注射,每点注射3μg／μ16-OHDA3μl。结果 术后两周出现缓慢旋转,4周旋转行为达到7转／分并保持稳定;形态学染色可见损毁1周后注射侧黑质酪氨酸羟化酶免疫组化阳性细胞减少20％,2周后减少38％,3～4周减少70％以上,6周后损伤趋缓。高效液相-电化学法活体检测纹状体内多巴胺的代谢产物3、4-二羟基苯乙酸(DOPAC)和高香草酸(HVA),发现注射侧和非注射侧相比含量分别下降98．33％和96．05％;组织匀浆检测损毁侧黑质多巴胺含量下降了73％以上,3、4-二羟基苯乙酸(DOPAC)含量下降60％。结论 纹状体内注射6-OHDA能够制备帕金森病大鼠模型。     

Increased melatonin may play dual roles in the striata of a 6-hydroxydopamine model of Parkinson's disease

AimsTo investigate dynamic changes and roles of melatonin (MLT) in the striata of 6-hydroxydopamine (6-OHDA)-treated rats.Main methodsA Parkinson's disease (PD) rat was established by a unilateral injection of 6-OHDA into the right substantia nigra pars compacta (SNc) and the right medial forebrain bundle (MFB) to achieve a complete lesion of the ipsilateral nigrostriatal DA system. Dialysates were collected in the lesioned striatum at different time intervals by in vivo microdialysis. In addition, both contralateral and ipsilateral striatum tissues were collected at two time intervals (10:00 and 22:00 h) at 3 and 6 weeks after lesioning. The levels of DA, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the dialysates, as well as MLT in the dialysates and tissues were determined using HPLC.Key findingsThe dialysate contents of DA, DOPAC and HVA in the lesioned striatum were significantly decreased (P < 0.001) in comparison with those in the controls or in the unlesioned side 3 weeks after lesioning while the extracellular level of MLT in the lesioned striatum in these corresponding time intervals distinctly increased when compared with those in the controls (P < 0.05). The tissue MLT contents increased in the bilateral striata in different degrees at 6 weeks post-lesion (P < 0.05). Moreover, increased MLT levels correlate well with rotations or DA changes in the lesioned striatum.SignificanceThese data suggest that 6-OHDA lesion manipulates the MLT secretion pattern. Increased striatal MLT level by a unilateral intracerebral injection of 6-OHDA may play dual roles in the progression of PD in rats.     

Controlled cortical impact injury affects dopaminergic transmission in the rat striatum

The therapeutic benefits of dopamine (DA) agonists after traumatic brain injury (TBI) imply a role for DA systems in mediating functional deficits post‐TBI. We investigated how experimental TBI affects striatal dopamine systems using fast scan cyclic voltammetry (FSCV), western blot, and d‐amphetamine‐induced rotational behavior. Adult male Sprague–Dawley rats were injured by a controlled cortical impact (CCI) delivered unilaterally to the parietal cortex, or were naïve controls. Amphetamine‐induced rotational behavior was assessed 10 days post‐CCI. Fourteen days post‐CCI, animals were anesthetized and underwent FSCV with bilateral striatal carbon fiber microelectrode placement and stimulating electrode placement in the medial forebrain bundle (MFB). Evoked DA overflow was assessed in the striatum as the MFB was electrically stimulated at 60 Hz for 10 s. In 23% of injured animals, but no naïve animals, rotation was observed with amphetamine administration. Compared with naïves, striatal evoked DA overflow was lower for injured animals in the striatum ipsilateral to injury (p < 0.05). Injured animals exhibited a decrease in V_max (52% of naïve, p < 0.05) for DA clearance in the hemisphere ipsilateral to injury compared with naïves. Dopamine transporter (DAT) expression was proportionally decreased in the striatum ipsilateral to injury compared with naïve animals (60% of naïve, p < 0.05), despite no injury‐related changes in vesicular monoamine transporter or D₂ receptor expression (DRD₂) in this region. Collectively, these data appear to confirm that the clinical efficacy of dopamine agonists in the treatment of TBI may be related to disruptions in the activity of subcortical dopamine systems.     

Protection of dopaminergic neurons by electroconvulsive shock in an animal model of Parkinson's disease

Electroconvulsive shock (ECS) improves motor function in Parkinson's disease. In rats, ECS stimulates the expression of various factors some of which have been proposed to exert neuroprotective actions. We have investigated the effects of ECS on 6-hydroxydopamine (6-OHDA)-injected rats. Three weeks after a unilateral administration of 6-OHDA, 85–95% nigral dopaminergic neurons are lost. Chronic ECS prevented this cell loss, protect the nigrostriatal pathway (assessed by FloroGold retrograde labeling) and reduce motor impairment in 6-OHDA-treated animals. Injection of 6-OHDA caused loss of expression of glial cell-line derived neurotrophic factor (GDNF) in the substantia nigra. Chronic ECS completely prevented this loss of GDNF expression in 6-OHDA-treated animals. We also found that protected dopaminergic neurons co-express GDNF receptor proteins. These results strongly suggest that endogenous changes in GDNF expression may participate in the neuroprotective mechanism of ECS against 6-OHDA induced toxicity.