Relative sparing of calretinin containing neurons in the substantia nigra of 6-OHDA treated rat parkinsonian model

A certain calcium binding protein (CaBP) has been known to exert a neuroprotective effect in various neurodegenerative diseases. Using the 6-OHDA induced rat Parkinsonian model, we examined if calretinin (CR), one of CaBP family, could play the similar role in the Parkinson's disease because CR is profusely localized in dopaminergic neurons of the substantia nigra pars compacta (SNPC) of the rat. Employing immunohistochemical analyses, we found that the survival rate of CR neurons was significantly higher than that of tyrosine hydroxylase (TH) neurons in the SNPC of the Parkinsonian rat. Furthermore double-labeled fluorescent microscopy revealed that almost all surviving TH neurons were also positive to CR. Our data suggest that CR-positive neurons are less vulnerable to 6-OHDA and CR in the dopaminergic neurons may have a protective function for survival of these neurons in the experimentally induced Parkinsonian rat.     

外源性kynurenic acid对大鼠黑质多巴胺能神经元损伤的保护作用研究

目的观察评价预先应用谷氨酸(Glu)受体拮抗剂kynurenic acid(KYNA)对黑质多巴胺(DA)能神经元及神经传导纤维损伤的保护性作用. 方法雌性SD大鼠40只,随机分为4组,每组10只,应用江湾I型C立体定向仪,在单侧黑质致密部及中脑被盖腹侧部, A组注射生理盐水,B组注射KYNA,C组注射KYNA和6-羟基多巴胺(6-OHDA), KYNA先于6-OHDA 30 min, D组注射6-OHDA.注射药物3 d后,进行症状观察,4周后处死大鼠.切片HE染色观察黑质细胞的形态特点,冰冻切片免疫组化特殊染色观察酪氨酸羟化酶(TH)阳性细胞及TH阳性纤维着色情况.结果正常黑质细胞体形较大,富含黑色素颗粒,可见尼氏体.TH着色结果提示B组与A组之间无显著差异,P>0.05.实验组C与A、B、D组比较均有显著性差异,P<0.01.结论外源性Glu受体拮抗剂KYNA通过阻滞Glu受体一定时间阶段内能减轻6-OHDA诱导的黑质DA能神经元毒性损害.     

KDI tripeptide of gamma1 laminin protects rat dopaminergic neurons from 6-OHDA induced toxicity

Our previous studies indicate that the KDI (Lys-Asp-Ile) tripeptide of gamma1 laminin protects central neurons from mechanical trauma and excitotoxicity. At least part of the neuroprotective effect of the KDI tripeptide may be mediated by its inhibitory function on ionotropic glutamate receptors. We studied the protective effect of the KDI tripeptide against 6-hydroxy-dopamine (6-OHDA) induced neurotoxicity in a rat experimental model of Parkinson's disease (PD). We found that a single unilateral injection of the KDI tripeptide into the substantia nigra before an injection of 6-OHDA protected the dopaminergic neurons from the neurotoxicity of 6-OHDA. Compared to rats treated with 6-OHDA alone, the KDI + 6-OHDA-treated substantia nigra was relatively intact with large numbers of dopaminergic neurons present at the injection side. In the rats treated with 6-OHDA alone, no dopaminergic neurons were detected, and the substantia nigra-area at the injection side was filled with blood-containing cavities. Quantification of the rescue effect of the KDI tripeptide indicated that, in animals receiving KDI before 6-OHDA, 33% of tyrosine hydroxylase-positive dopaminergic neurons of the substantia nigra were present as compared to the contralateral non-injected side. In animals receiving 6-OHDA alone, only 1.4% of the tyrosine hydroxylase expressing dopaminergic neurons could be verified. If this much protection were achieved in humans, it would be sufficient to diminish or greatly alleviate the clinical symptoms of PD. We propose that the KDI tripeptide or its derivatives might offer a neuroprotective biological alternative for treatment of PD.     

The Impact of Short and Long-Term Exercise on the Expression of Arc and AMPARs During Evolution of the 6-Hydroxy-Dopamine Animal Model of Parkinson’s Disease

The loss of nigral dopaminergic neurons typical in Parkinson’s disease (PD) is responsible for hyperexcitability of medium spiny neurons resulting in abnormal corticostriatal glutamatergic synaptic drive. Considering the neuroprotective effect of exercise, the changes promoted by exercise on AMPA-type glutamate receptors (AMPARs), and the role of activity-regulated cytoskeleton-associated protein (Arc) in the AMPARs trafficking, we studied the impact of short and long-term treadmill exercise during evolution of the unilateral 6-hydroxy-dopamine (6-OHDA) animal model of PD. Wistar rats were divided into sedentary and exercised groups, with and without lesion by 6-OHDA and followed up to 4 months. The exercised groups were subjected to a moderate treadmill exercise 3×/week. We measured the proteins tyrosine hydroxylase (TH), Arc, GluA1, and GluA2/3 in the striatum, substantia nigra, and motor cortex. Our results showed a higher reduction of TH expression in all sedentary groups when compared to all exercised groups in striatum and substantia nigra. In general, larger changes occurred in the striatum in the first and third months after training. After 1 month of exercise, there was significant increase of GluA2/3 with concomitant reduction of GluA1 and Arc. As a balanced system, these changes were reversed in the third month, showing an increase of Arc and GluA1 and decrease of GluA2/3. Similar results for GluAs and Arc were observed in the motor cortex of the exercised animals. These modifications may be relevant for corticostriatal circuits in PD, since the exercise-dependent plasticity can modulate GluAs expression and maybe neuronal excitability.     

Toxin-induced models of Parkinson’s disease

Parkinson’s disease (PD) is a common neurodegenerative disease that appears essentially as a sporadic condition. It results mainly from the death of dopaminergic neurons in the substantia nigra. PD etiology remains mysterious, whereas its pathogenesis begins to be understood as a multifactorial cascade of deleterious factors. Most insights into PD pathogenesis come from investigations performed in experimental models of PD, especially those produced by neurotoxins. Although a host of natural and synthetic molecules do exert deleterious effects on dopaminergic neurons, only a handful are used in living laboratory animals to recapitulate some of the hallmarks of PD. In this review, we discuss what we believe are the four most popular parkinsonian neurotoxins, namely 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, and paraquat. The main goal is to provide an updated summary of the main characteristics of each of these four neurotoxins. However, we also try to provide the reader with an idea about the various strengths and the weaknesses of these neurotoxic models.     

重组人促红细胞生成素预处理对黑质多巴胺能神经元凋亡的影响

目的研究重组人促红细胞生成素(rhEPO)对离体帕金森病模型中黑质多巴胺神经元凋亡的影响。方法以6-羟基多巴胺(6-OHDA)为毁损剂建立大鼠离体帕金森病(PD)模型。用6u/mlrhEPO预处理黑质多巴胺神经元,然后用免疫组化方法观察黑质中酪氨酸羟化酶(TH)免疫反应阳性细胞数和半胱天冬酶-3(Caspase-3)免疫反应阳性细胞数的变化,TUNEL法观察黑质中多巴胺神经元的凋亡情况。结果与6-OHDA组(44.2±5.0)相比,rhEPO预处理组TH免疫反应阳性细胞(63.8±6.2,P<0.01)增多;与6-OHDA组(22.3±2.8)相比,rhEPO预处理组多巴胺神经元中Caspase-3表达减少,Caspase-3免疫反应阳性细胞染色较淡,数量减少(13.7±1.8,P<0.01);与6-OHDA组(20.3±3.1)相比,rhEPO预处理组TUNEL阳性细胞染色较淡,数量减少(10.7±1.5,P<0.01)。结论rhEPO预处理可以减轻6-OHDA对离体帕金森病模型中多巴胺神经元的损伤,其机制可能与rhEPO抑制黑质多巴胺神经元凋亡有关。     

Estrogen interacts with the IGF-1 system to protect nigrostriatal dopamine and maintain motoric behavior after 6-hydroxdopamine lesions

The most prominent neurochemical hallmark of Parkinson's disease (PD) is the loss of nigrostriatal dopamine (DA). Animal models of PD have concentrated on depleting DA and therapies have focused on maintaining or restoring DA. Within this context estrogen protects against 6-hydroxdopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesions of the nigrostriatal DA pathway. Present studies tested the hypothesis that neuroprotective estrogen actions involve activation of the insulin-like growth factor-1 (IGF-1) system. Ovariectomized rats were treated with either a single subcutaneous injection of 17beta-estradiol benzoate or centrally or peripherally IGF-1. All rats were infused unilaterally with 6-OHDA into the medial forebrain bundle (MFB) to lesion the nigrostriatal DA pathway. Tyrosine hydroxylase (TH) immunocytochemistry confirmed that rats injected with 6-OHDA had a massive loss of TH immunoreactivity in both the ipsilateral substantia nigra compacta (60% loss) and the striatum (>95% loss) compared to the contralateral side. Loss of TH immunoreactivity was correlated with loss of asymmetric forelimb movements, a behavioral assay for motor deficits. Pretreatment with estrogen or IGF-1 significantly prevented 6-OHDA-induced loss of substantia nigra compacta neurons (20% loss) and TH immunoreactivity in DA fibers in the striatum (<20% loss) and prevented the loss of asymmetric forelimb use. Blockage of IGF-1 receptors by intracerebroventricular JB-1, an IGF-1 receptor antagonist, attenuated both estrogen and IGF-1 neuroprotection of nigrostriatal DA neurons and motor behavior. These findings suggest that IGF-1 and estrogen acting through the IGF-1 system may be critical for neuroprotective effects of estrogen on nigrostriatal DA neurons in this model of PD.     

Resistance of hypothalamic dopaminergic neurons to neonatal 6-hydroxydopamine toxicity

We studied the effects of neonatal intracisternal administration of the 6-hydroxydopamine (6-OHDA) following desipramine pretreatment on dopaminergic (DA) neurons in the rat hypothalamus and substantia nigra by immunocytochemistry with an antiserum against tyrosine hydroxylase (TH). Neonatal intracisternal 6-OHDA injection induced almost complete loss of the TH-immunoreactivity in the substantia nigra and the caudate-putamen when examined at final (adult) stage. However, in this stage, no difference of TH-immunoreactivity was observed in hypothalamic DA neurons in the arcuate nucleus (A 12), peri ventricular area (A14), zona incerta (A 13), and posterior hypothalamic area (All). In the initial (neonatal) stage after the 6-OHDA injection, nigral DA neurons started to degenerate in 12 h and were almost completely destructed in 96 h, but hypothalamic DA neurons did not show any degenerative change at any time examined. The route of the injection (cistern, third ventricle or lateral ventricle) of the toxin did not influence the distribution of damage. These data show that 6-OHDA is not equally toxic to all brain DA neurons in neonates, and that all hypothalamic DA neuronal groups resist the toxicity of 6-OHDA, despite their anatomical and functional differences.     

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).     

CX3CR1 Disruption Differentially Influences Dopaminergic Neuron Degeneration in Parkinsonian Mice Depending on the Neurotoxin and Route of Administration

Parkinson’s disease (PD) is characterized by progressive degeneration of dopaminergic neurons accompanied by an inflammatory reaction. The neuron-derived chemokine fractalkine (CX3CL1) is an exclusive ligand for the receptor CX3CR1 expressed on microglia. The CX3CL1/CX3CR1 signaling is important for sustaining microglial activity. Using a recently developed PD model, in which the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxin is delivered intranasally, we hypothesized that CX3CR1 could play a role in neurotoxicity and glial activation. For this, we used CX3CR1 knock-in mice and compared results with those obtained using the classical PD models through intraperitonal MPTP or intrastriatal 6-hydroxydopamine (6-OHDA). The striatum from all genotypes (CX3CR1^+/+, CX3CR1^+/GFP and CX3CR1-deficient mice) showed a significant dopaminergic depletion after intranasal MPTP inoculation. In contrast to that, we could not see differences in the number of dopaminergic neurons in the substantia nigra of CX3CR1-deficient animals. Similarly, after 6-OHDA infusion, the CX3CR1 deletion decreased the amphetamine-induced turning behavior observed in CX3CR1^+/GFP mice. After the 6-OHDA inoculation, a minor dopaminergic neuronal loss was observed in the substantia nigra from CX3CR1-deficient mice. Distinctly, a more extensive neuronal cell loss was observed in the substantia nigra after the intraperitoneal MPTP injection in CX3CR1 disrupted animals, corroborating previous results. Intranasal and intraperitoneal MPTP inoculation induced a similar microgliosis in CX3CR1-deficient mice but a dissimilar change in the astrocyte proliferation in the substantia nigra. Nigral astrocyte proliferation was observed only after intraperitoneal MPTP inoculation. In conclusion, intranasal MPTP and 6-OHDA lesion in CX3CR1-deficient mice yield no nigral dopaminergic neuron loss, linked to the absence of astroglial proliferation.     

Excitation of type II caudate neurons by systemic administration of dopamine agonists

Using chloral hydrate anesthetized rats, dopamine (DA) agonists were evaluated for their systemic effects on firing rates of DA neurons in rat substantia nigra pars compacta (SNPC) and postsynaptic type 11 neurons in the anterior caudate nucleus (CN), the major projection area for SNPC DA neurons. Intravenous injections of the indirect DA agonistd-amphetamine, but notl-amphetamine, excited spontaneously active CN neurons by a haloperidol-sensitive mechanism. Doses to achieve CN excitation were similar to those required to inhibit SNPC firing. This data is consistent with the theory thatd-amphetamine inhibition of SNPC DA neurons is dependent upon neuronal negative feedback pathways originating in CN. Intravenous injections of direct agonists apomorphine, which stimulates all DA receptor subtypes, and quinpirole, which only stimulates D₂ receptor subtypes, increased firing rates of spontaneously active CN neurons, but only at doses above those inhibiting firing rates of SNPC neurons. SKF 38393, a selective D₁ agonist, had little or no effect on the firing rates of DA neurons in SNPC, on type II anterior CN neurons, or on the effects of quinpirole on anterior CN neurons. It is concluded that excitation of type II anterior CN neurons is mediated via receptors of the D₂ subfamily. These results are compared to those reported elsewhere for type I CN neurons, and the possible relevance of these results for the role of DA in motor function is discussed.     

PGE(2) receptor EP1 renders dopaminergic neurons selectively vulnerable to low-level oxidative stress and direct PGE(2) neurotoxicity

Oxidative stress and increased cyclooxygenase-2 (COX-2) activity are both implicated in the loss of dopaminergic neurons from the substantia nigra (SN) in idiopathic Parkinson's disease (PD). Prostaglandin E(2) (PGE(2)) is one of the key products of COX-2 activity and PGE(2) production is increased in PD. However, little is known about its role in the selective death of dopaminergic neurons. Previously, we showed that oxidative stress evoked by low concentrations of 6-hydroxydopamine (6-OHDA) was selective for dopaminergic neurons in culture and fully dependent on COX-2 activity. We postulated that this loss was mediated by PGE(2) acting through its receptors, EP1, EP2, EP3, and EP4. Using double-label immunohistochemistry for specific EP receptors and tyrosine hydroxylase (TH), we identified EP1 and EP2 receptors on dopaminergic neurons in rat SN. EP2 receptors were also found in non-dopaminergic neurons of this nucleus, as were EP3 receptors, whereas the EP4 receptor was absent. PGE(2), 16-phenyl tetranor PGE(2) (a stable synthetic analogue), and 17-phenyl trinor PGE(2) (an EP1 receptor-selective agonist) were significantly toxic to dopaminergic cells at nanomolar concentrations; EP2- and EP3-selective agonists were not. We challenged dopaminergic neurons in embryonic rat mesencephalic primary neuronal cultures and tested whether these receptors mediate selective 6-OHDA toxicity. The nonselective EP1-3 receptor antagonist AH-6809 and two selective EP1 antagonists, SC-19220 and SC-51089, completely prevented the 40%-50% loss of dopaminergic neurons caused by exposure to 5 muM 6-OHDA. Together, these results strongly implicate PGE(2) activation of EP1 receptors as a mediator of selective toxicity in this model of dopaminergic cell loss.     

6-OHDA诱导大鼠多巴胺神经元选择性缺失的研究

目的 电压依赖性钙离子通道分布对6-羟基多巴胺（6-OHDA）诱导的SD大鼠多巴胺能神经元缺失的影响.方法 6-OHDA单侧脑内内侧前脑束（MFB）立体定位注射,术后10d观测行为学变化;并取脑固定,免疫组化酪氨酸羟化酶（TH）染色观察中脑黑质致密部（SNc）与腹侧背盖区（VTA）多巴胺能神经元的凋亡情况.并应用膜片钳全细胞记录技术,测量SNc与VTA多巴胺能神经元的电压依赖性钙离子通道的电流密度.结果 损伤侧的SNc区TH阳性细胞与对侧比较明显减少,而VTA区TH阳性细胞与对侧相比变化较小;全细胞记录电压膜片钳技术测量,发现SNc多巴胺能神经元钙通道电流密度与VTA相比明显较高.结论 该结果的发现,提示钙离子通道可能参与到帕金森氏病中脑多巴胺能神经元的选择性凋亡的机制.     

Brain-derived neurotrophic factor and substantia nigra dopaminergic neurons in Parkinson''s disease

BACKGROUND:Parkinson's disease (PD) is a chronic, progressive neurodegenerative central nervous system disease which occurs in the substantia nigra-corpus striatum system. The main pathological feature of PD is selective dopaminergic neuronal loss with distinctive Lewy bodies in populations of surviving dopaminergic neurons. In the clinical and neuropathological diagnosis of PD, brain-derived neurotrophic factor mRNA expression in the substantia nigra pars compacta is reduced by 70%, and surviving dopaminergic neurons in the PD substantia nigra pars compacta express less brain-derived neurotrophic factor (BDNF) mRNA (20%) than their normal counterparts. In recent years, knowledge surrounding the relationship between neurotrophic factors and PD has increased, and detailed pathogenesis of the role of neurotrophic factors in PD becomes more important.     

p-Quinone mediates 6-hydroxydopamine-induced dopaminergic neuronal death and ferrous iron accelerates the conversion of p-quinone into melanin extracellularly

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons in the substantia nigra (SN). 6-Hydroxydopamine (6-OHDA), a dopaminergic neurotoxin, is detected in human brains and the urine of PD patients. Using SH-SY5Y, a human neuroblastoma cell line, we demonstrated that 6-OHDA toxicity was determined by the amount of p-quinone produced in 6-OHDA auto-oxidation rather than by reactive oxygen species (ROS). Glutathione (GSH), which conjugated with p-quinone, provided significant protection whereas catalase, which detoxified hydrogen peroxide and superoxide anions, failed to block cell death caused by 6-OHDA. Although iron accumulated in the SN of patients with PD can cause dopaminergic neuronal degeneration by enhancing oxidative stress, we found that extracellular ferrous iron promoted the formation of melanin and reduced the amount of p-quinone. The addition of ferrous iron to the culture medium inhibited caspase-3 activation and apoptotic nuclear morphologic changes and blocked 6-OHDA-induced cytotoxicity in SH-SY5Y cells and primary cultured mesencephalic dopaminergic neurons. These data suggested that generation of p-quinone played a pivotal role in 6-OHDA-induced toxicity and extracellular iron in contrast to intracellular iron was protective rather than harmful because it accelerated the conversion of p-quinone into melanin.     

Neuroprotective and neurorescue effect of black tea extract in 6-hydroxydopamine-lesioned rat model of Parkinson's disease

In the present study, an attempt has been made to explore the neuroprotective and neuroreparative (neurorescue) effect of black tea extract (BTE) in 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease (PD). In the neuroprotective (BTE + 6-OHDA) and neurorescue (6-OHDA + BTE) experiments, the rats were given 1.5% BTE orally prior to and after intrastriatal 6-OHDA lesion respectively. A significant recovery in d-amphetamine induced circling behavior (stereotypy), spontaneous locomotor activity, dopamine (DA)-D2 receptor binding, striatal DA and 3-4 dihydroxy phenyl acetic acid (DOPAC) level, nigral glutathione level, lipid peroxidation, striatal superoxide dismutase and catalase activity, antiapoptotic and proapoptotic protein level was evident in BTE + 6-OHDA and 6-OHDA + BTE groups, as compared to lesioned animals. BTE treatment, either before or after 6-OHDA administration protected the dopaminergic neurons, as evident by significantly higher number of surviving tyrosine hydroxylase immunoreactive (TH-ir) neurons, increased TH protein level and TH mRNA expression in substantia nigra. However, the degree of improvement in motor and neurochemical deficits was more prominent in rats receiving BTE before 6-OHDA. Results suggest that BTE exerts both neuroprotective and neurorescue effects against 6-OHDA-induced degeneration of the nigrostriatal dopaminergic system, suggesting that possibly daily intake of BTE may slow down the PD progression as well as delay the onset of neurodegenerative processes in PD.     

Progressive degeneration of dopamine neurons in 6-hydroxydopamine rat model of Parkinson's disease does not involve activation of caspase-9 and caspase-3

6-Hydroxydopamine (6-OHDA), a neurotoxin that causes the death of dopamine (DA) neurons, is commonly used to produce experimental models of Parkinson's disease (PD) in rodents. In the rat model of PD first described by Sauer and Oertel, DA neurons progressively die over several weeks following a striatal injection of 6-OHDA. It is generally assumed that DA neurons die through apoptosis after exposure to 6-OHDA, but data supporting activation of a caspase enzymatic cascade are lacking. In this study, we sought to determine if caspases involved in the intrinsic apoptotic cascade play a role in the initial stages of 6-OHDA-induced death of DA neurons in the progressively lesioned rat model of PD. We found that injection of 6-OHDA into adult rat striatum did not activate caspase-9 or caspase-3 or increase levels of caspase-dependent cleavage products in the substantia nigra at various survival times up to 7 days after the lesion, even though this paradigm produced DA neuronal loss. These data suggest that in the adult rat brain DA neurons whose terminals are challenged with 6-OHDA do not die through a classical caspase-dependent apoptotic mechanism.     

SK channel function regulates the dopamine phenotype of neurons in the substantia nigra pars compacta

Parkinson's disease (PD) is characterized by loss of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNc). It is widely believed that replacing lost SNc DA neurons is a key to longer-term effective treatment of PD motor symptoms, but generating new SNc DA neurons in PD patients has proven difficult. Following loss of tyrosine hydroxylase-positive (TH+) SNc neurons in the rodent 6-hydroxy-DA (6-OHDA) model of PD, the number of TH+ neurons partially recovers and there is evidence this occurs via phenotype “shift” from TH− to TH+ cells. Understanding how this putative phenotype shift occurs may help increase SNc DAergic neurons in PD patients. In this study we characterize the electrophysiology of SNc TH− and TH+ cells during recovery from 6-OHDA in mice. Three distinct phenotypes were observed: (1) TH− were fast discharging with a short duration action potential (AP), short afterhyperpolarization (AHP) and no small conductance Ca²⁺-activated K⁺ (SK) current; (2) TH+ were slow discharging with a long AP, long AHP and prominent SK current; and (3) cells with features “intermediate” between these TH− and TH+ phenotypes. The same 3 phenotypes were present also in the normal and D2 DA receptor knock-out SNc suggesting they are more closely related to the biology of TH expression than recovery from 6-OHDA. Acute inhibition of SK channel function shifted the electrophysiological phenotype of TH+ neurons toward TH− and chronic (2 weeks) inhibition of SK channel function in normal mice shifted the neurochemical phenotype of SNc from TH+ to TH− (i.e. decreased TH+ and increased TH− cell numbers). Importantly, chronic facilitation of SK channel function shifted the neurochemical phenotype of SNc from TH− to TH+ (i.e. increased TH+ and decreased TH− cell numbers). We conclude that SK channel function bidirectionally regulates the DA phenotype of SNc cells and facilitation of SK channels may be a novel way to increase the number of SNc DAergic neurons in PD patients.     

NAIP protects the nigrostriatal dopamine pathway in an intrastriatal 6-OHDA rat model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the basal ganglia, associated with the inappropriate death of dopaminergic neurons of the substantia nigra pars compacta (SNc). Here, we show that adenovirally mediated expression of neuronal apoptosis inhibitor protein (NAIP) ameliorates the loss of nigrostriatal function following intrastriatal 6-OHDA administration by attenuating the death of dopamine neurons and dopaminergic fibres in the striatum. In addition, we also addressed the role of the cysteine protease caspase-3 activity in this adult 6-OHDA model, because a role for caspases has been implicated in the loss of dopamine neurons in PD, and because NAIP is also a reputed inhibitor of caspase-3. Although caspase-3-like proteolysis was induced in the SNc dopamine neurons of juvenile rats lesioned with 6-OHDA and in adult rats following axotomy of the medial forebrain bundle, caspase-3 is not induced in the dopamine neurons of adult 6-OHDA-lesioned animals. Taken together, these results suggest that therapeutic strategies based on NAIP may have potential value for the treatment of PD.