Retinal cholinergic and dopaminergic deficits of aged rats are improved following treatment with GM1 ganglioside

Selected cholinergic and dopaminergic markers were compared in the retina of aged (20–22-months-old) and young (3-months-old) rats before and after treatment with GM1 ganglioside. The dopaminergic markers, tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid were comparable in the young and aged animals and GM1 treatment did not alter them. In contrast, mazindol binding, a marker for the dopamine transporter, was diminished in the aged retina and treatment with GM1 restored binding to values found in the young animals. The cholinergic markers choline acetyltransferase and hemicholinium-3 binding, a marker for the high-affinity choline transport, were depressed in aged rats and GM1 corrected the deficits.     

Differential effects of scopolamine on in vivo binding of dopamine transporter and vesicular monoamine transporter radioligands in rat brain

The in vivo equilibrium specific binding of d-threo-[3H]methylphenidate, a radioligand for the dopamine transporter (DAT), and +-alpha-[3H]dihydrotetrabenazine, a radioligand for the vesicular monoamine transporter (VMAT2), were examined in rat brain with and without prior administration of 5 mg/kg scopolamine. Drug-treated animals exhibited a 30% increase in d-threo-[3H]methylphenidate binding to the DAT in the striatum relative to controls. No changes in specific binding of +-alpha-[3H]dihydrotetrabenazine were observed in any brain region following scopolamine pretreatment. Cholinergic drugs thus differentially affect in vivo specific binding of DAT and VMAT2 radioligands, suggesting this should be a consideration in selection of in vivo markers for imaging studies of dopaminergic terminals in the brain of animals and humans.     

百草枯对小鼠黑质多巴胺能神经元的选择性损害

目的:探讨百草枯对黑质部多巴胺能神经元的损害是否具有选择性。方法:用口服百草枯的途径,建立小鼠帕金森病模型;应用原位杂交技术观察DAT和VMAT2在不同脑区的mRNA表达水平并测定两者的比值,采用细胞计数观察百草枯干预后多巴胺能神经元的损害。结果:在黑质部DATmRNA和VMAT2mRNA的比值最高;在红核和下丘脑室旁核区域DATmRNA与VMAT2mRNA的比值和黑质部相比较低(P<0·01)。百草枯干预后黑质部的多巴胺能神经元减少37·7%;红核和下丘脑室旁核区的多巴胺能神经元分别减少12·2%和13·1%。结论:百草枯对黑质部多巴胺能神经元的损害具有相对选择性,其原因可能与黑质部DATmRNA和VMAT2mRNA的比值高有关。     

Motoric behavior in aged rats treated with GM1.

Aging is associated with impaired motor function. Nigrostriatal dopaminergic neurons, in part, regulate motoric behavior, and undergo degenerative changes during aging. GM1 ganglioside partially restores pre-synaptic dopaminergic markers and the number and morphology of dopaminergic neurons in the midbrain and striatum of Sprague--Dawley aged rats. These studies investigated whether GM1 treatment, 30 mg/kg, i.p. daily for 36 days, affects locomotor and stereotypic activity, as well as coordination, balance, and strength in aged rats. Under the treatment conditions used, GM1 did not improve the reduced locomotor and stereotypic behavior of the aged rats. While it partially improved performance on a square bridge test, GM1 had no effect on inclined screen and rod suspension tests. Although GM1 restored the decreased content of dopamine and homovanillic acid in the nigrostriatal neurons of the aged rats, it had no effect on the reduced D1 and D2 dopamine receptor binding and mRNA in the striatum. It appears, that despite the morphological and metabolic restoration of aged nigrostriatal neurons, GM1 has limited ability in improving age-associated motor deficits.     

Age-related changes in dopamine transporters and accumulation of 3-nitrotyrosine in rhesus monkey midbrain dopamine neurons: relevance in selective neuronal vulnerability to degeneration

Aging is the strongest risk factor for developing Parkinson's disease (PD). There is a preferential loss of dopamine (DA) neurons in the ventral tier of the substantia nigra (vtSN) compared to the dorsal tier and ventral tegmental area (VTA) in PD. Examining age-related and region-specific differences in DA neurons represents a means of identifying factors potentially involved in vulnerability or resistance to degeneration. Nitrative stress is among the factors potentially underlying DA neuron degeneration. We studied the relationship between 3-nitrotyrosine (3NT; a marker of nitrative damage) and DA transporters [DA transporter (DAT) and vesicular monoamine transporter-2 (VMAT)] during aging in DA subregions of rhesus monkeys. The percentage of DA neurons containing 3NT increased significantly only in the vtSN with advancing age, and the vtSN had a greater percentage of 3NT-positive neurons when compared to the VTA. The relationship between 3NT and DA transporters was determined by measuring fluorescence intensity of 3NT, DAT and VMAT staining. 3NT intensity increased with advancing age in the vtSN. Increased DAT, VMAT and DAT/VMAT ratios were associated with increased 3NT in individual DA neurons. These results suggest nitrative damage accumulates in midbrain DA neurons with advancing age, an effect exacerbated in the vulnerable vtSN. The capacity of a DA neuron to accumulate more cytosolic DA, as inferred from DA transporter expression, is related to accumulation of nitrative damage. These findings are consistent with a role for aging-related accrual of nitrative damage in the selective vulnerability of vtSN neurons to degeneration in PD.     

Immunochemical analysis of vesicular monoamine transporter (VMAT2) protein in Parkinson's disease

The vesicular monoamine transporter (VMAT2) has been suggested to be an excellent marker of presynaptic dopaminergic nerve terminals in the striatum of Parkinson's disease patients based on its high level of expression and insensitivity to drugs used to treat the disease. Previous in vivo imaging and postmortem binding studies have detected a loss in striatal VMAT2 binding in Parkinson's diseased (PD) brain; however, these techniques have poor spatial resolution and may suffer from nonspecific binding of some ligands. In this study, we use novel polyclonal antibodies to distinct regions of human VMAT2 to quantify and localize the protein. Western blot analysis demonstrated marked reductions in VMAT2 immunoreactivity in putamen, caudate, and nucleus accumbens of PD brain compared to control cases. Immunohistochemistry revealed VMAT2 immunoreactive fibers and puncta that were dense throughout the striatum of control brains, but which were drastically reduced in putamen of PD brains. In PD brains the caudate showed a significant degree of sparing along the border of the lateral ventricle and the nucleus accumbens was relatively preserved. The distribution of VMAT2 in striatum and its loss in PD paralleled that of the dopamine transporter (DAT), a phenotypic marker of dopamine neurons. Thus, immunochemical analysis of VMAT2 protein provides novel and sensitive means for localizing and quantifying VMAT2 protein and nigrostriatal dopamine terminals in PD. Furthermore, the relative expression of VMAT2 compared to that of DAT may predict the differential vulnerability of dopamine neurons in PD.     

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.     

Developmental and age-related changes of dopamine transporter, and dopamine D1 and D2 receptors in human basal ganglia

The developmental and age-related changes of the dopamine transporter (DAT), and the dopamine D1 and D2 receptor (D1R and D2R) subtypes were investigated in basal ganglia (BG) of human brain. DAT immunostaining was mainly observed in the neuropil, neurons, and glia of the striatum. The DAT-positive neuropil was detectable at 32 GW, a peak being reached at 9–10 years of age, with a decrease to 50–63 years of age. The developmental pattern of DAT immunoreactivity in neuron was similar to that of the neuropil. DAT-positive glia were observed in the BG at 32 GW, which increased slightly at 38–40 GW, and then did not obviously change until 6–8 months after birth. D2R-positive neurons were clearly observed at 19 GW, a peak being reached at 32 GW and 1–3 months of age in the globus pallidus and striatum, respectively, with a decrease after 9–10 years of age. D1R was expressed as early as D2R, but decreased after 6–8 months. Our results suggest that D1R and D2R expression is an intrinsic property of striatal neurons and is independent of dopaminergic innervation. D1R may play a more important role in neuronal maturation of the BG than D2R. D2R may be closely correlated with late neuronal development. The higher expression of DAT during adolescence may be related to function of the BG which learns complex behavioral patterns. The significance of the age-related decreases in DAT, D1R and D2R in the BG remains to be further investigated.