The neonatal lesion of the meso-telencephalic dopaminergic pathway increases intrastriatal D2 receptor levels and synthesis and this effect is reversed by neonatal dopaminergic rich-graft

Long-term ginsenoside administration prevents memory loss in aged female C57BL/6J mice by modulating the redox status and up-regulating the plasticity-related proteins in hippocampus

Memory impairment is considered to be one of the most prominent consequences of aging. Deterioration of memory begins in advance of old age in animals, including humans. The generation of reactive oxygen species (ROS) and/or free radicals-induced oxidative stress which is the major age-related changes, can lead to hippocampus damage and increase vulnerability to impaired learning and memory. Ginsenoside, the effective ingredient of ginseng, has been reported to have a neuron beneficial effect. In the present study, C57BL/6J mice aged 12 months were chronically treated with ginsenoside (three dose groups were given ginsenoside in drinking water for 8 months, the concentration of ginsenoside in drinking water was 0.028%, 0.056%, and 0.112% (w/v), respectively). Placebo-treated aged mice and young ones (4 months old) were used as controls. The efficacious effect of ginsenoside was manifested in the amelioration of memory impairment in aged mice by Morris water maze and step-down tests. Total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), and thiobarbituric acid reactive substances (TBARS) have been used as the biomarkers of oxidative stress. In ginsenoside treated groups, the activities of T-SOD and GSH-Px markedly increased, and the levels of TBARS and the content of protein carbonyl decreased significantly in serum and in hippocampus. The activation of lipofuscin formation, disruption or loss of cristae in mitochondria, the irregular nucleus and condensed chromatin laid against the nuclear membrane in pyramidal cells of hippocampal CA1 region, which are all related to oxidative stress, were also reduced after ginsenoside treatment. Processes of memory formation and functional plasticity are associated with postsynaptic density-95 (PSD-95), protein kinase Cγ subunit (PKCγ) and brain derived neurotrophic factor (BDNF). In the present study, we found that long-term ginsenoside treatment prevented age-related reductions of PSD-95, PKCγ, and BDNF in the hippocampus. These results demonstrated that long-term ginsenoside administration may prevent memory loss in aged C57BL/6J mice by modulating the redox status and up-regulating the plasticity-related proteins in hippocampus.

There is a limited critical period for dopamine's effects on D1 receptor expression in the developing rat neostriatum

Neonatal lesions of the dopamine (DA) system have different behavioral and neurochemical effects than lesions made in adulthood. Previous data from this laboratory have indicated that in the early postnatal period, lesions to the DA system induced by instrastriatal 6-hydroxydopamine (6-OHDA) result in a rapid and permanent loss of striatal D1 binding sites, but D2 receptor binding is unaffected. The length of the postnatal period within which neonatal instrastriatal 6-OHDA administration is effective in modulating D1 receptor binding is not known. To determine when D1 and D2 receptors are vulnerable to lesions of the DA system, we administered 6-OHDA intrastriatally to damage the DA innervation at different ages in the early postnatal period, at day of birth/postnatal day 1 (P0/1), P7 or P15 and examined DA receptor binding at P90 with quantitative autoradiography. Using [3H]mazindol binding to DA transporters (DAT) to verify the extent of the lesion, we then quantified the number of D1 binding sites using [3H]SCH23390 and D2 sites with [3H]spiroperidol. There were significant reductions in DAT sites at P0/1 (78 to 88%) and P7 (67 to 81%) but less significant changes at P15 (34 to 50% losses). The lesions were most effective for the dorsal caudate-putamen than more ventrally or in the nucleus accumbens. Our results demonstrate a significant reduction in D1 sites in all regions of the neostriatum following lesions at P0/1. The dorsal caudate-putamen was affected the most (51% loss, and the nucleus accumbens (41%) and ventral caudate-putamen less so (31%). No significant changes in D1 receptors were found at P7 or P15 and D2 receptors were unaffected with lesions in any of the age groups. The results indicate that there is a critical period for affecting expression of D1 receptors and this effect may, in addition, be related to the pattern of DA loss. Additionally, regulation of D2 receptors by this degree of loss of DA innervation does not occur during the first two weeks postnatally.

Phenotype of striatal cells expressing c-Fos following amphetamine treatment of rats with intrastriatal dopaminergic grafts

Activation of the nigrostriatal dopaminergic system by psychostimulants such as amphetamine increases c-Fos expression in the striatum, mostly in the striatonigral substance P-ergic pathway. This effect is greatly reduced in the neostriatum deprived of dopaminergic afferents. Dopaminergic grafts implanted into the denervated neostriatum restore the reactivity of the striatum to amphetamine. However, the number of striatal neurons expressing c-Fos is greatly increased in the graft-bearing striatum compared with the normal striatum. We examined whether this increase in the number of c-Fos-expressing neurons corresponds to the recruitment of a new neuron population, or whether it reflects an increase in the proportion of substance P-ergic neurons exhibiting activation of c-Fos. Adult rats received a unilateral 6-hydroxydopamine lesion of the ascending dopaminergic mesotelencephalic pathway, and a suspension of embryonic mesencephalic neurons was subsequently implanted into the denervated neostriatum. Three months after implantation, animals were injected with d-amphetamine (5 mg/kg) and killed 2 h later. In the first experiment, striatal sections were processed to visualize both c-Fos protein, by immunohistochemistry, and preproenkephalin A or substance P, by in situ hybridization. In the second experiment, c-Fos and neuropeptide Y were visualized on the same sections. In addition, some sections incubated with anti-c-Fos antibody were counterstained with toluidine blue in order to determine whether cholinergic neurons were expressing c-Fos following amphetamine treatment. The density of neurons expressing c-Fos following amphetamine treatment was three-fold higher in the graft-bearing striata than in the striata of control animals. Approximately 75% of the c-Fos expressing cells were substance P-ergic in control animals whereas 6% were enkephalinergic and only a few were neuropeptide Y-ergic or cholinergic. Similar proportions were found in the graft-bearing striatum, signifying that the pattern of activation of c-fos following amphetamine administration is not changed by the graft. Thus, the increased expression of c-Fos predominantly reflects a graft-induced increase in the proportion of neurons expressing c-Fos within the same population of neurons which normally expresses c-Fos in the striatum, i.e. the striatonigral substance P-ergic neurons; there is no recruitment of a new neuronal population. This increased activation of the striatonigral substance P-ergic pathway may underlie the abnormal behavioural reactions brought about by amphetamine-induced stimulation of the implanted dopaminergic neurons.

Changes in striatal immediate early gene expression following neonatal dopaminergic lesion and effects of intrastriatal dopaminergic transplants

To evaluate the functional integration of neonatal dopaminergic transplants within host brain we studied the postsynaptic effects induced by their stimulation by following the expression of immediate early genes c-fos, c-jun and egr-1. This study was conducted nine months after the intrastriatal implantation of embryonic mesencephalic neurons to rat pups having sustained a unilateral lesion of the nigrostriatal dopaminergic system. We examined whether, when challenged with d-amphetamine: (1) dopaminergic grafts transplanted into the previously denervated neonatal neostriatum lead to a normal activation of postsynaptic striatal neurons in term of immediate early genes activation; and (2) whether this activation is related to the action of the dopamine released from the grafts using a dopaminergic D1 antagonist. Following a mild stress-injection of saline-c-fos expression was high in the lesioned neostriatum when compared with control animals. This effect was only partially counteracted by a pre-treatment with the D1 antagonist SCH 23390, but was abolished by the graft. Administration of d-amphetamine increased c-fos expression in the neostriatum and the globus pallidus of the control group. This activation was partially blocked by the lesion. The transplant reversed the effect of the lesion and, moreover, led to a c-fos over-expression in the dorsolateral neostriatum and the globus pallidus. These overcompensations positively correlated with the abnormal rotation induced by d-amphetamine in the same animals. Pre-treatment with SCH 23390 blocked the effect of d-amphetamine on c-fos expression in control and grafted animals. Similar results were found for egr-1 but not c-jun expression. It is concluded that the neonatal lesion of the nigrostriatal dopaminergic pathway, in contrast to the adult-stage lesion, modifies the reactivity of c-fos in the neostriatum to stress, presumably in relation with compensatory reorganizations occurring following the neonatal lesion. Grafts made into neonates, when challenged with amphetamine, induce an abnormal c-fos expression which can predict the degree of overshoot observed for rotation activity. This over-expression, which depends upon the stimulation of D1 receptors, indicate an abnormal activation of postsynaptic target cells by the grafts.