Crosstalk between 6-OHDA-induced autophagy and apoptosis in PC12 cells is mediated by phosphorylation of Raf-1/ERK1/2.

Parkinson's disease (PD) is a degenerative brain disorder characterized by motor symptoms and loss of dopaminergic (DA) neurons in the substantia nigra. The mechanisms for DA cell death in PD have been extensively investigated using PC12 cells treated with a dopamine neurotoxin 6-hydroxydopamine (6-OHDA). 6-OHDA may induce both autophagy and apoptosis in PC12 cells. However, it remains unclear whether crosstalk occurs between autophagy and apoptosis in PC12 cells treated with 6-OHDA and whether Raf-1/ERK1/2 and their phosphorylation status play a role in autophagy. In this study, we used MDC staining assay and flow cytometry and found that 6-OHDA induced autophagy in PC12 cells. This induction was inhibited by the autophagy inhibitor 3-MA. Our electron microscopy observations also supported 6-OHDA induced autophagy in PC12 cells. Apoptosis of PC12 cells was increased with inhibition of autophagy by 3-MA. In addition, Inhibition of Raf-1 resulted in a decreased 6-OHDA-induced autophagy rate among PC12 cells. Phosphorylation levels of Raf-1 and ERK1/2 were increased in PC12 cells treated with 6-OHDA and inhibited by co-treatment with 6-OHDA and 3-MA. These data suggest that crosstalk between 6-OHDA-induced apoptosis and autophagy in PC12 cells may be regulated via the Raf-1/ERK1/2 signaling pathway. Our data suggest a mechanism for 6-OHDA toxicity in PC12 cells, contributing to our understanding of the pathogenesis of PD.

NF-κB p65/p52 plays a role in GDNF up-regulating Bcl-2 and Bcl-w expression in 6-OHDA-induced apoptosis of MN9D cell.

Glial-cell-line-derived neurotrophic factor (GDNF) has been shown to protect dopaminergic (DA) neurons against 6-hydroxydopamine (6-OHDA) toxicity. The mechanism underlying the antiapoptosis role of GDNF still needs further studies. We previously observed that nuclear factor-kappaB (NF-κB) signaling pathway, i.e. p65/p52, mediated the antiapoptosis role of GDNF in MN9D cells. Here, the DA cell line MN9D was used to explore the mechanisms underlying NF-κB p65/p52-mediated protection role of GDNF in DA neurons. The results showed that GDNF pretreatment blocked the apoptotic effects induced by 6-OHDA, with the upregulation of the antiapoptotic protein, Bcl-2 and Bcl-w, as well as the downregulation of the proapoptotic proteins, Bax and Bad. Furthermore, when sip100 plasmids were transfected into MN9D cells to inhibit the expression of p100, which was the precursor of p52, the effects of GDNF on upregulating Bcl-2 and Bcl-w were attenuated. These results indicated that GDNF could protect MN9D cells from apoptosis induced by 6-OHDA via upregulating Bcl-2 and Bcl-w expressions and downregulating Bax and Bad expressions. Moreover, NF-κB p65/p52 signaling mediated the effects of GDNF on Bcl-2 and Bcl-w expressions.

Role of toll-like receptor 4 and sex in 6-hydroxydopamine-induced behavioral impairments and neurodegeneration in mice.

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive loss of the nigrostriatal dopaminergic neurons that are associated with motor alterations and non-motor manifestations (such as depression). Neuroinflammation is a process with a critical role in the pathogenesis of PD. In this regard, toll-like receptor 4 (TLR4) is a central mediator of immune response in PD. Moreover, there are gender-related differences in the incidence, prevalence, and clinical features of PD. Therefore, we aimed to elucidate the role of TLR4 in the sex-dependent response to dopaminergic denervation induced by 6-hydroxydopamine (6-OHDA) in mice. Female and male adult wildtype (WT) and TLR4 knockout (TLR4-/-) mice were administered with unilateral injection of 6-OHDA in the dorsal striatum, and non-motor and motor impairments were evaluated for 30 days, followed by biochemistry analysis in the substantia nigra pars compacta (SNc), dorsal striatum, and dorsoventral cortex. Early non-motor impairments (i.e., depressive-like behavior and spatial learning deficits) induced by 6-OHDA were observed in the male WT mice but not in male TLR4-/- or female mice. Motor alterations were observed after administration of 6-OHDA in both strains, and the lack of TLR4 was also related to motor commitment. Moreover, ablation of TLR4 prevented 6-OHDA-induced dopaminergic denervation and microgliosis in the SNc, selectively in female mice. These results reinforced the existence of sex-biased alterations in PD and indicated TLR4 as a promising therapeutic target for the motor and non-motor symptoms of PD, which will help counteract the neuroinflammatory and neurodegenerative processes.

Dopaminergic agents: influence on serotonin in the molluscan nervous system.

Treatment of the mussel Mytilus edulis with 6-hydroxydopamine or with alpha-methyl-p-tyrosine decreased dopamine and increased serotonin in the nervous system. Treatment with dopamine decreased serotonin concentrations and prevented the effect of 6-hydroxydopamine. The serotonin concentration appears to be determined in part by the concentration of dopamine.

Compulsive, abnormal walking caused by anticholinergics in akinetic, 6-hydroxydopamine-treated rats.

In otherwise profoundly akinetic rats that had been severely depleted of brain catecholamines, anticholinergic drugs caused excessive walking. The effect did not appear until 10 days after surgery and then increased with time, suggesting that a phenomenon analogous to denervation supersensitivity may be involved. If the animals walked into corners, they were unable to turn around or back out. Their gait (extremely short steps) was reminiscent of that of patients with Parkinson's disease. The results are consistent with a mutually antagonistic interaction between cholinergic and dopaminergic brain systems and emphasize certain complexities in this interaction.

Depletion of brain catecholamines: failure of ocular dominance shift after monocular occlusion in kittens.

Monocularly deprived kittens were compared with littermates that had had their eyelids sutured for the same time but that had, in addition, been treated with 6-hydroxydopamine to deplete their forebrains of catecholamines. The visual cortices of all the catecholamine-depleted kittens showed high proportions of binocular neurons, in contrast to the control group, most of whose visual cortical neurons were driven exclusively by the nondeprived eye. Catecholamines may play an important role in the maintenance of cortical plasticity during the critical period.

New dopaminergic and indoleamine-accumulating cells in the growth zone of goldfish retinas after neurotoxic destruction.

Juvenile goldfish were allowed to grow for 3 months after dopaminergic or indoleamine-accumulating cells in their retinas had been destroyed by intravitreal injection of 6-hydroxydopamine or 5,7-dihydroxytryptamine, respectively. New cells of each type were found growing in concentric rings at the margin of the retina. To compensate for the loss of dopaminergic innervation in retinas treated with 6-hydroxydopamine, cells in the growth zone appeared to proliferate at a higher rate than those in untreated retinas and long processes were extended into the retina by the first dopaminergic cells to appear.

Compensatory increase in tyrosine hydroxylase activity in rat brain after intraventricular injections of 6-hydroxydopamine.

The neurotoxin 6-hydroxydopamine produced a permanent loss of endogenous norepinephrine and of 3H-labeled norepinephrine uptake sites in the hippocampus within 5 days. These losses were initially accompanied by parallel decreases in tyrosine hydroxylase activity and synaptosomal norepinephrine synthesis. Within 21 days, however, hippocampal tyrosine hydroxylase activity and norepinephrine synthesis rate increased three- to fivefold. These data suggest a novel form of plasticity in brain-damaged animals characterized by an increase in the capacity for transmitter biosynthesis in residual neurons.

Neural connections of sparrow pineal: role in circadian control of activity.

Surgical and chemical interference with the neural connections of the house sparrow (Passer domesticus) pineal does not abolish the free-running rhythm in constant darkness, unlike pinealectomy. Pineals transplanted to the anterior chamber of the eye are capable of restoring rhythmicity to pinealectomized birds in constant darkness. The avian pineal does not appear to be neurally coupled to other components of the circadian system.

beta1- and beta2-Adrenergic receptors in rat cerebral cortex are independently regulated.

Repeated administration of the tricyclic antidepressant desmethylimipramine to adult rats for 10 days caused a 40% decrease in the density of beta1-adrenergic receptors in the cerebral cortex but had no effect on the density of beta2-adrenergic receptors. Conversely, destruction of noradrenergic neurons by administration of 6-hydroxydopamine to neonatal rats caused a 64% increase in the density of beta1-adrenergic receptors in adult cerebral cortex with no change in the density of beta2-adrenergic receptors. These results suggest that the beta-adrenergic receptors in rat cortex involved in neuronal function are primarily of the beta1 subtype.

Environmental influences on body weight and behavior in developing rats after neonatal 6-hydroxydopamine.

There is less hyperactive motor activity and better avoidance performance in rat pups treated with 6-hydroxydopamine as neonates and reared with vehicle-treated littermates than in pups reared in litters composed solely of other 6-hydroxydopamine-treated animals. Thus, in this experimental model of hyperactivity, an environmental manipulation provides an alternative to pharmacologic agents in reducing activity and improving learning performance.

Striatal efferent fibers play a role in maintaining rotational behavior in the rat.

Rats in which ascending dopamine-containing neurons have been unilaterally destroyed by injections of 6-hydroxydopamine are known to rotate after being injected with apomorphine or L-dopa. The rotation is markedly reduced by either (i) ipsilateral electrocoagulations of the caudate-putamen or internal capsule or (ii) ipsilateral coronal knife cuts immediately rostral to the substantia nigra. Neostriatal efferent fibers, in particular the strionigral projection, appear to be required for the expression of this dopamine-dependent behavior.

Dopamine-sensitive adenylate cyclase: location in substantia nigra.

A dopamine-sensitive adenylate cyclase with characteristics similar to those measured in the striatum is present in the rat substantia nigra. Destruction of dopamine cell bodies by intranigral 6-hydroxydopamine application failed to abolish the response of nigral adenylate cyclase to dopamine. In contrast, brain hemitransection between the striatum and substantia nigra, or a more circumscribed lesion of striatonigral pathways, abolished the dopamine stimulation of adenylate cyclase in the substantia nigra. These results suggest that dopamine receptors within the substantia nigra are not located on dopamine cell bodies but are associated with a pathway, containing gamma-aminobutyric acid or substance P, which projects from forebrain structures to the substantia nigra.

Behavior of free-ranging macaques after intraventricular 6-hydroxydopamine.

Macaques (Macaca mulatta) observed in a free-ranging colony on Guayacan Island, Puerto Rico, were significantly different in their social interactions, initiatives, facial expressions, and postures after intraventricular 6-hydroxydopamine compared with sham-treated and field controls. This study extends the known effects of 6-hydroxydopamine and catecholamine depletion to the social interactions of a higher primate species under free-ranging conditions.

Presynaptic location and axonal transport of beta 1-adrenoreceptors in the rat brain.

Interruption of the ascending noradrenergic neurons of the locus coeruleus in the rat forebrain with 6-hydroxydopamine produced a progressive accumulation, proximal to the lesion, of tritiated dihydroalprenolol binding activity over 2 days. This accumulation could be blocked by interrupting the neurons closer to their cell bodies. Competitive binding studies with the beta 2 agonist Zinterol suggested that the accumulated beta-receptors were primarily of the beta 1 subtype. These results suggest that, in the rat brain, some beta 1-adrenoreceptors are located in presynaptic, noradrenergic locus coeruleus neurons and are transported in their axons.

6-Hydroxydopamine potentiates acute herpes simplex virus infection of the superior cervical ganglion in mice.

Treatment of mice with 6-hydroxydopamine increased herpes simplex virus replication in the superior cervical ganglion while it decreased the subsequent prevalence of latent infection. Preganglionic neurectomy failed to block this effect. These observations suggest that intrinsic neural events modify the outcome of viral infections of the nervous system.

Erythrosine (Red No. 3) and its nonspecific biochemical actions: what relation to behavioral changes?

Biochemical studies have shown that the ability of erythrosine to inhibit dopamine uptake into brain synaptosomal preparations is dependent on the concentration of tissue present in the assay mixture. Thus, the finding that erythrosine inhibits dopamine uptake (which, if true, would provide a plausible explanation of the Feingold hypothesis of childhood hyperactivity) may simply be an artifact that results from nonspecific interactions with brain membranes. In addition, although erythrosine given parenterally (50 milligrams per kilogram) did not alter locomotor activity of control of 6-hydroxydopamine-treated rats, erythrosine (50 to 300 milligrams per kilogram) attenuated the effect of punishment in a "conflict" paradigm.

Increased dopamine receptor sensitivity after estrogen treatment using the rat rotation model.

Estrogen was administered to male rats that had received unilateral injections of 6-hydroxydopamine into the striatum. Following this treatment, their duration of rotation increased in response to amphetamine. Estrogen treatment resulted in a corresponding increase in the number of striatal dopamine receptors. Therefore, both behavioral and biochemical evidence suggests that striatal dopamine function is influenced by peripherally administered estrogens. These results are relevant to the clinical cases of chorea associated with elevated concentrations of estrogen, which occur in pregnancy and during oral contraceptive use.

Dopamine receptor binding enhancement accompanies lesion-induced behavioral supersensitivity.

The binding of [3H]haloperidol to rat striatal dopamine receptors increases after lesion (made by injection of 6-hydroxydopamine) of the nigrostriatal dopamine pathway in those rats which are behaviorally supersensitive, as reflected by apomorphine-induced contralateral rotations. The enhanced binding is associated with an increased number of receptor sites with no change in their affinity.

Tetrahydrobiopterin in striatum: localization in dopamine nerve terminals and role in catecholamine synthesis.

The hydroxylase cofactor, tetrahydrobiopterin, and its biosynthetic system are localized in dopaminergic nerve terminals in the striatum. This conclusion is based on the nearly equivalent loss of tyrosine hydroxylase and tetrahydrobiopterin and its initial biosynthetic enzyme, guanosine triphosphate cyclohydrolase, after injection of 6-hydroxydopamine into the substantia nigra. The role of the hydroxylase cofactor in the regulation of dopamine synthesis is reassessed.