Acute and chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine administrations elicit similar microglial activation in the substantia nigra of monkeys.

Increasing evidence suggests a pivotal role for neuroinflammation in the pathogenesis of Parkinson disease, but whether activated microglia participate in disease progression remains unclear. To clarify this issue, we determined the numbers of activated microglial cells in the substantia nigra pars compacta and ventral tegmental area of monkeys subacutely and chronically exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Monkeys in the subacute MPTP treatment group were killed 1 week after the last MPTP injection; chronically treated monkeys were killed either 6 or 35 months after the last MPTP injection. Subacute MPTP administration induced loss of dopaminergic neurons in the substantia nigra pars compacta and ventral tegmental area and microglial activation in the same areas. Chronic MPTP treatment resulted in greater dopaminergic neuron depletion in both treatment groups. Both groups of chronic MPTP-treated monkeys showed increased numbers of activated microglial cells in the substantia nigra pars compacta that were similar to those of the subacute MPTP treatment group. These results indicate that microglial activation seems to be induced mainly by the toxic effects of MPTP and that it does not further progress once the toxin administration has been terminated. This suggests that the progressive degeneration of nigral cells in Parkinson disease may not necessarily be associated with progressively increased microglial activation.

Evidence for a dopaminergic innervation of the pedunculopontine nucleus in monkeys, and its drastic reduction after MPTP intoxication.

The involvement of the pedunculopontine nucleus (PPN) and the adjacent cuneiform nucleus (CuN), known as the mesencephalic locomotor area, in the pathophysiology of parkinsonian symptoms is receiving increasing attention. Taking into account the role of dopamine (DA) in motor control and its degeneration in Parkinson's disease, this neurotransmitter could induce dysfunction in the PPN and CuN through a direct dopaminergic innervation of these brainstem structures. This study provides the first demonstration that the PPN and CuN are innervated by dopamine transporter-bearing fibres in normal monkeys, which points to a novel dopaminergic system that targets the lower brainstem. Intoxication with MPTP induced a significant loss of dopamine transporter-positive fibres in the PPN and CuN of young (3-5 years old) acutely or chronically intoxicated monkeys compared with control animals. The more severe DA depletion found after chronic intoxication may explain, at least in part, deficits that appear late in the evolution of Parkinson's disease. A drastic loss of DA fibres was also observed in aged acutely intoxicated monkeys (about 30 years old) suggesting that age- and disease-related loss of dopaminergic fibres might be responsible for symptoms, such as gait disorders, that are more severe in elderly parkinsonian patients.

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) does not elicit long-lasting increases in cyclooxygenase-2 expression in dopaminergic neurons of monkeys.

To elucidate the role of the prostaglandin synthase cyclooxygenase-2 (Cox-2) and the mechanisms of dopaminergic (DA) neurodegeneration, monkeys were injected subacutely or chronically (n = 5/group) with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Chronically treated animals developed parkinsonian signs and were killed 6 months after the last treatment; tyrosine hydroxylase-expressing neurons decreased in all substantia nigra (SN) cell groups in both treatment groups. In untreated controls (n = 3), there was low Cox-2 expression in ventral SN DA neurons and high expression in ventral tegmental area neurons. In subacutely treated monkeys, Cox-2 expression increased in surviving DA cells, particularly in the ventrolateral SN. In chronically treated monkeys, enhanced Cox-2 expression appeared only in surviving ventral tegmental area and ventral SN neurons. Thus increased Cox-2 did not persist in other SN neurons after discontinuing 1-methyl-4-phenyl-1,2,36-tetrahydropyridine. Some DA neurons in treated but not control monkeys expressed the active nuclear form of phospho-c-Jun, but not the active form of nuclear factor-kappaB. We conclude that Cox-2 expression does not confer vulnerability to neurodegeneration in DA neurons and that it is unlikely that a subacute insult to DA neurons can perpetuate degeneration through Cox-2 activation. Other mechanisms, probably through the Jun N-terminal kinase cascade, lead to DA cell death in this model.

Striatal carotid body graft promotes differentiation of neural progenitor cells into neurons in the olfactory bulb of adult hemiparkisonian rats.

Progenitor cells generated in the subventricular zone (SVZ) migrate toward the olfactory bulb (OB), where they differentiate into neurons. Growth factors have been shown to promote neurogenesis in the SVZ/OB-system while dopaminergic lesion exerts an opposite effect. As carotid body (CB) cells express growth factors here we study the impact of intrastriatal CB graft on migration and differentiation of neural progenitor cells in the hemiparkinsonian rat SVZ/OB-system. Bromodeoxyuridine (BrdU) was given to intact, 6-hydroxydopamine (6-OHDA)-lesioned and 6-OHDA-lesioned animals transplanted with vehicle or rat CB cells. The migration of progenitor cells was assessed by the quantification of BrdU-labeled cells in the SVZ/OB-system and the neuronal differentiation by the proportion of newborn neurons in the OB. The graft survival was confirmed by CB cell morphology and their tyrosine hydroxylase expression. Some of these CB cells were stained with BrdU, thus indicating their ability for self-renewal. Grafted glomus cells also expressed brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), epidermal growth factor (EGF) and vascular endothelial growth factor (VEGF). The migration of neural progenitor cells was significantly decreased in 6-OHDA-lesioned respect to intact animals. We found a similar number of BrdU-labeled cells in sham-operated than in CB-grafted animals, suggesting that CB graft has no effect on progenitor cell migration. CB-grafted animals exhibited a significantly larger percentage of newborn cells (BrdU/Neuronal Nuclei-labeled cells) respect to 6-OHDA-lesioned and sham-operated animals. This study suggests that striatal CB graft might promote differentiation of SVZ progenitor cells into neurons, probably by the growth factors contained in CB cells.

Immunohistochemical characterization of the rat carotid body.

We studied the histochemical phenotype of carotid body (CB) cells in the adult rat. In addition to tyrosine hydroxylase (TH), type I cells expressed numerous growth factors such as glial cell line-derived neurotrophic factor (GDNF), basic fibroblast growth factor (bFGF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha), as well as the receptors p75, Ret, epidermal growth factor receptor (EGFR) and platelet-derived growth factor receptor-alpha (PDGFR-alpha). Type II cells expressed the glial fibrillary acid protein (GFAP), vimentin, the trophic factor bFGF and receptors p75, EGFR and PDGFR-alpha. Both types I and II cells exhibited a positive immunoreaction to markers of neural progenitor cells such as the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) and nestin, respectively, suggesting that CB contain some immature cells even at the adult stage. The possibility that these cells can be expanded and differentiated into mature neurons should be explored.

The number of dopaminergic cells is increased in the olfactory bulb of monkeys chronically exposed to MPTP.

We investigated the impact of the nigrostriatal lesion on the olfactory tyrosine hydroxylase-immunoreactive (TH-ir) cells in monkeys. The majority of these TH-ir cells appeared in the glomerular layer of the olfactory bulb and many were immature but functional dopaminergic neurons. In parkinsonian monkeys the number of olfactory dopaminergic neurons increased up to 100% as compared to controls, but their phenotype did not change. This increased TH-ir cell population might be a direct consequence of the nigral cell loss and contribute to the hyposmia reported by Parkinson's disease patients.