Aging of the Nigrostriatal Pathway in Humans

Abstract

Progressive degeneration of functionally related groups of neurons occurs in certain infective, toxic, nutritional and genetically determined neurological diseases. It also takes place in normal aging, and several of the regions that undergo selective decay with the passage of time seem to be the same target regions that are afflicted in degenerative disorders such as Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis (ALS). Infective etiology is relatively easy to exclude by a combination of immunological tests and transfer experiments. Genetic causation can be rendered unlikely when large kindreds are available for study. Nutritional deprivation and acute or subacute toxicity are accessible to explanation by examining the environment. The most difficult mechanism of pathogenesis to refute is chronic toxic damage, where the lesion may derive from long-term exposure to a relatively widespread noxious agent or agents. Variations in involvement of individuals within a population may stem from differing capacities to activate or inactivate a toxin. Inherent in this concept of etiology is recognition that compensatory potential within the central nervous system may contribute to prolonged existence of subclinical lesions so that a latent period may exist for several decades, between causal event and the onset of symptoms. Furthermore, progressive clinical deterioration may take place even though the cause may have been transient, many years before. The histological features associated with Parkinson's disease, Alzheimer's disease and ALS may be nonspecific indicators of neuronal "illness", there being a predilection for certain morphological markers to appear more frequently in particular circumstances and particular regions associated with the pathology of particular diseases. RESUME: Vieillissement du systeme nerveux et abiotrophie. Une degenerescence progressive de groupes de neurones qui sont relies entre eux par leur fonction survient dans certaines maladies neurologiques d'origine infectieuse, toxique, nutritionnelle ou genetique. Ce phenomene survient aussi dans le vieillissement normal et plusieurs regions qui subissent une degenerescence selective avec le temps semblent etre les memes regions qui sont la cible de maladies degeneratives comme la maladie de Parkinson, la maladie d'Alzheimer et la SLA. Une etiologie infectieuse est relativement facile a exclure au moyen d'une combinaison d'epreuves immunologiques et d'essais de transmission de la maladie. On peut pratiquement eliminer une etiologie genetique quand on peut etudier des grandes families. La carence nutritionnelle peut etre soumise a l'analyse epidemiologique. La toxicite aigiie et subaigile peut elle aussi generalement etre expliquable en examinant l'environnement. Le mecanisme pathogenique le plus difficile a refuter est l'intoxication chronique, le dommage pouvant alors resulter d'une exposition prolongee a un ou des agent(s) nocif(s) relativement repandu(s). Des variations dans le degre d'atteinte des individu...

The Association Between Parkinsonism, Alzheimer's Disease, and Mortality: A Comprehensive Approach

“…Autopsy studies of AD patients indicate that some patients with extrapyramidalism have a coincident diagnosis of IPD (nigral degeneration with Lewy Body formation), 5,26–28 others have nonspecific nigral changes, 28,29 and some have no structural nigral abnormalities 5,27–30 . In normal aging, there is a steady decline of nigral neurons and striatal dopamine and an increase in incidental Lewy bodies in the substantia nigra 31–33 . Interestingly, the specific pattern nigrostriatal neuronal loss in normal aging and AD with parkinsonism has been reported to be distinct from that of IPD, 30–33,34 suggesting that parkinsonism associated with aging and AD differs mechanistically from that of IPD and is not merely a subtle manifestation of that disease.…”

“…In normal aging, there is a steady decline of nigral neurons and striatal dopamine and an increase in incidental Lewy bodies in the substantia nigra 31–33 . Interestingly, the specific pattern nigrostriatal neuronal loss in normal aging and AD with parkinsonism has been reported to be distinct from that of IPD, 30–33,34 suggesting that parkinsonism associated with aging and AD differs mechanistically from that of IPD and is not merely a subtle manifestation of that disease.…”

Extracellular glutamate levels increase with age in the lateral striatum: Potential involvement of presynaptic D‐2 receptors

“…Progressive neuronal cell loss occurs during the course of natural aging and may be accelerated in agerelated neurodegenerative disorders such as senile dementia, Parkinson's disease, and Huntington's chorea (Calne and Peppard, 1987;Martin and Palmer, 1989;McGeer et al, 1989). The mechanisms responsible for age-related neuronal attrition are not understood, but some evidence suggests that glutamate, an excitatory amino acid neurotransmitter (Fonnum, 1984), may be involved in some neurodegenerative processes.…”

α-Synuclein, leucine-rich repeat kinase-2, and manganese in the pathogenesis of parkinson disease

“…The clinical features of PD include bradykinesia, postural instability, resting tremor, and rigidity which are predominantly associated with the progressive loss of dopaminergic neurons in the substantia nigra (SN) pars compacta (Cronford et al, 1995; Forman et al, 2005; Forno, 1996). It is believed that during normal aging approximately 0.1–0.2% of the dopaminergic neurons in this area are lost per year, but this rate is greatly accelerated in patients with PD and symptoms manifests when ~70–80% of these neurons have been lost (Calne and Peppard, 1987; Damier et al, 1999; Pakkenberg et al, 1991; Uversky, 2004). Another pathological hallmark of PD is the presence of α-synuclein proteiniacous inclusions, known as Lewy bodies (LBs) and Lewy neurites (LNs), in some of the remaining dopaminergic neurons (Cronford et al, 1995; Forman et al, 2005; Forno, 1996).…”