The degree of neuronal loss is related to disease duration and follows a stereotyped spatiotemporal progression (from the more caudal nigrosome N1 > N2 > N4 > N3 to the more rostral nigrosome N5) [11] consistently observed across PD patients and differing from normal aging or other neurodegenerative disorders [7]. While neuronal loss is particularly severe within the SN ventrolateral tier, involvement of other midbrain dopaminergic cell populations (medial and medioventral, A8, substantia nigra pars lateralis, central gray substance)

is less pronounced and Crizotinib in vitro may rather reflect some physiological aging-related decline [12]. Surviving nigral neurons frequently exhibit cytoplasmic protein inclusions referred to as LB or Lewy neurites if located in neuronal processes, which contain, among many others proteins, misfolded α-synuclein (α-SYN) and ubiquitin (Ub) [13]. It is still unclear if LBs themselves are the pathological entities interfering with normal cell function,

if they represent a cytoprotective mechanism similarly to aggresomes or a failed attempt to eliminate cytotoxic find more proteins such as misfolded α-SYN. The percentage of LB-bearing nigral cells appears to be stable over time (3.6% in average), suggesting that they are eliminated as the disease progresses when the afflicted neurons die. Thus, in the SN at least, LB may be closely related to nigral neuronal loss [14]. Current knowledge on LB structure, formation, composition and role in cell death is still limited and reviewed elsewhere (in [15]). Of note, LBs are not specific for PD, as they are found in other forms of parkinsonism collectively

termed “synucleopathies” (i.e., dementia with LB, multiple system atrophy), in Alzheimer’s disease (AD), as well as incidentally in aged people [16]. Neuronal loss and LB formation are neither confined to the midbrain and the SN, nor restricted to the dopaminergic neurochemical system. Based on neuropathological studies, PD is now rather viewed as a multisystem disorder affecting numerous Anacetrapib neuronal populations both in the central and peripheral nervous systems [17]. Dopaminergic neurons found outside the midbrain are unequally vulnerable to PD, partially lost in the retina [18] and enteric nervous system [19] while relatively spared in the hypothalamus or bone marrow [20]. Noradrenergic (i.e., locus coeruleus), cholinergic (i.e., dorsal motor nucleus of the vagus nerve (DMV), nucleus basalis of Meynert), serotoninergic (i.e., raphe nuclei) or glutamatergic (i.e., amygdala, cortex) systems are also affected in anatomical regions of predilection within the brain as well as nerve and ganglia of the autonomic system [17].