Cholinergic deficits and galaninergic hyperinnervation of the nucleus basalis of Meynert in Alzheimer's disease and Lewy body disorders.

AIMS: Galanin is a highly inducible neuroprotective neuropeptide and in Alzheimer's disease (AD), a network of galaninergic fibres has been reported to hypertrophy and hyperinnervate the surviving cholinergic neurons in the basal forebrain. We aimed to determine (i) the extent of galanin hyperinnervation in patients with AD and Lewy body disease and (ii) whether galanin expression relates to the neuropathological burden and cholinergic losses. METHODS: Galanin immunohistochemistry was carried out in the anterior nucleus basalis of Meynert of 27 Parkinson's disease (PD) cases without cognitive impairment (mild cognitive impairment [MCI]), 15 with PD with MCI, 42 with Parkinson's disease dementia (PDD), 12 with Dementia with Lewy bodies (DLB), 19 with AD, 12 mixed AD/DLB and 16 controls. Galaninergic innervation of cholinergic neurons was scored semiquantitatively. For a subgroup of cases (n = 60), cholinergic losses were determined from maximum densities of choline acetyltransferase positive (ChAT+ve) neurons and their projection fibres. Quantitative data for α-synuclein, amyloid beta and tau pathology were obtained from tissue microarrays covering cortical/subcortical regions. RESULTS: Significant losses of cholinergic neurons and their projection fibres were observed across all diseases. Galaninergic hyperinnervation was infrequent and particularly uncommon in established AD and DLB. We found that hyperinnervation frequencies are significantly higher in the transition between PD without MCI to PDD and that higher burdens of co-existent AD pathology impair this galaninergic response. CONCLUSIONS: Our results suggest that galanin upregulation represents an intrinsic response early in Lewy body diseases but which fails with increasing burdens of AD related pathology.

Axonal myelin decrease in the splenium in major depressive disorder.

The corpus callosum has become a key area of interest for researchers in severe mental illness. Disruptions in fractional anisotropy in the callosum have been reported in schizophrenia and major depressive disorder. No change has been reported in oligodendrocyte density and overall size of the callosum in either illness, suggesting that gross morphology is unchanged, but subtler organisational disruption may exist within this structure. Using high-resolution oil immersion microscopy, we examined the cross-sectional area of the nerve fibre and the axonal myelin sheath; and using standard high-resolution light microscopy, we measured the density of myelinated axons. These measurements were made in the splenium of the corpus callosum. Measures were taken in the sagittal plane in the callosal splenium to contrast with the previous similar examination of the callosal genu. Cases of major depressive disorder had significantly decreased mean myelin cross-sectional area (p = 0.014) per axon in the splenium than in controls or schizophrenia groups. There was no significant change in the density of myelinated axons. The results suggest a clear decrease of myelin in the axons of the callosal splenium in MDD, although this type of neuropathological study is unable to clarify whether this is caused by changes during life or has a developmental origin. In contrast with increased myelin in the callosal genu, this result suggests a longitudinal change in callosal myelination in major depressive disorder not present in normal or schizophrenic brains.

Review: Revisiting the human cholinergic nucleus of the diagonal band of Broca.

Although the nucleus of the vertical limb of the diagonal band of Broca (nvlDBB) is the second largest cholinergic nucleus in the basal forebrain, after the nucleus basalis of Meynert, it has not generally been a focus for studies of neurodegenerative disorders. However, the nvlDBB has an important projection to the hippocampus and discrete lesions of the rostral basal forebrain have been shown to disrupt retrieval memory function, a major deficit seen in patients with Lewy body disorders. One reason for its neglect is that the anatomical boundaries of the nvlDBB are ill defined and this area of the brain is not part of routine diagnostic sampling protocols. We have reviewed the history and anatomy of the nvlDBB and now propose guidelines for distinguishing nvlDBB from other neighbouring cholinergic cell groups for standardizing future clinicopathological work. Thorough review of the literature regarding neurodegenerative conditions reveals inconsistent results in terms of cholinergic neuronal loss within the nvlDBB. This is likely to be due to the use of variable neuronal inclusion criteria and omission of cholinergic immunohistochemical markers. Extrapolating from those studies showing a significant nvlDBB neuronal loss in Lewy body dementia, we propose an anatomical and functional connection between the cholinergic component of the nvlDBB (Ch2) and the CA2 subfield in the hippocampus which may be especially vulnerable in Lewy body disorders.

Bringing CLARITY to the human brain: visualization of Lewy pathology in three dimensions.

AIMS: CLARITY is a novel technique which enables three-dimensional visualization of immunostained tissue for the study of circuitry and spatial interactions between cells and molecules in the brain. In this study, we aimed to compare methodological differences in the application of CLARITY between rodent and large human post mortem brain samples. In addition, we aimed to investigate if this technique could be used to visualize Lewy pathology in a post mortem Parkinson's brain. METHODS: Rodent and human brain samples were clarified and immunostained using the passive version of the CLARITY technique. Samples were then immersed in different refractive index matching media before mounting and visualizing under a confocal microscope. RESULTS: We found that tissue clearing speed using passive CLARITY differs according to species (human vs. rodents), brain region and degree of fixation (fresh vs. formalin-fixed tissues). Furthermore, there were advantages to using specific refractive index matching media. We have applied this technique and have successfully visualized Lewy body inclusions in three dimensions within the nucleus basalis of Meynert, and the spatial relationship between monoaminergic fibres and Lewy pathologies among nigrostriatal fibres in the midbrain without the need for physical serial sectioning of brain tissue. CONCLUSIONS: The effective use of CLARITY on large samples of human tissue opens up many potential avenues for detailed pathological and morphological studies.

Axonal myelin increase in the callosal genu in depression but not schizophrenia.

BACKGROUND: Abnormalities in the anterior inter-hemispheric connectivity have previously been implicated in major depressive disorder. Disruptions in fractional anisotropy in the callosum and fornix have been reported in schizophrenia and major depressive disorder. Oligodendrocyte density and overall size of the callosum and fornix show no alteration in either illness, suggesting that gross morphology is unchanged but more subtle organizational disruption may exist within these brain regions in mood and affective disorders. METHOD: Using high-resolution oil-immersion microscopy we examined the cross-sectional area of the nerve fibre and the axonal myelin sheath, and using standard high-resolution light microscopy we measured the density of myelinated axons. These measurements were made in the genu of the corpus callosum and the medial body of the fornix at its most dorsal point. Measures were taken in the sagittal plane in the callosal genu and in the coronal plane at the most dorsal part of the fornix body. RESULTS: Cases of major depressive disorder had significantly greater mean myelin cross-sectional area (p = 0.017) and myelin thickness (p = 0.004) per axon in the genu than in control or schizophrenia groups. There was no significant change in the density of myelinated axons, and no changes observed in the fornix. CONCLUSION: The results suggest a clear increase of myelin in the axons of the callosal genu in MDD, although this type of neuropathological study is unable to clarify whether this is caused by changes during life or has a developmental origin.

Cholinergic manipulation of motor disability and L-DOPA-induced dyskinesia in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets.

Anti-cholinergic drugs are used in the treatment of Parkinson's disease (PD) and they can improve motor disability in some patients and may alter the expression of dyskinesia. We report the effects of anticholinergic and pro-cholinergic agents administered alone and combined with L-DOPA, on motor function in 1-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets. Administration of atropine to MPTP-treated marmosets, not previously exposed to L-DOPA, improved motor disability but this did not occur with other centrally acting anti-cholinergics. Motor disability was worsened by centrally acting pro-cholinergics. However, neither peripherally acting anti- nor pro-cholinergics produced any effect on motor disability or dyskinesia. In MPTP-treated marmosets previously primed with L-DOPA to exhibit dyskinesia, acute L-DOPA challenge induced both chorea and dystonia. In these animals, centrally acting anti-cholinergics including atropine and trihexyphenidyl reversed motor deficits, but induced chorea. Combined with L-DOPA, both centrally and peripherally acting anti-cholinergics reduced peak locomotor activity and produced more chorea than dystonia compared to L-DOPA alone. Centrally acting pro-cholinergics decreased locomotor activity, worsened motor disability and induced dystonia. Co-administered with L-DOPA, pro-cholinergics reduced locomotor activity and decreased chorea while increasing dystonia compared with L-DOPA alone. In conclusion, anti-cholinergics can increase chorea with and without L-DOPA but improve motor disability. Pro-cholinergics decrease the proportion of chorea when combined with L-DOPA, increase motor disability and antagonise L-DOPA's effectiveness. These data suggest that there may be a case for revisiting the use of anti-cholinergic drugs in the treatment of PD.

Neuropathological changes in the substantia nigra in schizophrenia but not depression.

Schizophrenia is a chronic, disabling neuropsychiatric disorder characterised by positive, negative and cognitive symptoms. The aetiology is not known, although genetic, imaging and pathological studies have implicated both neurodevelopmental and neurodegenerative processes. The substantia nigra is a basal ganglia nucleus responsible for the production of dopamine and projection of dopaminergic neurons to the striatum. The substantia nigra is implicated in schizophrenia as dopamine has been heavily implicated in the dopamine hypothesis of schizophrenia and the prevalent psychotic symptoms and the monoamine theory of depression, and is a target for the development of new therapies. Studies into the major dopamine delivery pathways in the brain will therefore provide a strong base in improving knowledge of these psychiatric disorders. This post-mortem study examines the cytoarchitecture of dopaminergic neurons of the substantia nigra in schizophrenia (n = 12) and depression (n = 13) compared to matched controls (n = 13). Measures of nucleolar volume, nuclear length and nuclear area were taken in patients with chronic schizophrenia and major depressive disorder against matched controls. Astrocyte density was decreased in schizophrenia compared to controls (p = 0.030), with no change in oligodendrocyte density observed. Significantly increased nuclear cross-sectional area (p = 0.017) and length (p = 0.021), and increased nucleolar volume (p = 0.037) in dopaminergic neurons were observed in schizophrenia patients compared with controls, suggesting nuclear pleomorphic changes. No changes were observed in depression cases compared to control group. These changes may reflect pathological alterations in gene expression, neuronal structure and function in schizophrenia.

Disturbed sleep in Parkinson's disease: anatomical and pathological correlates.

AIMS: Abnormal sleep is a common feature of Parkinson's disease (PD) and prodromal disorders of sleep are frequent (e.g. restless legs syndrome and rapid eye movement sleep behaviour disorder). However, the exact pathological basis of disturbed sleep remains as yet undefined. METHODS: To investigate this further, 32 PD cases were stratified into three groups: (1) PD with disturbed sleep, PD(S); (2) PD with dementia (PDD) and disturbed sleep, PDD(S); and (3) PD without disturbed sleep, PD(nS). The extent of α-synuclein (αSyn) and Alzheimer disease (AD)-type pathology [amyloid ß peptide (Aß) and tau] was assessed in 15 regions of the PD brain. RESULTS: The results demonstrate a significant association between disturbed sleep in PD and αSyn pathology in specific brainstem [locus coeruleus (P = 0.006) and raphe nuclei (P = 0.02)], hypothalamic [paramammillary nuclei (P = 0.04) and posterior nucleus (P = 0.02)], subcortical/limbic [amygdala (P = 0.03), thalamus (P = 0.01)] and cortical [entorhinal cortex (P = 0.01)] regions. A statistically significant increase of tau pathology was observed in the amygdala (P = 0.03), CA2 sector of the hippocampus (P = 0.01) and entorhinal cortex (P = 0.04) in PD cases with disturbed sleep. CONCLUSIONS: Pathological changes in these structures, residing in the brain circuitry relating to sleep physiology, strongly predict the presence of sleep disturbances in PD.

Changes in cortical thickness in the frontal lobes in schizophrenia are a result of thinning of pyramidal cell layers.

Decreased cortical thickness and reduced activity as measured by fMRI in the grey matter of the subgenual cingulate cortex have been reported in schizophrenia and bipolar disorder, and cortical grey matter loss has been reliably reported in the frontal and temporal lobes in schizophrenia. The aim of this study was to examine the thickness of each of the six cortical layers in the subgenual cingulate cortex, five frontal lobe and four temporal lobe gyri. We examined two separate cohorts. Cohort 1 examines the subgenual cingulate cortex (SCC) in schizophrenia (n = 10), bipolar disorder (n = 15) and major depressive disorder (n = 20) against control subjects (n = 19). Cohort two examines frontal and temporal gyri in schizophrenia (n = 16), major depressive disorder (n = 6) against matched controls (n = 32). The cohorts were selected with identical clinical criteria, but underwent different tissue processing to contrast the effect of chemical treatment on tissue shrinkage. Measurements of layer I-VI thickness were taken from cresyl-violet- and haematoxylin-stained sections in cohort one and from cresyl-violet- and H&E-stained sections in cohort two. SCC cortical thickness decreased in male subjects with bipolar disorder (p = 0.048), and male schizophrenia cases showed a specific decrease in the absolute thickness of layer V (p = 0.003). Compared to controls, the relative thickness of layer V in the crown of the SCC decreased in schizophrenia (p < 0.001). A significant decrease in total cortical thickness was observed across the frontal lobe in schizophrenia (p < 0.0001), with specific pyramidal layer thinning in layers III (p = 0.0001) and V (p = 0.005). There was no effect of lateralization. No changes were noted in temporal lobe cortical thickness. This study demonstrates diminished pyramidal layer thickness resulting in decreased frontal lobe thickness in schizophrenia.

Neuropathological changes in the nucleus basalis in schizophrenia.

The nucleus basalis has not been examined in detail in severe mental illness. Several studies have demonstrated decreases in glia and glial markers in the cerebral cortex in schizophrenia, familial bipolar disorder and recurrent depression. Changes in neocortical neuron size and shape have also been reported. The nucleus basalis is a collection of large cholinergic neurons in the basal forebrain receiving information from the midbrain and limbic system, projecting to the cortex and involved with attention, learning and memory, and receives regulation from serotonergic inputs. Forty-one cases aged 41-60 years with schizophrenia or major depressive disorder with age-matched controls were collected. Formalin-fixed paraffin-embedded coronal nucleus basalis sections were histologically stained for oligodendrocyte identification with cresyl-haematoxylin counterstain, for neuroarchitecture with differentiated cresyl violet stain and astrocytes were detected by glial fibrillary acid protein immunohistochemistry. Cell density and neuroarchitecture were measured using Image Pro Plus. There were larger NB oval neuron soma in the combined schizophrenia and major depression disorder groups (p = 0.038), with no significant change between controls and schizophrenia and major depression disorder separately. There is a significant reduction in oligodendrocyte density (p = 0.038) in the nucleus basalis in schizophrenia. The ratio of gemistocytic to fibrillary astrocytes showed a greater proportion of the former in schizophrenia (18.1 %) and major depressive disorder (39.9 %) than in controls (7.9 %). These results suggest glial cell abnormalities in the nucleus basalis in schizophrenia possibly leading to cortical-limbic disturbance and subcortical dysfunction.

Striatal Aß peptide deposition mirrors dementia and differentiates DLB and PDD from other parkinsonian syndromes.

Recent neuropathological studies have described widespread amyloid-ß peptide (Aß) deposition in the striatum of patients with Lewy body disorders, particularly in Parkinson's disease with dementia (PDD) and dementia with Lewy bodies (DLB). However, positron emission tomography (PET) studies using the [(11)C]PIB ligand, binding to Aß deposits, detects significant striatal pathology only in DLB and not in PDD. Employing immunohistochemistry, we examined striatal Aß deposition in the caudate nucleus and putamen of 52 PD, 41 PDD, 14 DLB, 7 multiple system atrophy (MSA) and 14 progressive supranuclear palsy (PSP) cases in relation to the presence of dementia. PD, MSA and PSP cases showed little or no Aß pathology in the striatum. In contrast, both PDD and DLB cases demonstrated significantly greater Aß deposition in the striatum when compared to PD, MSA and PSP groups. We conclude that striatal Aß pathology is common in both PDD and DLB and may reflect the development of dementia in these conditions. More detailed examination of the morphology of the Aß pathology suggests that it is the presence of cored amyloid plaques in DLB, but not PDD, that underlies the differences seen in PET imaging.

Homocysteine-induced endoplasmic reticulum protein (herp) is up-regulated in parkinsonian substantia nigra and present in the core of Lewy bodies.

BACKGROUND: Recent studies highlight the role of endoplasmic reticulum (ER) stress and aberrant protein degradation in the pathogenesis of neurodegenerative disorders. Herp which is encoded by the HERPUD 1 (homocysteine-inducible, endoplasmic reticulum stress-inducible, ubiquitin-like domain member 1) gene is a stress-response protein localized in the ER membrane of neurons and other cell types. Herp has been suggested to improve ER-folding, decrease ER protein load, and participate in ER-associated degradation (ERAD) of proteins. METHODS: Based on microarray expression profiling results we have predicted an increased expression of HERPUD1 in the substantia nigra of Parkinson's disease (PD) patients. We have now used brain tissue of some of the same and additional cases of sporadic PD to localize Herp mRNA and protein in individual cell types. RESULTS: We found expression of Herp in neurons and in glial cells including astrocytes. These findings were corroborated by in situ hybridization. Accumulation of Herp protein was also detected in the core of Lewy bodies suggesting a role in their formation. Hierarchical clustering analysis identified TWINKLE (PEO1) as the gene whose expression profile was most similar to that of Herp across the PD cohort. CONCLUSIONS: The nigral glial cells that expressed Herp at a high level resembled TUNEL-positive glia. While some of these cells likely undergo degeneration, the strong up-regulation of Herp in glia could help to explain the inflammation-like changes observed in PD ("neuroinflammation") as it has been shown that the unfolded protein response serves as an important regulator of inflammatory genes in other organs.

Clinical correlates of pathology in the claustrum in Parkinson's disease and dementia with Lewy bodies.

Dementia and visual hallucinations are common complications of Parkinson's disease (PD), yet their patho-anatomical bases are poorly defined. We studied alpha-synuclein (alphaSyn), tau and amyloid-beta (Abeta) pathology in the claustrum of 20 PD cases without dementia, 12 PD cases with dementia (PDD) and 7 cases with dementia with Lewy bodies (DLB). alphaSyn positivity was observed in 75% of PD cases without dementia and in 100% of PDD and DLB cases. Abeta was observed in the claustrum in 25% of PD, 58% of PDD and 100% of DLB cases. Tau was negligible in all cases restricting further analysis. Compared to PD cases without dementia, PDD cases demonstrated a significantly greater alphaSyn burden in the claustrum (p=0.0003). In addition, DLB cases showed a significantly increased alphaSyn deposition when compared to PDD (p=0.02) and PD without dementia (p=0.0002). A similar hierarchy, PD

DnaJB6 is present in the core of Lewy bodies and is highly up-regulated in parkinsonian astrocytes.

DnaJ/Hsp40 chaperones determine the activity of Hsp70s by stabilizing their interaction with substrate proteins. We have predicted, based on the in silico analysis of a brain-derived whole-genome transcriptome data set, an increased expression of DnaJ/Hsp40 homologue, subfamily B, member 6 (DnaJB6) in Parkinson's disease (PD; Moran et al. [2006] Neurogenetics 7:1-11). We now show that DnaJB6 is a novel component of Lewy bodies (LBs) in both PD substantia nigra and PD cortex and that it is strongly up-regulated in parkinsonian astrocytes. The presence of DnaJB6 in the center of LBs suggests an early and direct involvement of this chaperone in the neuronal disease process associated with PD. The strong concomitant expression of DnaJB6 in astrocytes emphasizes the involvement of glial cells in PD and could indicate a route for therapeutic intervention. Extracellular alpha-synuclein originating from intravesicular alpha-synuclein is prone to aggregation and the potential source of extracellular aggregates (Lee [2008] J. Mol. Neurosci. 34:17-22). The observed strong expression of DnaJB6 by astrocytes could reflect a protective reaction, so reducing the neuronal release of toxic alpha-synuclein and supporting the astrocyte response in PD might limit the progression of the disease process.

Dementia and visual hallucinations associated with limbic pathology in Parkinson's disease.

The pathological basis of dementia and visual hallucinations in Parkinson's disease (PD) is not yet fully understood. To investigate this further we have conducted a clinico-pathological study based on 30 post-mortem PD brains. PD cases were stratified into groups according to clinical characteristics as follows: (1) cognitively intact (n=9); (2) cases with severe dementia and visual hallucinations (n=12); (3) cases with severe dementia and no visual hallucinations (n=4); and (4) cases with severe visual hallucinations and no dementia (n=5). The extent of alpha-synuclein (alphaSyn), tau and amyloid beta peptide (Abeta) deposition was then examined in the CA2 sector of the hippocampus and in neocortical and subcortical areas known to subserve cognitive function. We find that dementia in PD is significantly associated with alphaSyn in the anterior cingulate gyrus, superior frontal gyrus, temporal cortex, entorhinal cortex, amygdaloid complex and CA2 sector of the hippocampus. Abeta in the anterior cingulate gyrus, entorhinal cortex, amygdaloid complex and nucleus basalis of Meynert is also associated with dementia as is tau in the CA2 sector of the hippocampus. alphaSyn burden in the amygdala is strongly related to the presence of visual hallucinations but only in those PD cases with concomitant dementia. Statistical analysis revealed that alphaSyn burden in the anterior cingulate gyrus could differentiate demented from non-demented PD cases with high sensitivity and specificity. We conclude that alphaSyn in limbic regions is related to dementia in PD as well as to visual hallucinations when there is an underlying dementia.

The dorsal motor nucleus of the vagus is not an obligatory trigger site of Parkinson's disease: a critical analysis of alpha-synuclein staging.

AIMS: It has been proposed that alpha-synuclein (alpha Syn) pathology in Parkinson's disease (PD) spreads in a predictable caudo-rostral way with the earliest changes seen in the dorsal motor nucleus of the vagus nerve (DMV). However, the reliability of this stereotypical spread of alpha Syn pathology has been questioned. In addition, the comparative occurrence of alpha Syn pathology in the spinal cord and brain has not been closely studied. METHODS: In order to address these issues, we have examined 71 cases of PD from the UK Parkinson's Disease Society Tissue Bank at Imperial College, London. The incidence and topographic distribution of alpha Syn pathology in several brain regions and the spinal cord were assessed. RESULTS: The most affected regions were the substantia nigra (SN; in 100% of cases) followed by the Nucleus Basalis of Meynert (NBM) in 98.5%. Fifty-three per cent of cases showed a distribution pattern of alpha Syn compatible with a caudo-rostral spread of alpha Syn through the PD brain. However, 47% of the cases did not fit the predicted spread of alpha Syn pathology and in 7% the DMV was not affected even though alpha Syn inclusions were found in SN and cortical regions. We also observed a high incidence of alpha Syn in the spinal cord with concomitant affection of the DMV and in a few cases in the absence of DMV involvement. CONCLUSIONS: Our results demonstrate a predominant involvement of the SN and NBM in PD but do not support the existence of a medullary induction site of alpha Syn pathology in all PD brains.

The medial and lateral substantia nigra in Parkinson's disease: mRNA profiles associated with higher brain tissue vulnerability.

Sporadic Parkinson's disease (PD) is characterized by progressive death of dopaminergic neurons within the substantia nigra. However, pathological cell death within this nucleus is not uniform. In PD, the lateral tier of the substantia nigra (SNl) degenerates earlier and more severely than the more medial nigral component (SNm). The cause of this brain regional vulnerability remains unknown. We have used DNA oligonucleotide microarrays to compare gene expression profiles from the SNl to those of the SNm in both PD and control cases. Genes expressed more highly in the PD SNl included the cell death gene, p53 effector related to PMP22, the tumour necrosis factor (TNF) receptor gene, TNF receptor superfamily, member 21, and the mitochondrial complex I gene, NADH dehydrogenase (ubiquinone) 1beta subcomplex, 3, 12 kDa (NDUFbeta3). Genes that were more highly expressed in PD SNm included the dopamine cell signalling gene, cyclic adenosine monophosphate-regulated phosphoprotein, 21 kDa, the activated macrophage gene, stabilin 1, and two glutathione peroxidase (GPX) genes, GPX1 and GPX3. Thus, there is increased expression of genes encoding pro-inflammatory cytokines and subunits of the mitochondrial electron transport chain, and there is a decreased expression of several glutathione-related genes in the SNl suggesting a molecular basis for pathoclisis. Importantly, some of the genes that are differentially regulated in the SNl are known to be expressed highly or predominantely in glial cells. These findings support the view that glial cells can be primarily affected in PD emphasizing the importance of using a whole tissue approach when investigating degenerative CNS disease.

Analysis of alpha-synuclein, dopamine and parkin pathways in neuropathologically confirmed parkinsonian nigra.

The identification of mutations that cause familial Parkinson's disease (PD) provides a framework for studies into pathways that may be perturbed also in the far more common, non-familial form of the disorder. Following this hypothesis, we have examined the gene regulatory network that links alpha-synuclein and parkin pathways with dopamine metabolism in neuropathologically verified cases of sporadic PD. By means of an in silico approach using a database of eukaryotic molecular interactions and a whole genome transcriptome dataset validated by qRT-PCR and histological methods, we found parkin and functionally associated genes to be up-regulated in the lateral substantia nigra (SN). In contrast, alpha-synuclein and ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) gene expression levels were significantly reduced in both the lateral and medial SN in PD. Gene expression for Septin 4, a member of the GTP-binding protein family involved in alpha-synuclein metabolism was elevated in the lateral parkinsonian SN. Additionally, catalase and mitogen-activated protein kinase 8 and poly(ADP-ribose) polymerase family member 1 (PARP1) known to function in DNA repair and cell death induction, all members of the dopamine synthesis pathway, were up-regulated in the lateral SN. In contrast, two additional PD-linked genes, glucocerebrosidase and nuclear receptor subfamily 4, group A, member 2 (NR4A2) showed reduced expression. We show that in sporadic PD, parkin, alpha-synuclein and dopamine pathways are co-deregulated. Alpha-synuclein is a member of all three gene regulatory networks. Our analysis results support the view that alpha-synuclein has a central role in the familial as well as the non-familial form of the disease and provide steps towards a pathway definition of PD.