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.

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.

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.

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.

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.

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.

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.

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.

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.

Comparative study of commercially available anti-alpha-synuclein antibodies

Immunohistochemistry for alpha-synuclein has become the histological technique of choice for the diagnosis for Parkinson's disease, Dementia with Lewy bodies and Multiple System Atrophy (http://www.ICDNS.org). Nevertheless, no standardised protocol has been proposed. We have reviewed 242 of the 270 studies published until June 2005 that mentioned immunohistochemistry for anti-alpha synuclein on human tissue and we found that only 75 (31%) used commercial antibodies. We also noted that protocols, particularly dilution and antigen unmasking, varied between studies, even when the same antibody was employed. In order to establish a standardised protocol for alpha-synuclein immunohistochemistry, which can be applied in diagnostic neuropathology we tested seven commercial monoclonal antibodies in brains of subjects with Parkinson's disease, dementia with Lewy bodies, multiple system atrophy, multiple sclerosis with incidental Lewy bodies and aged-matched normal brain and determined for each antibody the best suited protocol for antigen unmasking. We evaluated the intensity of immunolabelling in Lewy bodies, neuropil threads, dendrites, pre-synaptic terminals, granular cytoplasmic positivity, peri-axonal positivity, glial inclusions and non-specific immunolabelling. Although our results showed that all the antibodies detected alpha-synuclein inclusions, differences were noted between antibodies, particularly with regard to the detection of glial inclusions. From our study, the best antibodies of the seven tested appeared to be those directed against amino acids 116-131 and 15-123 and we suggest them to be used in routine diagnostic practice for alpha-synucleinopathies.

Transcriptome analysis reveals link between proteasomal and mitochondrial pathways in Parkinson’s disease

There is growing evidence that dysfunction of the mitochondrial respiratory chain and failure of the cellular protein degradation machinery, specifically the ubiquitin-proteasome system, play an important role in the pathogenesis of Parkinson's disease. We now show that the corresponding pathways of these two systems are linked at the transcriptomic level in Parkinsonian substantia nigra. We examined gene expression in medial and lateral substantia nigra (SN) as well as in frontal cortex using whole genome DNA oligonucleotide microarrays. In this study, we use a hypothesis-driven approach in analysing microarray data to describe the expression of mitochondrial and ubiquitin-proteasomal system (UPS) genes in Parkinson's disease (PD). Although a number of genes showed up-regulation, we found an overall decrease in expression affecting the majority of mitochondrial and UPS sequences. The down-regulated genes include genes that encode subunits of complex I and the Parkinson's-disease-linked UCHL1. The observed changes in expression were very similar for both medial and lateral SN and also affected the PD cerebral cortex. As revealed by "gene shaving" clustering analysis, there was a very significant correlation between the transcriptomic profiles of both systems including in control brains. Therefore, the mitochondria and the proteasome form a higher-order gene regulatory network that is severely perturbed in Parkinson's disease. Our quantitative results also suggest that Parkinson's disease is a disease of more than one cell class, i.e. that it goes beyond the catecholaminergic neuron and involves glia as well.

Whole genome expression profiling of the medial and lateral substantia nigra in Parkinson’s disease

We have used brain tissue from clinically well-documented and neuropathologically confirmed cases of sporadic Parkinson's disease to establish the transcriptomic expression profile of the medial and lateral substantia nigra. In addition, the superior frontal cortex was analyzed in a subset of the same cases. DNA oligonucleotide microarrays were employed, which provide whole human genome coverage. A total of 570 genes were found to be differentially regulated at a high level of significance. A large number of differentially regulated expressed sequence tags were also identified. Levels of mRNA sequences encoded by genes of key interest were validated by means of quantitative real-time polymerase chain reaction (PCR). Comparing three different normalization procedures, results based on the recently published GeneChip Robust Multi Array algorithm were found to be the most accurate predictor of real-time PCR results. Several new candidate genes which map to PARK loci are reported. In addition, the DNAJ family of chaperones is discussed in the context of Parkinson's disease pathogenesis.

A randomly assigned double-blind cross-over study examining the relative anti-parkinsonian tremor effects of pramipexole and pergolide

This study examined the relative anti-Parkinson's disease (PD) tremor potencies of pergolide and pramipexole in people with PD, using a 3-month double-blind cross-over design. Patients were randomly assigned to receive either pergolide and then pramipexole (n=9) or vice versa (n=8). The dose of the respective dopamine agonist was increased according to a titration schedule up to a maximum 1.5 mg t.d.s., with cross-over at 10 weeks. Assessments were performed at baseline, 4, 8 and 12 weeks. The primary outcome measures were the differences in the clinical (rest and postural) tremor scores on pergolide versus pramipexole. Seventeen PD patients (11 females and six males) with a mean age 68.4 years (range: 55-84 years) and a mean disease duration of 3.9 years (range: 2 months to 13 years) participated in the study. Twelve of the patients were taking other anti-parkinsonian medications. Two patients dropped out of the study whilst on pergolide. Fifteen of 16 patients were able to cross-over from one dopamine agonist to the other, without major retitration. There were no significant differences between the effects of the two drugs on the primary outcome measures, suggesting that the anti-PD tremor efficacies of dopaminergic medications are not dependent on differential affinities for dopamine receptor types.

Nuclear Hormone and Orphan Receptors: Their Role in Neuronal Differentiation and Cytoprotection and in the Pathogenesis of Parkinson’s Disease

Human nuclear hormone receptors (NHR) and orphan receptors (NOR) act as transcription factors in response to a wide range of circulating hormones and unknown ligands. A role for NHR and NOR in disorders of the subcortical dopaminergic pathways such as Parkinson's disease (PD) is suggested by a wealth of recent data including experimental observations. Both classes of receptors promote the formation of specific neuronal identities, tissue patterning during embryonic development and the maturation of vulnerable monoaminergic and cholinergic neurons. NHR and NOR are also known to exert a neuroprotective function on adult neurons. The scope of this review is to revisit the functional profile of these receptors with particular reference to their activity in the development of selected neuronal populations relevant to the pathophysiology of PD and to discuss how they may relate to the neuropathological and clinical expression of the disease.

Modafinil prevents the MPTP-induced increase in GABAA receptor binding in the internal globus pallidus of MPTP-treated common marmosets

The psychostimulant drug modafinil induces a reversal of motor deficits in MPTP treated primates and prevents MPTP toxicity to substantia nigra but its mechanism of action is not clear. In common marmosets acutely treated with MPTP in the presence or absence of modafinil, we have studied changes in GABA(A) receptor binding in the basal ganglia. MPTP treatment had no effect on [(3)H]-flunitrazepam (FNZ) binding density in the striatum or external globus pallidus (GPe) but increased [(3)H]-FNZ binding density in the internal globus pallidus (GPi). Administration of modafinil (10-100 mg/kg) with MPTP did not alter [(3)H]-FNZ binding density in the striatum or GPe. Low doses of modafinil (10 and 30 mg/kg) had no effect on the increased [(3)H]-FNZ binding density in the GPi but high dose modafinil (100 mg/kg) significantly decreased [(3)H]-FNZ binding density in GPi. These findings suggest that modafinil can selectively alter GABA binding density in the GPi either by preventing MPTP-induced toxicity or through an action on striatal output pathway related to its antiparkinsonian activity and its ability to inhibit MPTP toxicity.

Alterations in striatal neuropeptide mRNA produced by repeated administration of L-DOPA, ropinirole or bromocriptine correlate with dyskinesia induction in MPTP-treated common marmosets

Chronic administration of L-DOPA to MPTP-treated common marmosets induces marked dyskinesia while repeated administration of equivalent antiparkisonian doses of ropinirole and bromocriptine produces only mild involuntary movements. The occurrence of dyskinesia has been associated with an altered balance between the direct and indirect striatal output pathways. Using in situ hybridisation histochemistry, we now compare the effects of these drug treatments on striatal preproenkephalin-A (PPE-A) and adenosine A(2a) receptor mRNA expression as markers of the indirect pathway and striatal preprotachykinin (PPT) mRNA and preproenkephalin-B (PPE-B, prodynorphin) mRNA expression as markers of the direct pathway.The equivalent marked losses of specific [3H]mazindol binding in the striatum of all drug treatment groups confirmed the identical nature of the nigral cell loss produced by MPTP treatment. MPTP-induced destruction of the nigro-striatal pathway markedly increased the level of PPE-A mRNA in the caudate nucleus and putamen and decreased the levels of PPT and PPE-B mRNA relative to normal animals. Repeated treatment with L-DOPA for 30 days produced marked dyskinesia but had no effect on the MPTP-induced increase in PPE-A mRNA in the caudate nucleus and putamen. In contrast, L-DOPA treatment normalised the MPTP-induced decrease in the level of PPT and PPE-B mRNA. Repeated treatment with ropinirole produced little or no dyskinesia but markedly reversed the MPTP-induced elevation in PPE-A mRNA in the caudate nucleus and putamen. However, it had no effect on the decrease in PPT or PPE-B mRNA. Similarly, bromocriptine treatment which induced only mild dyskinesia attenuated the MPTP-induced elevation in PPE-A mRNA in the caudate nucleus and putamen with no effect on reduced striatal PPT or PPE-B mRNA. Neither MPTP treatment nor treatment with L-DOPA, bromocriptine or ropinirole had any effect on adenosine A(2a) receptor mRNA in the striatum. These patterns of alteration in striatal PPE-A and PPT and PPE-B mRNA produced by L-DOPA, bromocriptine and ropinirole show differential involvement of markers of the direct and indirect striatal output pathways related to improvement of locomotor activity and mirror the relative abilities of the drugs to induce dyskinesia.

Chronic high dose L-DOPA alone or in combination with the COMT inhibitor entacapone does not increase oxidative damage or impair the function of the nigro-striatal pathway in normal cynomologus monkeys

Parkinson's disease (PD) is characterised by a loss of pigmented dopaminergic neurones in the zona compacta of substantia nigra. The mechanisms underlying nigral cell death remain unknown but may involve oxidative damage. There has been concern that L-DOPA treatment may accelerate nigral pathology in PD through chemical and enzymatic oxidation to reactive oxygen species. In the present study, we examined tissues from normal macaque monkeys treated for 13 weeks with high doses of L-DOPA (in combination with the peripheral decarboxylase inhibitor, carbidopa) and/or the COMT inhibitor, entacapone. Plasma was analysed for changes in protein carbonyls as a marker of oxidative damage to protein. Cortical tissue was examined for changes in levels of protein carbonyls, lipid peroxidation and oxidative damage to DNA. The integrity of the nigro-striatal pathway was assessed by nigral tyrosine hydroxylase mRNA levels and specific [(3)H]mazindol binding to dopaminergic terminals in caudate-putamen. No alterations in plasma protein carbonyls were observed in any treatment group. An increase was found in the levels of protein carbonyls, lipid peroxidation and 5-OH uracil, but not other products of oxidative DNA damage, in cerebral cortex of monkeys treated with L-DOPA plus carbidopa or with L-DOPA plus carbidopa and entacapone but this was only statistically significant in the latter group. There was no change in nigral tyrosine hydroxylase mRNA levels or specific striatal [(3)H]mazindol binding in brain tissue from monkeys treated with either L-DOPA plus carbidopa or L-DOPA plus carbidopa and entacapone. The results show that in the normal monkeys L-DOPA does not provoke marked oxidative damage even at high doses, and that there is little or no potentiation of its effects by entacapone. Neither L-DOPA plus carbidopa nor L-DOPA plus carbidopa and entacapone led to obvious damage to the nigro-striatal pathway.