Glutamate decarboxylase-67 messenger RNA expression in normal human basal ganglia and in Parkinson's disease

Concerning neuromodulation as treatment of neurological and neuropsychiatric disorder: Insights gained from selective targeting of the subthalamic nucleus, para-subthalamic nucleus and zona incerta in rodents

Neuromodulation such as deep brain stimulation (DBS) is advancing as a clinical intervention in several neurological and neuropsychiatric disorders, including Parkinson's disease, dystonia, tremor, and obsessive-compulsive disorder (OCD) for which DBS is already applied to alleviate severely afflicted individuals of symptoms. Tourette syndrome and drug addiction are two additional disorders for which DBS is in trial or proposed as treatment. However, some major remaining obstacles prevent this intervention from reaching its full therapeutic potential. Side-effects have been reported, and not all DBS-treated individuals are relieved of their symptoms. One major target area for DBS electrodes is the subthalamic nucleus (STN) which plays important roles in motor, affective and associative functions, with impact on for example movement, motivation, impulsivity, compulsivity, as well as both reward and aversion. The multifunctionality of the STN is complex. Decoding the anatomical-functional organization of the STN could enhance strategic targeting in human patients. The STN is located in close proximity to zona incerta (ZI) and the para-subthalamic nucleus (pSTN). Together, the STN, pSTN and ZI form a highly heterogeneous and clinically important brain area. Rodent-based experimental studies, including opto- and chemogenetics as well as viral-genetic tract tracings, provide unique insight into complex neuronal circuitries and their impact on behavior with high spatial and temporal precision. This research field has advanced tremendously over the past few years. Here, we provide an inclusive review of current literature in the pre-clinical research fields centered around STN, pSTN and ZI in laboratory mice and rats; the three highly heterogeneous and enigmatic structures brought together in the context of relevance for treatment strategies. Specific emphasis is placed on methods of manipulation and behavioral impact.

Subchronic neurotoxicity of diazinon in albino mice: Impact of oxidative stress, AChE activity, and gene expression disturbances in the cerebral cortex and hippocampus on mood, spatial learning, and memory function

Diazinon (DZN) with prominent neurotoxic effects perturbs CNS function via multiple mechanisms. This investigation intends to explore mood, spatial learning, and memory dysfunction, acetylcholine esterase (AChE) activity, and neurodegeneration-related gene expression in the cortex and hippocampus regions of mice exposed to DZN for 63 consecutive days (subchronic exposure). Adult male albino mice were orally given sublethal DZN (DZNL = 0.1 mg/kg, DZNM = 1 mg/kg and DZNH = 10 mg/kg). All mice in the DZNH group died within 3 weeks postexposure. DZNL and DZNM caused body and brain weight loss (p < 0.05). Completing 9 weeks of DZN exposure, a marked decline in AChE activity and oxidative stress level was indicated in both brain regions (p < 0.05). Also, synaptophysin, vesicular acetylcholine transferase, and glutamate decarboxylase gene expressions were affected in both brain regions (p < 0.05). Furthermore, the present study revealed that DZN administration increased anxiety and depressive-like behaviors (p < 0.0001). Spatial learning and short- and long-memory were severely affected by DZNL and DZNM treatments (p < 0.0001). Taken together, subchronic exposure to low and medium doses of DZN can cause AChE inhibition, oxidative damage, and neurotransmitter disturbances in brain cells and induce neurodegeneration. These changes would impair mood, spatial learning, and memory function.

Decreased glutamic acid decarboxylase mRNA expression in prefrontal cortex in Parkinson's disease

Parkinson's disease (PD) patients typically suffer from motor disorders but mild to severe cognitive deficits can also be present. Neuropathology of PD primarily involves loss of dopaminergic neurons in the substantia nigra, pars compacta, although more widespread pathology from the brainstem to the cerebral cortex occurs at different stages of the disease. Cognitive deficits in PD are thought to involve the cerebral cortex, and imaging studies have identified the dorsolateral prefrontal cortex (DLPFC) as a possible site for some of the symptoms. GABAergic neurons in the cerebral cortex play a key role in the modulation of pyramidal neurons and alterations in muscimol binding to GABA(A) receptors have been reported in Brodmann area 9 (BA9) of the prefrontal cortex in PD patients (Nishino et al., 1988). In order to further assess the likelihood that GABAergic activity is altered in the prefrontal cortex in PD, gene expression of the 67 kilodalton isoform of the GABA-synthesizing enzyme, glutamic acid decarboxylase (GAD67 encoded by the GAD1 gene), was examined in BA9 of post-mortem brains from 19 patients and 20 controls using isotopic in situ hybridization histochemistry. GAD67 mRNA labeling was examined and quantified on X-ray films and emulsion radioautographs. We show that GAD67 mRNA labeling is significantly lower in PD compared to control cases. Analysis of emulsion radioautographs indicates that GAD67 mRNA labeling is decreased in individual neurons and is not paralleled by a decrease in the number of GAD67 mRNA-labeled neurons. Analysis of expression data from a microarray study performed in 29 control and 33 PD samples from BA9 confirms that GAD67 expression is decreased in PD. Another finding from the microarray study is a negative relationship between GAD67 mRNA expression and age at death. Altogether, the results support the possibility that GABAergic neurotransmission is impaired in the DLPFC in PD, an effect that may be involved in some of the behavioral deficits associated with the disease.

New insights into {gamma}-aminobutyric acid catabolism: Evidence for {gamma}-hydroxybutyric acid and polyhydroxybutyrate synthesis in Saccharomyces cerevisiae

The gamma-aminobutyrate (GABA) shunt, an alternative route for the conversion of alpha-ketoglutarate to succinate, involves the glutamate decarboxylase Gad1p, the GABA transaminase Uga1p and the succinate semialdehyde dehydrogenase Uga2p. This pathway has been extensively described in plants and animals, but its function in yeast remains unclear. We show that the flux through Gad1p is insignificant during fermentation in rich sugar-containing medium, excluding a role for this pathway in redox homeostasis under anaerobic conditions or sugar stress. However, we found that up to 4 g of exogenous GABA/liter was efficiently consumed by yeast. We studied the fate of this consumed GABA. Most was converted into succinate, with a reaction yield of 0.7 mol/mol. We also showed that a large proportion of GABA was stored within cells, indicating a possible role for this molecule in stress tolerance mechanisms or nitrogen storage. Furthermore, based on enzymatic and metabolic evidence, we identified an alternative route for GABA catabolism, involving the reduction of succinate-semialdehyde into gamma-hydroxybutyric acid and the polymerization of gamma-hydroxybutyric acid to form poly-(3-hydroxybutyric acid-co-4-hydroxybutyric acid). This study provides the first demonstration of a native route for the formation of this polymer in yeast. Our findings shed new light on the GABA pathway and open up new opportunities for industrial applications.

Fos expression following activation of the ventral pallidum in normal rats and in a model of Parkinson's Disease: implications for limbic system and basal ganglia interactions

The circuit-related consequences of activating the ventral pallidum (VP) are not well known, and lacking in particular is how these effects are altered in various neuropathological states. To help to address these paucities, this study investigated the brain regions affected by VP activation by quantifying neurons that stain for Fos-like immunoreactivity (ir). Fos-ir was assessed after intra-pallidal injections of the excitatory amino acid agonist, NMDA, or the GABA(A) antagonist, bicuculline in normal rats and in those rendered Parkinsonian-like by lesioning dopaminergic neurons with the neurotoxin, 6-OHDA. We hypothesized that activation of the VP will alter the activity state of brain regions associated with both the basal ganglia and limbic system, and that this influence would be modified in the Parkinsonian state. Blocking tonically activated GABA(A) receptors with bicuculline (50 ng/0.5 microl) elevated Fos-ir in the VP to 423% above the contralateral, vehicle-injected side. Likewise, intra-VP NMDA (0.23 microg or 0.45 microg/0.5 microl), dose-dependently increased the number of pallidal neurons expressing Fos-ir by 224 and 526%, respectively. At higher NMDA doses, the density of Fos-ir neurons was not elevated above control levels. This inverted U-shaped profile was mirrored by a VP output structure, the medial subthalamic nucleus (mSTN). The mSTN showed a 289% increase in Fos-ir neurons with intra-VP injections of 0.45 microg NMDA, and this response was halved following intra-VP injections of 0.9 microg NMDA. Of the 12 other brain regions measured, three showed VP NMDA-induced enhancements in Fos-ir: the frontal cortex, entopeduncular nucleus and substantia nigra pars reticulata, all regions associated with the basal ganglia. In a second study, we evaluated the NMDA activation profile in a rat model of Parkinson's Disease (PD) which was created by a unilateral injection of 6-OHDA into the rostral substantia nigra pars compacta. Comparisons of responses to intra-VP NMDA between the hemispheres ipsilateral and contralateral to the lesion revealed that Fos-ir cells in the pedunculopontine nucleus was reduced by 62%, whereas Fos-ir for the basolateral amygdala and STN was reduced by 32 and 42%, respectively. These findings support the concept that the VP can influence both the basal ganglia and the limbic system, and that that the nature of this influence is modified in an animal model of PD. As the VP regulates motivation and cognition, adaptations in this system may contribute to the mood and mnemonic disorders that can accompany PD.

Alterations in prodynorphin, proenkephalin, and GAD67 mRNA levels in the aged human putamen: correlation with Parkinson's disease

A real-time quantitative PCR approach was used to quantify mRNA levels corresponding to the neuropeptides enkephalin, dynorphin, and the 67-kDa isoform of glutamic acid decarboxylase (GAD67) in the human putamen from young and aged individuals as well as from aged patients affected by Parkinson's disease (PD). cDNA-specific primers were designed to amplify GAD67, proenkephalin (pENK), prodynorphin (pDYN), and the housekeeping genes glyceraldehydes-3-phosphate dehydrogenase (GAPDH) and guanine nucleotide binding protein, beta-peptide 2-like I (GNB2LI). GAPDH and GNB2LI mRNA levels were similarly expressed among the groups and were therefore used as endogenous reference genes. Normalized data showed that mRNA levels for both pENK and pDYN were reduced in the putamen of aged controls and aged individuals affected by PD, compared with young controls. In addition, we showed that GAD67 mRNA levels did not change during aging and PD. Further analyses showed no differences in mRNA levels, for pENK, pDYN, or GAD67 mRNA, between PD patients and aged matched controls. These findings contrast with animal models of parkinsonism, for which expression of pDYN, pENK, and GAD67 mRNA has been reported to change after striatal dopamine denervation. Compensatory mechanisms and regional differences within the human putamen as well as the severity index of the disease, clinical diagnosis, and response to phalmacological therapy are possible reasons for these results. The present study suggests that alteration of neuropeptide pathways in the human putamen may be involved in the functional deterioration of parts of the extrapyramidal system during aging.

Deep brain stimulation in a rat model modulates TH, CaMKIIa and Homer1 gene expression

High-frequency stimulation (HFS) of subthalamic nucleus (STN) is a therapy for late-stage Parkinson's disease. Its mechanisms of action are not yet fully understood. In the present study, gene expression analyses were performed in a rat model of Parkinson's disease, i.e. striatal 6-hydroxydopamine (6-OHDA) lesion. Using microarrays, gene expression was analysed in 1-mm-thick sagittal brain slices, including basal ganglia of five groups of male Wistar rats. These were unmanipulated rats (group A), unlesioned rats with implanted electrode but without stimulation (group B), unlesioned, stimulated rats (group C), 6-OHDA-lesioned rats with implanted electrode but without stimulation (group D), and finally 6-OHDA-lesioned and stimulated rats (group E). A statistically significant downregulation of tyrosine hydroxylase (TH) mRNA expression induced by 6-OHDA lesion and an HFS-induced TH upregulation in 6-OHDA-lesioned rats could be detected. It could be hypothesized that the HFS-induced upregulation of TH is the result of neuronal STN modulation and mediated via projections from STN to substantia nigra pars compacta. Furthermore, a downregulation of calcium/calmodulin-dependent protein kinase type IIA and Homer1 was observed. This downregulation could result in a reduced sensitivity towards glutamate in basal ganglia downstream of STN.

Subthalamic stimulation evokes complex EPSCs in the rat substantia nigra pars reticulata in vitro

The subthalamic nucleus (STN) plays an important role in movement control by exerting its excitatory influence on the substantia nigra pars reticulata (SNR), a major output structure of the basal ganglia. Moreover, excessive burst firing of SNR neurons seen in Parkinson's disease has been attributed to excessive transmission in the subthalamonigral pathway. Using the 'blind' whole-cell patch clamp recording technique in rat brain slices, we found that focal electrical stimulation of the STN evoked complex, long-duration excitatory postsynaptic currents (EPSCs) in SNR neurons. Complex EPSCs lasted 200-500 ms and consisted of an initial monosynaptic EPSC followed by a series of late EPSCs superimposed on a slow inward shift in holding current. Focal stimulation of regions outside the STN failed to evoke complex EPSCs. The late component of complex EPSCs was markedly reduced by ionotropic glutamate receptor antagonists (2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitro-quinoxalone) and by a GABAA receptor agonist (isoguvacine) when these agents were applied directly to the STN using a fast-flow microapplicator. Moreover, the complex EPSC was greatly enhanced by bath application of the GABAA receptor antagonists picrotoxin or bicuculline. These data suggest that recurrent glutamate synapses in the STN generate polysynaptic, complex EPSCs that are under tonic inhibition by GABA. Because complex EPSCs are expected to generate bursts of action potentials in SNR neurons, we suggest that complex EPSCs may contribute to the pathological burst firing that is associated with the symptoms of Parkinson's disease.

Expression of GAD65 and GAD67 immunoreactivity in MPTP-treated monkeys with or without l-DOPA administration

This study investigated the consequences of levodopa treatment on the expression of the 65- and 67-kDa isoforms of glutamate decarboxylase (GAD65 and GAD67) immunoreactivity in the basal ganglia and cortex of monkeys rendered Parkinsonian by systemic MPTP administration. All MPTP-treated monkeys showed Parkinsonian impairment and selective loss of tyrosine hydroxylase (TH) with sparing of GAD immunoreactive (-ir) fibers and terminals in basal ganglia. The distribution of GAD65- and GAD67-ir in the cortex, caudate, and putamen was not significantly different in MPTP vs. naïve monkeys nor as a function of L-DOPA treatment. In comparison, the expression of GAD67- but not GAD65-ir was augmented in the globus pallidus in MPTP-treated monkeys. Quantification revealed significant increases in number of GAD67-ir neurons in the external and internal segments of the globus pallidus while no significant difference in the number of GAD65-ir neurons was observed. L-DOPA treatment did not significantly change the number of GAD65- or GAD67-ir pallidal neurons following MPTP. These results support and extend the findings that transcriptional elevation of GAD67 occurs in the globus pallidus and demonstrate that GAD65 and GAD67 are differentially altered following lesion. The finding of elevated GAD67 expression in the pallidum is consistent with alterations in inhibitory neurocircuitry playing a key role in the pathophysiology of motor disturbances in Parkinson's disease.

GABAergic interneurons in human subthalamic nucleus

The subthalamic nucleus (STN) is considered a homogeneous structure composed essentially of projection neurons that exert a profound glutamate-mediated excitatory influence upon the main output structures of the basal ganglia. It is currently the most efficient target for deep brain stimulations designed to alleviate symptoms of Parkinson's disease. STN neurons were analyzed by applying stereological methods and single/double-immunostaining procedures to postmortem material obtained from normal individuals. Besides a multitude of closely packed projection neurons ( approximately 24.7 mum in diameter), the human STN (mean volume, 174.5 +/- 20.4 mm3; total neuronal density, 239.5 +/- 31.9 x 10(3)) contained smaller neurons (approximately 12.2 microm), which displayed glutamic acid decarboxylase (GAD)(65/67) immunoreactivity and shared the morphological features of interneurons described in Golgi studies of primate STN. These putative gamma-aminobutyric acid (GABA)ergic interneurons accounted for 7.5% of the total neuronal population of the STN. Although present throughout the nucleus, they were significantly more numerous in its posterior-ventral-medial sector, which belongs to the limbic/associative functional territory. Many projection neurons located dorsolaterally in the STN showed parvalbumin immunoreactivity and others lying ventromedially displayed calretinin immunostaining, but none of the GAD-positive interneurons expressed these calcium-binding proteins. Although less abundant than projection neurons, GABAergic interneurons might play a important role in the intrinsic organization of the STN. The morphological and chemical heterogeneity of the human STN reported here might have important implications in the functional organization of the basal ganglia.

Caloric restriction augments brain glutamic acid decarboxylase-65 and -67 expression

The ketogenic diet is a very low-carbohydrate, high-fat diet used to treat refractory epilepsy. We hypothesized that this diet may act by increasing expression of glutamic acid decarboxylase (GAD), the rate-limiting enzyme in gamma-aminobutyric acid (GABA) synthesis. Thus, we evaluated brain GAD levels in a well-established, seizure-suppressing, rodent model of the ketogenic diet. Because the diet is most effective when administered with a modest ( approximately 10%) calorie restriction, we studied three groups of animals: rats fed ad libitum standard rat chow (Ad lib-Std); calorie-restricted standard chow (CR-Std); and an isocaloric, calorie-restricted ketogenic diet (CR-Ket). We found that GAD67 mRNA was significantly increased in the inferior and superior colliculi and cerebellar cortex in both CR diet groups compared with control (e.g., by 45% in the superior colliculus and by 71% in the cerebellar cortex; P <.001). GAD65 mRNA was selectively increased in the superior colliculus and temporal cortex in both CR-Std and CR-Ket diet groups compared with ad lib controls. The only apparent CR-Ket-specific effect was a 30% increase in GAD67 mRNA in the striatum (P =.03). Enhanced GAD immunoreactivity was detected in parallel with the mRNA changes. These data clearly show that calorie restriction increases brain GAD65 and -67 expression in several brain regions, independent of ketogenic effects. These observations may explain why caloric restriction improves the efficacy of the ketogenic diet in treating epilepsy and suggest that diet modification might be useful in treatment of a number of brain disorders characterized by impaired GAD or GABA activity.

Experimental parkinsonism is associated with increased pallidal GAD gene expression and is reversed by site-directed antisense gene therapy

The levels of mRNA encoding the two isoforms of glutamic acid decarboxylase (GAD(65) and GAD(67)) were measured throughout the pallidal complex in normal and acutely (i.e., 1 month duration) and chronically (i.e., 5 years duration) parkinsonian 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) -treated monkeys as well as in monkeys exposed to MPTP but asymptomatic for parkinsonism. GAD(65) mRNA labeling was modestly increased in the mid/caudal internal globus pallidus (GPi) but not in the external globus pallidus (GPe) in parkinsonian monkeys, compared with normal and asymptomatic monkeys. GAD(67) mRNA expression was highly increased in the mid/caudal GPi, and modestly increased in the GPe in parkinsonian monkeys compared with normal and asymptomatic animals. Infusion of GAD(67) antisense oligodeoxynucleotides bilaterally into the GPi resulted in a transient reversal of akinesia and bradykinesia that was not produced by infusion of missense oligodeoxynucleotides. These data emphasize the role of GAD enzyme (particularly GAD(67)) and GABA in the GPi for the expression of parkinsonian motor signs and suggest that selective manipulation of GABAergic neurotransmission in the GPi may have therapeutic potential for treating parkinsonism.

Systemic administration of adenosine A(2A) receptor antagonist reverses increased GABA release in the globus pallidus of unilateral 6-hydroxydopamine-lesioned rats: a microdialysis study

The ability of adenosine A(2A) receptor antagonists to exhibit antiparkinsonian activity has recently been reported, but the mechanisms of action are still unknown. Since A(2A) receptors have been localized to GABAergic striatopallidal neurons, it is probable that these antagonists affect the activity of these neurons. In the present study, extracellular GABA basal levels were increased in the ipsilateral striatum and globus pallidus following a unilateral 6-hydroxydopamine lesion of the nigrostriatal pathway. The A(2A) receptor-selective antagonist KW-6002 (3mg/kg, p.o.) caused a marked and sustained decrease of extracellular GABA levels in the globus pallidus of the 6-hydroxydopamine-lesioned rats, whereas no changes in GABA levels were observed in the globus pallidus of the non-lesioned rats. Microinjection of the A(2A) receptor agonist CGS21680 (0.005-0.5 microg) into the striatum of non-lesioned animals increased GABA concentrations in the globus pallidus, which was abolished by the voltage-dependent Na(+) channel blocker tetrodotoxin (1 micromol/l) delivered locally to the globus pallidus via the dialysis membrane. Furthermore, intrapallidal infusion of CGS21680 (10 micromol/l) also increased GABA levels in the globus pallidus. These data indicate that GABA release from striatopallidal neurons is regulated through A(2A) receptors in both the striatum and globus pallidus. The reversal of the 6-hydroxydopamine-induced increase in pallidal GABA levels by KW-6002 suggests that the antiparkinsonian effects of A(2A) receptor antagonists occur on the striatopallidal neurons.

Expression of a glutamate decarboxylase homologue is required for normal oxidative stress tolerance in Saccharomyces cerevisiae

The action of gamma-aminobutyrate (GABA) as an intercellular signaling molecule has been intensively studied, but the role of this amino acid metabolite in intracellular metabolism is poorly understood. In this work, we identify a Saccharomyces cerevisiae homologue of the GABA-producing enzyme glutamate decarboxylase (GAD) that is required for normal oxidative stress tolerance. A high copy number plasmid bearing the glutamate decarboxylase gene (GAD1) increases resistance to two different oxidants, H(2)O(2) and diamide, in cells that contain an intact glutamate catabolic pathway. Structural similarity of the S. cerevisiae GAD to previously studied plant enzymes was demonstrated by the cross-reaction of the yeast enzyme to a antiserum directed against the plant GAD. The yeast GAD also bound to calmodulin as did the plant enzyme, suggesting a conservation of calcium regulation of this protein. Loss of either gene encoding the downstream steps in the conversion of glutamate to succinate reduced oxidative stress tolerance in normal cells and was epistatic to high copy number GAD1. The gene encoding succinate semialdehyde dehydrogenase (UGA5) was identified and found to be induced by H(2)O(2) exposure. Together, these data strongly suggest that increases in activity of the glutamate catabolic pathway can act to buffer redox changes in the cell.

Expression of NMDA receptor subunit mRNAs in neurochemically identified projection and interneurons in the human striatum

N-methyl-D-aspartate (NMDA) receptors are composed of subunits from two families: NR1 and NR2. We used a dual-label in situ hybridization technique to assess the levels of NR1 and NR2A-D messenger ribonucleic acid (mRNA) expressed in projection neurons and interneurons of the human striatum. The neuronal populations were identified with digoxigenin-tagged complementary RNA probes for preproenkephalin (ENK) and substance P (SP) targeted to striatal projection neurons, and somatostatin (SOM), glutamic acid decarboxylase 67 kD (GAD(67)), and choline acetyltransferase (ChAT) targeted to striatal interneurons. Intense NR1 signals were found over all striatal neurons. NR2A signals were high over GAD(67)-positive neurons and intermediate over SP-positive neurons. ENK-positive neurons displayed low NR2A signals, whereas ChAT- and SOM-positive neurons were unlabeled. NR2B signals were intense over all neuronal populations in striatum. Signals for NR2C and NR2D were weak. Only ChAT-positive neurons displayed moderate signals, whereas all other interneurons and projection neurons were unlabeled. Moderate amounts of NR2D signal were detected over SOM- and ChAT-positive neurons; GAD(67)- and SP-positive striatal neurons displayed low and ENK-positive neurons displayed no NR2D hybridization signal. These data suggest that all human striatal neurons have NMDA receptors, but different populations have different subunit compositions that may affect function as well as selective vulnerability.

Alterations in preproenkephalin and adenosine-2a receptor mRNA, but not preprotachykinin mRNA correlate with occurrence of dyskinesia in normal monkeys chronically treated with L-DOPA

Chronic treatment with L-DOPA induces dyskinesia in patients with Parkinson's disease (PD) and 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-treated monkeys, but is not thought to do so in normal humans or primates. However, we have shown that chronic oral high dose L-DOPA administration, with the peripheral decarboxylase inhibitor, carbidopa and with or without the peripherally acting catechol-O-methyl transferase (COMT) inhibitor, entacapone, to normal macaque monkeys for 13 weeks induced dyskinesia in a proportion of animals. In the present study, in situ hybridization histochemistry was used to investigate the effect of chronic L-DOPA administration on the activity of the direct and indirect striatal output pathways by measuring striatal preprotachykinin (PPT), preproenkephalin-A (PPE-A) and adenosine-2a (A2a) receptor gene expression in these monkeys. Overall there was no significant difference in striatal PPT, PPE-A and A2a receptor mRNA levels between normal animals and all L-DOPA (plus carbidopa and/or entacapone)-treated animals irrespective of whether or not dyskinesia occurred. However, when the level of PPE-A and A2a receptor mRNA was analysed in eight monkeys displaying marked dyskinesias as a result of L-DOPA (plus carbidopa with or without entacapone) treatment, there was a significant increase in PPE-A and A2a receptor mRNA message levels in the striatum compared with animals receiving identical treatment, but displaying few or no involuntary movements, and compared with normal controls. There was no difference in striatal PPT mRNA levels in monkeys exhibiting severe dyskinesia compared with those showing little or no dyskinesia after L-DOPA treatment or to normal controls. These results suggest that prolonged L-DOPA treatment alone has no consistent effect on either the direct or indirect pathways, as judged by striatal PPT, PPE-A or A2a receptor mRNA levels in normal monkeys. However, in monkeys exhibiting marked dyskinesia resulting from chronic L-DOPA treatment, abnormal activity is detected in the indirect striato-pallidal output pathway, as judged by striatal PPE-A and A2a receptor mRNA levels, indicating an imbalance between the direct and indirect striatal pathway which may explain the emergence of dyskinesia in these animals.

The external globus pallidus in patients with Parkinson's disease and progressive supranuclear palsy

Underactivity of the external segment of the globus pallidus is thought to contribute to the generation of parkinsonian hypokinetic symptoms in association with striatal dopaminergic dysfunction and overactivity of the subthalamus. These symptoms can be corrected by neurosurgical techniques aimed at normalizing subthalamic overactivity. The aim of the present study was to compare the amount of neurodegeneration and changes in the calcium-binding protein parvalbumin in the external segment of the globus pallidus in parkinsonian disorders. Cases with progressive supranuclear palsy were compared with cases with Parkinson's disease and control subjects. The number of neurones and neurofibrillary tangles was estimated using unbiased stereologic techniques. The external segment of the globus pallidus in Parkinson's disease was not significantly different from that in control subjects. In contrast, most patients with progressive supranuclear palsy had significant neurodegeneration of the external pallidum, particularly patients with significant degeneration of both the subthalamus and substantia nigra. These results suggest that the parkinsonian symptoms in progressive supranuclear palsy are caused by the degeneration of the external segment of the globus pallidus because such degeneration would increase thalamic inhibition through the basal ganglia output nuclei, particularly in patients with a loss of excitatory drive from the subthalamus.

Basal ganglia neuronal nitric oxide synthase mRNA expression in Parkinson's disease

Expression of nitric oxide synthase (NOS) mRNA in post mortem brain was studied in putamen, globus pallidus and subthalamic nucleus (STN) of neurologically normal control subjects and patients with Parkinson's disease (PD) using in situ hybridization histochemistry. In PD, a significant increase in NOS mRNA expression was observed in the dorsal two-thirds of the STN with respect to the ventral one-third of the STN. A significant increase in NOS mRNA expression per cell in the medial medullary lamina of the globus pallidus was also observed in PD. NOS mRNA expression was significantly reduced in PD putamen. These findings provide evidence of increased activity of STN neurotransmitter systems in PD and demonstrate for the first time in any species that basal ganglia nitric oxide systems can be selectively regulated in response to changes in dopaminergic input.

Continuous subcutaneous waking day apomorphine in the long term treatment of levodopa induced interdose dyskinesias in Parkinson's disease

OBJECTIVES

To determine whether continuous waking day dopaminergic stimulation with the dopamine agonist apomorphine can reduce levodopa induced dyskinesias in Parkinson's disease

METHODS

19 patients with severe unpredictable refractory motor fluctuations and functionally disabling levodopa induced dyskinesias were treated with continuous subcutaneous apomorphine monotherapy for a minimum duration of 2.7 years

RESULTS

A mean 65% reduction in dyskinetic severity and a mean 85% reduction in frequency and duration occurred. On discontinuing levodopa a concomitant reduction in off period time was also seen (35% of waking day "off" reduced to 10%)

CONCLUSION

Continuous waking day dopaminergic stimulation with apomorphine reset the threshold for dyskinesias and led to a pronounced reduction in their frequency. Apomorphine should be considered as a less invasive alternative to pallidotomy or deep cerebral stimulation in controlling levodopa induced interdose dose dyskinesias.