Studies on neurotransmitter markers of the basal ganglia in Pick's disease, with special reference to dopamine reduction

gamma-Aminobutyric acid (GABA), substance P and dopamine concentrations and choline acetyltransferase (ChAT) activity were measured in post-mortem cerebrocortical and basal ganglial areas of 14 controls and 4 patients with pathologically verified Pick's disease (1 classic case and 3 cases of the generalized form). GABA and substance P levels in the substantia nigra and the globus pallidus were generally decreased, corresponding to the moderate to severe loss of small neurones in the striatum. ChAT activities in the striatum varied from case to case, in proportion to various degrees of loss of large neurones in the striatum. These neurotransmitter abnormalities in Pick's disease were exactly the same as those in Huntington's disease. However, dopamine concentrations were markedly reduced in the striatum in Pick's disease, whereas striatal dopamine in Huntington's disease is reported to be increased. A dopamine reduction in the striatum of Pick's disease was more disproportionately prominent than expected for various degrees of nigral cell loss. This may be one of the important factors which prevents the generation of choreic movements in Pick's disease in spite of definite striatal atrophy similar to Huntington's disease.     

THIP treatment of Huntington's disease

We evaluated the therapeutic efficacy of gamma aminobutyric acid (GABA) system stimulation in four patients with classical Huntington's disease and one with the hypokinetic-rigid form. Orally administered THIP (4,5,6,7-tetrahydroisoxazolo-[5,4,-c] pyridin-3-ol), a novel GABA receptor agonist, failed to improve motor or cognitive function during a 2-week trial. At maximum levels, THIP mimicked another putative GABA agonist, muscimol, in causing unsteadiness of gait, diminished attention to sensory stimuli, and somnolence. These effects suggest that central GABA systems participate in the regulation of some human and behavioral functions. CSF content of homovanillic acid, a major metabolite of dopamine, increased during high-dose THIP therapy, suggesting that augmentation of dopaminergic function may have contributed to the drug's lack of efficacy.     

Elevated serotonin and reduced dopamine in subregionally divided Huntington's disease striatum

We measured the rostrocaudal distribution of serotonin, dopamine, and their metabolites in Huntington's disease striatum (caudate and putamen). Mean levels of serotonin or 5-hydroxyindoleacetic acid were elevated in most striatal subdivisions, whereas concentrations of dopamine or its metabolite homovanillic acid were slightly to markedly reduced. Dopamine and serotonin were at control levels in the nucleus accumbens and substantia nigra. Whereas the above-normal serotonin can most likely be accounted for by striatal atrophy, the reduced dopamine suggests either a marked down-regulation of nigrostriatal dopamine neurons or an actual reduction in the arborization of the striatal dopamine neurons. As experimental animal data suggest, the relative excess of striatal serotonin or one of its metabolites may facilitate the neurodegenerative process in Huntington's disease striatum.     

Neurochemistry of dopamine in Huntington's dementia and normal aging

We measured the dopamine metabolite homovanillic acid (HVA) in cerebrospinal fluid (CSF) before and after probenecid administration in normal controls and in patients with Huntington's disease. Baseline CSF HVA concentrations correlated positively with age in normal control subjects. Baseline CSF HVA concentrations were reduced in patients with Huntington's disease, and the degree of this reduction correlated with the severity of dementia and with the duration of disease. These results suggest that changes in the metabolism of dopamine by dopaminergic neurons may be associated with the dementia of Huntington's disease as well as with normal aging. These changes in dopaminergic functioning are apparently different in Huntington's disease than in normal aging and can be detected by measuring CSF HVA concentration.     

Protection of malonate-induced GABA but not dopamine loss by GABA transporter blockade in rat striatum

Previous work has shown that overstimulation of GABA(A) receptors can potentiate neuronal cell damage during excitotoxic or metabolic stress in vitro and that GABA(A) antagonists or GABA transport blockers are neuroprotective under these situations. Malonate, a reversible succinate dehydrogenase/mitochondrial complex II inhibitor, is frequently used in animals to model cell loss in neurodegenerative diseases such as Parkinson's and Huntington's diseases. To determine if GABA transporter blockade during mitochondrial impairment can protect neurons in vivo as compared with in vitro studies, rats received a stereotaxic infusion of malonate (2 micromol) into the left striatum to induce a metabolic stress. The nonsubstrate GABA transport blocker, NO711 (20 nmol) was infused in some rats 30 min before and 3 h following malonate infusion. After 1 week, dopamine and GABA levels in the striata were measured. Malonate caused a significant loss of striatal dopamine and GABA. Blockade of the GABA transporter significantly attenuated GABA, but not dopamine loss. In contrast with several in vitro reports, GABA(A) receptors were not a downstream mediator of protection by NO711. Intrastriatal infusion of malonate (2 micromol) plus or minus the GABA(A) receptor agonist muscimol (1 micromol), the GABA(A) Cl- binding site antagonist picrotoxin (50 nmol) or the GABA(B) receptor antagonist saclofen (33 nmol) did not modify loss of striatal dopamine or GABA when examined 1 week following infusion. These data show that GABA transporter blockade during mitochondrial impairment in the striatum provides protection to GABAergic neurons. GABA transporter blockade, which is currently a pharmacological strategy for the treatment of epilepsy, may thus also be beneficial in the treatment of acute and chronic conditions involving energy inhibition such as stroke/ischemia or Huntington's disease. These findings also point to fundamental differences between immature and adult neurons in the downstream involvement of GABA receptors during metabolic insult.     

CSF monamine metabolites in movement disorders and normal aging

We measured four monoamine metabolite levels in CSF before and after probenecid administration to normal controls and to patients with Huntington's disease (HD), dystonia, and tardive dyskinesia. We identified differences only for the dopamine metabolite homovanillic acid (HVA), which showed increased baseline values and decreased turnover in normal aging, but decreased baseline values and normal turnover in HD. These results suggest that dopamine neurons are linked both to normal aging and to HD and that CSF HVA studies can distinguish differences in the functioning of dopamine neurons in normal aging and HD.     

Pallidal GABA and chorea in Huntington's disease

Summary Neurochemical correlates of chorea in Huntington's disease were studied using striatal and pallidal tissue taken post mortem from patients with mild and severe chorea. While GABA was decreased in all these areas in Huntington's disease, patients with mild chorea had significantly less GABA in the medial pallidum than did those with severe chorea. There was no relationship between the degree of chorea and concentrations of dopamine or its metabolite. Thus the chorea of Huntington's disease may relate to the balance of residual GABAergic innervation between specific areas of the basal ganglia, consistent with primate models of dyskinesias.     

Isoniazid effects on choreiform movement and on GABA, HVA and 5-HIAA in CSF

Isoniazid was administered in 4-week open trial in patients with choreiform movement. Gamma-aminobutyric acid (GABA), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in CSF were measured before and after treatment. Isoniazid did not improve choreiform movement. CSF GABA levels were significantly increased after treatment, but HVA and 5-HIAA levels were not significantly altered. The findings suggest that isoniazid influenced brain GABA metabolism but did not influence dopamine and serotonin metabolism in patients with chorieform movement.     

Elevated gamma-aminobutyric acid level in striatal but not extrastriatal brain regions in Parkinson's disease: correlation with striatal dopamine loss

We measured the concentration of gamma-aminobutyric acid (GABA), glutamic acid, and o-phosphoethanolamine in autopsied brain of 9 patients who died with idiopathic Parkinson's disease and 10 control subjects. In the control striatum GABA showed an uneven rostrocaudal distribution pattern with rostral subdivisions containing about 40 to 50% higher levels. When compared with controls, GABA concentrations in Parkinson's disease striatum were generally elevated. The GABA elevation was most pronounced in the caudal subdivision of the putamen; this striatal subdivision also showed the most severe dopamine loss. We observed in the caudal putamen a significant negative correlation between the (elevated) GABA and (reduced) dopamine levels (the latter expressed as the sum of dopamine plus 3-methoxytyramine). Milder nonsignificant elevations of GABA levels were observed in intermediate and rostral putamen followed by the caudate head subdivisions. GABA levels were normal in all extrastriatal brain areas examined. Striatal glutamic acid levels were markedly elevated in 3 of the 9 patients with Parkinson's disease. We suggest that the altered GABA metabolism in the striatum, especially the putamen, is consequent to the nigrostriatal deficiency in this disorder. This secondary change in striatal GABA function is likely to contribute to the basal ganglia dysfunction produced by the striatal dopamine loss and thus may be related to certain aspects of parkinsonian symptomatology.     

Huntington's disease: treatment with dipropylacetic acid and gamma-aminobutyric acid.

Dipropylacetic acid (DPA), and anticonvulsant known to raise brain gamma-aminobutyric acid (GABA), was administered orally to eight patients with Huntington's disease. Both alone and in combination with high oral doses of GAGA, DPA failed to ameliorate and motor signs of this disorder. At maximum dose levels, combined DPA and GABA treatment led to an apparent increase in the central turnover of both dopamine and serotonin, as estimated by the oral probenecid-loading test. These latter observations may indicate a close functional interrelation between monoaminergic and GABAnergic neural pathways in the central nervous system of man.     

Changes of GABA receptors and dopamine turnover in the postmortem brains of parkinsonians with levodopa-induced motor complications.

Brain samples from 14 Parkinson's disease patients, 10 of whom developed motor complications (dyskinesias and/or wearing-off) on dopaminomimetic therapy, and 11 controls were analyzed. Striatal 3beta-(4-(125)I-iodophenyl)tropane-2beta-carboxylic acid isopropyl ester ([(125)I]RTI-121) -specific binding to dopamine transporter and concentration of dopamine were markedly decreased, but no association between level of denervation and development of motor complications was observed. The homovanillic acid/dopamine ratio of concentrations was higher in putamen of patients with wearing-off compared to those without. Striatal (35)S-labeled t-butylbicyclophosphorothionate ([(35)S]TBPS) and [(3)H]flunitrazepam binding to GABA(A) receptors were unchanged in patients with Parkinson's disease, whereas [(125)I]CGP 64213 -specific binding to GABA(B) receptors was decreased in the putamen and external segment of the globus pallidus of parkinsonian patients compared with controls. [(3)H]Flunitrazepam binding was increased in the putamen of patients with wearing-off compared to those without. [(35)S]TBPS-specific binding was increased in the ventral internal globus pallidus of dyskinetic subjects. These data suggest altered dopamine metabolism and increased GABA(A) receptors in the putamen related to the pathophysiology of wearing-off. The present results also suggest that an up-regulation of GABA(A) receptors in the internal globus pallidus is linked to the pathogenesis of levodopa-induced dyskinesias.     

Choreic movements and dopamine--implications to the underlying neural mechanisms involved

Choreic movement is one of the most attractive involuntary movements in terms of searches for the underlying mechanisms. Huntington's disease is a most popular disorder exhibiting choreic movements, in which the rather selective striatal degeneration is postulated to be responsible for the generation of choreic movements. In this respect, we have recently produced an experimental model of choreic movements in monkey by combined methods of kainic acid injection into the unilateral striatum and the oral administration of L-DOPA. The purpose of this paper is to summarize our experiment and to review the previous papers on experimental model of choreic movements in order to shed light on the underlying mechanisms of choreic movements. There are at least following three possible mechanisms in the generation of choreic movement. 1) A massive loss of GABAergic inhibitory neurones in the striatum induces disinhibitory effects on nigral dopaminergic neurones, which causes activation of dopaminergic neurones and choreic movements. However, a loss of GABA in the nigra does not always correlate with the generation of choreic movements. 2) A hypersensitive receptors for dopamine in the striatum may cause choreic movements. In fact, however, dopamine receptors are decreased or normal rather than increased not only in Huntington's disease but also in monkey models. 3) A massive loss of neurones in the striatum causes a loss of post-synaptic components of dopaminergic terminals. This may further cause rearrangements and compensatory changes in dopaminergic terminals in the spared striatum. These changes may activate pre-synaptic dopaminergic components which are further activated by the administration of L-DOPA. This hypothesis is mainly derived from the experimental model in monkey.     

Monoamine metabolism in the cerebrospinal fluid in Parkinson's disease: relationship to clinical symptoms and subsequent therapeutic outcomes

Summary We correlated monoamine concentrations in the cerebrospinal fluid from de novo (untreated) patients with Parkinson's disease with their clinical symptoms and therapeutic outcome after two years of L-dopa with/without other anti-parkinson medication. A significant correlation was found between the severity of some parkinsonian symptoms and the reduction in particular monoamines: Hoehn and Yahr's stage with dopamine, norepinephrine, and homovanillic acid: rigidity with dopamine; akinesia with dopamine and norepinephrine; freezing of gait with norepinephrine; and dementia with dopamine and homovanillic acid. Tremor had no correlations with the concentrations of the monoamines measured. Patients with dementia had a significantly increased level of epinephrine concentrations.Insufficient therapeutic responses of invidividual symptoms were associated with significantly decreased concentrations of particular monoamines before treatment: Hoehn and Yahr's stage with norepinephrine and epinephrine; akinesia with homovanillic acid and 5-hydroxyindoleacetic acid; and freezing of gait with dopamine, norepinephrine, homovanillic acid, and 5-hydroxyindoleacetic acid. These results suggest a significant correlation between the reduction in particular monoamines and the severity of some parkinsonian symptoms and their subsequent responses to L-dopa.     

Huntington chorea is not associated with hyperactivity of nigrostriatal dopaminergic neurons: studies in postmortem tissues and in rats with kainic acid lesions

We estimated dopamine release postmortem in the neostriatum of patients with Huntington disease (HD) and in controls. In HD, dopamine levels were unchanged in caudate and elevated in putamen, but homovanillic acid (HVA) and the ratio HVA:dopamine were unaltered in both nuclei. When rats were injected with kainic acid (an experimental model of HD), dopamine levels in striatum remained unchanged 2 to 30 days postoperatively; HVA and 3,4-dihydroxyphenylacetic acid (DOPAC) increased significantly from 2 to 18 days after injections but returned to normal levels later. These findings suggest that the nigrostriatal projection adapts to loss of striatal neurons that normally influence dopamine release and is not hyperactive in HD chorea.     

The cortical lesion of Huntington's disease: further neurochemical characterization, and reproduction of some of the histological and neurochemical features by N-methyl-D-aspartate lesions of rat cortex.

Huntington's disease is a progressive neurodegenerative disease in which the basal ganglia are preferentially affected. Recent evidence, however, suggests involvement of the cerebral cortex as well, with sparing of neurochemically defined subsets of gamma-aminobutyric acid (GABA)-ergic interneurons. In the present study, we examined changes in concentrations of the amino acid neurotransmitters GABA, glutamate, and aspartate in nine cortical regions from 23 patients with advanced Huntington's disease and 12 control brains. GABA concentrations were significantly increased in eight of the nine regions, consistent with a sparing of GABAergic local circuit neurons in the context of progressive cortical atrophy. Small but significant increases in glutamate were found in six of the nine regions, while aspartate levels were generally unaffected. Striate cortex (Brodmann's area 17) showed the most profound increases in GABA and glutamate. We also investigated the effects of powdering the excitotoxins N-methyl-D-aspartate (NMDA) or kainic acid onto the dura of rats. The resulting lesions were examined at 1 week and 6 months. The NMDA-induced lesions showed striking sparing of parvalbumin-positive neurons (a subset of GABAergic interneurons), and this sparing was reflected in neurochemical measurements of GABA; kainic acid lesions failed to display this selectivity. Somatostatin, cholecystokinin, and vasoactive intestinal polypeptide concentrations were spared by the NMDA-induced lesions, and substance P levels were significantly increased. These results provide evidence that NMDA excitotoxic lesions of cerebral cortex can produce a selective pattern of neuronal damage similar to that which occurs in Huntington's disease.     

Striatal dopamine depletion, dopamine receptor stimulation, and GABA metabolism: implications for the therapy of Parkinson's disease

Dopamine-denervated rat striata exhibit increased synaptosomal gamma-aminobutyric acid (GABA) synthetic capacity (glutamate decarboxylase activity) without an alteration in GABA transport capacity. Stimulating denervated striatal dopamine receptors with apomorphine selectively increases in vivo steady-state striatal GABA turnover. The striatal response in animals to isolated loss of dopamine innervation is an increase in glutamate decarboxylase activity, not the decrease frequently found in the brains of patients with Parkinson's disease. Neurochemical expression of denervated striatal dopamine receptor stimulation may involve increased synaptic activity of striatal GABA neurons. For these reasons, enhancement of basal ganglia GABA function may improve responsiveness to dopamimetic therapies in patients with Parkinson's disease.     

Free and conjugated GABA in human cerebrospinal fluid: Effect of degenerative neurologic diseases and isoniazid

gamma-Aminobutyric acid (GABA) was measured in CSF as such and following acid hydrolysis by the ion-exchange/fluorometric method. The conjugated GABA level was obtained by subtracting the free GABA level from the total GABA level. Results showed that at room temperature, while the free GABA level increased, the level of conjugated GABA decreased in a linear fashion during the first 24 h (r = -0.974; P less than 0.001). Aging and CSF conjugated GABA levels were inversely correlated (r = -0.613; P less than 0.05). Unlike free GABA levels, the levels of conjugated GABA were not altered in Huntington's disease, Parkinson's disease, cerebellar ataxias, dementias, epilepsy and multiple sclerosis compared to controls. In patients with Huntington's disease, on administration of isoniazid at 900 mg/day, along with pyridoxine at 100 mg/day, a 4-fold increase of both free (P less than 0.005) and conjugated GABA (P less than 0.0025) was seen. The results indicate that while total GABAergic peptides are not altered in several of the neurologic diseases studied, drugs such as isoniazid and/or pyridoxine can significantly elevate both free and conjugated GABA levels in human CSF.     

Intravenous probenecid loading. Effects on plasma and cerebrospinal fluid probenecid levels and on monoamine metabolites in cerebrospinal fluid.

Probenecid blocks the active transport from cerebrospinal fluid to blood of homovanillic acid and 5-hydroxyindoleacetic acid, thus increasing cerebrospinal fluid levels of these products of central monoamine metabolism. The half-life in plasma of probenecid given as a single intravenous infusion (40 mg per kilogram of body weight) to patients with either Huntington's chorea or Parkinson's disease averaged about 6.6 hours. In cerebrospinal fluid, peak values for homovanillic acid and 5-hydroxyindoleactic acid occurred in samples collected 8 hours after the 1-hour probenecid infusion was started. Even after 4 hours, however, levels of both monoamine metabolites were significantly increased. There was a positive correlation between cerebrospinal fluid levels of probenecid and the increase in 5-hydroxyindoleacetic acid but not homovanillic acid. Compared with the oral administration of probenecid, the intravenous infusion technique produced more consistent elevations in plasma and cerebrospinal fluid probenecid levels, greater increases in cerebrospinal fluid homovanillic acid values, and fewer gastrointestinal side effects.     

Sedative effects of apomorphine in an animal model of Huntington's disease.

The sedative effectiveness of apomorphine in a newly developed animal model of Huntington's disease was examined. The motor responses of rats with kainic acid lesions of the neostriatum to a sedative dose of apomorphine (50 micrograms/kg) was similar to that observed in intact controls. In contrast, compared to controls, a marked potentiation of the motor stimulant effects of dextroamphetamine was confirmed in the kainic acid-lesioned group. We suggest that the pathological changes underlying the symptoms observed in this animal model and in Huntington's disease do not include abnormalities in presynaptic dopamine receptors in the neostriatum.     

NMDA receptors modulate dopamine loss due to energy impairment in the substantia nigra but not striatum

Defects in energy metabolism have been detected in patients with Parkinson's disease and have been proposed as a contributing factor in the disease. Previous in vitro studies showed that NMDA receptors contribute to the loss of dopamine neurons caused by the metabolic inhibitor malonate. In vivo, it is not known whether this interaction occurs through a postsynaptic action on the cell body in the substantia nigra or through a presynaptic action at the dopamine terminal in the striatum. So we could discern the anatomical level of NMDA receptor involvement, rats were infused with malonate, either into the left striatum or into the left substantia nigra. NMDA receptors were locally blocked by an intranigral or intrastriatal coinfusion of malonate plus MK-801 followed by a second infusion of MK-801 3 h later. Animals were examined at 1 week for striatal and nigral dopamine and GABA levels. Intranigral infusion of malonate (0.5 micromol) produced an approximate 50% loss of both nigral dopamine and GABA. MK-801 (0.1 micromol) provided significant protection against both nigral dopamine and GABA loss and against anterograde damage to dopamine terminals in the striatum. Intrastriatal administration of malonate (2 micromol) produced a 68 and 35% loss of striatal dopamine and GABA, respectively. In contrast to intranigral administration, intrastriatal blockade of NMDA receptors did not protect against striatal dopamine loss, although GABA loss was significantly attenuated. Core body temperature monitored several hours throughout the experiment was unchanged. Consistent with a lack of effect of NMDA antagonists on malonate-induced toxicity to dopamine neurons in striatum, intrastriatal infusion of NMDA had a pronounced effect on long-term GABA toxicity with little effect of dopamine loss. These findings are consistent with a postsynaptic action of NMDA receptors on mediating toxicity to dopamine neurons during impaired energy metabolism.