Tauopathies with parkinsonism: clinical spectrum, neuropathologic basis, biological markers, and treatment options.

Tauopathies with parkinsonism represent a spectrum of disease entities unified by the pathologic accumulation of hyperphosphorylated tau protein fragments within the central nervous system. These pathologic characteristics suggest shared pathogenetic pathways and possible molecular targets for disease-modifying therapeutic interventions. Natural history studies, for instance, in progressive supranuclear palsy, frontotemporal dementia with parkinsonism linked to chromosome 17, corticobasal degeneration, and Niemann-Pick disease type C as well as in amyotrophic lateral sclerosis/Parkinson-dementia complex permit clinical characterization of the disease phenotypes and are crucial to the development and validation of biological markers for differential diagnostics and disease monitoring, for example, by use of neuroimaging or proteomic approaches. The wide pathologic and clinical spectrum of the tauopathies with parkinsonism is reviewed in this article, and perspectives on future advances in the understanding of the pathogenesis are given, together with potential therapeutic strategies.

Diffusion parameters in the striatum of rats with 6-hydroxydopamine-induced lesions and with fetal mesencephalic grafts.

Functional recovery after transplantation of dopaminergic cells into the lesioned striatum is dependent on widespread diffusion of the transmitter released by the graft. In the present study, we investigated the diffusion parameters of the extracellular space in the striatum of control, 6-hydroxydopamine-lesioned, intrastriatally grafted, and sham-grafted rats in vivo. We used two types of grafts-single macrografts or multiple micrografts. The real-time iontophoretic tetramethylammonium method enabled us to extract three extracellular space diffusion parameters: volume fraction, alpha, tortuosity, lambda, and nonspecific uptake of tetramethylammonium, k'. Compared with controls (alpha = 0.19, lambda = 1.59), in lesioned animals both alpha and lambda were lower (alpha = 0.14, lambda = 1.50). alpha and lambda were increased inside macro-and micrografts, where alpha = 0.24 and lambda = 1.80, and in sham-grafted areas, where alpha = 0.24 and lambda = 1.72. In regions outside the grafts (alpha = 0.15, lambda = 1.51) or in sham grafts (alpha = 0.14, lambda = 1.49), the values of alpha and lambda were similar to the values observed in lesioned striatum. Nonspecific uptake (k') did not differ among the groups. Our results show that, compared with control, alpha and lambda were decreased in dopamine-depleted areas and increased in areas with grafts. Multiple but smaller graft deposits, in contrast to their enlarged capability for dopaminergic reinnervation, impair the conditions for diffusion and extrasynaptic transmission in a larger area of the striatum than do single macrografts, presumably because of more extensive tissue damage, cell loss, and astrogliosis.

Modelling constant potential amperometry for investigations of dopaminergic neurotransmission kinetics in vivo.

Constant potential amperometry (CPA) was used for in vivo recording of extracellular dopamine (DA) after electrical stimulation of the medial forebrain bundle (MFB) (4 pulses, 2 mA, 20 or 100 Hz) in the striatum of the rat brain. CPA signals were analysed in the absence and presence of the DA uptake inhibitor nomifensine with the help of a mathematical model which considered both the influence of DA diffusion after its stimulated release and the Michaelis-Menten kinetics of cellular DA uptake from the extracellular space. We found an excellent conformity of experimentally obtained CPA signals and calculated curves. Mathematical analysis revealed that CPA signals were strongly influenced by DA diffusion. The kinetic parameters calculated from CPA signals in this study were in agreement with experimental determinations of Vmax and Km of extracellular DA uptake in other studies and reflect the particular pharmacological properties of nomifensine. CPA is a useful and efficient method for in vivo estimation of individual changes of DA kinetic parameters by pharmacological treatment.

Dopaminergic mRNA expression in the intact substantia nigra of unilaterally 6-OHDA-lesioned and grafted rats: an in situ hybridization study.

The present study was performed to investigate the influence of intrastriatal fetal mesencephalic grafts on dopaminergic mRNA expression in the non-lesioned substantia nigra pars compacta of unilaterally 6-hydroxydopamine-lesioned rats. The expression of dopamine transporter mRNA, synaptic vesicular monoamine transporter mRNA and tyrosine hydroxylase mRNA was assessed in adjacent cryostat sections using in situ hybridization. Rotational behavior induced by apomorphine and amphetamine as well as hybridization of striatal sections cut at the grafting coordinates were used to prove the functional recovery and the presence of grafted cells, respectively. After grafting, the number of rotations was decreased and hybridization signals overlying cells in the grafted striatum were detected. Mean grain densities overlying labeled neurons in the substantia nigra pars compacta of grafted rats were compared to those of shamgrafted rats and revealed differential expression of dopamine transporter mRNA, whereas synaptic vesicular monoamine transporter mRNA and tyrosine hydroxylase mRNA expression showed no difference. The results will be discussed in relation to previous in vitro and in vivo studies suggesting a reduction of functional dopamine transporter molecules in the contralateral striatum.

Striatal dopaminergic metabolism is increased by deep brain stimulation of the subthalamic nucleus in 6-hydroxydopamine lesioned rats.

Deep brain stimulation of the subthalamic nucleus is an established therapeutic strategy for patients with Parkinson's disease. Although the exact mechanisms of action remain unknown, it is noteworthy that dopaminergic medication can be markedly reduced after neurostimulation of the subthalamic nucleus. Previously, we have shown that deep brain stimulation of the subthalamic nucleus is followed by an increase of striatal extracellular dopamine metabolites in naive rats. In the present study we examined the effects of deep brain stimulation on striatal monoamine metabolism in the intrastriatal 6-hydroxydopamine rat model of Parkinson's disease. Deep brain stimulation of the subthalamic nucleus was followed by a delayed increase of extracellular 3,4-dihydroxyphenylacetic and homovanillic whereas dopamine levels were unchanged in stimulated rats and controls. Our results indicate that deep brain stimulation of the subthalamic nucleus affects significantly striatal dopaminergic metabolism in 6-hydroxydopamine lesioned rats.

The influence of pallidal deep brain stimulation on striatal dopaminergic metabolism in the rat.

Deep brain stimulation of the globus pallidus internus has been recently shown to alleviate parkinsonian symptoms and levodopa-induced dyskinesias. However, its exact mechanisms of action are unclear. Pallidal neurones are connected via various pathways to the dopaminergic nigrostriatal system. In the present study we investigated the hypothesis that deep brain stimulation of the entopeduncular nucleus (corresponds to the human internal pallidum) affects striatal dopaminergic metabolism in naive and 6-hydroxydopamine (6-OHDA) lesioned rats using microdialysis. Our results show that stimulation of the entopeduncular nucleus does not significantly affect striatal dopamine metabolism (of dopamine, 3, 4-dihdroxyphenylacetic acid and homovanillic acid) in naive and 6-OHDA-lesioned animals. They contrast with our previous observations that deep brain stimulation of the subthalamic nucleus increases striatal dopamine metabolism suggesting differential effects of these nuclei on striatal dopamine metabolism.

Comparison by microdialysis of striatal L-DOPA after its systemic administration in rats with probes implanted acutely or through a guide cannula.

Different methods of microdialysis probe implantation are utilized according to the purpose and needs of each particular study. However, very few experiments have systematically examined whether these different techniques have an impact on the obtained data. In the present study we examined the influence of two different microdialysis methods - acute probe implantation vs. insertion into a preimplanted guide cannula - on the striatal extracellular availability of systemically administered L-DOPA. Furthermore, we monitored the effects of L-DOPA administration on dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC). In rats that received a guide cannula 4 days prior to probe insertion and microdialysis, extracellular L-DOPA concentrations increased to concentrations that were about nine times higher than in rats with acute implantation of a microdialysis probe. Extracellular DOPAC concentrations were also higher in the chronic preparations but dopamine concentrations showed no differences between groups. Our results suggest that the observed differences may be due to inflammatory disruption of the BBB following chronic implantation of a guide cannula.

High frequency stimulation of the subthalamic nucleus influences striatal dopaminergic metabolism in the naive rat.

High frequency stimulation (HFS) of the subthalamic nucleus (STN) can partially alleviate motor symptoms in patients with Parkinson's disease (PD). However, the mechanism of action of HFS is incompletely understood. We investigated the effect of HFS (130 Hz) and low frequency stimulation (LFS, 20 Hz) of the STN on striatal dopaminergic transmission and metabolism using in vivo microdialysis in anaesthetized and freely moving rats. While LFS had no effect, HFS of the STN produced a delayed, stable and intensity-dependent increase of extracellular dopamine metabolites. Striatal extracellular levels of dopamine and 5-HIAA were not influenced by HFS or LFS in the present experimental paradigm. We conclude that HFS of the STN influences striatal dopaminergic metabolism in naive, nonlesioned rats.

Extracellular dopamine in the anterior nucleus accumbens is distinctly affected by ventral tegmental area administration of cholecystokinin and apomorphine: data from in vivo voltammetry.

The interaction of cholecystokinin (CCK) and dopamine (DA) in the mesolimbic system was investigated. The study focused on DAergic cells not containing colocalized CCK projecting from the ventral tegmental area (VTA) to the anterior nucleus accumbens (NA). Differential pulse voltammetry in pargyline pretreated and anesthetized rats was used to measure extracellular DA in the anterior NA following microinjection of apomorphine either alone or in combination with CCK-8s into the VTA. In agreement with an earlier study there was a dose-dependent increase in the DA signal in the anterior NA after microinjection of CCK-8s into the VTA. Apomorphine microinjected into the VTA produced a biphasic effect on extracellular DA in the anterior NA with an increase from basal levels of approximately 50% by 1 ng, whereas 10 ng was ineffective and 100 ng apomorphine caused a slight decrease in the DA signal. Apomorphine (1 ng) microinjected together with 1 ng CCK-8s produced an increase in the DA signal to approximately 180% of the baseline value, whereas the combination of 1 ng apomorphine and 100 ng CCK-8s was ineffective. When 100 ng apomorphine were microinjected in combination with either 1 ng or 100 ng CCK-8s, the DA signal in the anterior NA was unchanged. These results suggest that low doses of apomorphine injected into the VTA synergistically influence the effects of CCK-8s on extracellular DA in the anterior NA, whereas higher doses of apomorphine suppress the effect of CCK-8s on DAergic cells projecting to the anterior NA.

Hypericin and pseudohypericin: pharmacokinetics and effects on photosensitivity in humans.

Extracts of St. John's wort (Hypericum perforatum) are used in treatment of depression. They contain various substances with the naphthodianthrones hypericin and pseudohypericin as characteristic ingredients. These compounds were shown to cause phototoxicity in cell culture and in animals. A placebo-controlled randomized clinical trial with monitoring of hypericin and pseudohypericin plasma concentration was performed to evaluate the increase in dermal photosensitivity in humans after application of high dose hypericum extracts. The study was divided into a single dose and a multiple dose part. In the single dose period, each of 13 volunteers received in a double blind fourfold complete crossover design, either placebo, or 900, 1800 or 3600 mg of a standardized hypericum extract (LI 160) containing zero, 2.81, 5.62 and 11.25 mg of total hypericin (total hypericin is the sum of hypericin and pseudohypericin). Maximum total hypericin plasma concentrations were observed about 4 h after dosage and were 0, 0.028, 0.061 and 0.159 mg/L, respectively. Before and 4 h after drug intake, the subjects were exposed at small areas of their back to increasing doses of solar simulated irradiation (SSI, with combined ultraviolet A, UV-A, and UV-B light) and another part was exposed to selective UV-A light irradiation. Minimal erythema dose was determined 5, 20 and 68 h after irradiation. Comparison of SSI sensitivity without and with hypericum extract did not show and difference and there was no dose-related trend in light sensitivity. Sensitivity to selective UV-A light was increased only after the highest dose from a minimal tanning dose of 10.8 J/ cm2 (mean) after placebo to 8.7 J/cm2 after 3600 mg extract with marginal statistical significance (p = 0.03 by one sided paired t-test). There was no correlation between total hypericin plasma concentrations and photosensitivity. In the multiple dose part, 50 volunteers received 600 mg hypericum extract t.i.d. with a daily dose of 5.6 mg of total hypericin. Comparison of UV light sensitivity before dosing with day 15 of treatment showed a slightly increased SSI sensitivity expressed by decrease of the MED from 0.17 to 0.16 J/cm2 (p = 0.005 by Wilcoxon test), and similarly, sensitivity to UV-A light increased (the mean tanning dose decreased from 9.9 to 7.8 J/cm2, p < 0.0001). This increase in cutaneous light sensitivity could be compensated by reducing irradiation time by 21%. Doses used in this study were higher than typical doses in current commercial preparations. In spite of these high doses in the double blind single dose part, frequency of side effects was equal to placebo medication and UV light sensitivity was not or only marginally increased. The study does not, however, exclude phototoxic reactions with doses above 11.25 mg of total hypericin and plasma levels above 100 micrograms/L. Furthermore, phototoxicity may be different after application of pure hypericin, since some constituents in the plant extract may exhibit protective effects.

Unilateral fetal mesencephalic grafts in intact rats reduce amphetamine-induced dopamine release in both striata. An in vivo voltammetric study.

This study investigated amphetamine-induced striatal dopamine release after intraventricular unilateral fetal mesencephalic grafts in otherwise intact rats. Dopamine was monitored in vivo by differential pulse voltammetry. In grafted animals, amphetamine-induced dopamine release was decreased compared to sham-grafted, age-matched controls. This decrease was observed in the grafted as well as in the contralateral striatum five months after intraventricular grafting. There was no measurable effect of the graft on the amphetamine-induced rotational behaviour. Our results exceed former observations reporting decreased amphetamine-induced dopamine release in the contralateral striatum of 6-hydroxydopamine-lesioned and unilaterally-grafted rats which had been attributed to a reduction of dopamine transporters. Furthermore, it was shown that concerning this effect ventral mesencephalic grafts are independent of a previous 6-hydroxydopamine lesion.

Deficiency of glutathione S-transferases T1 and M1 as heritable factors of increased cutaneous UV sensitivity.

Glutathione S-transferases (GSTs) play a primary role in cellular defense against electrophilic chemical species and radical oxygen species. Because free radical attack is one mechanism of UV irradiation-caused skin damage, we investigated whether genetic variation at the GST loci GST T1 and GST M1 influences individual UVB sensitivity. In a double-blind clinical trial, 50 healthy volunteers were evaluated for minimal erythema dose of UVB irradiation, MED (J/cm2), skin types were assigned, and internal standard-controlled polymerase chain reaction (PCR) was used to identify their GST T1 and GST M1 genotypes. The five homozygous carriers of the GST T1 deletion (GST T1*0/0) presented with the most intensive inflammatory reactions after irradiation; they were significantly overrepresented among the highly UVB-sensitive subgroups (p = 0.006). Lack of GST M1 (GST M1*0/0, n = 27) tended to be more frequent only in UVB-sensitive subjects, and the proportion of the active GST M1 allelic variants *A and *B was similar in all UVB sensitivity subgroups. Three subjects with deficiencies in GST T1 and GST M1 had the most intense inflammatory responses. No effect of gender or genetic variations at the MC1R gene locus was established. Thus, heritable GST T1 deficiency may be a genetic determinant of individual skin sensitivity toward UV irradiation.

Cholecystokinin increases extracellular dopamine overflow in the anterior nucleus accumbens via CCK(B) receptors in the VTA assessed by in vivo voltammetry.

Differential pulse voltammetry was used to investigate the extracellular dopamine (DA) and DOPAC signal in the anterior part of nucleus accumbens (N.acc.) after microinjection of cholecystokinin (CCK) derivatives into the ventral tegmental area (VTA). Both the mixed CCK(A)/CCK(B) receptor agonist CCK-8s and the selective CCK(B) receptor agonist CCK-4 caused a dose-dependent increase in the DA signal after doses of 10 ng and 100 ng while CCK-8s had no effect on the DOPAC signal. The CCK(A) receptor antagonist L 364,718 (25 microg/kg i.p.) as well as the CCK(B) receptor antagonist L 365,260 (25 microg/kg i.p.) were administered prior to microinjection of 100 ng CCK-8s and L 365,260, but not L 364,718, completely inhibiting the DA increase produced by CCK-8s. Analysis of the tissue levels of DA and its main metabolites in the anterior part of N.acc. revealed no changes after CCK-8s microapplication into VTA. The presented data indicate a CCK(B) receptor-mediated increase in extracellular DA in the anterior N.acc. after microapplication of CCK derivatives into the VTA.

Foetal nigral cell suspension grafts influence dopamine release in the non-grafted side in the 6-hydroxydopamine rat model of Parkinson's disease: in vivo voltammetric data.

The present study employed differential-pulse voltammetry to assess the influence of foetal ventral mesencephalic grafts on dopamine overflow in the contralateral caudate putamen of the 6-hydroxydopamine rat model of Parkinson's disease. The experimental design involved measurements of dopamine overflow in the grafted and contralateral striatum. Control measurements of dopamine overflow were performed in 6-hydroxydopamine-lesioned rats only and the caudate putamen of normal control rats. Cell suspensions of foetal rat ventral mesencephalic tissue were grafted into the dopamine-depleted caudate putamen of unilaterally 6-hydroxydopamine-lesioned rats. At 6 weeks, animals with functional, mature grafts (as assessed by amphetamine-amplified behavioural asymmetry), were pretreated with pargyline (75 mg/kg i.p.), and both striatal sides were monitored for dopamine overflow for 90 min following amphetamine sulphate administration (5 mg/kg i.p.). The time course of dopamine overflow inside the graft was similar to that in the contralateral caudate putamen of the same animal, the normal control animal and the contralateral caudate putamen of 6-hydroxydopamine-lesioned animals. However, in grafted animals the mean dopamine overflow detected in the contralateral caudate putamen was approximately 34% lower than the concentration of dopamine detected in the contralateral caudate putamen of 6-hydroxydopamine-lesioned control animals and approximately 39% lower than the concentration of dopamine detected in the caudate putamen of the normal control animal. There was no statistical difference in the concentration of amphetamine-induced dopamine overflow between the caudate putamen contralateral to the 6-hydroxydopamine lesion and the caudate putamen of the normal control animal. These data suggest that intrastriatal foetal ventral mesencephalic suspension grafts reduce amphetamine-induced dopamine release in the contralateral non-grafted caudate putamen.

Grafts modulate dopamine transporters of the non-lesioned striatum.

The effect of intraventricular fetal mesencephalic grafts placed in the previously 6-hydroxydopamine (6-OHDA) lesioned striatum on the kinetics of [3H]dopamine (DA) uptake into striatal synaptosomes prepared from the non-lesioned (contralateral) striatum was studied in rats. Using WIN 35,065 as specific [3H]DA uptake inhibitor, the equilibrium dissociation constant (Km) of [3H]DA uptake into synaptosomes of the non-lesioned (contralateral) striatum did not differ between grafted and nongrafted controls 7 months after grafting. However, the maximal rate of specific [3H]DA uptake (Vmax) was markedly decreased in the non-lesioned striatum of grafted animals. This result indicates that fetal mesencephalic grafts reduce the [3H]DNA uptake in the non-lesioned (contralateral) striatum by reducing the number of functional DA transporters.

Fetal mesencephalic grafts decrease the rate of dopamine uptake in the non-lesioned striatum of unilaterally 6-OHDA lesioned rats: an in vivo voltammetric study.

In the present study the influence of intraventricular fetal mesencephalic grafts on the elimination rate of extracellular dopamine (DA) in the non-lesioned striatum of previously unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats was investigated. The elimination of DA was measured after electrical stimulation of the medial forebrain bundle in vivo before and after treatment with the high affinity uptake inhibitor GBR 12909 (20 mg/kg i.p.) using fast cyclic voltammetry (FCV). Rotational behavior induced by amphetamine (AMPH, 2 mg/kg i.p.) and tyrosine hydroxylase (TH) immunohistochemistry were used to prove the functional recovery and the ingrowth of the graft, respectively. After grafting, the number of rotations was decreased and TH-positive cells and fibers were found in the grafted striatum. Voltammetric measurements with the aid of a kinetic model revealed a smaller rate constant for the in vivo elimination of extracellular DA in the non-lesioned striatum of grafted rats compared to that of non-grafted controls. This effect was abolished after treatment with GBR 12909. Our results will be discussed in relation to the method used and according to recent investigations of the specific [3H]DA uptake into striatal synaptosomes in vitro. Based on these data we conclude that grafts, placed to the lesioned striatum, reduce the DA uptake rate in the non-lesioned striatum due to the reduction of the number of functional DA transporters.

Graft-induced reduction in [3H]dopamine uptake into the non-lesioned striatum.

The effect of intraventricular fetal mesencephalic grafts placed in the 6-hydroxydopamine (6-OHDA) lesioned striatum on [3H]dopamine (DA) uptake into synaptosomes was studied. Apomorphine (APO)- and amphetamine (AMPH)-induced rotational behaviour was continuously reduced by the grafts over 7 months. After this time, a non-significant increase in [3H]DA uptake into synaptosomes of the lesioned striatum and an approximately 40% decrease in [3H]DA uptake into synaptosomes of the non-lesioned striatum were found. Grafts placed in the non-lesioned striatum did not significantly change both rotational behaviour or [3H]DA uptake. The results show that unilateral fetal mesencephalic grafts producing behavioural improvement in the unilateral 6-OHDA lesioned rat induce changes in dopaminergic structures in the non-lesioned striatum.

Fetal mesencephalic grafts influence the dopamine release in the non-lesioned striatum of 6-OHDA-lesioned rats: a behavioral and in vivo voltammetric study.

This study was performed to investigate the effect of intraventricular fetal mesencephalic grafts on the non-lesioned nigro-striatal system of rats with unilateral lesions of dopaminergic neurones in the medial forebrain bundle and to analyze the involvement of the non-lesioned side in functional recovery due to grafts in this model. Grafts placed to the lesioned striatum produced a continuous decrease of apomorphine (APO, 0.25 mg/kg intraperitoneally (i.p.)) and amphetamine (AMPH, 5 mg/kg, i.p.) induced rotations over 7 months after grafting. Using differential pulse voltammetry (DPV) in anaesthetized and pargyline (75 mg/kg, i.p.) pretreated rats we found that 8 months after grafting in the lesioned striatum AMPH (5 mg/kg, i.p.) produced a higher increase of the dopamine (DA) signal (i.e., it became measurable), whereas in the non-lesioned striatum the same treatment produced a smaller increase of the DA signal, both compared to that in sham-grafted controls. After grafting onto the non-lesioned striatum, only a slight decrease of APO-induced rotations was observed, whereas AMPH-induced rotations were increased. In these animals AMPH did not produce a measurable DA signal in the lesioned striatum. The DA signal in the non-lesioned striatum was slightly higher than that of non-grafted controls. These results show clearly that unilateral fetal mesencephalic grafts producing behavioural recovery in the unilateral 6-OHDA model of the rat produce changes at dopaminergic mechanisms in the non-lesioned striatum.