Increased perivascular space volume in white matter and basal ganglia is associated with cognition in Parkinson's Disease

Perivascular spaces (PVS), fluid-filled compartments surrounding brain vasculature, are an essential component of the glymphatic system responsible for transport of waste and nutrients. Glymphatic system impairment may underlie cognitive deficits in Parkinson's disease (PD). Studies have focused on the role of basal ganglia PVS with cognition in PD, but the role of white matter PVS is unknown. This study examined the relationship of white matter and basal ganglia PVS with domain-specific and global cognition in individuals with PD. Fifty individuals with PD underwent 3T T1w magnetic resonance imaging (MRI) to determine PVS volume fraction, defined as PVS volume normalized to total regional volume, within (i) centrum semiovale, (ii) prefrontal white matter (medial orbitofrontal, rostral middle frontal, superior frontal), and (iii) basal ganglia. A neuropsychological battery included assessment of global cognitive function (Montreal Cognitive Assessment, and global cognitive composite score), and cognitive-specific domains (executive function, memory, visuospatial function, attention, and language). Higher white matter rostral middle frontal PVS was associated with lower scores in both global cognitive and visuospatial function. In the basal ganglia higher PVS was associated with lower scores for memory with a trend towards lower global cognitive composite score. While previous reports have shown that greater amount of PVS in the basal ganglia is associated with decline in global cognition in PD, our findings suggest that increased white matter PVS volume may also underlie changes in cognition.

Treadmill exercise delays the onset of non-motor behaviors and striatal pathology in the CAG140 knock-in mouse model of Huntington's disease

Depression, cognitive impairments, and other neuropsychiatric disturbances are common during the prodromal phase of Huntington's disease (HD) well before the onset of classical motor symptoms of this degenerative disorder. The purpose of this study was to examine the potential impact of physical activity in the form of exercise on a motorized treadmill on non-motor behavioral features including depression-like behavior and cognition in the CAG₁₄₀ knock-in (KI) mouse model of HD. The CAG₁₄₀ KI mouse model has a long lifespan compared to other HD rodent models with HD motor deficits emerging after 12months of age and thus provides the opportunity to investigate early life interventions such as exercise on disease progression. Motorized treadmill running was initiated at 4weeks of age (1h per session, 3 times per week) and continued for 6months. Non-motor behaviors were assessed up to 6months of age and included analysis of depression-like behavior (using the tail-suspension and forced-swim tests) and cognition (using the T-maze and object recognition tests). At both 4 and 6months of age, CAG₁₄₀ KI mice displayed significant depression-like behavior in the forced swim and tail suspension tests and cognitive impairment by deficits in reversal relearning in the T-maze test. These deficits were not evident in mice engaged in treadmill running. In addition, exercise restored striatal dopamine D2 receptor expression and dopamine neurotransmitter levels both reduced in sedentary HD mice. Finally, we examined the pattern of striatal expression of mutant huntingtin (mHTT) protein and showed that the number and intensity of immunohistochemical staining patterns of intranuclear aggregates were significantly reduced with exercise. Altogether these findings begin to address the potential impact of lifestyle and early intervention such as exercise on modifying HD progression.

The Effects of Exercise on Dopamine Neurotransmission in Parkinson's Disease: Targeting Neuroplasticity to Modulate Basal Ganglia Circuitry

Animal studies have been instrumental in providing evidence for exercise-induced neuroplasticity of corticostriatal circuits that are profoundly affected in Parkinson’s disease. Exercise has been implicated in modulating dopamine and glutamate neurotransmission, altering synaptogenesis, and increasing cerebral blood flow. In addition, recent evidence supports that the type of exercise may have regional effects on brain circuitry, with skilled exercise differentially affecting frontal-striatal related circuits to a greater degree than pure aerobic exercise. Neuroplasticity in models of dopamine depletion will be reviewed with a focus on the influence of exercise on the dorsal lateral striatum and prefrontal related circuitry underlying motor and cognitive impairment in PD. Although clearly more research is needed to address major gaps in our knowledge, we hypothesize that the potential effects of exercise on inducing neuroplasticity in a circuit specific manner may occur through synergistic mechanisms that include the coupling of an increasing neuronal metabolic demand and increased blood flow. Elucidation of these mechanisms may provide important new targets for facilitating brain repair and modifying the course of disease in PD.

Exercise modifies α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor expression in striatopallidal neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned mouse

The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic-acid-type glutamate receptor (AMPAR) plays a critical role in modulating experience-dependent neuroplasticity, and alterations in AMPAR expression may underlie synaptic dysfunction and disease pathophysiology. Using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of dopamine (DA) depletion, our previous work showed exercise increases total GluA2 subunit expression and the contribution of GluA2-containing channels in MPTP mice. The purpose of this study was to determine whether exercise-dependent changes in AMPAR expression after MPTP are specific to the striatopallidal (D2 R) or striatonigral (D1 R) medium spiny neuron (MSN) striatal projection pathways. Drd2 -eGFP-BAC transgenic mice were used to delineate differences in AMPAR expression between striatal D2 R-MSNs and D1 R-MSNs. Striatal AMPAR expression was assessed by immunohistochemical (IHC) staining, Western immunoblotting (WB) of preparations enriched for postsynaptic density (PSD), and alterations in the current-voltage relationship of MSNs. We found DA depletion results in the emergence of GluA2-lacking AMPARs selectively in striatopallidal D2 R-MSNs and that exercise reverses this effect in MPTP mice. Exercise-induced changes in AMPAR channels observed after DA depletion were associated with alterations in GluA1 and GluA2 subunit expression in postsynaptic protein, D2 R-MSN cell surface expression, and restoration of corticostriatal plasticity. Mechanisms regulating experience-dependent changes in AMPAR expression may provide innovative therapeutic targets to increase the efficacy of treatments for basal ganglia disorders, including Parkinson's disease.

Brief mitochondrial inhibition causes lasting changes in motor behavior and corticostriatal synaptic physiology in the Fischer 344 rat

The striatum is particularly vulnerable to mitochondrial dysfunction and this problem is linked to pathology created by environmental neurotoxins, stimulants like amphetamine, and metabolic disease and ischemia. We studied the course of recovery following a single systemic injection of the mitochondrial complex II inhibitor 3-nitropropionic acid (3-NP) and found 3-NP caused lasting changes in motor behavior that were associated with altered activity-dependent plasticity at corticostriatal synapses in Fischer 344 rats. The changes in synapse behavior varied with the time after exposure to the 3-NP injection. The earliest time point studied, 24h after 3-NP, revealed 3-NP-induced an exaggeration of D1 Dopamine (DA) receptor dependent long-term potentiation (LTP) that reversed to normal by 48 h post-3-NP exposure. Thereafter, the likelihood and degree of inducing D2 DA receptor dependent long-term depression (LTD) gradually increased, relative to saline controls, peaking at 1 month after the 3-NP exposure. NMDA receptor binding did not change over the same post 3-NP time points. These data indicate even brief exposure to 3-NP can have lasting behavioral effects mediated by changes in the way DA and glutamate synapses interact.

Differential regulation of the growth-associated proteins GAP-43 and superior cervical ganglion 10 in response to lesions of the cortex and substantia nigra in the adult rat

Investigation of the elements underlying synapse replacement after brain injury is essential for predicting the neural compensation that can be achieved after various types of damage. The growth-associated proteins superior cervical ganglion-10 and growth-associated protein-43 have previously been linked with structural changes in the corticostriatal system in response to unilateral deafferentation. To examine the regulation of this response, unilateral cortical aspiration lesion was carried out in combination with ipsilateral 6-hydroxydopamine lesion of the substantia nigra, and the time course of the contralateral cortical molecular response was followed. Unilateral cortical aspiration lesion in rats corresponds with an upregulation of superior cervical ganglion-10 mRNA at 3 and 10 days post-lesion, and protein, sustained from three to at least 27 days following lesion. With the addition of substantia nigra lesion, the response shifts to an upregulation of growth-associated protein-43 mRNA at 3 and 10 days post-lesion, and protein after 10 days. Nigral lesion alone does not alter contralateral expression of either gene. Likewise, motor function assessment using the rotorod test revealed no significant long-term deficits in animals that sustained only nigrostriatal damage, but cortical lesion was associated with a temporary deficit which was sustained when nigrostriatal input was also removed. Growth-associated protein-43 and superior cervical ganglion-10, two presynaptic genes that are postulated to play roles in lesion-induced sprouting, are differentially upregulated in corticostriatal neurons after cortical versus combined cortical/nigral lesions. The shift in contralateral gene response from superior cervical ganglion-10 to growth-associated protein-43 upregulation and associated behavioral deficit following combined cortical and nigral denervation suggest that nigrostriatal afferents regulate cortical lesion-induced gene expression and ultimate functional outcome.

Postnatal expression of alpha-synuclein protein in the rodent substantia nigra and striatum

A primary goal of our research is to elucidate the mechanisms involved in neuroplasticity of the basal ganglia in both development and in response to injury. One means to this aim is through the analysis of the ontological profile of proteins in the basal ganglia and to correlate their pattern of expression with morphological development. One protein thought to be important in neuroplasticity is alpha-synuclein. The purpose of this study was to characterize and compare the pattern of expression of alpha-synuclein protein using immunocytochemistry in the substantia nigra and striatum of the rodent in early postnatal and adult life. Our results demonstrate that there is a high level of expression of alpha-synuclein protein within cell bodies of the substantia nigra pars compacta in the 1st week of postnatal life that decreases both in intensity and number of immunoreactive cells between postnatal days 7 and 14. This is in contrast to the substantia nigra pars reticulata where alpha-synuclein protein expression in the neuropil increases after postnatal day 7. In the striatum, expression in early postnatal life is distributed in a mosaic-like fashion and becomes more diffuse after postnatal day 14. Our results support the findings of others that expression of alpha-synuclein is developmentally regulated and suggest that alpha-synuclein may play an important role in establishing the function of the basal ganglia. Understanding the role of alpha-synuclein in the normal basal ganglia may provide insights into the molecular mechanisms involved in neuroplasticity in response to injury.

Reliability and validity of a new global dyskinesia rating scale in the MPTP-lesioned non-human primate

Behavioral rating scales for dyskinesia in the non-human primate are frequently used to assess the efficacy of new treatments and to provide a clinical correlative with neurochemical and neuropathological changes. Although a large variety of different scales have been used in non-human primate studies, there is no single standardized scale, and none have been evaluated for reliability and validity. We are reporting a new global non-human primate dyskinesia rating scale (GPDRS) for the squirrel monkey, developed in the context of an independent study of dyskinesia. In this report we demonstrate the reliability and validity of this scale. The GPDRS is a single-item scale with well-defined points and brevity allowing for rapid and easy application for assessing the overall degree of dyskinesia. In this study, seven MPTP-lesioned and four non-lesioned (control) non-human primates were videotaped following treatment with either levodopa or water. To test inter- and intra-rater reliability, three examiners rated the videotape independently at two different time points and these assessments were compared. The validity of the scale was tested in two phases. First, examiners rated the videotape using the GPDRS and the Abnormal Involuntary Movement Scale (AIMS), a scale commonly used to rate dyskinesia in the non-human primate, and the ratings from each scale were compared. Second, validity was tested in the context of an independent dyskinesia study, in which the scale was used to distinguish between two treatment groups. The GPDRS was shown to have high inter- and intra-rater reliability and to be valid for the assessment of dyskinesia in the squirrel monkey. In this report we also demonstrate the inter- and intra-rater reliability of the AIMS.

The postnatal development of AMPA receptor subunits in the basal ganglia of the rat

In situ hybridization and immunohistochemistry were used to characterize the expression pattern of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors during postnatal development in the rat basal ganglia. All subunit transcripts showed some degree of developmental regulation. GluR1 and GluR2 are expressed at high levels in the neonate with reduced expression in the adult. GluR3 and GluR4 are expressed at significantly lower levels in both neonates and adults and have much more modest degrees of reduced expression in adults as compared with GluR1 and GluR2. Analysis of the flip and flop transcript isoforms indicates that GluR1 flip and flop and GluR2 flip are the predominately expressed splice variants in adults. Observed changes in the expression of the AMPA receptor transcripts indicate that there are fundamental differences in the expression of these receptor subunits in adults and neonates. This phenomenon may play a significant role in the establishment of proper synaptic circuitry within the developing basal ganglia in early postnatal life as well as contributing to differences in susceptibility to injury and disease in the aging brain.

Experimental models of Parkinson's disease: insights from many models

Toxin-induced and genetic experimental models have been invaluable in investigating idiopathic Parkinson's disease (PD). The neurotoxins--reserpine, 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and methamphetamine--have been used to develop parkinsonian models in a wide variety of species. Both 6-OHDA and MPTP can replicate the neurochemical, morphologic, and behavioral changes seen in human disease. The unilateral 6-OHDA rat model is an excellent model for testing and determining modes of action of new pharmacologic compounds. The nonhuman primate MPTP-induced parkinsonian model has behavioral features that best approximate idiopathic PD. These induced and genetic models have been used to study the pathophysiology of the degenerating nigrostriatal system and to evaluate novel therapeutic strategies. Important differences within these models provide insights into various aspects of the dopaminergic phenotype and its role as a target in disease. These models provide an avenue to evaluate many anti-parkinsonian compounds, such as levodopa, which was first evaluated in an animal model and is the gold standard of parkinsonian treatment today.

The native form of alpha-synuclein is not found in the cerebrospinal fluid of patients with Parkinson's disease or normal controls

Alpha-synuclein has recently been shown to be a major constituent of Lewy bodies in Parkinson's disease (PD). This observation led us to investigate the possibility that its detection in the cerebrospinal fluid (CSF) could be used as a marker for Lewy bodies in the central nervous system. In this study we determined the pattern of expression of alpha-synuclein in patients with sporadic Parkinson's disease (PD) and normal controls, using western immunoblotting in conjunction with an antibody that recognizes the carboxyl terminal of alpha-synuclein protein. The native 19 kDa band normally seen in brain homogenates was not found in the CSF of either parkinsonian patients or control subjects. However, a novel band was observed, which migrated at a position in the range of 42 kDa in CSF from both patients and controls. We conclude that alpha-synuclein cannot be used as a biomarker for Lewy bodies during life. However, further characterization of the 42 kDa protein may be of interest.

Role of nitric oxide in methamphetamine neurotoxicity: protection by 7-nitroindazole, an inhibitor of neuronal nitric oxide synthase

The role of nitric oxide (NO.) in the neurotoxic effects of methamphetamine (METH) was evaluated using 7-nitroindazole (7-NI), a potent inhibitor of neuronal nitric oxide synthase. Treatment of mice with 7-NI (50 mg/kg) almost completely counteracted the loss of dopamine, 3,4-dihydroxyphenylacetic acid, and tyrosine hydroxylase immunoreactivity observed 5 days after four injections of 10 or 7.5 mg/kg METH. With the higher dose of METH, this protection at 5 days occurred despite the fact that combined administration of METH and 7-NI significantly increased lethality and exacerbated METH-induced dopamine release (as indicated by a greater dopamine depletion at 90 min and 1 day). Combined treatment with 4 x 10 mg/kg METH and 7-NI also slightly increased the body temperature of mice as compared with METH alone. Thus, the neuroprotective effects of 7-NI are independent from lethality, are not likely to be related to a reduction of METH-induced dopamine release, and are not due to a decrease in body temperature. These results indicate that NO. formation is an important step leading to METH neurotoxicity, and suggest that the cytotoxic properties of NO. may be directly involved in dopaminergic terminal damage.

Monoamine oxidase-dependent metabolism of dopamine in the striatum and substantia nigra of L-DOPA-treated monkeys

The effects of monoamine oxidase (MAO) inhibitors on the metabolism of dopamine synthesized from exogenous L-DOPA were investigated in the striatum and substantia nigra of squirrel monkeys. Administration of a single dose of L-DOPA (methyl ester, 40 mg/kg, i.p.) caused a significant increase in the levels of dopamine, 3-4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) and in the DOPAC/dopamine ratio in the putamen, caudate and substantia nigra. These changes were more pronounced in the substantia nigra than in the striatum and within the striatum of L-DOPA-treated monkeys, levels of dopamine and its metabolites were higher in the putamen than in the caudate nucleus. When L-DOPA treatment was preceded by the injection of clorgyline or deprenyl at a concentration (1 mg/kg) which selectively inhibited MAO A or MAO B, respectively, striatal dopamine was increased while the striatal DOPAC and HVA levels and DOPAC/dopamine ratio were significantly reduced as compared to the values obtained with 1-DOPA alone. The two MAO inhibitors also counteracted the increase in the DOPAC and HVA levels and DOPAC/dopamine ratio induced by L-DOPA in the substantia nigra. Thus, both MAO A and MAO B contribute to the metabolism of dopamine when higher levels of this neurotransmitter are generated from L-DOPA in the squirrel monkey. The extent of reduction of dopamine catabolism (as assessed by the decrease in DOPAC and HVA levels) in the striatum and substantia nigra was similar with clorgyline and deprenyl even if the ratio MAO A/MAO B was approximately 1 to 10. This indicates that, though catalyzed by both MAO A and MAO B, dopamine deamination following treatment with L-DOPA preferentially involves MAO A.

In situ hybridization analysis of AMPA receptor subunit gene expression in the developing rat spinal cord

In early postnatal life the acquisition of mature morphological and molecular features of motor neurons is influenced by synaptic activity within the spinal cord. Glutamatergic synaptic neurotransmission is believed to play a central role in this process. We hypothesize that the repertoire of glutamate receptors expressed by neurons in the young spinal cord differ from those expressed in adults and such receptors support activity-dependent developmental plasticity. To explore this idea, we used in situ hybridization histochemistry to determine the distribution, temporal expression, and potential subunit composition of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors in the developing rat spinal cord and compared these findings with those in adult rats. We find qualitative and quantitative changes in alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit gene expression over the first month of postnatal life. alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit genes GluR1, 2 and 4 are expressed at greater levels throughout the spinal cord of the neonate versus the adult animals. The developmental down-regulation is most pronounced for GluR1 transcripts, less for GluR2 and GluR4 transcripts, and minimal for GluR3 transcripts. Analysis of flip and flop splice variants of each subunit show that receptors expressed by adult motor neurons are potentially composed of the subunits GluR1 flop, GluR2 flip, GluR3 flip and flop, and GluR4 flip. In neonatal motor neuron all subunits are potentially expressed (except GluR2 flop) with quantitatively the dominent subunits being the flip splice variants of GluR1, 2 and 4. Receptors in the substantia gelatinosa undergo equally dramatic, developmentally independent changes. Changes in the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit composition are likely to have an important effect on the electrophysiological properties of motor neurons and may form part of the molecular identity of neurons capable of undergoing activity-dependent developmental plasticity.

Quantitative and qualitative changes in AMPA receptor expression during spinal cord development

Synaptic activity in early postnatal life is important for the acquisition of mature structural and functional properties of neurons. Previous studies indicate that the mature molecular features of spinal motor neurons emerge during a period of activity-dependent development in early postnatal life. Since glutamatergic synaptic transmission provides the major excitatory drive into motor neurons, glutamate receptors are likely to play a central role in motor neuron activity-dependent development. To gain insight into this process, we have used receptor autoradiography, immunoblotting and immunohistochemistry to determine the distribution, temporal expression and potential subunit composition of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid subtype glutamate receptors in the developing rat spinal cord. Using two different ligands, [3H]-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and [3H]-6-cyano-7-nitroquinoxaline-2,3-dione, we find that alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid binding sites in the adult are largely restricted to the substantia gelatinosa. In marked contrast, during early postnatal life, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid binding sites are transiently expressed at high levels in the ventral horn. This parallels previous findings on the developmental regulation of N-methyl-D-aspartate receptor expression. Using alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit-specific antibodies we show by immunoblot analysis and immunohistology that, to varying degrees, the expression patterns of glutamate receptor subunit 1 and glutamate receptor subunits 2/3 are significantly developmentally regulated. The most conspicuous change is the downregulation of glutamate receptor 1 expression within motor neurons over the first three weeks of postnatal life. The qualitative and quantitative changes we observe in glutamate receptor expression in early postnatal life are likely to have a major impact on the electrophysiological properties of young motor neurons and thus may contribute to their activity-dependent development.

Recombinant plasmid conferring proline overproduction and osmotic tolerance

A recombinant plasmid carrying the proBA (pro-74) mutant allele which governs osmotic tolerance and proline overproduction was constructed by using the broad-host-range plasmid vector pQSR49. The physiological, biochemical, and genetic properties of strains carrying the pQSR49 derivatives pMJ101 and pMJ1, mutant and wild type, respectively, were investigated. pMJ101 conferred enhanced osmotolerance compared with strains carrying the wild type, pMJ1. These results are in contrast to those obtained previously with strains carrying recombinant plasmids based on pBR322 that failed to confer the osmotic tolerance phenotype. gamma-Glutamyl kinase (first step in proline biosynthesis) from strains carrying pMJ101 was 200-fold less sensitive to feedback inhibition than was the wild-type enzyme. As expected, the intracellular proline levels of strains carrying pMJ101 were more than an order of magnitude higher than those of the wild type. An analysis of copy number revealed that the pQSR49 constructs were present in the cell at a level six- to eightfold lower than those of the pBR322 recombinants, which may account for the difference in phenotype. We found that the genetic stability of the pQSR49 derivative in a variety of gram-negative bacteria was dependent on the insert orientation and the presence of foreign DNA on the plasmid. These factors may be significant in future studies aimed at expanding the osmotolerance phenotype to a broad range of gram-negative bacteria.