Parkinson’s disease is characterized by abundant α-synuclein (α-Syn) neuronal inclusions, known as Lewy bodies and Lewy neurites, and the massive loss of midbrain dopamine neurons. However, a cause-and-effect relationship between Lewy inclusion formation and neurodegeneration remains unclear. Here, we found that in wild-type nontransgenic mice, a single intrastriatal inoculation of synthetic α-Syn fibrils led to the cell-to-cell transmission of pathologic α-Syn and Parkinson’s-like Lewy pathology in anatomically interconnected regions. Lewy pathology accumulation resulted in progressive loss of dopamine neurons in the substantia nigra pars compacta, but not in the adjacent ventral tegmental area, and was accompanied by reduced dopamine levels culminating in motor deficits. This recapitulation of a neurodegenerative cascade thus establishes a mechanistic link between transmission of pathologic α-Syn and the cardinal features of Parkinson’s disease.
Kainate receptors are members of the glutamate receptor family that regulate synaptic function in the brain. They modulate synaptic transmission and the excitability of neurons; however, their contributions to neural circuits that underlie behavior are unclear. To understand the net impact of kainate receptor signaling, we generated knockout mice in which all five kainate receptor subunits were ablated (5ko). These mice displayed compulsive and perseverative behaviors, including over-grooming, as well as motor problems, indicative of alterations in striatal circuits. There were deficits in corticostriatal input to spiny projection neurons (SPNs) in the dorsal striatum and correlated reductions in spine density. The behavioral alterations were not present in mice only lacking the primary receptor subunit expressed in adult striatum (GluK2 KO), suggesting that signaling through multiple receptor types is required for proper striatal function. This demonstrates that alterations in striatal function dominate the behavioral phenotype in mice without kainate receptors.
Recent evidence has implicated the endocannabinoid (eCB) system in nicotine addiction. The eCB system also has an important role in reward mechanisms, and nicotine addiction has been associated with aberrant reward processing. Motivated by this evidence, we tested the hypothesis that eCB modulation of reward processing is altered in subjects with a nicotine addiction (NAD). For this purpose, we compared reward-related activity in NAD with healthy controls (HC) in a pharmacological magnetic resonance imaging (MRI) study using Δ(9)-tetrahydrocannabinol (THC) administration to challenge the eCB system. Eleven HC and 10 NAD participated in a 3-T functional MRI (fMRI) study with a double-blind, cross-over, placebo-controlled design, using a Monetary Incentive Delay (MID) paradigm with three reward levels. Reward activity in the nucleus accumbens (NAcc) and caudate putamen during anticipation and feedback of reward was compared after THC and placebo. fMRI results indicated a significant reduction of reward anticipation activity in the NAcc in NAD after THC administration, which was not present in HC. This is indicated by a significant group by drug by reward interaction. Our data show that THC significantly reduces the NAcc response to monetary reward anticipation in NAD. These results suggest that nicotine addiction is associated with altered eCB modulation of reward processing in the NAcc. This study adds important human data to existing evidence implicating the eCB system in nicotine addiction.
This study investigated the contribution of the new G protein-coupled estrogen receptor 1 (GPER1) in neuroprotection by 17β-estradiol in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson’s disease. In intact mice, administration of GPER1 agonist G1 reproduced the effect of 17β-estradiol in increasing striatal dopamine metabolite concentrations as well as the turnover of dopamine. GPER1 antagonist G15 blocked the effect of G1 on homovanillic acid/dopamine ratio and partially for 17β-estradiol. MPTP mice treated with G15 were more susceptible to MPTP toxicity with a greater decrease in striatal dopamine concentration and dopamine transporter specific binding. In MPTP mice, dopamine concentrations as well as dopamine and vesicular monoamine transporter 2 specific binding showed that G1 treatment was as potent as 17β-estradiol in protecting striatum and substantia nigra. G15 antagonized completely the neuroprotective effects of G1 in the striatum and substantia nigra as well as protection by 17β-estradiol in the striatum but partially in the substantia nigra. This study showed an important role of GPER1 in neuroprotection and that G1 is as potent as 17β-estradiol in mediating beneficial effects.
Parkinson’s disease (PD) involves the degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc) that is thought to cause the classical motor symptoms of this disease. However, motivational and affective impairments are also often observed in PD patients. These are usually attributed to a psychological reaction to the general motor impairment and to a loss of some of the neurons within the ventral tegmental area (VTA). We induced selective lesions of the VTA and SNc DA neurons that did not provoke motor deficits, and showed that bilateral dopamine loss within the SNc, but not within the VTA, induces motivational deficits and affective impairments that mimicked the symptoms of PD patients. Thus, motivational and affective deficits are a core impairment of PD, as they stem from the loss of the major group of neurons that degenerates in this disease (DA SNc neurons) and are independent of motor deficits.Molecular Psychiatry advance online publication, 12 February 2013; doi:10.1038/mp.2013.3.
Stiff person syndrome (SPS) is an autoimmune CNS disorder characterized by muscle rigidity, spasms and anxiety. The majority of patients have high-titer autoantibodies (ab) against glutamate decarboxylase (GAD65). A pathogenic role of SPS-associated IgG with ab against GAD65 has been shown for anxiety-like behavior but not for the core motor signs. We repetitively injected the purified IgG fraction of an SPS patient with severe motor impairment but without anxious comorbidity containing high titers of anti-GAD65 ab (SPS-IgG) into the lateral ventricle (i.c.v.) or intrathecally (i.th.) at the spinal level in experimental rats. We analyzed the effects on motor and anxiety-like behavior. Non-SPS human IgG fractions served as controls. Animals injected i.c.v. with SPS-IgG showed stiffness-like behavior with impaired walking ability and reduced grip strength of the upper limbs as well as postural and sensorimotor dysfunction. Testing for anxiety-like behavior revealed no significant differences between SPS and control IgG-treated rats. IgG deposits were found only in rats treated with SPS-IgG and were localized predominantly in CNS structures involved in motor control including globus pallidus, internal capsule, striatum and anterior thalamus. Double immunofluorescence staining revealed that predominantly GABAergic interneurons were positive for i.c.v. injected SPS-IgG. Rats injected i.th. with SPS-IgG did not present obvious motor symptoms and had a normal synaptic transmission at the spinal level. We conclude that SPS-like motor dysfunction can be induced in rats by passive transfer of IgG from an SPS-patient with high titer of anti-GAD65 ab. GABAergic dysfunction in supraspinal motor pathways rather than in the spinal cord may lead to motor deficits observed in the rats contrasting observations made in SPS with amphiphysin antibodies.
Tyrosine hydroxylase (TH)-immunoreactive (ir) neurons have been found in the striatum after dopamine depletion; however, little is known about the mechanism underlying their appearance or their functional significance. We previously showed an increase in striatal TH-ir neurons after L-DOPA treatment in mice with unilateral 6-OHDA lesions in the striatum. In the present study, we further examined the time-course and persistence of the effects of chronic L-DOPA treatment on the appearance and regulation of TH-ir neurons as well as their possible function. We found that the L-DOPA-induced increase in striatal TH-ir neurons is dose-dependent and persists for days after L-DOPA withdrawal, decreasing significantly 10 days after L-DOPA treatment ends. Using hemiparkinsonian D1 receptor knock-out (D1R-/-) and D2 receptor knock-out (D2R-/-) mice, we found that the D1R, but not the D2R, is required for the L-DOPA-induced appearance of TH-ir neurons in the dopamine-depleted striatum. Interestingly, our experiments in aphakia mice, which lack Pitx3 expression in the brain, indicate that the L-DOPA-dependent increase in the number of TH-ir neurons is independent of Pitx3, a transcription factor necessary for the development of mesencephalic dopaminergic neurons. To explore the possible function of L-DOPA-induced TH-ir neurons in the striatum, we examined dopamine overflow and forelimb use in L-DOPA-treated parkinsonian mice. These studies revealed a tight spatio-temporal correlation between the presence of striatal TH-ir neurons, the recovery of electrically stimulated dopamine overflow in the lesioned striatum, and the recovery of contralateral forelimb use with chronic L-DOPA treatment. Our results suggest that the presence of TH-ir neurons in the striatum may underlie the long-duration response to L-DOPA following withdrawal. Promotion of these neurons in the early stages of Parkinson’s disease, when dopamine denervation is incomplete, may be beneficial for maintaining motor function.
Elevated iron in the SNpc may play a key role in Parkinson’s disease (PD) neurodegeneration since drug candidates with high iron affinity rescue PD animal models, and one candidate, deferirpone, has shown efficacy recently in a phase two clinical trial. However, strong iron chelators may perturb essential iron metabolism, and it is not yet known whether the damage associated with iron is mediated by a tightly bound (eg ferritin) or lower-affinity, labile, iron pool. Here we report the preclinical characterization of PBT434, a novel quinazolinone compound bearing a moderate affinity metal-binding motif, which is in development for Parkinsonian conditions. In vitro, PBT434 was far less potent than deferiprone or deferoxamine at lowering cellular iron levels, yet was found to inhibit iron-mediated redox activity and iron-mediated aggregation of α-synuclein, a protein that aggregates in the neuropathology. In vivo, PBT434 did not deplete tissue iron stores in normal rodents, yet prevented loss of substantia nigra pars compacta neurons (SNpc), lowered nigral α-synuclein accumulation, and rescued motor performance in mice exposed to the Parkinsonian toxins 6-OHDA and MPTP, and in a transgenic animal model (hA53T α-synuclein) of PD. These improvements were associated with reduced markers of oxidative damage, and increased levels of ferroportin (an iron exporter) and DJ-1. We conclude that compounds designed to target a pool of pathological iron that is not held in high-affinity complexes in the tissue can maintain the survival of SNpc neurons and could be disease-modifying in PD.
- Proceedings of the National Academy of Sciences of the United States of America
- Published almost 4 years ago
Corticostriatal atrophy is a cardinal manifestation of Huntington’s disease (HD). However, the mechanism(s) by which mutant huntingtin (mHTT) protein contributes to the degeneration of the corticostriatal circuit is not well understood. We recreated the corticostriatal circuit in microfluidic chambers, pairing cortical and striatal neurons from the BACHD model of HD and its WT control. There were reduced synaptic connectivity and atrophy of striatal neurons in cultures in which BACHD cortical and striatal neurons were paired. However, these changes were prevented if WT cortical neurons were paired with BACHD striatal neurons; synthesis and release of brain-derived neurotrophic factor (BDNF) from WT cortical axons were responsible. Consistent with these findings, there was a marked reduction in anterograde transport of BDNF in BACHD cortical neurons. Subunits of the cytosolic chaperonin T-complex 1 (TCP-1) ring complex (TRiC or CCT for chaperonin containing TCP-1) have been shown to reduce mHTT levels. Both CCT3 and the apical domain of CCT1 (ApiCCT1) decreased the level of mHTT in BACHD cortical neurons. In cortical axons, they normalized anterograde BDNF transport, restored retrograde BDNF transport, and normalized lysosomal transport. Importantly, treating BACHD cortical neurons with ApiCCT1 prevented BACHD striatal neuronal atrophy by enhancing release of BDNF that subsequently acts through tyrosine receptor kinase B (TrkB) receptor on striatal neurons. Our findings are evidence that TRiC reagent-mediated reductions in mHTT enhanced BDNF delivery to restore the trophic status of BACHD striatal neurons.
The basal ganglia (BG) act as a cohesive functional unit that regulates motor function, habit formation, and reward/addictive behaviors, but the debate has only recently started on how the BG maintain wakefulness and suppress sleep to achieve all these fundamental functions of the BG. Neurotoxic lesioning, pharmacological approaches, and the behavioral analyses of genetically modified animals revealed that the striatum and globus pallidus are important for the control of sleep and wakefulness. Here, we discuss anatomical and molecular mechanisms for sleep-wake regulation in the BG and propose a plausible model in which the nucleus accumbens integrates behavioral processes with wakefulness through adenosine and dopamine receptors.