Brain Gene Expression in Systemic Hypothyroidism and Mouse Models of MCT8 Deficiency: The Mct8-Oatp1c1-Dio2 Triad

Background: The monocarboxylate transporter 8 (Mct8) protein is a primary thyroxine (T4) and triiodothyronine (T3) (thyroid hormone [TH]) transporter. Mutations of the MCT8-encoding, SLC16A2 gene alter thyroid function and TH metabolism and severely impair neurodevelopment (Allan-Herndon-Dudley syndrome [AHDS]). Mct8-deficient mice manifest thyroid alterations but lack neurological signs. It is believed that Mct8 deficiency in mice is compensated by T4 transport through the Slco1c1-encoded organic anion transporter polypeptide 1c1 (Oatp1c1). This allows local brain generation of sufficient T3 by the Dio2-encoded type 2 deiodinase, thus preventing brain hypothyroidism. The Slc16a2/Slco1c1 (MO) and Slc16a2/Dio2 (MD) double knockout (KO) mice lacking T4 and T3 transport, or T3 transport and T4 deiodination, respectively, should be appropriate models of AHDS. Our goal was to compare the cerebral hypothyroidism of systemic hypothyroidism (SH) caused by thyroid gland blockade with that present in the double KO mice. Methods: We performed RNA sequencing by using RNA from the cerebral cortex and striatum of SH mice and the double KO mice on postnatal days 21-23. Real-time polymerase chain reaction was used to confirm RNA-Seq results in replicate biological samples. Cell type involvement was assessed from cell type-enriched genes. Functional genomic differences were analyzed by functional node activity based on a probabilistic graphical model. Results: Each of the three conditions gave a different pattern of gene expression, with partial overlaps. SH gave a wider and highest variation of gene expression than MD or MO. This was partially due to secondary gene responses to hypothyroidism. The set of primary transcriptional T3 targets showed a tighter overlap, but quantitative gene responses indicated that the gene responses in SH were more severe than in MD or MO. Examination of cell type-enriched genes indicated cellular differences between the three conditions. Conclusions: The results indicate that the neurological impairment of AHDS is too severe to be fully explained by TH deprivation only.

Altered excitatory transmission in striatal neurons after chronic ethanol consumption in selectively bred crossed high alcohol-preferring mice

Genetic predisposition to heavy drinking is a risk factor for alcohol misuse. We used selectively bred crossed high alcohol-preferring (cHAP) mice to study sex differences in alcohol drinking and its effect on glutamatergic activity in dorsolateral (DLS) and dorsomedial (DMS) striatum. We performed whole-cell patch-clamp recording in neurons from male and female cHAP mice with 5-week alcohol drinking history and alcohol-naïve controls. In DMS, alcohol-naïve males' neurons displayed lower cell capacitance and higher membrane resistance than females' neurons, both effects reversed by drinking. Conversely, in DLS neurons, drinking history increased capacitance only in males and changed membrane resistance only in females. Altered biophysical membrane properties were accompanied by disrupted glutamatergic transmission. Drinking history increased spontaneous excitatory postsynaptic current (sEPSC) amplitude in DMS and frequency in DLS female neurons, compared to alcohol-naïve females, without effect in males. Acute ethanol differentially impacted DMS and DLS neurons by sex and drinking history. In DMS, acute alcohol significantly increased sEPSC frequency only in neurons from alcohol-naïve females, an effect that disappeared after drinking history. In DLS, acute alcohol had opposing effects in males and females based on drinking history. Estrous cycle also impacted DMS and DLS neurons differently: sEPSC amplitudes were higher in DMS cells from drinking history than alcohol-naïve females, whereas estrous cycle, not drinking history, modified DLS firing rate. Our data show sex differences in cHAP ethanol consumption and neurophysiology, suggesting differential dysregulation of glutamatergic drive onto DMS and DLS after chronic ethanol consumption.

Acrolein scavenger dimercaprol offers neuroprotection in an animal model of Parkinson's disease: implication of acrolein and TRPA1

BACKGROUND

The mechanisms underlying lesions of dopaminergic (DA) neurons, an essential pathology of Parkinson's disease (PD), are largely unknown, although oxidative stress is recognized as a key factor. We have previously shown that the pro-oxidative aldehyde acrolein is a critical factor in PD pathology, and that acrolein scavenger hydralazine can reduce the elevated acrolein, mitigate DA neuron death, and alleviate motor deficits in a 6-hydroxydopamine (6-OHDA) rat model. As such, we hypothesize that a structurally distinct acrolein scavenger, dimercaprol (DP), can also offer neuroprotection and behavioral benefits.

METHODS

DP was used to lower the elevated levels of acrolein in the basal ganglia of 6-OHDA rats. The acrolein levels and related pathologies were measured by immunohistochemistry. Locomotor and behavioral effects of 6-OHDA injections and DP treatment were examined using the open field test and rotarod test. Pain was assessed using mechanical allodynia, cold hypersensitivity, and plantar tests. Finally, the effects of DP were assessed in vitro on SK-N-SH dopaminergic cells exposed to acrolein.

RESULTS

DP reduced acrolein and reversed the upregulation of pain-sensing transient receptor potential ankyrin 1 (TRPA1) channels in the substantia nigra, striatum, and cortex. DP also mitigated both motor and sensory deficits typical of PD. In addition, DP lowered acrolein and protected DA-like cells in vitro. Acrolein's ability to upregulate TRPA1 was also verified in vitro using cell lines.

CONCLUSIONS

These results further elucidated the acrolein-mediated pathogenesis and reinforced the critical role of acrolein in PD while providing strong arguments for anti-acrolein treatments as a novel and feasible strategy to combat neurodegeneration in PD. Considering the extensive involvement of acrolein in various nervous system illnesses and beyond, anti-acrolein strategies may have wide applications and broad impacts on human health.

On the functional role of striatal and anterior cingulate GABA+ in stimulus-response binding

Successful response selection relies on constantly updating stimulus-response associations. The Theory of Event Coding (TEC) proposes that perception and action are conjointly coded in event files, for which fronto-striatal networks seem to play an important role. However, the exact neurobiochemical mechanism behind event file coding has remained unknown. We investigated the functional relevance of the striatal and anterior cingulate (ACC) GABAergic system using magnetic resonance spectroscopy (MRS). Specifically, the striatal and ACC concentrations of GABA+ referenced against N-acetylaspartate (NAA) were assessed in 35 young healthy males, who subsequently performed a standard event file task. As predicted by the TEC, the participants' responses were modulated by pre-established stimulus response bindings in event files. GABA+/NAA concentrations in the striatum and ACC were not correlated with the overall event binding effect. However, higher GABA+/NAA concentrations in the ACC were correlated with stronger event file binding processes in the early phase of the task. This association disappeared by the end of the task. Taken together, our findings show that striatal GABA+ levels does not seem to modulate event file binding, while ACC GABA+ seem to improve event file binding, but only as long as the participants have not yet gathered sufficient task experience. To the best of our knowledge, this is the first study providing direct evidence for the role of striatal and ACC GABA+ in stimulus-response bindings and thus insights into the brain structure-specific neurobiological aspects of the TEC.

Methylene blue and photobiomodulation recover cognitive impairment in hepatic encephalopathy through different effects on cytochrome c-oxidase

Mitochondrial dysfunction plays a central role in hepatic encephalopathy (HE), due to changes in enzyme cytochrome c-oxidase (CCO), causing a decline in brain metabolism. We used an HE animal model and applied intracranial administration of methylene blue (MB) and transcranial photobiomodulation (PBM), both targeting CCO, to determine their differential effects on recovering cognition. Five groups of rats were used: sham-operated group + saline (SHAM + SAL, n = 6), hepatic encephalopathy + SAL (HE + SAL, n = 7), SHAM + methylene blue (SHAM + MB, n = 7), HE + MB (n = 7), HE + PBM (n = 7). PBM animals were exposed transcranially to 670 +/- 10 nm LED light at a dose of 9 J/cm2 once a day for 7 days, and the MB and SAL groups were injected with 2.2 μg/0.5 μL in the accumbens. Cognitive dysfunction was evaluated on a striatal stimulus-response task using the Morris water maze. Our results showed cognitive improvement in the HE group when treated with MB. This improvement was accompanied by a decrease in CCO activity in the prefrontal cortex, dorsal striatum, and dorsal hippocampus. When comparing MB and PBM, we found that, although both treatments effectively improved the HE-memory deficit, there was a differential effect on CCO. A general decrease in CCO activity was found in the prefrontal and entorhinal cortices, dorsal striatum, and hippocampus when PBM, compared to MB, was applied. Our results suggest that mitochondrial dysfunction and brain metabolic decline in HE might involve CCO alteration and can be improved by administering MB and PBM.

Comparison of the sensitizing effects of cocaine and ethanol on histone deacetylase isoforms in the rat brain

Behavioral sensitization, an animal model of drug addiction, persists for a prolonged period after repeated exposure to drugs of abuse. The persistence of an addiction behavioral phenotype suggests long-lasting changes in gene regulation at the epigenetic level. We measured the expression of histone deacetylases (HDACs) isoforms in the prefrontal cortex and dorsal striatum following the development of sensitization to cocaine (15 mg/kg, administered five times) and ethanol (0.5 g/kg, administered 15 times) to investigate the epigenetic changes that mediate sensitization. Animals sensitized to ethanol exhibited augmented locomotor activity in response to the cocaine challenge. Similarly, those sensitized to cocaine exhibited increased locomotor activity in response to an ethanol challenge. These findings indicate cross-sensitization between ethanol and cocaine and suggest that a common molecular mechanism underlying the cross-sensitization. In animals sensitized to cocaine or ethanol, mRNA levels of class II HDACs (HDAC4 and HDAC5) were decreased in the prefrontal cortex and dorsal striatum, whereas acute treatments with either drug had no effect on the expression of class II HDACs. By contrast, class I HDACs (HDAC1 and HDAC2) responded to the acute cocaine challenge, whereas sensitization itself did not have a consistent effect on class I HDAC levels. These findings support the hypothesis of a common epigenetic mechanism underlying persistent behavioral sensitization induced by different drugs, which may be mediated by the altered expression of class II HDACs.

Exclusive labeling of direct and indirect pathway neurons in the mouse neostriatum by an adeno-associated virus vector with Cre/lox system

We developed an adeno-associated virus (AAV) vector-based technique to label mouse neostriatal neurons comprising direct and indirect pathways with different fluorescent proteins and analyze their axonal projections. The AAV vector expresses GFP or RFP in the presence or absence of Cre recombinase and should be useful for labeling two cell populations exclusively dependent on its expression. Here, we describe the AAV vector design, stereotaxic injection of the AAV vector, and a highly sensitive immunoperoxidase method for axon visualization.

For complete details on the use and execution of this protocol, please refer to Okamoto et al. (2020).

•

Exclusive labeling of two groups of neurons with different fluorescent proteins

•

Detailed protocols from stereotaxic virus injection to immunostaining methods

•

A signal enhancement method via peroxidase activity, BT-GO reaction

•

Significant improvement in a signal-to-noise ratio by the cost-effective reaction

Glutamate-induced modulation in energy metabolism contributes to protection of rat cortical slices against ischemia-induced damage

OBJECTIVES

Glutamate excitotoxicity contributes to neurodegeneration during cerebral ischemia. Recent studies in the protective effect of glutamate against ischemia and hypoxia have shown the need for questioning the role of glutamate in energy metabolism during ischemia. Current study investigates the effect of glutamate on energy substrate metabolites such as alpha-ketoglutarate, lactate, and pyruvate release during control, oxygen-glucose deprivation (OGD), and reoxygenation (REO) conditions.

METHODS

The effects of 0.5 and 2 mM glutamate on spontaneous alpha-ketoglutarate, lactate, and pyruvate release were tested in vitro, on acute rat cortical slices. Alpha-ketoglutarate, lactate, and pyruvate levels were determined by HPLC with UV detector.

RESULTS

We observed that glutamate added into medium significantly increased alpha-ketogluarate release under control conditions. Although OGD and REO also had a glutamate-like effect, only REO-induced rise further enhanced by glutamate. In contrast to alpha-ketoglutarate, both OGD and REO conditions caused significant declines in pyruvate and lactate outputs. While OGD and REO-induced declines in pyruvate outputs were further potentiated, lactate output was not altered by glutamate added into the medium. Glutamate and alpha-ketoglutarate, moreover, also ameliorated OGD- and REO-induced losses in 2,3,5-triphenyltetrazolium chloride staining with a similar degree.

CONCLUSION

These results indicate that glutamate probably increases alpha-ketoglutarate production as an alternative energy source for use in the TCA cycle under energy-depleted conditions. Thus, increasing the alpha-ketoglutarate production may represent a new therapeutic intervention for neurodegenerative disorders, including cerebral ischemia.

G-protein coupled receptor 88 knockdown in the associative striatum reduces psychiatric symptoms in a translational male rat model of Parkinson disease

BACKGROUND

In addition to motor disability, another characteristic feature of Parkinson disease is the early appearance of psychiatric symptoms, including apathy, depression, anxiety and cognitive deficits; treatments for these symptoms are limited by the development of adverse effects such as impulse-control disorders. In this context, we investigated the orphan G protein-coupled receptor 88 (GPR88) as a novel therapeutic target.

METHODS

We used lentiviral-mediated expression of specifically designed microRNA to knock down Gpr88 in a translational male rat model of early Parkinson disease obtained by dopamine loss in the dorsolateral striatum as a result of 6-hydroxydopamine lesions. We evaluated the impact of Gpr88 knockdown on the Parkinson disease model using behavioural, immunohistochemical and in situ hybridization studies.

RESULTS

Knockdown of Gpr88 in associative territories of the dorsal striatum efficiently reduced alterations in mood, motivation and cognition through modulation of the regulator of the G-protein signalling 4 and of the truncated splice variant of the FosB transcription factor. Knockdown of Gpr88 also reduced allostatic changes in striatal activity markers that may be related to patterns observed in patients and that provide support for an "overload" hypothesis for the etiology of the psychiatric symptoms of Parkinson disease.

LIMITATIONS

Behavioural tests assessing specific cognitive and motivational parameters are needed to further characterize the effects of the lesion and of Gpr88 knockdown in early-stage and advanced Parkinson disease models, presenting more extensive dopamine loss. Additional studies focusing on the direct and indirect striatal output pathways are also required, because little is known about the signalling pathways regulated by GPR88 in different striatal cell types.

CONCLUSION

GPR88 may constitute a highly relevant target for the treatment of the psychiatric symptoms of Parkinson disease.

Caloric restriction modulates the monoaminergic system and metabolic hormones in aged rats

Caloric restriction (CR) can attenuate the general loss of health observed during aging, being one of the mechanisms involved the reduction of hormonal alteration, such as insulin and leptin. This change could also prevent age-specific fluctuations in brain monoamines, although few studies have addressed the effects of CR on peripheral hormones and central neurotransmitters exhaustively. Therefore, the variations in brain monoamine levels and some peripheral hormones were assessed here in adult 4-month old and 24-month old male Wistar rats fed ad libitum (AL) or maintained on a 30% CR diet from four months of age. Noradrenaline (NA), dopamine (DA), serotonin (5-HT) and its metabolites were measured by high-performance liquid chromatography with electrochemical detection (HPLC-ED) in nine brain regions: cerebellum, pons, midbrain, hypothalamus, thalamus, hippocampus, striatum, frontal cortex, and occipital cortex. In addition, the blood plasma levels of hormones like corticosterone, insulin and leptin were also evaluated, as were insulin-like growth factor 1 and other basal metabolic parameters using enzyme-linked immunosorbent assays (ELISAs): cholesterol, glucose, triglycerides, albumin, low-density lipoprotein, calcium and high-density lipoprotein (HDLc). CR was seen to increase the NA levels that are altered by aging in specific brain regions like the striatum, thalamus, cerebellum and hypothalamus, and the DA levels in the striatum, as well as modifying the 5-HT levels in the striatum, hypothalamus, pons and hippocampus. Moreover, the insulin, leptin, calcium and HDLc levels in the blood were restored in old animals maintained on a CR diet. These results suggest that a dietary intervention like CR may have beneficial health effects, recovering some negative effects on peripheral hormones, metabolic parameters and brain monoamine concentrations.

IGF-1 inhibits MPTP/MPP+-induced autophagy on dopaminergic neurons through the IGF-1R/PI3K-Akt-mTOR pathway and GPER

Autophagy dysfunctions are involved in the pathogenesis of Parkinson's disease (PD). In the present study, we aimed to evaluate the involvement of G protein-coupled estrogen receptor (GPER) in the inhibitory effect of insulin-like growth factor-1 (IGF-1) against excessive autophagy in PD animal and cellular models. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment significantly induced mouse movement disorder and decreased the protein level of tyrosine hydroxylase (TH) in the substantia nigra (SN) and dopamine (DA) content in striatum. Along with the dopamine neuron injury, we observed significant upregulations of microtubule-associated light chain-3 II (LC3-II) and α-synuclein as well as a downregulation of P62 in MPTP-treated mice. These changes could be restored by IGF-1 pretreatment. Cotreatment with IGF-1R antagonist JB-1 or GPER antagonist G15 could block the neuroprotective effects of IGF-1. 1-Methy-4-phenylpyridinium (MPP⁺) treatment could also excessively activate autophagy along with the reduction of cell viability in SH-SY5Y cells. IGF-1 could inhibit the neurotoxicity through promoting the phosphorylation of Akt and mammalian target of rapamycin (mTOR), which could also be antagonized by JB-1 or G15. These data suggest that IGF-1 inhibits MPTP/MPP⁺-induced autophagy on dopaminergic neurons through the IGF-1R/PI3K-Akt-mTOR pathway and GPER.

Reconstitution of the Human Nigro-striatal Pathway on-a-Chip Reveals OPA1-Dependent Mitochondrial Defects and Loss of Dopaminergic Synapses

Stem cell-derived neurons are generally obtained in mass cultures that lack both spatial organization and any meaningful connectivity. We implement a microfluidic system for long-term culture of human neurons with patterned projections and synaptic terminals. Co-culture of human midbrain dopaminergic and striatal medium spiny neurons on the microchip establishes an orchestrated nigro-striatal circuitry with functional dopaminergic synapses. We use this platform to dissect the mitochondrial dysfunctions associated with a genetic form of Parkinson’s disease (PD) with OPA1 mutations. Remarkably, we find that axons of OPA1 mutant dopaminergic neurons exhibit a significant reduction of mitochondrial mass. This defect causes a significant loss of dopaminergic synapses, which worsens in long-term cultures. Therefore, PD-associated depletion of mitochondria at synapses might precede loss of neuronal connectivity and neurodegeneration. In vitro reconstitution of human circuitries by microfluidic technology offers a powerful system to study brain networks by establishing ordered neuronal compartments and correct synapse identity.

•

Long-term stable reconstitution of the human nigro-striatal neuronal circuit on-a-chip

•

Stable synaptic connectivity of the iPSC-derived nigro-striatal neuronal connections

•

Dopaminergic-specific synaptic identity of the iPSC-derived nigro-striatal pathway

•

PD-OPA1 DA axons show a severe loss and impairment of mitochondria

REM sleep behavior disorder in early Parkinson's disease predicts the rapid dopaminergic denervation

OBJECTIVE

To test the hypothesis that REM sleep behavior disorder (RBD) in early Parkinson's disease (PD) predicts rapid progression of dopaminergic denervation.

METHODS

123I-FP-CIT single photon emission computed tomography (SPECT) scans were performed sequentially at baseline, 1 year, 2 years, and 4 years in 416 de novo patients with PD. RBD screening questionnaire scores >5 at baseline placed the participant in the likely-RBD group. Temporal changes in the specific binding ratio (SBR; caudate, putamen. sum of both, striatum) were compared between the likely-RBD and the non-likely-RBD groups for more or less affected striatum with a repeated measure ANOVA.

RESULTS

Likely-RBD was reported in 37.7% of the drug-naïve PD patients at baseline. The likely-RBD and non-likely-RBD groups did not have significant differences in the baseline clinical features including gender, age, disease duration, UPDRS motor score, and striatal SBR. Striatal SBR decreased significantly over four years in both groups (P < .001). In the analysis of a more affected striatum, striatal SBR decreased significantly faster in the likely-RBD group than in the non-likely-RBD group (P < .05 for all), whereas it was not statistically significant for the less affected striatum. The mean striatal SBR value (mean value of both striata), especially the caudate SBR, indicated greater acceleration of denervation in the likely-RBD group than in the non-likely-RBD group over time (P < .05).

CONCLUSION

Likely-RBD in PD predicts accelerating dopaminergic denervation, thereby implicating it as a marker for a poor prognosis or distinctive subtype in PD.

L444P Gba1 mutation increases formation and spread of α-synuclein deposits in mice injected with mouse α-synuclein pre-formed fibrils

Parkinson disease is the most common neurodegenerative movement disorder, estimated to affect one in twenty-five individuals over the age of 80. Mutations in glucocerebrosidase 1 (GBA1) represent the most common genetic risk factor for Parkinson disease. The link between GBA1 mutations and α-synuclein accumulation, a hallmark of Parkinson disease, is not fully understood. Following our recent finding that Gba1 mutations lead to increased α-synuclein accumulation in mice, we have studied the effects of a single injection of mouse α-synuclein pre-formed fibrils into the striatum of Gba1 mice that carry a L444P knock-in mutation. We found significantly greater formation and spread of α-synuclein inclusions in Gba1-transgenic mice compared to wild-type controls. This indicates that the Gba1 L444P mutation accelerates α-synuclein pathology and spread.

Dysregulation of TFEB contributes to manganese-induced autophagic failure and mitochondrial dysfunction in astrocytes

Epidemiological and clinical studies have long shown that exposure to high levels of heavy metals are associated with increased risks of neurodegenerative diseases. It is widely accepted that autophagic dysfunction is involved in pathogenesis of various neurodegenerative disorders; however, the role of heavy metals in regulation of macroautophagy/autophagy is unclear. Here, we show that manganese (Mn) induces a decline in nuclear localization of TFEB (transcription factor EB), a master regulator of the autophagy-lysosome pathway, leading to autophagic dysfunction in astrocytes of mouse striatum. We further show that Mn exposure suppresses autophagic-lysosomal degradation of mitochondria and induces accumulation of unhealthy mitochondria. Activation of autophagy by rapamycin or TFEB overexpression ameliorates Mn-induced mitochondrial respiratory dysfunction and reactive oxygen species (ROS) generation in astrocytes, suggesting a causal relation between autophagic failure and mitochondrial dysfunction in Mn toxicity. Taken together, our data demonstrate that Mn inhibits TFEB activity, leading to impaired autophagy that is causally related to mitochondrial dysfunction in astrocytes. These findings reveal a previously unappreciated role for Mn in dysregulation of autophagy and identify TFEB as a potential therapeutic target to mitigate Mn toxicity.

ABBREVIATIONS

BECN1: beclin 1; CTSD: cathepsin D; DMEM: Dulbecco's Modified Eagle Medium; GFAP: glial fibrillary acid protein; GFP: green fluorescent protein; HBSS: hanks balanced salt solution; LAMP: lysosomal-associated membrane protein; LDH: lactate dehydrogenase; Lys Inh: lysosomal inhibitors; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAPK: mitogen-activated protein kinase; Mn: manganese; MTOR: mechanistic target of rapamycin kinase; OCR: oxygen consumption rate; PBS: phosphate-buffered saline; PFA: paraformaldehyde; PI: propidium iodide; ROS: reactive oxygen species; s.c.: subcutaneous; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy; TFEB: transcription factor EB.

Effects of animal handling on striatal DAT availability in rats

OBJECTIVE

Positron emission tomography (PET) is a non-invasive technique measuring quantification of physiological and biochemical processes in the living organism. However, there are many considerations including anesthesia and fasting to acquire small animal imaging. We aimed to evaluate the effects of anesthesia and fasting of rats in dopamine transporter (DAT) imaging acquisition.

METHODS

Male Sprague Dawley (SD) rats aged 7 weeks and weighing 180-260 g were used in this study. Rats were randomly divided by 4 groups. Group A was kept under anesthesia for 40 min and fasted over 12 h. Group B was only fasted over 12 h. Group C was only kept under anesthesia for 40 min. Group D was neither kept under anesthesia nor fasted over 12 h. PET scans were started at 40 min after ¹⁸F-FP-CIT injection and obtained for 20 min. Volumes-of-interest for striatum and extrastriatal area were used for ¹⁸F-FP-CIT PET analysis. Cerebellum was considered as a reference region. Specific binding ratio (SBR) was calculated as follows: [(uptake of target-uptake of cerebellum)]/(uptake of cerebellum).

RESULTS

SBR without fasting and anesthesia (group D) was significantly lower than those of other groups (vs group A, p = 0.0004; vs group B, p = 0.0377; vs group C, p = 0.0134). However, SBRs of extrastriatal area (p = 0.5120) were not affected by fasting and anesthesia.

CONCLUSIONS

In conclusion, the SBR of striatum was increased after anesthesia by isoflurane and fasting. When designing an experiment using DAT imaging, the effects of isoflurane and fasting should be considered.

Nemo-like kinase reduces mutant huntingtin levels and mitigates Huntington's disease

Nemo-like kinase (NLK), an evolutionarily conserved serine/threonine kinase, is highly expressed in the brain, but its function in the adult brain remains not well understood. In this study, we identify NLK as an interactor of huntingtin protein (HTT). We report that NLK levels are significantly decreased in HD human brain and HD models. Importantly, overexpression of NLK in the striatum attenuates brain atrophy, preserves striatal DARPP32 levels and reduces mutant HTT (mHTT) aggregation in HD mice. In contrast, genetic reduction of NLK exacerbates brain atrophy and loss of DARPP32 in HD mice. Moreover, we demonstrate that NLK lowers mHTT levels in a kinase activity-dependent manner, while having no significant effect on normal HTT protein levels in mouse striatal cells, human cells and HD mouse models. The NLK-mediated lowering of mHTT is associated with enhanced phosphorylation of mHTT. Phosphorylation defective mutation of serine at amino acid 120 (S120) abolishes the mHTT-lowering effect of NLK, suggesting that S120 phosphorylation is an important step in the NLK-mediated lowering of mHTT. A further mechanistic study suggests that NLK promotes mHTT ubiquitination and degradation via the proteasome pathway. Taken together, our results indicate a protective role of NLK in HD and reveal a new molecular target to reduce mHTT levels.

Dopaminergic Transmission Rapidly and Persistently Enhances Excitability of D1 Receptor-Expressing Striatal Projection Neurons

Substantia nigra dopamine neurons have been implicated in the initiation and invigoration of movement, presumably through their modulation of striatal projection neuron (SPN) activity. However, the impact of native dopaminergic transmission on SPN excitability has not been directly demonstrated. Using perforated patch-clamp recording, we found that optogenetic stimulation of nigrostriatal dopamine axons rapidly and persistently elevated the excitability of D1 receptor-expressing SPNs (D1-SPNs). The evoked firing of D1-SPNs increased within hundreds of milliseconds of stimulation and remained elevated for ≥ 10 min. Consistent with the negative modulation of depolarization- and Ca2+-activated K+ currents, dopaminergic transmission accelerated subthreshold depolarization in response to current injection, reduced the latency to fire, and transiently diminished action potential afterhyperpolarization. Persistent modulation was protein kinase A dependent and associated with a reduction in action potential threshold. Together, these data demonstrate that dopaminergic transmission potently increases D1-SPN excitability with a time course that could support subsecond and sustained behavioral control.

Genome-wide In Vivo CNS Screening Identifies Genes that Modify CNS Neuronal Survival and mHTT Toxicity

Unbiased in vivo genome-wide genetic screening is a powerful approach to elucidate new molecular mechanisms, but such screening has not been possible to perform in the mammalian central nervous system (CNS). Here, we report the results of the first genome-wide genetic screens in the CNS using both short hairpin RNA (shRNA) and CRISPR libraries. Our screens identify many classes of CNS neuronal essential genes and demonstrate that CNS neurons are particularly sensitive not only to perturbations to synaptic processes but also autophagy, proteostasis, mRNA processing, and mitochondrial function. These results reveal a molecular logic for the common implication of these pathways across multiple neurodegenerative diseases. To further identify disease-relevant genetic modifiers, we applied our screening approach to two mouse models of Huntington's disease (HD). Top mutant huntingtin toxicity modifier genes included several Nme genes and several genes involved in methylation-dependent chromatin silencing and dopamine signaling, results that reveal new HD therapeutic target pathways.

Decreased striatal vesicular monoamine transporter 2 (VMAT2) expression in a type 1 diabetic rat model: A longitudinal study using micro-PET/CT

AIMS

Diabetes mellitus is a risk factor for Parkinson's disease. These diseases share similar pathogenic pathways, such as mitochondrial dysfunction, inflammation, and altered metabolism. Despite these similarities, the pathogenic relationship between these two diseases is unclear. [¹⁸F]FP-(+)-DTBZ is a promising radiotracer targeting VMAT2, which has been used to measure β-cell mass and to diagnose Parkinson's disease. The aim of this study was to examine the effect of type 1 diabetes on VMAT2 expression in the striatum using [¹⁸F]FP-(+)-DTBZ.

MATERIALS AND METHODS

A longitudinal study of type 1 diabetic rats was established by intraperitoneally injecting male Wistar rats with streptozotocin. Rats injected with saline were used as the control group. Glucose level, body weight, and [¹⁸F]FP-(+)-DTBZ uptake in the striatum and pancreas were evaluated at 0.5, 1, 4, 6 and 12 months after STZ or saline injection.

RESULTS

At one-half month post-STZ injection, the glucose levels in these rats increased and then returned to a normal level at 6 months. Along with increased glucose levels, body weight was also decreased significantly and returned slowly to a normal level. β-Cell mass and striatal [¹⁸F]FP-(+)-DTBZ uptake were impaired significantly at 2 weeks post-STZ injection in type 1 diabetic rats and returned to a normal level at 6 and 4 months post-STZ injection.

CONCLUSIONS

Due to increased glucose levels and decreased β-cell mass, decreased [¹⁸F]FP-(+)-DTBZ uptake in the striatum was observed in type 1 diabetic rats. Decreased BCM and increased glucose levels were correlated with VMAT2 expression in the striatum which indicated DM is a risk factor for PD.

Intranasal glyphosate-based herbicide administration alters the redox balance and the cholinergic system in the mouse brain

Pesticide exposure is associated with cognitive and psychomotor disorders. Glyphosate-based herbicides (GlyBH) are among the most used agrochemicals, and inhalation of GlyBH sprays may arise from frequent aerial pulverizations. Previously, we described that intranasal (IN) administration of GlyBH in mice decreases locomotor activity, increases anxiety, and impairs recognition memory. Then, the aim of the present study was to investigate the mechanisms involved in GlyBH neurotoxicity after IN administration. Adult male CF-1 mice were exposed to GlyBH IN administration (equivalent to 50 mg/kg/day of Gly acid, 3 days a week, during 4 weeks). Total thiol content and the activity of the enzymes catalase, acetylcholinesterase and transaminases were evaluated in different brain areas. In addition, markers of the cholinergic and the nigrostriatal pathways, as well as of astrocytes were evaluated by fluorescence microscopy in coronal brain sections. The brain areas chosen for analysis were those seen to be affected in our previous study. GlyBH IN administration impaired the redox balance of the brain and modified the activities of enzymes involved in cholinergic and glutamatergic pathways. Moreover, GlyBH treatment decreased the number of cholinergic neurons in the medial septum as well as the expression of the α7-acetylcholine receptor in the hippocampus. Also, the number of astrocytes increased in the anterior olfactory nucleus of the exposed mice. Taken together, these disturbances may contribute to the neurobehavioural impairments reported previously by us after IN GlyBH administration in mice.

Multiscale Imaging Reveals Aberrant Functional Connectome Organization and Elevated Dorsal Striatal Arc Expression in Advanced Age

The functional connectome reflects a network architecture enabling adaptive behavior that becomes vulnerable in advanced age. The cellular mechanisms that contribute to altered functional connectivity in old age, however, are not known. Here we used a multiscale imaging approach to link age-related changes in the functional connectome to altered expression of the activity-dependent immediate-early gene Arc as a function of training to multitask on a working memory (WM)/biconditional association task (BAT). Resting-state fMRI data were collected from young and aged rats longitudinally at three different timepoints during cognitive training. After imaging, rats performed the WM/BAT and were immediately sacrificed to examine expression levels of Arc during task performance. Aged behaviorally impaired, but not young, rats had a subnetwork of increased connectivity between the anterior cingulate cortex (ACC) and dorsal striatum (DS) that was correlated with the use of a suboptimal response-based strategy during cognitive testing. Moreover, while young rats had stable rich-club organization across three scanning sessions, the rich-club organization of old rats increased with cognitive training. In a control group of young and aged rats that were longitudinally scanned at similar time intervals, but without cognitive training, ACC-DS connectivity and rich-club organization did not change between scans in either age group. These findings suggest that aberrant large-scale functional connectivity in aged animals is associated with altered cellular activity patterns within individual brain regions.

Subtle changes in striatal muscarinic M1 and M4 receptor expression in the DYT1 knock-in mouse model of dystonia

In early-onset generalized torsion dystonia, caused by a GAG deletion in TOR1A (DYT1), enhanced striatal cholinergic activity has been suggested to be critically involved. Previous studies have shown increased acetylcholine levels in the striatum of DYT1 knock-in (KI) mice. Ex vivo data indicated that muscarinic receptor antagonists normalize the activity of striatal cholinergic interneurons. Currently receptor subtype specific antagonists are developed for therapy, however, it is yet unknown whether the levels of targeted receptors are unaltered. In the present study, we firstly examined the expression of M1 and M4 receptors in DYT1 KI mice in comparison to wildtype mice. While no changes in mRNA were found in the motor cortex, the expression of M1 was higher in the striatum of DYT1 KI. However, M1 protein did not differ in striatum and cortex between the animal groups as shown by immunohistochemistry and western blot. M4 receptor protein, unaltered in the cortex, was slightly lower in lateral subparts of the striatum, but unchanged in somata of cholinergic interneurons and substance P immunoreactive projection neurons. Functional alterations of the cholinergic system and of aberrant striatal plasticity, demonstrated by previous studies, seem not to be related to overt changes in M1 and M4 expression. This critically informs the ongoing development of respective antagonists for therapy of dystonia.

CD200 is up-regulated in R6/1 transgenic mouse model of Huntington's disease

In Huntington's disease (HD), striatal medium spiny neurons (MSNs) are particularly sensitive to the presence of a CAG repeat in the huntingtin (HTT) gene. However, there are many evidences that cells from the peripheral immune system and central nervous system (CNS) immune cells, namely microglia, play an important role in the etiology and the progression of HD. However, it remains unclear whether MSNs neurodegeneration is mediated by a non-cell autonomous mechanism. The homeostasis in the healthy CNS is maintained by several mechanisms of interaction between all brain cells. Neurons can control microglia activation through several inhibitory mechanisms, such as the CD200-CD200R1 interaction. Due to the complete lack of knowledge about the CD200-CD200R1 system in HD, we determined the temporal patterns of CD200 and CD200R1 expression in the neocortex, hippocampus and striatum in the HD mouse models R6/1 and HdhQ111/7 from pre-symptomatic to manifest stages. In order to explore any alteration in the peripheral immune system, we also studied the levels of expression of CD200 and CD200R1 in whole blood. Although CD200R1 expression was not altered, we observed and increase in CD200 gene expression and protein levels in the brain parenchyma of all the regions we examined, along with HD pathogenesis in R6/1 mice. Interestingly, the expression of CD200 mRNA was also up-regulated in blood following a similar temporal pattern. These results suggest that canonical neuronal-microglial communication through CD200-CD200R1 interaction is not compromised, and CD200 up-regulation in R6/1 brain parenchyma could represent a neurotrophic signal to sustain or extend neuronal function in the latest stages of HD as pro-survival mechanism.

Influence of magnesium supplementation and L-type calcium channel blocker on haloperidol-induced movement disturbances

Haloperidol (Hal) is an antipsychotic related to movement disorders. Magnesium (Mg) showed benefits on orofacial dyskinesia (OD), suggesting its involvement with N-methyl-D-aspartate receptors (NMDAR) since it acts blocking calcium channels. Comparisons between nifedipine (NIF; a calcium channel blocker) and Mg were performed to establish the Mg mechanism. Male rats concomitantly received Hal and Mg or NIF for 28 days, and OD behaviors were weekly assessed. Both Mg and NIF decreased Hal-induced OD. Hal increased Ca²⁺-ATPase activity in the striatum, and Mg reversed it. In the cortex, both Mg and NIF decreased such activity. Dopaminergic and glutamatergic immunoreactivity were modified by Hal and treatments: i) in the cortex: Hal reduced D1R and D2R, increasing NMDAR immunoreactivity. Mg and NIF reversed this Hal influence on D1R and NMDAR, while only Mg reversed Hal effects on D2R levels; ii) in the striatum: Hal decreased D2R and increased NMDAR while Mg and NIF decreased D1R and reversed the Hal-induced decreasing D2R levels. Only Mg reversed the Hal-induced increasing NMDAR levels; iii) in the substantia nigra (SN): while Hal increased D1R, D2R, and NMDAR, both Mg and NIF reversed this influence on D2R, but only Mg reversed the Hal-influence on D1R levels. Only NIF reversed the Hal effects on NMDAR immunoreactivity. These findings allow us to propose that Mg may be useful to minimize Hal-induced movement disturbances. Mg molecular mechanism seems to be involved with a calcium channel blocker because the NIF group showed less expressive effects than the Mg group.