Mesencephalic Dopaminergic Neurons Research Articles

Cannabinoid type-1 receptor signaling in dopaminergic Engrailed-1 expressing neurons modulates motivation and depressive-like behavior.

The endocannabinoid system comprises highly versatile signaling functions within the nervous system. It is reported to modulate the release of several neurotransmitters, consequently affecting the activity of neuronal circuits. Investigations have highlighted its roles in numerous processes, including appetite-stimulating characteristics, particularly for palatable food. Moreover, endocannabinoids are shown to fine-tune dopamine-signaled processes governing motivated behavior. Specifically, it has been demonstrated that excitatory and inhibitory inputs controlled by the cannabinoid type 1 receptor (CB1) regulate dopaminergic neurons in the mesocorticolimbic pathway. In the present study, we show that mesencephalic dopaminergic (mesDA) neurons in the ventral tegmental area (VTA) express CB1, and we investigated the consequences of specific deletion of CB1 in cells expressing the transcription factor Engrailed-1 (En1). To this end, we validated a new genetic mouse line EN1-CB1-KO, which displays a CB1 knockout in mesDA neurons beginning from their differentiation, as a tool to elucidate the functional contribution of CB1 in mesDA neurons. We revealed that EN1-CB1-KO mice display a significantly increased immobility time and shortened latency to the first immobility in the forced swim test of adult mice. Moreover, the maximal effort exerted to obtain access to chocolate-flavored pellets was significantly reduced under a progressive ratio schedule. In contrast, these mice do not differ in motor skills, anhedonia- or anxiety-like behavior compared to wild-type littermates. Taken together, these findings suggest a depressive-like or despair behavior in an inevitable situation and a lack of motivation to seek palatable food in EN1-CB1-KO mice, leading us to propose that CB1 plays an important role in the physiological functions of mesDA neurons. In particular, our data suggest that CB1 directly modifies the mesocorticolimbic pathway implicated in depressive-like/despair behavior and motivation. In contrast, the nigrostriatal pathway controlling voluntary movement seems to be unaffected.

Therapeutic value of homeoprotein signaling pathways.

Cell signaling based on homeoprotein transfer is a pathway with developmental and physiological functions. For a few transcription factors of this family, primarily ENGRAILED1, ENGRAILED2 and OTX2, their physiological functions have led to therapeutic strategies in animal models of human diseases, including Parkinson's disease, amyotrophic lateral sclerosis, amblyopia and anxiety-related disorders. In mesencephalic dopaminergic neurons which degenerate in Parkinson's disease, ENGRAILED1/2 have cell autonomous activities, but their transducing properties enables their use as therapeutic proteins. In contrast, in spinal alpha-motoneurons, which are lost in amyotrophic lateral sclerosis, ENGRAILED1 is supplied by V1 interneurons. Thus, its use as a therapeutic protein to protect alpha-motoneurons against degeneration mimics its normal non-cell autonomous neurotrophic activity. OTX2, synthesized and secreted by the choroid plexus, is transferred to parvalbumin interneurons and exerts regulatory functions controlling cerebral cortex plasticity. Understanding the latter OTX2 function has led to strategies for manipulating visual acuity and anxiety-like behavior in adult mice. In this review, we describe these cases and what is known about the involved molecular mechanisms. Because the transduction sequences are conserved in most of the few hundred homeoproteins, we argue how this family of molecules constitutes an important reservoir of physiological knowledge, with potential consequences in the search for new therapeutic strategies.

Heterogeneity of mesencephalic dopaminergic neurons: From molecular classifications, electrophysiological properties to functional connectivity.

The mesencephalic dopamine (DA) system is composed of neuronal subtypes that are molecularly and functionally distinct, are responsible for specific behaviors, and are closely associated with numerous brain disorders. Existing research has made significant advances in identifying the heterogeneity of mesencephalic DA neurons, which is necessary for understanding their diverse physiological functions and disease susceptibility. Moreover, there is a conflict regarding the electrophysiological properties of the distinct subsets of midbrain DA neurons. This review aimed to elucidate recent developments in the heterogeneity of midbrain DA neurons, including subpopulation categorization, electrophysiological characteristics, and functional connectivity to provide new strategies for accurately identifying distinct subtypes of midbrain DA neurons and investigating the underlying mechanisms of these neurons in various diseases.

Enhanced production of mesencephalic dopaminergic neurons from lineage-restricted human undifferentiated stem cells

Current differentiation protocols for generating mesencephalic dopaminergic (mesDA) neurons from human pluripotent stem cells result in grafts containing only a small proportion of mesDA neurons when transplanted in vivo. In this study, we develop lineage-restricted undifferentiated stem cells (LR-USCs) from pluripotent stem cells, which enhances their potential for differentiating into caudal midbrain floor plate progenitors and mesDA neurons. Using a ventral midbrain protocol, 69% of LR-USCs become bona fide caudal midbrain floor plate progenitors, compared to only 25% of human embryonic stem cells (hESCs). Importantly, LR-USCs generate significantly more mesDA neurons under midbrain and hindbrain conditions in vitro and in vivo. We demonstrate that midbrain-patterned LR-USC progenitors transplanted into 6-hydroxydopamine-lesioned rats restore function in a clinically relevant non-pharmacological behavioral test, whereas midbrain-patterned hESC-derived progenitors do not. This strategy demonstrates how lineage restriction can prevent the development of undesirable lineages and enhance the conditions necessary for mesDA neuron generation.

MiR-218 Promotes Dopaminergic Differentiation and Controls Neuron Excitability and Neurotransmitter Release through the Regulation of a Synaptic-Related Genes Network.

In the brain, microRNAs (miRNAs) are believed to play a role in orchestrating synaptic plasticity at a higher level by acting as an additional mechanism of translational regulation, alongside the mRNA/polysome system. Despite extensive research, our understanding of the specific contribution of individual miRNA to the function of dopaminergic neurons (DAn) remains limited. By performing a dopaminergic-specific miRNA screening, we have identified miR-218 as a critical regulator of DAn activity in male and female mice. We have found that miR-218 is specifically expressed in mesencephalic DAn and is able to promote dopaminergic differentiation of embryonic stem cells and functional maturation of transdifferentiated induced DA neurons. Midbrain-specific deletion of both genes encoding for miR-218 (referred to as miR-218-1 and mir218-2) affects the expression of a cluster of synaptic-related mRNAs and alters the intrinsic excitability of DAn, as it increases instantaneous frequencies of evoked action potentials, reduces rheobase current, affects the ionic current underlying the action potential after hyperpolarization phase, and reduces dopamine efflux in response to a single electrical stimulus. Our findings provide a comprehensive understanding of the involvement of miR-218 in the dopaminergic system and highlight its role as a modulator of dopaminergic transmission.SIGNIFICANCE STATEMENT In the past decade, several miRNAs have emerged as potential regulators of synapse activity through the modulation of specific gene expression. Among these, we have identified a dopaminergic-specific miRNA, miR-218, which is able to promote dopaminergic differentiation and regulates the translation of an entire cluster of synapse related mRNAs. Deletion of miR-218 has notable effects on dopamine release and alters the intrinsic excitability of dopaminergic neurons, indicating a direct control of dopaminergic activity by miR-218.

Host-to-graft Propagation of α-synuclein in a Mouse Model of Parkinson's Disease: Intranigral Versus Intrastriatal Transplantation.

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and by the accumulation of misfolded α-synuclein (α-syn) in Lewy bodies. Ectopic transplantation of human fetal ventral mesencephalic DA neurons into the striatum of PD patients have provided proof-of-principle for the cell replacement strategy in this disorder. However, 10 to 22 y after transplantation, 1% to 27% of grafted neurons contained α-syn aggregates similar to those observed in the host brain. We hypothesized that intrastriatal grafts are more vulnerable to α-syn propagation because the striatum is not the ontogenic site of nigral DA neurons and represents an unfavorable environment for transplanted neurons. Here, we compared the long-term host-to-graft propagation of α-syn in 2 transplantation sites: the SNpc and the striatum. Two mouse models of PD were developed by injecting adeno-associated-virus2/9-human α-syn A53T into either the SNpc or the striatum of C57BL/6 mice. Mouse fetal ventral mesencephalic DA progenitors were grafted into the SNpc or into the striatum of SNpc or striatum of α-syn injected mice, respectively. First, we have shown a degeneration of the nigrostriatal pathway associated with motor deficits after nigral but not striatal adeno-associated-virus-hαsyn A53T injection. Second, human α-syn preferentially accumulates in striatal grafts compared to nigral grafts. However, no differences were observed for phosphorylated α-syn, a marker of pathological α-syn aggregates. Taken together, our results suggest that the ectopic site of the transplantation impacts the host-to-graft transmission of α-syn.

Sortilin acts as an endocytic receptor for α-synuclein fibril.

Cell-to-cell spreading of misfolded α-synuclein (αSYN) is supposed to play a key role in the pathological progression of Parkinson's disease (PD) and other synucleinopathies. Receptor-mediated endocytosis has been shown to contributes to the uptake of αSYN in both neuronal and glial cells. To determine the receptor involved in αSYN endocytosis on the cell surface, we performed unbiased, and comprehensive screening using a membrane protein library of the mouse whole brain combined with affinity chromatography and mass spectrometry. The candidate molecules hit in the initial screening were validated by co-immunoprecipitation using cultured cells; sortilin, a vacuolar protein sorting 10 protein family sorting receptor, exhibited the strongest binding to αSYN fibrils. Notably, the intracellular uptake of fibrillar αSYN was slightly but significantly altered, depending on the expression level of sortilin on the cell surface, and time-lapse image analyses revealed the concomitant internalization and endosomal sorting of αSYN fibrils and sortilin. Domain deletion in the extracellular portion of sortilin revealed that the ten conserved cysteines (10CC) segment of sortilin was involved in the binding and endocytosis of fibrillar αSYN; importantly, pretreatment with a 10CC domain-specific antibody significantly hindered αSYN fibril uptake. The presence of sortilin in the core structure of Lewy bodies and glial cytoplasmic inclusions in the brain of synucleinopathy patients was confirmed via immunohistochemistry, and the expression level of sortilin in mesencephalic dopaminergic neurons may be altered with disease progression. These results provide compelling evidence that sortilin acts as an endocytic receptor for pathogenic form of αSYN, and yields important insight for the development of disease-modifying targets for synucleinopathies.

Expression of olfactory receptor genes in non-olfactory tissues in the developing and adult zebrafish

Since the discovery of olfactory receptor (OR) genes, their expression in non-olfactory tissues have been reported in rodents and humans. For example, mouse OR23 (mOR23) is expressed in sperm and muscle cells and has been proposed to play a role in chemotaxis and muscle migration, respectively. In addition, mouse mesencephalic dopaminergic neurons express various ORs, which respond to corresponding ligands. As the OR genes comprise the largest multigene family of G protein-coupled receptors in vertebrates (over 400 genes in human and 1000 in rodents), it has been difficult to categorize the extent of their diverse expression in non-olfactory tissues making it challenging to ascertain their function. The zebrafish genome contains significantly fewer OR genes at around 140 genes, and their expression pattern can be easily analyzed by carrying out whole mount in situ hybridization (ISH) assay in larvae. In this study, we found that 31 out of 36 OR genes, including or104-2, or108-1, or111-1, or125-4, or128-1, or128-5, 133-4, or133-7, or137-3 are expressed in various tissues, including the trunk, pharynx, pancreas and brain in the larvae. In addition, some OR genes are expressed in distinct brain regions such as the hypothalamus and the habenula in a dynamic temporal pattern between larvae, juvenile and adult zebrafish. We further confirmed that OR genes are expressed in non-olfactory tissues by RT-PCR in larvae and adults. These results indicate tight regulation of OR gene expression in the brain in a spatial and temporal manner and that the expression of OR genes in non-olfactory tissues are conserved in vertebrates. This study provides a framework to start investigating the function of ORs in the zebrafish brain.

GPBAR1 preserves neurite and synapse of dopaminergic neurons via RAD21-OPCML signaling: Role in preventing Parkinson's disease in mouse model and human patients

Parkinson’s disease (PD) exhibits systemic impacts on the metabolism, while metabolic alteration contributes to the risk and progression of PD. Bile acids (BA) metabolism disturbance has been linked to PD pathology. Membrane-bound G protein-coupled bile acid receptor 1 (GPBAR1) is expressed in the brain and thought to be neuroprotective; however, the role of GPBAR1 in PD remains unknown. The current study aimed to explore the effect of GPBAR1 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice with dopaminergic (DA) neuron-specific Gpbar1 knockdown or central GPBAR1 activation. The underlying mechanisms were investigated using mesencephalic primary neurons analyzed. Our study found that GPBAR1 was reduced in the substantia nigra of PD patients and MPTP-PD mice, and its expression was negatively correlated with the severity of PD-related features. Genetic downregulation of Gpbar1 in mouse mesencephalic DA neurons exacerbated MPTP-induced neurobehavioral and neuropathological deficits, whereas activation of central GPBAR1 with INT-777 (INT) relieved it. Moreover, in vivo and in vitro experiments showed the neurite- and synapse-protective effects of GPBAR1 activation in PD model. Mechanistically, by promoting the nuclear localization of cohesin subunit RAD21, GPBAR1 activation increased opioid-binding cell adhesion molecule (Opcml) expression, thereby inhibiting neurite and synapse degeneration of DA neurons in PD model. Collectively, our findings demonstrate that GPBAR1 is implicated in PD pathogenesis and activation of central GPBAR1 with INT antagonizes neurodegenerative pathology in PD model. This neuroprotection, at least in part, is attributed to the RAD21-OPCML signaling in neurons. Hence, GPBAR1 may serve as a promising candidate target for PD treatment.

Toxic and Phenotypic Effects of AAV_Cre Used to Transduce Mesencephalic Dopaminergic Neurons.

A popular approach to spatiotemporally target genes using the loxP/Cre recombination system is stereotaxic microinjection of adeno-associated virus (AAV) expressing Cre recombinase (AAV_Cre) in specific neuronal structures. Here, we report that AAV_Cre microinjection in the ventral tegmental area (VTA) of ErbB4 Cyt-1-floxed (ErbB4 Cyt-1fl/fl) mice at titers commonly used in the literature (~1012–1013 GC/mL) can have neurotoxic effects on dopaminergic neurons and elicit behavioral abnormalities. However, these effects of AAV_Cre microinjection are independent of ErbB4 Cyt-1 recombination because they are also observed in microinjected wild-type (WT) controls. Mice microinjected with AAV_Cre (1012–1013 GC/mL) exhibit reductions of tyrosine hydroxylase (TH) and dopamine transporter (DAT) expression, loss of dopaminergic neurons, and they behaviorally become hyperactive, fail to habituate in the open field and exhibit sensorimotor gating deficits compared to controls microinjected with AAV_GFP. Importantly, these AAV_Cre non-specific effects are: (1) independent of serotype, (2) occur with vectors expressing either Cre or Cre-GFP fusion protein and (3) preventable by reducing viral titers by 1000-fold (1010 GC/mL), which retains sufficient recombination activity to target floxed genes. Our studies emphasize the importance of including AAV_Cre-injected WT controls in experiments because recombination-independent effects on gene expression, neurotoxicity and behaviors could be erroneously attributed to consequences of gene ablation.

Physiological and Pathological Functions of Neuronal Hemoglobin: A Key Underappreciated Protein in Parkinson's Disease.

The expression of Hemoglobin (Hb) is not restricted to erythrocytes but is also present in neurons. Hb is selectively enriched in vulnerable mesencephalic dopaminergic neurons of Parkinson’s disease (PD) instead of resistant neurons. Controversial results of neuronal Hb levels have been reported in postmortem brains of PD patients: although neuronal Hb levels may decline in PD patients, elderly men with higher Hb levels have an increased risk of developing PD. α-synuclein, a key protein involved in PD pathology, interacts directly with Hb protein and forms complexes in erythrocytes and brains of monkeys and humans. These complexes increase in erythrocytes and striatal cytoplasm, while they decrease in striatal mitochondria with aging. Besides, the colocalization of serine 129-phosphorylated (Pser129) α-synuclein and Hb β chains have been found in the brains of PD patients. Several underlying molecular mechanisms involving mitochondrial homeostasis, α-synuclein accumulation, iron metabolism, and hormone-regulated signaling pathways have been investigated to assess the relationship between neuronal Hb and PD development. The formation of fibrils with neuronal Hb in various neurodegenerative diseases may indicate a common fibrillization pathway and a widespread target that could be applied in neurodegeneration therapy.

Neuroprotective activity of a virus-safe nanofiltered human platelet lysate depleted of extracellular vesicles in Parkinson's disease and traumatic brain injury models.

Brain administration of human platelet lysates (HPL) is a potential emerging biotherapy of neurodegenerative and traumatic diseases of the central nervous system. HPLs being prepared from pooled platelet concentrates, thereby increasing viral risks, manufacturing processes should incorporate robust virus-reduction treatments. We evaluated a 19 ± 2-nm virus removal nanofiltration process using hydrophilic regenerated cellulose hollow fibers on the properties of a neuroprotective heat-treated HPL (HPPL). Spiking experiments demonstrated >5.30 log removal of 20-22-nm non-enveloped minute virus of mice-mock particles using an immuno-quantitative polymerase chain reaction assay. The nanofiltered HPPL (NHPPL) contained a range of neurotrophic factors like HPPL. There was >2 log removal of extracellular vesicles (EVs), associated with decreased expression of pro-thrombogenic phosphatidylserine and procoagulant activity. LC-MS/MS proteomics showed that ca. 80% of HPPL proteins, including neurotrophins, cytokines, and antioxidants, were still found in NHPPL, whereas proteins associated with some infections and cancer-associated pathways, pro-coagulation and EVs, were removed. NHPPL maintained intact neuroprotective activity in Lund human mesencephalic dopaminergic neuron model of Parkinson's disease (PD), stimulated the differentiation of SH-SY5Y neuronal cells and showed preserved anti-inflammatory function upon intranasal administration in a mouse model of traumatic brain injury (TBI). Therefore, nanofiltration of HPL is feasible, lowers the viral, prothrombotic and procoagulant risks, and preserves the neuroprotective and anti-inflammatory properties in neuronal pre-clinical models of PD and TBI.

Genomic, transcriptomic, and metabolomic profiles of hiPSC-derived dopamine neurons from clinically discordant brothers with identical PRKN deletions

We previously reported on two brothers who carry identical compound heterozygous PRKN mutations yet present with significantly different Parkinson’s Disease (PD) clinical phenotypes. Juvenile cases demonstrate that PD is not necessarily an aging-associated disease. Indeed, evidence for a developmental component to PD pathogenesis is accumulating. Thus, we hypothesized that the presence of additional genetic modifiers, including genetic loci relevant to mesencephalic dopamine neuron development, could potentially contribute to the different clinical manifestations of the two brothers. We differentiated human-induced pluripotent stem cells (hiPSCs) derived from the two brothers into mesencephalic neural precursor cells and early postmitotic dopaminergic neurons and performed wholeexome sequencing and transcriptomic and metabolomic analyses. No significant differences in the expression of canonical dopamine neuron differentiation markers were observed. Yet our transcriptomic analysis revealed a significant downregulation of the expression of three neurodevelopmentally relevant cell adhesion molecules, CNTN6, CNTN4 and CHL1, in the cultures of the more severely affected brother. In addition, several HLA genes, known to play a role in neurodevelopment, were differentially regulated. The expression of EN2, a transcription factor crucial for mesencephalic dopamine neuron development, was also differentially regulated. We further identified differences in cellular processes relevant to dopamine metabolism. Lastly, wholeexome sequencing, transcriptomics and metabolomics data all revealed differences in glutathione (GSH) homeostasis, the dysregulation of which has been previously associated with PD. In summary, we identified genetic differences which could potentially, at least partially, contribute to the discordant clinical PD presentation of the two brothers.

Immunolocalization of kappa opioid receptors in the axon initial segment of a group of embryonic mesencephalic dopamine neurons.

The dopamine mesolimbic system is a major circuit involved in controlling goal-directed behaviors. Dopamine D2 receptors (D2R) and kappa opioid receptors (KOR) are abundant Gi protein-coupled receptors in the mesolimbic system. D2R and KOR share several functions in dopamine mesencephalic neurons, such as regulation of dopamine release and uptake, and firing of dopamine neurons. In addition, KOR and D2R modulate each other functioning. This evidence indicates that both receptors functionally interact, however, their colocalization in the mesostriatal system has not been addressed. Immunofluorescent assays were performed in cultured dopamine neurons and adult mice’s brain tissue to answer this question. We observed that KOR and D2R are present in similar density in dendrites and soma of cultured dopamine neurons, but in a segregated manner. Interestingly, KOR immunolabelling was observed in the first part of the axon, colocalizing with Ankyrin in 20% of cultured dopamine neurons, indicative that KOR is present in the axon initial segment (AIS) of a group of dopaminergic neurons. In the adult brain, KOR and D2R are also segregated in striatal tissue. While the KOR label is in fiber tracts such as the striatal streaks, corpus callosum, and anterior commissure, D2R is located mainly within the striatum and nucleus accumbens, surrounding fiber tracts. D2R is also localized in some fibers that are mostly different from those positives for KOR. In conclusion, KOR and D2R are present in the soma and dendrites of mesencephalic dopaminergic neurons, but KOR is also found in the AIS of a subpopulation of these neurons.

Central dopaminergic control of cell proliferation in the colonic epithelium

Parkinson’s disease (PD) is an age-related neurodegenerative disease, mainly characterized by the loss of dopaminergic (DA) neurons in the substantia nigra. Several non-motor symptoms, including those associated with gastrointestinal dysfunction, precede the classical motor symptoms in PD. However, the mechanisms underlying gastrointestinal dysfunction in the prodromal phase of PD remain elusive. Here, we investigated the contribution of the central DA system to cell proliferation in the colonic epithelium. Degeneration of nigrostriatal DA pathway induced by striatal 6-hydroxydopamine (6-OHDA) injection resulted in a marked reduction in cell proliferation in the colonic epithelium as assessed by Ki-67 and bromodeoxyuridine labeling assays. RNA-sequencing analysis confirmed the suppression of cell cycle-related gene expression in the colonic epithelium of 6-OHDA-lesioned mice. Mesencephalic DA neuron degeneration also caused the gut microbiota dysbiosis. Moreover, 6-OHDA-lesioned mice showed profoundly increased vulnerability to dextran sulfate sodium-induced colitis. Together, our study uncovers a crucial role for the integrity of nigral DA neurons in the maintenance of colonic epithelial cell homeostasis. Our data also provide a new strategy for protecting intestinal homeostasis in PD.

The dopamine receptor agonist apomorphine stabilizes neurotoxic α-synuclein oligomers.

The misfolding and aggregation of the protein α-synuclein (aSyn) into potentially neurotoxic oligomers is believed to play a pivotal role in the neuropathogenesis of Parkinson's disease (PD). Herein, we explore how apomorphine (Apo), a nonselective dopamine D1 and D2 receptor agonist utilized in the therapy for PD, affects the aggregation and toxicity of aSyn in vitro. Our data indicated that Apo inhibits aSyn fibrillation leading to the formation of large oligomeric species (Apo-aSyn-O), which exhibit remarkable toxicity in mesencephalic dopaminergic neurons in primary cultures. Interestingly, purified Apo-aSyn-O, even at very low concentrations, seems to be capable of converting unmodified aSyn monomer into neurotoxic species. Collectively, our findings warn for a possible dangerous effect of Apo on aSyn misfolding/aggregation pathway.

Behavioral, Cellular and Molecular Responses to Cold and Mechanical Stimuli in Rats with Bilateral Dopamine Depletion in the Mesencephalic Dopaminergic Neurons

Pain is the major non-motor symptom in Parkinson’s disease (PD). Preclinical studies have mostly investigated mechanical pain by considering the decrease in a nociceptive threshold. Only a few studies have focused on thermal pain in animal models of PD. Therefore, the goal of this study was to assess the thermal nociceptive behavior of rats subjected to 6-hydroxydopamine (6-OHDA) administration, which constitutes an animal model of PD. Thermal plate investigation demonstrated significant thermal sensitivity to cold temperatures of 10 °C and 15 °C, and not to higher temperatures, in 6-OHDA-lesioned rats when compared with sham. 6-OHDA-lesioned rats also showed cold allodynia as demonstrated by a significant difference in the number of flinches, latency and reaction time to acetone stimulus. Ropinirole administration, a dopamine receptor 2 (D2R) agonist, blocked the acetone-induced cold allodynia in 6-OHDA-lesioned rats. In addition, mechanical hypersensitivity and static allodynia, as demonstrated by a significant difference in the vocalization threshold and pain score respectively, were noticed in 6-OHDA-lesioned rats. Acetone stimulus induced a significant increase in extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) phosphorylation, a pain process molecular marker, in the spinal dorsal horn (SDH), the insular and cingulate cortices in 6-OHDA-lesioned rats when compared to sham. In 6-OHDA-lesioned rats, there was a significant augmentation in the expression of both protein kinase C gamma (PKCγ) and glutamate decarboxylase 67 (GAD67) in the SDH. This highlighted an increase in excitation and a decrease in inhibition in the SDH. Overall, the present study demonstrated a clear cold thermal hypersensitivity, in addition to a mechanical one, in 6-OHDA-lesioned rats.

Altered Development of Mesencephalic Dopaminergic Neurons in SIDS: New Insights into Understanding Sudden Infant Death Pathogenesis.

Sudden infant death syndrome (SIDS) is defined as the unexpected sudden death of an infant under 1 year of age that remains unexplained after a thorough case investigation. The SIDS pathogenesis is still unknown; however, abnormalities in brain centers that control breathing and arousal from sleep, including dramatic changes in neurotransmitter levels, have been supposed in these deaths. This is the first study focusing on mesencephalic dopaminergic neurons, so far extensively studied only in animals and human neurological diseases, in SIDS. Dopaminergic structures in midbrain sections of a large series of sudden infant deaths (36 SIDS and 26 controls) were identified using polyclonal rabbit antibodies against tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, and the dopamine transporter, a membrane protein specifically expressed in dopaminergic cells. Dopamine-immunolabeled neurons were observed concentrated in two specific structures: the pars compacta of the substantia nigra and in the subnucleus medialis of the periaqueductal gray matter. Anatomical and functional degenerations of dopaminergic neurons in these regions were observed in most SIDS cases but never in controls. These results indicate that dopamine depletion, which is already known to be linked especially to Parkinson’s disease, is strongly involved even in SIDS pathogenesis.

Endoplasmic Reticulum Stress Is Associated with the Mesencephalic Dopaminergic Neuron Injury in Stressed Rats.

An increasing number of people are in a state of stress due to social and psychological pressures, which may result in mental disorders. Previous studies indicated that mesencephalic dopaminergic neurons are associated with not only reward-related behaviors but also with stress-induced mental disorders. To explore the effect of stress on dopaminergic neuron and potential mechanism, we established stressed rat models of different time durations and observed pathological changes in dopaminergic neurons of the ventral tegmental area (VTA) through HE and thionine staining. Immunohistochemistry coupled with microscopy-based multicolor tissue cytometry (MMTC) was employed to investigate the number changes of dopaminergic neurons. Double immunofluorescence labelling was used to investigate expression changes of endoplasmic reticulum stress (ERS) protein GRP78 and CHOP in dopaminergic neurons. Our results showed that prolonged stress led to pathological alteration in dopaminergic neurons of VTA, such as missing of Nissl bodies and pyknosis in dopaminergic neurons. Immunohistochemistry with MMTC indicated that chronic stress exposure resulted in a significant decrease in dopaminergic neurons. Double immunofluorescence labelling showed that the endoplasmic reticulum stress protein took part in the injury of dopaminergic neurons. Taken together, these results indicated the involvement of ERS in mesencephalic dopaminergic neuron injury induced by stress exposure.

Dietary Phytoestrogens: Neuroprotective Role in Parkinson's Disease.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive damage of mesencephalic dopaminergic neurons of the substantia nigra and the striatal projections. Recent studies suggest that estrogen and estrogen-like chemicals have beneficial effects on neurodegenerative diseases, particularly PD. Animal studies demonstrate that estrogen influences dopamine's synthesis, release, and metabolism. In vivo studies have also shown the significant beneficial effects of estrogen in shielding the brain from neurodegenerative processes like PD. Moreover, the expression and function of dopamine receptors can be modified by estrogen. Phytoestrogens are non-steroidal compounds derived from plants present in a large spectrum of foods, most specifically soy and in numerous dietary supplements. Phytoestrogens share structural and functional similarities with 17β-estradiol and can be used as an alternative treatment for PD because of estrogen's undesirable effects, such as the increased risk of breast and endometrial cancer, ischemic disorders, and irregular bleeding. Despite the beneficial effects of phytoestrogens, their impact on human health may depend on age, health status, and even the presence or absence of specific gut microflora. In addition to their antioxidant properties, soy products or phytoestrogens also exhibit neuroprotective activity in patients with PD via the interaction with estrogen receptors (ER) α and β, with a higher affinity for ERβ. Phytoestrogens offer a valuable model for fully exploring the biological effects of endocrine disruptors in general. However, observational studies and randomized controlled trials in humans have resulted in inconclusive findings within this domain. This review considered the evidence in animal models and human epidemiological data as to whether developmental exposure to various phytoestrogen classes adversely or beneficially impacts the neurobehavioral programming in PD.