Histamine-4 receptor antagonist JNJ7777120 inhibits pro-inflammatory microglia and prevents the progression of Parkinson-like pathology and behaviour in a rat model

The activation of microglial cells is presumed to play a key role in the pathogenesis of Parkinson's disease (PD). The activity of microglia is regulated by the histamine-4 receptor (H₄R), thus providing a novel target that may prevent the progression of PD. However, this putative mechanism has so far not been validated. In our previous study, we found that mRNA expression of H₄R was upregulated in PD patients. In the present study, we validated this possible mechanism using the rotenone-induced PD rat model, in which mRNA expression levels of H₄R-, and microglial markers were significantly increased in the ventral midbrain. Inhibition of H₄R in rotenone-induced PD rat model by infusion of the specific H₄R antagonist JNJ7777120 into the lateral ventricle resulted in blockade of microglial activation. In addition, pharmacological targeting of H₄R in rotenone-lesioned rats resulted in reduced apomorphine-induced rotational behaviour, prevention of dopaminergic neuron degeneration and associated decreases in striatal dopamine levels. These changes were accompanied by a reduction of Lewy body-like neuropathology. Our results provide first proof of the efficacy of an H₄R antagonist in a commonly used PD rat model, and proposes the H₄R as a promising target to clinically tackle microglial activation and thereby the progression of PD.     

Subthalamic deep brain stimulation differently alters striatal dopaminergic receptor levels in rats

High‐frequency stimulation (HFS) of the subthalamic nucleus (STN) is recognized as an effective treatment for the motor symptoms of Parkinson's disease (PD), but its mechanisms, particularly as concern dopaminergic transmission, remain unclear. The aim of this study was to evaluate changes in the expression of dopaminergic receptors (D₁, D₂, and D₃ receptors) after prolonged (4 h) unilateral STN‐HFS in anesthetized intact rats and rats with total dopaminergic denervation. We used [³H]SCH 23390, [¹²⁵I]iodosulpride, and [¹²⁵I]OH‐PIPAT to assess the densities of D₁R, D₂R, and D₃R, respectively, within different areas of the striatum—a major input structure of the basal ganglia—including the nucleus accumbens. We found that STN‐HFS increased D₁R levels in almost all of the striatal areas examined, in both intact and denervated rats. By contrast, STN‐HFS led to a large decrease in D₂R and D₃R levels, limited to the nucleus accumbens and independent of the dopaminergic state of the animals. These data suggest that the influence of STN‐HFS on striatal D₁R expression may contribute to its therapeutic effects on motor symptoms, whereas its impact on D₂R/D₃R levels in the nucleus accumbens may account for the neuropsychiatric side effects often observed in stimulated PD patients, such as postoperative apathy. © 2015 International Parkinson and Movement Disorder Society     

Homeostatic changes of the endocannabinoid system in Parkinson's disease

Endocannabinoids (eCBs) are endogenous lipids that bind principally type‐1 and type‐2 cannabinoid (CB₁ and CB₂) receptors. N‐Arachidonoylethanolamine (AEA, anandamide) and 2‐arachidonoylglycerol (2‐AG) are the best characterized eCBs that are released from membrane phospholipid precursors through multiple biosynthetic pathways. Together with their receptors and metabolic enzymes, eCBs form the so‐called “eCB system”. The later has been involved in a wide variety of actions, including modulation of basal ganglia function. Consistently, both eCB levels and CB₁ receptor expression are high in several basal ganglia regions, and more specifically in the striatum and in its target projection areas. In these regions, the eCB system establishes a close functional interaction with dopaminergic neurotransmission, supporting a relevant role for eCBs in the control of voluntary movements. Accordingly, compelling experimental and clinical evidence suggests that a profound rearrangement of the eCB system in the basal ganglia follows dopamine depletion, as it occurs in Parkinson's disease (PD). In this article, we provide a brief survey of the evidence that the eCB system changes in both animal models of, and patients suffering from, PD. A striking convergence of findings is observed between both rodent and primate models and PD patients, indicating that the eCB system undergoes dynamic, adaptive changes, aimed at restoring an apparent homeostasis within the basal ganglia network. © 2010 Movement Disorder Society     

Adenosine,adenosine A2A antagonists,and Parkinson's disease

Adenosine derived from the degradation of ATP/AMP functions as a signalling molecule in the nervous system through the occupation of A1, A2, and A3 adenosine receptors. Adenosine A_2A receptors have a selective localization to the basal ganglia and specifically to the indirect output pathway, and as a consequence offer a unique opportunity to modulate the output from the striatum that is believed critical to the occurrence of motor components of PD. Indeed, the ability of A_2A antagonists to modulate basal ganglia neurotransmission has been shown to be associated with improved motor function in experimental models of PD. This suggests that A_2A antagonists would be effective as a symptomatic treatment in humans without provoking marked dyskinesia. Indeed, the A_2A antagonist istradefylline reduces OFF time in moderate- to late-stage patients with PD already receiving dopaminergic therapy, with an increase in non-troublesome dyskinesia. Adenosine and adenosine receptors also exert actions relevant to pathogenesis in PD, raising the possibility of their use as neuroprotective agents. Both epidemiologic evidence and the current preclinical data strongly support a role for A_2A antagonists in protecting dopaminergic neurons and influencing the onset and progression of PD.     

Arbutin effectively ameliorates the symptoms of Parkinson’s disease: the role of adenosine receptors and cyclic adenosine monophosphate

An antagonistic communication exists between adenosinergic and dopaminergic signaling in the basal ganglia, which suggests that the suppression of adenosine A_2A receptors-cyclic adenosine monophosphate pathway may be able to restore the disrupted dopamine transmission that results in motor symptoms in Parkinson’s disease (PD). Arbutin is a natural glycoside that possesses antioxidant, anti-inflammatory, and neuroprotective properties. The purpose of this study was to investigate whether arbutin could ameliorate the symptoms of PD and to examine the underlying mechanism. In this study, Swiss albino mouse models of PD were established by the intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine for 4 successive days, with the concurrent intraperitoneal administration of arbutin (50 and 100 mg/kg) for 7 days. The results showed that arbutin significantly reduced lipid peroxidation, total nitrite levels, and inflammation in the substantia nigra and striatum of PD mouse models. In addition, arbutin decreased the activity of endogenous antioxidants, reduced the levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and γ-aminobutyric acid, and minimized neurodegeneration in the striatum. Arbutin also reduced the abnormal performance of PD mouse models in the open field test, bar test, pole test, and rotarod test. The therapeutic efficacy of arbutin was similar to that of madopar. The intraperitoneal injection of the A_2AR agonist {"type":"entrez-protein","attrs":{"text":"CGS21680","term_id":"878113053","term_text":"CGS21680"}}CGS21680 (0.5 mg/kg) attenuated the therapeutic effects of arbutin, whereas the intraperitoneal injection of forskolin (3 mg/kg) enhanced arbutin-mediated improvements. These findings suggest that arbutin can improve the performance of PD mouse models by inhibiting the function of the A_2AR and enhancing the effects of cyclic adenosine monophosphate. This study was approved by the Institutional Animal Ethics Committee (1616/PO/Re/S/12/CPCSEA) on November 17, 2019 (approval No. IAEC/2019/010).

Chinese Library Classification No. R453; R741; R363     

Pedunculopontine nucleus in the squirrel monkey: Projections to the basal ganglia as revealed by anterograde tract-tracing methods

The efferent projections of the pedunculopontine nucleus (PPN) to the ganglia have been studied in the squirrel monkey (Saimiri sciureus) with [³H]leucine and Phaseolus vulgaris-leucoagglutinin (PHA-L) as anterograde tracers. Following unilateral injections of [³H]leucine or PHA-L in the central portion of the PPN, numerous autoradiographic linear profiles or PHA-L-labeled fibers ascend to the forebrain, both ipsilaterally and contralaterally. These fibers form a compact bundle that courses in the central portion of the mesopontine tegmentum. At rostral mesencephalic levels, theis bundle splits into ventromedial and dorsolateral fascicles that arborize in basal ganglia and thalamic nuclei, respectively. The substantia nigra and the subthalamic nucleus are by far the most densely innervated structures of the basal ganglia. In these two nuclei, labeled fibers arborize profusely ipsilaterally and less abundantly contralaterally. The labeled fibers in the substantia nigra are thin and varicose and arborize almost exclusively in the pars compacta, where they closely surround the soma and proximal dendrites of dopaminergic neurons. In the subthalamic nucleus labeled fibers are also thin and appear to contact more than one neuron along their course. Numerous labeled fibers also occur in the pallidal complex, where they arborize most profusely in the internal segment. Several thick, labeled fibers oriented dorsolaterally in the pallidal complex give rise to thinner fibers that closley surround the soma and proximal dendrites of pallidal neurons. Some labeled fibers are also scattered in the striatum. These fibers abound in the peripallidal and ventral portions of the putamen, are more sparsely distributed in the remaining portion of the putamen as well as in the caudate nucleus, and are virtually absent in the ventral striatum. These results reveal that the PPN gives rise to a massive and highly ordered innervation of the basal ganglia in the squirrel monkey. This nucleus may thus act as an important relay in the basal ganglia circuitry in primates. © 1994 Wiley-Liss, Inc.     

Plasticity of afferent fibers to striatal neurons bearing D1 dopamine receptors in Parkinson's disease.

The loss of dopaminergic neurons in the substantia nigra provokes a plasticity of corticostriatal synapses in Parkinson's disease (PD). The corticostriatal pathway nevertheless makes synapses with neurons bearing D1 dopamine receptors (D1R) and/or D2 dopamine receptors. At the ultrastructural level, we analyzed the morphological characteristics of synapses formed by afferent fibers making asymmetric contacts with the dendritic spines of neurons identified by D1R immunoreactivity, in the striatum of control subjects and PD patients. A quantitative analysis of the morphological characteristics of the synapses and of the number of perforated synapses (considered to be very active) was performed. In PD, a 50% increase in the number of perforated synapses making contact with D1R dendritic spines was observed, whereas no change in the number of perforated synapses on non-D1R spines was observed. The change in the number of perforated synapses on D1R dendrites was associated with a slight but nonsignificant increase in the surface area of the corticostriatal afferent fibers and the surface of the mitochondria in these fibers (+29.0% and +34.6%, respectively). This suggests a hyperactivity of corticostriatal fibers in contact with D1R-bearing neurons of the direct pathway in the basal ganglia circuitry. Since stimulation of the direct pathway is thought to alleviate the clinical symptoms of PD, this suggests that the differences observed may be involved in compensatory mechanisms.     

Hydrogen sulfide functions as a neuromodulator to regulate striatal neurotransmission in a mouse model of Parkinson's disease

Hydrogen sulfide (H₂S), a novel endogenous gasotransmitter, has been considered a neuromodulator to enhance hippocampal long‐term potentiation and exerts neuroprotective effects against neurotoxin‐induced neurodegeneration in rodent models of Parkinson's disease (PD). However, whether H₂S can function as a neuromodulator to regulate the levels of nigrostriatal neurotransmitters and then impact the vulnerability of dopaminergic (DA) neurons in response to neurotoxins remains unknown. For this study, we prepared a 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine plus probenecid (MPTP/p)‐induced mouse subacute model of PD to explore the modulatory effect of H₂S on monoamine and amino acid neurotransmitters in the striatum of MPTP‐treated mice. This study shows that NaHS (an H₂S donor, 5.6 mg/kg/day, i.p.) administration improves the survival rate and significantly ameliorates the weight loss of MPTP‐treated mice. NaHS treatment attenuated MPTP‐induced neuronal damage, restored the diminution of DA neurons, and suppressed the overactivation of astrocytes in the mouse striatum. Additionally, NaHS upregulated striatal serotonin levels and modulated the balance of excitatory glutamate and the inhibitory γ‐aminobutyric acid system in response to MPTP challenge. The current study indicates that H₂S may function as an effective neuromodulator to regulate striatal neurotransmission and provides insight into the potential of H₂S for PD therapy. © 2014 Wiley Periodicals, Inc.     

Acupuncture inhibits neuroinflammation and gut microbial dysbiosis in a mouse model of Parkinson’s disease

Growing evidences show that gut microbiota is associated with the pathogenesis of Parkinson’s disease (PD) and the gut-brain axis can be promising target for the development of the therapeutic strategies for PD. Acupuncture has been used to improve brain functions and inflammation in neurological disorders such as PD, and to recover the gastrointestinal dysfunctions in various gastrointestinal disorders. Thus, we investigated whether acupuncture could improve Parkinsonism and gut microbial dysbiosis induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. First, we observed that acupuncture treatment at acupoints GB34 and ST36 could improve motor functions and comorbid anxiety in PD mice. Next, we found that acupuncture increased the levels of dopaminergic fibers and neurons in the striatum and the substantia nigra, respectively. Acupuncture also restored the overexpression of microglia and astrocyte as well as conversion of Bax and Bcl-2 expression in both the striatum and the substantia nigra, indicating that inflammatory responses and apoptosis were blocked by acupuncture. Additionally, via 16S rRNA sequence analysis, we observed that the relative abundance of 18 genera were changed in acupuncture-treated mice compared to the PD mice. Of them, Butyricimonas, Holdemania, Frisingicoccus, Gracilibacter, Phocea, and Aestuariispira showed significant correlations with anxiety as well as motor functions. Furthermore, the predicted functional analyses showed that acupuncture restored the physiology functions such as glutathione metabolism, methane metabolism, and PD pathway. In conclusion, we suggest that the effects of acupuncture on the enhanced motor function and the protection of the dopaminergic neurons may be associated with the regulation of the gut microbial dysbiosis and thus the inhibition of the neuroinflammation in the PD mice.     

Adenosine A2A receptor gene expression in the normal striatum and after 6-OH-dopamine lesion

Summary. Adenosine A_2A receptors are present on enkephalinergic medium sized striatal neurons in the rat and have an important function in the modulation of striatal output. In order to establish more accurately whether adenosine transmission is a generalized phenomenon in mammalian striatum we compared the A_2A R expression in the mouse, rat, cat and human striatum. Secondly we compared the modulation of enkephalin gene expression and A_2A receptor gene expression in rat striatal neurons after 6-OH-dopamine lesion of the substantia nigra. Hybridization histochemistry was performed with a ³⁵S-labelled radioactive oligonucleotide probe. The results showed high expression of A_2A adenosine receptor genes only in the medium-sized cells of the striatum in all examined species. In the rat striatum, expression of A_2A receptors was not significantly altered after lesion of the dopaminergic pathways with 6-OH-dopamine even though enkephalin gene expression was up-regulated. The absence of a change in A_2A receptor gene expression after 6-OH-dopamine treatment speaks against a dependency on dopaminergic innervation. The maintained inhibitory function of A_2A R on motor activity in spite of dopamine depletion could be partly responsible for the depression of locomotor activity observed in basal ganglia disorders such as Parkinson's disease. Received May 10, 1999; accepted November 24, 1999     

Basal ganglia organization in amphibians: development of striatal and nucleus accumbens connections with emphasis on the catecholaminergic inputs

To broaden our insight into the organization of the basal ganglia of amphibians, the development of the connections of the striatum and the nucleus accumbens was studied by means of tract-tracing techniques based on the transport of biotinylated dextran amines. In a number of experiments, these techniques were combined with tyrosine hydroxylase immunohistochemistry to identify the sources of catecholaminergic inputs to the striatum and the nucleus accumbens. Already at late embryonic stages, the basal telencephalon receives inputs from cells located in the amygdala, the thalamus, the suprachiasmatic nucleus, the raphe nucleus, and the rhombencephalic reticular formation. At these stages, the rostral part of the posterior tubercle seems to be the only source of the dopaminergic input to the basal telencephalon. During premetamorphosis, not only a differentiation between connections of the striatum and the nucleus accumbens could be made, but new sources of inputs were also detected in the mesencephalic and isthmic tegmentum, the parabrachial nucleus, and the nucleus of the solitary tract. Double-labeling experiments revealed that, at these stages, in addition to the posterior tubercle, cells within the mesencephalic tegmentum, the locus coeruleus, and the solitary tract nucleus contribute to the catecholaminergic innervation of the basal forebrain. During prometamorphic stages, a gradual increase occurs in the number of cells that project to the basal telencephalon. At the beginning of the metamorphic climax, the organization of the basal ganglia afferents largely resembles the pattern observed in juveniles and adults. Remarkably, during larval stages, the cells that contribute to the dopaminergic innervation of the basal forebrain show a rostrocaudal gradient in time of appearance. Moreover, the dopaminergic fibers reach the striatum earlier than the nucleus accumbens, and they precede markedly the development of the efferent connections of both brain structures. These developmental aspects are easily correlated with the situation in amniotes; therefore, the notion that amphibians share an essentially similar pattern of basal ganglia organization with other tetrapods is further strengthened. J. Comp. Neurol. 383:349-369, 1997. © 1997 Wiley-Liss, Inc.     

Increased brain-derived neurotrophic factor-containing axons in the basal ganglia of patients with multiple system atrophy.

Brain-derived neurotrophic factor (BDNF) has a neurotrophic effect not only on mesencephalic dopaminergic neurons, but also on striatal neurons. To investigate whether the abnormal expression of BDNF occurs in the basal ganglia of patients with Parkinson disease (PD) and multiple system atrophy (MSA), we compared the BDNF levels in the striatum and globus pallidus of patients with PD or MSA to controls using immunohistochemistry. Furthermore, to quantitatively evaluate the immunohistochemical changes in the striatum, image analysis of the putamen was performed. BDNF-positive nerve fiber bundles and fine granular structures were scattered throughout the striatum and globus pallidus of all samples. Most of these granular structures were observed in glial fibrillary acidic protein-positive astrocytes. In addition, BDNF-positive neurites were abundant in the striatum of all MSA patients, and numerous BDNF-positive varicose fibers were found in the globus pallidus of some MSA cases with particularly severe striatal involvement. These observations suggest that the upregulated expression of BDNF may occur as a protective mechanism in the striatum of MSA patients, and that severe striatal degeneration may cause the aberrant accumulation of BDNF in the striatal projection areas of the globus pallidus of MSA patients.     

Hydrogen sulfide enhances adult neurogenesis in a mouse model of Parkinson’s disease

Hydrogen sulfide (H₂S) is regarded to be a protectant against diseases of the central nervous system and cardiovascular system. However, the mechanism by which H₂S elicits neuroprotective effects in the progression of Parkinson’s disease (PD) remains unclear. To investigate the role of H₂S in delaying the pathological process of PD, we used the most common sodium hydrosulfide (NaHS) as an H₂S donor and established a mouse model of PD induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid (MPTP/p) in the present study. Our results show that H₂S reduced neuronal loss during the progression of PD. Notably, we found that H₂S exhibited protective effects on dopaminergic neurons. Excitingly, H₂S also increased the proliferation of neural stem cells in the subventricular zone. Next, we evaluated whether the neuroprotective effects of H₂S on dopaminergic neurons in PD are dependent on adult nerve regeneration by treating primary adult neural stem cells cultured ex vivo with 1-methyl-4-phenylpyridine. Our results show that H₂S could prevent nerve injury induced by 1-methyl-4-phenylpyridine, promote the growth of neurospheres, and promote neurogenesis by regulating Akt/glycogen synthase kinase-3β/β-catenin pathways in adult neural stem cells. These findings confirm that H₂S can increase neurogenesis in an adult mouse model of PD by regulating the Akt/glycogen synthase kinase-3β/β-catenin signaling pathway. This study was approved by the Animal Care and Use Committee of Nanjing Medical University, China (IACUC Approval No. 1601153-3).

Chinese Library Classification No. R453; R741; TQ125.1+2     

Neuromelanin Activates Microglia and Induces Degeneration of Dopaminergic Neurons: Implications for Progression of Parkinson’s Disease

In Parkinson’s disease (PD), there is a progressive loss of neuromelanin (NM)-containing dopamine neurons in substantia nigra (SN) which is associated with microgliosis and presence of extracellular NM. Herein, we have investigated the interplay between microglia and human NM on the degeneration of SN dopaminergic neurons. Although NM particles are phagocytized and degraded by microglia within minutes in vitro, extracellular NM particles induce microglial activation and ensuing production of superoxide, nitric oxide, hydrogen peroxide (H₂O₂), and pro-inflammatory factors. Furthermore, NM produces, in a microglia-depended manner, neurodegeneration in primary ventral midbrain cultures. Neurodegeneration was effectively attenuated with microglia derived from mice deficient in macrophage antigen complex-1, a microglial integrin receptor involved in the initiation of phagocytosis. Neuronal loss was also attenuated with microglia derived from mice deficient in phagocytic oxidase, a subunit of NADPH oxidase, that is responsible for superoxide and H₂O₂ production, or apocynin, an NADPH oxidase inhibitor. In vivo, NM injected into rat SN produces microgliosis and a loss of tyrosine hydroxylase neurons. Thus, these results show that extracellular NM can activate microglia, which in turn may induce dopaminergic neurodegeneration in PD. Our study may have far-reaching implications, both pathogenic and therapeutic.     

Preladenant, a selective A2A receptor antagonist, is active in primate models of movement disorders

Parkinson's Disease (PD) and Extrapyramidal Syndrome (EPS) are movement disorders that result from degeneration of the dopaminergic input to the striatum and chronic inhibition of striatal dopamine D₂ receptors by antipsychotics, respectively. Adenosine A_2A receptors are selectively localized in the basal ganglia, primarily in the striatopallidal (“indirect”) pathway, where they appear to operate in concert with D₂ receptors and have been suggested to drive striatopallidal output balance. In cases of dopaminergic hypofunction, A_2A receptor activation contributes to the overdrive of the indirect pathway. A_2A receptor antagonists, therefore, have the potential to restore this inhibitor imbalance. Consequently, A_2A receptor antagonists have therapeutic potential in diseases of dopaminergic hypofunction such as PD and EPS. Targeting the A_2A receptor may also be a way to avoid the issues associated with direct dopamine agonists. Recently, preladenant was identified as a potent and highly selective A_2A receptor antagonist, and has produced a significant improvement in motor function in rodent models of PD. Here we investigate the effects of preladenant in two primate movement disorder models. In MPTP-treated cynomolgus monkeys, preladenant (1 or 3 mg/kg; PO) improved motor ability and did not evoke any dopaminergic-mediated dyskinetic or motor complications. In Cebus apella monkeys with a history of chronic haloperidol treatment, preladenant (0.3–3.0 mg/kg; PO) delayed the onset of EPS symptoms evoked by an acute haloperidol challenge. Collectively, these data support the use of preladenant for the treatment of PD and antipsychotic-induced movement disorders.     

Adenosine–Dopamine Interactions in the Pathophysiology and Treatment of CNS Disorders

Adenosine–dopamine interactions in the central nervous system (CNS) have been studied for many years in view of their relevance for disorders of the CNS and their treatments. The discovery of adenosine and dopamine receptor containing receptor mosaics (RM, higher‐order receptor heteromers) in the striatum opened up a new understanding of these interactions. Initial findings indicated the existence of A_2AR‐D₂R heterodimers and A₁R‐D₁R heterodimers in the striatum that were followed by indications for the existence of striatal A_2AR‐D₃R and A_2AR‐D₄R heterodimers. Of particular interest was the demonstration that antagonistic allosteric A_2A‐D₂ and A₁‐D₁ receptor–receptor interactions take place in striatal A_2AR‐D₂R and A₁R‐D₁R heteromers. As a consequence, additional characterization of these heterodimers led to new aspects on the pathophysiology of Parkinson's disease (PD), schizophrenia, drug addiction, and l ‐DOPA‐induced dyskinesias relevant for their treatments. In fact, A_2AR antagonists were introduced in the symptomatic treatment of PD in view of the discovery of the antagonistic A_2AR–D₂R interaction in the dorsal striatum that leads to reduced D₂R recognition and G_i/o coupling in striato‐pallidal GABAergic neurons. In recent years, indications have been obtained that A_2AR‐D₂R and A₁R‐D₁R heteromers do not exist as heterodimers, rather as RM. In fact, A_2A‐CB₁‐D₂ RM and A_2A‐D₂‐mGlu₅ RM have been discovered using a sequential BRET‐FRET technique and by using the BRET technique in combination with bimolecular fluorescence complementation. Thus, other pathogenic mechanisms beside the well‐known alterations in the release and/or decoding of dopamine in the basal ganglia and limbic system are involved in PD, schizophrenia and drug addiction. In fact, alterations in the stoichiometry and/or topology of A_2A‐CB₁‐D₂ and A_2A‐D₂‐mGlu5 RM may play a role. Thus, the integrative receptor–receptor interactions in these RM give novel aspects on the pathophysiology and treatment strategies, based on combined treatments, for PD, schizophrenia, and drug addiction.     

Regulation of dopamine receptor and neuropeptide expression in the basal ganglia of monkeys treated with MPTP

In Parkinson's disease (PD), striatal dopamine deficiency has been associated with complex changes in the functional and neurochemical anatomy of the basal ganglia. In this study, we simultaneously analyzed the regulation of D1 and D2 dopamine receptors and levels of the neuropeptides, substance P, and enkephalin (ENK) in various basal ganglia nuclei following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic denervation of striatum in nonhuman primates. Both unilateral and bilateral lesioned animals were used for this study. Striatal dopamine deficiency resulted in distinct alterations in D1, D2, substance P, and enkephalin levels and distribution: (1) Both D1 and D2 protein levels were significantly up-regulated in striatum. (2) There was an overall up-regulation of striatal substance P expression following dopamine denervation. (3) Substance P distribution was 'reversed' in dopamine depleted striatum: striosomes, which normally express higher levels of substance P, showed decreased expression, whereas substance P expression was up-regulated in the matrix. (4) Substance P expression was up-regulated in the internal segment of the globus pallidus (GPi), but remained unchanged in substantia nigra (SN). (5) Enkephalin levels were increased in striatum and the external segment of the globus pallidus (GPe), but not in substantia nigra. All the changes were more pronounced in the bilateral lesioned monkeys, though the data represent a pooled statistical evaluation of unilateral and bilateral lesioned monkeys. Our studies indicate that D1 and D2 dopamine receptors and substance P and enkephalin undergo regulatory changes in response to nigrostriatal dopamine denervation. Simultaneous study of the alterations in these various components of the 'direct' and 'indirect' pathways in the same animals will enable better understanding of the pathophysiology of PD and its therapeutic targets.     

Neuroprotective Effect of Ghrelin in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Mouse Model of Parkinson’s Disease by Blocking Microglial Activation

Ghrelin is an endogenous ligand for growth hormone (GH) secretagogue receptor 1a (GHS-R1a) and is produced and released mainly from the stomach. It was recently demonstrated that ghrelin can function as a neuroprotective factor by inhibiting apoptotic pathways. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic neurotoxicity in rodents; previous studies suggest that activated microglia actively participate in the pathogenesis of Parkinson’s disease (PD) neurodegeneration. However, the role of microglia in the neuroprotective properties of ghrelin is still unknown. Here we show that, in the mouse MPTP PD model generated by an acute regimen of MPTP administration, systemic administration of ghrelin significantly attenuates the loss of substantia nigra pars compacta (SNpc) neurons and the striatal dopaminergic fibers through the activation of GHS-R1a. We also found that ghrelin reduced nitrotyrosine levels and improved the impairment of rota-rod performance. Ghrelin prevents MPTP-induced microglial activation in the SNpc and striatum, the expression of pro-inflammatory molecules tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β), and the activation of inducible nitric oxide synthase. The inhibitory effect of ghrelin on the activation of microglia appears to be indirect by suppressing matrix metalloproteinase-3 (MMP-3) expression in stressed dopaminergic neurons because GHS-R1a is not expressed in SNpc microglial cells. Finally, in vitro administration of ghrelin prevented 1-methyl-4-phenylpyridinium-induced dopaminergic cell loss, MMP-3 expression, microglial activation, and the subsequent release of TNF-α, IL-1β, and nitrite in mesencephalic cultures. Our data indicate that ghrelin may act as a survival factor for dopaminergic neurons by functioning as a microglia-deactivating factor and suggest that ghrelin may be a valuable therapeutic agent for neurodegenerative diseases such as PD.     

Intrastriatal administration of botulinum neurotoxin A normalizes striatal D2R binding and reduces striatal D1R binding in male hemiparkinsonian rats

Cerebral administration of botulinum neurotoxin A (BoNT‐A) has been shown to improve disease‐specific motor behavior in a rat model of Parkinson disease (PD). Since the dopaminergic system of the basal ganglia fundamentally contributes to motor function, we investigated the impact of BoNT‐A on striatal dopamine receptor expression using in vitro and in vivo imaging techniques (positron emission tomography and quantitative autoradiography, respectively). Seventeen male Wistar rats were unilaterally lesioned with 6‐hydroxydopamine (6‐OHDA) and assigned to two treatment groups 7 weeks later: 10 rats were treated ipsilaterally with an intrastriatal injection of 1 ng BoNT‐A, while the others received vehicle (n = 7). All animals were tested for asymmetric motor behavior (apomorphine‐induced rotations and forelimb usage) and for striatal expression of dopamine receptors and transporters (D₁R, D₂R, and DAT). The striatal D₂R availability was also quantified longitudinally (1.5, 3, and 5 months after intervention) in 5 animals per treatment group. The 6‐OHDA lesion alone induced a unilateral PD‐like phenotype and a 13% increase of striatal D₂R. BoNT‐A treatment reduced the asymmetry in both apomorphine‐induced rotational behavior and D₂R expression, with the latter returning to normal values 5 months after intervention. D₁R expression was significantly reduced, while DAT concentrations showed no alteration. Independent of the treatment, higher interhemispheric symmetry in raclopride binding to D₂R was generally associated with reduced forelimb akinesia. Our findings indicate that striatal BoNT‐A treatment diminishes motor impairment and induces changes in D₁ and D₂ binding site density in the 6‐OHDA rat model of PD.     

Extrapontine myelinolysis with parkinsonism after rapid correction of hyponatremia: high cerebrospinal fluid level of homovanillic acid and successful dopaminergic treatment

Extrapontine myelinolysis (EPM) is a demyelinating process of the brain. We report the case of an 11-year-old girl who developed EPM with parkinsonism. Magnetic resonance imaging revealed demyelinating patterns in the basal ganglia without central pontine lesions. The cerebrospinal fluid levels of homovanillic acid and 5-hydroxyindoleacetic acid were high at the time of onset and normalized upon complete recovery from extrapyramidal symptoms after a dopaminergic treatment. We speculated that demyelination of nerve fibers containing dopamine receptors in the striatum might be a main cause of these symptoms.