Number Of Dopamine Research Articles

Impact of age on the rotenone-induced sporadic Parkinson's disease model using Drosophila melanogaster

Rotenone, a naturally occurring toxin, has been used to induce sporadic Parkinson's disease (PD) in Drosophila melanogaster for decades. However, the age of flies varies considerably between studies in this model. To investigate the impact of age on the rotenone-induced PD model, we collected male flies at the age of 1, 5, 7, and 10 days post-eclosion, respectively. Then, flies were immediately exposed to a feeding medium supplemented with 250 μM rotenone for seven days. The motor ability of Drosophila was detected by negative geotaxis assay, and the number of dopamine (DA) neurons and tyrosine hydroxylase (TH) expression levels were evaluated. The results showed that both the motor deficits and mortality increased with age. The flies older than five days showed typical PD features, including the loss of DA neurons, decreased TH expression levels, and decreased locomotive ability. However, 1-day-old flies displayed an unstable motor deficit and little TH expression changes after seven days of rotenone exposure. Lastly, after 7 days of exposure to rotenone, the death rate of flies rapidly increased with increasing starting age. The death rates of 1-, 5-, 7-, and 10-days old flies were 10.0%, 22.8%, 41.5%, and 50.4%, respectively. The findings of this study suggest that age is a crucial factor impacting the Drosophila PD model. This information provides a reference for the age selection to use this model for future studies.

Reduced density of noradrenergic fibers without prominent neuron loss or tau pathology in the locus coeruleus in APP knock‐in mouse models of Aβ amyloidosis

AbstractBackgroundLocus coeruleus (LC) is a nucleus containing the cell bodies of noradrenergic neurons in the brain, and is one of the earliest regions affected by Alzheimer’s disease (AD). Norepinephrine (NE) is critical for cognitive functions as well as anti‐inflammatory and neuroprotective properties, both of which are implicated in AD. LC neurons are among the first to display tau pathology and that significant loss of forebrain noradrenergic projections is evident at prodromal stage of AD, suggesting that abnormality in LC‐NE system initiates the disease pathogenesis. However, mechanisms underlying neurodegeneration in LC‐NE system remain elusive. We have previously reported that AppNL‐G‐F/NL‐G‐F mice, which harbor three familial AD mutations (Swedish, Beyreuther/Iberian, and Arctic) exhibited cognitive deficits and severe neuroinflammation accompanied by massive amyloid‐β (Aβ) pathology. In this study, we asked whether and how LC‐NE system is altered in AppNL‐G‐F/NL‐G‐F mice.MethodTo ask whether AppNL‐G‐F/NL‐G‐F mice exhibit noradrenergic degeneration, we compared the density of norepinephrine transporter (NET)‐positive fibers in the cortex and hippocampus as well as the number of dopamine β‐hydroxylase (DBH)‐positive neurons in the LC between AppNL‐G‐F/NL‐G‐F and wild‐type (WT) C57BL/6J mice at 24 months of age. We also examined whether tau pathology occurs in the LC‐NE system in these mice.ResultHistochemical analyses revealed that 24‐month‐old AppNL‐G‐F/NL‐G‐F mice exhibited significant decreases in the density of NET‐positive fibers in the prefrontal and entorhinal cortices and the hippocampal CA1, the regions associated with learning and memory, compared to WT mice. In contrast, AppNL‐G‐F/NL‐G‐F mice did not display loss of DBH‐positive neurons in the LC even at 24 months of age. Furthermore, AppNL‐G‐F/NL‐G‐F mice did not develop prominent tau pathology either in the nerve terminals or in the cell bodies of LC neurons.ConclusionThis study demonstrates that Aβ pathology is sufficient to reduce the density of noradrenergic fibers independent of neuron loss and tau pathology in the LC. These results also suggest that age‐dependent accumulation of Aβ in the cortex or tau in the LC may additively and independently damage LC neurons from the nerve terminals or from the cell bodies, respectively.

The interactions of dopamine and oxidative damage in the striatum of patients with neurodegenerative diseases.

The striatum with a number of dopamine containing neurons, receiving projections from the substantia nigra and ventral tegmental area; plays a critical role in neurodegenerative diseases of motor and memory function. Additionally, oxidative damage to nucleic acid may be vital in the development of age‐associated neurodegeneration. The metabolism of dopamine is recognized as one of the sources of reactive oxygen species through the Fenton mechanism. The proposed interactions of oxidative insults and dopamine in the striatum during the progression of diseases are the hypotheses of most interest to our study. This study investigated the possibility of significant interactions between these molecules that are involved in the late‐stage of Alzheimer's disease (AD), Parkinson disease (PD), Parkinson disease dementia, dementia with Lewy bodies, and controls using ELISA assays, autoradiography, and mRNA in situ hybridization assay. Interestingly, lower DNA/RNA oxidative adducts levels in the caudate and putamen of diseased brains were observed with the exception of an increased DNA oxidative product in the caudate of AD brains. Similar changes were found for dopamine concentration and vesicular monoamine transporter 2 densities. We also found that downstream pre‐synaptic dopamine D1 Receptor binding correlated with dopamine loss in Lewy body disease groups, and RNA damage and β‐site APP cleaving enzyme 1 in the caudate of AD. This is the first demonstration of region‐specific alterations of DNA/RNA oxidative damage which cannot be viewed in isolation, but rather in connection with the interrelationship between different neuronal events; chiefly DNA oxidative adducts and density of vesicular monoamine transporter 2 densities in AD and PD patients.

The NLRP3 Inflammasome is Involved in the Pathogenesis of Parkinson’s Disease in Rats

The etiology and pathogenesis of Parkinson'sdisease (PD) are complicated and have not been fully elucidated, but an important association has been identified between inflammation and PD. In this study, we investigated the role of the nucleotide-binding oligomerization domain, leucine rich repeat and pyrin domain-containing (NLRP) 3 inflammasome, consisting of NLRP3, caspase-1 and cytokines of the IL-1 family, in lipopolysaccharide (LPS)-induced and 6-hydroxydopamine (6-OHDA)-induced PD rats. Microinjection of different doses of caspase-1 inhibitor (Ac-YVAD-CMK, 300 or 1200ng/rat) was performed for seven consecutive days. Then, rotational behavior, the number of dopamine (DA) neurons in the substantia nigra pars compacta (SNc), and the mRNA and protein expression levels of NLRP3 inflammasome components were measured 14 days after the microinjection setup was established. Results showed that high mRNA and protein expression levels of NLRP3 inflammasome components were observed in the injected side of the LPS- and 6-OHDA-induced PDrats; Ac-YVAD-CMK inhibited the mRNA and protein expression of NLRP3 inflammasome components in both LPS- and 6-OHDA-induced PD rats. Moreover, the number of rotations was significantly decreased, and the number of DA neurons in the SNc improved. Our data indicate that the NLRP3 inflammasome participates in the pathogenesis of PD and that inhibiting the downstream pathway of the NLRP3/caspase-1/IL-1β axis can alleviate the occurrence of PD symptoms, providing a new basis for the prevention and treatment of PD.

Dopamine D3 receptor‐preferring agonists induce neurotrophic effects on mesencephalic dopamine neurons

Anti-parkinsonian agents, pramipexole (PPX) and ropinirole (ROP), have been reported to possess neuroprotective properties, both in vitro and in vivo. The mechanisms underlying neuroprotection afforded by the D3-preferring receptor agonists remain poorly understood. The present study demonstrates that incubation of primary mesencephalic cultures with PPX and ROP or the conditioned medium from PPX- or ROP-treated primary cultures induced a marked increase in the number of dopamine (DA) neurons in the cultures. Similar effects can be observed after incubating with the conditioned medium derived from PPX- and ROP-treated substantia nigra astroglia. Meanwhile, PPX and ROP can protect the primary cells from insult of 1-methyl-4-phenylpyridinium (MPP+), the active metabolite of the neurotoxin 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP). Furthermore, the neurotrophic effects of PPX and ROP on mesencephalic dopamine neurons could be significantly blocked by D3 receptor antagonist, but not by D2 receptor antagonist. Moreover, we found that the levels of glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) in the conditioned medium of mesencephalic cultures treated with PPX and ROP were significantly increased. Blocking GDNF and BDNF with the neutralizing antibodies, the neurotrophic effects of PPX and ROP were greatly diminished. These results suggest that D3 dopamine receptor-preferring agonists, PPX and ROP, exert neurotrophic effects on cultured DA neurons by modulating the production of endogenous GDNF and BDNF, which may participate in their neuroprotection.

Is obesity an inflammatory condition?

Obesity may be a low-grade systemic inflammatory disease. Overweight and obese children and adults have elevated serum levels of C-reactive protein, interleukin-6, tumor necrosis factor-α, and leptin, which are known markers of inflammation and closely associated with cardiovascular risk factors and cardiovascular and non-cardiovascular causes of death. This may explain the increased risk of diabetes, heart disease, and many other chronic diseases in the obese. The complex interaction between several neurotransmitters such as dopamine, serotonin, neuropeptide Y, leptin, acetylcholine, melanin-concentrating hormone, ghrelin, nitric oxide, and cytokines and insulin and insulin receptors in the brain ultimately determines and regulates food intake. Breast-feeding of more than 12 mo is associated with decreased incidence of obesity. Breast milk is a rich source of long-chain polyunsaturated fatty acids (LCPUFAs) and brain is especially rich in these fatty acids. LCPUFAs inhibit the production of proinflammatory cytokines and enhance the number of insulin receptors in various tissues and the actions of insulin and several neurotransmitters. LCPUFAs may enhance the production of bone morphogenetic proteins, which participate in neurogenesis, so these fatty acids might play an important role in brain development and function. It is proposed that obesity is a result of inadequate breast feeding, which results in marginal deficiency of LCPUFAs during the critical stages of brain development. This results in an imbalance in the structure, function, and feedback loops among various neurotransmitters and their receptors, which ultimately leads to a decrease in the number of dopamine and insulin receptors in the brain. Hence, promoting prolonged breast feeding may decrease the prevalence of obesity. Exercise enhances parasympathetic tone, promotes antiinflammation, and augments brain acetylcholine and dopamine levels, events that suppress appetite. Acetylcholine and insulin inhibit the production of proinflammatory cytokines and provide a negative feedback loop for postprandial inhibition of food intake, in part, by regulating leptin action. Statins, peroxisome proliferator-activated receptor-γ binding agents, non-steroidal antiinflammatory drugs, and infant formulas supplemented with LCPUFAs, and LCPUFAs themselves, which suppress inflammation, may be beneficial in obesity.

Chronic methamphetamine administration inhibits cerebral ischemia-induced hyperactivity in Mongolian gerbils

The effect of single and chronic methamphetamine (MAP) administration on ischemia-induced hyperactivity was investigated and the mechanism of ischemia-induced hyperactivity was discussed. Ischemia-induced hyperactivity was recognized 3 h after ischemia. However, ischemia-induced hyperactivity at 1 day after ischemia was inhibited when MAP, in a dose of 10 mg/kg, was administered for 7 days and withdrawn for 7 days. It was reported that MAP treatment caused an irreversible decrease in the number of dopamine (DA) uptake sites. In addition to this, monoamine oxidase and the uptake of DA into the nerve terminals are disturbed by cerebral ischemia. Therefore, a lot of DA release happened during and immediately after ischemia, and a marked down-regulation of DA receptor occurred 24 h after ischemia in MAP-injected group. It is conceivable that the DA receptor, especially the presynaptic DA uptake site, is related to the occurrence of ischemia-induced hyperactivity. Further studies appear to be necessary to clarify acceptor susceptibility when neurotransmitters are normalized after transient ischemia.

A new computer-assisted two-way avoidance conditioning equipment for rats: Behavioral and pharmacological validation

A new PC-controlled two-way avoidance conditioning equipment for rats is described. The position of the rat within the two-compartment shuttle-box is monitored by means of 4 + 4 horizontal photocell beams. Experimental conditions and procedures, such as CS-UCS interval, photocell operations, shock strength, and so on, can conveniently be preset by the experimenter. The successful operation of the shuttle-box is evidenced by rapid and efficient acquisition of the avoidance behavior, and approximately 100% median avoidance performance was obtained within 5 successive days of training (20–25 trials per day). In a separate experiment, different groups of rats received avoidance training (0–5 sessions) at 8 weeks of age, and a retention avoidance performance was weak ( r = 0.33, NS), and performance during the acquisition process appears to be a poor predictor of final performance. As expected, a number of dopamine (DA) receptor blocking agents (DA D 1 and/or D 2 selective) produced a selective suppression of the avoidance behavior, that is, the suppression of avoidance responding was matched by a corresponding increase in escape responding (with no escape failures).

Densities of dopamine D 2 receptors are reduced in CNS regions of alcohol-preferring P rats

The densities of dopamine D 2 recognition sites labelled with [ 3H]sulpiride were determined in the caudate-putamen, nucleus accumbens (medial and lateral portions), olfactory tubercle, substantia nigra (pars reticulata and pars compacta), and ventral tegmental area (VTA) of alcohol-naive, selectively bred P ( N = 7) and NP ( N = 7) rats using quantitative autoradiography. The binding of [ 3H]sulpiride was 20–25% lower ( P < 0.05) in the caudate-putamen, medial and lateral nucleus accumbens, and VTA of the P compared with the NP rats. No significant differences were observed between the P and NP rats in the olfactory tubercle or substantia nigra. [ 3H]Sulpiride binding, using standard membrane preparations, established with Scatchard analysis that the difference in the densities of D 2 recognition sites in the caudate-putamen between the P and NP rats was due to lower B max values for the P line. The results indicate that the number of dopamine D 2 receptor sites is lower in several central nervous system regions of the P rats compared to NP rats.

Persistent effects of subchronic toluene exposure on spatial learning and memory, dopamine-mediated locomotor activity and dopamine D 2 agonist binding in the rat

The effects of subchronic inhalation exposure to toluene (80 ppm, for 4 weeks, 5 days/week, 6 h/day) was studied on spatial learning (postexposure days 3–6) and memory (postexposure day 14) using a water maze, on spontaneous and apomorphine-induced (1 mg/kg, subcutaneously (s.c.)) locomotor activity (postexposyre day 17) and on the binding parameters of the dopamine D 2 agonist S(−)[ N-propyl- 3H(N)]propylnorapomorphine ([H]NPA) in membrane preparations of the neostriatum of the rat. Toluene treatment was found to cause a statistically significant impairment in acquisition and retention of the spatial learning task. Furthermore, toluene significantly increased (2-fold) apomorphine-induced locomotion and caused a trend for a 50–60% increase in motility without any significant effect on rearing. Spontaneous locomotion, motility and rearing were not affected by toluene. Toluene treatment produced a significant 30–40% increase in the B max values of [ 3H]NPA and a trend for a 20–30% increase in the K D values. These results indicate that subchronic exposure to toluene in low concentrations causes a slight but persistent deficit in spatial learning and memory, a persistent increase in dopamine-mediated locomotor activity and an increase in the number of dopamine D 2 receptors in the rat.

Effects of chronic ethanol intake at a low dose on the rat brain dopaminergic system

The effects of 8-week ethanol treatment (3% v/v in drinking water) on the rat brain dopaminergic system were investigated. Chronic ethanol consumption induced a significant increase in the number of dopamine D 1 receptor sites in the caudate putamen. Conversely, no significant changes were observed in D 2 receptor density or affinity. Biochemical results were in agreement with behavioral data, as amphetamine-induced locomotor hyperactivity was significantly higher in ethanol-treated rats in comparison to controls. Moreover, grooming behavior in response to SKF 38393, a selective agonist of D 1 receptors was potentiated in ethanol-treated rats, whereas locomotor hyperactivity induced by LY 171555 (a selective agonist of D 2 receptors) was not affected by ethanol treatment. The results indicate that changes in dopamine receptors may occur in the central nervous system at levels of ethanol intake that do not induce tolerance or dependence.

Studies on the effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on central catecholamine neurons in C57 BL/6 mice. Comparison with three other strains of mice

The effect of the parkinson-inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on central catecholamine neurons in C57 BL/6 mice has been studied employing neuro- and histochemical techniques. The number of dopamine (DA) cell bodies in substantia nigra pars compacta (SNC) was reduced by 70% in MPTP-treated C57 BL/6 mice, as demonstrated both by tyrosine hydroxylase (TH) immunohistochemistry and conventional histology (Cresyl violet staining) and an almost complete loss of DA fibers in striatum was also found. A detailed analysis of the effects of MPTP on endogenous catecholamine levels in various brain regions revealed that MPTP caused a severe reduction of endogenous DA in substantia nigra and striatum (35 and 5% of control) which was accompanied by an increase in the 3,4-dihydroxyphenylacetic acid (DOPAC)/DA ratio. There was also a decrease of DA in nucleus accumbens and the olfactory tubercle to 41 and 44% of control, respectively, without any significant change in the DOPAC/DA ratio and density of TH-positive fibers. Small but significant decreases of the noradrenaline (NA) levels in septum, entorhinal cortex and frontal cortex were seen, although the uptake of [ 3H]NA in frontal cortex was not significantly changed. Minor MPTP-induced decreases of the serotonin levels in frontal cortex, occipital cortex and spinal cord were also seen. The MPTP treatment also induced a 55% increase of adrenaline levels in hypothalamus, while no changes were seen in pons-medulla and spinal cord. Comparing this with 3 other strains of mice, the MPTP-induced reduction of endogenous DA in striatum was most pronounced in C57 BL/6, less in N.M.R.I. and CBA/Ca mice, and least in Swiss-Webster. Concerning the effect of MPTP on cortical NA levels, the same relation was at hand except for C57 BL/6, where, as mentioned, the effect was merely detectable. No reduction of DA perikarya in SNC was seen in Swiss-Webster mice. These findings show that in mice major differences exist in sensitivity of catecholamine neurons to MPTP between different strains. The data show that MPTP can produce an almost complete, permanent and relatively selective degeneration of the nigrostriatal DA neurons in C57 BL/6 mice similar to that seen in primates. This strain may therefore serve as a useful model for studies on various aspects of MPTP-induced parkinsonism.

Genetic determination of mesencephalic tyrosine hydroxylase activity in the mouse

The hereditary factors that affect mesencephalic tyrosine hydroxylase (TH) activity were investigated in highly inbred mouse strains (CXBI/ByJ, C57BL/6ByJ, and BALB/cJ). The progenitor strains and their F1 hybrids, were compared for mesencephalic TH activity with each other and with replicated F2 generations. Quantitative and non-parametric genetic analysis of the data raise the possibility that there is a major gene with robust additive effect that is primarily responsible for the difference between the progenitor strains with intermediate and high mesencephalic TH activity. Strain differences in mesencephalic TH activity have been linked to differences in number of dopamine (DA) neurons in that area. If genetic variation of mesencephalic TH activity is entirely attributable to variation in number of mesencephalic dopamine (DA) neurons, identification of the genetic sources of variation of mesencephalic TH activity may take us a step closer to animal models and preparations that are needed in the study of the physiological and constitutional mechanisms of human disorders in which DA neurotransmission is involved.