Single intranasal administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in C57BL/6 mice models early preclinical phase of Parkinson's disease

Beneficial effects of L-arginine on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neuronal degeneration in substantia nigra of Balb/c mice

BACKGROUND

L-arginine has been recently investigated and proposed to reduce neurological damage after various experimental models of neuronal cellular damage. In this study, we aim to evaluate the beneficial effects of L-arginine administration on the numerical density of dark neurons (DNs) in the substantia nigra pars compacta (SNc) of Balb/c mice subjected to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration.

MATERIALS AND METHODS

Male Balb/c mice were randomly divided into 4 groups (n = 7 each): MPTP only; saline only (control); MPTP + L-arginine; and L-arginine only. The animals were infused intranasally with a single intranasal administration of the proneurotoxin MPTP (1 mg/nostril). L-arginine (300 mg/kg) was administrated intraperitoneally once daily for 1-week starting from 3 days after MPTP administration. Cavalieri principle method was used to estimate the numerical density of DNs in the SNc of different studied groups.

RESULTS

Twenty days following MPTP administration, the number of DNs was significantly increased when compared to sham-control and L-arginine-control groups (P < 0.05). Nevertheless, our results showed that L-arginine administration significantly decreased the numerical density of DNs in SNc of mice.

CONCLUSION

This investigation provides new insights in experimental models of Parkinson's disease, indicating that L-arginine represents a potential treatment agent for dopaminergic neuron degeneration in SNc observed in Parkinson's disease patients.

The novel mechanism of rotenone-induced α-synuclein phosphorylation via reduced protein phosphatase 2A activity

Rotenone has been shown to induce many parkinsonian features and has been widely used in chemical models of Parkinson's disease (PD). Its use is closely associated with α-synuclein (α-syn) phosphorylation both in vivo and in vitro. However, the mechanisms whereby rotenone regulates α-syn phosphorylation remain unknown. Protein phosphatase 2A (PP2A) has been shown to play an important role in α-syn dephosphorylation. We therefore investigated if rotenone caused α-syn phosphorylation by down-regulation of PP2A activity in mice. Rotenone increased the phosphorylation of α-syn at Ser129, consistent with the inhibition of PP2A activity by increased phosphorylation of tyrosine 307 at the catalytic subunit of PP2A (pTyr307 PP2Ac). We further explored the interactions among rotenone, PP2A, and α-syn in SK-N-SH cells and primary rat cortical neurons. Rotenone inhibited PP2A activity via phosphorylation of PP2Ac at Tyr307. The reduction in PP2A activity and rotenone cytotoxicity were reversed by treatment with the PP2A agonist, C2 ceramide, and the Src kinase inhibitor, SKI606. Immunoprecipitation experiments showed that rotenone induced an increase in calmodulin-Src complex in SK-N-SH cells, thus activating Src kinase, which in turn phosphorylated PP2A at Tyr307 and inhibited its activity. C2 ceramide and SKI606 significantly reversed the rotenone-induced phosphorylation and aggregation of α-syn by increasing PP2A activity. These results demonstrate that rotenone-reduced PP2A activity via Src kinase is involved in the phosphorylation of α-syn. These findings clarify the novel mechanisms whereby rotenone can induce PD.

Succinobucol, a Non-Statin Hypocholesterolemic Drug, Prevents Premotor Symptoms and Nigrostriatal Neurodegeneration in an Experimental Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by non-motor and motor disabilities. This study investigated whether succinobucol (SUC) could mitigate nigrostriatal injury caused by intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in mice. Moreover, the effects of SUC against MPTP-induced behavioral impairments and neurochemical changes were also evaluated. The quantification of tyrosine hydroxylase-positive (TH⁺) cells was also performed in primary mesencephalic cultures to evaluate the effects of SUC against 1-methyl-4-phenylpyridinium (MPP⁺) toxicity in vitro. C57BL/6 mice were treated with SUC (10 mg/kg/day, intragastric (i.g.)) for 30 days, and thereafter, animals received MPTP infusion (1 mg/nostril) and SUC treatment continued for additional 15 days. MPTP-infused animals displayed significant non-motor symptoms including olfactory and short-term memory deficits evaluated in the olfactory discrimination, social recognition, and water maze tasks. These behavioral impairments were accompanied by inhibition of mitochondrial NADH dehydrogenase activity (complex I), as well as significant decrease of TH and dopamine transporter (DAT) immunoreactivity in the substantia nigra pars compacta and striatum. Although SUC treatment did not rescue NADH dehydrogenase activity inhibition, it was able to blunt MPTP-induced behavioral impairments and prevented the decrease in TH and DAT immunoreactivities in substantia nigra (SN) and striatum. SUC also suppressed striatal astroglial activation and increased interleukin-6 levels in MPTP-intoxicated mice. Furthermore, SUC significantly prevented the loss of TH⁺ neurons induced by MPP⁺ in primary mesencephalic cultures. These results provide new evidence that SUC treatment counteracts early non-motor symptoms and neurodegeneration/neuroinflammation in the nigrostriatal pathway induced by intranasal MPTP administration in mice by modulating events downstream to the mitochondrial NADH dehydrogenase inhibition.

Improved neuroprotective effects of resveratrol-loaded polysorbate 80-coated poly(lactide) nanoparticles in MPTP-induced Parkinsonism

AIM

This study investigated the neuroprotective effects of resveratrol (RVT)-loaded polysorbate 80 (PS80)-coated poly(lactide) nanoparticles in a mouse model of Parkinson's disease (PD), and compared these effects with those from bulk RVT.

METHODS

C57BL/6 mice received for 15 days RVT intraperitoneally (nanoparticulate or non-nanoparticulate), as well as single intranasal administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that damages dopaminergic neurons and induces PD-related symptoms.

RESULTS

MPTP induced significant impairments on olfactory discrimination and social recognition memory, as well as caused striatal oxidative stress and reduced the expression of tyrosine hydroxylase in striatum. RVT-loaded nanoparticles (but not bulk) displayed significant neuroprotection against MPTP-induced behavioral and neurochemical changes.

CONCLUSION

These results point to RVT-loaded poly(lactide)-nanoparticles coated with PS80 a promising nanomedical tool and adjuvant therapy for PD.

Protective Effects of Streblus asper Leaf Extract on H2O2-Induced ROS in SK-N-SH Cells and MPTP-Induced Parkinson's Disease-Like Symptoms in C57BL/6 Mouse

This study investigated the effects of Streblus asper leaf extract (SA) on reactive oxygen species (ROS) in SK-N-SH cell culture and on motor functions and behaviors in MPTP-treated C57BL/6 mice. SK-N-SH cell viability after incubation with SA for 24 h was measured by MTT assay. Intracellular ROS levels of SK-N-SH cells were quantified after pretreatment with SA (0, 200, 600, and 1000 µg/mL) in the presence of H2O2 (300 µM). Male C57BL/6 mice were force-fed with water or 200 mg/kg/day SA for 32 days. Intraperitoneal injection of MPTP was used to induce Parkinson's disease-like symptoms. Catalepsy, beam balance ability, olfactory discrimination, social recognition, and spontaneous locomotor activity were assessed on days 19, 21, 23, 26, and 32, respectively. In cell culture, SA at 200, 600, and 1000 µg/mL significantly decreased ROS levels in H2O2-treated SK-N-SH cells. MPTP-treated C57BL/6 mice showed a significant change in all parameters tested when compared to the control group. Pretreatment and concurrent treatment with 200 mg/kg/day SA could antagonize the motor and cognitive function deficits induced by MPTP. The results show that SA possesses anti-Parkinson effects in MPTP-treated C57BL/6 mice and that reduction in ROS levels might be one of the mechanisms.

Decreased synaptic plasticity in the medial prefrontal cortex underlies short-term memory deficits in 6-OHDA-lesioned rats

Parkinson's disease (PD) is characterized by motor dysfunction associated with dopaminergic degeneration in the dorsolateral striatum (DLS). However, motor symptoms in PD are often preceded by short-term memory deficits, which have been argued to involve deregulation of medial prefrontal cortex (mPFC). We now used a 6-hydroxydopamine (6-OHDA) rat PD model to explore if alterations of synaptic plasticity in DLS and mPFC underlie short-term memory impairments in PD prodrome. The bilateral injection of 6-OHDA (20μg/hemisphere) in the DLS caused a marked loss of dopaminergic neurons in the substantia nigra (>80%) and decreased monoamine levels in the striatum and PFC, accompanied by motor deficits evaluated after 21 days in the open field and accelerated rotarod. A lower dose of 6-OHDA (10μg/hemisphere) only induced a partial degeneration (about 60%) of dopaminergic neurons in the substantia nigra with no gross motor impairments, thus mimicking an early premotor stage of PD. Notably, 6-OHDA (10μg)-lesioned rats displayed decreased monoamine levels in the PFC as well as short-term memory deficits evaluated in the novel object discrimination and in the modified Y-maze tasks; this was accompanied by a selective decrease in the amplitude of long-term potentiation in the mPFC, but not in DLS, without changes of synaptic transmission in either brain regions. These results indicate that the short-term memory dysfunction predating the motor alterations in the 6-OHDA model of PD is associated with selective changes of information processing in PFC circuits, typified by persistent changes of synaptic plasticity.

Effects of treadmill exercise on hippocampal neurogenesis in an MPTP /probenecid-induced Parkinson's disease mouse model

[Purpose] This study aimed to investigate the effect of treadmill exercise on non-motor function, specifically long-term memory, in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid-induced Parkinson’s disease mouse model. [Methods] A mouse model of Parkinson’s disease was developed by injecting 20 mg/kg of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 250 mg/kg of probenecid (P). We divided in into four groups: probenecid group, probenecid-exercise group, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid group, and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid-exercise group. Mice in the exercise groups ran on treadmill for 30 min/day, five times per week for 4 weeks. [Results] Latency in the passive avoidance test increased in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid-exercise group compared with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid group. In addition, the number of 5-bromo-2-deoxyuridine/NeuN-positive cells and 5-bromo-2-deoxyuridine/doublecortin-positive cells in the hippocampal dentate gyrus was higher in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid-exercise group than that in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid group. These changes were associated with the expression of brain-derived neurotrophic factor in the hippocampus. [Conclusion] Our results suggest that treadmill exercise may improve long-term memory in Parkinson’s disease mice by facilitating neurogenesis via increased expression of neurotrophic factors.

CX3CR1 Disruption Differentially Influences Dopaminergic Neuron Degeneration in Parkinsonian Mice Depending on the Neurotoxin and Route of Administration

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons accompanied by an inflammatory reaction. The neuron-derived chemokine fractalkine (CX3CL1) is an exclusive ligand for the receptor CX3CR1 expressed on microglia. The CX3CL1/CX3CR1 signaling is important for sustaining microglial activity. Using a recently developed PD model, in which the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxin is delivered intranasally, we hypothesized that CX3CR1 could play a role in neurotoxicity and glial activation. For this, we used CX3CR1 knock-in mice and compared results with those obtained using the classical PD models through intraperitonal MPTP or intrastriatal 6-hydroxydopamine (6-OHDA). The striatum from all genotypes (CX3CR1(+/+), CX3CR1(+/GFP) and CX3CR1-deficient mice) showed a significant dopaminergic depletion after intranasal MPTP inoculation. In contrast to that, we could not see differences in the number of dopaminergic neurons in the substantia nigra of CX3CR1-deficient animals. Similarly, after 6-OHDA infusion, the CX3CR1 deletion decreased the amphetamine-induced turning behavior observed in CX3CR1(+/GFP) mice. After the 6-OHDA inoculation, a minor dopaminergic neuronal loss was observed in the substantia nigra from CX3CR1-deficient mice. Distinctly, a more extensive neuronal cell loss was observed in the substantia nigra after the intraperitoneal MPTP injection in CX3CR1 disrupted animals, corroborating previous results. Intranasal and intraperitoneal MPTP inoculation induced a similar microgliosis in CX3CR1-deficient mice but a dissimilar change in the astrocyte proliferation in the substantia nigra. Nigral astrocyte proliferation was observed only after intraperitoneal MPTP inoculation. In conclusion, intranasal MPTP and 6-OHDA lesion in CX3CR1-deficient mice yield no nigral dopaminergic neuron loss, linked to the absence of astroglial proliferation.

Developmental exposure to manganese induces lasting motor and cognitive impairment in rats

Exposure to high manganese (Mn) levels may damage the basal ganglia, leading to a syndrome analogous to Parkinson's disease, with motor and cognitive impairments. The molecular mechanisms underlying Mn neurotoxicity, particularly during development, still deserve further investigation. Herein, we addressed whether early-life Mn exposure affects motor coordination and cognitive function in adulthood and potential underlying mechanisms. Male Wistar rats were exposed intraperitoneally to saline (control) or MnCl2 (5, 10 or 20 mg/kg/day) from post-natal day (PND) 8-12. Behavioral tests were performed on PND 60-65 and biochemical analysis in the striatum and hippocampus were performed on PND14 or PND70. Rats exposed to Mn (10 and 20 mg/kg) performed significantly worse on the rotarod test than controls indicating motor coordination and balance impairments. The object and social recognition tasks were used to evaluate short-term memory. Rats exposed to the highest Mn dose failed to recognize a familiar object when replaced by a novel object as well as to recognize a familiar juvenile rat after a short period of time. However, Mn did not alter olfactory discrimination ability. In addition, Mn-treated rats displayed decreased levels of non-protein thiols (e.g. glutathione) and increased levels of glial fibrillary acidic protein (GFAP) in the striatum. Moreover, Mn significantly increased hippocampal glutathione peroxidase (GPx) activity. These findings demonstrate that acute low-level exposure to Mn during a critical neurodevelopmental period causes cognitive and motor dysfunctions that last into adulthood, that are accompanied by alterations in antioxidant defense system in both the hippocampus and striatum.

α-Asarone attenuates microglia-mediated neuroinflammation by inhibiting NF kappa B activation and mitigates MPTP-induced behavioral deficits in a mouse model of Parkinson's disease

The selective loss of dopaminergic neurons in Parkinson's disease (PD) is associated with microglial activation. Therefore, the importance of early therapeutic intervention to inhibit microglial activation would be an effective strategy to alleviate the progression of PD. α-Asarone, an active compound found in Araceae and Annonaceae plant species has been used to improve various disease conditions including central nervous system disorders. In the present study the in vitro and in vivo therapeutic effects of α-asarone isolated from the rhizome of Acorus gramineus Solander was evaluated on microglia-mediated neuroinflammation and neuroprotection. Lipopolysaccharide (LPS)-stimulated BV-2 microglial cells were used to evaluate in vitro effects. 1-methyl-4 phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced mouse model of PD was developed to study the neuroprotective effects of α-asarone in vivo. The results indicated that α-asarone significantly attenuated the LPS-stimulated increase in neuroinflammatory responses and suppressed pro-inflammatory cytokine production in BV-2 cells. Mechanistic study revealed that α-asarone inhibited the LPS-stimulated activation via regulation of nuclear factor kappa-B by blocking degradation of inhibitor kappa B-alpha signaling in BV-2 microglial cells. In in vivo studies, MPTP intoxication to mice resulted in brain microglial activation and significant behavioral deficits. Prophylactic treatment with α-asarone suppressed microglial activation and attenuated PD-like behavioral impairments as assessed by the Y-maze and pole tests. Taken together, these data demonstrate that α-asarone is a promising neuroprotective agent that should be further evaluated and developed for future prevention and treatment of microglia-mediated neuroinflammatory conditions including PD.

Neuroprotective changes in degeneration-related gene expression in the substantia nigra following acupuncture in an MPTP mouse model of Parkinsonism: Microarray analysis

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the death of dopamine-generating cells in the substantia nigra (SN). Acupuncture stimulation results in an enhanced survival of dopaminergic neurons in the SN in Parkinsonism animal models. The present study investigated changes in gene expression profiles measured using whole transcript array in the SN region related to the inhibitory effects of acupuncture in a chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) Parkinsonism model. In this model, acupuncture stimulation at GB34 and LR3 attenuated the decrease in tyrosine hydroxylase in the SN region; stimulation at non-acupoints did not suppress this decrease. Gene array analysis revealed that 22 (10 annotated genes: Cdh1, Itih2, Mpzl2, Rdh9, Serping1, Slc6a13, Slc6a20a, Slc6a4, Tph2, and Ucma) probes that were up-regulated in MPTP animals relative to controls were exclusively down-regulated by acupuncture stimulation. In addition, 17 (two annotated genes: 4921530L21Rik and Gm13931) probes that were down-regulated in MPTP animals compared to controls were exclusively up-regulated by acupuncture stimulation. These findings indicate that the 39 probes (12 annotated genes) affected by MPTP and acupuncture may be responsible for the inhibitory effects of acupuncture on degeneration-related gene expression in the SN following damage induced by MPTP intoxication.

Behavioral phenotyping of Parkin-deficient mice: looking for early preclinical features of Parkinson's disease

There is considerable evidence showing that the neurodegenerative processes that lead to sporadic Parkinson's disease (PD) begin many years before the appearance of the characteristic motor symptoms. Neuropsychiatric, sensorial and cognitive deficits are recognized as early non-motor manifestations of PD, and are not attenuated by the current anti-parkinsonian therapy. Although loss-of-function mutations in the parkin gene cause early-onset familial PD, Parkin-deficient mice do not display spontaneous degeneration of the nigrostriatal pathway or enhanced vulnerability to dopaminergic neurotoxins such as 6-OHDA and MPTP. Here, we employed adult homozygous C57BL/6 mice with parkin gene deletion on exon 3 (parkin^−/−) to further investigate the relevance of Parkin in the regulation of non-motor features, namely olfactory, emotional, cognitive and hippocampal synaptic plasticity. Parkin^−/− mice displayed normal performance on behavioral tests evaluating olfaction (olfactory discrimination), anxiety (elevated plus-maze), depressive-like behavior (forced swimming and tail suspension) and motor function (rotarod, grasping strength and pole). However, parkin^−/− mice displayed a poor performance in the open field habituation, object location and modified Y-maze tasks suggestive of procedural and short-term spatial memory deficits. These behavioral impairments were accompanied by impaired hippocampal long-term potentiation (LTP). These findings indicate that the genetic deletion of parkin causes deficiencies in hippocampal synaptic plasticity, resulting in memory deficits with no major olfactory, emotional or motor impairments. Therefore, parkin^−/− mice may represent a promising animal model to study the early stages of PD and for testing new therapeutic strategies to restore learning and memory and synaptic plasticity impairments in PD.

A mouse model of non-motor symptoms in Parkinson's disease: focus on pharmacological interventions targeting affective dysfunctions

Non-motor symptoms, including psychiatric disorders, are increasingly recognized as a major challenge in the treatment of Parkinson's disease (PD). These ailments, which often appear in the early stage of the disease, affect a large number of patients and are only partly resolved by conventional antiparkinsonian medications, such as L-DOPA. Here, we investigated non-motor symptoms of PD in a mouse model based on bilateral injection of the toxin 6-hydroxydopamine (6-OHDA) in the dorsal striatum. This model presented only subtle gait modifications, which did not affect horizontal motor activity in the open-field test. Bilateral 6-OHDA lesion also impaired olfactory discrimination, in line with the anosmia typically observed in early stage parkinsonism. The effect of 6-OHDA was then examined for mood-related dysfunctions. Lesioned mice showed increased immobility in the forced swim test and tail suspension test, two behavioral paradigms of depression. Moreover, the lesion exerted anxiogenic effects, as shown by reduced time spent in the open arms, in the elevated plus maze test, and by increased thigmotaxis in the open-field test. L-DOPA did not modify depressive- and anxiety-like behaviors, which were instead counteracted by the dopamine D2/D3 receptor agonist, pramipexole. Reboxetine, a noradrenaline reuptake inhibitor, was also able to revert the depressive and anxiogenic effects produced by the lesion with 6-OHDA. Interestingly, pre-treatment with desipramine prior to injection of 6-OHDA, which is commonly used to preserve noradrenaline neurons, did not modify the effect of the lesion on depressive- and anxiety-like behaviors. Thus, in the present model, mood-related conditions are independent of the reduction of noradrenaline caused by 6-OHDA. Based on these findings we propose that the anti-depressive and anxiolytic action of reboxetine is mediated by promoting dopamine transmission through blockade of dopamine uptake from residual noradrenergic terminals.

Olfaction in three genetic and two MPTP-induced Parkinson's disease mouse models

Various genetic or toxin-induced mouse models are frequently used for investigation of early PD pathology. Although olfactory impairment is known to precede motor symptoms by years, it is not known whether it is caused by impairments in the brain, the olfactory epithelium, or both. In this study, we investigated the olfactory function in three genetic Parkinson’s disease (PD) mouse models and mice treated with MPTP intraperitoneally and intranasally. To investigate olfactory function, we performed electro-olfactogram recordings (EOGs) and an olfactory behavior test (cookie-finding test). We show that neither a parkin knockout mouse strain, nor intraperitoneal MPTP treated animals display any olfactory impairment in EOG recordings and the applied behavior test. We also found no difference in the responses of the olfactory epithelium to odorants in a mouse strain over-expressing doubly mutated α-synuclein, while this mouse strain was not suitable to test olfaction in a cookie-finding test as it displays a mobility impairment. A transgenic mouse expressing mutated α-synuclein in dopaminergic neurons performed equal to control animals in the cookie-finding test. Further we show that intranasal MPTP application can cause functional damage of the olfactory epithelium.

α-Synuclein in the olfactory system in Parkinson's disease: role of neural connections on spreading pathology

Parkinson's disease (PD) is a neurodegenerative disease characterized by bradykinesia, rigidity, resting tremor, and postural instability. Neuropathologically, intracellular aggregates of α-synuclein in Lewy bodies and Lewy neurites appear in particular brain areas according to a sequence of stages. Clinical diagnosis is usually established when motor symptoms are evident (corresponding to Braak stage III or later), years or even decades after onset of the disease. Research at early stages is therefore essential to understand the etiology of PD and improve treatment. Although classically considered as a motor disease, non-motor symptoms have recently gained interest. Olfactory deficits are among the earliest non-motor features of PD. Interestingly, α-synuclein deposits are present in the olfactory bulb and anterior olfactory nucleus at Braak stage I. Several lines of evidence have led to proposals that PD pathology spreads by a prion-like mechanism via the olfactory and vagal systems to the substantia nigra. In this context, current data on the temporal appearance of α-synuclein aggregates in the olfactory system of both humans and transgenic mice are of particular relevance. In addition to the proposed retrograde nigral involvement via brainstem nuclei, olfactory pathways could potentially reach the substantia nigra, and the possibility of centrifugal progression warrants investigation. This review analyzes the involvement of α-synuclein in different elements of the olfactory system, in both humans and transgenic models, from the hodological perspective of possible anterograde and/or retrograde progression of this proteinopathy within the olfactory system and beyond-to the substantia nigra and the remainder of the central and peripheral nervous systems.

Intranasal and subcutaneous administration of dopamine D3 receptor agonists functionally restores nigrostriatal dopamine in MPTP-treated mice

Parkinson's disease (PD) is a neurodegenerative disease with a hallmark motor defect caused by the death of dopaminergic neurons in the substantia nigra. Intranasal drug administration may be useful for Parkinson's treatment because this route avoids first-pass metabolism and increases bioavailability in the brain. In this study, we investigated the neuroprotection/neurorestoration effect of dopamine D3 receptor (D3R) agonists administered via both intranasal and subcutaneous routes in the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced PD mouse model. Furthermore, we employed D3R knock-out mice to validate the dependence on D3R signaling. We found that in wild-type mice, but not D3 receptor knockout mice, both intranasal and subcutaneous administration of D3R agonists rescue dopamine (DA) depletion in the striatum as well as DA neuronal death in the substantia nigra after MPTP treatment. Moreover, subcutaneous 7-OH-DPAT administration significantly improved gait performance (stride length and overall running speed) of MPTP-lesioned mice after 7 and 14 days of recovery. In addition, the distribution of D3 agonist 7-OH-DPAT was measured in designated brain areas by mass spectrometry analysis after subcutaneous and intranasal administration. Our data suggest that intranasal administration of D3R agonist would be a practical approach to treat PD.

Evaluation of nigrostriatal neurodegeneration and neuroinflammation following repeated intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in mice, an experimental model of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting approximately 1% of the population older than 60 years. The administration of the proneurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice is the most widely used approach to elucidate the mechanisms of cell death involved in PD. However, the magnitude of the PD-like neurodegeneration induced by MPTP depends on many variables, including the regimen of its administration. It has been demonstrated that intranasal (i.n.) administration of MPTP constitutes a new route of toxin delivery to the brain that mimics environmental exposure to neurotoxins. Previous data showed that mice submitted to chronic and acute i.n. MPTP treatment displayed a robust (~80%) and moderate (~55%) loss of striatal dopamine, respectively. However, little is known about the neurodegenerative and neuroinflammatory processes following a subacute i.n. MPTP administration in mice. Here, the C57BL/6 mice were infused intranasally with MPTP (1 mg/nostril/day) during 4 consecutive days. At 7 and 28 days after the last administration, the subacute i.n. MPTP regime decreased the tyrosine hydroxylase (TH)-labeling in the striatum (40-50%) and substantia nigra (25-30%) and increased the astrogliosis in such brain areas at both time points. Taken together, our data showed that the subacute administration of MPTP into the nasal cavity of C57BL/6 mice induces long-lasting neurodegeneration and neuroinflammation in the nigrostriatal pathway, thus representing a valuable animal model for the investigation of neuroprotective strategies in PD.

Parkin-knockout mice did not display increased vulnerability to intranasal administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

The loss of nigral dopaminergic neurons in Parkinson's disease (PD) is believed to result from interactions between genetic susceptibility and environmental factors. Although loss-of-function mutations in the parkin gene cause early-onset familial PD, the hybrid 129Sv-C57BL/6 parkin-deficient mice did not display spontaneous degeneration of the nigrostriatal pathway or enhanced vulnerability to neurotoxicity induced by 6-hydroxydopamine (6-OHDA) or intraperitoneal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication. We aimed to re-evaluate the role of parkin in a pure C57BL/6 background after an acute intranasal (i.n.) MPTP administration, a new route of toxin delivery to the brain that mimics environmental exposure to neurotoxins. We found that the deficiency of parkin gene modifies the D-amphetamine-induced locomotion in saline-treated animals. Intranasal MPTP induced Parkinsonism in parkin⁺/⁺ mice, through depletion of striatal dopamine, decreased number of dopaminergic neurons in the substantia nigra, and decreased D-amphetamine-induced hyperlocomotion. Additionally, the deletion of the parkin gene in a pure C57BL/6 background did not lead to increased vulnerability to i.n. MPTP-induced neurotoxicity. Moreover, the i.n. MPTP induced nigral astrogliosis predominantly in the pars reticulata in wild type and parkin⁻/⁻ mice. Taken together, these results showed that the absence of parkin did not modify the vulnerability of nigrostriatal dopaminergic pathway after i.n. MPTP intoxication, suggesting that independently of mouse strain, the endogenous parkin is not required for protection of this system. These findings also suggest that the development of familial parkin-linked PD is not associated with exposure to environmental factors that specifically affects the dopaminergic system.

Anosmia does not impair the anxiolytic-like effect of lavender essential oil inhalation in mice

AIM

The inhalation of Lavandula angustifolia (lavender) essential oil has anxiolytic-like effects in animal models and humans, but its mechanism of action is still not fully understood. The inhalation of essential oils can induce anxiolytic effects through the central nervous system (e.g., lung absorption and bloodstream transport) or stimulation of the olfactory system and secondary activation of brain regions. Thus, the main objective of the present study was to evaluate whether the perception of lavender essential oil aroma, when inhaled, is necessary to obtain its anxiolytic-like effects in mice tested in the marble-burying test.

MAIN METHODS

Anosmia was induced by irrigating the nasal cavity with zinc gluconate+zinc acetate so that the mice could not detect odors in the olfactory discrimination test. The marble-burying test was used to evaluate the anxiolytic-like effects of inhaled lavender essential oil.

KEY FINDINGS

Anosmia did not interfere with the anxiolytic-like effect of lavender essential oil inhalation in the marble-burying test at concentrations of 2.5% (number of marbles buried: vehicle, 4.7±1.0; zinc, 6.2±2.2; p>0.10) and 5% (number of marbles buried: vehicle, 3.4±0.8; zinc, 4.3±0.9; p>0.10). Lavender essential oil at a concentration of 0.5% was ineffective.

SIGNIFICANCE

These results suggest that olfactory system activation is unlikely to participate in the anxiolytic-like effect of lavender essential oil inhalation.

Vascular-derived TGF-β increases in the stem cell niche and perturbs neurogenesis during aging and following irradiation in the adult mouse brain

Neurogenesis decreases during aging and following cranial radiotherapy, causing a progressive cognitive decline that is currently untreatable. However, functional neural stem cells remained present in the subventricular zone of high dose-irradiated and aged mouse brains. We therefore investigated whether alterations in the neurogenic niches are perhaps responsible for the neurogenesis decline. This hypothesis was supported by the absence of proliferation of neural stem cells that were engrafted into the vascular niches of irradiated host brains. Moreover, we observed a marked increase in TGF-β1 production by endothelial cells in the stem cell niche in both middle-aged and irradiated mice. In co-cultures, irradiated brain endothelial cells induced the apoptosis of neural stem/progenitor cells via TGF-β/Smad3 signalling. Strikingly, the blockade of TGF-β signalling in vivo using a neutralizing antibody or the selective inhibitor SB-505124 significantly improved neurogenesis in aged and irradiated mice, prevented apoptosis and increased the proliferation of neural stem/progenitor cells. These findings suggest that anti-TGF-β-based therapy may be used for future interventions to prevent neurogenic collapse following radiotherapy or during aging.

Cognitive dysfunction and depression in Parkinson's disease: what can be learned from rodent models?

Parkinson's disease (PD) has for decades been considered a pure motor disorder and its cardinal motor symptoms have been attributed to the loss of dopaminergic (DAergic) neurons in the substantia nigra pars compacta and to nigral Lewy body pathology. However, there has more recently been a shift in the conceptualization of the disease, and its pathological features have now been recognized as involving several other areas of the brain and indeed even outside the central nervous system. There are a corresponding variety of intrinsic non-motor symptoms such as autonomic dysfunction, cognitive impairment, sleep disturbances and neuropsychiatric problems, which cannot be explained exclusively by nigral pathology. In this review, we will focus on cognitive impairment and affective symptoms in PD, and we will consider whether, and how, these deficits can best be modelled in rodent models of the disorder. As only a few of the non-motor symptoms respond to standard DA replacement therapies, the quest for a broader therapeutic approach remains a major research effort, and success in this area in particular will be strongly dependent on appropriate rodent models. In addition, better understanding of the different models, as well as the advantages and disadvantages of the available behavioural tasks, will result in better tools for evaluating new treatment strategies for PD patients suffering from these neuropsychological symptoms.

MPTP modulates hippocampal synaptic transmission and activity-dependent synaptic plasticity via dopamine receptors

Parkinson's disease (PD)-like symptoms and cognitive deficits are inducible by 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). Since cognitive abilities, including memory formations rely also on hippocampus, we set out to clarify the effects of MPTP on hippocampal physiology. We show that bath-application of MPTP (25 μM) to acute hippocampal slices enhanced AMPA receptor-mediated field excitatory postsynaptic potentials (AMPAr-fEPSPs) transiently, whereas N-methyl-D-aspartate (NMDA) receptor-mediated fEPSPs (NMDAr-fEPSPs) were facilitated persistently. The MPTP-mediated transient AMPAr-fEPSP facilitation was antagonized by the dopamine D2-like receptor antagonists, eticlopride (1 μM) and sulpiride (1 and 40 μM). In contrast, the persistent enhancement of NMDAr-fEPSPs was prevented by the dopamine D1-like receptor antagonist SCH23390 (10 μM). In addition, we show that MPTP decreased paired-pulse facilitation of fEPSPs and mEPSCs frequency. Regarding activity-dependent synaptic plasticity, 25 μM MPTP transformed short-term potentiation (STP) into a long-term potentiation (LTP) and caused a slow onset potentiation of a non-tetanized synaptic input after induction of LTP in a second synaptic input. This heterosynaptic slow onset potentiation required activation of dopamine D1-like and NMDA-receptors. We conclude that acute MPTP application affects basal synaptic transmission by modulation of presynaptic vesicle release and facilitates NMDAr-fEPSPs as well as activity-dependent homo- and heterosynaptic plasticity under participation of dopamine receptors.

Animal models of the non-motor features of Parkinson's disease

The non-motor symptoms (NMS) of Parkinson's disease (PD) occur in roughly 90% of patients, have a profound negative impact on their quality of life, and often go undiagnosed. NMS typically involve many functional systems, and include sleep disturbances, neuropsychiatric and cognitive deficits, and autonomic and sensory dysfunction. The development and use of animal models have provided valuable insight into the classical motor symptoms of PD over the past few decades. Toxin-induced models provide a suitable approach to study aspects of the disease that derive from the loss of nigrostriatal dopaminergic neurons, a cardinal feature of PD. This also includes some NMS, primarily cognitive dysfunction. However, several NMS poorly respond to dopaminergic treatments, suggesting that they may be due to other pathologies. Recently developed genetic models of PD are providing new ways to model these NMS and identify their mechanisms. This review summarizes the current available literature on the ability of both toxin-induced and genetically-based animal models to reproduce the NMS of PD.

Olfaction in Parkinson's disease and related disorders

Olfactory dysfunction is an early 'pre-clinical' sign of Parkinson's disease (PD). The present review is a comprehensive and up-to-date assessment of such dysfunction in PD and related disorders. The olfactory bulb is implicated in the dysfunction, since only those syndromes with olfactory bulb pathology exhibit significant smell loss. The role of dopamine in the production of olfactory system pathology is enigmatic, as overexpression of dopaminergic cells within the bulb's glomerular layer is a common feature of PD and most animal models of PD. Damage to cholinergic, serotonergic, and noradrenergic systems is likely involved, since such damage is most marked in those diseases with the most smell loss. When compromised, these systems, which regulate microglial activity, can influence the induction of localized brain inflammation, oxidative damage, and cytosolic disruption of cellular processes. In monogenetic forms of PD, olfactory dysfunction is rarely observed in asymptomatic gene carriers, but is present in many of those that exhibit the motor phenotype. This suggests that such gene-related influences on olfaction, when present, take time to develop and depend upon additional factors, such as those from aging, other genes, formation of α-synuclein- and tau-related pathology, or lowered thresholds to oxidative stress from toxic insults. The limited data available suggest that the physiological determinants of the early changes in PD-related olfactory function are likely multifactorial and may include the same determinants as those responsible for a number of other non-motor symptoms of PD, such as dysautonomia and sleep disturbances.

Olfactory dysfunction in Parkinson disease

Olfactory dysfunction is among the earliest nonmotor features of Parkinson disease (PD). Such dysfunction is present in approximately 90% of early-stage PD cases and can precede the onset of motor symptoms by years. The mechanisms responsible for olfactory dysfunction are currently unknown. As equivalent deficits are observed in Alzheimer disease, Down syndrome, and the Parkinson-dementia complex of Guam, a common pathological substrate may be involved. Given that olfactory loss occurs to a lesser extent or is absent in disorders such as multiple system atrophy, corticobasal degeneration, and progressive supranuclear palsy, olfactory testing can be useful in differential diagnosis. The olfactory dysfunction in PD and a number of related diseases with smell loss correlates with decreased numbers of neurons in structures such as the locus coeruleus, the raphe nuclei, and the nucleus basalis of Meynart. These neuroanatomical findings, together with evidence for involvement of the autonomic nervous system in numerous PD-related symptoms, suggest that deficits in cholinergic, noradrenergic and serotonergic function may contribute to the olfactory loss. This Review discusses the current understanding of olfactory dysfunction in PD, including factors that may be related to its cause.

Lithium and valproate prevent olfactory discrimination and short-term memory impairments in the intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) rat model of Parkinson's disease

We have recently demonstrated that rodents treated intranasally with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) display time-dependent impairments in olfactory, emotional, cognitive and motor functions associated with disruption of dopaminergic neurotransmission in different brain structures conceivably analogous to those observed during different stages of Parkinson's disease (PD). On the other hand, lithium (Li) and valproate (VPA) are two primary drugs used to treat bipolar mood disorder that have recently emerged as promising neuroprotective agents. The present data indicates that the pretreatment with Li (47.5 mg/kg) or VPA (200 mg/kg) by intraperitoneal route during 7 consecutive days was able to prevent olfactory discrimination and short-term memory impairments evaluated in the social recognition and step-down inhibitory avoidance tasks in rats infused with a single intranasal (i.n.) administration of MPTP (0.1 mg/nostril). Despite the absence of clear depressive-like responses following the current MPTP dose, Li and VPA treatment presented an antidepressant profile reducing the immobility time in the forced swimming test. Importantly, at this time no significant alterations on the locomotor activity of the animals were observed in the open field test. Moreover, Li and VPA prevented dopamine depletion in the olfactory bulb and striatum of MPTP-infused rats. These results provide new insights in experimental models of PD, indicating that Li and VPA may represent new therapeutic tools for the management of olfactory and cognitive symptoms associated to early preclinical phases of PD, together with their neuroprotective potential demonstrated in previous research.

Intranasal administration of neurotoxicants in animals: support for the olfactory vector hypothesis of Parkinson's disease

The causes of Parkinson's disease (PD) are unknown, but there is evidence that exposure to environmental agents, including a number of viruses, toxins, agricultural chemicals, dietary nutrients, and metals, is associated with its development in some cases. The presence of smell loss and the pathological involvement of the olfactory pathways in the early stages of PD are in accord with the tenants of the olfactory vector hypothesis. This hypothesis postulates that some forms of PD may be caused or catalyzed by environmental agents that enter the brain via the olfactory mucosa. In this article, we provide an overview of evidence implicating xenobiotics agents in the etiology of PD and review animal, mostly rodent, studies in which toxicants have been introduced into the nose in an attempt to induce behavioral or neurochemical changes similar to those seen in PD. The available data suggest that this route of exposure results in highly variable outcomes, depending upon the involved xenobiotic, exposure history, and the age and species of the animals tested. Some compounds, such as rotenone, paraquat, and 6-hydroxydopamine, have limited capacity to reach and damage the nigrostriatal dopaminergic system via the intranasal route. Others, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), readily enter the brain via this route in some species and influence the function of the nigrostriatal pathway. Intranasal infusion of MPTP in some rodents elicits a developmental sequence of behavioral and neurochemical changes that closely mimics that seen in PD. For this reason, such an MPTP rodent model appears to be an ecologically valid means for assessing novel palliative treatments for both the motor and non-motor symptoms of PD. More research is needed, however, on this and other ecologically valid models.

Anxiety in Parkinson's disease: a critical review of experimental and clinical studies

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting about 1% of the population older than 60 years. Classically, PD is considered as a movement disorder, and its diagnosis is based on the presence of a set of cardinal motor signs that are the consequence of a pronounced death of dopaminergic neurons in the substantia nigra pars compacta. There is now considerable evidence showing that the neurodegenerative processes leading to sporadic PD begin many years before the appearance of the characteristic motor symptoms, and that additional neuronal fields and neurotransmitter systems are also involved in PD, including olfactory structures, amygdala, caudal raphe nuclei, locus coeruleus, and hippocampus. Accordingly, adrenergic and serotonergic neurons are also lost, which seems to contribute to the anxiety in PD. Non-motor features of PD usually do not respond to dopaminergic medication and probably form the major current challenge in the clinical management of PD. Additionally, most studies performed with animal models of PD have investigated their ability to induce motor alterations associated with advanced phases of PD, and some studies begin to assess non-motor behavioral features of the disease. The present review attempts to examine results obtained from clinical and experimental studies to provide a comprehensive picture of the neurobiology and current and potential treatments for anxiety in PD. The data reviewed here indicate that, despite their high prevalence and impact on the quality of life, anxiety disorders are often under-diagnosed and under-treated in PD patients. Moreover, there are currently few clinical and pre-clinical studies underway to investigate new pharmacological agents for relieving these symptoms, and we hope that this article may inspire clinicians and researchers devote to the studies on anxiety in PD to change this scenario. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Effect of intermittent washout periods on progressive lesioning of the nigrostriatal pathway with 1-methyl-2-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

We have previously reported that a progressively increased dose of MPTP over the course of 4 weeks induces the gradual impairment of the nigrostriatal dopamine (DA) pathway and several behaviors [Goldberg et al. (in press) Neuroscience]. To our knowledge, this is the first report of specific behavioral deficits correlated with discrete thresholds of DA loss in this pathway. In that study, MPTP was administered 5 d/wk, with behavioral and tissue analysis being carried out 3 days following the final injection at each dose. However, in order to better represent long-term progressive neurodegeneration the present study introduced a washout period of 10 days between each increased dose of MPTP. This implementation also controlled for any transient de-activation of tyrosine hydroxylase (TH), the enzyme that catalyzes synthesis of DA, caused by MPTP-induced oxidative stress which has been suggested following acute administration of the toxin [Smeyne and Jackson-Lewis (2005) Brian Res Mol Brain Res 134:57-66]. Additionally, by the end of the previous study, there was an ultimate decrease of 62% in the mean number of TH-labeled neurons/section in the substantia nigra pars compacta (SNpc) and a 74% decrease in caudate putamen (CPu) TH optical density with continuous MPTP. In the present study, we find that the washout periods lead to a final 79% decrease in the mean number of TH-labeled SNpc neurons/section, and a similar 74% decrease in CPu TH following the 32 mg/kg MPTP dose. Additionally, a dose-dependent decrease was observed in the mean number of SNpc TH-ir neurons/section in the current study which was not seen in the continuous MPTP protocol. These results suggest that a washout period following each increased MPTP dose allows for observation of continued cell death that might occur during the week following MPTP administration, and for therapeutic interventions to be applied at any of several stages during progressive neurodegeneration.

Role of the glucose-dependent insulinotropic polypeptide and its receptor in the central nervous system: therapeutic potential in neurological diseases

Glucose-dependent insulinotropic polypeptide (GIP) is a 42-amino acid hormone, secreted from the enteroendocrine K cells, which has insulin-releasing and extra-pancreatic actions. GIP and its receptor present a widespread distribution in the mammalian brain where they have been implicated with synaptic plasticity, neurogenesis, neuroprotection and behavioral alterations. This review attempts to provide a comprehensive picture of the role of GIP in the central nervous system and to highlight recent findings from our group showing its potential involvement in neurological illnesses including epilepsies, Parkinson's disease and Alzheimer's disease.

Proanthocyanidin-rich fraction from Croton celtidifolius Baill confers neuroprotection in the intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine rat model of Parkinson's disease

We have recently demonstrated that rodents treated intranasally with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) suffered impairments in olfactory, cognitive and motor functions associated with time-dependent disruption of dopaminergic neurotransmission in different brain structures conceivably analogous to those observed during different stages of Parkinson's disease (PD). On the other hand, the proanthocyanidin-rich fraction (PRF) obtained from the bark of Croton celtidifolius Baill (Euphorbiaceae), a tree frequently found in the Atlantic forest in south Brazil, has been described to have several neurobiological activities including antioxidant and anti-inflammatory properties, which may be of interest in the treatment of PD. The present data indicated that the pretreatment with PRF (10 mg/kg, i.p.) during five consecutive days was able to prevent mitochondrial complex-I inhibition in the striatum and olfactory bulb, as well as a decrease of the enzyme tyrosine hydroxylase expression in the olfactory bulb and substantia nigra of rats infused with a single intranasal administration of MPTP (1 mg/nostril). Moreover, pretreatment with PRF was found to attenuate the short-term social memory deficits, depressive-like behavior and reduction of locomotor activity observed at different periods after intranasal MPTP administration in rats. Altogether, the present findings provide strong evidence that PRF from C. celtidifolius may represent a promising therapeutic tool in PD, thus being able to prevent both motor and non-motor early symptoms of PD, together with its neuroprotective potential.

Behavioral phenotyping of mouse models of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative movement disorder afflicting millions of people in the United States. The advent of transgenic technologies has contributed to the development of several new mouse models, many of which recapitulate some aspects of the disease; however, no model has been demonstrated to faithfully reproduce the full constellation of symptoms seen in human PD. This may be due in part to the narrow focus on the dopamine-mediated motor deficits. As current research continues to unmask PD as a multi-system disorder, animal models should similarly evolve to include the non-motor features of the disease. This requires that typically cited behavioral test batteries be expanded. The major non-motor symptoms observed in PD patients include hyposmia, sleep disturbances, gastrointestinal dysfunction, autonomic dysfunction, anxiety, depression, and cognitive decline. Mouse behavioral tests exist for all of these symptoms and while some models have begun to be reassessed for the prevalence of this broader behavioral phenotype, the majority has not. Moreover, all behavioral paradigms should be tested for their responsiveness to L-DOPA so these data can be compared to patient response and help elucidate which symptoms are likely not dopamine-mediated. Here, we suggest an extensive, yet feasible, battery of behavioral tests for mouse models of PD aimed to better assess both non-motor and motor deficits associated with the disease.