Fenofibrate promotes neuroprotection in a model of rotenone-induced Parkinson's disease.

Parkinson's disease is a neurodegenerative disease, the etiology of which remains unknown, but some likely causes include oxidative stress, mitochondrial dysfunction and neuroinflammation. Peroxisome-proliferator-activated receptor (PPAR) agonists have been studied in animal models of Parkinson's disease and have shown neuroprotective effects. In this study, we aimed to (1) confirm the neuroprotective effects of PPAR-alpha agonist fenofibrate. To this end, male rats received fenofibrate (100 mg/kg) orally for 15 days, 5 days before the intraperitoneal injections of rotenone (2.5 mg/kg for 10 days). After finishing the treatment with rotenone and fenofibrate, animals were subjected to the open field, the forced swim test and the two-way active avoidance task. Subsequently, rats were euthanized for measurement of dopamine and metabolites levels in the striatum and quantification of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra pars compacta (SNpc). In addition, we aimed to (2) evaluate the neuroprotective effects of fenofibrate on the accumulation of α-synuclein aggregates. Here, rats were treated for 5 days with fenofibrate continuing for over 28 days with rotenone. Then, animals were perfused for immunohistochemistry analysis of α-synuclein. The results showed that fenofibrate reduced depressive-like behavior and memory impairment induced by rotenone. Moreover, fenofibrate diminished the depletion of striatal dopamine and protected against dopaminergic neuronal death in the SNpc. Likewise, the administration of fenofibrate attenuated the aggregation of α-synuclein in the SNpc and striatum in the rotenone-lesioned rats. Our study confirmed that fenofibrate exerted neuroprotective effects because parkinsonian rats exhibited reduced behavioral, neurochemical and immunohistochemical changes, and importantly, a lower number of α-synuclein aggregates.

The roles of the nucleus accumbens core, dorsomedial striatum, and dorsolateral striatum in learning: performance and extinction of Pavlovian fear-conditioned responses and instrumental avoidance responses.

This study examined the effects of bilateral excitotoxic lesions of the nucleus accumbens core (NAc-co), dorsomedial striatum (DMS) or dorsolateral striatum (DLS) of rats on the learning and extinction of Pavlovian and instrumental components of conditioned avoidance responses (CARs). None of the lesions caused sensorimotor deficits that could affect locomotion. Lesions of the NAc-co, but not DMS or DLS, decreased unconditioned and conditioned freezing. The NAc-co and DLS lesioned rats learned the 2-way active avoidance task more slowly. These results suggest: (i) CARs depend on both Pavlovian and instrumental learning; (ii) learning the Pavlovian component of CARs depends on the NAc-co; learning the instrumental component of CARs depends on the DLS, NAc and DMS; (iii) although the NAc-co is also needed for learning the instrumental component, it is not clear whether it plays a role in learning the instrumental component per se or if it simply allows learning of the Pavlovian component which is a pre-condition for learning the instrumental component; (iv) we did not find evidence that the DMS and DLS play the same roles in habit and goal-directed aspects of the instrumental component of CARs as observed in appetitive motivated instrumental responding.

Antidepressant-like effect of celecoxib piroxicam in rat models of depression.

Beyond the current hypothesis of depression, several new biological substrates have been proposed for this disorder. The present study investigated whether the anti-inflammatory drugs celecoxib and piroxicam have antidepressant activity in animal models of depression. After acute administration, we observed antidepressant-like effects of celecoxib (10 mg/kg) and piroxicam (10 mg/kg) in the modified forced swim test in rats. Piroxicam increased serotonin and norepinephrine levels in the hippocampus. Prolonged (21-day) treatment with celecoxib (10 mg/kg) and piroxicam (10 mg/kg) rescued sucrose preference in a chronic mild stress model of depression. Additionally, the chronic mild stress-induced reduction of hippocampal glutathione was prevented by treatment with celecoxib and piroxicam. Superoxide dismutase in the hippocampus was increased after chronic mild stress compared with the non-stressed saline group. The non-stressed celecoxib and piroxicam groups and stressed piroxicam group exhibited an increase in hippocampal superoxide dismutase activity compared with the stressed saline group. Lipid hydroperoxide was increased in the stressed group treated with vehicle and non-stressed group treated with imipramine but not in the stressed groups treated with celecoxib and piroxicam. These results suggest that the antidepressant-like effects of anti-inflammatory drugs might be attributable to enhanced antioxidant defenses and attenuated oxidative stress in the hippocampus.

Opposite effects of bone marrow-derived cells transplantation in MPTP-rat model of Parkinson's disease: a comparison study of mononuclear and mesenchymal stem cells.

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model is a useful tool to study Parkinson's disease (PD) and was used in the present study to investigate the potential beneficial as well as deleterious effects of systemic bone-marrow mononuclear cell (BMMC) or mesenchymal stem cell (BM-MSC) transplantation. MPTP administration resulted in a breakdown of the blood-brain barrier and motor impairment in the open field test 24 h after surgery. Three and 7 days after receiving the lesion, the injured animals showed remaining motor impairment compared to the sham groups along with a significant loss of tyrosine hydroxylase-immunoreactive (TH-ir) cells in the substantia nigra pars compacta (SNpc). The MPTP-lesioned rats treated with BMMCs immediately after lesioning exhibited motor impairment similar to the MPTP-saline group, though they presented a significantly higher loss of TH-ir cells in the SNpc compared to the MPTP-saline group. This increased loss of TH-ir cells in the SNpc was not observed when BMMC transplantation was performed 24 h after MPTP administration. In contrast, in the MPTP animals treated early with systemic BM-MSCs, no loss of TH-ir cells was observed. BMMCs and BM-MSCs previously labeled with CM-DiI cell tracker were found in brain sections of all transplanted animals. In addition, cells expressing CD45, an inflammatory white blood cell marker, were found in all brain sections analyzed and were more abundant in the MPTP-BMMC animals. In these animals, Iba1+ microglial cells showed also marked morphological changes indicating increased microglial activation. These results show that systemic BMMC transplantation did not ameliorate or prevent the lesion induced by MPTP. Instead, BMMC transplantation in MPTP-lesioned rats accelerated dopaminergic neuronal damage and induced motor impairment and immobility behavior. These findings suggest that caution should be taken when considering cell therapy using BMMCs to treat PD. However, systemic BM-MSC transplantation that reaches the injury site and prevents neuronal damage after an MPTP infusion could be considered as a potential treatment for PD during the early stage of disease development.

Partial lesion of dopamine neurons of rat substantia nigra impairs conditioned place aversion but spares conditioned place preference.

Midbrain dopamine neurons play critical roles in reward- and aversion-driven associative learning. However, it is not clear whether they do this by a common mechanism or by separate mechanisms that can be dissociated. In the present study we addressed this question by testing whether a partial lesion of the dopamine neurons of the rat SNc has comparable effects on conditioned place preference (CPP) learning and conditioned place aversion (CPA) learning. Partial lesions of dopamine neurons in the rat substantia nigra pars compacta (SNc) induced by bilateral intranigral infusion of 6-hydroxydopamine (6-OHDA, 3µg/side) or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 200µg/side) impaired learning of conditioned place aversion (CPA) without affecting conditioned place preference (CPP) learning. Control experiments demonstrated that these lesions did not impair motor performance and did not alter the hedonic value of the sucrose and quinine. The number of dopamine neurons in the caudal part of the SNc positively correlated with the CPP scores of the 6-OHDA rats and negatively correlated with CPA scores of the SHAM rats. In addition, the CPA scores of the 6-OHDA rats positively correlated with the tissue content of striatal dopamine. Insomuch as reward-driven learning depends on an increase in dopamine release by nigral neurons, these findings show that this mechanism is functional even in rats with a partial lesion of the SNc. On the other hand, if aversion-driven learning depends on a reduction of extracellular dopamine in the striatum, the present study suggests that this mechanism is no longer functional after the partial SNc lesion.

Antidepressant and antioxidative effect of Ibuprofen in the rotenone model of Parkinson's disease.

Idiopathic Parkinson's disease is a neurodegenerative disorder that affects approximately 1 % of the population over 55 years of age. The disease manifests itself through motor and nonmotor symptoms induced mainly by the neurodegeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The possible mechanisms involved in this pathology include mitochondrial dysfunction, neuroinflammation, and oxidative stress. The present study evaluated the effects of the nonselective cyclooxygenase inhibitor ibuprofen on motor and depressive-like behavior induced by rotenone in rats. Rotenone (2.5 mg/kg, i.p., for 10 days) decreased tyrosine hydroxylase immunoreactivity in the SNpc, and ibuprofen treatment (15 mg/kg, p.o., for 22 days) blocked this impairment. We also found that rotenone-induced motor deficits (hypolocomotion) and depressive-like behavior, and ibuprofen was able to reverse these deficits. In addition to motor and nonmotor behaviors, we evaluated oxidative stress induced by rotenone. Rotenone administration depleted glutathione levels in the hippocampus and reduced catalase activity in both the hippocampus and striatum. Post treatment with ibuprofen blocked the depletion of glutathione induced by rotenone and increased the basal levels of this antioxidant in the striatum. Ibuprofen also restored catalase activity. The neuroprotective effects of ibuprofen against toxicity induced by rotenone appear to be attributable to its antioxidant properties, in addition to cyclooxygenase inhibition.

Induction of depressive-like behavior by intranigral 6-OHDA is directly correlated with deficits in striatal dopamine and hippocampal serotonin.

Among the non-motor phenomena of Parkinson's disease (PD) are depressive symptoms, with a prevalence of 40-70%. The reason for this high prevalence is not yet clear. The basal ganglia receives dopamine (DA) inputs from the substantia nigra pars compacta (SNpc), which is known to be impaired in PD patients. The neurotransmitter deficiency hypothesis of PD considers that low serotonin (5-hydroxytryptamine [5-HT]) activity in the brain in PD patients is a risk factor for depression. We investigated whether DA depletion promoted by the neurotoxin 6-hydroxydopamine (6-OHDA) is able to induce depressive-like behavior and neurotransmitter alterations that are similar to those observed in PD. To test this hypothesis, we performed intranigral injections of 6-OHDA in male Wistar rats and conducted motor behavior, depressive-like behavior, histological, and neurochemical tests. After the motor recovery period, 6-OHDA was able to produce anhedonia and behavioral despair 7, 14, and 21 days after neurotoxin infusion. These altered behavioral responses were accompanied by reductions of striatal DA. Additionally, decreases in hippocampal 5-HT content were detected in the 6-OHDA group. Notably, correlations were found between 5-HT and DA levels and swimming, immobility, and sucrose preference. Our results indicate that 6-OHDA produced depressive-like behavior accompanied by striatal DA and hippocampal 5-HT reductions. Moreover, DA and 5-HT levels were strongly correlated with "emotional" impairments, suggesting the important participation of these neurotransmitters in anhedonia and behavioral despair after 6-OHDA-induced nigral lesions.

Neuroprotective and antidepressant-like effects of melatonin in a rotenone-induced Parkinson's disease model in rats.

Parkinson׳s disease (PD) is a neurodegenerative disorder characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Systemic and intranigral exposure to rotenone in rodents reproduces many of the pathological and behavioral features of PD in humans and thus has been used as an animal model of the disease. Melatonin is a neurohormone secreted by the pineal gland, which has several important physiological functions. It has been reported to be neuroprotective in some animal models of PD. The present study investigated the effects of prolonged melatonin treatment in rats previously exposed to rotenone. The animals were intraperitoneally treated for 10 days with rotenone (2.5mg/kg) or its vehicle. 24h later, they were intraperitoneally treated with melatonin (10mg/kg) or its vehicle for 28 days. One day after the last rotenone exposure, the animals exhibited hypolocomotion in the open field test, which spontaneously reversed at the last motor evaluation. We verified that prolonged melatonin treatment after dopaminergic lesion did not alter motor function but produced antidepressant-like effects in the forced swim test, prevented the rotenone-induced reduction of striatal dopamine, and partially prevented tyrosine hydroxylase immunoreactivity loss in the SNpc. Our results indicate that melatonin exerts neuroprotective and antidepressant-like effects in the rotenone model of PD.

PPAR-α agonist fenofibrate protects against the damaging effects of MPTP in a rat model of Parkinson's disease.

Parkinson's disease (PD) is a chronic neurodegenerative disorder characterized by progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The etiology and pathogenesis of PD are still unknown, however, many evidences suggest a prominent role of oxidative stress, inflammation, apoptosis, mitochondrial dysfunction and proteosomal dysfunction. The peroxisome proliferator-activated receptor (PPAR) ligands, a member of the nuclear receptor family, have anti-inflammatory activity over a variety of rodent's models for acute and chronic inflammation. PPAR-α agonists, a subtype of the PPAR receptors, such as fenofibrate, have been shown a major role in the regulation of inflammatory processes. Animal models of PD have shown that neuroinflammation is one of the most important mechanisms involved in dopaminergic cell death. In addition, anti-inflammatory drugs are able to attenuate toxin-induced parkinsonism. In this study we evaluated the effects of oral administration of fenofibrate 100mg/kg 1h after infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the SNpc. First, we assessed the motor behavior in the open field for 24h, 7, 14 and 21 days after MPTP. Twenty-two days after surgery, the animals were tested for two-way active avoidance and forced swimming for evaluation regarding cognitive and depressive parameters, respectively. Twenty-three days after infusion of the toxin, we quantified DA and turnover and evaluated oxidative stress through the measurement of GSH (glutathione peroxidase), SOD (superoxide dismutase) and LOOH (hydroperoxide lipid). The data show that fenofibrate was able to decrease hypolocomotion caused by MPTP 24h after injury, depressive-like behavior 22 days after the toxin infusion, and also protected against decreased level of DA and excessive production of reactive oxygen species (ROS) 23 days after surgery. Thus, fenofibrate has shown a neuroprotective effect in the MPTP model of Parkinson's disease.

Neuroprotective effects of peroxisome proliferator-activated receptor alpha and gamma agonists in model of parkinsonism induced by intranigral 1-methyl-4-phenyl-1,2,3,6-tetrahyropyridine.

A large body of evidence suggests that peroxisome proliferator-activated receptor (PPAR) agonists may improve some of the pathological features of Parkinson's disease (PD). In the present study, we evaluated the effects of the PPAR-α agonist fenofibrate (100mg/kg) and PPAR-γ agonist pioglitazone (30mg/kg) in a rat model of parkinsonism induced by intranigral 1-methyl-4-phenyl-1,2,3,6-tetrahyropyridine (MPTP). Male Wistar rats were pretreated with both drugs for 5 days and received an infusion of MPTP. The experiments were divided into two parts. First, 1, 7, 14, and 21 days after surgery, the animals were submitted to the open field test. On days 21 and 22, the rats were subjected to the forced swim test and two-way active avoidance task. In the second part of the study, 24h after neurotoxin administration, immunohistochemistry was performed to assess tyrosine hydroxylase activity. The levels of dopamine and its metabolites in the striatum were determined using high-performance liquid chromatography, and fluorescence detection was used to assess caspase-3 activation in the substantia nigra pars compacta (SNpc). Both fenofibrate as pioglitazone protected against hypolocomotion, depressive-like behavior, impairment of learning and memory, and dopaminergic neurodegeneration caused by MPTP, with dopaminergic neuron loss of approximately 33%. Fenofibrate and pioglitazone also protected against the increased activation of caspase-3, an effector enzyme of the apoptosis cascade that is considered one of the pathological features of PD. Thus, PPAR agonists may contribute to therapeutic strategies in PD.

Behavioral, neurochemical and histological alterations promoted by bilateral intranigral rotenone administration: a new approach for an old neurotoxin.

Rotenone exposure in rodents provides an interesting model for studying mechanisms of toxin-induced dopaminergic neuronal injury. However, several aspects remain unclear regarding the effects and the accuracy of rotenone as an animal model of Parkinson's disease (PD). In order to counteract these limitations, this study characterized a precise neurotoxin-delivery strategy employing the bilateral intranigral administration protocol of rotenone as a reliable model of PD. We performed bilateral intranigral injections of rotenone (12 µg) and subsequent general activity (1, 10, 20, and 30 days after rotenone) and cognitive (7, 8, 15, and 30 days after rotenone) evaluations followed by neurochemical and immunohistochemical tests. We have observed that rotenone was able to produce a remarkable reduction on the percentage of tyrosine hydroxylase immunoreactive neurons (about 60%) within the substantia nigra pars compacta. Dopamine (DA) was severely depleted at 30 days after rotenone administration, similarly to its metabolites. In addition, an increase in DA turnover was detected at the same time-point. In parallel, striatal serotonin and its metabolite were found to be increased 30 days after the neurotoxic insult, without apparent modification in the serotonin turnover. Besides, motor behavior was impaired, mainly 1 day after rotenone. Furthermore, learning and memory processes were severely disrupted in different time-points, particularly at the training and test session (30 days). We now provide further evidence of a time-dependent neurodegeneration associated to cognitive impairment after the single bilateral intranigral administration of rotenone. Thus, it is proposed that the current rotenone protocol provides an improvement regarding the existing rotenone models of PD.

Characterization of motor, depressive-like and neurochemical alterations induced by a short-term rotenone administration.

BACKGROUND: Rotenone exposure in rodents provides an interesting model for studying mechanisms of toxin-induced dopaminergic neuronal injury. However, several aspects remain unclear regarding the effects and the accuracy of rotenone as an animal model of Parkinson's disease (PD). In this study, we investigated the motor and depressive-like behaviors associated to neurochemical alterations induced by a novel protocol of rotenone administration. METHODS: In the first experiment, we adopted the paw test to characterize an effective dose of rotenone able to promote nigrostriatal toxicity. In the second experiment, control and rotenone 2.5 mg/kg groups were injected (ip) for 10 consecutive days. RESULTS: This test indicated that intraperitonial (ip) rotenone at 2.5 and 5.0 mg/kg promoted a significant neurotoxicity to striatum and nucleus accumbens. However, only 2.5 mg/kg of rotenone was associated to a negligible mortality rate. Open-field tests were conducted on 1, 7, 14 and 21 day after the last day of treatment and showed an important locomotor impairment, confined to 1 and 7 day. Besides, rotenone affected dopamine levels and increased its turnover in the striatum. Modified forced swim test (performed on 22 day) and sucrose preference test (performed on 14 and 21 day) demonstrated that rotenone produced impairments in the swimming and immobility. In parallel, increments in the serotonin and noradrenaline turnovers were observed in the striatum and hippocampus of the rotenone group. CONCLUSIONS: These data suggest important participations of serotonin and noradrenaline in depressive-like behaviors induced by rotenone. Thus, it is proposed that the current rotenone protocol provides an improvement regarding the existing rotenonemodels of PD.

Acute but not chronic administration of pioglitazone promoted behavioral and neurochemical protective effects in the MPTP model of Parkinson's disease.

The present study investigated the neurochemical, motor and cognitive effects of pioglitazone in a rat model of Parkinson's disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In the first experiment, we administered MPTP, and 1h later administered a single oral dose of pioglitazone (5, 15 and 30 mg/kg). The following day, we performed the open-field test and neurochemical dose response curve. We demonstrated that 30 mg/kg of pioglitazone was capable of restoring striatal dopamine (DA) concentrations and motor behaviors. A second experiment was conducted to test the effects of two protocols (acute and chronic) of pioglitazone (30 mg/kg) administration in the open-field test, two-way active avoidance task and in the DA and metabolites levels. The acute protocol consisted of a single oral administration 1 h after MPTP, whereas the chronic protocol was performed with daily administrations starting 1 h after MPTP and ending 22 days after that. Results showed that neither protocol was able to reverse the cognitive impairment promoted by MPTP. We also demonstrated that acute treatment generated some level of neuroprotection, as confirmed by the absence of DA reduction in the group treated with pioglitazone in comparison to the sham group. By contrast, chronic treatment leaded to a reduction of striatal DA, close to MPTP administration alone. These findings suggest that acute administration of pioglitazone (30 mg/kg) was more efficient in generating beneficial effects on motor behaviors and in striatal DA levels. Nevertheless, we failed to demonstrate that pioglitazone administration improved performance on a dopamine-related cognitive task after MPTP.