Anxiety-like behavior induced by 6-OHDA animal model of Parkinson's disease may be related to a dysregulation of neurotransmitter systems in brain areas related to anxiety.

Anxiety in Parkinson's disease may represent a physiological reaction to the development of other symptoms during disease progression. However, evidence suggests that the incidence of anxiety disorders in Parkinson's disease may be related to neurochemical changes. The present study addresses the question whether dopamine, noradrenaline and serotonin levels in brain structures related to Parkinson's disease and anxiety are responsible for anxiety-like behavior by using an animal model of parkinsonism based in the bilateral injection of the neurotoxin 6-hydroxydopamine (6-OHDA) in the substantia nigra pars compacta. For this, one day after the injection of 6-OHDA, the animals exhibited hypolocomotion and a lower frequency of rearings in the open field test, which was spontaneously reversed on the last day of motor assessment (day 21). The 6-OHDA injection also induced anxiety-like behavior in the elevated plus maze and contextual fear conditioning test (day 21 and 24, respectively). Neurochemical analysis showed a reduction of dopamine and norepinephrine levels in the striatum, prefrontal cortex, and amygdala. In addition, while the serotonin levels were reduced in the striatum and prefrontal cortex, it was increased in the amygdala. The present study indicates that the model of 6-OHDA-induced parkinsonism in rats induced an anxiety-like behavior that may be related to a dysregulation of neurotransmitter systems in brain areas involved with anxiety such as the amygdala, prefrontal cortex and striatum.

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.

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.

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.

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.

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.

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.

Depressive-like behaviors alterations induced by intranigral MPTP, 6-OHDA, LPS and rotenone models of Parkinson's disease are predominantly associated with serotonin and dopamine.

Depression is a frequently encountered non-motor feature of Parkinson's disease (PD) and it can have a significant impact on patient's quality of life. Considering the differential pathophysiology of depression in PD, it prompts the idea that a degenerated nigrostriatal system plays a role in depressive-like behaviors, whilst animal models of PD are employed. Therefore, we addressed the question of whether dopamine (DA) depletion, promoted by the neurotoxins 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 6-hydroxydopamine (6-OHDA), lipopolysaccharide (LPS) and rotenone are able to induce depressive-like behaviors and neurotransmitters alterations similarly that encountered in PD. To test this rationale, we performed intranigral injections of each neurotoxin, followed by motor behavior, depressive-like behaviors, histological and neurochemical tests. After the motor recovery period, MPTP, 6-OHDA and rotenone were able to produce anhedonia and behavioral despair. These altered behavioral responses were accompanied by reductions of striatal DA, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) restricted to the 6-OHDA group. Additionally, decreases on the hippocampal serotonin (5-HT) content were detected for the MPTP, 6-OHDA and rotenone groups. Notably, strong correlations were detected among the groups when 5-HT and DA were correlated with swimming (r=+0.97; P=0.001) and immobility (r=-0.90; P=0.012), respectively. Our data indicate that MPTP, 6-OHDA and rotenone, but not LPS were able to produce depressive-like behaviors accompanied primarily by hippocampal 5-HT reductions. Moreover, DA and 5-HT strongly correlated with "emotional" impairments suggesting an important participation of these neurotransmitters in anhedonia and behavioral despair after nigral lesions promoted by the neurotoxins.