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

Stereological Evaluation of the Brains in Patients with Parkinson’s disease Compared to Controls

Parkinson’s disease (PD) is a chronic and progressive neurological disorder. A tetrad of bradykinesia, rigidity, tremor and postural instability are the core features of the disease. The aim of this study was to evaluate stereological changes in the brain of patients with PD and compare them with that of healthy controls. This case-control study was conducted on 29 patients with PD and 12 controls (C) in Zahedan, Iran. All subjects enrolled into the study through the convenience sampling method. MRI images of the brains of two groups in frontal and sagittal axis with consecutive 5mm distance slices were captured. Parameters including total volume (V) and volume density (Vv) of different parts of the brain were estimated based on Cavalries’ point counting stereological method. To analyze the data, descriptive statistics, Mann-Whitney U-Test applied for comparing the PD and C groups were used. Significance level was set at p<0.05. Our study showed that the volume of the brain and total volume and volume density (Vv) of cerebral hemispheres, cerebellum, ventricles, hippocampus, pons, mid brain and superior cerebellar peduncles in the PD group did not indicate significant difference from the control group. Total volume of brain stem in PD group wasn’t significantly different from the control group. The volume density of brain stem (p= 0.012) and total volume and volume density of middle cerebellar peduncle (p< 0.0001) in PD group were significantly larger than the control group. This study shows that PD stereological parameters related to volume and volume density of middle cerebellar peduncle and volume density of brain stem were significantly larger in patients compared to the controls. Therefore, stereological parameters can be used for early diagnosis and probably for follow-up in patients with PD.

Depressive-like effect of prenatal exposure to DDT involves global DNA hypomethylation and impairment of GPER1/ESR1 protein levels but not ESR2 and AHR/ARNT signaling

Several lines of evidence suggest that exposures to Endocrine Disrupting Chemicals (EDCs) such as pesticides increase the risks of neuropsychiatric disorders. Despite extended residual persistence of dichlorodiphenyltrichloroethane (DDT) in the environment, the mechanisms of perinatal actions of DDT that could account for adult-onset of depression are largely unknown. This study demonstrated the isomer-specific induction of depressive-like behavior and impairment of Htr1a/serotonin signaling in one-month-old mice that were prenatally exposed to DDT. The effects were reversed by the antidepressant citalopram as evidenced in the forced swimming (FST) and tail suspension (TST) tests in the male and female mice. Prenatally administered DDT accumulated in mouse brain as determined with gas chromatography and tandem mass spectrometry, led to global DNA hypomethylation, and altered the levels of methylated DNA in specific genes. The induction of depressive-like behavior and impairment of Htr1a/serotonin signaling were accompanied by p,p'-DDT-specific decrease in the levels of estrogen receptors i.e. ESR1 and/or GPER1 depending on sex. In contrast, o,p'-DDT did not induce depressive-like effects and exhibited quite distinct pattern of biochemical alterations that was related to aryl hydrocarbon receptor (AHR), its nuclear translocator ARNT, and ESR2. Exposure to o,p'-DDT increased AHR expression in male and female brains, and reduced expression levels of ARNT and ESR2 in the female brains. The evolution of p,p'-DDT-induced depressive-like behavior was preceded by attenuation of Htr1a and Gper1/GPER1 expression as observed in the 7-day-old mouse pups. Because p,p'-DDT caused sex- and age-independent attenuation of GPER1, we suggest that impairment of GPER1 signaling plays a key role in the propagation of DDT-induced depressive-like symptoms.

Brain infusion of α-synuclein oligomers induces motor and non-motor Parkinson's disease-like symptoms in mice

Parkinson's disease (PD) is characterized by motor dysfunction, which is preceded by a number of non-motor symptoms including olfactory deficits. Aggregation of α-synuclein (α-syn) gives rise to Lewy bodies in dopaminergic neurons and is thought to play a central role in PD pathology. However, whether amyloid fibrils or soluble oligomers of α-syn are the main neurotoxic species in PD remains controversial. Here, we performed a single intracerebroventricular (i.c.v.) infusion of α-syn oligomers (α-SYOs) in mice and evaluated motor and non-motor symptoms. Familiar bedding and vanillin essence discrimination tasks showed that α-SYOs impaired olfactory performance of mice, and decreased TH and dopamine levels in the olfactory bulb early after infusion. The olfactory deficit persisted until 45days post-infusion (dpi). α- SYO-infused mice behaved normally in the object recognition and forced swim tests, but showed increased anxiety-like behavior in the open field and elevated plus maze tests 20 dpi. Finally, administration of α-SYOs induced late motor impairment in the pole test and rotarod paradigms, along with reduced TH and dopamine content in the caudate putamen, 45 dpi. Reduced number of TH-positive cells was also seen in the substantia nigra of α-SYO-injected mice compared to control. In conclusion, i.c.v. infusion of α-SYOs recapitulated some of PD-associated non-motor symptoms, such as increased anxiety and olfactory dysfunction, but failed to recapitulate memory impairment and depressive-like behavior typical of the disease. Moreover, α-SYOs i.c.v. administration induced motor deficits and loss of TH and dopamine levels, key features of PD. Results point to α-syn oligomers as the proximal neurotoxins responsible for early non-motor and motor deficits in PD and suggest that the i.c.v. infusion model characterized here may comprise a useful tool for identification of PD novel therapeutic targets and drug screening.

Asiaticoside: Attenuation of rotenone induced oxidative burden in a rat model of hemiparkinsonism by maintaining the phosphoinositide-mediated synaptic integrity

Asiaticoside (AS), a triterpenoid saponin isolated from the Indian medicinal herb Centella asiatica is known to exert a neuroprotective effect by attenuating the neurobehavioral, neurochemical and pathological changes in animal models. However, its potential neuroprotection in rotenone-induced hemiparkinsonism which implicates phospholipid-mediated neurotransmission remains unclear. Therefore, we have investigated the neuroprotective effects of AS in rat model of ROT-infused hemiparkinsonism with respect to phosphoinositides-assisted cytodynamics and synaptic function. Adult male Sprague-Dawley rats (250-300g) were distributed randomly into 6 groups, with 6 rats in each group: Sham control, Vehicle control (DMSO-0.1%), ROT-infused group (6μg/μl/kg), AS-treated group (50mg/kg/day), Drug (AS) control and Levodopa (l-DOPA)-treated group (6mg/kg/day). At the end of the experimental period, the rats were sacrificed after performing behavioral analyses and the striatum regions were dissected out. Phosphoinositides (PI) are involved in intrinsic membrane signals that regulate intracellular membrane trafficking vesicle and endocytosis. We have assessed mRNA and protein expressions of genes involved in PI-mediated signaling and also in synaptic function (PI3K, PDK 1, PEBP, Stx 1A and TH) in addition to the levels of neurotransmitters and the enzymatic antioxidant profile. AS caused an improved working memory and motor co-ordination in the ROT group. It alters the levels of neurotransmitters (p<0.01), the expression of mRNA and protein assessed which were significantly affected (P<0.001) by rotenone, thus exhibiting its intervention in the progression of neurodegeneration. We demonstrate that AS can mediate distinct function in PI-assisted vesicle endocytosis, cytoprotective signaling and in the synaptic function thereby mitigating the ROT-infused hemiparkinsonism, however, its specific regulatory role remains to be unraveled.

Chlorpyrifos induces anxiety-like behavior in offspring rats exposed during pregnancy

Chlorpyrifos is a pesticide, member of the organophosphate class, widely used in several countries to manage insect pests on many agricultural crops. Currently, chlorpyrifos health risks are being reevaluated due to possible adverse effects, especially on the central nervous system. The aim of this study was to investigate the possible action of this pesticide on the behaviors related to anxiety and depression of offspring rats exposed during pregnancy. Wistar rats were treated orally with chlorpyrifos (0.01, 0.1, 1 and 10mg/kg/day) on gestational days 14-20. Male offspring behavior was evaluated on post-natal days 21 and 70 by the elevated plus-maze test, open field test and forced swimming test. The results demonstrated that exposure to 0.1, 1 or 10mg/kg/day of chlorpyrifos could induce anxiogenic-like, but not depressive-like behavior at post-natal day 21, without causing fetal toxicity. This effect was reversed on post-natal day 70.

Involvement of lateral habenula α1 subunit-containing GABAA receptor-mediated inhibitory transmission in the regulation of depression-related behaviors in experimental Parkinson's disease

The lateral habenula (LHb) plays an important role in the regulation of depression. At present, it is not clear whether GABA_A receptor-mediated inhibitory transmission in the LHb is involved in Parkinson's disease (PD)-associated depression. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra in rats induced depressive-like behaviors and led to hyperactivity of LHb neurons compared to sham-operated rats, which attribute to depletion of dopamine, and decreased synthesis and release of GABA and increased release of glutamate in the LHb. Intra-LHb injection of GABA_A receptor agonist muscimol produced antidepressant-like effects, while the injection of GABA_A receptor antagonist picrotoxin induced or increased the expression of depressive-like behaviors in sham-operated and the lesioned rats. However, the doses producing these behavioral effects in the lesioned rats were lower than those in sham-operated rats. Intra-LHb injection of muscimol decreased the firing rate of LHb neurons and increased the medial prefrontal cortex serotonin (5-HT) release; conversely, picrotoxin increased the firing rate of the neurons and decreased 5-HT release in two groups of rats. Compared to sham-operated rats, the duration of muscimol and picrotoxin action on the firing rate of the neurons and 5-HT release was prolonged in the lesioned rats. These changes in the lesioned rats were associated with up-regulation of the expression of α1 subunit-containing GABA_A receptors and reduction of GABA release in the LHb. Collectively, our findings suggest that degeneration of the nigrostriatal pathway impairs GABA_A receptor-mediated inhibitory transmission in the LHb, and the transmission is important for regulating PD-associated depression.

MPP+-Lesioned Mice: an Experimental Model of Motor, Emotional, Memory/Learning, and Striatal Neurochemical Dysfunctions

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces motor and nonmotor dysfunctions resembling Parkinson's disease (PD); however, studies investigating the effects of 1-methyl-4-phenylpyridinium (MPP⁺), an active oxidative product of MPTP, are scarce. This study investigated the behavioral and striatal neurochemical changes (related to oxidative damage, glial markers, and neurotrophic factors) 24 h after intracerebroventricular administration of MPP⁺ (1.8-18 μg/mouse) in C57BL6 mice. MPP⁺ administration at high dose (18 μg/mouse) altered motor parameters, since it increased the latency to leave the first quadrant and reduced crossing, rearing, and grooming responses in the open-field test and decreased rotarod latency time. MPP⁺ administration at low dose (1.8 μg/mouse) caused specific nonmotor dysfunctions as it produced a depressive-like effect in the forced swim test and tail suspension test, loss of motivational and self-care behavior in the splash test, anxiety-like effect in the elevated plus maze test, and short-term memory deficit in the step-down inhibitory avoidance task, without altering ambulation. MPP⁺ at doses of 1.8-18 μg/mouse increased tyrosine hydroxylase (TH) immunocontent and at 18 μg/mouse increased α-synuclein and decreased parkin immunocontent. The astrocytic calcium-binding protein S100B and glial fibrillary acidic protein (GFAP)/S100B ratio was decreased following MPP⁺ administration (18 μg/mouse). At this highest dose, MPP⁺ increased the ionized calcium-binding adapter molecule 1 (Iba-1) immunocontent, suggesting microglial activation. Also, MPP⁺ at a dose of 18 μg/mouse increased thiobarbituric acid reactive substances (TBARS) and glutathione (GSH) levels and increased glutathione peroxidase (GPx) and hemeoxygenase-1 (HO-1) immunocontent, suggesting a significant role for oxidative stress in the MPP⁺-induced striatal damage. MPP⁺ (18 μg/mouse) also increased striatal fibroblast growth factor 2 (FGF-2) and brain-derived neurotrophic factor (BDNF) levels. Moreover, MPP⁺ decreased tropomyosin receptor kinase B (TrkB) immunocontent. Finally, MPP⁺ (1.8-18 μg/mouse) increased serum corticosterone levels and did not alter acetylcholinesterase (AChE) activity in the striatum but increased it in cerebral cortex and hippocampus. Collectively, these results indicate that MPP⁺ administration at low doses may be used as a model of emotional and memory/learning behavioral deficit related to PD and that MPP⁺ administration at high dose could be useful for analysis of striatal dysfunctions associated with motor deficits in PD.

On the translocation of bacteria and their lipopolysaccharides between blood and peripheral locations in chronic, inflammatory diseases: the central roles of LPS and LPS-induced cell death

We have recently highlighted (and added to) the considerable evidence that blood can contain dormant bacteria. By definition, such bacteria may be resuscitated (and thus proliferate). This may occur under conditions that lead to or exacerbate chronic, inflammatory diseases that are normally considered to lack a microbial component. Bacterial cell wall components, such as the endotoxin lipopolysaccharide (LPS) of Gram-negative strains, are well known as potent inflammatory agents, but should normally be cleared. Thus, their continuing production and replenishment from dormant bacterial reservoirs provides an easy explanation for the continuing, low-grade inflammation (and inflammatory cytokine production) that is characteristic of many such diseases. Although experimental conditions and determinants have varied considerably between investigators, we summarise the evidence that in a great many circumstances LPS can play a central role in all of these processes, including in particular cell death processes that permit translocation between the gut, blood and other tissues. Such localised cell death processes might also contribute strongly to the specific diseases of interest. The bacterial requirement for free iron explains the strong co-existence in these diseases of iron dysregulation, LPS production, and inflammation. Overall this analysis provides an integrative picture, with significant predictive power, that is able to link these processes via the centrality of a dormant blood microbiome that can resuscitate and shed cell wall components.

Apathy and Impulse Control Disorders: Yin & Yang of Dopamine Dependent Behaviors

Neuropsychiatric symptoms are common non-motor symptoms in Parkinson's disease (PD). Apathy and impulse control disorders (ICD) are two opposite motivational expressions of a continuous behavioural spectrum involving hypo- and hyperdopaminergia. Both syndromes share pathological (decreased vs increased) dopamine receptor stimulation states. Apathy belongs to the spectrum of hypodopaminergic symptoms together with anhedonia, anxiety and depression. Apathy is a key symptom of PD which worsens with disease progression. Animal models, imaging and pharmacological studies concur in pointing out dopaminergic denervation in the aetiology of parkinsonian apathy with a cardinal role of decreased tonic D2/D3 receptor stimulation. ICDs are part of the hyperdopaminergic behavioural spectrum, which also includes punding, and dopamine dysregulation syndrome (DDS), which are all related to non-physiological dopaminergic stimulation induced by antiparkinsonian drugs. According to clinical data tonic D2/D3 receptor stimulation can be sufficient to induce ICDs. Clinical observations in drug addiction and PD as well as data from studies in dopamine depleted rodents provide hints allowing to argue that both pulsatile D1 and D2 receptor stimulation and the severity of dopaminergic denervation are risk factors to develop punding behavior and DDS. Imaging studies have shown that the brain structures involved in drug addiction are also involved in hyperdopaminergic behaviours with increase of bottom-up appetitive drive and decrease in prefrontal top down behavioural control.

Pioglitazone, a PPARγ agonist rescues depression associated with obesity using chronic unpredictable mild stress model in experimental mice

Pioglitazone, a peroxisome proliferator activated receptor gamma (PPARγ) agonist belonging to thiazolidinedione class, is mainly used in diabetes mellitus. Obese subjects are twice likely to become depressed than non-obese individuals. The biological mechanisms linking depression with obesity still remain poorly understood and there is immense need for better therapeutic intervention against such co-morbid disorders. The present study investigates the effect of pioglitazone on the chronic unpredictable mild stress (CUMS) induced depression in obese mice by using behavioral tests and biochemical estimations. Mice were fed with high fat diet (HFD) for 14 weeks and were further subjected to different stress procedures for 28 days to induce depressive behavior. Animals were administered orally with pioglitazone (30 mg/kg p.o.)/escitalopram (10 mg/kg p.o.)/vehicle (10 ml/kg p.o.) daily from day 15-28. Various behavioral paradigms such as sucrose preference test, forced swim test (FST), tail suspension test (TST) and elevated plus maze (EPM) were performed. Biochemical estimations including plasma glucose, total cholesterol, triglycerides, and total proteins were performed. The data obtained from behavioral assays and biochemical assessments indicated that obese animals exhibited severe depressive-like behavior compared to non-obese animals. Furthermore, obese animals subjected to CUMS worsen the depressive behavior compared to obese control animals. Repetitive treatment with pioglitazone reversed the CUMS induced behavioral and biochemical alterations in HFD fed obese mice which atleast in part may be mediated through improving altered plasma glucose. The study suggests that pioglitazone needs further attention with respect to molecular mechanisms that could provide a better therapeutic strategy against depression associated with obesity.

Serotonin7 receptors in the lateral habenular nucleus regulate depressive-like behaviors in the hemiparkinsonian rats

Preclinical studies indicate that serotonin7 (5-HT7) receptors may regulate depressive-like behaviors. Depression is a common symptom in Parkinson's disease (PD); however, its pathophysiology is unclear. Here we examined whether 5-HT7 receptors in the lateral habenular nucleus (LHb) involve in the regulation of PD-related depression. Unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta in rats induced depressive-like responses as measured by the sucrose preference and forced swim tests when compared to sham-operated rats. Intra-LHb injection of 5-HT7 receptor agonist AS19 (1, 2 and 4μg/rat) induced or increased the expression of depressive-like behaviors in sham-operated and the lesioned rats. Further, intra-LHb injection of 5-HT7 receptor antagonist SB269970 (1.5, 3 and 6μg/rat) produced antidepressant effects in the two groups of rats. However, the doses producing these effects in the lesioned rats were higher than those in sham-operated rats. Neurochemical results showed that intra-LHb injection of AS19 (4μg/rat) decreased dopamine and 5-HT levels in the medial prefrontal cortex, habenula and hippocampus in sham-operated and the lesioned rats; whereas SB269970 (6μg/rat) increased dopamine and 5-HT levels in these structures. In addition, noradrenaline levels in these structures were not changed after intra-LHb injection of AS19 or SB269970 in the two groups of rats. These findings suggest that activation or blockade of 5-HT7 receptors in the LHb may change the activity of LHb glutamate neurons, and then decreases or increases dopamine and 5-HT levels in the limbic and limbic-related brain regions, which are involved in the regulation of depressive-like behaviors.

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.

Curcumin ameliorates dopaminergic neuronal oxidative damage via activation of the Akt/Nrf2 pathway

Parkinson's disease (PD) is an age-related complex neurodegenerative disease that affects ≤ 80% of dopaminergic neurons in the substantia nigra pars compacta (SNpc). It has previously been suggested that mitochondrial dysfunction, oxidative stress and oxidative damage underlie the pathogenesis of PD. Curcumin, which is a major active polyphenol component extracted from the rhizomes of Curcuma longa (Zingiberaceae), has been reported to exert neuroprotective effects on an experimental model of PD. The present study conducted a series of in vivo experiments, in order to investigate the effects of curcumin on behavioral deficits, oxidative damage and related mechanisms. The results demonstrated that curcumin was able to significantly alleviate motor dysfunction and increase suppressed tyrosine hydroxylase (TH) activity in the SNpc of rotenone (ROT)-injured rats. Biochemical measurements indicated that rats pretreated with curcumin exhibited increased glutathione (GSH) levels, and reduced reactive oxygen species activity and malondialdehyde content. Mechanistic studies demonstrated that curcumin significantly restored the expression levels of heme oxygenase-1 and

NAD(P)H

quinone oxidoreductase 1, thus ameliorating ROT-induced damage in vivo, via the phosphorylation of Akt and nuclear factor erythroid 2-related factor 2 (Nrf2). Further studies indicated that the Akt/Nrf2 signaling pathway was associated with the protective role of curcumin in ROT-treated rats. Inhibiting the Akt/Nrf2 pathway using a lentiviral vector containing Nrf2-specific short hairpin RNA, or the phosphoinositide 3-kinase inhibitor LY294002, markedly reduced the expression levels of TH and GSH, ultimately attenuating the neuroprotective effects of curcumin against oxidative damage. These results indicated that curcumin was able to significantly ameliorate ROT-induced dopaminergic neuronal oxidative damage in the SNpc of rats via activation of the Akt/Nrf2 signaling pathway.

Paraquat and psychological stressor interactions as pertains to Parkinsonian co-morbidity

A number of epidemiological and experimental studies have implicated the non-selective herbicide, paraquat, in the development of sporadic Parkinson's disease (PD). While preclinical research has focused mainly on elucidating the nigrostriatal effects of paraquat, relatively little data are available concerning non-motor brain systems and inflammatory immune processes (which have been implicated in PD). Hence, in the present study, we sought to take a multi-system approach to characterize the influence of paraquat upon extra-nigrostriatal brain regions, as well ascertain whether the impact of the pesticide might be enhanced in the context of chronic intermittent stressor exposure. Our findings support the contention that paraquat itself acted as a systemic stressor, with the pesticide increasing plasma corticosterone, as well as altering neurochemical activity in the locus coeruleus, paraventricular nucleus of the hypothalamus, nucleus accumbens, dorsal striatum, and central amygdala. However, with the important exception striatal dopamine turnover, the stressor treatment did not further augment these effects. Additionally, paraquat altered inter-cytokine correlations and, to a lesser extent, circulating cytokine levels, and concomitant stress exposure modulated some of these effects. Finally, paraquat provoked significant (albeit modest) reductions of sucrose preference and weight gain, hinting at possible anhendonic-like or sickness responses. These data suggest that, in addition to being a well known oxidative stress generator, paraquat can act as a systemic stressor affecting hormonal and neurochemical activity, but largely not interacting with a concomitant stressor regimen.

REM sleep deprivation promotes a dopaminergic influence in the striatal MT2 anxiolytic-like effects

The aim of this study was to investigate the possible anxiolytic-like effects of striatal MT2 activation, and its counteraction induced by the selective blockade of this receptor. Furthermore, we analyzed this condition under the paradigm of rapid eye movement (REM) sleep deprivation (REMSD) and the animal model of Parkinson’s disease (PD) induced by rotenone. Male Wistar rats were infused with intranigral rotenone (12 μg/μL), and 7 days later were subjected to 24 h of REMSD. Afterwards the rats underwent striatal micro-infusions of selective melatonin MT2 receptor agonist, 8-M-PDOT (10 μg/μL) or selective melatonin MT2 receptor antagonist, 4-P-PDOT (5 μg/μL) or vehicle. Subsequently, the animals were tested in the open-field (OP) and elevated plus maze (EPM) tests. Results indicated that the activation of MT2 receptors produced anxiolytic-like effects. In opposite, the MT2 blockade did not show an anxiogenic-like effect. Besides, REMSD induced anxiolytic-like effects similar to 8-M-PDOT. MT2 activation generated a prevalent locomotor increase compared to MT2 blockade in the context of REMSD. Together, these results suggest a striatal MT2 modulation associated to the REMSD-induced dopaminergic supersensitivity causing a possible dopaminergic influence in the MT2 anxiolytic-like effects in the intranigral rotenone model of PD.

Decrease of gene expression of astrocytic 5-HT2B receptors parallels development of depressive phenotype in a mouse model of Parkinson's disease

Astrocytes contribute to pathogenesis of neuropsychiatric disorders, including major depression. Stimulation of astroglial 5-HT2B receptors transactivates epidermal growth factor receptors (EGFRs) and regulates gene expression. Previously we reported that expression of 5-HT2B receptors in cortical astrocytes is down-regulated in animals, which developed anhedonia in response to chronic stress; moreover this down-regulation as well as anhedonia, are reversed by chronic treatment with fluoxetine. In this study we have investigated whether astrocytic 5-HT2B receptor is involved in anhedonia in C57BL/6 mice model of Parkinson' disease (PD) induced by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for 7 days. The MPTP treatment induced anhendonia in 66.7% of animals. The appearance of depressive behavior was accompanied with motor deficiency and decrease of tyrosine hydroxylase (TH) expression. Expression of mRNA and protein of 5-HT2B receptor in animals that became anhedonic decreased to 77.3 and 79.3% of control groups, respectively; in animals that received MPTP but did not develop anhedonia the expression of 5-HT2B receptor did not change. Experiments with FACS-sorted isolated cells demonstrated that decrease in 5-HT2B receptor expression was confined to astrocytes, and did not occur in neurons. Fluoxetine corrected MPTP-induced decrease of 5-HT2B receptor expression and depressive behavior. Our findings indicate that regulation of gene expression of 5-HT2B receptors in astroglia may be associated with pathophysiological evolution of PD-induced depression.

Effects of Agmatine on Depressive-Like Behavior Induced by Intracerebroventricular Administration of 1-Methyl-4-phenylpyridinium (MPP(+))

Considering that depression is a common non-motor comorbidity of Parkinson's disease and that agmatine is an endogenous neuromodulator that emerges as a potential agent to manage diverse central nervous system disorders, this study investigated the antidepressant-like effect of agmatine in mice intracerebroventricularly (i.c.v.) injected with the dopaminergic neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)). Male C57BL6 mice were treated with agmatine (0.0001, 0.1 or 1 mg/kg) and 60 min later the animals received an i.c.v. injection of MPP(+) (1.8 µg/site). Twenty-four hours after MPP(+) administration, immobility time, anhedonic behavior, and locomotor activity were evaluated in the tail suspension test (TST), splash test, and open field test, respectively. Using Western blot analysis, we investigated the putative modulation of MPP(+) and agmatine on striatal and frontal cortex levels of tyrosine hydroxylase (TH) and brain-derived neurotrophic factor (BDNF). MPP(+) increased the immobility time of mice in the TST, as well as induced an anhedonic-like behavior in the splash test, effects which were prevented by pre-treatment with agmatine at the three tested doses. Neither drug, alone or in combination, altered the locomotor activity of mice. I.c.v. administration of MPP(+) increased the striatal immunocontent of TH, an effect prevented by the three tested doses of agmatine. MPP(+) and agmatine did not alter the immunocontent of BDNF in striatum and frontal cortex. These results demonstrate for the first time the antidepressant-like effects of agmatine in an animal model of depressive-like behavior induced by the dopaminergic neurotoxin MPP(+).

Early use of oleanolic acid provides protection against 6-hydroxydopamine induced dopamine neurodegeneration

Oleanolic acid is a triterpenoid that has been shown to possess antioxidant properties. In this study we investigated the effects of oleanolic acid in a parkinsonian rat model. Unilateral 6-hydroxydopamine (6-OHDA) lesions were carried out on postnatal day (PND) 60 in 4 groups viz. (1) Rats that started oleanolic acid treatment 7 days prior to lesion. (2) Rats not treated with oleanolic acid. (3) Rats that started oleanolic acid treatment 1 day post-lesion. (4) Rats treated with oleanolic acid 7 days post-lesion. The degree of forelimb impairment was assessed using limb use asymmetry and forelimb akinesia tests. Neurochemical changes were assessed using a Dopamine ELISA kit and mitochondrial apoptosis was measured using a mitochondrial apoptosis detection kit. In this study, animals injected with 6-OHDA displayed forelimb use asymmetry that was ameliorated by treatment with oleanolic acid 7 days pre- and 1 day post-lesion. In the cylinder test, rats injected with 6-OHDA favored using the forelimb ipsilateral (unimpaired) to the lesioned hemisphere while rats treated with oleanolic acid used the forelimb contralateral (impaired) to the lesioned hemisphere significantly more. Rats treated with oleanolic acid 7 days pre- and 1 day post-lesion had more dopamine in the striatum than the non-treated or the 7 days after lesion rats. Similarly, 6-OHDA-induced membrane depolarization was decreased in rats that received oleanolic acid treatment pre- or immediately post-lesion. This suggests that early treatment with oleanolic acid protects dopamine neurons from the toxic effects of 6-OHDA.

Reconceptualizing anhedonia: novel perspectives on balancing the pleasure networks in the human brain

Anhedonia, the lack of pleasure, has been shown to be a critical feature of a range of psychiatric disorders. Yet, it is currently measured primarily through subjective self-reports and as such has been difficult to submit to rigorous scientific analysis. New insights from affective neuroscience hold considerable promise in improving our understanding of anhedonia and for providing useful objective behavioral measures to complement traditional self-report measures, potentially leading to better diagnoses and novel treatments. Here, we review the state-of-the-art of hedonia research and specifically the established mechanisms of wanting, liking, and learning. Based on this framework we propose to conceptualize anhedonia as impairments in some or all of these processes, thereby departing from the longstanding view of anhedonia as solely reduced subjective experience of pleasure. We discuss how deficits in each of the reward components can lead to different expressions, or subtypes, of anhedonia affording novel ways of measurement. Specifically, we review evidence suggesting that patients suffering from depression and schizophrenia show impairments in wanting and learning, while some aspects of conscious liking seem surprisingly intact. Furthermore, the evidence suggests that anhedonia is heterogeneous across psychiatric disorders, depending on which parts of the pleasure networks are most affected. This in turn has implications for diagnosis and treatment of anhedonia.

Chronic amitriptyline treatment attenuates nigrostriatal degeneration and significantly alters trophic support in a rat model of parkinsonism

In addition to alleviating depression, long-term adaptive changes induced by antidepressants may regulate neural plasticity in the diseased brain, providing symptomatic and disease-modifying effects in Parkinson's disease. The present study investigated whether chronic treatment with a frequently prescribed tricyclic antidepressant was neuroprotective in a 6-hydroxydopamine (6-OHDA) rat model of parkinsonism. In lesioned animals, chronic amitriptyline (AMI; 5 mg/kg) treatment resulted in a significant sparing of tyrosine hydroxylase-immunoreactive (THir) neurons in the substantia nigra pars compacta (SNpc) compared with saline treatment. Additionally, striatal fibers were preserved and functional motor deficits were attenuated. Although 6-OHDA lesions did not induce anhedonia in our model, the dose of AMI utilized had antidepressant activity as demonstrated by reduced immobility. Recent in vitro and in vivo data provide evidence that trophic factors such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) may be key mediators of the therapeutic response to antidepressants. Therefore, we investigated whether AMI mediates changes in these specific trophic factors in the intact and degenerating nigrostriatal system. Chronic AMI treatment mediates an increase in nigral BDNF both before and during ongoing degeneration, suggesting it may contribute to neuroprotection observed in vivo. However, over time, AMI reduced BDNF levels in the striatum, indicating tricyclic therapy differentially regulates trophic factors within the nigrostriatal system. Combined, these results suggest that AMI treatment attenuates dopamine neuron loss and elicits significant trophic changes relevant to dopamine neuron survival.

Activation of serotonin(2C) receptors in the lateral habenular nucleus increases the expression of depression-related behaviors in the hemiparkinsonian rat

The roles of lateral habenular nucleus (LHb) glutamate neurons and serotonin2C (5-HT2C) receptors in depression are poorly understood, particularly in Parkinson's disease-associated depression. Here we assessed the importance of LHb glutamate neurons and 5-HT2C receptors for depressive-like behaviors in sham-operated rats and rats with unilateral 6-hydroxydopamine lesions of the substantia nigra. The lesion induced depressive-like responses compared to sham-operated rats. Intra-LHb injection of potent, selective 5-HT2C receptor agonist Ro60-0175 decreased sucrose consumption and increased immobility time in sham-operated rats, indicating the induction of depressive-like responses, and intra-LHb injection of Ro60-0175 further increased the expression of depressive-like behaviors in the lesioned rats. Activation of LHb 5-HT2C receptors by the local administration of Ro60-0175 increased the firing rate of EAAC1 (a neuronal glutamate transporter)-positive neurons and percentage of the neurons with burst-firing pattern in the two groups of rats. Compared to sham-operated rats, the duration of Ro60-0175 action on the firing rate of EAAC1-positive neurons was markedly prolonged in the lesioned rats. Intra-LHb injection of Ro60-0175 decreased dopamine, 5-HT and noradrenaline levels in the medial prefrontal cortex, habenula, hippocampus and amygdala in sham-operated and the lesioned rats. The lesion did not change the percentage of EAAC1/5-HT2C receptor co-expressing neurons in the LHb. These findings indicate that activation of 5-HT2C receptors in the LHb increases firing activity of LHb glutamate neurons and then decreases monoamine levels in several brain regions, which increase the expression of depressive-like behaviors. Further, our results also suggest that the lesion leads to hyperfunctionality of 5-HT2C receptors on glutamate neurons of the LHb.

An update on the rotenone models of Parkinson's disease: their ability to reproduce the features of clinical disease and model gene-environment interactions

Parkinson's disease (PD) is the second most common neurodegenerative disorder that is characterized by two major neuropathological hallmarks: the degeneration of dopaminergic neurons in the substantia nigra (SN) and the presence of Lewy bodies in the surviving SN neurons, as well as other regions of the central and peripheral nervous system. Animal models have been invaluable tools for investigating the underlying mechanisms of the pathogenesis of PD and testing new potential symptomatic, neuroprotective and neurorestorative therapies. However, the usefulness of these models is dependent on how precisely they replicate the features of clinical PD with some studies now employing combined gene-environment models to replicate more of the affected pathways. The rotenone model of PD has become of great interest following the seminal paper by the Greenamyre group in 2000 (Betarbet et al., 2000). This paper reported for the first time that systemic rotenone was able to reproduce the two pathological hallmarks of PD as well as certain parkinsonian motor deficits. Since 2000, many research groups have actively used the rotenone model worldwide. This paper will review rotenone models, focusing upon their ability to reproduce the two pathological hallmarks of PD, motor deficits, extranigral pathology and non-motor symptoms. We will also summarize the recent advances in neuroprotective therapies, focusing on those that investigated non-motor symptoms and review rotenone models used in combination with PD genetic models to investigate gene-environment interactions.

Effect of Ginkgo biloba extract on lipopolysaccharide-induced anhedonic depressive-like behavior in male rats

The peripheral administration of lipopolysaccharide (LPS) induces depressive-like behavior. Anhedonia is a core symptom of depression, defined as a loss of the capacity to experience pleasure. The present study used the sucrose preference test to investigate the influence of Ginkgo biloba extract (EGb 761) on LPS-induced anhedonia in male rats. The animals were randomly divided into four groups: (I) vehicle + saline, (II) vehicle + LPS, (III) EGb 761 + saline, and (IV) EGb 761 + LPS. Saline or LPS (100 µg/kg) was administered intraperitoneally 2 h before the sucrose preference test. Sucrose consumption was recorded 2, 4, 6, 13, and 24 h after 100 µg/kg of LPS or saline injection in the dark phase of the light/dark cycle. Dopamine and serotonin levels in the nucleus accumbens were measured. Our results indicated that the vehicle + LPS group exhibited a significant decrease in sucrose intake compared with the vehicle + saline group. The EGb 761 + LPS group showed more sucrose and food consumption than the vehicle + LPS group. Additionally, compared with the EGb 761 + LPS group, the vehicle + LPS group had less dopamine levels in the nucleus accumbens. Treatment with EGb 761 had no effect on water intake. Our results suggest that EGb 761 may be useful for reducing anhedonic depressive-like behavior.

Impact of endocrine-disrupting chemicals on neural development and the onset of neurological disorders

Even though high doses of organic pollutants are toxic, relatively low concentrations have been reported to cause long-term alterations in functioning of individual organisms, populations and even next generations. Among these pollutants are dioxins, polychlorinated biphenyls, pesticides, brominated flame retardants, plasticizers (bisphenol A, nonylphenol, and phthalates) as well as personal care products and drugs. In addition to toxic effects, they are able to interfere with hormone receptors, hormone synthesis or hormone conversion. Because these chemicals alter hormone-dependent processes and disrupt functioning of the endocrine glands, they have been classified as endocrine-disrupting chemicals (EDCs). Because certain EDCs are able to alter neural transmission and the formation of neural networks, the term neural-disrupting chemicals has been introduced, thus implicating EDCs in the etiology of neurological disorders. Recently, public concern has been focused on the effects of EDCs on brain function, concomitantly with an increase in neuropsychiatric disorders, including autism, attention deficit and hyperactivity disorder as well as learning disabilities and aggressiveness. Several lines of evidence suggest that exposure to EDCs is associated with depression and could result in neural degeneration. EDCs act via several classes of receptors with the best documented mechanisms being reported for nuclear steroid and xenobiotic receptors. Low doses of EDCs have been postulated to cause incomplete methylation of specific gene regions in the young brain and to impair neural development and brain functions across generations. Efforts are needed to develop systematic epidemiological studies and to investigate the mechanisms of action of EDCs in order to fully understand their effects on wildlife and humans.

Depression in Parkinson's disease

Depression is a frequent comorbid disorder of Parkinson's disease; however, little is known about its pathomechanisms. Although depression is an important factor negatively affecting the quality of life of parkinsonian patients, it often remains undiagnosed and therefore untreated. Furthermore, antidepressant therapy is problematic because of the need to combine antidepressant drugs with antiparkinsonian treatments. The present paper gives an overview of characteristic features of Parkinson's disease-associated depression, experimental studies on its animal models, potential mechanisms involved in its occurrence and possible strategies for treatment.

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.

Performance of motor associated behavioural tests following chronic nicotine administration

Background

Nicotine has shown potential therapeutic value for neurodegenerative diseases though there are concerns that it may induce behavioural deficits.

Purpose

The present study sought to determine the effect of chronic nicotine administration on overall motor functions and coordination.

Methods

Forty adult female and male Wistar rats were randomly grouped into 4 groups. Treated groups were administered nicotine via subcutaneous injections at doses of 0.25, 2 and 4 mg/kg body weight for 28 days. Control groups received normal saline. All animals were monitored for the first few minutes after each injection for any observed immediate effect of drug administration. Motor associated behavioural tests performed include: open field test, string test for grip strength and limb impairment, movement initiation and step test.

Results

Nicotine induced muscular convulsions within the first 1-5 minutes following daily subcutaneous injections, throughout the period of administration. This was observed to be more severe in females. Nicotine did not produce major alterations in overall motor functions and coordination in both females and males.

Conclusion

The present study shows chronic nicotine treatment produces muscular convulsion but no major deficit in overall motor function and coordination and that any observed alterations may just be transient effects.

Putative role of monoamines in the antidepressant-like mechanism induced by striatal MT2 blockade

It has been observed that the secretion pattern of melatonin is modified in Parkinson's disease (PD). Hence, it is hypothesized that dysregulations of melatonin MT2 receptors may be involved in the installation of depression in PD patients. Together with recent evidence based on the use of the intranigral rotenone model of PD, have led to the hypothesis that modulating the striatal MT2 receptor could provide a more comprehensive understanding of the antidepressant properties triggered. To further investigate this issue, male Wistar rats were infused with intranigral rotenone (12μg/μL) and seven days later subjected to a rapid eye movement sleep deprivation (REMSD) for 24h. After, we injected within the striatum the MT2 selective agonist, 8-M-PDOT (10μg/μL), the MT2 selective antagonist, 4-P-PDOT (5μg/μL) or vehicle. Subsequently, they were tested in the forced swimming test and were allowed to perform the sleep rebound (REB). Then, the rats were re-tested, and the striatum, hippocampus and substantia nigra pars compacta (SNpc) were collected for neurochemical purposes. Results indicated substantial antidepressant effects promoted by the blockade of striatal MT2 receptors that were potentiated by REMSD. MT2 activation increased DA levels in the striatum and hippocampus, while MT2 blockade increase DA in the SNpc. 4-P-PDOT treatment of the rotenone REMSD group generated a decrement in 5-HT levels within the striatum, hippocampus and SNpc. However, increased 5-HT turnover was observed among these structures. Therefore, we demonstrated the neurochemical antidepressant effect induced by striatal MT2 blockage associated with REMSD in the rotenone model of 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.

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.

Pramipexole but not imipramine or fluoxetine reverses the "depressive-like" behaviour in a rat model of preclinical stages of Parkinson's disease

Depression is a frequent comorbid disorder in Parkinson's disease and may antedate its motor symptoms. However, mechanisms underlying Parkinson's disease-associated depression are unknown and its current medication is insufficient. The aim of the present study was to compare antidepressant-like effects of imipramine, fluoxetine and pramipexole in a model of preclinical stages of Parkinson's disease in rats. 6-Hydroxydopamine was bilaterally injected into the ventrolateral region of the caudate-putamen in rats. This treatment induced moderate decreases in the levels of dopamine and its metabolites in the caudate-putamen, nucleus accumbens and frontal cortex and reduced the density of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra pars compacta and ventral tegmental area. The lesion increased immobility measured in the forced swimming test without influencing locomotor activity. Chronic (13 days) administration of pramipexole (1mg/kg sc/twice a day) reversed prolongation of the immobility time in lesioned animals but did not stimulate their locomotion. Chronic pramipexole activated dopaminergic transmission in the brain structures which might contribute to its effectiveness in the forced swimming test. In contrast, the 13-day administration of imipramine (10mg/kg ip/day) and fluoxetine (10mg/kg ip/day) did not shorten the immobility time in lesioned rats but reduced their locomotion. The present study indicates that already a moderate lesion of dopaminergic neurons induces "depressive-like" behaviour in animals which is reversed by chronic administration of the antiparkinsonian drug, pramipexole.

Oral supplements of aqueous extract of tomato seeds alleviate motor abnormality, oxidative impairments and neurotoxicity induced by rotenone in mice: relevance to Parkinson's disease

Although tomato seeds (an industrial by-product) are known to contain several bioactive compounds, studies describing their health effects are limited. Previously, we evidenced that aqueous extract of tomato seeds (TSE) markedly attenuated rotenone (ROT)-induced oxidative stress and neurotoxicity in Drosophila system. This study investigated the neuroprotective effect of TSE in a chronic ROT model of neurotoxicity in mice. Initially, we assessed the potential of oral supplements of TSE to modulate the levels of endogenous markers of oxidative stress in brain regions of mice. Subsequently, employing a co-exposure paradigm, the propensity of TSE (100 mg/kg bw, 3 weeks) to attenuate ROT-induced behavioral phenotype (gait abnormalities, anxiety-like state), oxidative dysfunctions and neurotoxicity was examined. We found that mice provided with TSE supplements exhibited progressive improvement in gait pattern and exploratory behavior. TSE markedly offset ROT-induced oxidative impairments, restored reduced glutathione levels, antioxidant defenses (superoxide dismutase, glutathione peroxidase) and protein carbonyls content in brain regions. Specifically, TSE effectively diminished ROT induced elevation in the activity levels of acetylcholinesterase and restored the dopamine levels in striatum. Interestingly, in mitochondria, TSE was able to restore the activity of mitochondrial complexes and redox state. Collectively, our findings in the chronic ROT model demonstrate the ability of TSE to alleviate behavioral phenotype, oxidative stress, mitochondrial dysfunction and neurotoxicity. Further studies in dopaminergic cell models are necessary to understand the precise molecular mechanism/s by which tomato seed bioactives offer significant neuroprotection.

Activation of prelimbic 5-HT1A receptors produces antidepressant-like effects in a unilateral rat model of Parkinson's disease

Depression is a common symptom in Parkinson's disease (PD), but its pathophysiology remains unclear. Several lines of studies have revealed that the prelimbic (PrL) sub-region of the ventral medial prefrontal cortex and 5-HT1A receptors are involved in the regulation of depression. In this study, we examined whether complete unilateral lesions of the medial forebrain bundle (MFB) using 6-hydroxydopamine in rats are able to induce depressive-like behaviors, the role of PrL 5-HT1A receptors in the regulation of these behaviors, and co-localization of 5-HT1A receptor and neuronal glutamate transporter EAAC1-immunoreactive (EAAC1-ir) neurons in the PrL. The MFB lesions induced depressive-like responses as measured by the sucrose preference and forced swim tests when compared to sham-operated rats. The intra-PrL injection of 5HT1A receptor agonist 8-OH-DPAT (50, 100, and 500ng/rat) increased sucrose consumption, and decreased immobility time in both sham-operated and the lesioned rats, indicating the induction of antidepressant effects. Furthermore, the intra-PrL injection of 5HT1A receptor antagonist WAY-100635 (60, 120, and 240ng/rat) showed a decrease in sucrose consumption, and an increase in immobility time, indicating the induction of depressive-like responses. However, the effective doses in the lesioned rats were higher than those in sham-operated rats, which attribute to down-regulation of 5-HT1A receptor expression on EAAC1-ir neurons in the PrL of the lesioned rats. These findings suggest that unilateral lesions of the MFB in rats may induce depressive-like behaviors, and 5-HT1A receptors of the PrL play an important role in the regulation of these behaviors.

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.