101,869 research outputs found
STUDY OF THE ROLE OF THE SEROTONINERGIC SYSTEM IN THE BRAIN FUNCTIONALITY AND IN THE VULNERABILITY TO PSYCHOPATHOLOGIES:A GENETIC APPROACH
No full textPsychiatric pathologies are the second leading cause of disability worldwide with about 10% of the general population that manifest at least one symptom during their lifetime. This, together with the only partial effectiveness of the treatments adopted to date, make these illnesses an important burden for the society as well as for families and patients.
The first theory elaborated to explain the onset of psychiatric pathologies is the monoaminergic hypothesis that postulated how low levels of monoamines such as serotonin in the brain could be at the basis of depressive episodes and of other mood disorders. In line, human studies highlighted how alterations in different genes coding for different players involved in the serotoninergic system can be related to an increased susceptibility for psychopathologies.
Despite this linkage seems striking, different aspects of these pathologies cannot be explained with a direct causal relationship, making this hypothesis part of a bigger picture that also involves the environmental factors as well as other mechanisms.
On these bases, understanding the complexity of the systems that are modulated by serotoninergic alterations could give novel insights in understanding these such heterogeneous diseases.
To better clarify this aspect, during my PhD I took advantage of different genetically modified animal models characterized by alterations in the serotoninergic system. In particular, we evaluated the effect of low functionality of the serotonin transporter (SERT) on brain functions and we confirmed the pathological-like behavior of SERT-/- rats, characterized by a massive presence of serotonin in the extracellular compartments of the whole body. Moreover, we perform molecular analyses that confirmed alterations in different systems such as the neuroplastic mechanisms, the GABAergic system, and the dendritic spine functionality. Furthermore, we evaluated if a positive environment could ameliorate the behavior and the molecular abnormalities of SERT-/- rats finding a restorative effect of one month of enriched environment both on the anhedonic and anxiety-like behavior and on the molecular abnormalities.
Moreover, by altering the expression of the isoforms 1 or 2 of the tryptophan hydroxylase (TPH) enzyme, responsible for the production of serotonin in the periphery or in the brain respectively, we took into consideration TPH1-/- and TPH2-/- rats. More specifically, we worked on TPH2-/- rats, which do not have serotonin in the central nervous system and are characterized by an aggressive behavior and low anxiety levels at adulthood. Interestingly, we found that the lack of brain-serotonin was counteracted by an upregulation in the neurotrophin Brain-derived neurotrophic factor (Bdnf) expression. Moreover, we found that this compensatory mechanism was present also at early adolescence, while at post-natal day 10, when the blood-brain-barrier is not completely formed and we cannot distinguish between central and peripheral serotonin, Bdnf expression was lowered. Interestingly, this increased neuroplasticity at adulthood was not enough to cope with an acute stress such as one hour of restraint stress. Indeed, while wild-type rats showed an activation of the Bdnf machinery and of the transcription of the immediate early genes, this effect was reduced in TPH2-/- rats. Accordingly, we found that the hypothalamic pituitary adrenal (HPA) axis and specifically its genomic pathway activation was much more consistent in TPH2+/+ than in TPH2-/- rats.
Interestingly, we observed similar results also in TPH1-/- rats that showed a dramatic reduction in serotonin levels in different peripheral organs. Indeed, the lack of peripheral serotonin was able to reduce the anxiety-like behavior in these rats suggesting that also the peripheral pool of this molecule can alter brain functionality. Moreover, this positive effect on their behavior was sustained, at central level, by an increased expression of Bdnf. Nevertheless, also in this case, we found deficits in the reaction to the acute stress. Indeed, we found that the increased transcription of Bdnf and of the immediate early gene Arc happened specifically in wild-type while not in TPH1-/- rats. Similarly, the upregulation in the glucocorticorticoid responsive gene transcription was lower in a condition of absence of peripheral serotonin.
All the molecular analyses were conducted in the prefrontal cortex, a brain region highly innervated by serotoninergic fibers and involved in environmental changes response and in behavioral adaptations.
These results highlighted how these genetically modified animal models can be useful to study the role of serotonin in the modulation of brain functionality and the mechanisms involved in this process. Moreover, these findings supported the serotonin involvement in brain development and functionality. Ultimately, the data collected in this thesis give novel insights on the brain pathways affected by serotonin and on the role of this system in shaping the reaction to environmental stimuli in the field of psychiatric disorders
G Protein-Dependent Activation of the PKA-Erk1/2 Pathway by the Striatal Dopamine D1/D3 Receptor Heteromer Involves Beta-Arrestin and the Tyrosine Phosphatase Shp-2
No full textThe heteromer composed of dopamine D1 and D3 receptors (D1R-D3R) has been defined as a structure able to trigger Erk1/2 and Akt signaling in a G protein-independent, beta-arrestin 1-dependent way that is physiologically expressed in the ventral striatum and is likely involved in the control of locomotor activity. Indeed, abnormal levels of D1R-D3R heteromer in the dorsal striatum have been correlated with the development of L-DOPA-induced dyskinesia (LID) in Parkinson's disease patients, a motor complication associated with striatal D1R signaling, thus requiring Gs protein and PKA activity to activate Erk1/2. Therefore, to clarify the role of the D1R/D3R heteromer in LID, we investigated the signaling pathway induced by the heteromer using transfected cells and primary mouse striatal neurons. Collectively, we found that in both the cell models, D1R/D3R heteromer-induced activation of Erk1/2 exclusively required the D1R molecular effectors, such as Gs protein and PKA, with the contribution of the phosphatase Shp-2 and beta-arrestins, indicating that heterodimerization with the D3R abolishes the specific D3R-mediated signaling but strongly allows D1R signals. Therefore, while in physiological conditions the D1R/D3R heteromer could represent a mechanism that strengthens the D1R activity, its pathological expression may contribute to the abnormal PKA-Shp-2-Erk1/2 pathway connected with LID
Enrichment environment positively influences depression- and anxiety-like behavior in serotonin transporter knockout rats through the modulation of neuroplasticity, spine and GABAergic markers
No full textThe serotonin transporter (5-HTT in humans, SERT in rodents) is the main regulator of serotonergic transmission in the brain. The short allelic variant of the 5-HTT gene is in humans associated with psychopathologies and may enhance the vulnerability to develop depression after exposure to stressful events. Interestingly, the short allele also increases the sensitivity to a positive environment, which may buffer the vulnerability to depression. Since this polymorphism does not exist in rodents, male SERT knockout (SERT-/-) rats were tested to explore the molecular mechanisms based on this increased predisposition. This article investigates the influences of a positive manipulation, namely, enriched environment (EE), on the depressive-like behavior observed in SERT-/- rats. We found that one month of EE exposure normalized the anhedonic and anxious-like phenotype characteristics of this animal model. Moreover, we observed that EE exposure also restored the molecular alterations in the prefrontal cortex by positively modulating the expression of the neurotrophin Bdnf, and of spines and gamma-aminobutyric acid (GABA)ergic markers. Overall, our data confirm the depression-like phenotype of SERT-/- rats and highlight the ability of EE to restore behavioral and molecular alterations, thus promoting the opportunity to use EE as a supporting non-pharmacological approach to treat mood disorders
Centella asiatica l. Phytosome improves cognitive performance by promoting bdnf expression in rat prefrontal cortex
No full textA wide range of people in the world use natural remedies as primary approaches against illnesses. Accordingly, understanding the mechanisms of action of phytochemicals has become of great interest. In this context, Centella asiatica L. is extensively used, not only as anti-inflammatory or antioxidant agent but also as brain tonic. On this basis, the purpose of this study was to evaluate whether the chronic administration of C. asiatica L. to adult male rats was able to improve the expression of Bdnf, one of the main mediators of brain plasticity. Moreover, we assessed whether the treatment could affect the cognitive performance in the novel object recognition (NOR) test. We confirmed the presence of the main compounds in the plasma. Furthermore, C. asiatica L. administration induced an increase of Bdnf in the prefrontal cortex, and the administration of the higher dose of the extract was able to improve cognitive performance. Finally, the increase in the preference index in the NOR test was paralleled by a further increase in Bdnf expression. Overall, we highlight the ability of C. asiatica L. to affect brain functions by increasing Bdnf expression and by enhancing the cognitive performance
Chronic Treatment with a Phytosomal Preparation Containing Centella asiatica L. and Curcuma longa L. Affects Local Protein Synthesis by Modulating the BDNF-mTOR-S6 Pathway
No full textBrain derived neurotrophic factor (Bdnf) is the most diffuse neurotrophin in the central nervous system and it is crucial for the proper brain development and maintenance. Indeed, through the binding to its high affinity receptor TRKB and the activation of different intracellular cascades, it boosts cell survival, neurite growth and spine maturations mechanisms. Here, we evaluated if the chronic oral treatment for 10 days with a phytosomal preparation containing Centella asiatica L. and Curcuma longa L. could improve Bdnf levels in the prefrontal cortex of adult rats. Interestingly we found an increased expression of Bdnf with main effect of the treatment on the mTOR-S6 downstream signaling pathway. Accordingly, we found an increase in the expression of eukaryotic elongation factor (eEF2) with a shift towards the phosphorylated form thus increasing the transcription of Oligophrenin-1, a protein carrying the upstream Open Reading Frame (uORF) which reduction is paralleled by memory dysfunctions. These results show the ability of the phytosome to enhance mTOR-S6 regulated transcription and suggest the possibility to use this preparation in subjects with impairments in neuroplastic mechanisms, memory and cognitive abilities
17-β-estradiol potentiates the neurotrophic and neuroprotective effects mediated by the dopamine D3/acetylcholine nicotinic receptor heteromer in dopaminergic neurons
No full textDopaminergic neurons express a heteromer composed of the dopamine D3 receptor and the alpha 4 beta 2 nicotinic acetylcholine receptor, the D3R-nAChR heteromer, activated by both nicotine and dopamine D2 and D3 receptors agonists, such as quinpirole, and crucial for dopaminergic neuron homeostasis. We now report that D3RnAChR heteromer activity is potentiated by 17-beta-estradiol which acts as a positive allosteric modulator by binding a specific domain on the alpha 4 subunit of the nicotinic receptor protomer. In mouse dopaminergic neurons, in fact, 17-beta-estradiol significantly increased the ability of nicotine and quinpirole in promoting neuron dendritic remodeling and in protecting neurons against the accumulation of alpha-synuclein induced by deprivation of glucose, with a mechanism that does not involve the classical estrogen receptors. The potentiation induced by 17 beta-estradiol required the D3R-nAChR heteromer since either nicotinic receptor or dopamine D3 receptor antagonists and interfering TAT-peptides, but not the estrogen receptor antagonist fulvestrant, specifically prevented 17-beta-estradiol effects. Evidence of estrogens neuroprotection, mainly mediated by genomic mechanisms, have been provided, which is in line with epidemiological data reporting that females are less likely to develop Parkinson's Disease than males. Therefore, potentiation of D3R-nAChR heteromer activity may represent a further mechanism by which 17-beta-estradiol reduces dopaminergic neuron vulnerability
Recent Advances in Dopamine D3 Receptor Heterodimers: Focus on Dopamine D3 and D1 Receptor–Receptor Interaction and Striatal Function
No full textRepeated testing modulates chronic unpredictable mild stress effects in male rats
No full textDepression is a highly prevalent, debilitating mental disorder. Chronic unpredictable mild stress (CUMS) is the most widely applied model to study this affliction in rodents. While studies incorporating CUMS prior to an intervention often require long-lasting stress effects that persist after exposure is ceased, the longevity of these effects is rarely studied. Additionally, it is unclear whether behavioural assessments can be performed before and after interventions without repeated testing effects. In rats, we investigated CUMS effects on components of depressive-like behaviour both acutely after stress cessation and after a recovery period, as well as effects of repeated testing. We observed acute disruptions of the circadian locomotor rhythm and a reduced sucrose preference immediately after CUMS exposure. While circadian locomotor rhythm effects persisted up until four weeks after stress cessation, independently of repeated testing, sucrose preference effects did not. Interestingly, CUMS animals tested once after a recovery period of four weeks showed reduced anxiety-like behaviour in the open field and elevated plus maze compared to their control group and repeatedly-tested CUMS animals. These findings suggest that distinct CUMS-induced components of depressive-like behaviour are affected differentially by recovery time and repeated testing; these aspects should be considered carefully in future study designs
Chronic Restraint Stress Inhibits the Response to a Second Hit in Adult Male Rats : A Role for BDNF Signaling
No full textDepression is a recurrent disorder, with about 50% of patients experiencing relapse. Exposure to stressful events may have an adverse impact on the long-term course of the disorder and may alter the response to a subsequent stressor. Indeed, not all the systems impaired by stress may normalize during symptoms remission, facilitating the relapse to the pathology. Hence, we investigated the long-lasting effects of chronic restraint stress (CRS) and its influence on the modifications induced by the exposure to a second hit on brain-derived neurotrophic factor (BDNF) signaling in the prefrontal cortex (PFC). We exposed adult male Sprague Dawley rats to 4 weeks of CRS, we left them undisturbed for the subsequent 3 weeks, and then we exposed animals to one hour of acute restraint stress (ARS). We found that CRS influenced the release of corticosterone induced by ARS and inhibited the ability of ARS to activate mature BDNF, its receptor Tropomyosin receptor kinase B (TRKB), and their associated intracellular cascades: the TRKB-PI3K-AKT), the MEK-MAPK/ERK, and the Phospholipase C γ (PLCγ) pathways, positively modulated by ARS in non-stressed animals. These results suggest that CRS induces protracted and detrimental consequences that interfere with the ability of PFC to cope with a challenging situation
The absence of serotonin in the brain alters acute stress responsiveness by interfering with the genomic function of the glucocorticoid receptors
No full textAlterations in serotonergic transmission have been related to a major predisposition to develop psychiatric pathologies, such as depression. We took advantage of tryptophan hydroxylase (TPH) 2 deficient rats, characterized by a complete absence of serotonin in the brain, to evaluate whether a vulnerable genotype may influence the reaction to an acute stressor. In this context, we investigated if the glucocorticoid receptor (GR) genomic pathway activation was altered by the lack of serotonin in the central nervous system. Moreover, we analyzed the transcription pattern of the clock genes that can be affected by acute stressors. Adult wild type (TPH2(+/+)) and TPH2-deficient (TPH2(-/-)) male rats were sacrificed after exposure to one single session of acute restraint stress. Protein and gene expression analyses were conducted in the prefrontal cortex (PFC). The acute stress enhanced the translocation of GRs in the nucleus of TPH2(+/+) animals. This effect was blunted in TPH2(-/-) rats, suggesting an impairment of the GR genomic mechanism. This alteration was mirrored in the expression of GR-responsive genes: acute stress led to the up-regulation of GR-target gene expression in TPH2(+/+), but not in TPH2(-/-) animals. Finally, clock genes were differently modulated in the two genotypes after the acute restraint stress. Overall our findings suggest that the absence of serotonin within the brain interferes with the ability of the HPA axis to correctly modulate the response to acute stress, by altering the nuclear mechanisms of the GR and modulation of clock genes expression
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