Alessandro Valzania

Prefrontal/amygdalar system determines stress coping behavior through 5-HT/GABA connection.

Coping is defined as the behavioral and physiological effort made to master stressful situations. The ability to cope with stress leads either to healthy or to pathogenic outcomes. The medial prefrontal cortex (mpFC) and amygdala are acknowledged as having a major role in stress-related behaviors, and mpFC has a critical role in the regulation of amygdala-mediated arousal in response to emotionally salient stimuli. Prefrontal cortical serotonin (5-hydroxytryptamine (5-HT)) is involved in corticolimbic circuitry, and GABA has a major role in amygdala functioning. Here, using mice, it was assessed whether amygdalar GABA regulation by prefrontal 5-HT is involved in processing stressful experiences and in determining coping outcomes. First (experiment 1), bilateral selective 5-HT depletion in mpFC of mice reduced GABA release induced by stress in basolateral amygdala (BLA) and passive coping in the Forced Swimming Test (FST) (experiment 2). Moreover, prefrontal-amygdala disconnection procedure that combined a selective unilateral 5-HT depletion of mpFC and infusion of an inhibitor of GABA synthesis into the contralateral BLA, thereby to disrupt prefrontal-amygdalar serial connectivity bilaterally, showed that disconnection selectively decreases immobility in the FST. These results point to prefrontal/amygdala connectivity mediated by 5-HT and GABA transmission as a critical neural mechanism in stress-induced behavior.

Adversity in childhood and depression: Linked through SIRT1

Experiencing an adverse childhood and parental neglect is a risk factor for depression in the adult population. Patients with a history of traumatic childhood develop a subtype of depression that is characterized by earlier onset, poor treatment response and more severe symptoms. The long-lasting molecular mechanisms that are engaged during early traumatic events and determine the risk for depression are poorly understood. In this study, we altered adult depression-like behavior in mice by applying juvenile isolation stress. We found that this behavioral phenotype was associated with a reduction in the levels of the deacetylase sirtuin1 (SIRT1) in the brain and in peripheral blood mononuclear cells. Notably, peripheral blood mRNA expression of SIRT1 predicted the extent of behavioral despair only when depression-like behavior was induced by juvenile—but not adult—stress, implicating SIRT1 in the regulation of adult behavior at early ages. Consistent with this hypothesis, pharmacological modulation of SIRT1 during juvenile age altered the depression-like behavior in naive mice. We also performed a pilot study in humans, in which the blood levels of SIRT1 correlated significantly with the severity of symptoms in major depression patients, especially in those who received less parental care during childhood. On the basis of these novel findings, we propose the involvement of SIRT1 in the long-term consequences of adverse childhood experiences.

Regulation of nucleus accumbens transcript levels in mice by early-life social stress and cocaine.

Much interest has been piqued regarding the quality of ones environment at early ages in modulating the susceptibility to drug addiction in adulthood. However, the molecular mechanisms that are engaged during early trauma and mediate the risk for drug addiction are poorly understood. In rodents, exposure to early-life stress alters the rewarding effects of cocaine, amphetamine, and morphine in adulthood. Recently, we demonstrated that the exposure of juvenile mice to social threat (Social Stress, S-S) promoted cocaine-seeking behavior and relapse of cocaine-seeking after periods of withdrawal, compared with unhandled controls (UN) and with juvenile mice that experienced only daily isolation in a novel environment (no social stress, NS-S). Interestingly, while the exposure to NS-S slightly increased cocaine-seeking behavior compared with UN, the same was not sufficient to promote cocaine reinstatement. In this study, we examined the long-term transcriptional changes that are induced by S-S compared to NS-S and linked the increased susceptibility of S-S mice to cocaine reinstatement. To this end, we performed genome-wide RNA sequencing analysis in the nucleus accumbens (NAC), which revealed that 89 transcripts were differentially expressed between S-S and NS-S mice. By Gene Ontology classification, these hits were enriched in genes that mediate cell proliferation, neuronal differentiation, and neuron/forebrain development. Eleven of these genes have been reported to be involved in substance use disorders, and the remaining genes are novel candidates in this area. We characterized 4 candidates with regard to their significant neurobiological relevance (ZIC1, ZIC2, FABP7, and PRDM12) and measured their expression in the NAC by immunohistochemistry. These findings provide insights into novel molecular mechanisms in NAC that might be associated with the risk of relapse in cocaine-dependent individuals.

When chocolate seeking becomes compulsion: gene-environment interplay.

Background Eating disorders appear to be caused by a complex interaction between environmental and genetic factors, and compulsive eating in response to adverse circumstances characterizes many eating disorders. Materials and Methods We compared compulsion-like eating in the form of conditioned suppression of palatable food-seeking in adverse situations in stressed C57BL/6J and DBA/2J mice, two well-characterized inbred strains, to determine the influence of gene-environment interplay on this behavioral phenotype. Moreover, we tested the hypothesis that low accumbal D2 receptor (R) availability is a genetic risk factor of food compulsion-like behavior and that environmental conditions that induce compulsive eating alter D2R expression in the striatum. To this end, we measured D1R and D2R expression in the striatum and D1R, D2R and α1R levels in the medial prefrontal cortex, respectively, by western blot. Results Exposure to environmental conditions induces compulsion-like eating behavior, depending on genetic background. This behavioral pattern is linked to decreased availability of accumbal D2R. Moreover, exposure to certain environmental conditions upregulates D2R and downregulates α1R in the striatum and medial prefrontal cortex, respectively, of compulsive animals. These findings confirm the function of gene-environment interplay in the manifestation of compulsive eating and support the hypothesis that low accumbal D2R availability is a “constitutive” genetic risk factor for compulsion-like eating behavior. Finally, D2R upregulation and α1R downregulation in the striatum and medial prefrontal cortex, respectively, are potential neuroadaptive responses that parallel the shift from motivated to compulsive eating.

Stress-induced activation of ventral tegmental mu-opioid receptors reduces accumbens dopamine tone by enhancing dopamine transmission in the medial pre-frontal cortex

RationaleEndogenous opioids could play a major role in the mesocorticolimbic dopamine (DA) responses to stress challenge. However, there is still no direct evidence of an influence of endogenous opioids on any of these responses.ObjectiveWe assessed whether and how endogenous opioids modulate fluctuations of mesocortical and mesoaccumbens DA tone in rats during a first experience with restraint stress.MethodWe first evaluated the effects of systemic naltrexone (NTRX) on DA outflow in the medial prefrontal cortex (mpFC) and in the nucleus accumbens (NAc) through dual-probe microdialysis. Second, we assessed the effect of perfusion, through reverse microdialysis, of direct DA receptor agonists in mpFC on NAc DA outflow in NTRX-pretreated stressed rats. Finally, we tested the effects of ventral tegmental area (VTA) perfusion of NTRX, the selective mu1 antagonist naloxonazine and the selective delta antagonist naltrindole on mpFC and NAc DA outflow in stressed rats, with multiple probe experiments.ResultsSystemic NTRX, at behaviorally effective doses, selectively prevented the increase of mpFC DA levels and the reduction of NAc DA levels observable during prolonged restraint. Local co-perfusion of D1 and D2 agonists in mpFC recovered inhibition of NAc DA in NTRX-pretreated restrained rats. Finally, intra-VTA perfusion of either NTRX or the mu1 antagonist, but not the delta antagonist, mimicked the effects of systemic NTRX.ConclusionDuring prolonged experience with a novel unavoidable/uncontrollable stressor, endogenous opioids, through stimulation of mu1 receptors in the VTA, elevate mesocortical DA tone thus reducing DA tone in the NAc DA.

Corticolimbic catecholamines in stress: a computational model of the appraisal of controllability

Appraisal of a stressful situation and the possibility to control or avoid it is thought to involve frontal-cortical mechanisms. The precise mechanism underlying this appraisal and its translation into effective stress coping (the regulation of physiological and behavioural responses) are poorly understood. Here, we propose a computational model which involves tuning motivational arousal to the appraised stressing condition. The model provides a causal explanation of the shift from active to passive coping strategies, i.e. from a condition characterised by high motivational arousal, required to deal with a situation appraised as stressful, to a condition characterised by emotional and motivational withdrawal, required when the stressful situation is appraised as uncontrollable/unavoidable. The model is motivated by results acquired via microdialysis recordings in rats and highlights the presence of two competing circuits dominated by different areas of the ventromedial prefrontal cortex: these are shown having opposite effects on several subcortical areas, affecting dopamine outflow in the striatum, and therefore controlling motivation. We start by reviewing published data supporting structure and functioning of the neural model and present the computational model itself with its essential neural mechanisms. Finally, we show the results of a new experiment, involving the condition of repeated inescapable stress, which validate most of the model’s predictions.

Social threat exposure in juvenile mice promotes cocaine-seeking by altering blood clotting and brain vasculature

Childhood maltreatment is associated with increased severity of substance use disorder and frequent relapse to drug use following abstinence. However, the molecular and neurobiological substrates that are engaged during early traumatic events and mediate the greater risk of relapse are poorly understood and knowledge of risk factors is to date extremely limited. In this study, we modeled childhood maltreatment by exposing juvenile mice to a threatening social experience (social stressed, S‐S). We showed that S‐S experience influenced the propensity to reinstate cocaine‐seeking after periods of withdrawal in adulthood. By exploring global gene expression in blood leukocytes we found that this behavioral phenotype was associated with greater blood coagulation. In parallel, impairments in brain microvasculature were observed in S‐S mice. Furthermore, treatment with an anticoagulant agent during withdrawal abolished the susceptibility to reinstate cocaine‐seeking in S‐S mice. These findings provide novel insights into a possible molecular mechanism by which childhood maltreatment heightens the risk for relapse in cocaine‐dependent individuals.

Histone deacetylase 5 modulates the effects of social adversity in early life on cocaine-induced behavior

Psychostimulants induce stable changes in neural plasticity and behavior in a transcription-dependent manner. Further, stable cellular changes require transcription that is regulated by epigenetic mechanisms that alter chromatin structure, such as histone acetylation. This mechanism is typically catalyzed by enzymes with histone acetyltransferase or histone deacetylase (HDAC) activity. Class IIa HDACs are notable for their high expression in important regions of the brain reward circuitry and their neural activity-dependent shuttling in and out of the cell nucleus. In particular, HDAC5 has an important modulatory function in cocaine-induced behaviors and social defeat stress-induced effects. Although a mutation in HDAC5 has been shown to cause hypersensitive responses to chronic cocaine use whether this response worsens during chronic early life stress has not been examined yet. In this study, we exposed mouse pups to two different early life stress paradigms (social isolation, ESI, and social threat, EST) to determine whether the heterozygous null mutation in HDAC5 (HDAC5+/-) moderated the effects of exposure to stress in early life on adult cocaine-induced conditioned place preference (CPP). Notably, HDAC5+/- mice that had been exposed to ESI were more susceptible to developing cocaine-induced CPP and more resistant to extinguishing this behavior. The same effect was not observed for HDAC5+/- mice experiencing EST, suggesting that only ESI induces behavioral changes by acting precisely through HDAC5-related biological pathways. Finally, an analysis of c-Fos expression performed to discover the neurobiological substrates that mediated this phenotype, identified the dorsolateral striatum as an important structure that mediates the interaction between HDAC5 mutation and ESI. Our data demonstrate that decreased HDAC5 function is able to exacerbate the long-term behavioral effects of adverse rearing environment in mouse.

Early-onset behavioral and neurochemical deficits in the genetic mouse model of phenylketonuria

Phenylketonuria (PKU) is one of the most common human inborn errors of metabolism, caused by phenylalanine hydroxylase deficiency, leading to high phenylalanine and low tyrosine levels in blood and brain causing profound cognitive disability, if untreated. Since 1960, population is screened for hyperphenylalaninemia shortly after birth and submitted to early treatment in order to prevent the major manifestations of the disease. However, the dietetic regimen (phenylalanine free diet) is difficult to maintain, and despite the recommendation to a strict and lifelong compliance, up to 60% of adolescents partially or totally abandons the treatment. The development and the study of new treatments continue to be sought, taking advantage of preclinical models, the most used of which is the PAHenu2 (BTBR ENU2), the genetic murine model of PKU. To date, adult behavioral and neurochemical alterations have been mainly investigated in ENU2 mice, whereas there are no clear indications about the onset of these deficiencies. Here we investigated and report, for the first time, a comprehensive behavioral and neurochemical assay of the developing ENU2 mice. Overall, our findings demonstrate that ENU2 mice are significantly smaller than WT until pnd 24, present a significant delay in the acquisition of tested developmental reflexes, impaired communicative, motor and social skills, and have early reduced biogenic amine levels in several brain areas. Our results extend the understanding of behavioral and cerebral abnormalities in PKU mice, providing instruments to an early preclinical evaluation of the effects of new treatments.

Dopamine loss alters the hippocampus-nucleus accumbens synaptic transmission in the Tg2576 mouse model of Alzheimer's disease

The functional loop involving the ventral tegmental area (VTA), dorsal hippocampus and nucleus accumbens (NAc) plays a pivotal role in the formation of spatial memory and persistent memory traces. In particular, the dopaminergic innervation from the VTA to the hippocampus is critical for hippocampal-related memory function and alterations in the midbrain dopaminergic system are frequently reported in Alzheimers disease (AD), contributing to age-related decline in memory and non-cognitive functions. However, much less is known about the hippocampus-NAc connectivity in AD. Here, we evaluated the functioning of the hippocampus-to-NAc core connectivity in the Tg2576 mouse model of AD that shows a selective and progressive degeneration of VTA dopaminergic neurons. We show that reduced dopaminergic innervation in the Tg2576 hippocampus results in reduced synaptic plasticity and excitability of dorsal subiculum pyramidal neurons. Importantly, the glutamatergic transmission from the hippocampus to the NAc core is also impaired. Chemogenetic depolarisation of Tg2576 subicular pyramidal neurons with an excitatory Designer Receptor Exclusively Activated by Designer Drugs, or systemic administration of the DA precursor levodopa, can both rescue the deficits in Tg2576 mice. Our data suggest that the dopaminergic signalling in the hippocampus is essential for the proper functioning of the hippocampus-NAc excitatory synaptic transmission.