Behavioral Phenotyping of Dopamine Transporter Knockout Rats: Compulsive Traits, Motor Stereotypies, and Anhedonia

Deficiency of histamine H2 receptors in parvalbumin-positive neurons leads to hyperactivity, impulsivity, and impaired attention

Attention deficit hyperactivity disorder (ADHD), affecting 4% of the population, is characterized by inattention, hyperactivity, and impulsivity; however, its neurophysiological mechanisms remain unclear. Here, we discovered that deficiency of histamine H2 receptor (H2R) in parvalbumin-positive neurons in substantia nigra pars recticulata (PVSNr) attenuates PV+ neuronal activity and induces hyperactivity, impulsivity, and inattention in mice. Moreover, decreased H2R expression was observed in PVSNr in patients with ADHD symptoms and dopamine-transporter-deficient mice, whose behavioral phenotypes were alleviated by H2R agonist treatment. Dysfunction of PVSNr efferents to the substantia nigra pars compacta dopaminergic neurons and superior colliculus differently contributes to H2R-deficiency-induced behavioral disorders. Collectively, our results demonstrate that H2R deficiency in PV+ neurons contributes to hyperactivity, impulsivity, and inattention by dampening PVSNr activity and involving different efferents in mice. It may enhance understanding of the molecular and circuit-level basis of ADHD and afford new potential therapeutic targets for ADHD-like psychiatric diseases.

Impact of excessive sucrose intake on mouse behavior across different developmental stages

This study aimed to elucidate the effects of sucrose (SUC) consumption on neurodevelopmental processes through behavioral changes in rodents and determine whether these effects could be because of sweet taste, energy supply, or both. Mice were divided into five groups based on the time of SUC or sucralose (SUR, a noncaloric sweetener) administration: for 6 days from gestation day (GTD) 7, to birth from GTD13 and for 15 days from postnatal day (PND) 21, PND38, and PND56. SUC and SUR administration did not impact body weight. However, food intake in the PND56 group and water intake in the GTD13 and PND56 groups were increased by SUC and SUR administration. Amphetamine (0.5, 1, 2, and 3 mg/kg), a dopamine reuptake inhibitor, administration to assess alterations in the dopaminergic system induced increases in distance traveled after SUC administration in the GTD13 and PND21 groups compared with that in the control (vehicle administration) group. In contrast, the SUR group showed a decrease in the distance traveled in the PND56 group. Although there were no differences in locomotor activity and foraging behavior, SUC preference increased in the SUC group regarding the GTD13 and PND38 groups. The correlations between SUC preference and foraging behavior and between SUC preference and amphetamine response varied in both groups according to the developmental stage. Excessive SUC consumption might affect neural function at different developmental stages, as it could affect brain function through complex mechanisms involving sweet taste and energy supply and influence the dopaminergic system.

Rats Lacking the Dopamine Transporter Display Inflexibility in Innate and Learned Behavior

Playing a key role in the organization of striatal motor output, the dopamine (DA)-ergic system regulates both innate and complex learned behaviors. Growing evidence clearly indicates the involvement of the DA-ergic system in different forms of repetitive (perseverative) behavior. Some of these behaviors accompany such disorders as obsessive-compulsive disorder (OCD), Tourette's syndrome, schizophrenia, and addiction. In this study, we have traced how the inflexibility of repetitive reactions in the recently developed animal model of hyper-DA-ergia, dopamine transporter knockout rats (DAT-KO rats), affects the realization of innate behavior (grooming) and the learning of spatial (learning and reversal learning in T-maze) and non-spatial (extinction of operant reaction) tasks. We found that the microstructure of grooming in DAT-KO rats significantly differed in comparison to control rats. DAT-KO rats more often demonstrated a fixed syntactic chain, making fewer errors and very rarely missing the chain steps in comparison to control rats. DAT-KO rats' behavior during inter-grooming intervals was completely different to the control animals. During learning and reversal learning in the T-maze, DAT-KO rats displayed pronounced patterns of hyperactivity and perseverative (stereotypical) activity, which led to worse learning and a worse performance of the task. Most of the DAT-KO rats could not properly learn the behavioral task in question. During re-learning, DAT-KO rats demonstrated rigid perseverative activity even in the absence of any reinforcement. In operant tasks, the mutant rats demonstrated poor extinction of operant lever pressing: they continued to perform lever presses despite no there being reinforcement. Our results suggest that abnormally elevated DA levels may be responsible for behavioral rigidity. It is conceivable that this phenomenon in DAT-KO rats reflects some of the behavioral traits observed in clinical conditions associated with endogenous or exogenous hyper-DA-ergia, such as schizophrenia, substance abuse, OCD, patients with Parkinson disease treated with DA mimetics, etc. Thus, DAT-KO rats may be a valuable behavioral model in the search for new pharmacological approaches to treat such illnesses.

Trace amine-associated receptor 1 (TAAR1) agonism for psychosis: a living systematic review and meta-analysis of human and non-human data

Background

Trace amine-associated receptor 1 (TAAR1) agonism shows promise for treating psychosis, prompting us to synthesise data from human and non-human studies.

Methods

We co-produced a living systematic review of controlled studies examining TAAR1 agonists in individuals (with or without psychosis/schizophrenia) and relevant animal models. Two independent reviewers identified studies in multiple electronic databases (until 17.11.2023), extracted data, and assessed risk of bias. Primary outcomes were standardised mean differences (SMD) for overall symptoms in human studies and hyperlocomotion in animal models. We also examined adverse events and neurotransmitter signalling. We synthesised data with random-effects meta-analyses.

Results

Nine randomised trials provided data for two TAAR1 agonists (ulotaront and ralmitaront), and 15 animal studies for 10 TAAR1 agonists. Ulotaront and ralmitaront demonstrated few differences compared to placebo in improving overall symptoms in adults with acute schizophrenia (N=4 studies, n=1291 participants; SMD=0.15, 95%CI: -0.05, 0.34), and ralmitaront was less efficacious than risperidone (N=1, n=156, SMD=-0.53, 95%CI: -0.86, -0.20). Large placebo response was observed in ulotaront phase-III trials. Limited evidence suggested a relatively benign side-effect profile for TAAR1 agonists, although nausea and sedation were common after a single dose of ulotaront. In animal studies, TAAR1 agonists improved hyperlocomotion compared to control (N=13 studies, k=41 experiments, SMD=1.01, 95%CI: 0.74, 1.27), but seemed less efficacious compared to dopamine D 2 receptor antagonists (N=4, k=7, SMD=-0.62, 95%CI: -1.32, 0.08). Limited human and animal data indicated that TAAR1 agonists may regulate presynaptic dopaminergic signalling.

Conclusions

TAAR1 agonists may be less efficacious than dopamine D 2 receptor antagonists already licensed for schizophrenia. The results are preliminary due to the limited number of drugs examined, lack of longer-term data, publication bias, and assay sensitivity concerns in trials associated with large placebo response. Considering their unique mechanism of action, relatively benign side-effect profile and ongoing drug development, further research is warranted.

Registration

PROSPERO-ID: CRD42023451628.

Reduced dopamine transporter availability in drug-naive adult attention-deficit/hyperactivity disorder

Aim

This study aimed to clarify the abnormalities in dopamine transporter (DAT) availability in drug-naive adult patients with attention-deficit/hyperactivity disorder (ADHD) and the relationship between ADHD symptoms and abnormalities in DAT availability.

Methods

Single-photon emission tomography (SPECT) was performed using iodine-123-β-carbomethoxy-3β-(4-iodophenyltropane) (I-123 β CIT) as a tracer to measure in vivo DAT availability in 20 drug-naive patients with ADHD [mean age ± standard deviation (SD)]: 25 ± 3.44 years; male:female = 11:9] and 20 age- and sex-matched healthy controls (HCs) (mean age ± SD: 23.9 ± 2.27 years). Comparisons of DAT availability between HCs and adult patients with ADHD and the association between symptom severity and DAT availability within the ADHD group were analyzed using Statistical Parametric Mapping 12.

Results

Drug-naive adults with ADHD showed significantly reduced DAT availability in the bilateral nucleus accumbens compared with HCs. Correlation analyses revealed a negative correlation between the severity of inattentive symptoms in adult patients with ADHD and DAT availability in the bilateral heads of the caudate nucleus, indicating the association between severe inattentive symptoms and lower DAT availability in the caudate nucleus.

Conclusion

In drug-naive adult patients with ADHD, DAT availability was reduced in the nucleus accumbens, an important part of the reward system. This finding indicates the importance of the DAT in the reward system in the pathogenesis of ADHD. Inattentiveness was associated with DAT availability in the caudate nucleus, suggesting involvement of the cortico-striato-thalamo-cortical circuit.

Simulated Dopamine Modulation of a Neurorobotic Model of the Basal Ganglia

The vertebrate basal ganglia play an important role in action selection-the resolution of conflicts between alternative motor programs. The effective operation of basal ganglia circuitry is also known to rely on appropriate levels of the neurotransmitter dopamine. We investigated reducing or increasing the tonic level of simulated dopamine in a prior model of the basal ganglia integrated into a robot control architecture engaged in a foraging task inspired by animal behaviour. The main findings were that progressive reductions in the levels of simulated dopamine caused slowed behaviour and, at low levels, an inability to initiate movement. These states were partially relieved by increased salience levels (stronger sensory/motivational input). Conversely, increased simulated dopamine caused distortion of the robot's motor acts through partially expressed motor activity relating to losing actions. This could also lead to an increased frequency of behaviour switching. Levels of simulated dopamine that were either significantly lower or higher than baseline could cause a loss of behavioural integration, sometimes leaving the robot in a 'behavioral trap'. That some analogous traits are observed in animals and humans affected by dopamine dysregulation suggests that robotic models could prove useful in understanding the role of dopamine neurotransmission in basal ganglia function and dysfunction.

Antioxidant system alterations and physiological characteristics of neonatal and juvenile DAT-KO rats

Dopamine transporter knockout (DAT-KO) rats represent a valuable rodent model for studying the molecular and phenotypical outcomes of the effects of excessive dopamine accumulation in the synaptic cleft and the prolonged action of dopamine on neurons. Animals with DAT deficiency are characterized by hyperactivity, stereotypy, cognitive deficits, and impairments in behavioral and biochemical indicators. Several key pathophysiological mechanisms are known to be common to psychiatric, neurodegenerative, metabolic, and other diseases. Among these mechanisms, oxidative stress systems play a particularly important role. One of the main antioxidant systems in the brain is glutathione: specifically, glutathione S-transferase, glutathione reductase, and catalase play a significant role in the regulation of vital oxidative processes, and their dysfunction has been shown in Parkinson's disease, Alzheimer's disease, and other neurodegenerative diseases. The current study aimed to analyze the dynamics of the activity levels of glutathione reductase and glutathione S-transferase in erythrocytes, as well as catalase in the blood plasma, of DAT-deficient, homo- and heterozygous, neonatal and juvenile rats (both male and female). Their behavioral and physiological parameters were evaluated at the age of 1.5 months. For the first time, changes in physiological and biochemical parameters were shown in DAT-KO rats at 1.5 months of postnatal life. The key role of glutathione S-transferase, glutathione reductase, and catalase in the regulation of oxidative stress in DAT-KO rats at the 5th week of life was demonstrated. A positive effect of a slightly increased dopamine level on memory function was shown in DAT-heterozygous animals.

Loss of the parkinsonism-associated protein FBXO7 in glutamatergic forebrain neurons in mice leads to abnormal motor behavior and synaptic defects

Mutations in PARK15, which encodes for the F-box protein FBXO7 have been associated with Parkinsonian Pyramidal syndrome, a rare and complex movement disorder with Parkinsonian symptoms, pyramidal tract signs and juvenile onset. Our previous study showed that systemic loss of Fbxo7 in mice causes motor defects and premature death. We have also demonstrated that FBXO7 has a crucial role in neurons as the specific deletion in tyrosine hydroxylase-positive or glutamatergic forebrain neurons leads to late-onset or early-onset motor dysfunction, respectively. In this study, we examined NEX-Cre;Fbxo7fl/fl mice, in which Fbxo7 was specifically deleted in glutamatergic projection neurons. The effects of FBXO7 deficiency on striatal integrity were investigated with HPLC and histological analyses. NEX-Cre;Fbxo7fl/fl mice revealed an increase in striatal dopamine concentrations, changes in the glutamatergic, GABAergic and dopaminergic pathways, astrogliosis and microgliosis and little or no neuronal loss in the striatum. To determine the effects on the integrity of the synapse, we purified synaptic membranes, subjected them to quantitative mass spectrometry analysis and found alterations in the complement system, endocytosis and exocytosis pathways. These neuropathological changes coincide with alterations in spontaneous home cage behavior. Taken together, our findings suggest that FBXO7 is crucial for corticostriatal projections and the synaptic integrity of the striatum, and consequently for proper motor control.

Inheritance of wild and truncated DAT alleles from grand-parents: Opposite transgenerational consequences on the behavioral phenotype in adolescent DAT heterozygous rats

Dopamine plays important roles in implicit memory and motivation of behavior. Environmental inputs can produce transgenerational epigenetic changes. This concept also includes the uterus: experimentally, we sought to create hyper-dopaminergic uterine conditions through ineffective dopamine-transporter (DAT) protein, obtained by inserting a stop-codon into the SLC6A3 gene. By crossing WT-dam with KO-sire (or vice-versa), we obtained a 100% DAT-heterozygous (HET) offspring with known derivation of the wild allele: MAT rats are offspring of WT-female and KO-male; PAT rats are offspring of KO-female and WT-male. We reconstructed inheritance of alleles, by crossing PAT-male with MAT-female or vice-versa, obtaining GIX (PAT-male with MAT-female) and DIX (MAT-male with PAT-female) rats (such offspring present specular paths in allele inheritance from grandparents). We conducted three experiments: first, we assessed maternal behaviour (four epigenotypes: WT, MAT, PAT and WHZ=HET-pups fostered-to-a WT-dam); in the second, we analysed sleep-wake cycles of GIX and DIX epigenotypes with their WIT siblings as controls; in the third, we explored the impact of WT or MAT mother on WT or HET pups. MAT-dams (with GIX-pups) express excessive licking/grooming. However, in the mere presence of "sick" epigenotype, PAT-dams (with DIX-pups) and also WHZ (i.e., WT-dams but with HET-pups) expressed greater nest-building care towards the offspring, compared to "true-wild" litters (WT-dams with WT-pups). In Exp. 2 at adolescence, GIX epigenotype showed locomotor hyperactivity during late waking-phase, while DIX epigenotype exhibited pronounced hypoactivity compared to controls. In Exp. 3, we confirmed that HET adolescent pups receiving cares from a MAT-dam may develop additional hyperactivity when awake, but additional hypoactivity during rest-hours. Thus, behavioral changes observed in DAT-heterozygous offspring have opposite courses based on of DAT-allele inheritance from a grandparent through the sire or the dam. In conclusion, behavioural changes in the offspring have antithetic courses with respect to inheritance of DAT-allele via sperm or egg.

Behavioral domains in compulsive rats: implications for understanding compulsive spectrum disorders

Introduction

Compulsive behavior has been proposed as a transdiagnostic trait observed in different neuropsychiatric disorders, such as obsessive-compulsive disorder, autism, and schizophrenia. Research Domain Criteria (RDoC) strategy could help to disentangle the neuropsychological basis of compulsivity for developing new therapeutic and preventive approaches. In preclinical research, the selection of high-drinker (HD) vs. low-drinker (LD) animals by schedule-induced polydipsia (SIP) is considered a putative model of compulsivity, which includes a well-differentiated behavioral pattern.

Methods

The purpose of this research was to assess the cognitive control and the negative valence system domains in a phenotype of compulsive HD rats. After the selection of animals as HD or LD, we assessed behavioral inflexibility by probabilistic spatial reversal learning (PSRL), motor and cognitive impulsivity by variable delay-to-signal (VDS), and risky decision-making by rodent gambling task (rGT).

Results

HD rats performed fewer reversals and showed less probability of pressing the same lever that was previously reinforced on PSRL, more premature responses after the exposure to longer delays on VDS, and more disadvantageous risky choices on rGT. Moreover, HD animals performed more perseverative responses under the punishment period on rGT.

Discussion

These results highlight that HD compulsive phenotype exhibits behavioral inflexibility, insensitivity to positive feedback, waiting impulsivity, risky decision-making, and frustrative non-reward responsiveness. Moreover, these findings demonstrate the importance of mapping different behavioral domains to prevent, treat, and diagnose compulsive spectrum disorders correctly.

Accelerated high frequency rTMS induces time-dependent dopaminergic alterations: a DaTSCAN brain imaging study in healthy beagle dogs

Aim

The neurobiological effects of repetitive transcranial magnetic stimulation are believed to run in part through the dopaminergic system. Accelerated high frequency rTMS (aHF-rTMS), a new form of stimuli delivery, is currently being tested for its usefulness in treating human and canine mental disorders. However, the short-and long-term neurobiological effects are still unclear, including the effects on the dopaminergic system. In aHF-rTMS, multiple sessions are delivered within 1 day instead of one session per day, not only to accelerate the time to response but also to increase clinical efficacy. To gain more insight into the neurobiology of aHF-rTMS, we investigated whether applying five sessions in 1 day has direct and/or delayed effects on the dopamine transporter (DAT), and on dopamine metabolites of cerebrospinal fluid (CSF) in beagles.

Materials and methods

Thirteen beagles were randomly divided into two groups: five active stimulation sessions (n = 9), and 5 sham stimulation sessions (n = 4). Using DaTSCAN, DAT binding indices (BI) were obtained at baseline, after 1 day, 1 month, and 3 months post stimulation. CSF samples were collected after each scan.

Results

Active aHF-rTMS significantly reduced striatal DAT BI 1 day post-active stimulation session (p < 0.01), and the effect lasted to 1 month (p < 0.01). No significant DAT BI change was found in sham group. No significant changes in dopamine metabolites of CSF were found.

Conclusion

Although no significant effects on CSF dopamine metabolites were observed, five sessions of active aHF-rTMS significantly decreased striatal DAT BI after 1 day and up to 1 month post stimulation, indicating immediate and delayed effects on the brain dopaminergic system. Our findings in healthy beagles further substantiate the assumption that (a)HF-rTMS affects the brain dopaminergic system and it may pave the way to apply (a)HF-rTMS treatment in behaviorally disturbed dogs.

Dopamine Transporter Deficient Rodents: Perspectives and Limitations for Neuroscience

The key element of dopamine (DA) neurotransmission is undoubtedly DA transporter (DAT), a transmembrane protein responsible for the synaptic reuptake of the mediator. Changes in DAT's function can be a key mechanism of pathological conditions associated with hyperdopaminergia. The first strain of gene-modified rodents with a lack of DAT were created more than 25 years ago. Such animals are characterized by increased levels of striatal DA, resulting in locomotor hyperactivity, increased levels of motor stereotypes, cognitive deficits, and other behavioral abnormalities. The administration of dopaminergic and pharmacological agents affecting other neurotransmitter systems can mitigate those abnormalities. The main purpose of this review is to systematize and analyze (1) known data on the consequences of changes in DAT expression in experimental animals, (2) results of pharmacological studies in these animals, and (3) to estimate the validity of animals lacking DAT as models for discovering new treatments of DA-related disorders.

Behavioral profile of adult zebrafish acutely exposed to a selective dopamine uptake inhibitor, GBR 12909

BACKGROUND

The dopamine transporter (DAT) is the main regulator of dopamine concentration in the extrasynaptic space. The pharmacological inhibition of the DAT results in a wide spectrum of behavioral manifestations, which have been identified so far in a limited number of species, mostly in rodents.

AIM

Here, we used another well-recognized model organism, the zebrafish (Danio rerio), to explore the behavioral effects of GBR 12909, a highly-affine selective DAT blocker.

METHODS

We evaluated zebrafish locomotion, novelty-related exploration, spatial cognition, and social phenotypes in the novel tank, habituation and shoaling tests, following acute 20-min water immersion in GBR 12909.

RESULTS

Our findings show hypolocomotion, anxiety-like state, and impaired spatial cognition in fish acutely treated with GBR 12909. This behavioral profile generally parallels that of the DAT knockout rodents and zebrafish, and it overlaps with behavioral effects of other DAT-inhibiting drugs of abuse, such as cocaine and D-amphetamine.

CONCLUSION

Collectively, our data support the utility of zebrafish in translational studies on DAT targeting neuropharmacology and strongly implicate DAT aberration as an important mechanisms involved in neurological and psychiatric diseases.

Noradrenergic Modulation of Learned and Innate Behaviors in Dopamine Transporter Knockout Rats by Guanfacine

Investigation of the precise mechanisms of attention deficit and hyperactivity disorder (ADHD) and other dopamine-associated conditions is crucial for the development of new treatment approaches. In this study, we assessed the effects of repeated and acute administration of α2A-adrenoceptor agonist guanfacine on innate and learned forms of behavior of dopamine transporter knockout (DAT-KO) rats to evaluate the possible noradrenergic modulation of behavioral deficits. DAT-KO and wild type rats were trained in the Hebb-Williams maze to perform spatial working memory tasks. Innate behavior was evaluated via pre pulse inhibition (PPI). Brain activity of the prefrontal cortex and the striatum was assessed. Repeated administration of GF improved the spatial working memory task fulfillment and PPI in DAT-KO rats, and led to specific changes in the power spectra and coherence of brain activity. Our data indicate that both repeated and acute treatment with a non-stimulant noradrenergic drug lead to improvements in the behavior of DAT-KO rats. This study further supports the role of the intricate balance of norepinephrine and dopamine in the regulation of attention. The observed compensatory effect of guanfacine on the behavior of hyperdopaminergic rats may be used in the development of combined treatments to support the dopamine-norepinephrine balance.

Heterozygote Dopamine Transporter Knockout Rats Display Enhanced Cocaine Locomotion in Adolescent Females

Cocaine is a powerful psychostimulant that is one of the most widely used illicit addictive. The dopamine transporter (DAT) plays a major role in mediating cocaine's reward effect. Decreases in DAT expression increase rates of drug abuse and vulnerability to comorbid psychiatric disorders. We used the novel DAT transgenic rat model to study the effects of cocaine on locomotor behaviors in adolescent rats, with an emphasis on sex. Female rats showed higher response rates to cocaine at lower acute and chronic doses, highlighting a higher vulnerability and perceived gender effects. In contrast, locomotor responses to an acute high dose of cocaine were more marked and sustained in male DAT heterozygous (HET) adolescents. The results demonstrate the augmented effects of chronic cocaine in HET DAT adolescent female rats. Knockout (KO) DAT led to a level of hyperdopaminergia which caused a marked basal hyperactivity that was unchanged, consistent with a possible ceiling effect. We suggest a role of alpha synuclein (α-syn) and PICK 1 protein expressions to the increased vulnerability in female rats. These proteins showed a lower expression in female HET and KO rats. This study highlights gender differences associated with mutations which affect DAT expression and can increase susceptibility to cocaine abuse in adolescence.

Transformer maze for the evaluation of the learning and memory in rodents

Background

Currently, different types of mazes are used to assess spatial learning and memory of rodents. The typical disadvantage is the inability to separate and exclude coincidences of the result of random choice with the correct one. The other problem is the impossibility of knowing whether the animal is guided by particular cues of the environment, or a map.

New method

Our novel transformer maze can be used to test learning and memory of rodents and their navigation. It is a multiple T-maze with passages in the interior walls. Its modular design allows to quickly change routes. The task can include external signals; for example, the colors of the interior walls, or it can be used without any cues.

Results

We compared Wistar and dopamine transporter heterozygous (DAT-HET) rats’ behavior in this novel paradigm using the black color of the wall as a cue. Entering a cul-de-sac compartment was considered an error. While Wistar rats learned the rule abruptly with the total number of errors rapidly decreasing, DAT-HET rats’ errors decreased gradually. We suppose that this reflects different strategies: insightful learning behavior is typical for Wistar rats, and trial-and-error learning is typical for DAT-HET rats.

Comparison with existing methods

The diversity of the chains of choices gives us confidence that trained animals do not make a choice randomly and are guided precisely by the cues. Moreover, we propose to use the same arena for a task with route-based navigation without any cues, and for a task with a visible and invisible feeder to study the path integration navigation within one box.

Conclusions

We suggest that the transformer maze could be a valuable tool for behavioral and pharmacological research to study learning, memory and navigation mechanisms.

Research models of neurodevelopmental disorders: The right model in the right place

Neurodevelopmental disorders (NDDs) are a heterogeneous group of impairments that affect the development of the central nervous system leading to abnormal brain function. NDDs affect a great percentage of the population worldwide, imposing a high societal and economic burden and thus, interest in this field has widely grown in recent years. Nevertheless, the complexity of human brain development and function as well as the limitations regarding human tissue usage make their modeling challenging. Animal models play a central role in the investigation of the implicated molecular and cellular mechanisms, however many of them display key differences regarding human phenotype and in many cases, they partially or completely fail to recapitulate them. Although in vitro two-dimensional (2D) human-specific models have been highly used to address some of these limitations, they lack crucial features such as complexity and heterogeneity. In this review, we will discuss the advantages, limitations and future applications of in vivo and in vitro models that are used today to model NDDs. Additionally, we will describe the recent development of 3-dimensional brain (3D) organoids which offer a promising approach as human-specific in vitro models to decipher these complex disorders.

Effects of Atomoxetine on Motor and Cognitive Behaviors and Brain Electrophysiological Activity of Dopamine Transporter Knockout Rats

Changes in dopaminergic and noradrenergic transmission are considered to be the underlying cause of attention deficit and hyperactivity disorder (ADHD). Atomoxetine (ATX) is a selective norepinephrine transporter (NET) inhibitor that is currently used for ADHD treatment. In this study, we aimed to evaluate the effect of atomoxetine on the behavior and brain activity of dopamine transporter knockout (DAT-KO) rats, which are characterized by an ADHD-like behavioral phenotype. Prepulse inhibition (PPI) was assessed in DAT-KO and wild type rats after saline and ATX injections, as well as behavioral parameters in the Hebb-Williams maze and power spectra and coherence of electrophysiological activity. DAT-KO rats demonstrated a pronounced behavioral and electrophysiological phenotype, characterized by hyperactivity, increased number of errors in the maze, repetitive behaviors and disrupted PPI, changes in cortical and striatal power spectra and interareal coherence. Atomoxetine significantly improved PPI and decreased repetitive behaviors in DAT-KO rats and influenced behavior of wild-type rats. ATX also led to significant changes in power spectra and coherence of DAT-KO and wild type rats. Assessment of noradrenergic modulation effects in DAT-KO provides insight into the intricate interplay of monoaminergic systems, although further research is still required to fully understand the complexity of this interaction.

Different sensitivity to anesthesia according to ECoG data in dopamine transporter knockout and heterozygous rats

Dopamine in the brain is involved in many important functions, including the regulation of wakefulness. There is also some evidence suggesting that the dopamine function is crucial in anesthetic function. The state of anesthesia is characterized by a change in the level of consciousness and a change in brain electrical activity. Due to impaired mechanisms of dopamine transportation back to the synaptic terminal, dopamine transporter (DAT) knockout and heterozygous rats have increased levels of the extracellular dopamine. In our work, we registered ECoG disturbances in knockout and heterozygous rats, as well as disturbances in tone and activity in acute experiments under the anesthesia Zoletil (tiletamine and zolazepam) from the somatosensory cortex using a NeuroNexus flat multielectrode array to study gamma activity. We also used four low-resistance electrodes to control the slow rhythm. Both low-resistance and high-resistance electrodes showed differences in the ECoG spectrum of heterozygotes and total knockouts from the wild type and from each other. Heterozygous rats for the DAT gene (HET) showed increased rapid beta and gamma activity and decreased slow delta activity, while complete knockouts (KO), on the contrary, showed increased delta activity and decreased beta and gamma activity. Thus, the ECoG spectrum of HET is shifted to the right, while that of KO is shifted to the left. Full knockouts also showed decreased spatial synchronization in the 30-100 Hz gamma range compared to the wild type (WT). It is assumed that sedation of HET and KO is shifted towards opposite directions compared to WT under the same anesthesia conditions.

Dopamine Transporter Knockout Rats Show Impaired Wellbeing in a Multimodal Severity Assessment Approach

In preclinical psychiatry research, animals are central to modeling and understanding biological mechanisms of behavior and psychiatric disorders. We here present the first multimodal severity assessment of a genetically modified rat strain used in psychiatric research, lacking the dopamine transporter (DAT) gene and showing endophenotypes of several dopamine-associated disorders. Absence of the DAT leads to high extracellular dopamine (DA) levels and has been associated with locomotor hyperactivity, compulsive behaviors and stereotypies in the past. The German Animal Welfare Law, which is based on the EU Directive (2010/63/EU), requires a prospective severity assessment for every animal experiment, depending on the extent of the expected degree of pain, suffering, distress or lasting harm that the animals will experience. This should consider all procedures but also the impact of the genotype on the phenotype. Therefore, we examined multiple parameters indicating animal welfare, like burrowing behavior, social interaction, saccharin preference, baseline stress hormone levels and nesting behavior. Additionally, a footprint analysis was performed and home cage activity was analyzed for a more detailed characterization of locomotion. DAT KO rats demonstrated reduced burrowing, social interaction and saccharin preference. We also found pronounced stereotypies and alterations in the gait analysis in DAT KO rats. Moreover, we confirmed the hyperactivity and the impaired sensorimotor gating mechanisms to assure that our rats are exhibiting the correct phenotype. In conclusion, we provide evidence that DAT KO rats show alterations in natural behavior patterns and deduce that the marked stereotypies are a sign for coping difficulties, both indicating a negative influence of the genotype on wellbeing. We suggest to assess further rat models in an objectified severity assessment as previously done in mice to create a relative severity assessment based on scientific evidence. Until then, we propose the classification of homozygous DAT KO rats as “moderate” in accordance with the criteria of the EU directive 2010/63.

Neuroplastic changes in c-Fos, ΔFosB, BDNF, trkB, and Arc expression in the hippocampus of male Roman rats: differential effects of sexual activity

Sexual activity causes differential changes in the expression of markers of neural activation (c-Fos and ΔFosB) and neural plasticity (Arc and BDNF/trkB), as determined either by Western Blot (BDNF, trkB, Arc, and ΔFosB) or immunohistochemistry (BDNF, trkB, Arc, and c-Fos), in the hippocampus of male Roman high (RHA) and low avoidance (RLA) rats, two psychogenetically selected rat lines that display marked differences in sexual behavior (RHA rats exhibit higher sexual motivation and better copulatory performance than RLA rats). Both methods showed (with some differences) that sexual activity modifies the expression levels of these markers in the hippocampus of Roman rats depending on: (i) the level of sexual experience, that is, changes were usually more evident in sexually naïve than in experienced rats; (ii) the hippocampal partition, that is, BDNF and Arc increased in the dorsal but tended to decrease in the ventral hippocampus; (iii) the marker considered, that is, in sexually experienced animals BDNF, c-Fos, and Arc levels were similar to those of controls, while ΔFosB levels increased; and (iv) the rat line, that is, changes were usually larger in RHA than RLA rats. These findings resemble those of early studies in RHA and RLA rats showing that sexual activity influences the expression of these markers in the nucleus accumbens, medial prefrontal cortex, and ventral tegmental area, and show for the first time that also in the hippocampus sexual activity induces neural activation and plasticity, events that occur mainly during the first phase of the acquisition of sexual experience and depend on the genotypic/phenotypic characteristics of the animals.

Dopamine-transporter heterozygous rats carrying maternal wild-type allele are more vulnerable to the development of compulsive behavior

Compulsivity is defined as an unstoppable tendency towards repetitive and habitual actions, which are reiterated despite negative consequences. Polydipsia is induced preclinically by intermittent reward leading rodents to ingest large amounts of fluids. We focused on the role of dopamine transporter (DAT) and inheritance factors in compulsive behavior. Our sample consisted of DAT heterozygous (HET) rats with different genetic inheritance (MAT-HET, born from WT-dams x KO-fathers; MIX-HET, born from HET-dams x KO-fathers). As controls, we used both wild-type (WT) rats and their socially-isolated (WTi) siblings. We ran the schedule-induced polydipsia (SIP) protocol, to induce compulsive behavior; then the Y-maze and marble-burying tests, to verify its actual development. Only MAT-HET (who inherited the functional DAT allele from the WT mother) is vulnerable to developing compulsive behavior. MAT-HET rats drank increasingly more water during SIP and showed significant perseverance in the Y-maze test and exhibited compulsive actions in the marble-burying test. Interestingly, compulsive behaviors of MAT-HET rats correlate with expression ex-vivo of different genes in different areas. Regarding the prefrontal cortex (PFC), D2R correlates with Y-maze "perseverance" in addition to BDNF; considering the amygdala (AMY), both D3R and OXTR correlate with SIP "licks". Indeed, compulsivity may be linked to D2R and BDNF in PFC, while extreme anxiety in MAT-HET rats may be associated with D3R and OXTR in the amygdala. These results confirm some similarities between MAT-HET and DAT-KO subjects and link the epigenetic context of the DAT gene to the development of compulsive behavior. This article is protected by copyright. All rights reserved.

Dopamine, Erectile Function and Male Sexual Behavior from the Past to the Present: A Review

Early and recent studies show that dopamine through its neuronal systems and receptor subtypes plays different roles in the control of male sexual behavior. These studies show that (i) the mesolimbic/mesocortical dopaminergic system plays a key role in the preparatory phase of sexual behavior, e.g., in sexual arousal, motivation and reward, whereas the nigrostriatal system controls the sensory-motor coordination necessary for copulation, (ii) the incertohypothalamic system is involved in the consummatory aspects of sexual behavior (penile erection and copulation), but evidence for its role in sexual motivation is also available, (iii) the pro-sexual effects of dopamine occur in concert with neural systems interconnecting the hypothalamus and preoptic area with the spinal cord, ventral tegmental area and other limbic brain areas and (iv) D₂ and D₄ receptors play a major role in the pro-sexual effects of dopamine. Despite some controversy, increases or decreases, respectively, of brain dopamine activity induced by drugs or that occur physiologically, usually improves or worsens, respectively, sexual activity. These findings suggest that an altered central dopaminergic tone plays a role in mental pathologies characterized by aberrant sexual behavior, and that pro-erectile D₄ receptor agonists may be considered a new strategy for the treatment of erectile dysfunction in men.

Personalization of pharmacological treatments for ADHD: Why it is advisable and possible options to achieve it

Abstract:

Attention-deficit hyperactivity disorder is a neurodevelopmental disorder diagnosed primarily in children, although it is also present in adults. Patients present inattention, impulsivity, and hyperactivity symptoms that create difficulties in their daily lives. Pharmacological treatment with stimulants or non-stimulants is used most commonly to reduce ADHD symptoms. Although generally effective and safe, pharmacological treatments have different effects among patients, including lack of response and adverse reactions. The reasons for these differences are not fully understood, but they may derive from the highly diverse etiology of ADHD. Strategies to guide optimal pharmacological treatment selection on the basis of individual patients’ physiological markers are being developed. In this review, we describe the main pharmacological ADHD treatments used and their main drawbacks. We present alternatives under study that would allow the customization of pharmacological treatments to overcome these drawbacks and achieve more reliable improvement of ADHD symptoms.

Anxiety predicts impulsive-compulsive behaviours in Parkinson's disease: Clinical relevance and theoretical implications

Patients with Parkinson's disease (PD) often present symptoms of anxiety, depression and apathy. These negative affect manifestations have been recently associated with the presence of impulsive compulsive behaviours (ICBs). However, their relation with the use of dopamine replacement therapy (DRT), a renewed risk factor for ICBs, is still not fully understood. Elucidating the role of these different ICBs predictors in PD could inform both prevention/intervention recommendations as well as theoretical models. In the present study, we have analysed data collected in 417 PD patients, 50 patients with Parkinsonian symptoms but with scan without evidence of dopaminergic deficit (SWEDD), and 185 healthy controls (HC). We examined each patient's clinical profile over a two-year time window, investigating the role of both negative affect and DRT on ICBs. Results confirmed the presence of higher levels of anxiety in both the clinical groups, and of higher level of ICBs in SWEDD patients, respect to both PD and HC. Mixed model analyses revealed a statistically significant association between anxiety and ICBs in the SWEDD patients who did not take any DRT. Findings suggest the independence between anxiety and DRT in ICBs development, and provide new evidence for the motivational opponency theoretical framework.

Behavioral Phenotype in Heterozygous DAT Rats: Transgenerational Transmission of Maternal Impact and the Role of Genetic Asset

Dopamine transporter (DAT) is involved in dopamine (DA) reuptake in presynaptic terminals. Deletion of DAT results in a hyperdopaminergic KO-rat phenotype. To conduct our studies in heterozygous DAT rats, several pedigree lines were created, with known derivation of the allele (i.e., maternal or paternal). Our purpose was to elucidate the role of parental origin rather than maternal care, assessing if maternal maltreatments generated sequelae in female offspring. In the first experiment, female rats and their pups were observed during postnatal lactation. Control dams were WT and heterozygous ones were MAT (but K-MAT, with previous experience of early maltreatment by their KO adoptive dams). WT dams were highly attracted to their offspring (predictably, they spent a lot of time licking their pups); in contrast, K-MAT dams showed strangely comparable levels of caring for their pups and exploring the environment. Subsequently, peculiar features of the circadian cycle were found in adolescent rats with different epigenotypes (WT, MUX = offspring of MAT father, MIK = offspring of K-MAT dam). The MIK epigenotype produced locomotor hyperactivity also during resting hours, well above typical values. The MUX epigenotype, on the other hand, was less active and presented a depression-like profile. This study is unique: maltreatment was generated in a spontaneous way from a DAT-KO mother to offspring. We highlight how future studies will address separate contributions by genotype and upbringing. In conclusion, paternal-allele asset generates sequelae diametrically opposed to the inheritance of early maternal trauma.

DAT-truncated epigenetics: heterozigosity of the grand-mother rat temperates the vulnerable phenotype in second-generation offspring

Behavioral phenotype differs among epigenotypes of dopamine-transporter heterozygous (DAT-HET) rats. Epigenetic regulations act through trans-generational effects, referring to phenotypic variations emerging at second or third generation. To investigate trans-generational influences exerted by maternal grandmothers, we developed breeding schemes where only the genotype of maternal grandmothers varied. Heterozygous females, to serve as MAT vs MIX mothers, were generated, respectively, from WTxKO=MAT and MATxKO=MIX breeding, with KO males acting as grandfather. The HET experimental groups, generated from either MAT or MIX mothers, were called MIX-by-MAT and MIX² (male-fathers KO; asset-M: wild\healthy-allele from dam); or SOT and SIX (male-fathers WT; asset-P: mutated-allele from dam). Thus, sequelae of first-encounter between wild\healthy and mutated DAT-alleles (in maternal-lineage) were compared at first- (MAT-dam, WT-grandmother) vs. at second- (MIX-dam, HET-grandmother) generation. We characterized, within these epigenotypes, (1) circadian home-cage activity; (2) preference for social stimuli. Marked alterations of circadian activity appeared in HETs, if offspring of MAT-dams, compared to MIX² (HET offspring of MIX-dams) which, in turn, were undistinguishable from WT-controls. A clear-cut social preference by WT-rats was expressed towards SIX compared to SOT stimulus-rats, confirming reduced social motivations. In conclusion, significant epigenetic modulations took place in DAT-HET rats, as a function of maternal grandmother's genotype.

Keeping Track of the Genealogy of Heterozygotes Using Epigenetic Reference Codes and Breeding Tables

Studying neurobehavioral consequences of the hypofunctional dopamine transporter (DAT) across several generations entails the need to monitor allelic transmission to offspring, taking into account both maternal and paternal inheritance. Since each type of heterozygote expresses differential phenotypes, based on lineage of inheritance for wild and mutated alleles (from male or female ancestors), it is important to track transgenerational epigenetic effects. We deemed it essential to assign specific abbreviations identifying their characteristics. Therefore, we devised a Mendelian-inspired table to keep track of these. Starting from two progenitors (WT and KO) we named resulting heterozygous progenies MAT and PAT to differentiate them based on inheritance of the wild allele (from the mother or father). Tracing subsequent generations, similar logic has been followed: if coupling HET dams with KO males, initials “M” [(grand)maternal] and “P” [(grand)paternal] are kept, but “AT” is turned into “IX” (MIX and PIX), while if breeding HETs with WTs, “M” is changed to “W” resembling an upside down “M” and “P” to “S” for “sperm” (WAT and SOT). To underline the development within “hyperdopaminergic-uterus” a central letter “U” is added (MUX, PUX, and QULL), while a Greek initial (μAT, μIX, and νIX) underlines the uterine-worsened origin of the allele. In HET × HET breeding (GIX and DIX), the mutated allele can be inherited from both sides of the genealogical line. However, when the mother is MAT, wild and mutated alleles encounter for the first time, causing putative anomalies in the progeny. Replacing dam with a second-generation female (MIX and MUX) may mitigate epigenetic effects on third-generation offspring; therefore suffixes (“-f,” “-fu,” “-ϕ,” and “-ϕu”) emphasize that subsequent-generation dams imply that the alleles already encountered in HET (rather than WT) grand-dams.

Dopaminergic modulation of the circadian activity and sociability: Dissecting parental inheritance versus maternal styles as determinants of epigenetic influence

In mammalians, social life and circadian rhythms find their neurobiological basis in a network that includes the dopaminergic system. The malfunctioning of dopamine pathways can lead to various disorders such as Attention-Deficit/Hyperactivity and Obsessive/compulsive disorders. A useful research approach is to exploit animal models that carry a functional silencing of SLC6A3 gene, encoding the dopamine transporter (DAT). Hyperactivity, working memory deficits, and asocial tendencies are core features in truncated-DAT rats, for example. We investigated how inheritance and maternal caring style influence circadian rhythms and social behaviours in DAT heterozygous (HET) rats, belonging to four groups: Mat-P, Mat-M, Mix-P, and Mix-M (Mat label stands for care from wild-type dam, Mix label stands for care by heterozygous dam; M label stands for maternal wild-DAT and P label stands for paternal wild-DAT). In Experiment 1, we monitored 24/7 the spontaneous locomotor activity of peri-adolescent subjects. Hyperactivity occurred only in P-asset subjects (with maternal-origin truncated-DAT allele) at specific bins of the day. In Experiment 2, we observed social interactions of the same rats. Mix-M subjects (raised by HET dams and/or inheriting the wild-DAT allele from mothers) tend to interact with all rats; Mat-P (cared by WT dams and/or inheriting the truncated-DAT allele from mothers) seem to be ignored, when acting as stimulus subjects. Overall, results confirm complex modulations for circadian cycle and social life: flexible DAT expression in HET subjects depends on epigenetic combinations of parental inheritance and early experiential factors. Once confirmed, these data could shed light on trans-generational contributions to dopaminergic-related disorders.

Dopamine transporter silencing in the rat: systems-level alterations in striato-cerebellar and prefrontal-midbrain circuits

Silencing of dopamine transporter (DAT), a main controlling factor of dopaminergic signaling, results in biochemical and behavioral features characteristic for neuropsychiatric diseases with presumed hyperdopaminergia including schizophrenia, attention deficit hyperactivity disorder (ADHD), bipolar disorder, and obsessive-compulsive disorder (OCD). Investigation of DAT silencing thus provides a transdiagnostic approach towards a systems-level understanding of common underlying pathways. Using a high-field multimodal imaging approach and a highly sensitive cryogenic coil, we integrated structural, functional and metabolic investigations in tandem with behavioral assessments on a newly developed preclinical rat model, comparing DAT homozygous knockout (DAT-KO, N = 14), heterozygous knockout (N = 8) and wild-type male rats (N = 14). We identified spatially distributed structural and functional brain alterations encompassing motor, limbic and associative loops that demonstrated strong behavioral relevance and were highly consistent across imaging modalities. DAT-KO rats manifested pronounced volume loss in the dorsal striatum, negatively correlating with cerebellar volume increase. These alterations were associated with hyperlocomotion, repetitive behavior and loss of efficient functional small-world organization. Further, prefrontal and midbrain regions manifested opposite changes in functional connectivity and local network topology. These prefrontal disturbances were corroborated by elevated myo-inositol levels and increased volume. To conclude, our imaging genetics approach provides multimodal evidence for prefrontal-midbrain decoupling and striato-cerebellar neuroplastic compensation as two key features of constitutive DAT blockade, proposing them as transdiagnostic mechanisms of hyperdopaminergia. Thus, our study connects developmental DAT blockade to systems-level brain changes, underlying impaired action inhibition control and resulting in motor hyperactivity and compulsive-like features relevant for ADHD, schizophrenia and OCD.

Animal Models of ADHD?

To describe animals that express abnormal behaviors as a model of Attention-Deficit Hyperactivity Disorder (ADHD) implies that the abnormalities are analogous to those expressed by ADHD patients. The diagnostic features of ADHD comprise inattentiveness, impulsivity, and hyperactivity and so these behaviors are fundamental for validation of any animal model of this disorder. Several experimental interventions such as neurotoxic lesion of neonatal rats with 6-hydroxydopamine (6-OHDA), genetic alterations, or selective inbreeding of rodents have produced animals that express each of these impairments to some extent. This article appraises the validity of claims that these procedures have produced a model of ADHD, which is essential if they are to be used to investigate the underlying cause(s) of ADHD and its abnormal neurobiology.

Modulation of Spatial Memory Deficit and Hyperactivity in Dopamine Transporter Knockout Rats via α2A-Adrenoceptors

Attention deficit hyperactivity disorder (ADHD) is manifested by a specific set of behavioral deficits such as hyperactivity, impulsivity, and inattention. The dopamine neurotransmitter system is postulated to be involved in the pathogenesis of ADHD. Guanfacine, a selective α2A-adrenoceptor agonist, is prescribed for ADHD treatment. ADHD also is known to be associated with impairment of multiple aspects of cognition, including spatial memory, however, it remains unclear how modulation of the norepinephrine system can affect these deficits. Hyperdopaminergic dopamine transporter knockout (DAT-KO) rats are a valuable model for investigating ADHD. The DAT-KO rats are hyperactive and deficient in spatial working memory. This work aimed to evaluate the effects of noradrenergic drugs on the fulfillment of spatial cognitive tasks by DAT-KO rats. The rats were tested in the Hebb - Williams maze during training and following noradrenergic drugs administration. The efficiency of spatial orientation was assessed as to how fast the animal finds an optimal way to the goal box. Testing in a new maze configuration allowed us to evaluate the effects of drug administration after the acquisition of the task rules. The behavioral variables such as the distance traveled, the time to reach the goal box, and the time spent in the error zones were analyzed. It has been observed that α2A-adrenoceptor agonist Guanfacine (0.25 mg/kg) had only a minimal inhibitory effect on hyperactivity of DAT-KO rats in the maze but significantly ameliorated their perseverative pattern of activity and reduced the time spent in the error zones. In contrast, α2A-adrenoceptor antagonist Yohimbine, at the dose of 1 mg/kg, increased the distance traveled by DAT-KO rats and elevated the number of perseverative reactions and the time spent in the error zones. Guanfacine caused minimal effects in wild-type rats, while Yohimbine altered several parameters reflecting a detrimental effect on the performance in the maze. These data indicate that modulation of α2A-adrenoceptor activity potently affects both dopamine-dependent hyperactivity and cognitive dysfunctions. Similar mechanisms may be involved in the beneficial effects of Guanfacine on cognitive deficits in ADHD patients. This study further supports the translational potential of DAT-KO rats for testing new pharmacological drugs.

Trace amine-associated receptor 1 (TAAR1): Potential application in mood disorders: A systematic review

There is a need for innovation with respect to therapeutics in psychiatry. Available evidence indicates that the trace amine-associated receptor 1 (TAAR1) agonist SEP-363856 is promising, as it improves measures of cognitive and reward function in schizophrenia. Hedonic and cognitive impairments are transdiagnostic and constitute major burdens in mood disorders. Herein, we systematically review the behavioural and genetic literature documenting the role of TAAR1 in reward and cognitive function, and propose a mechanistic model of TAAR1's functions in the brain. Notably, TAAR1 activity confers antidepressant-like effects, enhances attention and response inhibition, and reduces compulsive reward seeking without impairing normal function. Further characterization of the responsible mechanisms suggests ion-homeostatic, metabolic, neurotrophic, and anti-inflammatory enhancements in the limbic system. Multiple lines of evidence establish the viability of TAAR1 as a biological target for the treatment of mood disorders. Furthermore, the evidence suggests a role for TAAR1 in reward and cognitive function, which is attributed to a cascade of events that are relevant to the cellular integrity and function of the central nervous system.

Social Interactions of Dat-Het Epi-Genotypes Differing for Maternal Origins: The Development of a New Preclinical Model of Socio-Sexual Apathy

Social interaction is essential for life but is impaired in many psychiatric disorders. We presently focus on rats with a truncated allele for dopamine transporter (DAT). Since heterozygous individuals possess only one non-mutant allele, epigenetic interactions may unmask latent genetic predispositions. Homogeneous "maternal" heterozygous offspring (termed MAT-HET) were born from dopamine-transporter knocked-out (DAT-KO) male rats and wild-type (WT) mothers; "mixed" heterozygous offspring (termed MIX-HET) were born from both DAT-heterozygous parents. Their social behavior was assessed by: partner-preference (PPT), social-preference (SPT) and elicited-preference (EPT) tests. During the PPT, focal MIX-HET and MAT-HET males had a choice between two WT females, one in estrous and the other not. In the SPT, they met as stimulus either a MIX-HET or a WT male. In the EPT, the preference of focal male WT rats towards either a MIX- or a MAT-HET stimulus was tested. MIX-HET focal males showed an abnormal behavior, seeming not interested in socializing either with a female in estrous or with another male if MIX-HET. Focal MAT-HET males, instead, were very attracted by the female in estrous, but totally ignored the MIX-HET male. We assessed the expression of noradrenaline transporter (NET) in prefrontal cortex, hippocampus and hypothalamus, finding differences between the two offspring. MIX-HETs' hypothalamus and hippocampus showed less NET than MAT-HETs, while the latter, in turn, showed higher NET than WTs. These behavioral differences between heterozygous groups may be attributed to different maternal cares received. Results allow preclinical understanding of epigenetic factors involved in social-behavior abnormalities, typical of many psychiatric disorders.

Altering the development of the dopaminergic system through social play in rats: Implications for anxiety, depression, hyperactivity, and compulsivity

Dopamine is essential to many functions like reward, motivation, and attention; when its neural pathways do not function properly, various disorders (e.g., anxiety, depression, hyperactivity, compulsions) can arise. Truncated-DAT rats display persistent stereotypies and aggressiveness; hence they are a new valuable animal model to study the pathogenesis of these disorders. The focus of research is often on the individual epigenetic determinants and much less on the impact of social experiences. Here, we investigate the developmental impact of the social environment on adolescent wild type (WT) rats. We divided subjects at weaning into three groups: living with another adolescent (WT Peer), with a WT adult, or with a truncated-DAT one, and we observed homecage social behavior of these pairs (play, jump, victory, and "bullying") during whole adolescence. When adult, we observed the same subjects in plus maze, forced swim, and social preference tests to measure levels of anxiety, depression, and quality of social interactions. Compared to the other groups, WT rats that had spent their adolescence with a truncated-DAT adult as companion show more anxious, depressive, hyperactive, impulsive, and compulsive behaviours. Results confirm that social interactions and healthy play (i.e., when play has behavioural, social, and psychomotor rewards that support the cognitive, emotional and physical development of the individual) are essential to neurobehavioral maturation. Conversely, anomalous interactions like poor play and "bullying" in developing rats may impact onto their dopaminergic system. Consequently, an impoverished social play could be one of the factors contributing to the appearance of putative indexes of attention deficit hyperactivity disorder (ADHD) and\or obsessive-compulsive disorder (OCD).

Evolutionary conservations, changes of circadian rhythms and their effect on circadian disturbances and therapeutic approaches

The circadian rhythm is essential for the interaction of all living organisms with their environments. Several processes, such as thermoregulation, metabolism, cognition and memory, are regulated by the internal clock. Disturbances in the circadian rhythm have been shown to lead to the development of neuropsychiatric disorders, including attention-deficit hyperactivity disorder (ADHD). Interestingly, the mechanism of the circadian rhythms has been conserved in many different species, and misalignment between circadian rhythms and the environment results in evolutionary regression and lifespan reduction. This review summarises the conserved mechanism of the internal clock and its major interspecies differences. In addition, it focuses on effects the circadian rhythm disturbances, especially in cases of ADHD, and describes the possibility of recombinant proteins generated by eukaryotic expression systems as therapeutic agents as well as CRISPR/Cas9 technology as a potential tool for research and therapy. The aim is to give an overview about the evolutionary conserved mechanism as well as the changes of the circadian clock. Furthermore, current knowledge about circadian rhythm disturbances and therapeutic approaches is discussed.

Patterns of Restricted and Repetitive Behaviors in Autism Spectrum Disorders: A Cross-Sectional Video Recording Study. Preliminary Report

BACKGROUND

Several instruments have been proposed to investigate restricted, repetitive behaviors (RRBs) in individuals with Autism Spectrum Disorder (ASD). Systematic video observations may overcome questionnaire and interview limitations to investigate RRBs. This study aimed to analyze stereotypic patterns through video recordings and to determine the correlation between the number and appearance of RRBs to ASD severity.

METHODS

Twenty health professionals wearing a body cam recorded 780 specific RRBs during everyday activities of 67 individuals with ASD (mean age: 14.2 ± 3.72 years) for three months. Each stereotypy was classified according to its complexity pattern (i.e., simple or complex) based on body parts and sensory channels involved.

RESULTS

The RRBs spectrum for each subject ranged from one to 33 different patterns (mean: 11.6 ± 6.82). Individuals with a lower number of stereotypies shown a lower ASD severity compared to subjects with a higher number of stereotypies (p = 0.044). No significant differences were observed between individuals exhibiting simple (n = 40) and complex patterns (n = 27) of stereotypies on ASD severity, age, sex, and the number of stereotypes.

CONCLUSIONS

This study represents the first attempt to systematically document expression patterns of RRBs with a data-driven approach. This may provide a better understanding of the pathophysiology and management of RRBs.

Frontoparietal hyperconnectivity during cognitive regulation in obsessive-compulsive disorder followed by reward valuation inflexibility

Obsessive-compulsive disorder (OCD) is characterized by cognitive deficits and altered reward processing systems. An imbalance between cognitive and reward pathways may explain the lack of control over obsessions followed by rewarding compulsive behaviors. While the processes of emotional cognitive regulation are widely studied in OCD, the mechanisms of cognitive regulation of reward are poorly described. Our goal was to investigate the OCD impact on cognitive regulation of reward at behavioral and neural functioning levels. OCD and control participants performed a functional magnetic resonance imaging task where they cognitively modulated their craving for food pictures under three cognitive regulation conditions: indulge/increase craving, distance/decrease craving, and natural/no regulation of craving. After regulation, the participants gave each picture a monetary value. We found that OCD patients had fixed food valuation scores while the control group modulated these values accordingly to the regulation conditions. Moreover, we observed frontoparietal hyperconnectivity during cognitive regulation. Our results suggest that OCD is characterized by deficits in cognitive regulation of internal states associated with inflexible behavior during reward processing. These findings bring new insights into the nature of compulsive behaviors in OCD.

"Himalayan Bridge": A New Unstable Suspended Bridge to Investigate Rodents' Venturesome Behavior

While both risk-taking and avoidant behaviors are necessary for survival, their imbalanced expression can lead to impulse-control and anxiety disorders, respectively. In laboratory rodents, the conflict between risk proneness and anxiety can be studied by using their innate fear of heights. To explore this aspect in detail and investigate venturesome behavior, here we used a "Himalayan Bridge," a rat-adapted version of the suspended wire bridge protocol originally developed for mice. The apparatus is composed of two elevated scaffolds connected by bridges of different lengths and stability at 1 m above a foam rubber-covered floor. Rats were allowed to cross the bridge to reach food, and crossings, pawslips, turnabouts, and latencies to cross were measured. Given the link between risky behavior and adolescence, we used this apparatus to investigate the different responses elicited by a homecage mate on the adolescent development of risk-taking behavior. Thus, 24 wild-type (WT) subjects were divided into three different housing groups: WT rats grown up with WT adult rats; control WT adolescent rats (grown up with WT adolescents), which showed a proclivity to risk; and WT rats grown up with an adult rat harboring a truncated mutation for their dopamine transporter (DAT). This latter group exhibited risk-averse responses reminiscent of lower venturesomeness. Our results suggest that the Himalayan Bridge may be useful to investigate risk perception and seeking; thus, it should be included in the behavioral phenotyping of rat models of psychiatric disorders and cognitive dysfunctions.

A New Paradigm for Training Hyperactive Dopamine Transporter Knockout Rats: Influence of Novel Stimuli on Object Recognition

Attention deficit hyperactivity disorder (ADHD) is believed to be connected with a high level of hyperactivity caused by alterations of the control of dopaminergic transmission in the brain. The strain of hyperdopaminergic dopamine transporter knockout (DAT-KO) rats represents an optimal model for investigating ADHD-related pathological mechanisms. The goal of this work was to study the influence of the overactivated dopamine system in the brain on a motor cognitive task fulfillment. The DAT-KO rats were trained to learn an object recognition task and store it in long-term memory. We found that DAT-KO rats can learn to move an object and retrieve food from the rewarded familiar objects and not to move the non-rewarded novel objects. However, we observed that the time of task performance and the distances traveled were significantly increased in DAT-KO rats in comparison with wild-type controls. Both groups of rats explored the novel objects longer than the familiar cubes. However, unlike controls, DAT-KO rats explored novel objects significantly longer and with fewer errors, since they preferred not to move the non-rewarded novel objects. After a 3 months' interval that followed the training period, they were able to retain the learned skills in memory and to efficiently retrieve them. The data obtained indicate that DAT-KO rats have a deficiency in learning the cognitive task, but their hyperactivity does not prevent the ability to learn a non-spatial cognitive task under the presentation of novel stimuli. The longer exploration of novel objects during training may ensure persistent learning of the task paradigm. These findings may serve as a base for developing new ADHD learning paradigms.

Perinatal Dietary Polyunsaturated Fatty Acids in Brain Development, Role in Neurodevelopmental Disorders

n-3 and n-6 polyunsaturated fatty acids (PUFAs) are essential fatty acids that are provided by dietary intake. Growing evidence suggests that n-3 and n-6 PUFAs are paramount for brain functions. They constitute crucial elements of cellular membranes, especially in the brain. They are the precursors of several metabolites with different effects on inflammation and neuron outgrowth. Overall, long-chain PUFAs accumulate in the offspring brain during the embryonic and post-natal periods. In this review, we discuss how they accumulate in the developing brain, considering the maternal dietary supply, the polymorphisms of genes involved in their metabolism, and the differences linked to gender. We also report the mechanisms linking their bioavailability in the developing brain, their transfer from the mother to the embryo through the placenta, and their role in brain development. In addition, data on the potential role of altered bioavailability of long-chain n-3 PUFAs in the etiologies of neurodevelopmental diseases, such as autism, attention deficit and hyperactivity disorder, and schizophrenia, are reviewed.

ADHD: Reviewing the Causes and Evaluating Solutions

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder in which patients present inattention, hyperactivity, and impulsivity. The etiology of this condition is diverse, including environmental factors and the presence of variants of some genes. However, a great diversity exists among patients regarding the presence of these ADHD-associated factors. Moreover, there are variations in the reported neurophysiological correlates of ADHD. ADHD is often treated pharmacologically, producing an improvement in symptomatology, albeit there are patients who are refractory to the main pharmacological treatments or present side effects to these drugs, highlighting the importance of developing other therapeutic options. Different non-pharmacological treatments are in this review addressed, finding diverse results regarding efficacy. Altogether, ADHD is associated with different etiologies, all of them producing changes in brain development, leading to the characteristic symptomatology of this condition. Given the heterogeneous etiology of ADHD, discussion is presented about the convenience of personalizing ADHD treatment, whether pharmacological or non-pharmacological, to reach an optimum effect in the majority of patients. Approaches to personalizing both pharmacological therapy and neurofeedback are presented.

Effects of Tyrosine and Tryptophan in Rats with Diet-Induced Obesity

Amino acids tyrosine (Tyr) and tryptophan (Trp) play a significant role in the regulation of energy metabolism, locomotor activity, and eating behavior. We studied the possibility of modulating these processes in obesity by increasing the pool of Tyr and Trp in the experimental diet. As a model of obesity, we used Wistar rats fed a diet with an excess specific energy value (HFCD) for 64 days. Trp led to a normalization of the rats’ body weight almost to the control level, but increased anxiety-like behavior and decreased long-term memory. The consumption of amino acids resulted in increased grip strength and impairment of short-term memory. The locomotor activity of animals decreased with age as a result of Tyr consumption, while Trp, on the contrary, prevented this. The Tyr supplementation led to the normalization of triglycerides and LDL. In the spleen cell lysates, amino acids suppressed the production of proinflammatory cytokines. The liver tissue morphology showed that the consumption of Tyr noticeably weakened the signs of fatty degeneration. The addition of Trp, on the contrary, led to an unfavorable effect, consisting of the appearance of a high number of large rounded fatty vacuoles. The data obtained indicate a more pronounced anti-inflammatory effect of Tyr as compared to Trp.

Micro-Vesicles of Moringa oleifera Seeds in Heterozygous Rats for DAT Gene: Effects of Oral Intake on Behavioral Profile and Hematological Parameters

Previous studies have shown multiple biological properties of Moringa oleifera, a plant native to Africa and Asia. In the present study, potential physiological properties of microvesicles extracted from Moringa oleifera seeds were assessed. For this purpose, we investigated behavioral profile and hematological parameters in a recent rat model characterized by dysregulation in dopamine transporter, a key regulator of dopaminergic system. Experimental design consisted of male Wistar-DAT rats aged between two and four months: wild-type (WT) (n = 5) and heterozygous (DATHET) (n = 4) control groups, which drank tap water; WT (n = 5) and DATHET (n = 6) groups which drank a solution of Moringa microvesicles and water (2: 68 mL per day), which was orally administered for two months. Rats were monitored for spontaneous locomotor activity on a 24/7 basis. In the early lit hours, treated DATHET subjects showed higher locomotor activity, proposing a sleep-delay effect of Moringa. In forced swimming test, WT subjects who took Moringa exhibited more depressive behavior. In DATHET rats, Moringa seemed to potentiate the struggle to find a way out, counteracting an initial panic. Hemoglobin and hematocrit underwent opposite changes in either genotype, supporting the opposite effects on behavioral phenotype observed. Future work is clearly needed to further explore these preliminary profiles.

Early Adolescence Prefrontal Cortex Alterations in Female Rats Lacking Dopamine Transporter

Monoamine dysfunctions in the prefrontal cortex (PFC) can contribute to diverse neuropsychiatric disorders, including ADHD, bipolar disorder, PTSD and depression. Disrupted dopamine (DA) homeostasis, and more specifically dopamine transporter (DAT) alterations, have been reported in a variety of psychiatric and neurodegenerative disorders. Recent studies using female adult rats heterozygous (DAT+/-) and homozygous (DAT-/-) for DAT gene, showed the utility of those rats in the study of PTSD and ADHD. Currently, a gap in the knowledge of these disorders affecting adolescent females still represents a major limit for the development of appropriate treatments. The present work focuses on the characterization of the PFC function under conditions of heterozygous and homozygous ablation of DAT during early adolescence based on the known implication of DAT and PFC DA in psychopathology during adolescence. We report herein that genetic ablation of DAT in the early adolescent PFC of female rats leads to changes in neuronal and glial cell homeostasis. In brief, we observed a concurrent hyperactive phenotype, accompanied by PFC alterations in glutamatergic neurotransmission, signs of neurodegeneration and glial activation in DAT-ablated rats. The present study provides further understanding of underlying neuroinflammatory pathological processes that occur in DAT-ablated female rats, what can provide novel investigational approaches in human diseases.

A novel paradigm for assessing olfactory working memory capacity in mice

A decline in working memory (WM) capacity is suggested to be one of the earliest symptoms observed in Alzheimer's disease (AD). Although WM capacity is widely studied in healthy subjects and neuropsychiatric patients, few tasks are developed to measure this variation in rodents. The present study describes a novel olfactory working memory capacity (OWMC) task, which assesses the ability of mice to remember multiple odours. The task was divided into five phases: context adaptation, digging training, rule-learning for non-matching to a single-sample odour (NMSS), rule-learning for non-matching to multiple sample odours (NMMS) and capacity testing. During the capacity-testing phase, the WM capacity (number of odours that the mice could remember) remained stable (average capacity ranged from 6.11 to 7.00) across different testing sessions in C57 mice. As the memory load increased, the average errors of each capacity level increased and the percent correct gradually declined to chance level, which suggested a limited OWMC in C57 mice. Then, we assessed the OWMC of 5 × FAD transgenic mice, an animal model of AD. We found that the performance displayed no significant differences between young adult (3-month-old) 5 × FAD mice and wild-type (WT) mice during the NMSS phase and NMMS phase; however, during the capacity test with increasing load, we found that the OWMC of young adult 5 × FAD mice was significantly decreased compared with WT mice, and the average error was significantly increased while the percent correct was significantly reduced, which indicated an impairment of WM capacity at the early stage of AD in the 5 × FAD mice model. Finally, we found that FOS protein levels in the medial prefrontal cortex and entorhinal cortex after the capacity test were significantly lower in 5 × FAD than WT mice. In conclusion, we developed a novel paradigm to assess the capacity of olfactory WM in mice, and we found that OWMC was impaired in the early stage of AD.

The Role of Zebrafish and Laboratory Rodents in Schizophrenia Research

Schizophrenia is a severe disorder characterized by positive, negative and cognitive symptoms, which are still not fully understood. The development of efficient antipsychotics requires animal models of a strong validity, therefore the aims of the article were to summarize the construct, face and predictive validity of schizophrenia models based on rodents and zebrafish, to compare the advantages and disadvantages of these models, and to propose future directions in schizophrenia modeling and indicate when it is reasonable to combine these models. The advantages of rodent models stem primarily from the high homology between rodent and human physiology, neurochemistry, brain morphology and circuitry. The advantages of zebrafish models stem in the high fecundity, fast development and transparency of the embryo. Disadvantages of both models originate in behavioral repertoires not allowing specific symptoms to be modeled, even when the models are combined. Especially modeling the verbal component of certain positive, negative and cognitive symptoms is currently impossible.

Translational approach to understanding momentary factors associated with alcohol consumption

Multiple interindividual and intra-individual factors underlie variability in drinking motives, challenging clinical translatability of animal research and limiting treatment success of substance use-related problems. Intra-individual variability refers to time-dependent continuous and discrete changes within the individual and in substance use research is studied as momentary variation in the internal states (craving, stressed, anxious, impulsive and tired) and response to external triggers (stressors, drug-associated environmental cues and social encounters). These momentary stimuli have a direct impact on behavioural decisions and may be triggers and predictors of substance consumption. They also present potential targets for real-time behavioural and pharmacological interventions. In this review, we provide an overview of the studies demonstrating different momentary risk factors associated with increased probability of alcohol drinking in humans and changes in alcohol seeking and consumption in animals. The review also provides an overview of pharmacological interventions related to every individual risk factor.