Laurent Galineau

Serotoninergic neurotransmission is affected by n-3 polyunsaturated fatty acids in the rat

We explored the effects of chronic α‐linolenic acid dietary deficiency on serotoninergic neurotransmission. In vivo synaptic serotonin (5‐HT) levels were studied in basal and pharmacologically stimulated conditions using intracerebral microdialysis in the hippocampus of awake 2‐month‐old rats. We also studied the effects of reversion of the deficient diet on fatty acid composition and serotoninergic neurotransmission. A balanced (control) diet was supplied to deficient rats at different stages of development, i.e. from birth, 7, 14 or 21 days of age. We demonstrated that chronic n‐3 polyunsaturated fatty acid dietary deficiency induced changes in the synaptic levels of 5‐HT both in basal conditions and after pharmacological stimulation with fenfluramine. Higher levels of basal 5‐HT release and lower levels of 5‐HT‐stimulated release were found in deficient than in control rats. These neurochemical modifications were reversed by supply of the balanced diet provided at birth or during the first 2 weeks of life through the maternal milk, whereas they persisted if the balanced diet was given from weaning (at 3 weeks of age). This suggests that provision of essential fatty acids is durably able to affect brain function and that this is related to the developmental stage during which the deficiency occurs.

Ontogeny of the dopamine and serotonin transporters in the rat brain: an autoradiographic study

Damage to monoaminergic systems during the period of brain development is thought to be involved in several neurodevelopmental disorders. We investigated the maturation of the dopamine and serotonin transporters in rat cerebral regions containing the soma and projections of dopaminergic and serotoninergic neurons in an extensive study from the end of embryonic life (E(18)) to adult stages (until P(70)). The membrane transporters were measured by quantitative autoradiography using specific radioprobes. We demonstrated that the dopamine and serotonin transporters have different patterns of development. The dopamine transporter density increased from E(18) to P(28) where it reached the adult level and then remained stable until P(70). The maturation of serotonin transporters followed a triphasic profile in all areas: (i). an increase leading to a peak obtained between P(0) and P(14) in cell bodies and at P(21) in nerve endings; (ii). a decrease to reach adult levels at P(21) in raphe nuclei and at P(28) in projections areas; and (iii). a plateau until P(70). This demonstrated that the last week of embryonic life and the first two postnatal weeks are critical periods in the development of the dopaminergic and serotoninergic systems at which time they could be particularly vulnerable to injury.

Prenatal MDMA exposure delays postnatal development in the rat: a preliminary study.

3,4-methylenedioxymethamphetamine or MDMA (ecstasy) is a synthetic illicit drug which is widely consumed throughout the world. Drug abuse during pregnancy may have an impairing effect on the progeny of drug-abusing mothers. The purpose of the present study was to assess the effect of prenatal MDMA exposure on the progeny development, using a rat model. Pregnant animals were injected daily with MDMA (10 mg/kg) between the 13th and 20th days of gestation. Male and female pups were then tested throughout the lactation period on the appearance and improvement of physical and sensory motor parameters. Appearance of some physical features (eyes opening and incisor eruption) and neurological reflexes as well as improving performances in negative geotaxis, gait and inclined board tests were delayed in pups prenatally exposed to MDMA compared to saline-treated pups. In contrast, functions that are necessary for survival such as forelimb reflex (that enables suckling) were present in both groups. At four weeks of age, MDMA animals recovered to normal level in all studied parameters. The delay in physical and neurological reflex development could be interpreted as alterations in maturation of some neuronal circuitries induced by prenatal MDMA exposure.

Unsupervised Spectral Clustering for Segmentation of Dynamic PET Images

Segmentation of dynamic PET images is needed to extract the time activity curves (TAC) of regions of interest (ROI). These TAC can be used in compartmental models for in vivo quantification of the radiotracer target. While unsupervised clustering methods have been proposed to segment PET sequences, they are often sensitive to initial conditions or favour convex shaped clusters. Kinetic spectral clustering (KSC) of dynamic PET images was recently proposed to handle arbitrary shaped clusters in the space in which they are identified. While improved results were obtained with KSC compared to three state of art methods, its use for clinical applications is still hindered by the manual setting of several parameters. In this paper, we develop an extension of KSC to automatically estimate the parameters involved in the method and to make it deterministic. First, a global search procedure is used to locate the optimal cluster centroids from the projected data. Then an unsupervised clustering criterion is tailored and used in a global optimization scheme to automatically estimate the scale parameter and the weighting factors involved in the proposed Automatic and Deterministic Kinetic Spectral Clustering (AD-KSC). We validate the method using GATE Monte Carlo simulations of dynamic numerical phantoms and present results on real dynamic images. The deterministic results obtained with AD-KSC agree well with those obtained with optimal manual parameterization of KSC, and improve the ROI identification compared to three other clustering methods. The proposed approach could have significant impact for quantification of dynamic PET images in molecular imaging studies.

Cortical areas involved in behavioral expression of external pallidum dysfunctions: A PET imaging study in non-human primates

Abstract The external pallidum (GPe) is a component of the indirect pathway centrally placed in the basal ganglia. Studies already demonstrated that the pharmacological disinhibition of the sensorimotor, associative, and limbic GPe produced dyskinesia, hyperactivity, and compulsive behaviors, respectively. The aim of this study was to investigate the cortical regions altered by the disinhibition of each GPe functional territory. Thus, 5 macaques were injected with bicuculline in sensorimotor, associative, and limbic sites of the GPe producing dyskinesia, hyperactivity, and compulsive behaviors, and underwent in vivo positron tomography with 18F‐2‐fluoro‐2‐deoxy‐D‐glucose to identify cortical dysfunctions related to GPe disinhibition. Blood cortisol levels were also quantified as a biomarker of anxiety for each condition. Our results showed that pallidal bicuculline injections in anesthetized animals reproducibly modified the activity of specific ipsilateral and contralateral cortical areas depending on the pallidal territory targeted. Bicuculline injections in the limbic GPe led to increased ipsilateral activations in limbic cortical regions (anterior insula, amygdala, and hippocampus). Injections in the associative vs. sensorimotor GPe increased the activity in the ipsilateral midcingulate vs. somatosensory and parietal cortices. Moreover, bicuculline injections increased blood cortisol levels only in animals injected in their limbic GPe. These are the first functional results supporting the model of opened cortico‐striato‐thalamo‐cortical loops where modifications in a functional pallidal territory can impact cortical activities of the same functional territory but also cortical activities of other functional territories. This highlights the importance of the GPe as a crucial node in the top‐down control of the cortico‐striato‐thalamo‐cortical circuits from the frontal cortex to influence the perception, attention, and emotional processes at downstream (or non‐frontal) cortical levels. Finally, we showed the implication of the ventral pallidum with the amygdala and the insular cortex in a circuit related to aversive processing that should be crucial for the production of anxious disorders. HighlightsPallidal activations impact preferentially cortical targets of opened loops.GPe is crucial for the top‐down control of cortico‐striato‐thalamo‐cortical loops.The ventral pallidum, amygdala and insula are parts of a circuit.This circuit is related to aversive processing.This circuit could be involved in the production of anxious disorders.

Longitudinal Changes in Brain Metabolic Activity after Withdrawal from Escalation of Cocaine Self-Administration

The chronic and relapsing nature of addiction suggests that drugs produce persistent adaptations in the brain that make individuals with drug addiction particularly sensitive to drug-related cues and stress and incapable of controlling drug-seeking and drug-taking behavior. In animal models, several long-lasting neuroadaptations have been described. However, few studies have used brain-imaging techniques to provide a complete picture of brain functioning in the course of withdrawal from cocaine. In this study, we allowed rats to self-administer cocaine under short-access (1-h/day) or long-access (6-h/day) conditions and used 2-deoxy-2-(18F)fluoro-d-glucose (18FDG) positron emission tomography scanning to investigate the longitudinal changes in metabolic activity 1 and 4 weeks after discontinuation of cocaine self-administration. We found that compared to naive rats, both long-access and short-access rats showed significant disruptions in basal brain metabolic activity. However, compared to short-access, long-access rats showed more intense, and long-lasting neuroadaptations in a network of brain areas. In particular, abstinence from extended access to cocaine was associated with decreased metabolic activity in the anterior cingulate cortex, the insular cortex, and the dorsolateral striatum, and increased metabolic activity in the mesencephalon, amygdala, and hippocampus. This pattern is strikingly similar to that described in humans that has led to the proposal of the Impaired Response Inhibition and Salience Attribution model of addiction. These results demonstrate that extended access to cocaine leads to persistent neuroadaptations in brain regions involved in motivation, salience attribution, memory, stress, and inhibitory control that may underlie increased risks of relapse.

Workflow methodology for rat brain metabolome exploration using NMR, LC–MS and GC–MS analytical platforms

Graphical abstract Figure. No caption available. HighlightsMetabolomics approach requires to be optimized for each biological matrix used.At present, no method standardization for rodent brain metabolomics.Designing of methodology for each pre‐analytical step (tissue lysis, extraction…).Complementary information on rat brain metabolome using NMR, LC–MS, GC–MS. Abstract We developed a multi‐platform approach for the metabolome exploration of rat brain tissue, using liquid chromatography coupled with mass spectrometry (LC–MS), nuclear magnetic resonance spectroscopy (NMR) and gas‐chromatography coupled with mass spectrometry (GC–MS). The critical steps for metabolite exploration of cerebral tissues are tissue lysis and metabolites extraction. We first evaluated the impact of freeze‐drying compared to wet tissue metabolites extraction using NMR and LC–MS with a reversed phase liquid chromatography. Then, we compared four metabolite extraction methods Based on the number of metabolites extracted, their intensity and their coefficient of variation (%CV), the most reproducible protocol (one‐step extraction with acetonitrile on lyophilized material) was chosen to further evaluate the impact of sample mass on method performance (3, 6, and 9 mg were essayed). GC–MS analysis was also investigated by analyzing four different methoximation/silylation derivatization combinations. The optimal analytical protocols were proposed to establish the reliability required to realize untargeted brain tissue metabolomics exploration. The most reliable workflow was then exemplified by analyzing three rat brain regions (cerebellum, frontal and parietal cortices, n = 12) by 1H NMR, LC–MS and GC–MS, allowing their clustering based on their metabolic profiles. We present here an example of development of methodology that should be done before running analysis campaigns.

Prenatal Exposure to Methylphenidate Affects the Dopamine System and the Reactivity to Natural Reward in Adulthood in Rats

Background: Methylphenidate (MPH) is a commonly-used medication for the treatment of children with Attention-Deficit/Hyperactivity Disorders (ADHD). However, its prescription to adults with ADHD and narcolepsy raises the question of how the brain is impacted by MPH exposure during pregnancy. The goal of this study was to elucidate the long-term neurobiological consequences of prenatal exposure to MPH using a rat model. Methods: We focused on the effects of such treatment on the adult dopamine (DA) system and on the reactivity of animals to natural rewards. Results: This study shows that adult male rats prenatally exposed to MPH display elevated expression of presynaptic DA markers in the DA cell bodies and the striatum. Our results also suggest that MPH-treated animals could exhibit increased tonic DA activity in the mesolimbic pathway, altered signal-to-noise ratio after a pharmacological stimulation, and decreased reactivity to the locomotor effects of cocaine. Finally, we demonstrated that MPH rats display a decreased preference and motivation for sucrose. Conclusions: This is the first preclinical study reporting long-lasting neurobiological alterations of DA networks as well as alterations in motivational behaviors for natural rewards after a prenatal exposure to MPH. These results raise concerns about the possible neurobiological consequences of MPH treatment during pregnancy.

Optimized spectral clustering for segmentation of dynamic PET images

The quantification of dynamic PET images requires the definition of regions of interest. The manual delineation is a time consuming and unreproducible process due to the poor resolution of PET images. Approaches were proposed in the literature to classify the kinetic profiles of voxels, however, they are generally either sensitive to initial conditions or favor convex shaped clusters. Recently we have proposed a kinetic spectral clustering (KSC) method for segmentation of dynamic PET images that has the advantage of handling clusters with arbitrary shape in the space in which they are identified. However, its use for clinical applications is still hindered by the manual setting of several parameters. In this paper, we propose an extension of KSC to make it automatic (ASC). A new unsupervised clustering criterion is tailored and a global optimization by a probabilistic metaheuristic algorithm is used to select the scale parameter and the weighting factors involved in the method. We validate our approach with GATE Monte Carlo simulations. Results obtained with ASC compare closely with those obtained with optimal manual parameterization of KSC, and outperform those obtained with two other approaches from the literature.

Mise au pointTroubles psychiatriques et ganglions de la base : une validation expérimentaleBasal ganglia and psychiatric disorders: An experimental validation☆

Abnormal movements and behavioral disorders are characteristic manifestations observed in certain neuropsychiatric diseases such as Tourettes syndrome or Huntington Disease. Together with brain imaging findings, the clinical data could suggest a relationship with basal ganglia dysfunction. In the first part of this review, we recall the anatomic relationships existing, via segregated cortico-cortical circuits, between these structures and the cortical areas having motor and cognitive or motivational-emotional attributes. This structure suggests that in pathologies like Parkinsons or Huntington disease cognitive and motivational-emotional disorders as well motor disturbances could be related to lesions or dysfunctions involving individual or combined zones of the basal ganglia. The second part of the paper focuses on a description of the various methodologies used to explore these relationships: behavioral, anatomic and brain imaging methods are used in non-human primate models in order to reproduce motor and behavioral disturbances and to determine the neuronal circuits involved. Microinjection of bicucullin into the external globus pallidus has been found to induce localized and reversible neuronal activation. Abnormal movements can be obtained from the motor territory of the external globus pallidus whereas hyperactivity with attentional deficit or stereotypies have been obtained from the associative or limbic territory of the same structure. In the striatum, the same pharmacological activation can induce either abnormal movements from motor and associative functional territories or behavioural changes with hyperactivity or, on the contrary, hypoactivity from associative functional territory with stereotyped behavior and sexual manifestations when the microinjections were done in the limbic striatum. Anatomic studies as well as brain imaging using PET confirm the involvement of segregated anatomic pathways through the basal ganglia in behavioral as well as motor disorders.