Cognitive flexibility is an important mechanism enabling organisms to adapt to their changing environment. Different brain structures are involved in this complex process. It has been repeatedly shown that the striatum is one of the key structures controlling cognitive flexibility. Striatum receives rich input from different brain regions while its output is rather uniform. Striatal functions and signalling are greatly modulated by dopamine and acetylcholine. A number of studies have shown involvement of striatal acetylcholine and its receptors in the control of cognitive flexibility but very little is known about the role of M4 muscarinic acetylcholine receptors. These receptors are inhibitory, and they have been shown to induce long-term depression in striatal medium spiny neurons, therefore opposing the action of the dopamine D1 receptors. We hypothesize that the inhibitory effect of M4 muscarinic acetylcholine receptors may supress spiny projection neurons coding for outdated and no longer effective behavioural strategy and thus they may be necessary for the flexible change of behaviour. In the present thesis, I investigated the effects of pharmacological antagonism of M4 receptors on cognitive flexibility of mice tested in a simple reversal learning paradigm. Key words: striatum; cholinergic...

This thesis deals with effects of some chosen 7-methoxitacrine (7-MEOTA) analogues on enzymatic activity of acetylcholinesterase (AChE). 7-MEOTA is a derivative of tacrine, which had been used for symptomatic treatment of Alzheimer's disease (AD), until drugs with better therapeutic index were developed. 7-MEOTA the same way as tacrine therapeutically acts by inhibition of acetylcholinesterase and a neurotransmitter acetylcholine rise in the organism. It shows similar strength and type of inhibition, but it's less toxic contrary to tacrine. Some of the previously examined analogues of 7-MEOTA were as strong or even stronger AChE inhibitors than 7-MEOTA and so promising future medicaments. However, all the compounds analyzed in this thesis showed weaker enzymatic reaction inhibition and AChE affinity. For each of the examined compounds IC50, Ki and Ki' were calculated and AChE inhibition type was determined. All the 7-MEOTA analogues showed a mixed type of the inhibition. The theoretical part of this thesis deals with manifestations and origins of AD, its genetic factors etc. and tries to show some of the anthropological findings a theories connected with the theme.

This thesis deals with effects of some chosen 7-methoxitacrine (7 MEOTA) analogues on enzymatic activity of acetylcholinesterase (AChE). 7-MEOTA is a derivative of tacrine, which had been used for symptomatic treatment of Alzheimer's disease (AD), until drugs with better therapeutic index were developed. 7-MEOTA the same way as tacrine therapeutically acts by inhibition of acetylcholinesterase and a neurotransmitter acetylcholine rise in the organism. It shows similar strength and type of inhibition, but it's less toxic contrary to tacrine. Some of the previously examined analogues of 7-MEOTA were as strong or even stronger AChE inhibitors than 7-MEOTA and so promising future medicaments. However, all the compounds analyzed in this thesis showed weaker enzymatic reaction inhibition and AChE affinity. For each of the examined compounds IC50, Ki and Ki' were calculated and AChE inhibition type was determined. All the 7 MEOTA analogues showed a mixed type of the inhibition. The theoretical part of this thesis deals with manifestations and origins of AD, its genetic factors etc. and tries to show some of the anthropological findings a theories connected with the theme. Powered by TCPDF (www.tcpdf.org)

Introduction : La dystonie est définie comme un syndrome de cocontractions musculaires soutenues aboutissant à des mouvements répétitifs et des postures anormales. Cependant la physiopathologie des dystonies reste mal comprise. Les études menées chez l’homme soulignent le rôle crucial des ganglions de la base dans la physiopathologie des dystonies. Des données récentes obtenues chez le rongeur suggèrent l’implication d’un désordre de la transmission cholinergique striatale mais es modèles qu’ils soient génétiques ou pharmacologiques n’aboutissent pas toujours à un phénotype de dystonie. C’est pourquoi il était important de proposer une étude chez le primate non humain, visant à vérifier notre hypothèse de travail, à savoir : est-ce qu’une augmentation de la transmission cholinergique dans le putamen est capable d’induire un phénotype clinique de dystonie similaire à celui rencontré chez l’homme.Méthodes : Nous avons réalisé des infusions chroniques d’un agoniste muscarinique non sélectif (Oxotremorine) au sein du territoire sensori-moteur du striatum chez le primate non-humain. Les symptômes cliniques induits par ce produit ont été évalués à l’aide de l’échelle de Burke-Fahn-Marsden (BFM) adaptée à l’animal. Nous avons également utilisé une approche électromyographique pour caractériser l’activité musculaire en lien avec la clinique ainsi que des enregistrements de l’activité Multi-Unitaire et Unitaire au sein des ganglions de la base afin d’établir des corrélations électro-cliniques.Résultats : Les infusions d’Oxotremorine nous ont permis d’observer : (i) des postures et des mouvements anormaux similaires aux mouvements dystoniques rencontrés en pathologie humaine ; (ii) une fréquence de décharge neuronale anormalement basse dans le GPi (13,5Hz) et un pattern de décharge de type « bursty » principalement lorsque les symptômes sont sévères ; (iii) une activité oscillatoire (28-30Hz) au sein du putamen, du GPe et du GPi; (iv) l’absence de cohérence de l’activité oscillatoire entre ces structures ; (v) que le GPi est la seule structure à présenter une cohérence de l’activité oscillatoire.Conclusion : Nos travaux démontrent pour la première fois qu’un modèle de dystonie chronique peut être obtenu chez le primate non humain par augmentation du tonus cholinergique dans le putamen. Ce travail valide l’hypothèse de l’implication des interneurones cholinergiques dans la physiopathologie des dystonies. Ils confortent l’idée qu’une augmentation du tonus cholinergique peu à elle seule induire un phénotype de dystonie. / Introduction: Dystonia is defined as a syndrome of sustained muscular cocontractions leading to repetitive movements and abnormal postures. However, the pathophysiology of dystonia remains poorly understood. Studies in humans emphasize the crucial role of basal ganglia in the pathophysiology of dystonia. Recent data in rodents suggest the involvement of a disorder in the striatal cholinergic transmission. But these genetic or pharmacological rodent models do not always express the phenotype of dystonia. Therefore, it was important to propose a primate study to test whether an increase of cholinergic transmission within the putamen is able to induce a clinical phenotype of dystonia similar to that seen in humans.Methods: To verify our hypothesis, we chronically infused non-selective muscarinic agonist (Oxotremorine) in the sensory-motor striatum in non-human primates. Dystonic clinical symptoms induced by this drug were assessed using the Burke-Fahn-Marsden (BFM) scale adapted to animals. We used electromyographic approach to characterize muscular activity linked to clinical symptoms, and we recorded Multi-Unit and Single-Unit neuronal activity in basal ganglia to establish electro-clinical correlations.Results: The infusions of Oxotremorine allowed us to observe: (i) abnormal postures and movements similar to the dystonic movements encountered in human pathology; (ii) an abnormally low neuronal firing frequency in the GPi (13.5Hz) and a bursty firing pattern mainly when the symptoms where severe; (iii) oscillatory activity (28-30Hz) within the putamen, GPe and GPi; (iv) the lack of coherence of the oscillatory activity between these structures; (v) that the GPi is the only structure to present a coherence of the oscillatory activity.Conclusion: We have demonstrated for the first time that a model of chronic dystonia can be obtained in non-human primates by increasing cholinergic tone in the putamen. This work validates the hypothesis of an involvement of cholinergic interneurons and striatal acetylcholine levels in the pathophysiology of dystonia.

Pesticidas organofosforados são amplamente usados e seu uso constitui um grave problema de saúde pública. A ação clássica destes compostos é a inibição irreversível da acetilcolinesterase, promovendo acúmulo de acetilcolina nas sinapses e hiperestimulação colinérgica. No entanto, as consequências da exposição a baixas doses podem se estender a outros mecanismos de ação e sistemas neurotransmissores. Considerando que crianças constituem um grupo particularmente vulnerável aos efeitos de pesticidas, neste trabalho investigamos os efeitos da exposição aos organofosforados metamidofós (MET) e clorpirifós (CPF) durante o desenvolvimento sobre os sistemas colinérgico e serotoninérgico e sobre o comportamento de camundongos. Para isso, camundongos suíços foram expostos a injeções subcutâneas de MET, clorpirifós ou veículo do terceiro (PN3) ao nono (PN9) dias de vida pós-natal. As doses de exposição foram previamente escolhidas através da construção de uma curva dose-resposta que identificou como mais adequadas para este estudo as doses de 1mg/kg de MET e 3mg/kg de CPF, as quais promoveram em torno de 20% de inibição da acetilcolinesterase. Em PN10, parte dos animais foi sacrificada e foram avaliados os sistemas colinérgico e serotoninérgico no tronco encefálico e córtex cerebral. De PN60 a PN63, os animais foram submetidos a uma bateria de testes comportamentais. Em seguida, estes animais também foram sacrificados tendo sido avaliados os sistemas colinérgico e serotoninérgico. Em PN10, MET e CPF causaram alterações que sugerem aumento da atividade colinérgica respectivamente no tronco e córtex em fêmeas. No sistema serotoninérgico, apenas CPF promoveu alterações, aumentando a ligação ao receptor 5HT1A e transportador 5HT em fêmeas e diminuindo na ligação ao 5HT2. Em PN63, a atividade da acetilcolinesterase foi reestabelecida em todos os grupos. Ainda assim, MET diminuiu a atividade da colina acetiltransferase no córtex e a ligação ao transportador colinérgico no tronco. Quanto aos efeitos do CPF, no tronco, houve redução da atividade da colina acetiltransferase em fêmeas e aumento em machos. Sobre o sistema serotoninérgico, MET e CPF promoveram diminuições no 5HT1A respectivamente no tronco e córtex das fêmeas e CPF aumentou a ligação no córtex de machos. A ligação ao 5HT2 foi aumentada após o tratamento com MET e ao transportador 5HT foi diminuída em fêmeas após o tratamento com clorpirifós. Sobre o comportamento, identificamos comportamento associado à depressão em animais expostos a MET e aumento dos níveis de ansiedade, além de prejuízo de aprendizado/memória após exposição à CPF. Desta forma, nossos resultados indicam que a exposição à metamidofós e clorpirifós durante o desenvolvimento é capaz de alterar, de diferentes formas, a atividade colinérgica e serotoninérgica, mesmo que as doses de exposição sejam toxicologicamente equivalentes. Foram verificados efeitos nas vias neuroquímicas logo após a exposição e após um longo período de interrupção do tratamento, indicando efeitos tardios em sistemas importantes que podem estar associados às alterações comportamentais. Finalmente, o presente estudo reforça a associação epidemiológica entre pesticidas e alterações psiquiátricas e a capacidade da programação de alterações a longo-prazo quando a exposição se dá durante o desenvolvimento. / Organophosphate pesticides are widely used and its use consist on a severe public health problem. The classic effect of these compounds involve irreversible inhibition of the enzyme acetylcholinesterase, causing an accumulation of acetylcholine at cholinergic synapses and, consequently, cholinergic hyperstimulation. However, when the doses of exposure are low, other the mechanisms of action may play a role and other neurotransmitter systems may be affected. Considering that children are particularly vulnerable to effects of these compounds, in this study we investigated the effects of methamidophos and chlorpyrifos organophosphate exposure during development on cholinergic and serotonergic systems and behavior. For this purpose, Swiss mice received subcutaneous injections of methamidophos or chlorpyrifos, or vehicle from the third to the nineth postnatal day (PN3 - PN9). Initially, a dose-response study was performed and the doses of 1mg/kg methamidophos and 3mg/kg chlorphrifos, which promoted 20% inhibition of acetylcholinesterase activity in brain were chosen to be used in the next set of experiments. At PN10, one day after exposure, a group of animals was sacrificed and the brainstem and cortex collected and stored to further analysis of cholinergic and serotonergic systems. From PN60 to PN63 the animals were submitted to behavioral tests in order to evaluate: anxiety, locomotor activity, decision making, depressive-like behavior and learning/memory. After the last test, the animals were sacrificed and the brainstem and cortex collected and stored to further analysis of cholinergic and serotonergic systems. At PN10, methamidophos and chlorpyrifos promoted alterations that suggest an increase of cholinergic activity respectively on the brainstem and cortex of females. As for the serotonergic system: only chlorpyrifos elicited alterations: There were increases in 5HT1A receptor and 5HT transporter binding in females and a decrease in 5HT2 receptor binding. At PN63, the activity of acetylcholinesterase had returned to control levels. Despite that, methamidophos elicited a decrease in the activity of choline acetyltransferase in the cortex and in choline transporter binding in the brainstem. As for the serotonergic system, methamidophos and chlorpyrifos promoted decreased 5HT1A receptor binding respectively in the brainstem and cortex of females and chlorpyrifos increased its binding in males. Methamidophos exposure elicited increased 5HT2 binding whereas chlorpyrifos exposure decreased female 5HT transporter binding. Methamidophos elicited behavioral alterations suggestive of increased depressive-like behavior while chlorpyrifos exposure was associated to increased anxiety levels and memory/learning deficits. Our results indicate that metamidophos and chlorpyrifos exposure during development distinctively affect the cholinergic and serotonergic systems even at toxicologically equivalent doses. There were immediate and late-emergent neurochemical effects that may play a role on the behavioral outcomes. Finally, the present study reinforces the epidemiologic association between pesticides exposure and mood disorders and suggest that organophosphate exposure during early development programs for late effects.

<p>This thesis examines developmental neurotoxic effects of polybrominated diphenyl ethers (PBDEs), PBDE 99, PBDE 153, and the fully brominated PBDE 209, after exposure during the newborn period in rodents.</p><p>Our environment contains vast numbers of contaminants, including the flame retardants, PBDEs. The PBDEs are widely found in the environment and are increasing in human milk. Individuals can be exposed to PBDEs during their whole lifetime, and especially during the lactation period. The neonatal period, coinciding with the lactation period, is characterized in many mammalian species by rapid growth and development of the immature brain. It has been shown that numerous toxicants can induce permanent disorders in brain function when administered to the neonatal mouse during the brain growth spurt (BGS). In mice and rats this period is postnatal, spanning over the first 3-4 weeks of life, while in humans, BGS begins during the third trimester of pregnancy and continues throughout the first two years of life.</p><p>The present studies identified a defined critical period during BGS in mice when the brain is vulnerable to insults of low doses of PBDEs and that it is the presence of PBDEs or their metabolites in the brain during this critical period that is crucial to evoking neurotoxic effects. The effects observed are permanent altered spontaneous behavior, reduced habituation, deficits in learning and memory, and disturbances in the cholinergic system. These effects worsen with age.</p><p>The ability of PBDEs to induce neurotoxic effects does not appear to be gender-, strain- or species-specific, because the neurotoxic effects are induced in rats and male and female mice of different strains.</p><p>The developmental neurotoxic effects of PBDEs are similar to those observed for polychlorinated biphenyls (PCBs) and possible interactive effects of PBDEs and other environmental contaminants are therefore of concern.</p>

This thesis examines developmental neurotoxic effects of polybrominated diphenyl ethers (PBDEs), PBDE 99, PBDE 153, and the fully brominated PBDE 209, after exposure during the newborn period in rodents. Our environment contains vast numbers of contaminants, including the flame retardants, PBDEs. The PBDEs are widely found in the environment and are increasing in human milk. Individuals can be exposed to PBDEs during their whole lifetime, and especially during the lactation period. The neonatal period, coinciding with the lactation period, is characterized in many mammalian species by rapid growth and development of the immature brain. It has been shown that numerous toxicants can induce permanent disorders in brain function when administered to the neonatal mouse during the brain growth spurt (BGS). In mice and rats this period is postnatal, spanning over the first 3-4 weeks of life, while in humans, BGS begins during the third trimester of pregnancy and continues throughout the first two years of life. The present studies identified a defined critical period during BGS in mice when the brain is vulnerable to insults of low doses of PBDEs and that it is the presence of PBDEs or their metabolites in the brain during this critical period that is crucial to evoking neurotoxic effects. The effects observed are permanent altered spontaneous behavior, reduced habituation, deficits in learning and memory, and disturbances in the cholinergic system. These effects worsen with age. The ability of PBDEs to induce neurotoxic effects does not appear to be gender-, strain- or species-specific, because the neurotoxic effects are induced in rats and male and female mice of different strains. The developmental neurotoxic effects of PBDEs are similar to those observed for polychlorinated biphenyls (PCBs) and possible interactive effects of PBDEs and other environmental contaminants are therefore of concern.

The focus of this thesis was to investigate developmental neurotoxic effects of different persistent and non-persistent environmental pollutants, alone or in binary mixtures, when exposure occurs during a critical period of brain development, in mice. The compounds investigated included a perfluorinated compound, perfluorohexane sulphonate (PFHxS), and four different pesticides, endosulfan, cypermethrin, chlorpyrifos and carbaryl. Both persistent and non-persistent pollutants are detected in the environment and in humans, which shows that exposure to these compounds is occurring in real life. Humans can therefore be exposed to various pollutants during their whole lifetime, starting from the gestational period to adulthood. Furthermore, exposure to environmental pollutants is rarely exclusive to a single compound, but rather occurs through combinations of various pollutants present in the environment. Exposure to environmental pollutants during human brain development have been suggested to be a possible cause for neuropsychiatric disorders, such as autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD). Previous studies have shown that chemicals can induce irreversible disorders in brain function when exposure to these chemicals occurs during a critical defined period of the brain development known as the brain growth spurt (BGS). The BGS is characterized by a rapid growth and development of the immature brain. In humans, and mice, this period also overlaps the lactation period indicating that newborns and toddlers can be exposed via mothers’ milk as well. This thesis has shown that a single oral exposure to PFHxS, endosulfan, cypermethrin, chlorpyrifos or carbaryl can induce developmental neurotoxic effects in mice, when exposure occurs during a critical period of brain development. These effects are manifested as persistent altered adult spontaneous behavior in a novel home environment, modified habituation, altered susceptibility of the cholinergic system and changed levels of neuroproteins in the mouse brain. Furthermore, a single neonatal co-exposure to a binary mixture of carbaryl/chlorpyrifos or PFHxS/endosulfan can interact and exacerbate the adult behavioral effects. These effects were seen at dosages were the single compound did not elicit a response or induced a much weaker behavioral effect. This indicates that risk assessments conducted on single compounds might underestimate interaction effects of mixtures when co-exposed.

Animal models are crucial to improve the knowledge of the mechanisms underlying the different pathological processes. These models are also excellent tools to facilitate the research of new targets for the treatment of different diseases and to evaluate the benefit/risk ratio of the potential new treatments. We have focussed this research work in the study of a new potential targets for pain, cognitive and eating disorders using new animal models developed in our laboratory. We first investigated the effects of the interaction between cannabinoids and nicotine on cognitive processes and metabolism using different behavioural models and new experimental devices. In a second part of this work, we investigated new therapeutic targets for neuropathic pain and for this purpose we developed a new behavioural model to improve the study of the therapeutic potential and possible side-effects of novel compounds. / Los modelos animales son cruciales para mejorar el conocimiento sobre los mecanismos que constituyen la base de los diversos procesos patológicos. Estos modelos representan también excelentes herramientas para facilitar la investigación de nuevas dianas para el tratamiento de estas enfermedades y para evaluar el cociente beneficio/riesgo de los nuevos tratamientos potenciales. Este trabajo de investigación se encuentra centrado en el estudio de nuevos dianas terapéuticas para el dolor, los procesos cognitivos y los desórdenes alimentarios utilizando nuevos modelos animales desarrollados en nuestro laboratorio. En primer lugar, hemos investigado los efectos de la interacción entre los cannabinoinoides y la nicotina a nivel los procesos cognitivos y del metabolismo usando diversos modelos comportamentales y nuevos dispositivos experimentales. En una segunda parte de este trabajo, hemos estudiado nuevas dianas terapéuticas para el dolor neuropático y hemos desarrollado para este propósito un nuevo modelo comportamental que permite evaluar el potencial terapéutico y los posibles efectos secundarios de nuevos compuestos.

Pesticidas organofosforados são amplamente usados e seu uso constitui um grave problema de saúde pública. A ação clássica destes compostos é a inibição irreversível da acetilcolinesterase, promovendo acúmulo de acetilcolina nas sinapses e hiperestimulação colinérgica. No entanto, as consequências da exposição a baixas doses podem se estender a outros mecanismos de ação e sistemas neurotransmissores. Considerando que crianças constituem um grupo particularmente vulnerável aos efeitos de pesticidas, neste trabalho investigamos os efeitos da exposição aos organofosforados metamidofós (MET) e clorpirifós (CPF) durante o desenvolvimento sobre os sistemas colinérgico e serotoninérgico e sobre o comportamento de camundongos. Para isso, camundongos suíços foram expostos a injeções subcutâneas de MET, clorpirifós ou veículo do terceiro (PN3) ao nono (PN9) dias de vida pós-natal. As doses de exposição foram previamente escolhidas através da construção de uma curva dose-resposta que identificou como mais adequadas para este estudo as doses de 1mg/kg de MET e 3mg/kg de CPF, as quais promoveram em torno de 20% de inibição da acetilcolinesterase. Em PN10, parte dos animais foi sacrificada e foram avaliados os sistemas colinérgico e serotoninérgico no tronco encefálico e córtex cerebral. De PN60 a PN63, os animais foram submetidos a uma bateria de testes comportamentais. Em seguida, estes animais também foram sacrificados tendo sido avaliados os sistemas colinérgico e serotoninérgico. Em PN10, MET e CPF causaram alterações que sugerem aumento da atividade colinérgica respectivamente no tronco e córtex em fêmeas. No sistema serotoninérgico, apenas CPF promoveu alterações, aumentando a ligação ao receptor 5HT1A e transportador 5HT em fêmeas e diminuindo na ligação ao 5HT2. Em PN63, a atividade da acetilcolinesterase foi reestabelecida em todos os grupos. Ainda assim, MET diminuiu a atividade da colina acetiltransferase no córtex e a ligação ao transportador colinérgico no tronco. Quanto aos efeitos do CPF, no tronco, houve redução da atividade da colina acetiltransferase em fêmeas e aumento em machos. Sobre o sistema serotoninérgico, MET e CPF promoveram diminuições no 5HT1A respectivamente no tronco e córtex das fêmeas e CPF aumentou a ligação no córtex de machos. A ligação ao 5HT2 foi aumentada após o tratamento com MET e ao transportador 5HT foi diminuída em fêmeas após o tratamento com clorpirifós. Sobre o comportamento, identificamos comportamento associado à depressão em animais expostos a MET e aumento dos níveis de ansiedade, além de prejuízo de aprendizado/memória após exposição à CPF. Desta forma, nossos resultados indicam que a exposição à metamidofós e clorpirifós durante o desenvolvimento é capaz de alterar, de diferentes formas, a atividade colinérgica e serotoninérgica, mesmo que as doses de exposição sejam toxicologicamente equivalentes. Foram verificados efeitos nas vias neuroquímicas logo após a exposição e após um longo período de interrupção do tratamento, indicando efeitos tardios em sistemas importantes que podem estar associados às alterações comportamentais. Finalmente, o presente estudo reforça a associação epidemiológica entre pesticidas e alterações psiquiátricas e a capacidade da programação de alterações a longo-prazo quando a exposição se dá durante o desenvolvimento. / Organophosphate pesticides are widely used and its use consist on a severe public health problem. The classic effect of these compounds involve irreversible inhibition of the enzyme acetylcholinesterase, causing an accumulation of acetylcholine at cholinergic synapses and, consequently, cholinergic hyperstimulation. However, when the doses of exposure are low, other the mechanisms of action may play a role and other neurotransmitter systems may be affected. Considering that children are particularly vulnerable to effects of these compounds, in this study we investigated the effects of methamidophos and chlorpyrifos organophosphate exposure during development on cholinergic and serotonergic systems and behavior. For this purpose, Swiss mice received subcutaneous injections of methamidophos or chlorpyrifos, or vehicle from the third to the nineth postnatal day (PN3 - PN9). Initially, a dose-response study was performed and the doses of 1mg/kg methamidophos and 3mg/kg chlorphrifos, which promoted 20% inhibition of acetylcholinesterase activity in brain were chosen to be used in the next set of experiments. At PN10, one day after exposure, a group of animals was sacrificed and the brainstem and cortex collected and stored to further analysis of cholinergic and serotonergic systems. From PN60 to PN63 the animals were submitted to behavioral tests in order to evaluate: anxiety, locomotor activity, decision making, depressive-like behavior and learning/memory. After the last test, the animals were sacrificed and the brainstem and cortex collected and stored to further analysis of cholinergic and serotonergic systems. At PN10, methamidophos and chlorpyrifos promoted alterations that suggest an increase of cholinergic activity respectively on the brainstem and cortex of females. As for the serotonergic system: only chlorpyrifos elicited alterations: There were increases in 5HT1A receptor and 5HT transporter binding in females and a decrease in 5HT2 receptor binding. At PN63, the activity of acetylcholinesterase had returned to control levels. Despite that, methamidophos elicited a decrease in the activity of choline acetyltransferase in the cortex and in choline transporter binding in the brainstem. As for the serotonergic system, methamidophos and chlorpyrifos promoted decreased 5HT1A receptor binding respectively in the brainstem and cortex of females and chlorpyrifos increased its binding in males. Methamidophos exposure elicited increased 5HT2 binding whereas chlorpyrifos exposure decreased female 5HT transporter binding. Methamidophos elicited behavioral alterations suggestive of increased depressive-like behavior while chlorpyrifos exposure was associated to increased anxiety levels and memory/learning deficits. Our results indicate that metamidophos and chlorpyrifos exposure during development distinctively affect the cholinergic and serotonergic systems even at toxicologically equivalent doses. There were immediate and late-emergent neurochemical effects that may play a role on the behavioral outcomes. Finally, the present study reinforces the epidemiologic association between pesticides exposure and mood disorders and suggest that organophosphate exposure during early development programs for late effects.