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Une sous-population des neurones à dopamine (DA) du mésencéphale ventral du rat et de la souris étant connue pour exprimer l'ARN messager du transporteur vésiculaire 2 du glutamate (VGLUT2), nous avons eu recours à l'immunocytochimie en microscopie électronique, après simple ou double marquage de l'enzyme de synthèse tyrosine hydroxylase (TH) et de VGLUT2, pour déterminer la présence de l'une et/ou l'autre protéine dans les terminaisons (varicosités) axonales de ces neurones et caractériser leur morphologie ultrastructurale dans diverses conditions expérimentales. Dans un premier temps, des rats jeunes (P15) ou adultes (P90), ainsi que des rats des deux âges soumis à l'administration intraventriculaire cérébrale de la cytotoxine 6-hydroxydopamine (6-OHDA) dans les jours suivant la naissance, ont été examinés, afin d'étayer l'hypothèse d'un rôle de VGLUT2 au sein des neurones DA, au cours du développement normal ou pathologique de ces neurones. Chez le jeune rat, ces études ont montré: i) la présence de VGLUT2 dans une fraction importante des varicosités axonales TH immunoréactives du coeur du noyau accumbens ainsi que du néostriatum; ii) une augmentation de la proportion de ces terminaisons doublement marquées dans le noyau accumbens par suite de la lésion 6-OHDA néonatale; iii) le double marquage fréquent des varicosités axonales appartenant à l'innervation DA aberrante (néoinnervation), qui se développe dans la substance noire, par suite de la lésion 6-OHDA néonatale. Des différences significatives ont aussi été notées quant à la dimension des terminaisons axonales marquées pour la TH seulement, VGLUT2 seulement ou TH et VGLUT2. Enfin, à cet âge (P15), toutes les terminaisons doublement marquées sont apparues dotées d'une spécialisation membranaire synaptique, contrairement aux terminaisons marquées pour la TH ou pour VGLUT2 seulement. Dans un deuxième temps, nous avons voulu déterminer le devenir du double phénotype chez le rat adulte (P90) soumis ou non à la lésion 6-OHDA néonatale. Contrairement aux observations recueillies chez le jeune rat, nous avons alors constaté: i) l'absence complète de terminaisons doublement marquées dans le coeur du noyau accumbens et le néostriatum d'animaux intacts, de même que dans les restes de la substance noire des animaux 6-OHDA lésés; ii) une très forte baisse de leurnombre dans le coeur du noyau accumbens des animaux 6-OHDA lésés. Ces observations, suggérant une régression du double phénotype TH/VGLUT2 avec l'âge, sont venues renforcer l'hypothèse d'un rôle particulier d'une co-libération de glutamate par les neurones mésencéphaliques DA au cours du développement. Dans ces conditions, il est apparu des plus intéressants d'examiner l'innervation DA méso-striatale chez deux lignées de souris dont le gène Vglut2 avait été sélectivement invalidé dans les neurones DA du cerveau, ainsi que leurs témoins et des souris sauvages. D'autant que malgré l'utilisation croissante de la souris en neurobiologie, cette innervation DA n'avait jamais fait l'objet d’une caractérisation systématique en microscopie électronique. En raison de possibles différences entre le coeur et la coque du noyau accumbens, l'étude a donc porté sur les deux parties de ce noyau ainsi que le néostriatum et des souris jeunes (P15) et adultes (P70-90) de chaque lignée, préparées pour l'immunocytochimie de la TH, mais aussi pour le double marquage TH et VGLUT2, selon le protocole précédemment utilisé chez le rat. Les résultats ont surpris. Aux deux âges et quel que soit le génotype, les terminaisons axonales TH immunoréactives des trois régions sont apparues comparables quant à leur taille, leur contenu vésiculaire, le pourcentage contenant une mitochondrie et une très faible incidence synaptique (5% des varicosités, en moyenne). Ainsi, chez la souris, la régression du double phénotype pourrait être encore plus précoce que chez le rat, à moins que les deux protéines ne soient très tôt ségréguées dans des varicosités axonales distinctes des mêmes neurones DA. Ces données renforcent aussi l’hypothèse d’une transmission diffuse (volumique) et d’un niveau ambiant de DA comme élément déterminant du fonctionnement du système mésostriatal DA chez la souris comme chez le rat. / Knowing that a subset of rat and mouse mesencephalic dopamine (DA) neurons expresses the mRNA of the vesicular glutamate transporter type 2 (VGLUT2), we used electron microscopic immunocytochemistry, after single or double labeling of the biosynthetic enzyme tyrosine hydroxylase (TH) and of VGLUT2, to determine the presence of one and/or both proteins in axon terminals (varicosities) of these neurons and characterize their ultrastructural morphology under various experimental conditions. At first, young (P15) or adult (P90) rats, subjected or not to cerebro-ventricular administration of the cytotoxin 6-hydroxydopamine (6-OHDA) a few days after birth, were examined in order to investigate the role of VGLUT2 in DA neurons during normal and pathological development of these neurons. In the young rats, these studies revealed: i) the presence of VGLUT2 in a significant fraction of TH immunoreactive varicosities in the core of the nucleus accumbens and the neostriatum; ii) an increase in the proportion of dually labeled terminals in the nucleus accumbens following neonatal 6-OHDA lesion; iii) frequent double labeling of TH varicosities belonging to the aberrant DA innervation (neoinnervation) which develops in the substantia nigra following neonatal 6-OHDA lesion. Significant differences were also noted in the size of the axon terminals labeled for TH only, VGLUT2 only, or TH and VGLUT2. Finally, at this age (P15), all the dually labeled terminals appeared equipped with a synaptic membrane specialization, unlike the terminals labeled for TH or for VGLUT2 only. In a second step, we sought to determine the fate of the dual phenotype in adult rats (P90) subjected or not to the neonatal 6-OHDA lesion. In contrast with the observations made in young rats, we found: i) a complete absence of dually labeled terminals in the core of the nucleus accumbens and striatum of intact animals, as well as in the remains of the substantia nigra after neonatal 6-OHDA lesion; ii) a sharp decline of their number in the core of the nucleus accumbens of 6-OHDA-lesioned animals. These findings, suggesting a regression of the dual TH/VGLUT2 phenotype with age, reinforced the hypothesis of a specific role of the co-release of glutamate from midbrain DA neurons during development. Under these conditions, it was of considerable interest to examine the DA meso-striatal innervation in two strains of mice whose Vglut2 gene has been selectively invalidated in DA neurons, as well as in their control littermates and wild-type mice. This issue was particularly relevant with the increasing use of genetically modified mice in neurobiology; indeed, this DA innervation had never been systematically characterized by electron microscopy. Because of possible differences between the core and shell of the nucleus accumbens, the study included both parts of this nucleux as well as the striatum of young (P15) and adult (P70-90) mice of each strain, prepared for TH immunocytochemistry, and also for double labeling of TH and VGLUT2, according to the protocol previously used in rats. The results were surprising. At both ages, regardless of the genotype, the TH immunoreactive axon terminals of the three regions appeared comparable in size, vesicle content, percent with mitochondria, and exceeding low frequency of synaptic membrane specialization (5% of varicosities, on average). Thus, in mice, the regression of the dual phenotype might be even more precocious than in rats, unless the two proteins are segregated very early in different axon terminals of the same DA neurons. These data also strenghten the hypothesis of a diffuse (volume) transmission and of an ambient level of DA as determinant elements in the functioning of the meso-striatal DA system in mice as well as rats.

Indiana University-Purdue University Indianapolis (IUPUI) / Alcohol and cocaine are commonly co-abused drugs, and those meeting criteria for both cocaine and alcohol use disorders experience more severe behavioral and health consequences than those with a single disorder. Chronic alcohol (ethanol) drinking increased the reinforcing and dopamine (DA) neuronal stimulating effects of ethanol within mesolimbic regions of the central nervous system (CNS) of alcohol-preferring (P) rats. The objectives of the current study were to determine if chronic continuous ethanol drinking produced: (1) alterations in the sensitivity of the nucleus accumbens shell (AcbSh) to the reinforcing effects of cocaine, (2) changes in the magnitude and time course of the local stimulating effects of cocaine on posterior ventral tegmental area (pVTA) DA neurons, and (3) a persistence of alterations in the stimulating effects of cocaine after a period of protracted abstinence. Female P rats received continuous, free-choice access to water and 15% v/v ethanol for at least 10 wk (continuous ethanol-drinking; CE) or access to water alone (ethanol-naïve; N). A third group of rats received the same period of ethanol access followed by 30 d of protracted abstinence from ethanol (ethanol-abstinent; Ab). CE and Ab rats consumed, on average, 6-7 g/kg/d of ethanol. Animals with a single cannula aimed at the AcbSh responded for injections of cocaine into the AcbSh during four initial operant sessions. Cocaine was not present in the self-infused solution for the subsequent three sessions, and cocaine access was restored during one final session. Animals with dual ipsilateral cannulae aimed at the AcbSh and the pVTA were injected with pulsed microinfusions of cocaine into the pVTA while DA content was collected for analysis through a microdialysis probe inserted into the AcbSh. During the initial four sessions, neither CE nor N rats self-infused artificial cerebrospinal fluid (aCSF) or 0.1 mM cocaine into the AcbSh. CE, but not N, rats self-administered 0.5 mM cocaine into the AcbSh, whereas both groups self-infused concentrations of 1.0, 2.0, 4.0, or 8.0 mM cocaine. When cocaine access was restored in Session 8, CE rats responded more on the active lever and obtained more infusions of 0.5, 1.0, 2.0, or 4.0 mM cocaine compared to N rats. Microinjection of aCSF into the pVTA did not alter AcbSh DA levels in N, CE, or Ab rats. Microinjections of 0.25 mM cocaine into the pVTA did not significantly alter AcbSh DA levels in N animals, moderately increased DA levels in CE rats, and greatly increased DA levels in Ab rats. Microinjections of 0.5 mM cocaine into the pVTA modestly increased AcbSh DA levels in N animals, robustly increased DA levels in CE rats, and did not significantly alter DA levels in Ab rats. Microinjections of 1.0 or 2.0 mM cocaine into the pVTA modestly increased AcbSh DA levels in N animals but decreased DA levels in CE and Ab rats. Overall, long-term continuous ethanol drinking by P rats enhanced both the reinforcing effects of cocaine within the AcbSh and the stimulatory and inhibitory effects of cocaine on pVTA DA neurons. Alterations in the stimulatory and inhibitory effects of cocaine on pVTA DA neurons were not only enduring, but also enhanced, following a period of protracted abstinence from ethanol exposure. Translationally, prevention of chronic and excessive alcohol intake in populations with a genetic risk for substance abuse may reduce the likelihood of subsequent cocaine use.

A amígdala expandida central (EAc) inclui os núcleos central da amígdala (CeA), intersticial lateral da estria terminal (BSTl), intersticial do ramo posterior da comissura anterior (IPAC) e amígdala expandida sublenticular (SLEA). A EAc e a concha do acumbens possuem densa inervação dopaminérgica, implicada em processos motivacionais, e cuja origem foi estudada com a técnica de dupla marcação celular, combinando-se imunofluorescência para o traçador retrógrado Fluoro-Gold e para a tirosina hidroxilase. Nossos resultados indicam que a inervação dopaminérgica do CeA e BSTl é semelhante, se originando em igual proporção da área tegmental ventral (A10) e do núcleo dorsal da rafe/substância cinzenta periaquedutal (A10dc). A inervação dopaminérgica da SLEA, IPAC e concha do acumbens se origina principalmente do grupo A10. Com um anticorpo específico para dopamina vimos que parte da projeção do A10dc para o CeA é de fato dopaminérgica. Os grupos dopaminérgicos diencefálicos não inervam a EAc e a concha do acumbens. / The central extended amygdala (EAc) includes the central amygdaloid nucleus (CeA), lateral bed nucleus of the stria terminalis (BSTl), interstitial nucleus of the posterior limb of the anterior commissure (IPAC) and sublenticular extended amygdala (SLEA). The dopaminergic innervation of the EAc and nucleus accumbens shell is functionally related to motivational processes. Its origin was studied by combining immunofluorescence to tyrosine hydroxylase and Fluoro-Gold, used as retrograde tracer. Our results show that dopaminergic fibers to the CeA and BSTl derive in equal proportion from neurons in ventral tegmental area (A10) and in dorsal raphe nucleus/periaqueductal gray (A10dc). Dopaminergic inputs to SLEA, IPAC and accumbens shell arise mainly from A10 neurons. Using a dopamine antibody, we confirmed that A10dc projections to CeA are in part dopaminergic. Futhermore, the present data indicate that the diencephalic dopaminergic groups do not project to EAc and accumbens shell.

A major challenge in the field of neuroscience is to link behavior with specific neuronal circuitries and cellular events. One way of facing this challenge is to identify unique cellular markers and thus have the ability to, through various mouse genetics tools, mimic, manipulate and control various aspects of neuronal activity to decipher their correlation to behavior. The Vesicular Glutamate Transporter 2 (VGLUT2) packages glutamate into presynaptic vesicles for axonal terminal release. In this thesis, VGLUT2 was used to specifically target cell populations within the basal ganglia of mice with the purpose of investigating its connectivity, function and involvement in behavior. The motor and limbic loops of the basal ganglia are important for processing of voluntary movement and emotions. During such physiological events, dopamine plays a central role in modulating the activity of these systems. The brain reward system is mainly formed by dopamine projections from the ventral tegmental area (VTA) to the ventral striatum. Certain dopamine neurons within the VTA exhibit the ability to co-release dopamine and glutamate. In paper I, glutamate and dopamine co-release was targeted and our results demonstrate that the absence of VGLUT2 in dopamine neurons leads to perturbations of reward consumption and reward-associated memory, probably due to reduced DA release observed in the striatum as detected by in vivo chronoamperometry. In papers II and IV, VGLUT2 in a specific subpopulation within the subthalamic nucleus (STN) was identified and targeted. Based on the described role of the STN in movement control, we hypothesized that the mice would be hyperlocomotive. As shown in paper II, this was indeed the case. In paper IV, a putative reward-related phenotype was approached and we could show reduced operant-self administration of sugar and altered dopamine release levels suggesting a role for the STN in reward processes. In paper III, we investigated and identified age- and sex-dimorphisms in dopamine kinetics in the dorsal striatum of one of the most commonly used mouse lines worldwide, the C57/Bl6J. Our results point to the importance of taking these dimorphisms into account when utilizing the C57/Bl6J strain as model for neurological and neuropsychiatric disorders.

Made available in DSpace on 2016-06-02T19:22:52Z (GMT). No. of bitstreams: 1 2640.pdf: 532825 bytes, checksum: 85901050327f52892439c98345181eee (MD5) Previous issue date: 2009-09-24 / Financiadora de Estudos e Projetos / Nicotine and psychostimulants are often abused in combination. Drug abuse often begins during adolescence. Exposure to drugs of abuse during adolescence can have long-term consequences. We have previously demonstrated that adolescent rats pretreated with amphetamine displayed behavioral sensitization to nicotine, which persisted until adulthood. Moreover, the pretreatment with nicotine during adolescence sensitized adolescent and adult animals to amphetamine-induced locomotor activation. In the present study we investigated whether the behavioral cross-sensitization between nicotine and amphetamine is related to changes in dopamine or serotonin neurotransmission. To this end adolescent rats (post-natal day 28) were treated with nicotine (0.4 mg/Kg), amphetamine (5.0 mg/Kg) or saline during seven days. Three or thirty days after the last injection animals received an acute injection of nicotine (0.4 mg/Kg), amphetamine (5.0 mg/Kg for adolescents or 1.0 mg/Kg for adults) or saline. Thirty minutes after challenge rats were sacrificed, decapitated and brains removed. Nucleus accumbens (NAcc) and prefrontal cortex (PFC) were dissected and prepared for HPLC (high performance liquid chromatography) analysis. Dopamine, DOPAC, HVA, serotonin and 5-HIAA were measured in these brain regions. Our results showed that: 1) repeated administration of nicotine attenuated the acute effect of amphetamine on NAcc dopamine levels of adolescent rats; 2) repeated administration of nicotine increased the acute effect of amphetamine on PFC dopamine levels of adolescent rats; 3) repeated administration of nicotine, during adolescence, increased the acute effect of amphetamine on PFC dopamine of adult rats. The behavioral cross-sensitization shown previously is not related to alterations in NAcc and PFC concentrations of neurotransmitters and its metabolites. However, neuroadaptations induced by repeated nicotine during adolescence endures until adulthood. / Uma característica comum das substâncias que causam dependência é o aumento gradual e progressivo da atividade locomotora observado após a administração repetida, esse fenômeno é denominado sensibilização comportamental. A sensibilização comportamental resulta de adaptações neuroquímicas e moleculares do sistema dopaminérgico mesocorticolímbico. Foi demonstrado anteriormente a sensibilização cruzada entre nicotina e anfetamina em animais adolescentes e que esse fenômeno permanece até a idade adulta. Nesse trabalho investigamos se a administração repetida com nicotina ou anfetamina, durante a adolescência, pode alterar o efeito agudo dessas substâncias e se essas neuroadaptações persistem até a idade adulta. Para tanto, administramos, por sete dias, nicotina (0,4 mg/Kg), anfetamina (5,0 mg/Kg) ou salina a ratos adolescentes. Três ou trinta dias após a última injeção os animais receberam injeção aguda de nicotina (0,4 mg/Kg), anfetamina (5,0 mg/Kg para adolescentes e 1,0 mg/Kg para adultos) ou salina. Trinta minutos após as injeções os ratos foram sacrificados, decapitados e seus encéfalos removidos. O núcleo acumbens (NAc) e o córtex pré-frontal (CPF) foram retirados e preparados para determinação de dopamina, serotonina e seus metabólitos por cromatografia líquida de alta resolução (HPLC). Os resultados encontrados mostram que: 1) o pré-tratamento com nicotina atenuou o efeito agudo da anfetamina sobre a concentração tecidual de dopamina no Nac de ratos adolescentes; 2) o prétratamento com nicotina aumentou o efeito agudo da anfetamina sobre a concentração tecidual de dopamina no CPF de ratos adolescentes; 3) o prétratamento com nicotina na adolescência aumentou o efeito agudo da anfetamina sobre a concentração tecidual de dopamina no CPF de ratos adultos. Estes resultados não se relacionam à sensibilização cruzada observada anteriormente, mas o tratamento repetido com nicotina promoveu alterações em animais adolescentes que podem ser observadas também na vida adulta.

A amígdala expandida central (EAc) inclui os núcleos central da amígdala (CeA), intersticial lateral da estria terminal (BSTl), intersticial do ramo posterior da comissura anterior (IPAC) e amígdala expandida sublenticular (SLEA). A EAc e a concha do acumbens possuem densa inervação dopaminérgica, implicada em processos motivacionais, e cuja origem foi estudada com a técnica de dupla marcação celular, combinando-se imunofluorescência para o traçador retrógrado Fluoro-Gold e para a tirosina hidroxilase. Nossos resultados indicam que a inervação dopaminérgica do CeA e BSTl é semelhante, se originando em igual proporção da área tegmental ventral (A10) e do núcleo dorsal da rafe/substância cinzenta periaquedutal (A10dc). A inervação dopaminérgica da SLEA, IPAC e concha do acumbens se origina principalmente do grupo A10. Com um anticorpo específico para dopamina vimos que parte da projeção do A10dc para o CeA é de fato dopaminérgica. Os grupos dopaminérgicos diencefálicos não inervam a EAc e a concha do acumbens. / The central extended amygdala (EAc) includes the central amygdaloid nucleus (CeA), lateral bed nucleus of the stria terminalis (BSTl), interstitial nucleus of the posterior limb of the anterior commissure (IPAC) and sublenticular extended amygdala (SLEA). The dopaminergic innervation of the EAc and nucleus accumbens shell is functionally related to motivational processes. Its origin was studied by combining immunofluorescence to tyrosine hydroxylase and Fluoro-Gold, used as retrograde tracer. Our results show that dopaminergic fibers to the CeA and BSTl derive in equal proportion from neurons in ventral tegmental area (A10) and in dorsal raphe nucleus/periaqueductal gray (A10dc). Dopaminergic inputs to SLEA, IPAC and accumbens shell arise mainly from A10 neurons. Using a dopamine antibody, we confirmed that A10dc projections to CeA are in part dopaminergic. Futhermore, the present data indicate that the diencephalic dopaminergic groups do not project to EAc and accumbens shell.

Bien que la neurotransmission glutamatergique joue un rôle pivot dans le développement et l’expression de la sensibilisation comportementale aux amphétamines, le rôle spécifique de certaines structures glutamatergiques qui projettent sur l’aire tegmentale ventrale et/ou le noyau accumbens n’est pas encore bien caractérisé. Nous montrons que l’hippocampe dorsal, la partie prélimbique du cortex préfrontal et l’amygdale basolatérale joue un rôle prépondérant dans les réponses locomotrices induites par l’administration aiguë (développement de la sensibilisation) et chronique (expression de la sensibilisation) d’amphétamines, suggérant les réponses locomotrices aux amphétamines impliquent un ensemble de structures glutamatergiques corticolimbiques. Par la suite, nous nous sommes intéressés au rôle de la neurotransmission glutamatergique associée aux récepteurs NMDA dans le noyau accumbens, qui est considéré comme le noyau clé de l’expression de la sensibilisation, sur le développement à court terme de la sensibilisation aux amphétamines. De plus, nous montrons le développement de la sensibilisation à court terme aux amphétamines requiert l’activation concomitante de certains récepteurs NMDA au glutamate et nicotiniques à l’acétylcholine dans le noyau accumbens. De plus, l’activation concomitante de ces récepteurs sous tend également la libération de dopamine induite par les amphétamines dans le noyau accumbens. L’ensemble de ces données montre que la neurotransmission glutamatergique, et les structures glutamatergiques qui projettent sur l’aire tegmentale ventrale et/ou le noyau accumbens, joue un rôle majeur dans la sensibilisation comportementale à court terme aux amphétamines. / Although it is well admitted that the glutamatergic neurotransmission plays a pivotal role in the development and expression of behavioral sensitization to amphetamine, the specific role of glutamatergic structures that project to the ventral tegmental and/or the nucleus accumbens is less well studied. We showed that the dorsal hippocampus, the prelimbic part of the prefrontal cortex and the basolateral amygdala play a critical role in both acute (development of sensitization) and chronic (expression of sensitization) locomotor responses induced by amphetamine, suggesting that behavioral responses to amphetamine are mediated by circuitry of corticolimbic glutamatergic structures. Next, we investigated the role of glutamatergic NMDA receptors contained in the nucleus accumbens, which is seen as the key structure for the expression of sensitization, in the development of short term sensitization to amphetamine. Interestingly, we showed that, contrasting with the current dichotomous thinking that has attributed specialized functions to the ventral tegmental area and the nucleus accumbens, respectively in the development and the expression of behavioral sensitization, concomitant activation of certain types of NMDA and nicotinic receptors in the nucleus accumbens is also required for the development of short term sensitization. Furthermore, we showed that concomitant activation of these receptors sustained the amphetamine-induced dopamine release in the nucleus accumbens. All these data show that glutamatergic neurotransmission, and glutamatergic structures which project onto mésoaccumbens system, plays a major role in short-term behavioral sensitization to amphetamine.

很多行為的建構基礎是來自酬賞動機，而個體的行為表現通常是動態的歷程，其中對酬賞物的“價值”比較，是決定行為是否輸出或輸出多少的重要關鍵。在鼠類的動物行為模式中，可以利用甜液舔飲來進行這種對比(contrast)歷程的實驗。在受試可先後獲得兩次舔飲機會的實驗情境中，若兩管濃度皆為4%的蔗糖液先後間隔特定時距出現，受試會隨訓練天數增加而增加對兩管糖液的舔飲表現。若第一管4%蔗糖液之後會呈現濃度較高的32%蔗糖液，受試舔飲第一管同為濃度4%蔗糖液的表現會隨訓練天數增加而先增後減。這兩組受試對第一管糖液的舔飲量差異，即稱為預期性對比效果。一般認為此現象是受試等待與預期較高酬賞價值的糖液，而抑制當前較低酬賞價值糖液的舔飲。過去對此現象的研究主要關注在行為層面的探討，然而其相關神經機制的研究並不多，本研究的目的即在於探討與習得或形成預期性對比行為有關的神經機制。一般認為預期性對比效果的習得包含多階段的歷程，可能與多種心理行為面向有關，因此很有可能是經由多元性的神經機制參與。預期性對比效果的形成與否與兩糖液呈現的間距長短有很大的關係。本研究實驗一以0.5分鐘、2分鐘以及6分鐘三個不同的糖液間距引發的預期對比效果，從當中選取可有效形成預期性對比效果的0.5分鐘為實驗二糖液間距的依據。實驗二分別以興奮性神經毒素破壞依核核心區、眶前額皮質區以及杏仁體基側核區等三個神經區域。結果顯示杏仁核基側核區破壞不影響預期性對比效果的習得，而依核核心區以及眶前額皮質的破壞使受試無法習得預期性對比效果。綜合以上結果，預期性對比效果的習得是依靠有效的糖液呈現間距去進行酬賞比較，腦中依核核心區及眶前額皮質區與該種對比有關。 / Many types of behavior are constructed on the basis of reward motivation, which can be run in dynamic processes. Among those processes potentially involved, the reward comparison is a key determinant for the magnitude of behavioral output. The licking of sweet solution in the rat can be used as an animal model to investigate the contrast effect derived from reward comparison. In which, the subjects presented two sweet solutions in a sequential order each day may suppress intake of the first solution if the second solution is preferred. This phenomenon is termed anticipatory contrast effect (ACE). It is hypothesized that ACE could be built via an inhibition process associated with subject’s waiting for a preferred solution as presented by a less preferred solution. Most of the previous studies were mainly focused on the behavioral aspects of ACE. The present study intended to investigate the neural mechanisms of ACE. In considering that the formation of ACE requires multiple-stage processes, this study presumed that more than one brain area could be involved in mediating those psycho-behavioral processes. Experiment 1 was intended to establish behavioral model by manipulating the effectiveness of different inter-solution interval (ISI; 0.5, 2.0, and 6.0 min). The results showed that the ISI of 0.5 min is the critical parameters for the successful formation of ACE, which was then applied in Experiment 2. Experiment 2 investigated the effects of excitotoxin lesion conducted by ibotenic acid in the nucleus accumbens core (NACc), orbitofrontal cortex (OFC) or basolateral amygdala (BLA) on the acquisition of ACE. The result showed the rats with NACc or OFC lesion significantly failed to acquire ACE, but no such impairment appeared to BLA lesion. Together, these data suggest that the formation of ACE is depended upon the ISI leading to an effective reward comparison, and the NACc or OFC is involved in such a contrast processing.

本研究以心理興奮性藥物(psychosimulants)引發之行為致敏化作為探討環境與藥物的配對學習如何影響個體長期使用藥物後對藥物的反應。首先於實驗一建立安非他命引發自發活動致敏化基本模式，以及不同的重複注射情境下致敏化的表現，結果顯示經由本實驗操弄注射情境的程序可有效引發在測試箱、飼養籠，和第三處的安非他命致敏化表現，並且致敏化自發活動表現量在測試箱組顯著高於飼養籠組和第三處組。實驗二對致敏化形成歷程中可能與安非他命配對的刺激進行消除，以釐清致敏化形成歷程中連結學習的要素，結果顯示消除程序沒有降低致敏化活動量的效果。實驗三使用中樞注射麩胺酸受體拮抗劑NBQX於依核以影響致敏化的連結學習歷程，結果顯示該操弄可阻斷在飼養籠重複注射安非他命引發的行為致敏化。測試箱組經過該操弄後其致敏化活動量顯著降低但仍有顯著的致敏化活動量表現。實驗四分別破壞前額葉皮質兩處次級區塊以瞭解其在致敏化連結學習歷程中扮演的角色，結果顯示破壞背側前額葉皮質只阻斷在飼養籠注射安非他命所引起的行為致敏化，破壞腹側前額葉皮質只阻斷測試箱組行為致敏化。綜合上述研究結果顯示安非他命引發致敏化的形成深受藥物配對的環境影響而可區分環境相依與環境獨立之行為致敏化，環境相依行為致敏化的行為機制可由場合建立的觀點加以解釋。在依核內之麩胺酸傳導和前額葉皮質次級區塊之功能在兩種行為致敏化上的差異可以反應環境相依和環境獨立行為致敏化的潛在神經機制可能有所不同。 / The present study investigated the neurobehavioral mechanisms of d-amphetamine (AMP) induced behavioral sensitization, with the aim to elucidate the role of associative learning between the context and drug. Experiment 1 compared the sensitization effects of repeated (AMP) conducted in three different contexts by the measurement of locomotion activity. The results showed that behavioral sensitization of locomotion was significantly induced AMP repeatedly injected in each of the contexts. However, the magnitudes of behavioral sensitization were different among those three conditions. The highest degree of sensitized locomotion was observed in the group with repeated AMP conducted in the test box in comparing to the other two groups with drug administration in the home cage and a third place, Experiment 2 was designed to examine the effects of extinction on the injection procedure and the contextual cue on the behavioral sensitization of AMP induced in the test box, the home cage, and a third place. The resu lts clearly indicate all three types of locomotion sensitization were resistant to the manipulation of extinction. Experiment 3 tested the effects of NBQX, a glutamatergic AMPA receptor antagonist, infused into the nucleus accumbens on the establishment of behavioral sensitization of AMP induced in the test box and the home cage. This intra-accumbens NBQX treatment significantly suppressed the formation of behavioral sensitization of AMP induced in the home cage, but not in the test box. Experiment 4 investigated the lesion effects of medial prefrontal cortex (mPFC) on the establishment of behavioral sensitization of AMP induced in the test box and the home cage. Two subareas of the mPFC, dorsal and ventral parts, were lesioned by ibotenic acid. The findings indicated a double dissociation existing in the mPFC subareas for the behavioral sensitization of AMP induced in different contexts. The lesion of ventral mPFC inhibited the formation of behavioral sensitization of AMP induced in the test box, whereas the lesion of dorsal mPFC attenuated the AMP sensitization induced at the home cage. Together, these data suggest that the association of the repeated drug effects pairing to the context is critical for the development of behavioral sensitization. Such sensitization can further be differentiated into the context-depentdent and context-independent forms based on the uniqueness of contextual cue in the environment where drug is administered. Different neural substrates are involved in the establishment of behavioral sensitization of AMP.