Thesis advisor: John P. Christianson / Trauma and exposure to extreme stressors greatly increases a person’s vulnerability to developing mental illnesses like post-traumatic stress disorder (PTSD). Patients with PTSD often have impaired fear and safety learning, and despite the fact that women are more than twice as likely to develop PTSD, much of the research on this disorder has relied on the use of male subjects. This paper will review potential contributors to the sex differences seen in PTSD and fear-related learning. Our group has found that female rats show greater fear discrimination abilities than their male counterparts, but show no difference in levels of safety learning. Analysis of specialized extracellular matrix structures called perineuronal nets (PNNs) revealed that females displayed a much higher density of PNNs in the basolateral amygdala (BLA) than males, but not in the prefrontal cortex (PFC). / Thesis (BS) — Boston College, 2017. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Psychology.

Chez les mammifères, le néocortex constitue une structure remarquablement plastique assurant leurs multiples capacités d’adaptation et d’apprentissage. Par exemple, l’apprentissage associatif permet à chaque individu d’apprendre les relations entre un événement particulier (un danger par exemple) et les signaux environnementaux qui y sont associés, afin d’en anticiper les conséquences s’il se reproduit dans le futur. Dans le cas de la peur conditionnée, l'apprentissage associatif améliore les capacités de discrimination des signaux de menace et de sécurité, garantissant ainsi une représentation précise de l'environnement. Ce processus comportemental est en partie dépendant de l'interaction entre deux structures cérébrales: le cortex préfrontal (PFC) et le complexe basolatéral de l'amygdale (BLA). Bien que le PFC puisse encoder à la fois les mémoires de menace et de sécurité qui seraient recrutées préférentiellement après l'apprentissage, on ignore toujours si une telle représentation discriminative existe réellement, et si oui, les mécanismes neuronaux et synaptiques qui en sont à l'origine. Au cours de mon travail de thèse, j'ai démontré que l'activité des neurones excitateurs du PFC est nécessaire à la discrimination entre les signaux de menace et de sécurité grâce à la formation d'ensembles spécifiques de neurones. Au cours de l'apprentissage, les neurones pyramidaux sont potentialisés et recrutés au sein de ses ensembles grâce à l'association au niveau dendritique d'événements synaptiques non-linéaires issus des entrées sensorielles avec des entrées synaptiques provenant de la BLA. En conclusion, nos données fournissent la preuve d'un nouveau mécanisme synaptique qui associe, pendant l'apprentissage, l'expérience perçue avec l’état émotionnel transmis par la BLA permettant ainsi la formation d'ensembles neuronaux dans le cortex préfrontal. / The ability of an organism to predict forthcoming events is crucial for survival, and depends on the repeated contingency and contiguity between sensory cues and the events (i.e. danger) they must predict. The resulting learned association provides an accurate representation of the environment by increasing discriminative skills between threat and safety signals, most likely as a result of the interaction between the prefrontal cortex (PFC) and the basolateral amygdala (BLA). Although it suggests that local neuronal networks in the PFC might encode opposing memories that are preferentially selected during recall by recruiting specific cortical or subcortical structures, whether such a discriminative representation is wired within discrete prefrontal circuits during learning and by which synaptic mechanisms remain unclear. Here, the work at issue demonstrates that discrimination learning of both safe and fear-conditioned stimuli depends on full activity of the frontal association cortex, and is associated with the formation of cue-specific neuronal assemblies therein. During learning, prefrontal pyramidal neurons were potentiated through sensory-driven dendritic non-linearities supported by the activation of long-range inputs from the basolateral amygdala (BLA). Taken together, these data provide evidence for a new synaptic level mechanism that coincidently link (or meta-associate) during learning features of perceived experience with BLA mediated emotional state into prefrontal memory assemblies.

Les mammifères, comme par exemple les rongeurs, soumis à des expériences aversives présentent des réponses comportementales de peur caractéristiques notamment une réponse d'immobilisation (freezing) ou d'évitement. Alors que le rôle du cortex préfrontal dorso-médian (CPFdm) dans l’acquisition ainsi que l’expression du freezing a déjà été expérimentalement établi, son implication dans l’encodage des réponses d’évitement de peur ainsi que l’interaction entre les circuits neuronaux préfrontaux impliqués dans le freezing et/ou l’évitement restent mal compris. Afin de répondre à ces questions, nous avons développé au laboratoire un paradigme expérimental permettant à une souris d’acquérir et d’exprimer le freezing ou l’évitement lors de la présentation d'un même stimulus aversif et ceci en fonction du contexte environnant. Ainsi, nous avons pu déterminer si les mêmes circuits neuronaux dans le cortex préfrontal dorso-médian encodent les deux réponses de peur, le freezing et l’évitement. Nous avons mis en oeuvre au cours de ce travail des approches comportementales, de traçage neuroanatomique, d'immunohistochimie, d'enregistrements extracellulaires in vivo et intracellulaires in vitro ainsi que des approches optogénétiques. Nos résultats indiquent que (i) le CPFdm et les régions dorsales de la substance grise périaqueducale sont activés pendant le comportement d'évitement, (ii) une sous population de neurones du CPFdm encode le comportement d'évitement mais pas le freezing, (iii) cette population neuronale projette sur le dl/lPAG, (iv) l'activation et l'inhibition optogénétique de cette projection induit et bloque l'apprentissage de l'évitement, respectivement et (v) l'apprentissage de l'évitement est associé à la mise en place d'une plasticité des afférences préfrontales sur le dl/lPAG. Dans leur ensemble ces résultats démontrent pour la première fois que la plasticité dépendante de l'activité des neurones du CPFdm projettant sur le dl/lPAG contrôle l'apprentissage de l'évitement de peur. / Mammals, including rodents show a broad range of defensive behaviors as a mean of coping with threatful stimuli including freezing and avoidance behaviors. Several studies emphasized the role of the dorsal medial prefrontal cortex (dmPFC) in encoding the acquisition as well as the expression of freezing behavior. However the role of this structure in processing avoidance behavior and the contribution of distinct prefrontal circuits to both freezing and avoidance responses are largely unknown. To further investigate the role of dmPFC circuits in encoding passive and active fear-coping strategies, we developed in the laboratory a novel behavioral paradigm in which a mouse has the possibility to either passively freeze to an aversive stimulus or to actively avoid it as a function of contextual contingencies. Using this behavioral paradigm we investigated whether the same circuits mediate freezing and avoidance behaviors or if distinct neuronal circuits are involved. To address this question, we used a combination of behavioral, neuronal tracing, immunochemistry, single unit and patch clamp recordings and optogenetic approaches. Our results indicate that (i) dmPFC and dorsolateral and lateral periaqueductal grey (dl/lPAG) sub-regions are activated during avoidance behavior, (ii) a subpopulation of dmPFC neurons encode avoidance but not freezing behavior, (iii) this neuronal population project to the dl/lPAG, (iv) the optogenetic activation or inhibition of this pathway promoted and blocked the acquisition of conditioned avoidance and (v) avoidance learning was associated with the development of plasticity at dmPFC to dl/lPAG synapses. Together, these data demonstrate for the first time that activity-dependent plasticity in a subpopulation of dmPFC cells projecting to the dl/lPAG pathway controls avoidance learning.

A administração sistêmica de canabidiol (CBD), o principal constituinte não psicomimético da Cannabis sativa, induz efeito antidepressivo em modelos préclínicos. O mecanismo de ação do canabidiol, no entanto, permanece pouco conhecido, podendo envolver a ativação de receptores serotoninérgicos do tipo 1A (5-HT1A). Ademais, as estruturas encefálicas envolvidas nesses efeitos permanecem desconhecidas. O córtex pré-frontal medial ventral (CPFmv), dividido em infra-límbico (IL) e pré-límbico (PL), recebe densa inervação serotoninérgica e desempenha importante papel na modulação da resposta emocional ao estresse e na neurobiologia da depressão. Dessa forma, o objetivo do presente trabalho foi avaliar a hipótese de que a administração de canabidiol no CPFmv, diferenciado em PL e IL, produz efeito tipo-antidepressivo por meio da ativação de receptores 5- HT1A. Para tanto, ratos Wistar canulados bilateralmente no CPFmv, receberam CBD (10, 30, 60 nmol/0,2?l) ou veículo intra-PL e CBD (30, 45 e 60nmol/0,2?l) ou veículo intra-IL e foram submetidos ao teste do nado forçado ou ao teste do campo aberto. Outro grupo de animais recebeu microinjeção (intra PL ou IL) do agonista de receptores 5-HT1A, 8-OH-DPAT (5, 10nmol/0,2?l) e foram submetidos aos mesmos testes. Um grupo adicional recebeu um antagonista 5-HT1A, WAY1006365 (10, 30nmol/0,2?l), seguido pela administração de 8-OH-DPAT (10nmol0,2?l) ou CBD (10 nmol0,2?l) intra-PL, ou 8-OH-DPAT (10nmol0,2?l) ou CBD (45 nmol0,2?l) intra-IL, e avaliados no teste do nado forçado. Os resultados demonstraram que a administração de CBD e de 8-OH-DPAT, intra-PL e intra-IL, reduziu significativamente o tempo de imobilidade no teste do nado forçado, um efeito tipoantidepressivo, sem alterar a atividade locomotora dos animais no teste do campo aberto. Além disso, a administração de WAY100635 intra-PL e intra-IL não alterou o tempo de imobilidade per se, mas foi capaz de bloquear os efeitos da administração do CBD e do 8-OH-DPAT. Esses resultados sugerem que a administração local do CBD no CPFmv induz efeito tipo-antidepressivo por meio da ativação de receptores 5-HT1A. Portanto, é possível que o CPFmv esteja envolvido no efeito tipoantidepressivo induzido pelo CBD. / Systemic administration of cannabidiol (CBD), the main non-psychotomimetic constituent of Cannabis sativa, induces antidepressant-like effects in pre-clinical models. The mechanism of action of Cannabidiol, which remains poorly understood, may involve serotonergic type 1A receptors activation (5-HT1A). Furthermore, the brain structures involved in these effects are still unknown. The ventral medial prefrontal cortex (vmPFC), divided in infra-limbic (IL) and pre-limbic (PL) subregions, receives dense serotonergic innervation and plays an important role in the modulation of emotional responses to stress and in the neurobiology of depression. Thus, the aim of this study was evaluate the hypothesis that the administration of cannabidiol into the vmPFC, differentiated into IL and PL, would induce antidepressant-like effect by activating 5-HT1A receptors. Therefore, male Wistar rats with cannulae bilaterally implanted into the Il and PL were given CBD (10, 30, 45, 60 nmol/0,2?l) or vehicle and were submitted to the forced swimming test or to the open field test. Another group of animals received microinjections (intra PL or IL) of the 5- HT1A agonist 8-OH-DPAT (5, 10nmol/0,2?l) and was submitted to the same tests. An additional group received an 5-HT1A antagonist, WAY100635 (10, 30 nmol/0,2?l.), followed by the administration of 8-OH-DPAT (10 nmol/0,2?l) or CBD (10 nmol0,2?l) intra-PL, or 8-OH-DPAT (10nmol0,2?l) or CBD (45 nmol0,2?l) intra- IL, and avaluated in the forced swimming test. The results showed that CBD and 8- OH-DPAT administration, intra-PL and intra-IL, significantly reduced the immobility time in the forced swimming test, an antidepressant-like effect, without changing the locomotor activity of the animals in the open field test. Moreover, the administration of WAY100635, intra-PL and intra-IL, did not change the immobility time per se, but blocked the CBD- and 8-OH-DPAT-induced effects. These results suggest that the local administration of CBD into the vmPFC induces antidepressant-like effects through the activation of 5-HT1A receptors. Therefore, it is possible that the vmPFC is involved in CBD-induced antidepressant-like effect.

A participação do córtex pré-frontal na memória episódica verbal e seu envolvimento na estratégia organizacional semântica têm sido demonstrados em vários estudos de neuroimagem funcional. Entretanto nenhum estudo anterior investigou os efeitos do treino cognitivo com uso de estratégia semântica sobre a cirtuitaria neural. No presente estudo Investigou-se a codificação da memória episódica verbal, por meio de ressonância magnética funcional (RMf). Quinze voluntários viram listas de palavras apresentadas em três condições de organização semântica: 1) RE relacionada estruturada, 2) RNE relacionada não estruturada e 3) NR não relacionada, antes e após trinta minutos de treino com uso de estratégia organizacional semântica. O principal objetivo foi verificar os efeitos do treino no padrão de ativação neural. Observou-se a participação de uma ampla rede de estruturas cerebrais. O giro frontal inferior e o córtex frontal ventrolateral foram mais ativados após o treino. O córtex pré-frontal dorsolateral e o órbito-frontal foram ativados nas condições RNE e RE antes do treino, as quais permitiram a manipulação e o uso organizacional da estratégia semântica. Os resultados sugerem que: 1) a ativação do giro frontal inferior BA 45 e do córtex pré-frontal ventrolateral BA 47 após o treino pode estar associada ao melhor desempenho da memória episódica verbal. 2) o córtex órbito-frontal BA 11 esteja possivelmente envolvido na mobilização de estratégias e o córtex pré-frontal dorsolateral BA 46 e 9 na manutenção e uso da estratégia mais eficiente / The participation of prefrontal cortex in episodic verbal memory and its involvement in organizational semantic strategy has been demonstrated in several studies of functional neuroimage. However any previous study investigated the effects of cognitive training with semantic organizational strategy use under neural circuitry. At the present study verbal episodic memory encoding were investigated, through functional magnetic resonance (fMRI). Words lists were visually presented to fifteen volunteers in three organizational semantic conditions: 1) RS related structured, 2) RNS related unstructured e 3) UR unrelated, before and after thirty minutes in organizational semantic strategy training. The main objective was to verify the effects of training on neural activation circuitry. The participation of an active broad structure cerebral network was observed. After training the inferior frontal gyrus and the ventrolateral prefrontal cortex were mainly activated. The dorsolateral prefrontal cortex and o orbitofrontal cortex were activated in RNS and RS conditions before training; witch enabled the application and manipulation of semantic organizational strategy. This result suggest: 1) better performance on retrieval and strategy uses after training might be associated to modification of neural activation pattern, and 2) orbitofrontal cortex BA 11 possibly is involved in strategies mobilization, and dorsolateral prefrontal cortex BA 46 e 9 in the uses and maintenance the most efficient strategy

The hippocampal-medial prefrontal circuit has been shown to serve a critical role in decision making and goal directed actions. While the hippocampus (HF) exerts a direct influence on the medial prefrontal cortex (mPFC), there are no direct return projections from the mPFC to the HF. The nucleus reuniens (RE) of the midline thalamus is strongly reciprocally connected with the HF and mPFC and represents the major link between these structures. We investigated the role of RE in functions associated with the hippocampus and the mPFC -- or their interactions. Using two different inactivation techniques (pharmacological and chemogenetic), we sought to further define the role of RE in spatial working memory (SWM) and behavioral flexibility using a modified delayed non-match to sample (DNMS) working memory task. We found that the reversible inactivation of RE with muscimol critically impaired SWM performance, abolished well-established spatial strategies and produced a profound inability to correct non-rewarded, incorrect choices on the T-maze (perseverative responding). We observed similar impairments in SWM following the chemogenetic (DREADDs) inactivation of RE or selective RE projections to the ventral HF. In addition, we showed that the inhibition of RE terminals to the dorsal or ventral HF altered task related behaviors by increasing or decreasing the time to initiate the task or reach the reward, respectively. Finally, we examined discharge properties of RE cells across sleep-wake states in behaving rats. We found that the majority of RE cells discharge at high rates of activity in waking and REM and at significantly reduced rates in SWS, with a subpopulation firing rhythmically in bursts during SWS. We identified five distinct subtypes of RE cells that discharged differently across vigilant states; those firing at highest rates in waking (W1, W2), in REM sleep (R1, R2) and SWS (S1). Given the differential patterns of activity of these cells, we proposed they may serve distinct functions in waking – and possibly in SWS/REM sleep. In sum, our findings indicate that RE is critically involved in mnemonic and executive functions and the heterogeneous activity of these cells support a role for RE in arousal/attention, spatial working memory and cognition. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Activation in the hippocampus (HC) and prefrontal cortex (PFC) is critical to accurately retrieve overlapping sequences. Experiments 1 and 2 tested the hypotheses that activation in and interaction between HC and PFC increases as overlap between sequences increases in a non-spatial task. Experiment 3 tested the hypothesis that theta oscillations are involved in orchestrating interactions between HC and PFC in a spatial task with overlapping elements. In the first two studies, 17 participants (aged 18-34; 11 female) learned sequences consisting of a picture frame, face, and scene. Conditions varied by degree of overlap. Using fMRI, Experiment 1 tested how degree of overlap affected HC and PFC activation. In overlapping sequences, middle and posterior HC were active when predictability of the correct response increased, dorsolateral PFC was active when participants were able to ascertain the correct set of sequences, and ventrolateral PFC was active when inhibition of interfering associations was required. Experiment 2 examined functional connectivity of HC and PFC during disambiguation. Low- and high-overlap conditions were associated with increased connectivity in separate regions at different times indicating that retrieval under the two conditions used different neural networks and strategies. Low-overlap trials were associated with increased connectivity between HC and prefrontal and parietal regions. High-overlap trials showed increased connectivity between lateral PFC and visual areas, indicating that imagery may be necessary for accurate performance. Using EEG recording, Experiment 3 examined theta activity during retrieval of well-learned, overlapping and non-overlapping mazes in 17 participants (aged 18-34, 11 female). Theta activity increased in overlapping mazes during the first of four hallways, suggesting participants were looking ahead to upcoming turns in the maze. Theta activity increased at the beginning and choice point of the third overlapping hallway, possibly in response to interference from the paired, overlapping maze. These studies provide evidence that (1) overlapping associations in non-spatial sequences elicit interactions between hippocampus and lateral prefrontal cortex, (2) increasing the degree of overlap changes the neural processes required to perform the task, and (3) theta power increases in response to increased cognitive demand and maintenance of sequence information needed to differentiate between overlapping spatial routes.

Switching between a state of fear and safety is a critical aspect of adaptive behavior. Aversive and non-aversive associations must be formed quickly and reliably but remain malleable as these associations change dynamically. When these associations become biased towards aversive associations by traumatic and stressful circumstances, as in PTSD, fear generalization and impaired fear extinction arise. These changes are associated with reduced activity in the medial prefrontal cortex (mPFC) and enhanced activity in the basolateral amygdala (BLA). It has been hypothesized that the mPFC mediates top-down control of the BLA to signal safety. It has previously been demonstrated that synchronous activity within the mPFC-BLA circuit is strongly engaged during fear conditioning, but it is unknown how activity in this circuit changes to mediate aversive discrimination. We investigated how the mPFC and BLA cooperate to mediate successful discrimination between aversive and non-aversive stimuli both for learned and innately-valent associations. Extracellular elecrophysiological recordings were obtained simultaneously form the mPFC and BLA in mice during innate anxiety, fear discrimination, and fear extinction. Local field potentials were recorded in both structures along with single unit recordings from the BLA. We discovered that fear was associated with enhanced theta-frequency synchrony and theta-gamma coupling within the mPFC-BLA circuit. On the other hand, safety was associated with predominant mPFC-to-BLA directionality of synchronous information flow and enhanced fast gamma frequency activity in both structures. Interestingly, gamma oscillations in the BLA were strongly coupled to theta frequency activity arising in the mPFC. This data is consistent with entrainment of inhibitory circuits in the BLA by mPFC input to mediate safety.

The ventral hippocampus (vHPC), medial prefrontal cortex (mPFC), and basolateral amygdala (BLA) are each required for the expression of anxiety-like behavior. Yet the role of each individual element of the circuit is unclear. The projection from the vHPC to the mPFC has been implicated in anxiety-related neural synchrony and spatial representations of aversion. The role of this projection was examined using multi-site neural recordings combined with optogenetic terminal inhibition. Inhibition of vHPC input to the mPFC disrupted anxiety and mPFC representations of aversion, and reduced theta synchrony in a pathway-, frequency- and task-specific manner. Moreover, bilateral, but not unilateral, inhibition altered physiological correlates of anxiety in the BLA, mimicking a safety-like state. These results reveal a specific role for the vHPC-mPFC projection in anxiety-related behavior and the spatial representation of aversive information within the mPFC. Moreover, these data suggested that theta-frequency input from the vHPC plays a causal role in anxiety-like behavior. Next, it was investigated whether optogenetic stimulation of the vHPC-mPFC at a theta frequency was sufficient to increase anxiety. Stimulating the vHPC input to the mPFC with a sinusoidal light pattern at 8 Hz significantly increased anxiety behavior. The anxiogenic effect of vHPC terminal stimulation was frequency- (8 Hz but not 20 Hz) and pattern- (sinusoids but not pulses) specific. To understand how pulses and sinusoidal light modulate mPFC neurons differentially, mPFC pyramidal neurons were recorded both in vitro and in vivo while stimulating vHPC terminals with the same sinusoidal or pulsatile patterns. In vitro, sinusoidal stimulation increased the rate of spontaneous EPSCs, while pulses evoked strong, stimulus-locked EPSCs. In vivo, sinusoidal stimulation of vHPC terminals increased the phase-locking of mPFC single unit spiking to the optical stimulation pattern without changing overall firing rates. Together, these results suggest that sinusoidal stimulation at 8 Hz enhances theta-frequency activity in mPFC neurons as well as anxiety-related behavior. Moreover, they suggest that theta-frequency components of neural activity play a privileged role in vHPC-mPFC communication and hippocampal-dependent forms of anxiety.

L'adaptation comportementale est primordiale pour faire face à l'environnement flexible dans lequel les individus évoluent chaque Jour, notamment par l'élaboration de comportements d'exploration ou de vérification. Le cortex préfrontal a depuis longtemps été considéré comme le siège du contrôle exécutif nécessaire à la genèse de ces comportements. Deux régions semblent essentielles: le cortex préfrontal latéral (LPFC) et le cortex midcingulaire (MCC). Bien que diverses théories attribuent à ces régions les fonctions d'évaluation des performances et de contrôle cognitif respectivement, leurs rôles dans les comportements de recherche d'information restent imprécis, et cela malgré l'apport potentiel aussi bien dans un contexte normal que pathologique (i.e. troubles obsessionnels compulsifs). Pour mieux comprendre la spécificité de ces régions dans les comportements d’exploration, les travaux que nous avons menés au cours de cette thèse emploient différentes approches comportementales et électrophysiologiques chez les primates humains et non humains. Ils ont permis de (1) raffiner la compréhension de l'implication des régions frontales dans le contrôle cognitif et l'effort attentionnel, (2) développer des tâches comportementales induisant des vérifications, basées sur le Jugement des performances ou l'évaluation de l'environnement, et (3) souligner la spécificité des comportements de vérification. En particulier, nos enregistrements intracérébraux chez le singe en comportement montrent l'importance du MCC pour signaler le besoin d'explorer sur la base de l'évaluation des performances, tandis que le LPFC contribue à la mise en oeuvre de la conduite comportementale à adopter / Behavioural adaptation is an essential element of our quest to survive and flourish in a volatile environment, in particular by the use of exploration and verification behaviours. The prefrontal cortex has long been considered a critical source of these behaviours given it role in executive control. Two regions appear to be particularly critical – the lateral prefrontal cortex (LPFC), and the midcingulate cortex (MCC). Although numerous theories associate these regions with the functions of performance evaluation and cognitive control, the role of these regions in the search for information remains lacking, despite the importance of these behaviours and their apparent role in pathologies such as obsessive compulsive disorders. This thesis seeks to understand the specific roles of these regions in exploratory behaviours, employing a range of behavioural and electrophysiological techniques in both human and non human primates. The work here helps to refine our understanding of the role of frontal cortical regions in cognitive control and attentional effort. Moreover, we have developed a number of behavioural tasks that induce verification behavior based on subjects’ evaluation of their own performance or on an evaluation of the environment. Our work reveals the specificity of verification behaviour as well as specific roles for the MCC and LPFC in this search for information. Our intra cerebral recordings in monkeys working on such tasks underline the importance of the MCC for signalling the need to explore the environment on the basis of performance evaluation, whilst we have also shown the role of LPFC in the implementation of the necessary behavioural adaptations