Long-term potentiation of transmission at neocortical synapses in slices of rat sensorimotor cortex and the involvement of NMDA receptors

1. Long-term potentiation (LTP) is an enduring activity-dependent increase in synaptic efficacy which has been considered as a neural substrate for learning and memory. 2. LTP was induced in 22% of postsynaptic potentials (p.s.p.s) and 87% of field potentials evoked by stimulation of the subcortical white matter and recorded in layers III, V & VI of slices of adult rat sensorimotor cortex. Conditioning paradigms used were either high frequency stimulation of an afferent pathway or the repetitive pairing of an afferent volley with a postsynaptic injection of depolarizing current. Intracellularly recorded LTP was found to be input specific, homosynaptic and associative. 3. D-2-amino-5-phosphonopentanoic acid (AP5) was used to assess the involvement of N-methyl-D-aspartate (NMDA) receptors in neurotransmission and in the induction and expression of LTP in the neocortex. The majority of p.s.p.s (89%) and field potentials (80%) were mediated in part by NMDA receptors. A non-NMDA receptor mediated component always preceded a NMDA receptor mediated one. 4. AP5 blocked the induction of LTP in field potentials recorded in 5 out of 7 slices; following washout of AP5, a second, identical set of conditioning stimuli induced LTP. 5. AP5 applied 15-20 minutes after the induction of LTP, reduced the magnitude of potentiated field potentials in 13 out of 13 slices and 4 out of 4 potentiated p.s.p.s. A potentiated non-NMDA receptor mediated component preceded a potentiated NMDA receptor mediated one. 6. In most cases, the onset latency of the potentiated component of p.s.p.s was delayed by ~2ms after the onset of synaptic activity. This delay was not voltage-dependent. LTP appeared to be a property of intrinsic neocortical connections but not of the fastest conducting afferents, possibly arising from outside the neocortex

Rôle de deux groupes de vésicules dans la transmission synaptique

Les synapses formées par les fibres moussues (FM) sur les cellules principales de la région CA3 (FM-CA3) jouent un rôle crucial pour la formation de la mémoire spatiale dans l’hippocampe. Une caractéristique des FM est la grande quantité de zinc localisée avec le glutamate dans les vésicules synaptiques recyclées par la voie d’endocytose dépendante de l’AP3. En combinant l’imagerie calcique et l’électrophysiologie, nous avons étudié le rôle des vésicules contenant le zinc dans la neurotransmission aux synapses FM-CA3. Contrairement aux études précédentes, nous n’avons pas observé de rôle pour le zinc dans l’induction des vagues calciques. Nos expériences ont révélé que les vagues calciques sont dépendantes de l’activation des récepteurs métabotropiques et ionotropiques du glutamate. D’autre part, nos données indiquent que les vésicules dérivées de la voie dépendante de l’AP3 forment un groupe de vésicules possédant des propriétés spécifiques. Elles contribuent principalement au relâchement asynchrone du glutamate. Ainsi, les cellules principales du CA3 de souris n’exprimant pas la protéine AP3 avaient une probabilité inférieure de décharge et une réduction de la synchronie des potentiels d’action lors de la stimulation à fréquences physiologiques. Cette diminution de la synchronie n’était pas associée avec un changement des paramètres quantiques ou de la taille des groupes de vésicules. Ces résultats supportent l’hypothèse que deux groupes de vésicules sont présents dans le même bouton synaptique. Le premier groupe est composé de vésicules recyclées par la voie d’endocytose utilisant la clathrine et participe au relâchement synchrone du glutamate. Le second groupe est constitué de vésicules ayant été recyclées par la voie d’endocytose dépendante de l’AP3 et contribue au relâchement asynchrone du glutamate. Ces deux groupes de vésicules sont nécessaires pour l’encodage de l’information et pourraient être importants pour la formation de la mémoire. Ainsi, les décharges de courte durée à haute fréquence observées lorsque les animaux pénètrent dans les places fields pourraient causer le relâchement asynchrone de glutamate. Finalement, les résultats de mon projet de doctorat valident l’existence et l’importance de deux groupes de vésicules dans les MF qui sont recyclées par des voies d’endocytoses distinctes et relâchées durant différents types d’activités.Mossy fiber-CA3 pyramidal cell synapses play a crucial role in the hippocampal formation of spatial memories. These synaptic connections possess a number of unique features substantial for its role in the information processing and coding. One of these features is presence of zinc co-localized with glutamate within a subpopulation of synaptic vesicles recycling through AP3-dependent bulk endocytosis. Using Ca2+ imaging and electrophysiological recordings we investigated role of these zinc containing vesicles in the neurotransmission. In contrast to previous reports, we did not observe any significant role of vesicular zinc in the induction of large postsynaptic Ca2+ waves triggered by burst stimulation. Moreover, our experiments revealed that Ca2+ waves mediated by Ca2+ release from internal stores are dependent not only on the activation of metabotropic, but also ionotropic glutamate receptors. Nevertheless, subsequent experiments unveiled that the vesicles derived via AP3-dependent endocytosis primary contribute to the asynchronous, but not synchronous mode of glutamate release. Futhermore, knockout mice lacking adaptor protein AP3 had a reduced synchronization of postsynaptic action potentials and impaired information transfer; this was not associated with any changes in the synchronous release quantal parameters and vesicle pool size. These findings strongly support the idea that within a single presynaptic bouton two heterogeneous pools of releasable vesicles are present. One pool of readily releasable vesicles forms via clathrin mediated endocytosis and mainly participates in the synchronous release; a second pool forms through bulk endocytosis and primarily supplies asynchronous release. The existence of two specialized pools is essential for the information coding and transfer within hippocampus. It also might be important for hippocampal memory formation. In contrast to low firing rates at rest, dentate gyrus granule cells tend to fire high frequency bursts once an animal enters a place field. These burst activities, embedded in the lower gamma frequency, should be especially efficient in the triggering of substantial asynchronous glutamate release. Therefore, the results of my PhD project for the first time provide strong evidence for the presence and physiological importance of two vesicle pools with heterogeneous release and recycling properties via separate endocytic pathways within the same mossy fiber bouton

Contributions of synaptic filters to models of synaptically stored memory

The question of how neural systems encode memories in one-shot without immediately disrupting previously stored information has puzzled theoretical neuroscientists for years and it is the central topic of this thesis. Previous attempts on this topic, have proposed that synapses probabilistically update in response to plasticity inducing stimuli to effectively delay the degradation of old memories in the face of ongoing memory storage. Indeed, experiments have shown that synapses do not immediately respond to plasticity inducing stimuli, since these must be presented many times before synaptic plasticity is expressed. Such a delay could be due to the stochastic nature of synaptic plasticity or perhaps because induction signals are integrated before overt strength changes occur.The later approach has been previously applied to control fluctuations in neural development by low-pass filtering induction signals before plasticity is expressed. In this thesis we consider memory dynamics in a mathematical model with synapses that integrate plasticity induction signals to a threshold before expressing plasticity. We report novel recall dynamics and considerable improvements in memory lifetimes against a prominent model of synaptically stored memory. With integrating synapses the memory trace initially rises before reaching a maximum and then falls. The memory signal dissociates into separate oblivescence and reminiscence components, with reminiscence initially dominating recall. Furthermore, we find that integrating synapses possess natural timescales that can be used to consider the transition to late-phase plasticity under spaced repetition patterns known to lead to optimal storage conditions. We find that threshold crossing statistics differentiate between massed and spaced memory repetition patterns. However, isolated integrative synapses obtain an insufficient statistical sample to detect the stimulation pattern within a few memory repetitions. We extend the modelto consider the cooperation of well-known intracellular signalling pathways in detecting storage conditions by utilizing the profile of postsynaptic depolarization. We find that neuron wide signalling and local synaptic signals can be combined to detect optimal storage conditions that lead to stable forms of plasticity in a synapse specific manner.These models can be further extended to consider heterosynaptic and neuromodulatory interactions for late-phase plasticity.<br/

Reconsolidation of appetitive memory and sleep: functional connectomics and plasticity

Introduzione: La dipendenza da cibo \ue8 un disturbo comportamentale caratterizzato da modelli maladattativi di consumo alimentare, in cui alimenti ricchi in zuccheri, sale e/o grassi possono indurre una dipendenza tale da essere paragonata ai disturbi relativi all\u2019abuso di sostanze. Alla base di questo processo vi \ue8 l\u2019associazione tra questi cibi altamente palatabili e la sensazione piacevole e rinforzante indotta dal loro consumo, che pu\uf2 essere codificata in una nuova memoria maladattativa sottostante il disturbo di dipendenza. Infatti, le nuove informazioni che riceviamo quotidianamente dall\u2019esterno vengono processate dal nostro cervello tramite un primo stadio di codifica e un secondo stadio di consolidamento, durante il quale vengono stabilizzate in una nuova memoria e integrate nella rete cerebrale di conoscenze preesistenti. Tuttavia, dopo il suo consolidamento, una memoria pu\uf2 essere destabilizzata e riportata ad uno stato di labilit\ue0 che ne permette la modifica e l\u2019eventuale integrazione con nuove informazioni. Infine, un nuovo processo di stabilizzazione chiamato riconsolidamento \ue8 necessario affinch\ue9 la traccia mnemonica aggiornata sia nuovamente stabilizzata. Da recenti studi, \ue8 noto come il sonno sia rilevante sia per il consolidamento che per il riconsolidamento della memoria. Tuttavia, mentre \ue8 chiaro come il consolidamento che avviene durante il sonno permetta la stabilizzazione a lungo termine delle tracce mnemoniche, non \ue8 ancora stato del tutto chiarito il ruolo del sonno nel processo di riconsolidamento. Scopo: Date queste premesse, e nota l\u2019importanza dell\u2019interazione tra amigdala basolaterale (BLA) e ippocampo nel riconsolidamento delle memorie appetitive, gli obiettivi della presente tesi erano: i) valutare come l\u2019amigdala BLA e ippocampo interagiscono in termini di potenziali locali durante la riattivazione della memoria strumentale effettuata o durante la fase di attivit\ue0 o durante la fase di inattivit\ue0 del ciclo circadiano dei roditori; ii) valutare come il richiamo della memoria effettuato durante la fase attiva o quella inattiva possa influenzare il successivo processo di riconsolidamento, e iii) trovare, in-vivo, un marker di riattivazione della memoria appetitiva. Metodi: Sono stati utilizzati 32 ratti maschi, ceppo Sprague Dawley, a cui sono stati impiantati due elettrodi profondi: uno in BLA e uno in ippocampo, per la registrazione dei potenziali locali. I ratti sono stati sottoposti ad un protocollo comportamentale in gabbia operante di auto-somministrazione di saccarosio, composto da quattro stadi: addestramento (i), in cui i ratti imparavano l\u2019associazione tra la pressione di una leva e l\u2019emissione di un pellet di saccarosio; astinenza (ii), durante la quale i soggetti non venivano esposti al contesto di addestramento; riattivazione o non riattivazione (iii) della memoria strumentale in gabbia operante, svolta o durante la fase di attivit\ue0, o durante la fase di inattivit\ue0; test di ricaduta (iv). I potenziali locali sono stati analizzati per lo stadio (iii) in modo da ottenere la potenza delle oscillazioni theta e gamma per i due elettrodi profondi; tali frequenze sono state scelte in quanto rilevanti per i processi mnemonici. Infatti, il richiamo della memoria \ue8 correlato alla sincronizzazione delle onde theta (4-12 Hz) tra BLA e altre aree cerebrali quali l\u2019area CA1 dell\u2019ippocampo, ed \ue8 inoltre correlato alle basse gamma (30-60 Hz) nell\u2019ippocampo. Infine, l\u2019accoppiamento tra le onde theta e gamma nell\u2019ippocampo \ue8 un noto metodo di comunicazione tra sotto-aree ippocampali nel corso dei processi di memoria. Risultati: I risultati hanno mostrato la presenza di una correlazione inversa tra la potenza delle basse gamma nell\u2019area CA1 ippocampale e il tasso di risposta durante lo stadio di richiamo della memoria nella fase di attivit\ue0, indipendentemente dal fatto che i soggetti stessero o meno premendo la leva. Le basse gamma potrebbero quindi rappresentare un marker di correlazione per il richiamo della memoria appetitiva. Inoltre, la potenza di basse e alte gamma ippocampali aumenta durante le epoche di pressione di leva quando il richiamo della memoria viene effettuato nella fase di inattivit\ue0, suggerendo che le onde gamma potrebbero essere dei marker correlazionali specifici per la componente strumentale del richiamo della memoria effettuato durante la fase di inattivit\ue0. Conclusioni e limitazioni: Per concludere, i risultati hanno mostrato l\u2019importanza delle frequenze basse gamma nel richiamo delle memorie appetitive, tuttavia non hanno mostrato alcuna differenza a livello delle onde theta, n\ue9 a livello della BLA. Di conseguenza, si conclude che il protocollo utilizzato nella presente tesi non ha mostrato una sensibilit\ue0 sufficientemente elevata nell\u2019evidenziare i cambiamenti ipotizzati a livello dei potenziali locali. Lo svolgimento di ulteriori esperimenti che andranno a determinare misure di connettomica quali coerenza e accoppiamento, sia intra- che inter- area, aiuter\ue0 a determinare se e come le due aree comunicano tra di loro.Introduction: Food addiction is a behavioural disorder in which individuals develop maladaptive patterns of food consumption. Particularly, food containing processed sugars, salt, fat etc. can be addictive, and refined food consumption behaviours may meet the criteria for substance use disorders. For these characteristics, food addiction can also be considered a memory disorder. Memories in the brain are processed as follows: new information is encoded and then long-term consolidated through a process allowing its integration into already existing knowledge networks. After a memory has been consolidated, it can be destabilized and brought back to a labile state, requiring a new re-stabilization process called reconsolidation. Memory consolidation is known to require sleep. In fact, sleep allows new memory traces to long-term stabilize. Sleep also seems to influence memory reconsolidation; however, its involvement in this process is not yet clear. Aim: Given these premises, the goals of the project were: to evaluate how basolateral amygdala (BLA) and hippocampus interact in terms of local field potentials (LFPs) when appetitive instrumental memory is retrieved either during active or inactive phase of rats circadian rhythm; to evaluate how retrieving the memory in the activity vs inactivity phase influences following memory reconsolidation; and to find an in vivo electrophysiological marker of appetitive memory retrieval. In fact, it has been shown that BLA and dorsal hippocampus interaction is crucial for appetitive memory reconsolidation. Methods: Thirty-two male Sprague Dawley rats were implanted with in-depth electrodes for LFPs recordings in BLA and dorsal hippocampal CA1 and subject to a behavioural protocol apt to induce appetitive memory retrieval. The behavioural procedure consisted of four stages: training (i), in which animals learned lever pressing \u2013 sucrose reward association; abstinence (ii), during which subjects were not exposed to the training context; memory retrieval or no retrieval (iii): instrumental memory reactivation or no reactivation, performed either during active or inactive phase; and relapse test (iv), during which sucrose-seeking behaviour was analysed. Theta and gamma oscillations powers were analysed during stage (iii). In fact, they are known to be involved in memory processes. Memory retrieval has been shown to correlate with theta (4-12 Hz) synchronization between BLA and other brain areas (such as hippocampal CA1) and with low gamma (30-60 Hz) in hippocampus. Particularly, theta-gamma cross-frequency coupling has been shown to be used as a mean of communication between hippocampal sub-areas during memory processing. Results: Results showed an inverse correlation between hippocampal CA1 low gamma power and reactivation rate of responding (either when rats were lever pressing or not) when reactivation was performed during the active phase. This suggests that low gamma may be a correlational marker of instrumental sucrose memory retrieval, independent of whether rats were lever-pressing or not. Moreover, hippocampal CA1 gamma bands increased when lever pressing during instrumental memory reactivation while in the inactive phase, suggesting that both low and high gamma bands may be correlational markers to actual instrumental responding retrieval during the inactive phase. Conclusions and limitations: In conclusion, results showed that low gamma is relevant in sucrose appetitive memory retrieval. However, no difference was observed in the theta frequency band, nor at the level of BLA. Therefore, the current protocol did not have the sensitivity to detect predicted changes in LFPs. Further experiments would help investigating if and how the two areas interact, by determining connectomics measures such as coherence and coupling within and between areas

Using MapReduce Streaming for Distributed Life Simulation on the Cloud

Distributed software simulations are indispensable in the study of large-scale life models but often require the use of technically complex lower-level distributed computing frameworks, such as MPI. We propose to overcome the complexity challenge by applying the emerging MapReduce (MR) model to distributed life simulations and by running such simulations on the cloud. Technically, we design optimized MR streaming algorithms for discrete and continuous versions of Conway’s life according to a general MR streaming pattern. We chose life because it is simple enough as a testbed for MR’s applicability to a-life simulations and general enough to make our results applicable to various lattice-based a-life models. We implement and empirically evaluate our algorithms’ performance on Amazon’s Elastic MR cloud. Our experiments demonstrate that a single MR optimization technique called strip partitioning can reduce the execution time of continuous life simulations by 64%. To the best of our knowledge, we are the first to propose and evaluate MR streaming algorithms for lattice-based simulations. Our algorithms can serve as prototypes in the development of novel MR simulation algorithms for large-scale lattice-based a-life models.https://digitalcommons.chapman.edu/scs_books/1014/thumbnail.jp

Neurochemistry

Neurochemistry is a flourishing academic field that contributes to our understanding of molecular, cellular and medical neurobiology. As a scientific discipline, neurochemistry studies the role of chemicals that build the nervous system, it explores the function of neurons and glial cells in health and disease, it discovers aspects of cell metabolism and neurotransmission, and it reveals how degenerative processes are at work in the nervous system. Accordingly, this book contains chapters from a variety of topics that fall into the following broad sections: I. Neural Membranes and Intracellular Signaling, II. Neural Processing and Intercellular Signaling, III. Growth, Development and Differentiation, and IV. Neurodegenerative Diseases. The book presents comprehensive reviews in these different areas written by experts in their respective fields. Neurodegeneration and neuronal diseases are featured prominently and are a recurring theme throughout most chapters. This book will be a most valuable resource for neurochemists and other scientists alike. In addition, it will contribute to the training of current and future neurochemists and, hopefully, will lead us on the path to curing some of the biggest challenges in human health