The amygdala, in particular its basolateral part (BLA), plays a critical role in binding affective qualities to otherwise neutral stimuli, and in eliciting emotional behaviors. Plasticity of inputs to BLA projection neurons involved in emotional memory has been extensively studied. However, how BLA neurons collectively process sensory information to encode and stabilize emotional memories is unknown. Precise coordination of BLA network activities seems critical. Specifically, timed integration of salient stimuli, and synchrony with hippocampal theta oscillations appear to be important. Recent reports suggest that GABAergic neurons may be instrumental in shaping ensemble activity in the BLA. Studies of neocortex and hippocampus showed that diverse GABAergic interneuron types play highly specific roles in coordinating network operations. The presence of similar interneuron populations in the BLA suggests comparable mechanism may govern its activities. However, GABAergic cell types and their functions have not been characterized.

Die NADPHd-Färbung stellt bekanntermaßen Neurone dar, die die neuronale NOS exprimieren. Die Anfärbung der Neurone ist in ihrer Qualität dabei mit Golgi-basierten Versilberungstechniken vergleichbar. Aufgrund dieser Eigenschaften ermöglicht diese Methode morphologische und funktionelle Untersuchungen. Somit ist sie geradezu zur Bearbeitung neuropathologischer Fragestellungen prädestiniert. Im Putamen werden durch diese Technik vorwiegend Interneurone angefärbt. Anhand morphologischer Kriterien wurden die nitrinergen Neurone klassifiziert. Im menschlichen Putamen konnten dabei 12 Neuronentypen (NADPHd I bis XII) unterschieden werden, die nur zum Teil in bereits bestehende Klassifikationssysteme eingeordnet werden konnten. Ausgehend von dieser Klassifikation ist es möglich, in vergleichenden Studien Veränderungen NADPHd-positiver Neurone im Rahmen neurodegenerativer Erkrankungen festzustellen. Im Falle der vorliegenden Arbeit wurde dabei das Putamen schizophrener Patienten untersucht. Aufgrund der geringen Anzahl von drei untersuchten schizophrenen Gehirnen ließen sich nur vorläufige Aussagen in Bezug auf Unterschiede NADPHd-positiver Neurone im Putamen Gesunder und Schizophrener treffen. Solche Unterschiede wurden in der Morphologie dieser Neurone gefunden, aber auch in deren Dichte: Im Putamen Schizophrener lag die Dichte NADPHd-positiver Neurone signifikant unter der bei der gesunden Kontrollgruppe ermittelten Dichte. Neben diesem numerischen Unterschied konnten auch morphologisch auffällige Neurone gefunden werden, die in der gesunden Kontrollgruppe nicht vorhanden waren. Sowohl im Claustrum als auch in der das Claustrum umgebenden weißen Substanz der Capsulae externa et extrema konnten NADPHd-positive Neurone nachgewiesen werden. Die NADPHd-positiven Neurone des Claustrums ließen sich zum Teil nach bereits bestehenden Einteilungen klassifizieren. In den äußeren Kapseln lagen sie zumeist parallel zur Richtung der Fasermassen angeordnet und zählten zu den interstitiellen Zellen der weißen Substanz. / The NADPHd-staining is known to stain selectively neurons expressing the neuronal NOS. The staining results are comparable to Golgi impregnation techniques because not only the cell soma is stained but also the dendrites. Thus, morphological and functional aspects can be examined using that techniqe. This method was used to stain, characterize and classify nNOS-positive neurons of the human putamen. Predominantly, interneurons were stained. They displayed a homogenous staining of the cell soma and the dendrites showing clear morphological differences. The interneurons could be classified into 12 different types (NADPHd I to XII) which only partially corresponded to previously described neuron types. Based on this classification system of a healthy brain, it is possible to find abnormalities of NADPHd-positive interneurons in neurodegenerative diseases. In this study, the putamen of three schizophrenic subjects was examined. Differences could not only be found for the morphology of NADPHd-positive interneurons but also for their frequency: The number of NADPHd-positive interneurons was significantly reduced in the putamen of schizophrenics. However, since only three brains of schizophrenics were examined these results can only be judged preleminary. In the claustrum and in the white matter surrounding the claustrum NADPHd-positive neurons were found as well. Regarding the claustrum, the NADPHd-positive neurons fit partially in previous classification systems. The NADPHd-positive neurons of the external capsules were part of the interstitial cells of the white matter.

Precursores neurais originados na zona subventricular (ZSV) de algumas espécies animais possuem uma rota de migração neuronal destinada ao bulbo olfatório principal (BOP), onde os neuroblastos migrantes se diferenciam em interneurônios. Esta corrente migratória é mantida na idade adulta. A compreensão de como se organiza na idade fetal é essencial para a compreensão geral e estabelecimento de novas terapias celulares. O objetivo deste estudo é caracterizar a composição celular e organização morfológica da ZSV e da corrente rostral migratória (CRM) em encéfalos de fetos caninos. A ZSV, CRM e BOP foram obtidos de fetos caninos de aproximadamente 57 dias de idade gestacional. O tecido foi analisado através de coloração de Nissl, método de imunohistoquímica de dupla marcação com duplacortina (DCX), fator de transcrição SOX2, proteína glial fibrilar ácida (GFAP), calbindina (CALB), calretinina (CALR) e tirosina-hidroxilase (TH). Foram feitas a análise relativa da expressão da imunorreatividade e análise quantitativa de colocalização celular, além do método de microscopia eletrônica de transmissão. Os resultados mostram que a ZSV dorsal possui células imunorreativas (ir) para o DCX ao longo da parede ventricular, dispostas tangencialmente e fileiras de células SOX2-ir foram encontradas na mesma orientação. A imunorreatividade de GFAP foi mais forte na ZSV dorsal e as células possuem fibras dirigidas tangencialmente adjacentes ao ventrículo lateral e fibras orientadas radialmente em direção ao córtex. A CRM de feto de cão tem início na ZSV anterior e segue caudalmente ao redor da cabeça do núcleo caudado e desce na vertical até se curvar rostralmente em direção ao BOP onde termina na camada de células granulares (CCG). A CRM tem aparência homogênea e densa e possui células positivas para o DCX nas porções iniciais e para SOX2 e GFAP por toda a extensão. Não houve células positivas para CALB, CALR e TH em nenhuma região da ZSV e CRM. No BOP, os resultados mostraram que a camada glomerular (CG) possui células imunorreativas a CALR, TH, SOX2 e GFAP. Na camada plexiforme externa (CPE) houve células imunorreativas a CALB, CALR, SOX2 e GFAP e na CCG, houve células imunorreativas a CALR, SOX2 e GFAP. Na análise de colocalização, foram encontrados na CG neurônios CALR que colocalizam com células SOX2 e uma baixa colocalização de neurônios TH e células SOX2. Na CPE, foi observado um baixo número de colocalização de neurônios CALR e CALB e na CCG, as células SOX2 colocalizam com os neurônios CALR. As conclusões mostram que o feto de cão possui uma CRM em direção BOP, com imunorreatividade celular para DCX, SOX2 e GFAP na ZSV e CRM e para CALB, CALR, TH, SOX2 e GFAP nas principais camadas do BOP / Neural precursors originated in the subventricular zone (SVZ) of some animal species have a migration route destined for main olfactory bulb (MOB), where migrants neuroblasts differentiate into olfactory interneurons. This migratory stream is maintained in adulthood. Understanding how it is organized in fetal age is essential for general understanding and establishment of new cell therapies. The aim of this study is characterize the cellular composition and morphological organization of the SVZ and rostral migratory stream (RMS) of brains of canine fetuses. The SVZ, RMS and MOB was obtained from canine fetuses of the approximately 57 gestacional days-old. The tissue was analyzed by Nissl staining and by immunohistochemical methods for double labelling with doublecortin (DCX), transcription factor SOX2, glial fibrillary acid protein (GFAP), calbindin (CALB), calretinin (CALR) and tyrosinehydroxylase (TH). Semiquantitative analysis of immunoreactivity and quantitative analysis of colocalization were realized, besides ultrastructural analysis by electron microscopy. The results show that in dorsal SVZ, DCX immunoreactive cells were found along the ventricular wall, arranged tangentially and lines of SOX2 cells were also found in the same orientation. The GFAP immunostaining is stronger in dorsal SVZ with tangentially directed fibers near the lateral ventricle and radially oriented fibers toward the cortex. The RMS of dog fetus begins at anterior SVZ and follows caudally around the head of the caudate nucleus and vertically descends to bend rostrally into the MOB, where it ends in the granular cell layer (GCL).The RMS have SOX2 positive cells on entire length, showing a homogeneous appearance and high cell density. There is no positive CALB cells or CALR in any region of the SVZ and RMS. The results of the MOB show that the glomerular layer (GL) there were cells immunoreactive to CALR, TH, SOX2 and GFAP. In the external plexiforme layer (EPL) there were immunoreactive cells for CALR, CALB, SOX2 and GFAP and, the GCL, the prevalence is higher for CALR neurons, SOX2-ir and GFAP-ir cells. In colocalization analysis, they were found a some CALR positive neurons in GL that colabeled with SOX2 cells and a low colocalization of TH neurons and SOX2 cells. In EPL, was observed a low colocalization number of CALR and CALB neurons and in GCL, SOX2 cells colabeled with CALR neurons. The conclusions show that the dog fetus has a RMS directed to the MOB, with cellular immunoreactivity for DCX, SOX2 and GFAP in the ZSV and RMS and cellular immunoreactivity for SOX2 CALB, CALR, TH and GFAP in main olfactory bulb layers

Pendant des décennies, la plasticité synaptique a été considérée comme le substrat principal de la plasticité fonctionnelle cérébrale. Récemment, plusieurs études expérimentales indiquent que des régulations à long terme de l’excitabilité intrinsèque participent à la plasticité dépendante de l’activité. En effet, la modulation des canaux ioniques dépendants du potentiel, lesquels régulent fortement l’excitabilité intrinsèque et l’intégration des entrées synaptiques, a été démontrée essentielle dans les processus d’apprentissage. Cependant, la régulation, dépendante de l’activité, du courant ionique activé par l’hyperpolarisation (Ih) et ses conséquences sur l’induction de futures plasticités reste à éclaircir, tout comme la présence d’une régulation de conductances dépendantes du potentiel dans les neurones inhibiteurs. Dans la première partie de ma thèse, nous caractérisons les mécanismes d’induction et d’expression de la plasticité à long terme de l’excitabilité (LTP-IE) dans les interneurons en panier de la région CA1 exprimant la parvalbumine. Dans une seconde partie, le rôle de Ih dans la régulation homéostatique de l’excitabilité neuronale induite par des manipulations de l’activité neuronale dans sa globalité a été étudié. Dans la troisième étude, nous montrons que la magnitude de la Dépression à Long Terme (LTD) détermine le sens de la régulation de Ih dans les neurones pyramidaux de CA1. En conclusion, cette thèse montre qu’à la fois dans les neurones excitateurs et inhibiteurs, les régulations des conductances dépendantes du potentiel aident à maintenir une relative stabilité dans l’activité du réseau. / Synaptic plasticity has been considered for decades as the main substrate of functional plasticity in the brain. Recently, experimental evidences suggest that long-lasting regulation of intrinsic neuronal excitability may also account for activity-dependent plasticity. Indeed, voltage-dependent ionic channels strongly regulate intrinsic excitability and inputs integration and their regulation was found to be essential in learning process. However, activity-dependent regulation of the hyperpolarization-activated ionic current (Ih) and its consequences for future plasticity remain unclear, so as the presence of any voltage-dependent conductances regulation in inhibitory neurons. In the first part of this thesis, we report the characterization of the induction and expression mechanisms of Long-Term Potentiation of Intrinsic Excitability (LTP-IE) in CA1 parvalbumin-positive basket interneurons. In a second part, the role of Ih in the homeostatic regulation of intrinsic neuronal excitability induced by global manipulations of neuronal activity was reported. In the third experimental study, we showed that the magnitude of Long-term Depression (LTD) determines the sign of Ih regulation in CA1 pyramidal neurons. In conclusion, this thesis shows that in both excitatory and inhibitory neurons, activity-dependent regulations of voltage-dependent conductances help to maintain a relative stability in the network activity.

<p>Horizontal cells are retinal interneurons that modulate the output from photoreceptors. Two horizontal cell (HC) subtypes are commonly identified in the vertebrate retina: axon-bearing and axon-less HCs. In this work, we have identified Isl1 as a novel HC marker and demonstrated that Lim1 and Isl1 distinguish axon-bearing and axon-less HCs, respectively. In the chick retina, axon-less HCs are furthermore split into two different subtypes based on the expression of GABA and TrkA.</p><p>We have demonstrated that during early chick retinogenesis, HCs expressing either Lim1 or Isl1 are generated consecutively as two equally large sub-groups at different time points. Moreover, these newborn HCs undertake an unexpected bi-directional migration before settling in their final laminar position. Different HC subtypes complete this migration at different times.</p><p>We investigated the role of activin signaling during HC subtype generation. Activin or its inhibitor follistatin was administrated during the main phase of HC generation and analyzed when HCs had completed migration. Activin caused a significant decrease in both HC subtypes and decreased the proliferation of retinal precursor cells. Follistatin increased the number of late born (Isl1+) HCs, which migrated to the HC-layer during a prolonged migration period. Both treatments affected retinal histology, but only activin influenced the generation of retinal populations other than HCs. These effects were most likely mediated by altered proliferation in certain retinal precursor cells.</p><p>The data on HC subtype ratios, birth-dates, migration, apoptosis and extrinsic activin modulation favor a scenario where the mature proportions of HC subtypes are generated sequentially from a specific HC-precursor cell lineage early in development and remain stable thereafter. These proportions are not adjusted by apoptosis, but rather by the combined actions of transcription factors and extrinsic signaling. Our studies on HC subtypes and their development promises to facilitate future studies on HC development, evolution and function.</p>

Horizontal cells are retinal interneurons that modulate the output from photoreceptors. Two horizontal cell (HC) subtypes are commonly identified in the vertebrate retina: axon-bearing and axon-less HCs. In this work, we have identified Isl1 as a novel HC marker and demonstrated that Lim1 and Isl1 distinguish axon-bearing and axon-less HCs, respectively. In the chick retina, axon-less HCs are furthermore split into two different subtypes based on the expression of GABA and TrkA. We have demonstrated that during early chick retinogenesis, HCs expressing either Lim1 or Isl1 are generated consecutively as two equally large sub-groups at different time points. Moreover, these newborn HCs undertake an unexpected bi-directional migration before settling in their final laminar position. Different HC subtypes complete this migration at different times. We investigated the role of activin signaling during HC subtype generation. Activin or its inhibitor follistatin was administrated during the main phase of HC generation and analyzed when HCs had completed migration. Activin caused a significant decrease in both HC subtypes and decreased the proliferation of retinal precursor cells. Follistatin increased the number of late born (Isl1+) HCs, which migrated to the HC-layer during a prolonged migration period. Both treatments affected retinal histology, but only activin influenced the generation of retinal populations other than HCs. These effects were most likely mediated by altered proliferation in certain retinal precursor cells. The data on HC subtype ratios, birth-dates, migration, apoptosis and extrinsic activin modulation favor a scenario where the mature proportions of HC subtypes are generated sequentially from a specific HC-precursor cell lineage early in development and remain stable thereafter. These proportions are not adjusted by apoptosis, but rather by the combined actions of transcription factors and extrinsic signaling. Our studies on HC subtypes and their development promises to facilitate future studies on HC development, evolution and function.

Noise-like activity (NLA) refers to spontaneous subthreshold fluctuations in membrane potential. In this thesis, we examine the role that synaptic channel fluctuations play in contributing to NLA by comparing a detailed biophysical model to experimental data from whole-intact hippocampal interneurons. To represent the contribution from synaptic channel fluctuations, we switch the synapses in the model from traditional to Markovian formalisms and demonstrate statistically relevant increases the standard deviation; power-law scaling exponent; and power spectral density in the 5-100 Hz and 1-5 kHz ranges. However, while synaptic channel fluctuations have a definite effect, we found that they were significantly more subtle than the synaptic response to network activity. This indicates that synaptic channel fluctuations do indeed play a significant role in subthreshold noise, but, overall, synaptic NLA is dominated by the synaptic response to presynaptic network activity.

Noise-like activity (NLA) refers to spontaneous subthreshold fluctuations in membrane potential. In this thesis, we examine the role that synaptic channel fluctuations play in contributing to NLA by comparing a detailed biophysical model to experimental data from whole-intact hippocampal interneurons. To represent the contribution from synaptic channel fluctuations, we switch the synapses in the model from traditional to Markovian formalisms and demonstrate statistically relevant increases the standard deviation; power-law scaling exponent; and power spectral density in the 5-100 Hz and 1-5 kHz ranges. However, while synaptic channel fluctuations have a definite effect, we found that they were significantly more subtle than the synaptic response to network activity. This indicates that synaptic channel fluctuations do indeed play a significant role in subthreshold noise, but, overall, synaptic NLA is dominated by the synaptic response to presynaptic network activity.

This dissertation creates practical methods for Poincaré return mappings of individual and networked neuron models. Elliptic bursting models are found in numerous biological systems, including the external Globus Pallidus (GPe) section of the brain; the focus for studies of epileptic seizures and Parkinson's disease. However, the bifurcation structure for changes in dynamics remains incomplete. This dissertation develops computer-assisted Poincaré ́maps for mathematical and biologically relevant elliptic bursting neuron models and central pattern generators (CPGs). The first method, used for individual neurons, offers the advantage of an entire family of computationally smooth and complete mappings, which can explain all of the systems dynamical transitions. A complete bifurcation analysis was performed detailing the mechanisms for the transitions from tonic spiking to quiescence in elliptic bursters. A previously unknown, unstable torus bifurcation was found to give rise to small amplitude oscillations. The focus of the dissertation shifts from individual neuron models to small networks of neuron models, particularly 3-cell CPGs. A CPG is a small network which is able to produce specific phasic relationships between the cells. The output rhythms represent a number of biologically observable actions, i.e. walking or running gates. A 2-dimensional map is derived from the CPGs phase-lags. The cells are endogenously bursting neuron models mutually coupled with reciprocal inhibitory connections using the fast threshold synaptic paradigm. The mappings generate clear explanations for rhythmic outcomes, as well as basins of attraction for specific rhythms and possible mechanisms for switching between rhythms.

<p>The basal ganglia form an important structure centrally placed in the brain. They receive input from motor, associative and limbic areas, and produce output mainly to the thalamus and the brain stem. The basal ganglia have been implied in cognitive and motor functions. One way to understand the basal ganglia is to take a look at the diseases that affect them. Both Parkinson's disease and Huntington's disease with their motor problems are results of malfunctioning basal ganglia. There are also indications that these diseases affect cognitive functions. Drug addiction is another example that involves this structure, which is also important for motivation and selection of behaviour.</p><p>In this licentiate thesis I am laying the groundwork for a detailed model of the striatum, which is the input stage of the basal ganglia. The striatum receives glutamatergic input from the cortex and thalamus, as well as dopaminergic input from substantia nigra. The majority of the neurons in the striatum are medium spiny (MS) projection neurons that project mainly to globus pallidus but also to other neurons in the striatum and to both dopamine producing and GABAergic neurons in substantia nigra. In addition to the MS neurons there are fast spiking (FS) interneurons that are in a position to regulate the firing of the MS neurons. These FS neurons are few, but connected into large networks through electrical synapses that could synchronise their effect. By forming strong inhibitory synapses on the MS neurons the FS neurons have a powerful influence on the striatal output. The inhibitory output of the basal ganglia on the thalamus is believed to keep prepared motor commands on hold, but once one of them is disinhibited, then the selected motor command is executed. This disinhibition is initiated in the striatum by the MS neurons.</p><p>Both MS and FS neurons are active during so called up-states, which are periods of elevated cortical input to striatum. Here I have studied the FS neurons and their ability to detect such up-states. This is important because FS neurons can delay spikes in MS neurons and the time between up-state onset and the first spike in the MS neurons is correlated with the amount of calcium entering the MS neuron, which in turn might have implications for plasticity and learning of new behaviours. The effect of different combinations of electrical couplings between two FS neurons has been tested, where the location, number and strength of these gap junctions have been varied. I studied both the ability of the FS neurons to fire action potentials during the up-state, and the synchronisation between neighbouring FS neurons due to electrical coupling. I found that both proximal and distal gap junctions synchronised the firing, but the distal gap junctions did not have the same temporal precision. The ability of the FS neurons to detect an up-state was affected by whether the neighbouring FS neuron also received up-state input or not. This effect was more pronounced for distal gap junctions than proximal ones, due to a stronger shunting effect of distal gap junctions when the dendrites were synaptically activated.</p><p>We have also performed initial stochastic simulations of the Ca²⁺-calmodulin-dependent protein kinase II (CaMKII). The purpose here is to build the knowledge as well as the tools necessary for biochemical simulations of intracellular processes that are important for plasticity in the MS neurons. The simulated biochemical pathways will then be integrated into an existing model of a full MS neuron. Another venue to explore is to build striatal network models consisting of MS and FS neurons and using experimental data of the striatal microcircuitry. With these different approaches we will improve our understanding of striatal information processing.</p>