Transmissible spongiform encephalopathies (TSEs) or prion diseases are defined by infectivity and by the pathological damage they produce in the central nervous system (CNS), typically involving spongiform degeneration or vacuolation, deposition of abnormal PrP (PrPSc), glial activation and neuronal loss. Much of our understanding of the TSEs has derived from the study of murine scrapie models. The molecular basis of pathological changes is not clear, in particular the relationship between the deposition of PrPSc and neuronal dysfunction. A typical feature of TSE disease is neuronal loss, although the mechanisms leading to this loss are poorly understood. Apoptosis has been proposed as an important mechanism of TSE associated cell death, but which pathways are involved are still to be determined. The main aims of this thesis are to investigate the progression of the characteristic neuropathological changes observed in the TSE infected brain and to analyse the mechanisms involved in neuronal loss. In this study two contrasting scrapie mouse models were used : the ME7/CV model , and the 87V/VM model in which neuronal loss is targeted to different areas of the hippocampus, the CA1, and CA2 respectively. The role of the caspase-dependent pathway of apoptosis in the neuronal loss was investigated. The results of analysis of pro-apoptotic markers of disease in the two scrapie mouse models differed. The results observed in the ME7/CV scrapie mouse model suggest that apoptosis may not be the main mechanism of neuronal loss, whereas the 87V/VM model showed some indication that apoptosis may be involved. Detailed studies in the progression of neurodegenerative changes in the ME7/CV scrapie mouse model revealed that the initial pathological change observed in the hippocampus was the deposition of PrPSc followed by a glial response, spongiform change and subsequent neuronal degeneration. The role of the cytoskeleton and synaptic dysfunction in the neuronal damage observed in the CA1 of the ME7 infected hippocampus was analysed. Cytoskeletal disruption was observed in the post-synaptic dendritic spine, and the apical dendrites of CA1 neurons at 160days, a time point at which neurons are known to be lost. Changes in the expression of the pre-synaptic protein, synaptophysin and the post-synaptic protein PSD-95 were not observed until the terminal stage of disease when the neuronal loss is profound. In conclusion, this research suggests that the mechanisms of neuronal loss may follow different biochemical pathways, which might not necessarily involve an apoptotic mechanism. Cytoskeletal disruption in the post-synaptic dendritic spine plays a major role in the neuronal dysfunction observed in ME7 infected CA1 neurons, although the post synaptic density does not seem to be involved .Pre-synaptic changes and disruption to the innervation of CA1 neurons is not apparent until the end stages of disease. The trigger for this cytoskeletal disruption and the subsequent neuronal loss may be the early deposition of PrPSc in the extracellular space but the precise mechanisms involved are still to be elucidated. The identification of the key events involved in the mechanisms of neruodegeneration in TSE diseases may lead to the development of therapeutic strategies to inhibit the neurodegenerative process.

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O sistema nervoso simpático é escassamente descrito em livros na anatomia veterinária e encontra-se pouca informação a respeito de seu funcionamento em grandes mamíferos. O conceito atual da estrutura e função dos gânglios simpáticos deriva de estudos desenvolvidos no gânglio cervical superior (GCC) em animais de laboratório, devido ao seu grande tamanho, facilidade de acesso e multiplicidade de território de inervação nestas espécies. A ganglionectomia unilateral do GCC causou condição patológica associada à síndrome de Horner com sinais associados à anisocoria, enoftalmia, ptose e hipertermia de orelha. Aplicando-se métodos estereológicos, objetivamos investigar a neuroplasticidade do G CC em condições de exigência funcional em diferentes períodos de tempo. A neuroplasticidade foi investigada em vista dos aspectos morfoquantitativos, tamanho e número total de neurônios. Objetivou-se encontrar variação, ou não, no tamanho dos neurônios, na densidade neuronal, no número de neurônios secundários à ganglionectomia unilateral do GCC. Alterações macroscópicas revelaram um aumento médio de 8%, 3% e 11% em comprimento, largura e espessura para os gânglios operados no grupo I. Para o grupo II encontraram-se aumentos em 4% para comprimento e largura e 5% em espessura, enquanto que para o grupo III, 29% de aumento foram encontrados para comprimento, 4% em largura e 7% em espessura. Os gânglios controle e operados apresentaram diferença significativa (p = 0,0001) na densidade neuronal (Nv). Os gânglios operados apresentaram diminuição na densidade neuronal em média de 89% para o grupo I, 65% para o grupo II e 47% para o grupo III. Esta redução reflete a distribuição heterogênea dos neurônios no gânglio operado. Um aumento no volume neuronal global foi significativamente detectado (p = 0,0001), o gânglio operado apresentou aumentos médios de 13% para o grupo I, 24% para o grupo II e 29% para o grupo III, sugestivo de maior exigência funcional em resposta à ganglionectomia. O numero total de neurônios apresentou diferenças significativas (p = 0,0514) e dois efeitos distinto nos gânglios operados. No grupo I observou-se um aumento de 3% no numero total de neurônios enquanto que uma redução foi determinada para os grupos II (8%) e III (20%). A avaliação global dos resultados leva-nos a inferir duas hipóteses associadas e consecutivas: 1) a hipertrofia neuronal estaria associada a um mecanismo compensatório para a re-inervação contralateral sendo que a maior exigência funcional poderia levar estes neurônios à morte, seguido de hipertrofia de tecido não-neuronal cicatricial refletido na diminuição da densidade neuronal; 2) a hipertrofia neuronal estaria associada a um mecanismo compensatório à morte celular determinada pela maior exigência funcional. As alterações quantitativas principais secundárias à ganglionectomia unilateral do GCC no gânglio remanescente estão associadas à: perda significativa no número total de neurônios a partir da 8ª semana de evolução da doença, perda significativa na densidade neuronal a partir da 8ª semana e aumento significativo na área e volume neuronal. / The sympathetic nervous system is briefly described in veterinary anatomy text-books and there is little information so far concerning its function in large mammal species. The current concept of the structure and function of the sympathetic ganglia is derived from studies on the cranial cervical ganglia (CCG) carried out in laboratory animals due to very attractive characteristics of CCG in these species such as large size, accessibility and multiplicity of target organs. The CCG unilateral ganglionectomy caused a pathological condition associated with Horner´s syndrome which includes anisocoria, enophtalmos, ptosis and increase in the temperature of ear as a result of peripheral vasodilatation. Using stereology-designed methods, we aimed to study CCG neuroplasticity under experimental functional overloading along distinct periods of time. Neuroplasticity was investigated according to morphoquantitative aspects, mostly size and total number of neurons. We wanted to find out whether or not neuron size, numerical density and nerve cell numbers would vary as a result of CCG ganglionectomy. Gross anatomic differences were considered to the increase in the operated ganglia, means of 8%, 3% and 11% for length, width and thickness, respetively in the group I. For group II it was encountered means increases of 4% for length and width and 5% in thickness. Group III showed means values of 29% increase in length, 4% in width and 7% in thickness. Control and operated sheep CCG revealed significant difference (p=0.0001) in the neuronal density (Nv). The operated ganglia revealed reduction in the neuronal density of 89% for group I, 65% for group II and 47% for group III. This reduction in the operated ganglia reflects its inhomogeneous distribution of neurons. An increase in the global neuronal volume was significantly detected (p= 0.0001), the operated ganglia showed increases in the means of 13% for group I, 24% for group II and 29% for group III, suggesting a functional overload response for the unilateral ganglionectomy. The total number of neurons presented significant differences (p = 0.0514) and two distinct effects in the operated ganglia. In the group I, an increase of 3% was encountered meanwhile reduction in the total number was associated to groups II (8%) and group III (20%). An overlook of the results suggests two consecutive and associated hypotheses: 1) the hypertrophy of neurons would be associated to a compensatory mechanism for contralateral re-innervation although the functional overload would drive these neurons to cellular death, followed by hypertrophy of non-neuronal tissue as reflected in the neuronal density; 2) the neuronal hypertrophy would be associated to a compensatory mechanism to cellular death caused by the functional overload The main quantitative changes in the remaining ganglia are: Significant loss in the total number of neurons from the 8th week of evoloution of the disease; Significant decrease in the numerical density (Nv) from the 8th week and significant increase in both neuron area and neuron volume.

O sistema nervoso simpático é escassamente descrito em livros na anatomia veterinária e encontra-se pouca informação a respeito de seu funcionamento em grandes mamíferos. O conceito atual da estrutura e função dos gânglios simpáticos deriva de estudos desenvolvidos no gânglio cervical superior (GCC) em animais de laboratório, devido ao seu grande tamanho, facilidade de acesso e multiplicidade de território de inervação nestas espécies. A ganglionectomia unilateral do GCC causou condição patológica associada à síndrome de Horner com sinais associados à anisocoria, enoftalmia, ptose e hipertermia de orelha. Aplicando-se métodos estereológicos, objetivamos investigar a neuroplasticidade do G CC em condições de exigência funcional em diferentes períodos de tempo. A neuroplasticidade foi investigada em vista dos aspectos morfoquantitativos, tamanho e número total de neurônios. Objetivou-se encontrar variação, ou não, no tamanho dos neurônios, na densidade neuronal, no número de neurônios secundários à ganglionectomia unilateral do GCC. Alterações macroscópicas revelaram um aumento médio de 8%, 3% e 11% em comprimento, largura e espessura para os gânglios operados no grupo I. Para o grupo II encontraram-se aumentos em 4% para comprimento e largura e 5% em espessura, enquanto que para o grupo III, 29% de aumento foram encontrados para comprimento, 4% em largura e 7% em espessura. Os gânglios controle e operados apresentaram diferença significativa (p = 0,0001) na densidade neuronal (Nv). Os gânglios operados apresentaram diminuição na densidade neuronal em média de 89% para o grupo I, 65% para o grupo II e 47% para o grupo III. Esta redução reflete a distribuição heterogênea dos neurônios no gânglio operado. Um aumento no volume neuronal global foi significativamente detectado (p = 0,0001), o gânglio operado apresentou aumentos médios de 13% para o grupo I, 24% para o grupo II e 29% para o grupo III, sugestivo de maior exigência funcional em resposta à ganglionectomia. O numero total de neurônios apresentou diferenças significativas (p = 0,0514) e dois efeitos distinto nos gânglios operados. No grupo I observou-se um aumento de 3% no numero total de neurônios enquanto que uma redução foi determinada para os grupos II (8%) e III (20%). A avaliação global dos resultados leva-nos a inferir duas hipóteses associadas e consecutivas: 1) a hipertrofia neuronal estaria associada a um mecanismo compensatório para a re-inervação contralateral sendo que a maior exigência funcional poderia levar estes neurônios à morte, seguido de hipertrofia de tecido não-neuronal cicatricial refletido na diminuição da densidade neuronal; 2) a hipertrofia neuronal estaria associada a um mecanismo compensatório à morte celular determinada pela maior exigência funcional. As alterações quantitativas principais secundárias à ganglionectomia unilateral do GCC no gânglio remanescente estão associadas à: perda significativa no número total de neurônios a partir da 8ª semana de evolução da doença, perda significativa na densidade neuronal a partir da 8ª semana e aumento significativo na área e volume neuronal. / The sympathetic nervous system is briefly described in veterinary anatomy text-books and there is little information so far concerning its function in large mammal species. The current concept of the structure and function of the sympathetic ganglia is derived from studies on the cranial cervical ganglia (CCG) carried out in laboratory animals due to very attractive characteristics of CCG in these species such as large size, accessibility and multiplicity of target organs. The CCG unilateral ganglionectomy caused a pathological condition associated with Horner´s syndrome which includes anisocoria, enophtalmos, ptosis and increase in the temperature of ear as a result of peripheral vasodilatation. Using stereology-designed methods, we aimed to study CCG neuroplasticity under experimental functional overloading along distinct periods of time. Neuroplasticity was investigated according to morphoquantitative aspects, mostly size and total number of neurons. We wanted to find out whether or not neuron size, numerical density and nerve cell numbers would vary as a result of CCG ganglionectomy. Gross anatomic differences were considered to the increase in the operated ganglia, means of 8%, 3% and 11% for length, width and thickness, respetively in the group I. For group II it was encountered means increases of 4% for length and width and 5% in thickness. Group III showed means values of 29% increase in length, 4% in width and 7% in thickness. Control and operated sheep CCG revealed significant difference (p=0.0001) in the neuronal density (Nv). The operated ganglia revealed reduction in the neuronal density of 89% for group I, 65% for group II and 47% for group III. This reduction in the operated ganglia reflects its inhomogeneous distribution of neurons. An increase in the global neuronal volume was significantly detected (p= 0.0001), the operated ganglia showed increases in the means of 13% for group I, 24% for group II and 29% for group III, suggesting a functional overload response for the unilateral ganglionectomy. The total number of neurons presented significant differences (p = 0.0514) and two distinct effects in the operated ganglia. In the group I, an increase of 3% was encountered meanwhile reduction in the total number was associated to groups II (8%) and group III (20%). An overlook of the results suggests two consecutive and associated hypotheses: 1) the hypertrophy of neurons would be associated to a compensatory mechanism for contralateral re-innervation although the functional overload would drive these neurons to cellular death, followed by hypertrophy of non-neuronal tissue as reflected in the neuronal density; 2) the neuronal hypertrophy would be associated to a compensatory mechanism to cellular death caused by the functional overload The main quantitative changes in the remaining ganglia are: Significant loss in the total number of neurons from the 8th week of evoloution of the disease; Significant decrease in the numerical density (Nv) from the 8th week and significant increase in both neuron area and neuron volume.