The timing of regeneration in the amphibian olfactory system

• Autor(a) principal: Hawkins,Sara Joy
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/15444
• topic: Biologia molecular; Olfato; Células estaminais; Sistema nervoso central - Interacção celular; Circuitos neuronais - Regeneração (Biologia)

Comprehending the mechanisms that make lifelong neurogenesis possible has a clear interest for the better understanding of the basic principles that govern cellular and molecular interactions in the nervous system, as well as a relevant clinical interest. The limited ability of the central nervous system to generate new neurons in order to replace those that have been lost is a formidable obstacle to recovery from neuronal damage caused by injury or neurodegenerative disease. The olfactory system (OS) is an ideal system to study the process of neuronal recovery after injury, as it is known for its lifelong capacity to replenish cells lost during natural turnover, as well as its remarkable ability to regenerate after severe lesion. The olfactory epithelium (OE) shows neurogenesis throughout life. Newly differentiated olfactory receptor neurons (ORNs) are continuously reintegrated into an existing circuitry to maintain the sense of smell. The aim of this thesis is to describe the morphological and functional alterations that occur over time in the OS of larval Xenopus laevis, after transection of the olfactory nerve (ON). Results obtained using immunohistochemistry essays, as well as sensory neuron labeling and calcium imaging techniques, indicate that ORN cell death reaches its peak 48 hours after transection, and that proliferating stem cells found in the basal cell layer of the OE are quickly upregulated after lesion. Supporting cells seem to maintain both morphological and functional integrity after transection of the ON. The OE recovers its original morphological structure 1 week after transection, at which time the first axons reach the olfactory bulb (OB) and begin the process of reinnervation. Spontaneous activity of mitral/tufted cells occurs in the OB during the first weeks after transection but no odor-induced activity is observed. After 3-4 weeks glomerular responses were observed in some animals upon application of stimulus, but the response and glomerular morphology are clearly altered as compared to control. After 6-7 weeks responses seem to have fully recovered, indicating that the OS of larval X. laevis recovers morphologically and functionally 6-7 weeks after ON transection.