Les travaux de cette thèse ont investigué les effets de plasticité induits au niveau sous-cortical : à long terme, par l'étude des effets de l'expertise (linguistique et musicale) et à court terme par l'étude des effets attentionnels. Notre hypothèse était que l'expertise linguistique renforce l'encodage automatique des sons natifs au niveau des indices linguistiques les plus importants. Les réponses complexes du tronc cérébral se sont avérées plus robustes pour les sons natifs avec un renforcement spécifique de l'encodage des fréquences formantiques qui jouent un rôle important dans la discrimination des phonèmes, ce qui confirme l'hypothèse de départ. Nous avons montré que les différences d'expertise linguistique sont compensées par la pratique musicale grâce à un renforcement de l'encodage neuronal des indices linguistiques importants (formants). La comparaison des réponses neuronales recueillies en condition d'écoute passive et active (tapping) a révélé une représentation de la fréquence fondamentale plus robuste lors de l'écoute active des sons, confirmant l'influence des processus top-down sur l'encodage sous-cortical des sons de parole. En entraînant l'attention au rythme d'un stimulus sur deux via une tâche de tapping, nous avons observé une modulation significative de la représentation du son en fonction de la phase du tapping, révélant ainsi les effets d’une dynamique oscillatoire (attentionnelle) au niveau de la voie auditive sous-corticale. En conclusion, ce travail de thèse a permis de révéler la nature dynamique de la perception auditive, en montrant une modulation de l'encodage des sons au niveau sous-cortical à plusieurs échelles. / The work of this thesis focused on the effects of plasticity at the brainstem level: over a long-timescale, by studying experience-dependent plasticity (linguistic and musical experience) and over a short-timescale, by studying the effect of attention. We hypothesized that linguistic experience would strengthen the automatic processing of native sounds especially on linguistically-relevant dimensions. Neural representations were more robust for the native sounds, with a specific neural enhancement of formant frequencies that play an important role in phonemes discrimination. These findings support the hypothesis that language experience shapes subcortical processing of speech and that this plasticity is sensitive to what is relevant for the listener. These language differences were compensated by musical expertise in non-native musicians by strengthening the encoding of the fundamental frequency and the formants. Comparing neural responses recorded under passive and active (tapping) listening conditions revealed an enhancement of the fundamental frequency during active listening, which is consistent with our prediction that subcortical processing is modulated by top-down processes. Moreover, by entraining the attentional cycles with the phase of the tapping (one out two stimuli), we observed that sound representations were significantly modulated at the same pace, revealing an effect of a fast oscillatory (attentional) dynamic over subcortical auditory processing. To conclude, this work revealed the dynamic nature of auditory perception, showing that subcortical encoding of speech sounds is modulated at different timescales.

As vias suprabulbares assim como núcleos bulbares são de vital importância na modulação cardiovascular. As informações aferentes que chegam ao NTS ascendem a áreas suprabulbares por neurônios noradrenérgicos (NORérgicos) projetando-se principalmente a neurônios pré-autonômicos do núcleo paraventricular do hipotálamo (PVN) em sua maioria ocitocinérgicos (OTérgicos) e vasopressinérgicos (VPérgicos), os quais se projetam a áreas bulbares, fechando um pronto circuito modulatório. É nossa hipótese de trabalho que a hipertensão e/ou o treinamento possam alterar a plasticidade de vias NORérgicas ascendentes as quais, modificando a sinalização aferente, desencadeariam respostas plásticas e funcionais nos neurônios pré-autonômicos do PVN, alterando a modulação cardiovascular nestas situações. Objetivo: estudar o funcionamento da alça suprabulbar de modulação autonômica, avaliando os efeitos sequenciais da hipertensão e do treinamento sobre a sinalização NORérgica ascendente e sobre a plasticidade/atividade de neurônios OTérgicos e VPérgicos do PVN que se projetam a áreas bulbares de controle cardiovascular. Material e Métodos: Protocolo I - Ratos Wistar adultos foram submetidos a T de baixa intensidade (50-60% da capacidade máxima, 5 dias/semana, 1h/dia) ou foram mantidos sendentários (S) por 8 semanas. Após registros da hemodinâmica basal nas semanas 0 (S0=T0), 1 (T1), 2 (T2), 4 (T4) e 8 (T8 e S8) [protocolo Análise Temporal do Treinamento], após 8 semanas de T ou S [para protocolo de lesão seletiva dos neurônios NORérgicos ascendentes pela saporina], e, após 12 semanas de T ou S [para os protocolos SHAM & DAS] os ratos foram eutanasiados para perfusão e fixação do encéfalo. Cortes (30 &um;m) do PVN foram processados para imuno-histoquímica de dupla marcação para OT e dopamina beta-hidroxilase (DBH); imagens foram adquiridas pelo microscópio de fluorescência e confocal e analizadas pelo ImageJ e pelo Imaris, respectivamente. Protocolo II - SHR e WKY (4 semanas de idade no início dos protocolos) foram mantidos sedentários (S) por 8 semanas. Nas semanas experimentais 0, 1, 2, 4 e 8 avaliamos os parâmetros funcionais (valores basais PA e FC) e a imunoistoquímica para VP e DBH; em outro protocolo, realizamos cirurgia Sham ou DAS em animais SHR e Wistar de 41 dias e, após a 13ª semana realizamos estudos funcionais e a análise imunoistoquímica para DBH e VP. Resultados: S determinou no PVN diminuição idade-dependente da OTir em todos os subnúcleos magnocelular (mg), dorsal cap (dc), ventromedial (vm) e posterior (Po), sem alterações significativas de DBHir, e e sem alteração de OTir em aréas bulbares, como DMV, NTS, BVLc e BVLr. T induziu aumento a partir de T2 da síntese de DBH no NTS caudal, intermediário e BVLc, e o T induziu uma diminuição da de DBH no BVLr. No PVNvm e Po houve pronto aumento da OTir em T2 vs S0, e DBHir em T2 vs S0, e aumento de botões sinápticos NORérgicos em neurônios OTérgicos, e bradicardia de repouso entre T4 e T8, sem alterar a pressão arterial. A remoção dos barorreceptores diminuiu a densidade das projeções OTérgica no NTS intermediário, BVLr e no PVN mg, dc, vm e Po, além disso a desnervação sino-aórtica bloqueiou todos os efeitos induzidos pelo treinamento, como o aumento de DBHir no NTS caudal e intermediário, no caudal e rostral VLM e em todo PVN (mg, dc, vm e Po) e impediu o aumento de OTir em ambas as aréas do bulbo quando comparamos DAS -T vs. SHAM-T. No protocolo de saporina, a marcada redução das projeções NORérgicas induziu um significativa queda na síntese de OT em todo o PVN medial e posterior, e o T não foi capaz em aumentar a OTir. Em áreas bulbares, observamos que a DBHx induziu redução na DBHir e de neurônios NORérgicos no NTS caudal e intermediário e BVLc, porém não houve alteração no BVLr em animais S. No grupo DBHx-T houve aumento na síntese proteíca de DBH em todo o bulbo, com exceção do BVLr. Houve uma marcada redução das projeções Otérgicas em todo bulbo, mas não houve alteração da OTir em DBHx, e não foi observado bradicardia de repouso. No protocolo II, WKY e SHR, de 28 dias, possuem PA semelhantes, qual aumentou a partir de S2 apenas em SHR. Animais SHR em fase pré-hipertensiva já possuem FC aumentada, comparado com os WKY, permanecendo com valores superiores até o final do protocolo, em ambas as linhagens houve uma diminuição da FC basal idade depende. Com a técnica de imunoistoquímica de fluorescência, observamos que a VPir é maior em SHR (vs. WKY) durante as 8 semanas de avaliação apenas no PVNmg, no PVNvm e posterior o conteúdo de VP é semelhante entre as duas linhagens em S0 (4 semanas de vida), porém há um aumento significativo e progressivo a partir da S1, apenas em animais SHR. Com os experimentos DAS, observamos a eficácia da cirurgia da remoção dos barorreceptores, devido a ausência da resposta reflexa bradicardica e taquicardia em animais DAS. A DASimpediu o desenvolvimento da hipertensão em animais SHR, assim como houve um bloqueio do aumento de VP em todo PVN medial (mg, vm e dc) e PVN posterior. Conclusão: A observação de que a instalação da bradicardia de repouso (a partir de T4) ocorria após o aumento da densidade de neurônios OTérgicos do PVN que se projetam ao complexo solitário-vagal sugere que alterações induzidas pelo T no controle autonômico do coração são dependentes da maior modulação OTérgica ao complexo solitário-vagal desencadeado pela sinalização NORérgica ascendente. O bloqueio destes efeitos sugere ainda que a sinalização carreada pelos barorreceptores e quimirreceptores periféricos é um fator decisivo em desencadear os efeitos benéficos do T ao sistema cardiovascular. Podemos concluir também que o aumento da PA é acompanhado pelo aumento do conteúdo de VP em áreas que contém neurônios pré-autonômicos, e que os baro e quimiorreceptores desempenham papel chave no desenvolvimento da hipertensão. / Suprabulbar pathways as well as brainstem nuclei are of vital importance in cardiovascular modulation. The afferent information arriving at the NTS ascends to suprabulbar areas by noradrenergic (NORergic) neurons projecting mainly to ocitocinergics (OTergics) and vasopressinergic (VPergicos) pre-autonomic neurons of the Paraventricular Nucleus of Hypothalamus (PVN), which they project to brainstem areas, closing a modulatory circuit. It is our hypothesis that hypertension and / or training may alter the plasticity of ascending NORergic pathways which, by modifying afferent signaling, would trigger plastic and functional responses in pre-autonomic PVN neurons, altering cardiovascular modulation in these situations. Aim: To study the functioning of suprabulbar pathway in autonomic modulation, evaluating the sequential effects of hypertension and training on ascending NORergic signaling and on the plasticity / activity of OTergic and VPergic neurons projecting to cardiovascular control brainstem areas. Methods: Protocol I -Adult Wistar rats were submitted to training (T) of low intensity (50-60% of the maximum capacity, 5 days / week, 1h / day) or were kept in the sententary (S) for 8 weeks. After recording baseline hemodynamics at weeks 0 (S0 and T0), 1 (T1), 2 (T2), 4 (T4) and 8 (T8 and S8) [Time course protocol]; after 8 weeks of T or S [ for protocol of selective lesion of ascending NORergic neurons by saporin]; and after 12 weeks of T or S [for the SHAM & Sino aortic denervation (SAD) protocols] the rats were euthanized for perfusion and fixation of the brain. Slices (30 m) of the PVN were processed for immunohistochemistry double-labelling for OT and dopamine beta-hydroxylase (DBH); images were acquired by fluorescence and confocal microscopy and analyzed by ImageJ and Imaris, respectively. Protocol II - SHR and WKY (4 weeks old at the beginning of protocols) were kept sedentary (S) for 8 weeks. In the experimental weeks 0, 1, 2, 4, 8 we evaluated the functional [parameters baseline arterial pressure (AP) and heart rate (HR)] and immunohistochemistry for VP and DBH; in another protocol, we performed Sham or SAD surgery in SHR and Wistar animals of 41 days. After the 13th week we performed functional studies and immunohistochemical analysis for DBH and VP. Results: Within PVN, there was age-dependent reduction in S group of OT immunoreactivity (ir) all magnocellular (mg), dorsal cap (dc), ventromedial (vm) and posterior (Po) subnuclei, without significant changes in DBHir, and a decrease of OTir in brainstem areas such as DMV, caudal and intermediate NTS, CVLM and RVLM. T induced increase from T2 in the synthesis of DBH in the NTS caudal, intermediate and CVLM, and T induced a decrease in DBH in RVLM. In PVNvm and Po, there was a rapid increase of OTir in T2 vs S0, and DBHir in T2 vs S0, an increase of NORergic synaptic boutons in OTergic neurons and resting bradycardia between T4 and T8, without altering blood pressure. Removal of the baroreceptors decreased the density of the OTergic projections in the NTS intermediate, RVLM and in the PVN mg, dc, vm and Po. Furthermore sino-aortic denervation blocked all training-induced effects, such as increased DBHir in the caudal and intermediate NTS, within caudal and rostral VLM and in the whole PVN (mg, dc, vm and Po) and prevented the increase of OTir in both areas of the brainstem when we compared SAD-T vs. SHAM-T. In the saporin protocol, the marked reduction of the NORergic projections induced a significant decrease in OT synthesis throughout the medial and posterior PVN, and the T was not able to increase the OTir. In the S group on the brainstem areas, we observed that DBHx induced reduction in DBHir and NORergic neurons in the caudal and intermediate NTS and CVLM, but there was no change in RVLM. In the DBHx-T group there was an increase in protein synthesis of DBH in the whole brainstem, with the exception of RVLM. There was a marked reduction of the OTergics projections in every brainstem, but there was no change of OTir in DBHx, and there was no resting bradycardia. In protocol II, WKY and SHR, of 28 days, have similar PA, which increased from S2 only in SHR. SHR animals in the prehypertensive phase already have HR increased, compared with WKY, remaining with higher values until the end of the protocol, in both strain there was a decrease in HR baseline age dependent. With the fluorescence immunohistochemistry technique, we observed that VPir is higher in SHR (vs. WKY) during the 8-week evaluation only in PVNmg, in PVNvm and posterior the VP content is similar between the two strains in S0 (4 weeks of life), but there is a significant and progressive increase from S1, only in SHR animals. With the SAD experiments, we observed the efficacy of baroreceptor removal surgery, due to the absence of bradycardic and tachycardia reflex response in SAD animals. SAD prevented the development of hypertension in SHR animals, as well as a blockade of the increase of VP in all medial PVN (mg, vm and dc) and posterior PVN. Conclusion: The observation that the installation of resting bradycardia (from T4) occurred after increasing the density of PVN OTergic neurons projecting to the solitary-vagal complex suggests that T-induced changes in the autonomic control of the heart are dependent of the greater modulation OTergic to the solitary-vagal complex triggered by ascending NORergic signaling. The blockade of these effects also suggests that the signaling carried by the baroreceptors and peripheral chemoreceptors is a decisive factor in triggering the beneficial effects of T on the cardiovascular system. We can also conclude that increased BP is accompanied by increased VP content in areas containing pre-autonomic neurons, and that baro and chemoreceptors play a key role in the development of hypertension.

Introdução: Os limiares do potencial evocado auditivo de estado estável (PEAEE) em neonatos e lactentes até o sexto mês de vida auxiliam a predizer os limiares psicoacústicos em um período que os mesmos não respondem precisamente a testes comportamentais. Objetivo: Caracterizar os limiares dos PEAEE relacionadas à idade em neonatos e lactentes a termo, a fim de averiguar a influência do processo maturacional na resposta elétrica do sistema auditivo. Metodologia: Estudo transversal, no qual foram avaliados 60 neonatos e lactentes divididos em três grupos: GI - zero a um mês e 29 dias, n=20; GII - dois a três meses e 29 dias, n=20; GIII - quatro a seis meses, n=20. O PEAEE foi pesquisado utilizando-se tons puros nas frequências portadoras de 0,5, 1, 2 e 4 kHz modulados 100% em amplitude e 20% em frequência, com modulação de 91,406, 93,750, 96,094 e 98,437 Hz, respectivamente, na intensidade variando de 60 a 0 dB NA, apresentados por meio de fones de inserção ER-3A, de forma simultânea e monoaural; eletrodos em Fz (ativo), Oz (referência) e Fpz (terra); ganho de 50000, filtro passa banda 1-300 Hz, 6 dB/oitava. O Real-Ear to Dial Difference (REDD) foi mensurado no conduto auditivo externo (CAE) usando-se um microfone sonda de silicone do equipamento Hearing aid Analyzer FONIX FP 35 (Frye Electronics) . Resultados: Houve diferença estatisticamente significante entre os grupos para os valores de REDD apenas na frequência de 4 kHz, o que não foi observado para os limiares dos PEAEE. Com relação à variável frequência portadora, observou-se diferença significante tanto para o REDD quanto para o PEAEE, com associação entre os mesmos, ou seja, os limiares dos PEAEE decresceram para o intervalo de frequência de 0,5 a 2,5 kHz e cresceram quando a frequência aumentou para 4 kHz ocorrendo o inverso no REDD. Conclusão: A caracterização dos limiares dos PEAEE nos primeiros seis meses de vida demonstrou que um mesmo limiar pode ser utilizado como referência de normalidade para esta faixa etária, com valores distintos para as diferentes frequências portadoras. A influência da amplificação do CAE nos limiares dos PEAEE deve ser considerada, havendo a possibilidade de a mesma mascarar a influência do processo maturacional na resposta elétrica do sistema auditivo. / Introduction: The thresholds of the auditory steady-state evoked potentials (ASSEP) in newborns and infants up to the sixth month of life help to predict the psychoacoustic thresholds in a period in which they do not precisely respond to behavioral tests. Objective: To characterize the thresholds of ASSEP related to age in term newborns and infants, so as to verify the influence of the maturational process on the hearing systems electric response. Methodology: A cross-sectional study which assessed 60 newborns and infants divided into three groups: GI - zero to a month and 29 days, n=20; GII two to three months and 29 days, n=20; GIII four to six months, n=20. The ASSEP research used pure tones in the carrier frequencies of 0,5, 1, 2 and 4 kHz modulated 100% in amplitude and 20% in frequency, with a modulation of 91,406, 93,750, 96,094 and 98,437 Hz, respectively, in the intensity, ranging from 60 to 0 dB NA, presented through ER-3A insertion phones, simultaneous and mono-aurally; electrodes in Fz (active), Oz (reference) and Fpz (ground); gain of 50000, pass band filter 1-300 Hz, 6 dB/octave. The Real-Ear to Dial Difference (REDD) was measured in the external auditory canal (EAC) by using a silicone probe microphone of the Hearing aid Analyzer FONIX FP 35 equipment (Frye Electronics) . Results: A statistically significant difference was seen among the groups for REDD values only in the frequency of 4 kHz, but not observed for ASSEP thresholds. In relation to the carrier frequency variable, a significant difference was observed for both REDD and ASSEP, with association among them, that is, the ASSEP thresholds decreased for the frequency interval 0,5 to 2,5 kHz and increased when the frequency was 4 kHz, the opposite occurring for REDD. Conclusion: The characterization of ASSEP thresholds in the first six months of life showed that the same threshold can be used as a normality reference for this age range, with distinct values for the different carrier frequencies. The influence of EAC amplification in the ASSEP thresholds should be taken into account, since it may mask the influence of the maturational process on the auditory systems electric response.

A desnutrição proteico-calórica é um dos maiores problemas de saúde pública no Brasil, especialmente no Nordeste, acometendo, com maior frequência, crianças pré-escolares e determinando possíveis comprometimentos, não só no crescimento ponderal como intelectual e cognitivo, podendo ocasionar déficits irreversíveis, dependendo da sua intensidade e duração. Considerando-se a importância da integridade anatomofisiológica do sistema auditivo periférico e central para o adequado desenvolvimento da plenitude das habilidades auditivas, de linguagem e aquisição de aprendizagem, torna-se fundamental a reflexão sobre os possíveis efeitos deletérios da desnutrição no sistema nervoso auditivo, para que possíveis anormalidades auditivas sejam identificadas e tratadas nessa população. O objetivo deste estudo foi caracterizar as respostas do Potencial Evocado Auditivo de Tronco Encefálico, com estímulos clique e tone burst, em crianças de zero a 60 meses, desnutridas e eutróficas, com função auditiva periférica íntegra, bem como compará-las. Foram examinadas 111 crianças de zero a 60 meses, sendo 57 desnutridas e 54 normonutridas, com avaliação otorrinolaringológica, imitanciometria e Emissões Otoacústicas Evocadas Transientes dentro dos padrões de normalidade. A seguir, os Potenciais Evocados Auditivos do Tronco Encefálico por estímulo clique e tone burst foram registrados. Na análise dos dados, observou-se que as latências das ondas I, III e V e dos interpicos III-V a 80 dBNA com estímulo clique eram significativamente maiores em crianças desnutridas, quando comparadas às eutróficas, assim como do intervalo I-V na faixa etária de 0-24 meses. As latências da onda V nas intensidades de 60, 40 e 30 dBNA também foram significativamente maiores em crianças desnutridas. Na análise do Potencial Evocado Auditivo de Tronco Encefálico tone burst, a onda V mostrou latência maior nas crianças desnutridas em todas as intensidades e frequências testadas, entretanto, essa diferença nas crianças de zero a 24 meses só foi significativa em 2000 Hz; nas de 25 a 60 meses foi significativa apenas em 500 Hz a 80 dBNA, em 2000 Hz a 30 dBNA e em 4000 Hz a 60, 40 e 30 dBNA. Crianças desnutridas apresentaram alterações no Potencial Evocado Auditivo do Tronco Encefálico, caracterizadas pelo atraso na latência das ondas e dos intervalos interpicos, quando comparadas às eutróficas, sugerindo déficit de condução na via auditiva. Sendo assim, concluiu-se que a desnutrição pode provocar efeitos deletérios no processo de desenvolvimento e maturação do sistema nervoso auditivo. / Introduction: protein calorie malnutrition is one of the biggest public health problems in Brazil, especially in the northeast, affecting most often preschool children and determining possible compromises not only the weight growth but also intellectual and cognitive development, which may cause irreversible deficit, depending on its intensity and duration. Considering the importance of anatomical and physiological integrity of the peripheral and central auditory system for the proper development of the fullness of auditory skills, language, and acquisition of learning, this brings out a fundamental reflection over the possible deleterious effects of malnutrition in the auditory nervous system, so that possible auditory abnormalities are identified and addressed in this population. The objective of this study was to characterize the response of the auditory brainstem evoked potentials test with click and tone burst stimuli in malnourished and eutrophic children from 0 to 60 months of age, with normal peripheral auditory function, as well as to compare them. Casuistic and Method: One hundred and eleven children from 0 to 60 months of age were examined, being 57 malnourished and 54 eutrophic. They underwent ENT evaluation, including impedanciometry and transient evoked otoacoustic emission (TEOAE) being those within normal ranges. Folowing, the auditory brainstem evoked potentials with click and tone burst were registered in the intensity of 80, 60, 40 and 30 dBNA. Results: In the analysis of the results, the latencies of waves I, III and V and the interpeak III-V 80 dBNA latencies with click stimuli were significantly higher in all malnourished children, when compared to the eutrophic children, as well as I-V interpeak interval in the 0-24 months of age group. The wave V in 60, 40 and 30 dBNA latencies were also significantly higher in malnourished children. In the analysis of the tone burst auditory brainstem evoked potentials wave V latency showed higher in malnourished children in all intensities and frequencies tested, however this difference in children from 0-24 months were significant only in 2000 Hz; in children from 25-60 months were significant only at 500 Hz to 80 dBHL, in 2000 Hz at 30 dBHL and 4000 Hz to 60, 40, and 30 dBHL.Malnourished children present a higher range of alterations in auditory brainstem evoked potentials, characterized by delayed wave latencies and higher interpeak intervals when compared with eutrophic children, suggesting a peripheral and central deficit in the auditory pathway, thus concluded that malnutrition may cause deleterious effects in the development and maturation of the auditory nervous system.

This work seeks to more fully characterize how the representation of English vowels changes with increasing sound level in the frequency following response (FFR) of normal-hearing adult subjects. It further seeks to help inform the design of brain-computer interfaces (BCI) that exploit the FFR for hearing aid (HA) applications. The results of three studies are presented, followed by a theoretical examination of the potential BCI space as it relates to HA design. The first study examines how the representation of a long vowel changes with level in normal hearing subjects. The second study examines how the representation of four short vowels changes with level in normal hearing subjects. The third study utilizes machine learning techniques to automatically classify the FFRs captured in the second study. Based in-part on the findings from these three studies, potential avenues to pursue with respect to the utilization of the FFR in the automated fitting of HAs are proposed. The results of the first two studies suggest that the FFR to vowel stimuli presented at levels in the typical speech range provide robust and differentiable representations of both envelope and temporal fine structure cues present in the stimuli in both the time and frequency domains. The envelope FFR at the fundamental frequency (F0) was generally not monotonic-increasing with level increases. The growth of the harmonics of F0 in the envelope FFR were consistent indicators of level-related effects, and the harmonics related to the first and second formants were also consistent indicators of level effects. The third study indicates that common machine-learning classification algorithms are able to exploit features extracted from the FFR, both in the time and frequency domains, in order to accurately predict both vowel and level classes among responses. This has positive implications for future work regarding BCI-based approaches to HA fitting, where controlling for clarity and loudness are important considerations.

Recent studies have shown that the Sudden Infant Death Syndrome (SIDS) is related to abnormal control of respiration (Ischemic degeneration of the brainstem may play an important role in altered respiratory control leading to death). In our studies we have examined brainstem ganglioside compositions in samples derived from SIDS victims and appropriate controls. Gangliosides are acidic glycosphingolipids that contain sialic acid. The high concentration of gangliosides in the central nervous system (CNS) implies that these lipids play an important role in CNS function. Some studies have indicated that gangliosides may function as receptor site determinants or modifiers, and in neural transmission. In our studies we used the Tettamanti, et al methodology to extract gangliosides, and High Performance Thin Layer Chromatography (HPTLC) and laser densitometry techniques for ganglioside analysis. The results of these analyses are being employed to establish lipid profile patterns to determine if there are significant variations in these lipid patterns between SIDS and control groups.

There is much evidence supporting the idea that pelagic larvae of coral reef fishes are active participants in their dispersal and return to a reef, however, the mechanisms used to navigate are still uncertain. It has been proposed that sensory cues, such as hearing, play a role. Sound is a potentially important cue for organisms in marine environments, especially in noisy environments like coral reefs. Sensory organs, including otolithic organs, of most coral reef fish form within the first few days of life. The auditory brainstem response (ABR) technique was used to measure hearing on a wide size range of sergeant majors (Abudefduf saxatilis). Complete audiograms were measured for 32 fish ranging in size from 11-121 mm. Significant effects of standard length on hearing thresholds at 100 and 200 Hz were detected. At these lower frequencies, thresholds increased with an increase in size. All fish were most sensitive to the lower frequencies (100-400 Hz). The frequency range that fish could detect sounds was dependent upon the size of the fish; the larger fish (>50mm) were more likely to respond to higher frequencies (1000-1600 Hz). A. saxatilis have poor hearing sensitivity in comparison to audiograms of other hearing generalists including other species of Pomacentrids. Due to the high hearing thresholds found in this study in comparison to recorded ambient reef noise, it is unlikely that sound plays a significant role in the navigation of the pelagic larvae of sergeant majors to the return of the reef from large distances.

Objective: The air conduction click is currently the most widespread stimulus used to estimate the pure tone audiogram as part of auditory brainstem response (ABR) testing. The click is characterized by its broad spectral content and rapid onset, which may not make it the best choice for frequency specificity. An alternative stimulus is a short duration tone burst stimuli with notched noise masking. When obtaining an ABR using standard unmasked tone bursts, the brief stimulus onset may cause spectral splatter producing response contributions from unwanted regions of the cochlea; thus reducing the frequency specificity of the ABR. Notched noise masking used in conjunction with the tone burst ABR, limits the evoked response to those frequencies within the notch, thereby reducing the likelihood of spectral splatter and increasing frequency specificity. The presence of a sloping sensory hearing impairment creates additional difficulties for achieving frequency specificity because of the likelihood that lower frequency cochlea regions, with less sensory damage, will contribute to the evoked response. It is theorized that notched noise masking will reduce the neural contributions from regions of the cochlear outside those within the notch, resulting in more frequency specific results than those achieved with a standard unmasked tone burst stimulus. The present study was designed to investigate the differences in Wave V latency between the notched noise ABR and the standard unmasked tone burst ABR as a measure of frequency specificity. Design: Twenty-five participants with normal hearing in at least one ear and 16 participants with bilateral SNHL participated in this investigation. Each participant was given an audiological evaluation, a click ABR screening to determine neural synchrony, a standard tone burst ABR and a notched noise tone burst ABR. Results: An Analysis of Variance (ANOVA) failed to reveal any significant Wave V latency differences between the ABRs obtained with unmasked tone bursts versus ABRs obtained with a notched noise tone burst. Conclusion: The results of this study do not support the use of notched noise tone bursts for improved ABR frequency specificity. This finding is contrary to previously reported results (Stapells & Picton, 1981), which indicated improved frequency specificity when obtaining a tone burst ABR in notched noise versus a standard unmasked tone burst ABR.

Doctor of Philosophy(PhD) / This thesis addresses the neurochemistry and function of specific nuclei in the autonomic nervous system that are crucial mediators of cardiorespiratory regulation. The primary aim is to build on previous knowledge about muscarinic cholinergic mechanisms within cardiorespiratory nuclei located in the ventrolateral medulla oblongata. The general focus is characterisation of gene expression patterns of specific muscarinic receptor subtypes in central nuclei involved in blood pressure control and respiratory control in normal rats. The findings were subsequently extended by characterisation of muscarinic receptor gene expression patterns in 1) a rat model of abnormal blood pressure control (hypertension) (Chapter 3) 2) a rat model of cholinergic sensitivity (Chapter 5) 3) the rat ventral respiratory group (Chapter 6) The results of a series of related investigations that ensued from the initial aims more finely characterise the neurocircuitry of the ventrolateral medulla, from a specifically cholinoceptive approach. All five muscarinic receptor subtypes are globally expressed in the ventrolateral medulla but only the M2R mRNA was significantly elevated in the VLM of hypertensive animals compared to their normotensive controls and in the VLM of animals displaying cholinergic hypersensitivity compared to their resistant controls. Surprisingly, M2R mRNA is absent in catecholaminergic cell groups but abundant in certain respiratory nuclei. Two smaller projects involving gene expression of other neurotransmitter / neuromodulators expressed in cardiorespiratory nuclei were also completed during my candidature. Firstly, the neurochemical characterisation of enkephalinergic neurons in the RVLM, and their relationship with bulbospinal, catecholaminergic neurons in hypertensive compared to normotensive animals was carried out (Chapter 4). A substantial proportion of sympathoexcitatory neurons located in the RVLM were enkephalinergic in nature. However, there was no significant difference in preproenkephalin expression in the RVLM in hypertensive compared to normotensive animals. Secondly, the identification and distribution of components of the renin-angiotensin aldosterone system (RAAS) within the brainstem, and differences in gene expression levels between hypertensive and normotensive animals was also investigated. The RAAS data was not included in this thesis, since the topic digresses substantially from other chapters and since it is published (Kumar et al., 2006). The mRNA expression aldosterone synthase, mineralocorticoid receptor (MR1), 12-lipoxygenase (12-LO), serum- and glucocorticoid- inducible kinase and K-ras) were found to be present at all rostrocaudal levels of the ventrolateral medulla. Expression of MR1 mRNA was lower in the RVLM of SHR compared with WKY rats and 12-LO mRNA levels were lower in the CVLM in SHR compared with WKY rats. Otherwise, there was no difference in gene expression level, or the method of detection was not sensitive enough to detect differences in low copy transcripts between hypertensive and normotensive animals.

This thesis tests the hypothesis that increased neuronal cell death in SIDS infants is related to the ability of risk factors, such as prone sleeping, to expose infants to intermittent hypercapnic hypoxia (IHH). Based on the hypothesis that the NMDA system is linked to neuronal death, by way of excitotoxicity, correlations were also sought between cell death and changes in NMDA receptor (NR1) expression in brainstem nuclei controlling cardiorespiratory function. The first aim of this study was to verify that increased neuronal cell death occurs in SIDS infants. To verify a piglet model of SIDS risk factors, brainstem changes were examined in piglets exposed to IHH, and comparisons were made to changes seen in SIDS infants. The NMDA receptor was characterised in controls for both the human infant and the piglet groups. Comparisons of neuronal changes were made with SIDS infants, and piglets exposed to IHH. Non-radioactive in-situ hybridisation and immunohistochemistry were performed on formalin fixed and paraffin embedded brainstem tissue to identify markers of cell death (caspase-3, active caspase-3, and TUNEL), and to examine NR1 mRNA and protein expressions. Staining was quantified using computerised image analysis software. Eight nuclei from the brainstem medulla (caudal in piglets, and mid in infants), and two nuclei from the rostral pons (infants) were studied. The first dataset included human infants aged 1-6 months with a diagnosis of SIDS (n=15) or non-SIDS (n=10). The second dataset comprised developing piglets aged 13-14 days, with controls (n=6), against those exposed to IHH for 2 (n=6) or 4 (n=5) days. Increased neuronal cell death was not verified in the SIDS infants, but abnormalities in NR1 expression were present in selected nuclei of the medulla. Piglets exposed to IHH had increased neuronal cell death and changes in NR1 in selected nuclei of the medulla. There was also a positive correlation between increased cell death and high NR1 levels. Preliminary data showed that SIDS infants who usually slept prone had some differences in NR1 compared to those who did not usually sleep prone. From these findings, it was concluded that IHH may underlie the abnormalities in NMDA receptor expression that are present in the brainstem of SIDS infants. Although IHH can induce an increase in neuronal cell death, its significance in the aetiology of SIDS is not known. In piglets, IHH induced cell death correlated with high NMDA expression in some brainstem nuclei, supporting the hypothesis that excitotoxicity may be involved in the mechanism for cell death. Moreover, this thesis presents for the first time, �preliminary pathological proof� of an association between prone sleeping and abnormal NMDA receptor expression in SIDS infants.