Thèse (M.Sc.)--Université Laval, 2002. / Certaines légendes d'ill. sur f. opposé, avec foliation. Bibliogr.: f. 58-62. Publié aussi en version électronique.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Christine L. Duvauchelle. Vita. Includes bibliographical references.

Thesis (Ph.D.)--Boston University. / The literature concerning the physiology of the mammalian adrenal cortex is voluminous. However, little has been reported on the physiology of the adrenal cortex of the hamster, Mesocricetus auratus. The present investigation of the effects of adrenalectomy in the hamster was initiated in order that fundamental data such as survival time, electrolyte levels, and changes in estrus cycle of the female could be determined. Since the golden hamster is being used more and more as a laboratory animal, this data would serve as a basis for further investigation. All results obtained in the study of the hamster are compared and contrated to those reported for the rat, the most commonly used laboratory animal in endocrinological investigation. A great many phenomena have been observed by endocrinologists which have demonstrated an apparent interrelationship between the adrenal cortices and gonads of mammals. These phenomena are so numerous that Parkes (1945) was forced to adopt an artificial classification of these interrelationships in orer to review the field with some order and clarity. The effects of adrenalectomy in the hamster were such that it was felt that in this study greater emphasis should be placed on the interrelationships between the gonads and the adrenal cortices than on any other aspect of the adrenal cortical physiology of the animals. It was hoped thereby that the mechanisms involved in these interrelationships would be further elucidated. [Truncated]

Thesis (Ph.D.)--Boston University / The present research stemmed from (a) Mayer's finding that there is no generalization between contralateral sites in the visual cortex of the albino rat (when the sites were stimulated by way of implanted electrodes, one being used as a conditioned stimulus, the other as a test stimulus in order to measure the extent of generalization); (b) anatomical data on the visual cortex, e.g., Nauta and Bucher's finding of rich inter-connections among the cells of the visual cortex of the same side (in the rat), and similar findings by Sholl with regard to the cat; and (c) the work of Myers, who found (with cats) that interocular transfer always appears unless both the posterior corpus callosum and the decussating fibers of the optic chiasm are cut. If (1) generalization between the activity of different parts of the brain on intact neural inter-connections between these areas (as suggested by Myers' research) and (2) cells in the ipsilateral visual cortex of rats are richly interconnected (as Nauta and Bucher,report}, then one should expect substantial generalization from one site in the visual cortex to another on the same side [TRUNCATED].

MRI provides a powerful tool to investigate brain structure in living humans. However a major challenge is interpreting the biological underpinnings of changes at this scale. This dissertation describes investigations into the problem of linking microscale post mortem cortical cytoarchitecture with millimeter-scale measures of cortical anatomy accessible through in vivo MRI. Chapter 1 introduces the problem and previous work done to address it. The following two chapters apply classical atlases of cortical cytoarchitecture to understanding morphological changes both in health (Chapter 2) and in disease (Chapter 3). Chapter 2 demonstrates that sensory processing hierarchies exhibit increasing gradients of cortical thickness, related to changes in cortical cytoarchitecture. In Chapter 3, cytoarchitectonically described differences in gyral and sulcal laminar structure were used to create markers of laminar change from MRI changes in schizophrenia. Classical measurements of histology have limitations; they are observer dependent, two-dimensional with limited coverage of the cortex. To address these issues, Chapters 4-6 document work carried on BigBrain, a 3D 20$\mu$m resolution histological dataset. I created a high-resolution 3D atlas of laminar cytoarchitecture, which was mapped to MRI-compatible cortical surface reconstructions. Chapter 4 records the development of an automated 1D profile-based approach to laminar analysis, revealing basic principles of cortical cytoarchitecture. In Chapter 5 this approach was extended to identify 6 cortical layers throughout the isocortex. These tools can be used to segment 1D cortical intensity profiles derived from any modality. In Chapter 6, the analysis of cortical gradients initially identified using MRI cortical thickness in Chapter 2 was replicated and extended using novel histological data. First histological cortical thicknesses were tested for the same patterns organization measured on in vivo MRI in Chapter 2. These analyses were extended to test which layers contributed most to overall thickness. High-resolution, complete maps of cortical cytoarchitecture mapped to MRI-template cortical surface reconstructions, are a powerful tool and dataset for the neuroimaging community. They offer new possibilities for linking cortical microstructure to in vivo neuroimaging.

The pedunculopontine tegmental nucleus (PPTg) has been argued to be involved in mediating neural processing relating to executive functions (Winn, 1998). Since it shares connections with fronto-striatal circuitry this proposal is not surprising. However, research examining the functions of structures within this system has frequently ignored the contribution of PPTg. The delayed spatial win-shift (DSWS) task is a task that measures spatial working memory and, as such, has been used by Phillips and colleagues to reveal the involvement of ventral striatal structures in this form of "executive" behaviour. This suggests that structures interconnected with PFC share in some way frontal functions. As might be expected from its connections, the involvement of PPTg in the same task has also been demonstrated (Keating & Winn, 2001). The current research was designed to assess further the involvement of PPTg in the DSWS task, and to compare this directly to the involvement of prefrontal cortex (PFC). In order to achieve this, rats with excitotoxic lesions of PPTg and medial PFC were assessed on the DSWS task, in addition to rats with crossed unilateral disconnection of medial PFC/PPTg. Statistically, results demonstrated both PPTg and medial PFC lesions produced similar impairments in the test phase of DSWS, characterised by increased errors, earlier error occurrence, and slower latencies. In contrast, disconnection lesions of medial PFC/PPTg produced an impairment that was fundamentally different. It was concluded that while this supports the importance of PPTg functioning within fronto-striatal systems, the pattern of impairment shown by disconnected rats suggested that this function may not be executive per se but might be necessary for executive functions to influence behaviour.

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No description available.

The primary auditory cortex (area AI) plays an important role in the localization of static sound sources. However, little is known concerning how it processes information about sound source motion. This study was undertaken to investigate the responses of single neurons in the primary auditory cortex of the cat to correlates of auditory motion in space. Diotic and dichotic changes in sound intensity presented through earphones simulated auditory motion in four directions: toward and away from the receiver along the midline, into the ipsilateral hemifield and into the contralateral hemifield. Different rates of intensity change simulated sound source velocity. Results indicate that AI neurons can be highly selective to intensity correlates of auditory motion. Three major classes of neurons were encountered: neurons sensitive to motion toward or away from the receiver, neurons sensitive to ipsilateral- or contralateral-directed motion, and monaural-like neurons. The different classes of direction-selective neurons were spatially segregated from each other and appeared to occur in clusters or columns in the cortex. In addition to their selectivity for different directions of simulated sound source motion, AI neurons also responded selectively to the rate and excursion of intensity changes, a correlate of sound source velocity. The major determinants of direction and velocity selectivity were interactions between the following response properties of AI neurons: binaural interaction type, ear dominance, on/off responses, and monotonicity of rate/intensity function. These findings suggest that neural processing of auditory motion may involve neural mechanisms distinct from those involved in static sound localization, and indicate that some neurons in the primary auditory cortex may be part of a specialized motion-detecting mechanism in the auditory system. / Arts, Faculty of / Psychology, Department of / Graduate

The posterior parietal cortex (PPC) is a cortical region receiving inputs from different sensory modalities which has been shown to subserve a visuospatial function. The potential contribution of PPC in audiospatial behaviours and recognition of amodal spatial correspondences were postulated and assessed in the present study. Adult male Long- Evans rats received PPC lesions by aspiration, and they were compared to sham operated control rats on three behavioural tasks. In the Morris water maze, the rats had to learn to use the distal visual cues to locate an escape platform hidden in the pool. In an open field task, the rats were assessed on their reactions to a spatial relocation of a visual or an auditory object. In a spatial cross-modal transfer (CMT) task (Tees & Buhrmann, 1989), rats were trained to respond to light signals using spatial rules, and were then subjected to transfer tests using comparable sound signals. Results from the Morris water maze, the open field, and the initial training phase of the spatial CMT task confirmed a visuospatial deficit in PPC lesioned rats. However, if given sufficient training, PPC lesioned rats could learn the location of a hidden platform in the Morris water maze, and they could also acquire spatial rules in the CMT task. Such results indicated that the visuospatial deficits in PPC lesioned rats were less severe than previously thought. On the other hand, a persistent navigational difficulty characterized by a looping pattern of movement was observed in the PPC lesioned rats in the Morris water maze. Results from the open field indicated that PPC was less involved in audiospatial behaviours. Moreover, results also indicated that PPC was not necessary for spatial CMT. Hence, data from the present study did not support the idea that PPC played an essential role in supramodal spatial abilities in the rats. Instead, data from the spatial CMT task seemed to imply a role of PPC in managing conflicting spatial information coming from different sensory modalities. / Arts, Faculty of / Psychology, Department of / Graduate