Thesis (M.S.)--Ohio University, November, 2006. / Title from PDF t.p. Includes bibliographical references.

Thesis (Ph.D.)--Kent State University, 2007. / Title from PDF t.p. (viewed Jan. 16, 2007) Advisor: Chet C. Sherwood. Includes bibliographical references (p. 165-198)

The spatial arrangement of neuronal responses in primary auditory cortex (A1) has so far been investigated by using microelectrode recording techniques or imaging of the intrinsic signal, which led to controversial results, at present still discussed. On the other hand, two-photon calcium imaging allows us to investigate the cortical functions at an unprecedented level of spatial detail, and has recently offered new insight into the fine-scale organization of frequency responses in A1. In this thesis, I used two-photon calcium imaging to compare, for the first time, the fine-scale cortical representation of sound frequency to that of two other sound features, crucial for survival and communication in all mammals: differences in intensity between the two ears (interaural level differences; ILDs), and frequency modulation (FM). I found that most neurons in layers II-III of the mouse A1 were tuned to ILDs favouring the contralateral ear, but midline and ipsilateral tuning were present too. Binaural preferences were heterogeneously distributed in space, both on the fine scale (within ∼ 200 μm) and on the global one (up to ∼ 1 mm). Moreover, A1 neurons were mostly tuned to slow FM sweeps within the range of those used in species-specific calls. Cells activated by similar rates tended to be spatially proximal, indicating a level of local organization similar to the one I found for frequency tuning, and higher than that of ILD responses. Finally, I set the groundwork for two-photon studies of the A1 of the ferret, by presenting the first evidence of the microscopic organization of the tonotopic map in this species. My results shed light on some long-held questions about the response properties of A1, and confirm two-photon imaging as a powerful tool for investigating the processing of sensory signals in the cortex of both small and large mammals.

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Intracerebral injections of the neurotoxin 6-OHDA into the dorsal bundle (DB) causes selective depletion of cortical noradrenaline (NA) stores. The cortical neurons may then develop supersensitivity to NA and this may be measurable by the level of cAMP accumulation. Seven days was chosen as a period of time from injection to the development of the supersensitive response, and ten weeks was taken as the long-term period to measure permanent effects of this treatment. At seven days there was a significant increase in maximal stimulation and a slight, but not significant, shift of the dose-response curve. The baseline values of cAMP remained unchanged. The effect of the cAMP system after ten weeks post-injection consisted of a significant shift of the dose-response curve to the left, corresponding to a lowering of K[sub D], and a significant increase in both baseline and maximal stimulation levels, or V[sub max], of cAMP. The very high responsiveness of the adenylate cyclase system during the end of the second post-natal week was characterized by higher baseline levels of cAMP and greater cAMP accumulation in response to all NA concentrations tested. However, there was no significant shift of the dose-response curve. Kindling had no effect on the NA-stimulated cAMP response, showing unchanged basal and maximal stimulation levels in both anterior and posterior cortical slices. These results are discussed in terms of our present knowledge of the role of cAMP as a component of the post-synaptic receptor complex. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate

The present study was undertaken to evaluate the effects of ultra low concentrations (10-9 or 10-14 M) of morphine on neurite elongation in cultured neurons dissociated from rat spinal cords and cerebral cortex. In fetal serum (FS) or fetal serum-free supplemented with cAMP media, the length of longest neurite was significantly increased by 10-9 or 10-14 M morphine. For example, 10-14 M morphine increased neurite length by 24±0.5% and 27±0.3% in spinal cord neurons, and 18±0.2% and 17±0.6% in cortical neurons. Morphine (10-6 M) had no significant effect on neurite length of spinal and cortical neurons. The relative frequency distribution of neurite length revealed 61±2.7% of spinal neurons and 48±2.6% of cortical neurons are responsive to ultra low concentrations of morphine. In the responsive populations, morphine (10 -14 M) enhanced the neurite outgrowth in spinal neurons by 58±0.9% and 48±1.2% and in cortical neurons by 31±0.6% and 28±0.9% in FS and cAMP-supplemented media, respectively. Pretreatment with naloxone did not prevent the morphine effect. The result shows that morphine at ultra low concentrations enhances neurite outgrowth of spinal and cortical neurons via a naloxone-independent mechanism.

This document only includes an excerpt of the corresponding thesis or dissertation. To request a digital scan of the full text, please contact the Ruth Lilly Medical Library's Interlibrary Loan Department (rlmlill@iu.edu).

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This thesis is missing page 18, the other copies of the thesis are missing it as well. - Digitization Centre / The work reported in this thesis concerns a possible quantitative relationship between two bioelectric phenomena of the cat cerebral cortex: neuronal discharge and slow potentials. A review of literature dealing with research related to the present topic is given. This is followed by descriptions of the experimental procedure employed and the results obtained. A subsequent discussion in terms of current neurophysiological concepts relates present findings with those of other known research. The accompanying bibliography represents a fairly complete coverage of contemporary and recent experimental and theoretical work related to the present topic. / Thesis / Master of Arts (MA)