Thesis (M.S.)--Eastern Illinois University, 2009. / Includes bibliographical references (leaves 114-120).

Thesis (Ph. D.)--Florida State University, 2006. / Advisor: Debra Ann Fadool, Florida State University, College of Arts and Sciences, Dept. of Biological Science. Title and description from dissertation home page (viewed June 15, 2006). Document formatted into pages; contains xiii, 112 pages. Includes bibliographical references.

There are some discrepancies in the literature regarding the response of the "induced waves" of the olfactory bulb to odorous stimuli. This work was designed to resolve the controversy by relating the different types of response to alertness of the animal and to concentration of the odour. The envelope of 40 Hz activity from the olfactory bulbs of unanaesthetised cats was recorded on a polygraph, and found to vary with respiration. The animal's nose projected into a stream of clean air to which odorant could be added at different fixed rates for about a minute at intervals. The amplitude of induced wave activity during the stimulus was compared to that shortly before it. Odour concentrations were varied within a 5 x 10⁶ -fold range and the logarithm taken. The alertness of the cat was estimated on a 5-point scale. The data for the middle alertness category were eliminated and those of the two extreme groups subjected to statistical analysis by multiple regression. The percentage change in integrated induced wave activity during stimulus as compared to that during control in a drowsy cat was found to be independent of stimulus concentration and could be in either direction but usually increased. In an aroused cat regression to a third order polynomial was statistically significant (p < 0.02) and accounted for 0.34 of the variability. This result appears surprisingly good in view of the enormous spontaneous variation in the signal and the unreliability of the stimulus, both as to its exact concentration and in the resemblance of its presentation parameters to a square wave. It would be worth while to repeat this study with more animals, more odours and a. better olfactometer design. The shape of the regression was predicted as follows. At low concentrations an alert cat would show an olfactory response in the form of a depression of induced waves. At intermediate concentrations an alarm response would sometimes increase alertness, augmenting the induced waves. At high concentrations the trigeminal-to-autonomic noxious vapour response would intervene, mechanically reducing access of air to olfactory receptors and/ or respiration. A drowsy cat on the other hand might be subject to alerting by any suprathreshold concentration, or could ignore the stimulus with or without perceiving it. Effects of non-olfactory stimuli and spontaneous variations were in fact far more obvious than most of the "olfactory responses". / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

The ultrastructural effects of chemical modification on olfactory receptors were investigated with scanning electron microscopy, transmission electron microscopy and fluorescent microscopy. Mason and Morton (1984) hypothesized that a two-step chemical treatment would covalently modify receptor proteins. Their two-step protocol was modified in an attempt to label olfactory receptor proteins and the ultra structural effects of the original two-step protocol were examined.

Animals have evolved sensory systems that afford innate and adaptive responses to stimuli in the environment. Innate behaviors are likely to be mediated by hardwired circuits that respond to invariant predictive cues over long periods of evolutionary time. However, most stimuli do not have innate value. Over the lifetime of an animal, learning provides a mechanism for animals to update the predictive value of cues through experience. Sensory systems must therefore generate neuronal representations that are able to acquire value through learning. A fundamental challenge in neuroscience is to understand how and where value is imposed in brain during learning. The olfactory system is an attractive sensory modality to study learning because the anatomical organization is concise in that there are relatively few synapses separating the sense organ from brain areas implicated in learning. Thus, the circuits for learned olfactory behaviors appear to be relatively shallow and therefore more experimentally accessible than other sensory systems. The goal of this thesis is to characterize the representation and function of neural circuits involved in olfactory associative learning. Odor perception is initiated by the binding of odors onto olfactory receptors expressed in the sensory epithelium. Each olfactory receptor neuron (ORN) expresses one of 1500 different receptor genes, the expression of which pushes the ORN to project with spatial specificity onto a defined loci within the olfactory bulb, the olfactory glomeruli. Therefore, each and every odor evokes a stereotyped map of glomerular activity in the bulb. The projection neurons of the olfactory bulb, mitral and tufted (M/T) cells, send axons to higher brain areas, including a significant input to the primary olfactory cortex, the piriform cortex. Axons from M/T cells project diffusely to the piriform without apparent spatial preference; as a consequence, the spatial order of the bulb is discarded in the piriform. In agreement with anatomical data, electrophysiological and optical imaging studies also demonstrate that individual odorants activate sparse subsets of neurons across the piriform without any spatial order. Moreover, individual piriform neurons exhibit discontinuous receptive fields that defy chemical or perceptual categorization. These observations suggests that piriform neurons receive random subsets of glomerular input. Therefore, odor representations in piriform are unlikely to be hardwired to drive specific behaviors. Rather, this model suggests that value must be imposed upon the piriform through learning. Indeed, the piriform has been shown to be both sufficient and necessary for aversive olfactory learning without affecting innate odor responses. However, how value is imposed on odor representations in the piriform and downstream associational areas remain largely unknown. We first developed a strategy to track neural activity in a population of neurons across multiple days in deep brain areas using 2-photon endoscopic imaging. This allowed us to assay changes in neural responses to odors during learning in piriform and in downstream associative areas. Using this technique, we first observe that piriform odor responses are unaffected by learning, so learning must therefore impose discernable changes in neural activity downstream of piriform. Piriform projects to multiple downstream areas that are implicated in appetitive associative learning, such as the orbitofrontal cortex (OFC). Imaging of neural activity in the OFC reveal that OFC neurons acquire strong responses to conditioned odors (CS+) during learning. Moreover, multiple and distinct CS+ odors activatethe same population of OFC neurons, and these responses are gated by context and internal state. Together, our imaging data shows that an external and sensory representation in the piriform is transformed into an internal and cognitive representation of value in the OFC. Moreover, we found that optogenetic silencing of the OFC impaired the ability of mice to acquire learned associations. Therefore, the robust representation of expected value of the odor cues is necessary for the formation of appetitive associations. We made an important observation: once the task has been learned with a set of odors, the OFC representation decays after learning has plateaued and remains silent even when mice encounter novel odors they haven’t previously experienced. Moreover, silencing the OFC when it was not actively engaged during the subsequent learning of new odors had no effect on learning. These sets of imaging and silencing experiments reveal that the OFC is only important during initial learning; once task structure has been acquired, it is no longer needed. Task performance after initial task acquisition must therefore be accommodated by other brain regions that can store the learned association for long durations. We therefore searched for other brain regions that held learned associations long-term. In the medial prefrontal cortex (mPFC), we observe that the learned representation persists throughout the entire course of training. Unlike the OFC, not only does this representation encode the positive expected value of CS+ odors, it also encodes the negative expected value of CS- odors in a non-overlapping ensemble of neurons. We further show through optogenetic silencing that this representation is necessary for task performance after the task structure has already been acquired. Therefore, while the OFC representation is required for initial task acquisition, the mPFC representation is required for subsequent appetitive learning and performance. Why would a learned representation vanish in the OFC and betransfered elsewhere? We hypothesize that the brain may allocate a portion of its real estate to be a cognitive playground where experimentation and hypothesis testing takes place. Once this area solves a task, it may unload what it has learned to storage units located elsewhere to free up space to learn new tasks. We further imaged another associative area, the basolateral amygdala (BLA), and found a representation of positive value that appears to be generated from a Hebbian learning mechanism. However, the silencing of this representation during learning had no effect. This suggests that while multiple and distributed brain areas encode cues that predict the reward, not all may be necessary for the learning process or for task performance. In summary, we have described a series of experiments that map the representation and function of different associational areas that underlie learning. The data and the techniques employed have the potential to significantly advance the understanding of learned behavior.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 108-123). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 108-123). Also available on the Internet.

The primary olfactory pathway in adult mammals has retained a remarkable potential for self-repair. Olfactory ensheathing cells (OECs), specialized glial cells within the olfactory nerve, are thought to play an important role in the ongoing growth and replenishment of sensory connections in this system. To gain insight into novel molecules that could mediate OEC-supported growth of axons within the olfactory nerve, gene expression profiling experiments revealed very high expression of the fibulin-3 glycoprotein in OECs. To date, research on fibulin-3 has been limited and mainly focused on its involvement in Doyne honeycomb retinal dystrophy, vasculogenesis and tumor formation. As the extracellular matrix associated with OECs is thought to be an important contributor to a growth-permissive environment, the main aim of this thesis was to define a putative role for fibulin-3 during olfactory receptor neuron replacement and regeneration. This hypothesis was investigated in a series of in vitro and in vivo experiments that involved lentiviral vectors to manipulate fibulin-3 gene expression in OECs as well as the use of knock-out mice. Using genetically-modified OECs, experimental data showed that increased levels of fibulin-3 induced morphological changes in OECs and also impeded their migration. Lentiviral vector-mediated expression of fibulin-3 in OECs also had an inhibitory effect on neurite outgrowth from dorsal root ganglion explants. On the other hand, knock-down of fibulin-3 levels via siRNA technology resulted in reduced proliferation. Comparative lesioning experiments in fibulin-3 knock-out and wild-type mice allowed for further assessment of a role for fibulin-3 in olfactory nerve repair in vivo. Two experimental injury models, i.e. epithelial (Triton-X) lesioning and olfactory bulbectomy, were employed. The results obtained were in line with in vitro observations. A lack of fibulin-3 in knock-out mice resulted in a seemingly augmented regeneration of the olfactory epithelium at 10 days post-injury. However, at the latest recovery time point of 42 days post-injury, an impaired recovery of the olfactory epithelium from the experimental insults was observed. Although the precise mechanism for the latter phenomenon is not yet fully understood, our data point towards several factors which include vascular abnormalities and altered cell proliferation within the olfactory epithelium. Additionally, the precise protein distribution of another wide-spread family of extracellular matrix molecules, the laminins, was investigated in this thesis. It was of interest to investigate the spatiotemporal expression of laminin isoforms during iii olfactory nerve development and regeneration as these molecules may have distinct roles in promoting olfactory sensory neuron growth and patterning. In situ hybridization and immunohistochemical studies concluded that laminin-211 and laminin-411 were the most likely candidates to play such a role. In summary, this thesis provides new insights into the role of the extracellular matrix, fibulin-3 in particular, in regulating cell migration, division and axonal growth in the primary olfactory pathway. Such knowledge also gives a greater understanding of the molecular mechanisms by which OEC transplants may enhance axonal regeneration elsewhere in the CNS.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 6 uppsatser.

The roles of Ca2 + and cAMP in olfactory transduction were explored using agents which affect calcium channels and second messenger systems. These agents were applied at certain calculated final concentrations onto olfactory epithelia of urethane-anesthetized frogs (Sana PiPlens) by two-sec aerosol spray. During extracellular recording, saturated vapors of isoamyl acetate were delivered every 100 sec in 0.3 sec pulses to produce an electroolfactogram (EOG). Inorganic cations that block inward calcium currents inhibit EOG responses with the following rank order: (La3+) > (Zn2+, Cd2+) > (Al3+, Ca2+, Sr2+) > (Co2+). Application of 7.5 mM La3+ eradicates £0G's, while Ba2+ (which can carry more current that Ca2+) initially produces significant enhancement (F=43.04, p<0.001, df=19). Magnesium ion has no effect on EOG's at 7.5 mM, while 1.5 X 10"4M Ca2+ is significantly inhibitory (F=5.74; p=0.0355; df=12). Control aerosol sprays of distilled water depress EOG's by an average of 5%. The organic calcium channel antagonists diltiazem and verapamil inhibit EOG's by 17% and 36X, respectively, at a concentration of 1.5 X 10~*M. Verapamil produces significant inhibition (F=17.17; p=0.002; df=ll) at 1.5 X 10" 5 M, while the 1,4-dihydropyridine calcium channel antagonists, nicardipine and nifedipine, do not inhibit beyond 1% DMSO controls. Several calmodulin antagonists decrease EOG's, but without correlation to their anti-calmodulin potency. Application of 1.5 X 10"*M chlorpromazine and N-(6-aminohexyl)-5-chloro-l-naphthalenesulfonamide inhibit EOG's by 31% and 27%, respectively, while trifluoperazine inhibits by 23%. Dibutyryl cAMP, a lipophilic mimic of cAMP, produces 54% inhibition at 1.5 X 10" *M. Dibutyryl cGMP, cGMP, cAMP, and adenosine all decrease EOG's by less than 15% compared to distilled water controls. Forskolin, a reversible activator of adenylate cyclase, inhibits EOG's by 57% at 1.5 X 10"5M, which is significant beyond the 1% DMSO controls (F=17.17; p=0.002; df=ll). These data support the hypothesis that Ca2+ participates in olfactory transduction. Calcium ions could serve as charge carriers, second messengers, or both. Cyclic AMP could be involved with the primary excitatory process or sensory adaptation, or both.