Neuroplastic changes in motor representations within the primary motor cortex (M1) have been described after peripheral manipulations and implicated in motor learning and adaptation processes. It is unclear whether dental manipulations, which may result in altered oral sensorimotor functions, are associated with analogous changes within face-M1. This project applied intracortical microstimulation (ICMS) and recordings of evoked muscle electromyographic (EMG) activity to test if changes occur in the ICMS-defined motor representations of tongue-protrusion (genioglossus, GG) and jaw-opening (anterior-digastric, AD) muscles within face-M1 and adjacent face primary somatosensory cortex (face-S1) following trimming or extraction of the rat’s right mandibular incisor, or a change in diet consistency. ICMS mapping was carried out in anaesthetised adult male rats. Consistent with previous findings, AD and GG had extensive motor representations showing considerable overlap in naïve and sham control rats. AD and GG motor representations were also found within face-S1. Left and right AD (LAD, RAD) had significantly larger representations with shorter onset latency of ICMS-evoked EMG responses within contralateral face-M1. A change in diet consistency for 2-3 weeks was not associated with significant changes in AD and GG motor representations within face-M1. Compared to control rats, iii incisor trimming out of occlusion for a period of 1 week resulted, 1 day later, in a significantly longer GG onset latency in ipsilateral than in contralateral face-M1; 1 week later, despite a regain of normal occlusion, GG and GG/AD overlapping representations were significantly larger and the centre of gravity (at AP 4.0) was significantly deeper in contralateral than in ipsilateral face-M1. Incisor extraction was associated, 1 week later, with significantly larger RAD and RAD/GG overlapping representations and a lateral shift of LAD and RAD centre of gravity. Extraction also induced significant changes in AD and GG motor representations within the contralateral face-S1. These novel findings indicate that face-M1 can undergo neuroplastic changes in association with intraoral manipulations and also suggest similar neuroplastic capabilities for face-S1 motor outputs. These findings contribute to our understanding of the role of face-M1 and face-S1 in sensorimotor adaptations to an altered oral state and provide the basis for several future studies.

A great deal of our current understanding about the biology of neurodegenerative diseases has come from studying the function of genes linked to inherited forms of these disorders. Work performed in animal models, including vertebrates as well as invertebrates, has been instrumental in deciphering the cellular, physiological and behavioural deficits arising from the expression of disease-causing genes. Using the fruit fly, Drosophila melanogaster, as a model we examined the normal and aberrant function of two genes linked to the onset of neurodegeneration in humans, presenilin and superoxide dismutase. Drosophila is an extremely versatile model and in many ways is ideal for studying the genetic basis of human disease. The high degree of genetic conservation coupled with low genetic redundancy make this model particularly well suited for studying the function of disease causing genes. We demonstrate a novel genetic,physical and physiological interaction between presenilin and calmodulin and describe how this interaction impacts a very early cellular defect associated with Alzheimer?s Disease, intracellular calcium dyshomeostasis. We also describe progressive locomotory deficits in flies expressing mutant alleles of the superoxide dismutase gene, which have been linked to the onset of familial amyotrophic lateral sclerosis. Collectively, our work demonstrates that Drosophila can be used to study the cellular, physiological and behavioural basis of human neurodegenerative diseases and may provide a model to identify novel therapeutic avenues for neurodegenerative diseases.

This thesis represents a culmination of work which seeks to examine the prelimbic and anterior cingulate cortex (ACC) during trace fear memory across sleep and wakefulness states. In order to accomplish this task, a technical platform needed to be developed. Accordingly, the first chapter demonstrates that fear behavior can recorded utilizing neck electromyography (EMG). The second chapter examines the role of the ACC in trace fear memory, discovering that many neurons have premotor activity related to freezing behavior. Additionally, auditory-evoked potentials in the ACC demonstrate learning curves which match learning curves of fear. We suggest that the ACC is involved in affective-motor integration. The third chapter examines how genetic enhancement of trace fear learning, with calcium/calmodulin-dependent protein kinase IV (CaMKIV) over-expressed mice, can influence electro-cortical potentials during wakefulness, learning and sleep. We found that CaMKIV potentiates electro-cortical brain waves during learning and sleep. In particular 4-7.5Hz rhythms were potentiated in CaMKIV over-expressed mice during learning, and are likely to be localized to regions of the prelimbic cortex. Taken together the results of this thesis demonstrate that the trace fear memory paradigm engages the ACC and prelimbic regions, as evidenced at the single cell and cortical field potential level, for sensory-affective and premotor functions related to anticipating painful stimulation. CaMKIV appears to be a protein which modulates learning and electro-cortical potentials and may be a potential target for sleep-dependent memory consolidation in the prefrontal cortex.

A challenge in the treatment of central nervous system (CNS) diseases is the transport of drug candidates into the brain. Inositol stereoisomers have show promise as therapeutic agents for CNS disorders. scyllo-Inositol was an effective prophylactic and therapeutic for Alzheimer’s disease (AD) in TgCRND8 mice, a model of AD. This suggests inositol stereoisomers have excellent CNS bioavailability. They enter the brain through inositol transporters, of which there are three: one hydrogen myo-inositol transporter (HMIT) and two sodium myo-inositol transporters (SMIT1, SMIT2). HYPOTHESIS: Given the high CNS bioavailability of inositol stereoisomers, it may be possible to use inositol transporters to shuttle other compounds into the CNS. OBJECTIVES: 1. To confirm the CNS bioavailability of the two main inositol stereoisomers, myo- and scyllo-inositol, in both TgCRND8 and wild-type mice. 2. To examine inositol transporter expression in the brains, as a function of time and disease pathology, in both groups. 3. To evaluate the flexibility of the inositol transporters for transporting compounds by determining the substrate structural features required for active transport. RESULTS: myo-Inositol and scyllo-inositol accumulated in the brain following oral administration. Disease pathology did not alter baseline inositol levels or uptake. Brain subregional transporter expression was unaltered as a function of age or disease pathology. In vitro cell culture experiments found HMIT inactive and therefore not a contender for drug transport. In contrast SMIT1 and SMIT2 were both active and competitive transport assays, revealed distinct criteria for active transport through each system. However, both were stringent in the substitutions to the structure of myo-inositol possible to maintain active transport. CONCLUSION: Active transport through the inositol transporters is very sensitive to changes in the structure of myo-inositol and only conservative changes are possible. Therefore, these transporters would not make effective shuttling systems for drug transport into the brain.

While the hippocampus may play an essential role in the expression of memories soon after training, over time these memories are thought to become increasingly dependent on coordinated activity in a broad network of cortical and subcortical brain regions. However, the distributed nature of this representation has made it challenging to define the neural elements of the memory trace, and lesion and electrophysiological approaches provide only a narrow window into what is appreciated to be a much more global network. Here global mapping approaches are used to identify networks of brain regions that are activated and co-activated following recall of recent and remote contextual fear memory in mice. Analysis of Fos expression across 84 brain regions allowed for the description of brain-wide activity and interactivity of brain regions associated with memory expression. Activity analysis revealed that remote memory engages a broad collection of cortical and subcortical regions in comparison to recent memory expression. Interactivity analyses revealed that functional connectivity associated with fear memories depends on memory age and is altered in mutant mice that exhibit premature forgetting. In-depth functional connectivity analysis of remote long-term fear memory indicates that memory recall engages a network that has a distinct thalamic-hippocampal-cortical signature. This network is concurrently integrated and segregated and therefore has small-world properties as well as a resilient core of highly inter-connected regions. Centrality measures identify a collection of regions that may play a critical role in the function of the network including expected regions such as the anterior cingulate cortex and prelimbic cortex as well as novel regions including the reuniens thalamic nucleus. Post conditioning lesions of the reuniens lead to mild deficits in contextual fear memory expression providing support for the idea that identified hub regions may play a critical role in the function of the network. These results identify and describe functional activity and interactivity of brain regions underlying recent and remote fear memory expression and provide strong evidence for reorganization and distribution of the functional organization of memories over time.

The number of people living with Alzheimer’s Disease (AD) is projected to increase dramatically over the next few decades, making the search for treatments and tools to measure the progression of AD increasingly urgent. The antisaccade task, a hands- and language-free metric, may provide a functional index of the Dorsolateral Prefrontal Cortex (DLPFC), which is damaged in the later stages of AD. Patients with AD make significantly more antisaccade errors than controls, however, performance in mild AD has remained unexplored. We hypothesized that mild patients will make more errors than controls. Thirty AD patients and 31 age-match controls completed both laptop-based and clinical versions of the antisaccade task. Two thirds of patients with AD made significantly more errors and corrected less of their errors than age-matched controls. Our findings indicate that antisaccade impairments exist in mild AD, suggesting DLPFC pathology may be present earlier than suggested by previous studies.

The purpose of this study was to investigate a) PTTG expression in pituitary adenoma subtypes, b) the correlation between PTTG expression and clinico-pathological variables in patients with Cushing’s disease with ACTH secreting pituitary adenomas, and c) PTTG expression in brain tumour subtypes. PTTG expression was investigated in 89 pituitary and 88 brain tumours, and 54 ACTH adenomas of patients with Cushing’s disease. Our results show that PTTG is expressed in the cytoplasm of pituitary adenoma cells, and at higher levels in GH adenomas, with lower PTTG expression levels being exhibited by PRL adenomas. Significant differences were noted between PTTG expression in medically treated and non-treated GH adenomas. However, PTTG expression in ACTH adenomas did not correlate with clinico-pathological variables, making it an unsuitable prognostic indicator in such tumours. In brain neoplasms, PTTG was expressed at higher levels in malignant tumours, whereas in less aggressive tumours, PTTG expression was considerably lower.

The Notch receptor and its ligands constitute a ubiquitous signaling pathway found throughout all multicellular animal life. In addition to its highly conserved function in development, a growing body of evidence suggests Notch signaling has important roles to play in adult processes, including long-term memory (LTM) formation. Building on previous work showing a specific requirement for the Notch1 receptor in spatial memory in mice, I show here a similar requirement for the Notch ligand Jag1. Mice with mutations to Dll1 (another Notch ligand) and Lfng (a Notch regulatory protein) do not display such phenotypes. I propose a model in which signaling between Notch pathway components found in the adult mouse hippocampus (such as Notch1 and Jag1) is required for LTM encoding, with no requirement for pathway components not expressed in this tissue (such as Dll1 and Lfng).

Auditory sensitivity has often been measured by identifying neural threshold in real-time (online) which can introduce bias in the audiograms that are produced. We tested this by recording auditory nerve activity of the notodontid moth Nadata gibbosa elicited by bat-like ultrasound and analysing the response offline. We compared this audiogram with a published online audiogram showing that the bias introduced can result in a difference in the audiogram shape. In the second part of our study we compared offline audiograms using spike number as threshold with others that used spike period and stimulus/spike latency, variables that have been suggested as providing behaviourally functional criteria. These comparisons reveal that functional audiograms are more flatly tuned than simple spike audiograms. The shapes of behavioural audiograms are discussed in the context of the selection pressure that maintains their shape, bat predation.

Anatomical connectivity and single neuron coding suggest a dissociation of information representation within the lateral and medial entorhinal cortex, a brain region with widespread connections to cortical areas. We aimed to expand this idea by examining differential contribution of these two sub-regions to the retrieval of non-spatial and spatial memory. Inactivation of lateral, but not medial regions severely impaired the retrieval of recently and remotely acquired non-spatial memory while spatial memory remained intact. To link functioning of the lateral entorhinal cortex with the known roles of the hippocampus and medial prefrontal cortex for memory retrieval, communication with these two regions was detected as synchronized oscillations in local field potentials. We found that stronger communication between the lateral entorhinal and prefrontal cortex during stimulus-free periods correlated with better memory performance. The lateral entorhinal cortex therefore may serve as a gateway of memory-related information between the medial prefrontal and other cortical regions.