Divided attention, or the ability to respond to more than one task simultaneously, is an important skill for navigating complex social, communicative, academic, and professional settings. The purpose of the current study was to understand the association between the volume of the posterior cerebellum and divided attention in individuals with autism spectrum disorders (ASDs) and control participants. It was hypothesized that the ASD group would have worse divided attention abilities and smaller posterior cerebellar volumes compared to the control group. Furthermore, reduced posterior cerebellar volume was expected to be associated with weaker divided attention abilities. Participants were young adult males with high-functioning autism spectrum disorders (n=15) and controls matched for age, handedness, and nonverbal IQ (n=19). Results showed partial support for worse divided attention performance in ASDs and for a positive association between posterior cerebellar volume and divided attention performance. There were no group differences in posterior cerebellar volume, and accounting for intracranial volume did not affect findings. Limitations of the current study and future directions are discussed. / text

Neurodegenerative diseases are characterized by progressive degeneration of selective neurones in the nervous system and the formation of protein inclusions in surviving neurones. The mechanisms underlying neurodegeneration and neuroprotection in the nervous system remain elusive. Ubiquitin is one of the hallmarks of neuropathological inclusions in the majority of neurodegenerative diseases, including Alzheimer’s disease and Parkinson’s disease. Therefore, dysfunction of the ubiquitin proteasome system has been implicated in disease cause and/or progression. This thesis investigates a unique conditional genetic mouse model of neurodegeneration caused by conditional genetic 26S proteasomal depletion in mouse forebrain neurones. We have identified potential proteins targeted for ubiquitination in brain using bio-affinity chromatography of zinc finger protein ZNF216 coupled with mass spectrometry. This lead to the identification of several potential ubiquitinated proteins involved in gene expression and regulation. We have also investigated the global brain proteome in response to 26S proteasomal depletion in neurones using two-dimensional fluorescence difference in-gel electrophoresis coupled to mass spectrometry for protein identification. Several differentially expressed proteins were identified in the 26S proteasome-depleted cortex. Astrocytic intermediate filament proteins glial acid fibrillary protein and vimentin, as well as the antioxidant peroxiredxoin-6, were upregulated. Mitochondrial fumarate hydratase and stathmin-1, involved in the tricarboxylic acid cycle and cytoskeletal microtubule dynamics respectively, were downregulated. These proteins have been validated by biochemical and immunohistochemical approaches. Further analysis of oxidative stress revealed increased lipid and protein oxidation that may be involved in the neurodegeneration associated with 26S proteasomal depletion. However, we also show increased phospholipase A2 activity associated with peroxiredoxin-6 expression that may have additional roles in neurodegenerative and/or neuroprotective functions. Interestingly, the levels of reactive oxygen species were inversely correlated with the upregulation of peroxiredoxin-6. We suggest that peroxiredoxin-6 may play an important role in the brain in the protection against oxidative stress and our studies may improve our physiological and pathological understanding of neurodegenerative disease.

The work presented in this thesis is intended to contribute towards the understanding of the cerebral vascular behaviour in response to changes in neuronal activation. The blood oxygenation-level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal provides an indirect measure of neuronal activation, arising from a combination of metabolic and vascular (blood flow and blood volume) changes local to the activation. Therefore the BOLD signal is dependent on local vascular properties as well as on the neuronal activation, leading to a variability of the BOLD signal, based on the underlying vascular structure. It has become an important goal to improve understanding of the mechanisms underlying the BOLD signal in order to separate out this vascular variability from the underlying correspondence with the neuronal activation. The effect of field strength on the temporal characteristics of the BOLD haemodynamic response function is investigated. An earlier BOLD response onset has been measured with increasing static magnetic field strength, consistent with an earlier microvascular (compared with macrovascular) signal response. This result can be used to improve haemodynamic models of the BOLD signal. Hypercapnia, a vasodilator, has been used both to assess the relationship between transverse relaxation and blood oxygenation at 3 and 7 Tesla and to identify vascular heterogeneity between two equivalent brain regions. A tight, linear relationship was found between the level of hypercapnia and transverse relaxation at both 3 and 7 Tesla, whilst the change in transverse relaxation due to hypercapnia increased 2.1 ± 0.5 fold from 3 to 7 Tesla, indicating an approximately linear relationship across field strength. In a separate experiment, a vascular asymmetry was found between the left and right precentral gyri using hypercapnia. This result highlights the need to account for the vascular contribution to the BOLD signal before using this BOLD signal to make comparisons of neuronal activity across brain regions. Finally, an improved model for calibrated BOLD has been proposed and implemented, which requires fewer assumptions than existing approaches. This uses the BOLD response to some task, repeated both at normoxia and hyperoxia. To assess the validity of this model, the effects of paramagnetic oxygen molecules are considered, both dissolved in blood plasma and in airspaces adjacent to the brain. These effects were found to be small, except for in the frontal cortex.

The standard memory consolidation model assumes that new memories are temporarily stored in the hippocampus and later transferred to the neocortex, during deep sleep, for long-term storage, signifying the importance of studying functional and structural cortico-hippocampal interactions. Our work offers a thorough analysis on such interactions between neocortex and hippocampus, along with a detailed study of their intrinsic dynamics, from two complementary perspectives: statistical data analysis and computational modelling. The first part of this study reviews mathematical tools for assessing directional interactions in multivariate time series. We focus on the notion of Granger Causality and the related measure of generalised Partial Directed Coherence (gPDC) which we then apply, through a custom built numerical package, to electrophysiological data from the medial prefrontal cortex (mPFC) and hippocampus of anaesthetized rats. Our gPDC analysis reveals a clear lateral-to-medial hippocampus connectivity and suggests a reciprocal information flow between mPFC and hippocampus, altered during cortical activity. The second part deals with modelling sleep-related intrinsic rhythmic dynamics of the two areas, and examining their coupling. We first reproduce a computational model of the cortical slow oscillation, a periodic alteration between activated (UP) states and neuronal silence. We then develop a new spiking network model of hippocampal areas CA3 and CA1, reproducing many of their intrinsic dynamics and exhibiting sharp wave-ripple complexes, suggesting a novel mechanism for their generation based on CA1 interneuronal activity and recurrent inhibition. We finally couple the two models to study interactions between the slow oscillation and hippocampal activity. Our simulations propose a dependence of the correlation between UP states and hippocampal spiking on the excitation-to-inhibition ratio induced by the mossy fibre input to CA3 and by a combination of the Schaffer collateral and temporoammonic input to CA1. These inputs are shown to affect reported correlations between UP states and ripples.

The G1uN3 subunits of the NMDA receptor are thought to reduce the Ca 2+ permeability and Mg2+ sensitivity of NMDA receptors. cRNA for rat NMDA receptor subunits were injected into Xenopus oocytes and responses were recorded using two electrode voltage clamp at -100, -75 and -50 mV. G1uN1-1a/2A, GluN1-1a/2A/3A and G1uN1-1a/2A/3B containing receptors were characterised using Mgz+, memantine, philanthotoxin-343, methoctramine and MK-801. IC50 values were calculated and generally showed significant increases between those containing G1uN1-1a/2A/3 subunits and G1uN1-1a/2A, while those with G1uN3B were found to be significantly higher than G1uN3A. Activity was also typically shown to be partially restored with mutations at the N and N+1 site asparagines of G1uN3A. As the ICS0 was only partially restored the changes cannot be attributed to the loss of the N-site alone. Further differences may be due to a constricted threonine ring within the M3 vestibule region, or due to continued reduced flux through the channel. Another possibility is that to restore block it may require both the double N and N+1 mutation at the N-site. Multi-target-directed ligands combine two pharmacophores to produce drugs which retain the properties of the constituents. Memantine has been approved for use in Alzheimer's disease and there is a search for drugs that have similar actions. A range of multi-target compounds were tested to determine if NMDA receptor blockade activity was obtained. The pharmacophores explored were tacrine, donepezil, lipoic acid carvedilol and dimebon. The most promising compounds were carbacrine(3) (tacrine and carvedilol) and lipocrine (lipoic acid and tacrine), and it was found that the former was equipotent and the latter more potent than memantine. Potency was likely due to the tacrine moiety. These compounds should be further categorised to determine if they retain the kinetics that gives memantine its favourable side effect profile.

Single doses of phenobarbitone decreased the turnover rate of dopamine (DA) and noradrenaline (NA) and increased the whole brain levels of 5- hydroxytryptamine (5-RT) and gamma-aminobutyric acid (GABA) . Habituation to phenobarbitone increased the levels of DA in striata and midbrain and decreased that of cerebral hemispheres, leaving the total amount unchanged. Habituation resisted the depletion otherwise caused by alpha-methyl-p-tyrosine (alpha-m.p.t.) in the striata for DA and in the cerebral hemispheres for both DA and NA. Withdrawal of phenobarbitone decreased the levels of DA in the striata and both catecholamines in the cerebral hemispheres. Withdrawal increased the depletion of DA in the striata and cerebral hemispheres and that of NA in the cerebral hemispheres and midbrain caused by alpha-m.p.t. Withdrawal convulsions increased the levels of DA in the striata and decreased it in the cerebral hemispheres, leaving the total amount unchanged. NA was less in this group than it was in controls. Alpha-m.p.t. protected animals from convulsions. This group showed less DA in the striata and in the cerebral hemispheres and less NA in midbrain. Habituation to phenobarbitone increased the levels of 5-HT and 5-HIAA. Withdraiwal returned both levels to control values. While withdrawal convulsions decreased the levels of 5-HT, 5-HIAA levels were increased. Single doses of phenytoin increased the levels of DA in striata and NA in midbrain. It also increased the l levels of 5-HIAA in whole brain and decreased the depletion of 5-HIAA caused by p-chlorophenylalanine (p-c.p.a.) or pargyline. Long term administration of phenytoin increa sed the levels of dopamine in the striata and the midbrain and decreased that of the cerebral hemispheres. It also produced an increase in the level s of NA in the cerebral hemispheres. Similar effects were observed after alpha-m.p.t. Whole brain levels of 5-HT and 5- HIAA were increased after long term treatment with phentoin. Single doses of carbamazepine increased the levels of NA in the midbrain and decreased the depletion of 5-HIAA after p-c.p.a. and pargyline. The long term treatment with carbamazepine increased the total brain levels of 5- HT and 5-HIAA and those of DA in the striata and cerebral hemispheres and for NA in the cerebral hemispheres and midbrain. The same effect was seen after alpha-m.p.t. While NA and GABA levels were decreased in the primary focal area oneweek after cobalt implantation, 5-HIAA levels were increased. The same effect was seen for NA and 5-HIAA levels two weeks after cobalt implantation.

Odour Binding Proteins (OBPs) are found in the olfactory system of a range of species. Whilst invertebrate OBP function is well understood, the exact function of these proteins in the vertebrate nasal mucus is not fully understood. Multiple subtypes of rat OBPs have been identified and found to share less than 30% sequence identity. Studies have suggested each rat OBP binds to particular sets of odours, which may afford them a particularly important role within the olfactory system, pre-sorting odours. This study focuses on OBP3, closely examining the binding interaction of this protein with a range of odours. This has been done using Isothermal Titration Calorimetry which revealed that the binding of the highest affinity ligands, the heterocyclic compounds, is enthalpically driven. A defined odour series, the gamma-lactones showed that despite increasing ligand size and hydrophobicity, the free energy of binding of these ligands is maintained. Interactions with both 2-isobutylthiazole and the gamma-lactones were examinedusing NMR spectroscopy, which required the NMR assignment of OBP3 to be determined. In addition a homology model of OBP3 was created in order to structurally map the per-residue changes of OBP3 upon binding. It has been found that OBP3 is able to subtly adjust in order to accommodate each of these ligands. Protein engineering of the OBP3 binding pocket has been used to highlight the importance of its size and hydrophobicity. The importance of a tyrosine residue that appears to cover the opening to the binding pocket and is conserved across both the aBPs and the lipocalins family they are part of, has been demonstrated. Mutagenesis has also revealed the importance of a number of key residues for the binding of 2-isobutylthiazole. The ability to rationally improve the affinity of OBP3 for a particular odour has also been demonstrated.

Electrical stimulation of the heel or toes evokes short latency polysynaptic reflexes in muscles of the ankle extensor medial gastrocnemius (MG), the ankle flexor tibialis anterior (TA) and the knee flexor biceps femoris (BF), the co-ordinated actions of which form an organized protective withdrawal response. Previous studies in the rabbit have shown that such reflexes are enhanced (sensitized) or inhibited by application of the chemogenic agent mustard oil (MO) to various areas of the body surface in a manner that reinforces the protective function of these responses. The organization of these ‘sensitization fields’ was strictly controlled by supraspinal pathways from the brain. The aim of the present experiments was therefore to extend these studies of the spatial organization of sensitization of withdrawal reflexes into the rat, the species most commonly used in pain research. Patterns of facilitation and inhibition of spinal reflexes were obtained and compared in decerebrate spinalized, decerebrate non-spinal, and Alfaxan- anaesthetized rats by applying mustard oil to sixteen different body locations including sites on the ipsilateral and contralateral hindlimbs as well as other off limb areas such as the snout and tail. It was found that in decerebrate spinalized animals, MO application to ipsilateral hindlimb sites enhanced but never inhibited reflex responses in the limb, whilst MO treatment to off limb sites was without effect. In contrast in anaesthetized animals the prevalent effect of MO was inhibition from treatment sites distributed across the entire animal. Reflexes in animals with an intact spinal cord (decerebrate or anaesthetized) were facilitated or inhibited by MO application to ipsilateral hindlimb sites in a way that resembled the modular organization of reflexes per se and previous sensitization studies in the rabbit. However clear differences were also observed in the effects of MO between the two species, including modulation of the heel-MG extensor response in spinalized animals, which in rabbit was inhibited by MO application to the ipsilateral toes whereas in the rat no inhibition by MO was found in spinalized animals. Sensitization of hindlimb reflexes by MO in the rat therefore seems to be influenced by descending inhibitory and facilitatory pathways. These influences were further investigated in subsequent studies. Whilst the predominant effect of spinalization was a loss of inhibition and an expansion of sensitization fields, in the toes-evoked TA reflex the reverse was noted with regard to MO treatment of distal ipsilateral sites. In this case, facilitation found in non-spinal animals did not occur in the equivalent spinalized cohort, and thereby implies that a descending facilitatory pathway is also implicated in the control of spinal reflex excitability in this model. In decerebrate rats, the noradrenergic α2-adrenoceptor antagonist RX 821002 or the serotonergic 5-HT3 receptor antagonist ondansetron were administered directly to the spinal cord (intrathecally, i.t.) either alone (dose-response studies) or as a single dose between two successive MO applications to one of three ipsilateral skin sites on the hindlimb (heel, metatarsophalangeal joints or flexion of the ankle). Cumulative i.t. doses of RX 821002 revealed the presence of tonic descending inhibition of all reflex responses as well as preventing MO-evoked inhibition (and possibly facilitation) of reflex responses suggesting the involvement of the α2-adrenoceptor subtype in mediating these effects in this model. On the other hand, cumulative i.t. ondansetron administration resulted in a decrease in the magnitude of reflex responses, thus indicating that 5-HT3 receptors are indeed implicated in tonic descending facilitation of spinal reflexes. In addition i.t. ondansetron revealed that potentiation (and possibly inhibition) of reflexes following an acute chemogenic insult appears to involve the actions of serotonin at 5-HT3 receptors in the spinal cord. These studies therefore show that the organization of sensitization of hindlimb reflexes in the rat are modulated by supraspinal influences that exist as a balance of descending facilitatory and inhibitory pathways, mediated at least in part by serotonergic 5-HT3 receptors and noradrenergic α2-adrenoceptors.

This PhD thesis examines the relationship between Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal dementia (FTD). ALS is a rapidly progressive neurodegenerative movement disorder characterized by muscle weakness, spasticity and abnormal reflexes. In a very small subset of patients (5-15%), ALS is associated with FTD. Furthermore, a larger subset of patients who do not suffer from overt dementia, develop subtle deficits in cognition and behaviour (up to 50%). The changes have mostly been observed in the domains of executive functions, language and behavioural functioning. These observations have led some researchers to propose a continuum of dysfunction between ALS and FTD, ranging from an absence of neuropsychological abnormalities to mild, subclinical changes to a profile consistent with a full-blown FTD-syndrome in ALS. FTD consists of three subsyndromes; the first ‘executive-behavioural’ type, frontal variant FTD (fvFTD), is predominantly characterized by behaviour abnormalities, difficulties with using strategies and social judgement. In contrast, the other two types mainly involve problems with ‘language’, including a central degradation of knowledge for words, objects, people (semantic dementia; SD) as well as complications with speaking, spelling and the sounds of language (progressive non-fluent aphasia; PNFA). The current study aims to explore whether the cognitive-behavioural deficits found in nondemented ALS-patients can be classified as subclinical forms of the first two FTDsyndromes, i.e. fvFTD and SD. In addition, the study further examined whether executive and language impairments co-exist or rather occur independently. To answer the research questions, a battery of neuropsychological tests was employed, adapted to patients’ speech and motor disabilities, as well as behavioural questionnaires. The data revealed there was evidence of both executive and language involvement characteristic of FTD, albeit to a subtle extent. ALS-patients showed deficits on a test of Theory of Mind (ToM). On this test, participants were asked to judge the thoughts and feelings of another, using the direction of eye gaze, a cue considered to be important for social interaction. Results indicated that ALS patients had difficulties with affective ToM, i.e. recognizing feelings of others, and this effect was not driven by perceptual or attentional difficulties. In addition, patients exhibited a subtle deficit with empathy as well as a range of behavioural abnormalities. Furthermore, ALS-patients showed abnormal performance on a complex multi-modal semantic association task which involved assigning the correct picture iii to the sound of an object. This central deficit emerged in the presence of normal audio-visual information processing and episodic memory functions. Moreover, a category-specific deficit for man-made objects was detected in patients. Individual case-analyses showed that various subsets of patients were impaired on the language and executive tasks. These analyses also showed that executive and language problems can occur independently as well as simultaneously in patients with ALS. In addition, analysis of individual cases revealed that some patients’ performance on the decision making tasks was similar to that found in patients with either orbitofrontal or dorsolateral dysfunction, while there was little if any evidence of a pattern of impairment similar to that seen with anterior cingulate dysfunction. The observed difficulties with social cognition and semantic processing indicate that executive and language problems, characteristic of the two FTD syndromes, can be detected in patients with classical ALS.

Eating Disorder research has highlighted the role of neuropsychological functioning, informing the treatment of Anorexia Nervosa. There is ambiguity in the data relating to cognitive impairment in Bulimia Nervosa, with the latest review providing inconclusive results. Executive function impairments in the area of set shifting and inhibition reported in BN are proposed to relate to traits of compulsivity and impulsivity. Other psychological disorders have also demonstrated executive function impairments. Among anxiety disorders, only PTSD and OCD have strong evidence of executive function deficits while a number of studies point towards executive function deficits in depression. This thesis aims to investigate the specificity of cognitive impairments seen in a group of female outpatients with bulimia nervosa, using a clinical comparison group of anxious and/or depressed female outpatients. Methods A systematic review was conducted to address a gap in the anxiety disorder literature and assess the neuropsychological profile of panic disorder. In order to address the main study aims, a comparison between a group of patients with BN and an anxious depressed group was conducted on neuropsychological measures of the Trail Making Test, Wisconsin Card Sorting Test, Hayling and Brixton tasks, Stroop and Verbal Fluency. In addition, psychological symptoms were assessed using SCL-90-R, Yale- Brown Obsessive Compulsive Scale and the Self-liking Self Competence scale. Social problems solving skills were assessed as a potential real world effect of executive function difficulties associated with eating disorders. The relationships between psychological and neuropsychological variables were investigated. Results The systematic review concluded that there was limited evidence of specific impairment in short term memory in panic disorder. The empirical study indicated no group differences on the above neuropsychological measures. Groups also did not differ on NART estimated IQ or self reported psychological symptoms. No relationships were found between psychological symptoms and neuropsychological measures. Few individual participants were found to be impaired on neuropsychological measures in either group. However, those impaired in the BN group were exclusively impaired on the non-perseverative errors and categories completed variables of the WCST, which is thought to be related to impulsivity. Conclusion These findings suggest that the neuropsychological profile of bulimia is broadly similar to that of an anxious and/or depressed clinical group on measures of set shifting and inhibition. Although there was evidence of a deficit in inhibition among patients with bulimia further investigation is required.