Life Sciences Commons^™

Neural Responses To Magnetic Orientation Information In Songbirds, Madeleine Ir Brodbeck

Electronic Thesis and Dissertation Repository

Effective navigation and orientation is essential for animals to survive. The study of migratory birds provides insights into these processes, particularly through mechanisms like the geomagnetic compass, which uses Earth's magnetic field for directional information. A brain region in songbirds relevant to this is cluster N, known for its potential role in processing geomagnetic information. Notably, cluster N appears exclusive to nocturnally migratory birds, being active solely at night, and lesion studies reveal that an intact cluster N is necessary for geomagnetic compass orientation. However, given the scarcity of empirical data concerning cluster N, substantial questions persist regarding its function. …

The Modulation Of Lfp Characteristics In The Freely Moving Common Marmoset, William Jm Assis

Electronic Thesis and Dissertation Repository

The hippocampus is a neural structure critical for navigation. Neurons in this region, along with others, create a functional network which generates large-amplitude modulations known as local field potential (LFP) activity. Prior LFP research has predominantly used rodent animal models, however recent studies have shown that frequencies associated with navigation in other mammals do not correlate to those of the rodent. We hypothesized that LFP characteristics in the common marmoset are modulated by the speed and axis of travel of the animal. Two marmosets were placed in a free moving 3-dimensional environment where movement and neurological activity were recorded. Results …

Investigating The Role Of Atrx In Glutamatergic Hippocampal Neurons, Renee Tamming

Electronic Thesis and Dissertation Repository

Mutations in ATRX, a Snf2-type chromatin remodeler, frequently lead to intellectual disability. However, the function of ATRX within the brain in cognition and synaptic transmission are incompletely understood. The aim of this study was to investigate the role of ATRX in the adult mouse brain. While complete loss of ATRX in the embryonic mouse brain results in perinatal lethality, mosaic expression of ATRX stunted growth and perturbed circulating IGF-1 levels. Mosaic expression of ATRX also impaired adult cognition, specifically recognition memory and spatial learning and memory. However, there were confounding factors that led me to a new model in …

Effect Of Atrx Inactivation On Hippocampal Synaptic Plasticity In Mice, Radu Gugustea

Electronic Thesis and Dissertation Repository

The ATRX gene encodes an ATP-dependent chromatin remodeling factor and gene mutations cause developmental defects and intellectual disability. Conditional ablation of Atrx in mouse postnatal forebrain excitatory neurons (ATRX-KO) leads to spatial learning and memory impairments. Thus, we hypothesized that hippocampal synaptic transmission and plasticity are disrupted in ATRX-KO mice. Long-term potentiation (LTP), a cellular correlate of memory, and input-output relation of paired-pulse responses were studied in urethane-anesthetized mice in vivo. Theta-burst stimulation (TBS) of stratum oriens induced robust basal dendritic LTP in CA1 of both ATRX-KO and control mice, while paired-pulse facilitation (PPF) during baseline was lower in ATRX-KO …

The Effect Of Seizures (Afterdischarges) On Hippocampal Long-Term Potentiation, Vishaka Rajan

Electronic Thesis and Dissertation Repository

This study investigated whether an electrographic seizure, or an afterdischarge (AD), inhibits long-term potentiation (LTP) in the hippocampus. Neuromodulation by acetylcholine (ACh) and genetic modification by loss of the ATRX gene on LTP was also examined through the use of VAchT knockout mice and ATRX knockout mice, respectively. Evoked potentials were recorded in the hippocampal CA1 region in freely behaving mice and urethane-anesthetized mice. Basal dendritic LTP was suppressed when elicited 1 h after an AD in all behaving mice, regardless of mouse genotype; LTP was unaffected when induced 1 day or 1 week following an AD. At 1 h …

Object Processing In The Medial Temporal Lobe: Influence Of Object Domain, Anna Blumenthal

Electronic Thesis and Dissertation Repository

We live in a rich visual world, surrounded by many different kinds of objects. While we may not often reflect on it, our ability to recognize what an object is, detect whether an object is familiar or novel, and bring to mind our general knowledge about an object, are all essential components of adaptive behavior. In this dissertation, I investigate the neural basis of object representations, focusing on medial temporal lobe (MTL) structures, namely, perirhinal cortex, parahippocampal cortex, and hippocampus. I use what type of thing an object is, or more specifically, the broader category (e.g., “face” or “house”) or …

Winter Warming Affects The Onset Of Reproduction But Not Cognition Or The Hippocampus In Black-Capped Chickadees (Poecile Atricapillus), Robert J. Martin

Electronic Thesis and Dissertation Repository

The effects of overwinter temperature on behaviour and cognition, hippocampal volume, and reproductive timing were studied in Black-capped chickadees (Poecile atricapillus). I hypothesized that overwinter temperature would have varied effects for Black-capped chickadees that overwinter in northern climates. I found that temperature had no effect on behaviour and cognition, or hippocampal volume, but temperature did influence reproductive timing. Birds that experienced warmer winter conditions had significantly more developed gonads than birds that experienced colder conditions. These results suggest that while birds are clearly sensitive to ambient winter temperature, temperature only modulates some processes and not all. These studies …

Modulation Of Synaptic Plasticity By Hippocampal Theta Rhythm, Clayton Law

Electronic Thesis and Dissertation Repository

The hippocampal theta rhythm facilitates memory formation. This study investigated the temporal relation of long-term potentiation (LTP) with the hippocampal theta rhythm. Theta rhythm consists of a wave of somatodendritic depolarization, but the depolarization of apical and basal dendrites of hippocampal CA1 pyramidal cells peak at a similar theta phase. Thus, we hypothesize that the population spike excitability evoked by excitation of the apical and basal dendrites peak at a similar phase of the theta rhythm. We also expect that LTP at the basal and apical dendritic synapses to be maximal at a similar theta phase.

Rats (~300 g) were …

Sex And Seasonal Differences In Cognition And The Brain In Brood-Parasitic Brown-Headed Cowbirds (Molothrus Ater), Mélanie F. Guigueno

Electronic Thesis and Dissertation Repository

The hypothesis underlying all of neuroecology proposes that natural selection can modify cognition and its neural mechanisms if these modifications enhance fitness. I tested for sex and seasonal differences in cognition and the brain of brood-parasitic brown-headed cowbirds (Molothrus ater) and the closely related non-brood-parasitic red-winged blackbird (Agelaius phoeniceus) to determine whether cognitive and neural patterns were associated with space use and singing in the wild. Cowbirds show a reversal of sex-typical space use often seen in mammals with only female cowbirds parasitizing, searching for, and revisiting host nests. Cowbird and blackbird males sing more than …

Abnormal Hippocampal Activation In Freely Behaving Mice Deficient For The Vesicular Acetylcholine Transporter, Shahin Moallem

Electronic Thesis and Dissertation Repository

Acetylcholine (Ach) has a fundamental role in cortical activation. The activation of the hippocampus, a cortex implicated in cognitive and sensorimotor functions, is characterized by an increase in power and frequency of oscillations in the theta (4-10 Hz) and gamma (30-100 Hz) frequency range. We studied hippocampal activation in two mutant mouse lines with deficiency in cholinergic functionality: VAChT KD^HET (HET), and VAChT^{Nkx2.1-Cre-flox/flox} (KO). We hypothesized that the mutant mice, relative to wild-type (WT) mice, will manifest abnormal theta and gamma oscillations during different behaviors, and in response to muscarinic cholinergic antagonist scopolamine hydrochloride and to the NMDA …

Resting-State Functional Network Disruptions In A Rodent Model Of Mesial Temporal Lobe Epilepsy (Tle), Ravnoor Singh Gill

Electronic Thesis and Dissertation Repository

Mesial temporal lobe epilepsy (TLE) is the most common form of drug-refractory epilepsy. The clinical application of non-invasively mapped networks using resting-state functional magnetic resonance imaging (rsfMRI) in humans has been rather limited due to heterogeneous (varying etiology, drugs, onset, latent period, etc.) patient groups. We employed a pharmacological (kainic acid) rodent model of TLE to measure the extent of functional network disruptions using rsfMRI, and study selected behaviors and olfactory to hippocampus transmission. Graph theoretical network modelling and analysis revealed significant increase in functional connectivity connectivity to the temporal lobe (hippocampus) in epileptic-rats compared to controls in the limbic …

Differential Effects Of Early-Life Seizures On Neuronal Inhibition In The Hippocampus Of Seizure-Prone And Seizure-Resistant Rats, Amir Abbas Mohseni Zonoozi

Electronic Thesis and Dissertation Repository

The aim of this study is to investigate the long-term physiological consequences of early-life seizures in rats of different genetic backgrounds. Rats bred to be prone (Fast) or resistant (Slow) to amygdala kindling were induced with status epilepticus (SE) on postnatal day (PND) 10 by injecting 3 mg/kg i.p. kainic acid; SE consisted of seizures for 2 h, including stage 5 seizures (lying down with four limb tonic-clonic convulsions). Littermates injected with the same volume of saline i.p. served as controls. On PND 40-55, population spikes (PSs) were recorded at the CA1 pyramidal cell layer in hippocampal slices in vitro …

Placental Insufficiency Resulting In Fetal Growth Restriction Alters Synaptic Development And Neuronal Myelination In Guinea Pigs At Term, Karolina Piorkowska

Electronic Thesis and Dissertation Repository

Aberrant neuronal connectivity in utero may underlie the association between fetal growth restriction (FGR) and increased risk for later cognitive disorders and encephalopathy. This study examines changes in synaptic development and myelination focussing on the hippocampus using a guinea pig model of placental insufficiency. Placental insufficiency was induced at mid-gestation by uterine artery ligation or cauterization which produced fetuses with a range of body weight and proportion at term. Synaptic markers, synaptophysin and synaptopodin, were decreased in FGR animals suggesting fewer synapses were formed and furthermore that fewer synapses matured with symmetrical growth restriction when compared to appropriate for gestational …

Synaptic And Systems Memory Consolidation In The Black-Capped Chickadee (Poecile Atricapillus), Matthew Barrett

Electronic Thesis and Dissertation Repository

ABSTRACT

Memory consolidation - the time-dependent stabilization of information- involves two processes: 1) synaptic consolidation and 2) systems consolidation. Synaptic consolidation uses a series of protein synthesis cascades that make lasting changes in the underlying neural architecture of a memory. Systems consolidation involves the reorganization of memory such that, with the passage of time, memory that is initially hippocampus-dependent can be retrieved and activated independent of the hippocampus. Black-capped chickadees (Poecile atricapillus) store and relocate food using hippocampus-dependent spatial memory. In Chapter 2 inhibition of protein synthesis by anisomycin, either 0 and 2 h or 4 and 6 …

Septal Modulation Of The Hippocampus, Siew Kian Tai

Electronic Thesis and Dissertation Repository

The medial septum (MS) is the main source of acetylcholine to the hippocampus, a structure involved in memory and Alzheimer’s disease (AD). Learning and memory involve long-term changes in synaptic strengths, and are suggested to be facilitated by a brain wave, theta rhythm in the hippocampus. Since medial septal neurons influence hippocampal neural activity, lesion of two neuronal populations in the MS, cholinergic and GABAergic, was performed by intraseptal infusion of 192 IgG-saporin and orexin-saporin, respectively. I hypothesized that 1) activation of cholinergic cells by vestibular stimulation induces an atropine-sensitive theta rhythm, modulates synaptic transmission and enhances long-term potentiation (LTP), …