Donald A. Wilson - US grants

The goal of this research is to understand how the expression of mature olfactory system function is influenced by sensory input during ontogeny. Specifically, the proposed research is an investigation of the effects of early unilateral olfactory deprivation on olfactory bulb physiology and function. While early unilateral olfactory deprivation has been shown to produce profound changes in olfactory bulb anatomy, the functional consequences of this deprivation are not known. The proposed research will examine several functional measures under a variety of deprivation conditions. First, response patterns of bulb output neurons, mitral/tufted cells, to odors will be examined after varying durations of deprivation. Second, the effects of deprivation on the activity of bulb interneurons will be assayed using paired-pulse stimulation. Third, the role of glomerular layer dopamine, which is severely reduced by deprivation, will be examined. Fourth, behavior odor detection thresholds following deprivation will be determined. Finally, the age sensitivity and reversibility of deprivation effects on these measures will be determined.

The goal of this research is to understand the neural mechanisms of associative learning in infants. Specifically, the proposed research investigates the neural substrates of postnatal olfactory learning in newborn rats. This early learning is associated with specific changes in neural structure and function in the olfactory bulb, the first central relay for olfactory information processing. Our previous work has demonstrated that output neurons in the olfactory bulb, mitral/tufted cells, modify their response patterns to odors learned during the early postnatal period. Furthermore, we have found that mitral/tufted cells receive convergent information about both odor stimuli and "reward" stimuli. Importantly, both the behavioral and neural consequences of early learning are norepinephrine (NE) dependent, as is at least one component of mitral/tufted cell response to reward. The proposed experiments examine how mitral/tufted cells are modified during olfactory associative learning and uses a combination of neurophysiological and neuropharmacological techniques to further explore the neural substrates of the descending "reward" input to the olfactory bulb. Based on preliminary data, a specific circuit is proposed for convergence of odor and reward information in the bulb involving the primary olfactory nerve and centrifugal inputs to the bulb which are known to primarily terminate on GABAergic interneurons. Each of these components will be examined in relation to early learning. The results will provide important information regarding the neural pathways and pharmacology involved in a critical form of learning expressed soon after birth in many animals including humans.

Description (adapted from applicant's abstract) Habituation, a simple form of nonassociative memory, is a common feature of sensory systems and is characterized as a decrease in responsiveness to repeated stimuli. Sensory habituation allows filtering of less significant, or predictable events than other mechanisms such as receptor adaptation. Disorders of sensory filtering have been implicated in disease states such as autism. The present proposal examines mechanisms of olfactory habituation in the anterior piriform cortex (aPCX). The aPCX is an ideal model system to study habituation because of its relatively simple and well described synaptic organization, and the extensive knowledge of its synaptic physiology. Preliminary results demonstrate that aPCX neurons habituate more rapidly than simultaneously recorded afferent activity from the main olfactory bulb, and that this habituation is associated with a decrease in afferent synaptic efficacy. The proposed work is divided into four basic experiments. The first will further describe odor habituation in the aPCX and main olfactory bulb, with particular attention paid to characterizing its time course and odor specificity. Specific responses will be correlated with cell morphology and location by intracellular filling and imaging of recorded cells. The second experiment will further examine synaptic correlates of odor habituation by measuring the efficacy of identified synapses within the aPCX. (This aim has already been partially met by results obtained since the application was submitted, that indicate that there is a decrease in synaptic afferents with odor habituation.) The third and fourth experiments will test specific hypotheses of odor response plasticity with a combination of intracellular recording and pharmacological manipulations. The third is specifically aimed at the role of decreased excitation in odor habituation, particularly LTD mediated through NMDA receptors. The fourth will examine the role of increased inhibition in habituation, produced through either GABAA or GABAB receptors. Together, it is hoped that these studies will provide important information into both the mechanisms of habituation and synaptic mechanisms of information processing in the olfactory system.

DESCRIPTION (provided by applicant): Alzheimer's disease (AD), the sixth leading cause of death in the United States, currently affects over 5 million North Americans and their families as well as the United States health care system. Impaired olfactory perceptual acuity, including deficits in odor identification, detection and discrimination are often observed early in the progression of AD. Understanding the neural basis for these sensory deficits is important in that 1) their etiology may unveil new insights into AD pathogenesis and 2) olfactory screens may serve as early-indicators of AD when combined with neuropsychological examinations. SPECIFIC AIMS: This proposal describes an experimental strategy aimed at understanding the contributions of amyloid-2 (A2) to olfactory system dysfunction. Behavioral, neurophysiological and molecular experiments will be performed in mice which overexpress human mutations of Amyloid 2 Precursor Protein (APP). Aim 1 will test the hypothesis that progressive A2 burden and AD-like olfactory perceptual deficits are related to abnormal odor information processing at local and global levels in AP transgenic mice. The remaining two aims will utilize novel genetic models of A2 remediation to examine methods to rescue/preserve olfactory function in APP transgenics. AIM 2 wil test the hypothesis that chronic enhancement of A2 degradation improves olfactory processing and perception by using mice which lack the protease inhibitor cystatin B (CBKO). AIM 3 will use mice over expressing the protease inhibitor cystatin C (CysC) to test the hypothesis that preventing A2 aggregation improves olfactory procesing and perception. These ongoing studies are the first to directly assess the contributions of A2 to olfactory perceptual dysfunction.

DESCRIPTION (provided by applicant): Cortical processing of sensory information plays a critical role in sensory discrimination, object recognition and memory. Cortical sensory processing has been shown to be highly dynamic, with past experience, current context and expectations shaping how the world is perceived on a moment by moment basis. Disorders of sensory processing constitute a major component of impairments induced by CNS disease and aging, as well as congenital disorders such as schizophrenia and autism. A largely overlooked aspect of odor processing is the role of top-down inputs in shaping olfactory cortical activity based on past-experience, expectation and context. Here we propose to explore the role of the lateral entorhinal cortex (LEC) in both odor processing and top-down control of piriform cortex (PCX ) and olfactory bulb. The LEC is both a component of the olfactory cortex (receives direct input from the olfactory bulb) and is a major component of the temporal lobe/limbic system memory circuitry as the primary afferent to the hippocampal formation. Importantly, the LEC also sends a strong projection back to the PCX and olfactory bulb - a pathway not well understood. There are three specific aims, each supported by new preliminary data, that test novel, specific hypotheses about the function of LEC in olfaction. In Specific Aim 1 we will extend our initial work showing significantly more selective single-unit odor receptive fields in LEC compared to PCX. First we will use in vivo intracellular recording in anesthetized animals to allow odor RF characterization of identified LEC cell types, and second we will compare single-unit and ensemble odor evoked activity in the awake, freely moving LEC and PCX to novel and familiar odors. These data will be the first to characterize olfactory sensory physiology of this region of olfactory cortex, and test our hypothesis that odor coding becomes more precise, in an experience-dependent manner, in this neocortical component of the olfactory cortex. In Aim 2, using optogenetic and reversible lesion techniques we will extend our preliminary data to test the hypothesis that LEC feedback to PCX functions in a highly cell specific manner to shape both PCX neuron odor RF's and temporal structure of PCX activity. This top-down influence may contribute to both perceptual acuity and odor memory as tested in Aim 3. In Aim 3 we will extend our preliminary data in awake, freely moving animals performing odor discrimination tasks to test our hypothesis that LEC top-down input shapes odor acuity both by modulating ongoing PCX odor-evoked activity and by contributing to anticipatory PCX single-unit and ensemble activity, prior to odor onset. Each Aim uses innovative concepts and techniques to test specific hypotheses regarding the role of a structure that serves not only as a component of the olfactory cortex, but also as a critical component of temporal lobe memory circuits.

DESCRIPTION (provided by applicant): Fetal alcohol spectrum disorder (FASD) is one of the primary causes of intellectual disability in western nations, with neurobehavioral hallmarks such as deficits in learning, memory and mood. While it is known that developmental ethanol exposure can disrupt sleep structure, here we propose that developmental ethanol exposure may induce long-lasting disruption of neural activity patterns during sleep which are known to be important for memory consolidation and synaptic homeostasis. If so, this would create a situation wherein the normal ability of the nervous system to repair and readjust itself during sleep would be impaired, resulting in a daily insult to nervous system function long after the ethanol exposure ended. Specifically, in this proposal (PA- 12-177: Alcohol abuse, sleep disorders and circadian rhythms [R01]) we plan to explore the effects of binge- like ethanol exposure of prenatal or neonatal mice on long-term changes in sleep-associated activity in the olfacto-hippocampal pathway, and to begin to explore the role of GABAergic interneurons in this network activity. While prolonged exposure paradigms may align more closely to common etiologies of FASD, the binge model allows a more precise dissection of mechanisms, and thus potential avenues of treatment. Aim 1 is to test the hypothesis that early ethanol exposure induces long-term modification of both local (within region) and global (between regions) network activity within the olfacto-hippocampal pathway during slow-wave sleep. We will explore the long-lasting effects of early ethanol exposure on sleep related changes in single-unit activity and regional coherence, and predict specific disruptions in sleep structure, spike train temporal structure and in resting state functional connectivity during sleep that could result in cognitive and behavioral deficits. Aim 2 is to test the hypothesis that early ethanol exposure induces long-term modification of GABAergic interneuron structure and function in hippocampus and piriform cortex. We will explore the long-lasting effects of early ethanol exposure on GABAergic cell survival and, using a novel transgenic model, test whether disturbance in a specific GABAergic cell class known to be important for controlling neural synchrony mimics developmental ethanol's effects on neural circuit function in waking and sleep. Finally, Aim 3 will explore the hypothesis that neuroprotectants delivered at the time of the early ethanol exposure, or GABAergic or slow-wave sleep manipulations in adults can prevent or repair sleep disruption and its effects on cognition. If successful, the data could open a new window into both understanding and repair of early ethanol-induced neural and cognitive impairment. Furthermore, this collaborative proposal brings an established researcher in another field into the ethanol field (Wilson).

ABSTRACT Apolipoprotein E (ApoE) genotype, the primary carrier of cholesterol within the brain, is an important determinant of an individual's risk for developing Alzheimer's disease (AD). While the ?2 allele (ApoE2) appears to be protective, ApoE4 increases the risk for the disease. Growing evidence, including our findings within this application, argue that ApoE genotype affects the endosomal and exosomal pathways. In young ApoE2 mice, our preliminary studies have shown that neuronal early endosomes are reduced in size and number while a greater number of exosomes are seen in the brain extracellular space as compared to mice expressing the human ApoE3 allele, the neutral-risk allele in humans, or mice expressing the pathogenic ApoE4 allele, which leads to abnormally enlarged early endosomes and lower levels of exosomes in older mice. We propose that exosomes, secreted vesicles generated within endosomal compartments, help clear endosomal vesicular content from the endocytic pathway, thus contributing to the preservation of neuronal endosomal function during aging. Additionally, we hypothesize that the facile movement of cargo through the endocytic pathway in ApoE2 carriers contributes to efficient lysosomal function. This combination of endosomal and exosomal changes driven by ApoE2 suggests interrelated, and potentially additive, neuroprotective cellular processes. We propose to test our hypothesis that expression of the ApoE2 allele results in protective changes within the endosomal and exosomal pathways by examining humanized ApoE mouse brain at various ages as well as ApoE genotyped human brain tissue (Aim 1). In brain-derived endosomes and exosomes we will examine the lipidome and proteome and in exosomes, RNAs to identify molecular alterations that mediate protective ApoE2 endosomal and exosomal functions. To tie ApoE2 cell biology to brain function we focus on the olfactory system. Several recent studies, including both mouse and human data in part from our group, demonstrate that olfactory sensory physiology and perception may be especially sensitive biomarkers of ApoE genotype. For example, ApoE4 carriers have impaired odor identification (humans), impaired odor memory and olfactory system hyperexcitability (mice). In Aim 2, we will examine both olfactory sensory physiology and behavior to test the hypothesis that the ApoE2 isoform modulates olfactory function and can rescue ApoE4 deficits. Finally, in preliminary studies we have shown that a high fat/cholesterol diet causes neuronal endosomal pathway pathology in wild-type mice. In Aim 3, we will test our hypothesis that ApoE2-induced efficiencies in the endosomal and exosomal pathways protect from dietary lipid-induced endosomal pathway abnormalities. The overall objectives of our study are to characterize interconnected cellular pathways that we propose are protective in individuals expressing ApoE2 and to determine whether maintaining efficient endosomal and exosomal function through ApoE2 expression reduces neuronal vulnerability and cognitive deficits during aging, focusing in part on the highly informative olfactory system.