David J. Bucci, PhD - US grants

The results of recent studies indicate that selective lesions of the cholinergic neurons projecting from the substantia innominata (SI)/nucleus basalis (nBM) to cortical regions produce deficits in increasing, but not decreasing attention to a conditioned stimulus in rats. As a complementary approach to these lesion studies, neurobiological methods will be used in the proposed research to examine in greater detail the cortical systems involved in attentional processing. Expression of c-fos , as a possible neuronal indicator of cholinergic activation, will be used to anatomically map the cortical systems involved in incrementing attention to a cue (Specific Aim 1). Once a behaviorally-induced c-fos response is established, the effect of removal of SI/nBM cholinergic neurons on both behavioral performance and c-fos induction will be examined, to determine if the observed cortical activation depends on basal forebrain cholinergic input (Specific Aim 2). The results of neuropsychological studies have shown that certain regions of cortex, such as parietal cortex, are involved in the regulation of attentional processes. Our preliminary findings indicate that discrete cortical regions (e.g., within parietal cortex) are activated at different timepoints when attention is increased. The cholinergic projections to specific cortical regions will be removed to examine the role of discrete corticopetal subunits and cortical regions in increasing attention (Specific Aim 3). These studies may provide an important and useful animal model that bears on our understanding of mechanisms of attention in humans. Such a model may be of particular use in identifying the basis of attentional deficits associated with aging, Alzheimer's Disease, and schizophrenia.

Recent anatomical studies have identified a region of cortex in the rat, termed postrhinal cortex, that may be homologous to the parahippocampal cortex of primates. In both monkeys and rats, the primary cortical afferents of this region arise from visual association cortex and visuospatial regions such as posterior parietal cortex, suggesting that this region is involved in visuospatial function. Consistent with this concept are preliminary findings indicating that the postrhinal cortex plays a role in specific aspects of spatial memory as well as visuospatial attention. The goal of the proposed research is to further explore the function of this circuitry in spatial cognition. Neuroanatomical methods will be used to examine in detail the topographical and laminar pattern of visuospatial input to the postrhinal cortex (Specific Aim 1), as well as the intrinsic organization of the visual association, posterior parietal, and postrhinal cortices (Specific Aim 2). Neurophysiological methods will be used to examine the encoding of visuospatial information in postrhinal cortex while rats perform a spatial memory task and a visuospatial precueing task designed to measure attentional function (Specific Aim 3). The proposed experiments will be conducted with the purpose of furthering our understanding of the role of medial temporal lobe structures in cognitive function. Findings from these studies may have direct bearing on the neurobiological bases of cognition in both normal and brain-damage humans.

Deficits in attentional function are associated with a variety of conditions in humans, including schizophrenia, attention-deficit disorder, as well as neuropathological (i.e., Alzheimer's disease) and normal aging. The occurrence of deficits in this context, however, has provided little information about the precise neural substrates underlying attention. Such information would provide insight into the biological bases of attentional dysfunction and possibly inform new methods of therapeutic intervention. Additionally, a better understanding of the neurobiology of attention may help identify the biological mechanisms by which stimuli are selected and gain access to further processing, such as long-term memory. In primates, a cortical network including the cingulate, frontal, and posterior parietal (PPC) cortices has been postulated to mediate attentional function. Indeed, impaired PPC function has been linked to attentional deficits in Alzheimer s disease, Parkinson s disease, schizophrenia, and dyslexia. Recent neuroanatomical studies have now identified a region in the rat brain that may be anatomically homologous to the PPC of primates. However, very few studies have addressed the specific behavioral functions of the rat PPC as it is now defined. Further understanding of PPC function in rats would allow subsequent research to take advantage of techniques more readily available in rodents (e.g., gene & protein expression) to explore the neurobiological mechanisms underlying attentional function. In the proposed research, a neural inactivation approach will be developed to more accurately ;haracterize the contribution of the rat PPC to attentional processes. Rats will be trained in a classical conditioning paradigm designed to increase attention to behaviorally-important stimuli. The PPC will be temporarily inactivated at the point in the procedures when attention is manipulated, to assess the importance of PPC function in this aspect of attentional processing. This approach will form the foundation for a more extensive research program which will explore the function of putative subregions of PPC as well as other components of the cortical attention network in different aspects of attention.

The educational component of this Early Career project is designed to enrich undergraduate neuroscience education at the University of Vermont. The educational activities will increase the exposure of undergraduates to neuroscience and foster the development of professional skills. First, a Behavioral Neuroscience Research Series will be incorporated into introductory psychology classes to provide early exposure to research opportunities. An upper-level Neuroscience Seminar will be developed, focusing on current "hot" topics in neuroscience selected from the list of Symposia scheduled for the Society for Neuroscience Annual Meeting. Students will also accompany Dr. Bucci to the Annual Meeting. A third activity involves increasing undergraduate participation in research by supporting student research projects in Dr. Bucci's laboratory. Lastly, an Undergraduate Neuroscience Club will be established to enhance interaction among neuroscience students and to foster the development of scientific and professional skills.
The research component of the project will test hypotheses concerning the involvement of multiple brain systems in processing environmental stimuli. Animals are routinely bombarded by numerous stimuli, and it is believed that the extent to which a stimulus is processed, or attended to, influences how much learning will occur. The ability to alter levels of stimulus processing has adaptive value in that it permits an individual to actively devote resources to learning about cues that are behaviorally important while ignoring unimportant cues. The first phase of the project will test the hypothesis that two competing brain systems are involved in increasing the processing of important stimuli versus decreasing the processing of irrelevant stimuli. Subsequent studies will determine if and how these processing pathways interact, using both lesion approaches and monitoring neural activity in specific brain regions. The planned studies will inform theories of learning as well as provide valuable insight into the brain mechanisms of stimulus processing and memory.

DESCRIPTION (provided by applicant): Attention Deficit/Hyperactivity Disorder (ADHD) is one of the most common childhood psychological disorders, occurring in as many as 3-5% of children. The symptoms of ADHD, including inattention, restlessness, impulsivity, and hyperactivity, often lead to significant difficulties in functioning. Dysfunction of central dopaminergic and noradrenergic systems is thought to play a major role in producing this impairment. A recent clinical study by members of our group provides preliminary evidence that nicotine treatment ameliorates the deficits in behavioral inhibition in adolescents suffering from ADHD. Interestingly, adolescents with ADHD are twice as likely to become cigarette smokers and tobacco users as those without ADHD, a trend that continues into adulthood. The positive effects of nicotine on cognitive processing and inhibition may contribute to the higher risk of chronic tobacco use/abuse. At the present time, the reasons underlying the vulnerability of individuals with ADHD to use/abuse tobacco are poorly understood, as are the neurobiological mechanisms by which nicotine exerts its beneficial effects. To fill this gap in the existing literature, this R21 application will develop a research partnership between existing basic and clinical investigators to explore the role of cholinergic systems in the cognitive and behavioral symptomatology of ADHD and possible links to substance abuse. Basic studies of the behavioral and neurobiological mechanisms of cholinergic involvement related to ADHD will have direct bearing on clinical research by 1) providing additional insight into the etiology of ADHD, 2) improving the characterization of behavioral and neurochemical deficits associated with this disorder, 3) guiding future drug development (e.g., cholinergic therapies), and 4) facilitating the identification of individuals who may be at high risk for substance abuse. Consistent with the recent recommendations of the National Advisory Mental Health Council Behavioral Science Workgroup (2000), the primary outcome of our collaboration will be the development of a coherent Translational Research Agenda to develop this area of research. In addition, the proposed activities will generate valuable preliminary data for subsequent full-scale studies and preparation of follow-up research applications (e.g., R01, R24).

It is widely accepted that the hippocampus and other medial temporal lobe structures have a critical role in many forms of learning and memory. However, little is known about the contributions of regions such as the retrosplenial cortex (RSP), which is heavily interconnected with medial temporal lobe regions. Indeed, the RSP is well positioned as an interface between the sensory neocortex, thalamus, and medial temporal lobe structures. One theory is that RSP serves to integrate sensory and limbic information for subsequent mnemonic processing by medial temporal lobe regions. Another theory is that RSP is a site of long term storage of information processed by the medial temporal lobe. The proposed studies will test specific hypotheses concerning the contribution of RSP to the medial temporal lobe memory system using a combination of experimental lesion, neural activation, and learning-theoretical approaches. The resulting data will not only provide new insight into the function of RSP but also add to our understanding of the basic mechanisms of information processing in cortico-hippocampal circuits. Moreover, the data will be useful for determining how different components of these circuits interact, and aid in the development of new models of cortico-hippocampal function. Carrying out the proposed studies will also provide valuable research training and opportunities for undergraduates at Dartmouth College, and use new initiatives to promote science education and research training particularly in groups that are typically underrepresented in the sciences. At a community level, research findings will also be used to expose the local community to basic research in learning and memory through an outreach program developed in collaboration with a local science museum.

DESCRIPTION (provided by applicant): Although recent anti-smoking campaigns and legislation have achieved success in reducing the number of adult cigarette smokers, other populations have been not so positively affected. For instance, there continues to be high rates of nicotine use in adolescents as well as in various clinical populations, including those with schizophrenia or Attention- Deficit/Hyperactivity Disorder (ADHD). Despite substantial research, it remains unclear why nicotine use is high in these groups. Various theories have been proposed, including the notion that nicotine is used to alleviate dysfunctional reward systems and that nicotine is used to self-medicate for cognitive impairment. Nicotine has beneficial effects on functions such as attention and memory, lending support to the latter theory. However, little is known about the effects of nicotine and the role of nicotinic acetylcholine receptors in regulating inhibitory behavior. Deficits in inhibition are considered among the core impairments in ADHD and are also associated with schizophrenia. Likewise, normal adolescence is often characterized by impulsivity and inhibitory deficits. To fill this gap in the literature, the proposed experiments will determine how nicotine effects inhibition using an animal model of response inhibition that is analogous to inhibition tasks commonly used in research with humans. Our preliminary data indicate that nicotine specifically enhances the ability of rats to withhold a learned response, as has been observed in humans with ADHD. Thus, the first objective will be to determine which subtype(s) of nicotinic acetylcholine receptor mediates the beneficial effects of nicotine on inhibition. This will be done using pharmacological approaches in both normal rats and a strain of rats commonly used as a model of ADHD. The second objective is to determine the brain systems through which nicotine affects inhibition. These studies will use a combination of approaches consisting of selective cholinergic denervation of the prefrontal cortex or hippocampus, and treatment with nicotinic receptor subtype-specific compounds. Finally, the third objective is to test for sex differences in the effects of nicotine on inhibitory behavior. These final experiments are based on growing reports of sex differences in cognitive dysfunction in disorders such as ADHD and differences in smoking rates between males and females. Together, these results of the proposed studies will provide new insight into how nicotine affects inhibitory behavior and promote the development of enhanced smoking cessation and treatment regimens.

The mammalian hippocampus is essential for binding together individual objects or events with the place and time in which they occur ('episodic memory'). An essential part of this process is the binding together of stimuli that compose the environment, or context. For example, a person recognizes his/her home in part because various individual sensory stimuli have been linked together as a "unit" that is identified collectively. These units of associated stimuli remain labile and can be updated as circumstances change. Thus, contextual learning/memory provides an organism with several adaptive advantages, including the ability to recognize and predict where a biologically significant stimulus may be located. Information regarding the physical and temporal context in which the object/event occurs is provided to the hippocampus by a network of specific cortical regions; yet, it is unknown how the components of this network contribute to processing contextual information. This project will illuminate the how the different regions that compose the where/when pathway contribute to contextual learning/memory. Addressing these issues will lead to the development of a new model of cortico-hippocampal function and provide essential information regarding the basic organizing principles of the mammalian hippocampal memory system.

Sophisticated behavioral methods will be combined with innovative neurobiological techniques (recordings and designer receptor-based manipulations of cell populations in awake, behaving animals) to determine how the restrosplenial cortex (RSC) and the postrhinal cortex (POR) contribute to contextual learning and memory. Other studies will determine how the RSC and the POR interact at the synaptic level during learning. Carrying out the proposed studies will also provide valuable research training and opportunities for undergraduates at Dartmouth College, and use new initiatives to promote science education and research training, particularly in groups that are typically underrepresented in the sciences. At a community level, research findings will also be used to expose the local community to basic research in learning and memory through an outreach program developed in collaboration with a local science museum.

Project Summary/Abstract This project is aimed at understanding the neural mechanisms of learning and memory. An extensive literature has documented the role of the hippocampus, retrosplenial cingulate cortex and anterior thalamus in memory functions. Damage to these brain regions is a primary cause of the memory impairments seen in Alzheimer's disease, age-related memory decline, and various human amnesic syndromes and learning disabilities. Abnormalities in these structures have also been implicated in depression, anxiety and schizophrenia. Understanding the function of these systems is crucial for the development of treatment strategies for patients with these conditions. The memory role of the hippocampus has been well documented and, although they have not been studied as extensively, the retrosplenial cortex and anterior thalamus are also known to play a critical role in learning and memory. However, the precise contribution of each of these brain regions to the learning process remains unclear. Recent findings suggest that these closely interconnected structures form a functional circuit which mediates spatial and contextual memory. The proposed experiments are focused on understanding how memory-related information is represented by neurons in the retrosplenial cortex, and how interactions of the retrosplenial cortex, hippocampus and anterior thalamus support memory functions. In order to investigate this, neuronal activity will be recorded in these brain regions as rats perform various spatial and contextual memory tasks. Optogenetic, chemogenetic and neurochemical methods will be used to suppress neuronal activity in various components of this circuit in order to assess their contributions to functioning in the broader memory circuit. By monitoring neuronal responses as subjects learn and the effects of temporary inactivation within the circuit, it will be possible to determine how memory related information is processed and how memory may fail when damage occurs within the circuit.

Project Summary Individuals with fear disorders such as post-traumatic stress disorder (PTSD) experience excessively strong and intrusive fear memories about stimuli that were encountered during a prior trauma, including individual sounds or visual stimuli (?cue-specific? fear memory) or the combination of stimuli that together define the place in which the event occurred (?contextual? fear memory). The memories may have been formed recently or long ago (?remote? memories), in which case they may plague a person for a substantial portion of his/her life. The development of effective therapies depends on a thorough understanding the neural mechanisms that underlie these different types of fear memories, as well as fear extinction, which is the basis for exposure- based therapy commonly used to reduce fear in humans. To date, a substantial body of research has identified discrete neural systems that support recent versus remote contextual memory, and other studies have identified the substrates of recently-acquired cue-specific memory and extinction, but very little work has focused on the brain mechanisms involved in remote cue- specific memory and extinction. This is important to resolve particularly with respect to PTSD since individuals often do not seek therapy until long after the traumatic event, especially in cases of combat trauma or sexual assault. To address this, the proposed research advances a new theoretical model of the neural circuits that underlie remote cue-specific fear memory and extinction. This model is based on new data from our laboratory and combines state-of-the art chemogenetic and optogentic-anatomical approaches to test the hypotheses that a) communication between the retrosplenial cortex and secondary sensory cortices is necessary for remote cue-specific fear memory, and b) the postrhinal cortex mediates the context-dependency of extinction of remote cue-specific fear.