Diana S. Woodruff-Pak - US grants

The model system of classical conditioning of the eyeblink response in rabbits an(i humans has he potential to elucidate brain mechanisms involved in learning, memory, and aging. Considerable evidence exists that memory has at least two major forms: one requiring conscious recollection of specific learning episodes ("explicit" memory), and the other involving the expression of learning hat is automatic, without conscious or deliberate recollection ("implicit" memory). Studies of classical conditioning in human aging are of particular significance because data may elaborate or challenge theoretical perspectives on memory systems. Research is proposed: (a) to describe more extensively age differences in classical conditioning over the adult human life span, (b) to test hypotheses about mechanisms involved in age effects on classical conditioning, and (c) to explore he cohesion of the theoretical construct of implicit memory in normal older adults and patients with focal brain lesions. A major aim of the first study is to determine the age period when the largest age differences in eyeblink conditioning occur. Adults aged 30-99 years will be classically , conditioned and will be assessed on a battery of neuropsychological tests. We hypothesize that age differences will emerge in the period between 45 and 55 years of age -- a period when the decline in reaction time and Purkinje cell loss accelerate. Simple reaction time and neuropsychological measures of timing (cerebellar function) should be the best predictors of efficiency of classical conditioning. A major aim of the second study is to determine whether there are conditions of optimal timing of the CS-US interval between the conditioned and unconditioned stimulus for middle-aged and older adults when associative learning will be equal to that in the young. A major tim of the third study is to determine how much of the effect of age on classical conditioning is due to health. A major aim of the fourth study is to explore brain memory systems in patients with focal lesions and the role of focal brain damage in implicit and explicit memory tasks. Data from :his project will link behavioral aging effects to the cerebellum and associate learning and memory deficits in aging to this brain structure which is understudied by gerontologists. Results will extend he empirical base of knowledge on aging and eyeblink classical conditioning as a form of implicit memory. We expect to demonstrate that implicit memory tasks are performed in a consistent manner in focal lesion patients, but are dissociated (with some implicit memory tasks showing stability while others show decline) in normal aging when brain changes are not focal.

The focus of the proposal is Research Objective 18-Animal Models of Aging: Development of new informative mammalian models for aging research, including genetically defined and/or genetically altered animals. We aim to develop a mouse model for aging using the neurobiologically and behaviorally well-characterized eyeblink classical conditioning paradigm. The proposal represents entry into a new targeted, high priority area to develop a behavioral aging model in a short-lived species in which transgenic strains are available. The PI received NIA support to investigate eyeblink conditioning in aging rabbits and humans. Technical difficulties prevented the use of rat models of eyeblink conditioning until the late 1980s, and mouse models until the mid-1990s. With the rise of the mouse as biomedicine's model mammal, there are compelling reasons to implement a mouse model of aging and eyeblink conditioning. Five hypothesis-driven steps are proposed to establish a data base for inbred mice of the C57BL/6J strain aged 3-30 months. Hypotheses are based on previous research on eyeblink conditioning in other mammals, including humans. Mice will be tested in the delay and trace eyeblink conditioning procedures with several intervals between the CS and US balanced to assess the effects of CS-US interval and trace interval. It has been established that the essential role of the cerebellum in eyeblink conditioning is comparable in all mammals, including mice. We will evaluate the role of the hippocampus in the delay and trace procedures (documented in rabbits and humans but unknown in mice) in mice so that age-related effects can be better interpreted. Acoustic startle, Prepulse inhibition, Rotorod, and Morris swim task will be tested in all mice to assess for sensory and motor function and to integrate eyeblink conditioning data into the existing literature on behavior and aging in mice. Because of the striking parallels in behavior and raging in rabbits and humans, the rabbit eyeblink conditioning model has been used extensively as a preclinical test of cognition-enhancing drugs. Transgenic mice with AD-neuropathology tested on eyeblink conditioning will be an improved preclinical animal model. Eyeblink conditioning is impaired in normal human aging as early as the age-decade of 40s, and the 400 ms delay conditioning paradigm has a 95% sensitivity for Alzheimer's disease (AD). A mouse model of eyeblink conditioning and aging provides a means to assess a form of learning and memory in normal and transgenic mice that translates directly on a neurobiological and behavioral level to a test applicable in the assessment of human aging and the clinical assessment of AD.

[unreadable] DESCRIPTION (provided by applicant): The large knowledge base on neurobiological and behavioral aspects of associative learning in the eyeblink classical conditioning model in rabbits will be used to identify sites of action and possible mechanisms for cognition enhancing drugs. Eyeblink conditioning reveals natural age-related deficits with striking parallels in several species including humans. In patients with Alzheimer's disease (AD) eyeblink classical conditioning is profoundly impaired, making the procedure relevant for preclinical studies of cognition-enhancing drugs. In addition to parallels with human behavior and neurobiology, the essential neural circuitry for this form of learning has been localized in the cerebellum, with modulatory circuits identified in hippocampus and neocortex. The proposed research is innovative because it has a focus on novel pathways through which cognition-enhancing drugs may affect learning and memory. In addition to septohippocampal acetylcholine (ACh) routes of action, experiments will assess acetylcholinesterase inhibition (AChE-I) and nicotinic acetylcholine receptors (nAChRs) in cerebellum and cerebellar contributions to the facilitation of learning. The cerebellum is essential in classical eyeblink conditioning, but it also plays a demonstrated role in a diverse group of other cognitive functions. Normal age-related decline in cerebellar volume is well documented, yet the cerebellum is seldom studied as a target for drug action. As a brain structure preserved in AD better than the hippocampus, the cerebellum may be a useful target for drug action. Young and older rabbits will be assessed using delay (for which the cerebellum is essential) and trace (for which the hippocampus and the cerebellum are essential) eyeblink conditioning procedures. Aim 1 focuses on site(s) of action of drugs known to ameliorate learning impairment in young and older rabbits using systemic drug injection, 600 and 750 ms delay conditioning, and AChE-I and nAChR binding in cerebellum and hippocampus. Aim 2 focuses on site(s) of action of drugs known to ameliorate learning impairment in young and older rabbits using systemic drug injection, 600 and 750 ms trace conditioning, and AChE-I and nAChR binding in cerebellum and hippocampus. The targets of Aim 3 are the medial septum, cerebellar cortex, and interpositus nucleus where drugs will be infused and acquisition in the delay and trace procedures will be assessed. These studies will likely support hypotheses about ACh mechanisms in learning and memory and may identify the cerebellum as an additional site of drug action. [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): The large knowledge base on neurobiological and behavioral aspects of associative learning in the eyeblink classical conditioning model in rabbits will be used to identify sites of action and possible mechanisms for cognition enhancing drugs. Eyeblink conditioning reveals natural age-related deficits with striking parallels in several species including humans. In patients with Alzheimer's disease (AD) eyeblink classical conditioning is profoundly impaired, making the procedure relevant for preclinical studies of cognition-enhancing drugs. In addition to parallels with human behavior and neurobiology, the essential neural circuitry for this form of learning has been localized in the cerebellum, with modulatory circuits identified in hippocampus and neocortex. The proposed research is innovative because it has a focus on novel pathways through which cognition-enhancing drugs may affect learning and memory. In addition to septohippocampal acetylcholine (ACh) routes of action, experiments will assess acetylcholinesterase inhibition (AChE-I) and nicotinic acetylcholine receptors (nAChRs) in cerebellum and cerebellar contributions to the facilitation of learning. The cerebellum is essential in classical eyeblink conditioning, but it also plays a demonstrated role in a diverse group of other cognitive functions. Normal age-related decline in cerebellar volume is well documented, yet the cerebellum is seldom studied as a target for drug action. As a brain structure preserved in AD better than the hippocampus, the cerebellum may be a useful target for drug action. Young and older rabbits will be assessed using delay (for which the cerebellum is essential) and trace (for which the hippocampus and the cerebellum are essential) eyeblink conditioning procedures. Aim 1 focuses on site(s) of action of drugs known to ameliorate learning impairment in young and older rabbits using systemic drug injection, 600 and 750 ms delay conditioning, and AChE-I and nAChR binding in cerebellum and hippocampus. Aim 2 focuses on site(s) of action of drugs known to ameliorate learning impairment in young and older rabbits using systemic drug injection, 600 and 750 ms trace conditioning, and AChE-I and nAChR binding in cerebellum and hippocampus. The targets of Aim 3 are the medial septum, cerebellar cortex, and interpositus nucleus where drugs will be infused and acquisition in the delay and trace procedures will be assessed. These studies will likely support hypotheses about ACh mechanisms in learning and memory and may identify the cerebellum as an additional site of drug action. [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): Using the model system of eyeblink classical conditioning and other forms of learning and memory (hippocampus-dependent contextual fear conditioning, cerebellum-dependent rotorod), we propose to investigate structural and functional changes and associated mechanisms in the cerebellum and hippocampus over the life span in the mouse. Normal aging affects eyeblink classical conditioning similarly in all species in which older organisms have been tested, including humans. Mice - with their short life span, mapped genome, and capacity to perform a number of cognitive and behavioral tasks - are an invaluable resource to use for understanding causes of age-related impairment in learning and memory. Various brain structures and associated cognitive capacities are differentially affected in normal aging. In hippocampus- dependent learning and memory, aging is associated with reduced functional capacity of CA1 pyramidal cells, but neuron number is stable. Cerebellum-dependent learning and memory is associated with Purkinje cell loss and age-related impairment in morphology as well as function. Traditionally, cerebellar and hippocampal substrates of learning, memory, and aging have been studied independently. The major aim of this proposal is to use mouse models to test hypotheses about cerebellar-dependent and hippocampus- dependent mechanisms responsible for age-related deficits in learning and memory. Aim 1 addresses associations between neuron and glia numbers in cerebellar cortex and deep nuclei and hippocampal CA1 fields and several forms of learning and memory in C57BL/6 mice. Aim 2 explores neuron and glia number and learning in young homozygous and aging heterozygous Purkinje cell degeneration (pcd) mutant mice. Aims 3 and 4 examine functional aging of neurons in hippocampal and cerebellar slices, respectively. Aim 5 initiates pilot testing of the potential of GABA infusions to ameliorate impaired learning. Relevance: Research over the life span of mice using measures with parallels to human aging has the potential to extend knowledge about individual variation and differential aging in brain regions that are the substrates of learning and memory. The extended life expectancy of people in the United States and the world adds urgency to the need to identify causes and treatments for age-related cognitive deficits. This proposal has the potential to expand perspectives and devise treatments to facilitate learning and memory in older adults. [unreadable] [unreadable]