Paul E. Gold - US grants

memory; epinephrine; neurotransmitter metabolism; neuropsychology; learning; appetite; vagus nerve; glucose metabolism; antiadrenergic agents; norepinephrine; avoidance behavior; high performance liquid chromatography; vagotomy; laboratory rat; adrenalectomy;

DESCRIPTION (provided by applicant): Administration of glucose enhances learning and memory in rodents and humans, and is especially effective in reversing age-related impairments in memory. This research project will examine whether age-related changes in the regulation of blood and brain glucose contribute to age-related impairments of learning and memory. Training is often accompanied by increases in circulating epinephrine levels, with subsequent increases in circulating glucose levels, in a manner related to endogenous modulation of learning and memory. Recent evidence suggests that, in aged male Fischer 344 rats, there is an uncoupling between epinephrine release from the adrenal medulla and subsequent increases in blood glucose levels, resulting in diminished responses of circulating glucose levels to training. The reduced responses of blood glucose levels may significantly influence brain processes important for learning and memory. In the brain, extracellular glucose levels in the hippocampus are depleted while rats are tested on a hippocampus dependent spontaneous alternation task. As compared to young adult rats, aged rats perform poorly on this task and exhibit exaggerated depletion of glucose in the hippocampus during behavioral testing. Injections (i.p.) of glucose block the depletion in the hippocampus and also enhance performance on the alternation task in aged rats. Together, these findings suggest that altered control of glucose levels in blood and brain during aging may contribute to age-related impairments of memory. Using young and old rats, the proposed experiments will examine the contribution of age-related changes in responses of glucose to training to age-related changes in learning and memory. Proposed experiments will examine changes in circulating and brain glucose responses to training in aged rats, assessing the relationship of these changes to learning and memory. The experiments will determine whether the depletion of extracellular glucose levels in the hippocampus, prominent in aged rats, is evident also in the striatum and prefrontal cortex. These experiments include measures of changes in extracellular brain glucose levels during training with and without treatments that enhance learning and memory in aged rats and also assess the efficacy in enhancing learning and memory of microinjections of glucose directly into those brain areas in which glucose is depleted by training.

This is an application to investigate glucose effects on memory in rodents. Using injections directly into the medial septum, amygdala and hippocampus, the first set of experiments determines which drug effects on learning and memory are sensitive to additional direct brain injections of glucose. Using intraseptal drug injections and microdialysis/HPLC measures of acetylcholine release in the hippocampal formation, the second set of experiments determines whether, regardless of the primary target of glucose actions, an output which predicts drug effects on learning and memory is release of acetylcholine. A third set of experiments employs determines whether 2-deoxyglucose uptake in the amygdala is depressed by intra-amygdala injections of morphine, muscimol, scopolamine, propranolol or AP5 and restored only in the first two instances (paralleling known and predicted behavioral results) by additional treatment with glucose. A fourth set of experiments determines whether, like glucose and glucose metabolites can attenuate memory impairments after intraseptal morphine injections. These findings provide initial evidence regarding the contribution of glucose metabolism to glucose effects on learning and memory.

Largely on the basis of lesion studies, different neural systems appear to be responsible for learning and remembering different classes of information. However, most learning experiences contain information that crosses the classes served by these distinct neural systems. The main goal of this project is to determine whether modulators of memory processing regulate the relative participation of different brain systems during learning, thereby regulating what different rats learn in those situations. The proposed experiments use direct brain injections of glucose and morphine, together with in vivo microdialysis/HPLC measures of acetylcholine output, to study learning and memory in rodents. Three tasks and three brain areas will be tested: conditioned place preference learning, amygdala-dependent; place learning, hippocampus-dependent; response learning, striatum-dependent. The first set of experiments uses direct injections of glucose and morphine, treatments which enhance and impair learning and memory processes where injected. Because each of the anatomical systems can at times interfere with learning by another system, some predictions include apparently paradoxical impairment and enhancement of learning by appropriate injections of glucose and morphine. The second set of experiments determines whether training-related increases in acetylcholine are restricted to those neural systems activated by different training procedures. Included is one task in which rats can learn using either of two strategies. Because each strategy is likely to require major participation by a different neural system, measures of acetylcholine output in each system during training might reveal what an individual rat is learning, i.e. which strategy it employs during learning. The third set of experiments determines whether glucose enhancement of learning and memory is accompanied by augmented acetylcholine release only in the neural system activated by specific training. The findings of these experiments may lead to a new view of how modulators of memory regulate the relative participation of different memory systems during learning.

DESCRIPTION (provided by applicant): This proposal examines the effects of chronic stress on the balance between multiple memory systems. Chronic stress impairs learning and memory on many tasks, though there are some reports of no effect or enhanced learning after chronic stress. Current findings indicate that different memory systems interact in a manner that includes instances of competition, often demonstrated by showing that lesions or pharmacological inactivation of one system can enhance learning of a task typically associated with a different neural system. By using in vivo microdialysis coupled to sensitive assay procedures, it is possible to examine release of acetylcholine during the course of training rats in mazes, with sample collection timed to match only a few training trials. Findings from studies such as these have shown that release of acetylcholine in several neural systems is a useful marker of the extent to which a system is activated by training. For example, when rats are trained on a T-maze that can be learned using either place (hippocampus-dependent) or response (striatum-dependent) solutions, acetylcholine release before and during training predicts which rats use each solution. This proposal will use such procedures to determine whether chronic stress produces a shift in which neural system is preferentially activated during learning, thereby impairing learning of some tasks and enhancing learning of other tasks. In addition, this proposal will examine simultaneously acetylcholine release in the hippocampus and striatum, at baseline and in response to training, to determine whether chronic stress results in different profiles of acetylcholine release associated with changes in cognitive processing. Thus, the findings of these experiments may offer a basis for apparently discrepant behavioral findings after chronic stress. More generally, the findings address the key issue of whether chronic stress results in a change in the balance between neural systems, thereby altering the strategy selected by a rat faced with a new problem to solve.

[unreadable] DESCRIPTION (provided by applicant): Protein synthesis inhibitors impair the formation of new memories, block analogs of memory such as long-term potentiation and depression, and block other instances of neural change including drug tolerance and extinction. These findings provide the foundation for the view that memory and other durable changes in the brain are formed by processes dependent on de novo protein synthesis. However, amnesias produced by protein synthesis inhibitors may be mediated by consequences of inhibition of protein synthesis other than loss of new proteins needed for memory formation. Using in vivo microdialysis in combination with local brain injections, we recently obtained findings showing extraordinary changes in neurotransmitter release after injections of the protein synthesis inhibitor, anisomycin, into the amygdala. Release of norepinephrine, dopamine and serotonin at the site of injection soared initially before falling well below baseline values during the subsequent hours. In addition, anisomycin-induced amnesia was attenuated by co-administration of drugs aimed at blocking the consequences of neurotransmitter release soon after anisomycin injection or at reversing the consequences of later depressed release. These findings suggest that neurotransmitter responses to the drug, rather than protein synthesis per se, may account for anisomycin-induced impairments in memory. The results thereby raise significant questions about some of the fundamental support for many theories about the molecular bases of memory. This proposal will test the generality of the recent findings by: (1) examining the effects on release of biogenic amines of intra- amygdala injections of cycloheximide, which inhibits protein synthesis by a mechanism different that of anisomycin, and (2) examining the effects on release of biogenic amines of protein synthesis inhibitors administered directly to the hippocampus. The results of these experiments will extend the recent findings obtained with one inhibitor (anisomycin) and one brain region (amygdala) to determine whether protein synthesis inhibition more generally impairs memory by altering neurotransmitter actions. These findings may place the mechanisms underlying the effects of protein synthesis inhibitors on memory within the context of modulation of memory by monoamines and other neurotransmitters. A central tenet of contemporary models of memory and neural plasticity is that the underlying brain changes pass through two major phases, an early protein synthesis- independent phase and a later protein synthesis-dependent phase. These views have become fundamental and rarely questioned properties of the molecular basis of memory formation. These views have also been applied to the mechanisms underlying a wide range of other forms of brain changes, including drug abuse and relapse, epilepsy, and organization of motor cortex and other brain areas during development and during reorganization after stroke. In each of these contexts, the basic evidence is that protein synthesis inhibitors block enduring neural changes - i.e. memory, drug relapse, epilepsy, or motor cortex organization - by blocking mechanisms of change that require protein synthesis. Our recent findings call into question the interpretation of data obtained with the most commonly used protein synthesis inhibitor, anisomycin, by provided clear evidence that the effects on memory are mediated by neurotransmitter responses to the insult of protein synthesis inhibition. The research proposed here examines key properties regarding the generality of these findings, across brain areas and across drugs that interfere with protein synthesis. If these findings are indeed general, will require a reconsideration of basic molecular mechanisms underlying many forms of neural plasticity, with direct applications of the findings to neural processes of memory, development, drug abuse, and epilepsy among other functions in brain and cognition. [unreadable] [unreadable] [unreadable]

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Hormonal responses to an experience can gate how well and for how long the experience is remembered. Epinephrine (adrenaline) is one such hormonal regulator of memory strength and durability. Recent findings by the PI, using an electrophysiological model of memory called long-term potentiation (LTP), demonstrate that epinephrine also modulates the strength and durability of connections between neurons known as synapses in brain areas involved in memory in rats. Specifically, an injection of epinephrine extends LTP durability from minutes, seen without epinephrine, to days. This proposal examines the neural sites and molecular mechanisms important to this conversion of short- to long-lasting LTP by epinephrine. Aim 1 will test actions at two brain regions, the hippocampus and amygdala, important in memory formation. Epinephrine likely modulates LTP strength and durability indirectly via specific receptors in the amygdala and directly influences LTP strength through receptors in the hippocampus, the site of change in synaptic strength. Aim 2 will examine molecular events involved in the conversion to long lasting synaptic strength, focusing on the activation of one protein, CREB, that regulates the expression of many genes. Predictions are that increases in CREB activity will correspond to increased durability of synaptic strength. Results from these studies will lend insight into how stress hormones, a component of strong emotions, lead to strong memories. The scientific impact of these experiments is potentially broad with findings that will advance knowledge in fields of mechanisms of memory, neuroendocrinology, and neurophysiology, extending basic findings to fields of learning, reproduction, and animal behavior. This project will provide extensive, unique research experiences for undergraduate and high-school students, with progress assessed by PIs and students using portfolios of written, technical, and subjective reports. Together with the varied outreach programs the PIs conduct, these opportunities will impact a wide and diverse group of prospective scientists.

Although neurons receive most of the attention in brain research, a second cell type, glial cells, comprise as many or more of the cells in the brain. Astrocytes are a major type of glial cell. These cells function to regulate brain metabolism, including the energy use of neurons. Past findings from this laboratory and others indicate that glucose provision to the brain enhances memory functions. Adult mammalian brains use glucose as the major source of energy. This project will determine whether and how astrocytes regulate memory formation by controlling energy use in the brain. The general hypothesis is that ECF glucose levels are sufficient to meet energy requirements under low-need conditions. But when the need is greater, for example during activation to support more intense cognitive functions, astrocytes break down energy reserves stores to provide neurons with a rapid energy boost. These experiments use new methods to measure brain energy substances in awake rats during memory testing, together with pharmacological treatments that identify the necessity of different metabolic routes during memory processing. The role of brain energy metabolism in making new memories identifies a new set of biological processes that regulate the highest functions of the brain, opening new avenues for investigation of brain processes with potentially high impact in scientific investigations of the brain and its functions. In addition to the scientific impact, the project will have direct impact on science education and training at the postdoctoral, graduate, undergraduate and K-12 level. The PI has mentored students at all these levels and, relatively uniquely, includes high school students in the research team. The PI will bring information from this research project to the public through regular participation in outreach programs to secondary school students and education forums for the elderly.

? DESCRIPTION (provided by applicant): Exposure to drugs of abuse alter neuronal functioning, evident as both altered biology of the neurons and altered behaviors. Some of these changes long outlast the drug exposure. In parallel, there is also considerable evidence that exposure to drugs of abuse alters glial astrocyte morphology and function. Astrocytic glycogen serves as an energy reserve in the brain and its degradation is initiated during neuronal activation. Glycogen is metabolized on demand to lactate, which is then transported into neurons to serve as an energy substrate. Recent findings indicate that the contribution of astrocytes to energy metabolism in neurons is a key regulator of memory and neural plasticity. However, changes in astrocyte form and function have not been directly associated with the alteration in cognitive functions after exposure to drugs of abuse. We recently found that learning experiences, obtained during a single 1-hr training session, alter astrocytic glycogen storage and lactate production 30 days later in rats; these changes vary with task and brain area. This project extends these findings to test the effects of cocaine and morphine treatments on changes in glycogen levels and lactate production up to 30 days after drug exposure together with functional measures of astrocyte activity during later learning. Based on previously identified cognitive changes that differ after morphine and cocaine exposure, a multiple memory systems approach is applied here using neurochemical measures in striatum and hippocampus together with training on tasks that differentially engage these brain areas. This project will tes the hypotheses that cocaine and morphine exposure result in long-term changes in the contributions of astrocytes to brain energy metabolism with important consequences for enduring effects of drug experience on cognitive functions. The findings from these experiments may be foundational for future investigations into the nature of long-lasting changes in cognition and brain after drug experience. The contributions of astrocytes to altered bioenergetics after drug exposure, together with altered learning and memory abilities, may open new approaches to understanding and ameliorating the long-term consequences of drug exposures on brain and behavior.