Craig W. Berridge - US grants

9420620 Berridge A region at the top of the brainstem known as the locus coeruleus sends nerve cell processes to a number of locations throughout the forebrain and is believed to modulate behavioral and cognitive functions. It is already known the locus coeruleus cells change their rate of electrical signaling during different behavioral states, and it has been presumed that as the cells change their electrical activity they change the amount of the brain chemical norepinephrine which the secrete onto forebrain sites. Dr. Berridge's group will test the exact relationship between state-dependent changes in locus coeruleus electrical activity and norepinephrine secretion. This work will provide new insights into the mechanisms controlling the release of norepinephrine and should therefore provide a better understanding of the natural processes that modulate functions such as learning and memory, and reactions to stress. ***

DESCRIPTION: (Applicant's Abstract) Stimulant drug abuse is a highly prevalent problem that constitutes a major public health concern. To gain better insight into mechanisms contributing to stimulant drug abuse, the neurochemical mechanisms subserving the behavioral effects of these drugs have been intensively examined. Neurochemically, these drugs increase synaptic concentrations of dopamine (DA) and norepinephrine (NE). Evidence indicates that actions of DA within the striatum and nucleus accumbens are critical components of the rewarding and locomotor activating effects of stimulants. In contrast, NE appears to serve a minimal contributory role in these behavioral actions of stimulants. The potent rewarding effects of these drugs are superimposed upon an alert behavioral state (e.g. prolonged periods of waking/enhanced alertness). The ability of stimulants to maintain waking and enhance alertness has long been exploited and is a contributing factor to the widespread use/abuse of these drugs. However, the degree to which NE or DA participates in the "arousal"-enhancing actions of stimulants and which anatomical site(s) subserve such actions remains enigmatic. A variety of observations suggest that the locus-coeruleus (LC)-noradrenergic system participates in the modulation of behavioral state. Previous studies by the PI demonstrated potent actions of LC on EEG and behavioral indices of waking via actions of beta-receptors located within a region of the basal forebrain encompassing the medial septum and the posterior shell of the nucleus accumbens (MS). Preliminary studies indicate that potent arousal-enhancing effects are observed following amphetamine infusions into this region (e.g. induction and maintenance of waking). These observations suggest that, at least some of, the arousal-enhancing actions of stimulants may be due to enhanced release of NE within MS. The proposed studies assess the degree to which amphetamine acts within this region of the basal forebrain to enhance EEG, EMG, and behavioral indices of arousal and to assess the degree to which NE participates in these actions. Utilizing a combination of anesthetized and unanesthetized preparations, local infusions, in vivo microdialysis to assess NE release, and EEG, EMG, and behavioral measures, these studies will provide novel information concerning the degree to which NE participates in the behavioral effects of stimulants. Information obtained in these studies may provide insight into mechanisms subserving, and treatment of, stimulant drug abuse.

DESCRIPTION (provided by applicant): Low doses of amphetamine-like stimulants exert arousal- and attention-enhancing actions. The ability of stimulants to enhance alert waking has long-been exploited and is a contributing factor to the widespread illicit use of these drugs. Additionally, these drugs are used widely in the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. The neurochemical mechanisms subserving the behavioral effects of moderate-to-high doses of these drugs have been examined intensively. Neurochemically, these drugs increase synaptic concentrations of dopamine (DA) and norepinephrine (NE). Evidence indicates that actions of DA within the striatum and nucleus accumbens are critical components of the rewarding and locomotor activating effects of stimulants. The rewarding effects of these drugs are superimposed upon an alert behavioral state (e.g. prolonged periods of waking/enhanced alertness). Previous studies by the PI demonstrate potent actions of the locus coeruleus-noradrenergic system on EEG and behavioral indices of waking via actions of beta-and alpha1 -receptors located within the medial basal forebrain. Additionally, the PI has demonstrated that amphetamine acts within the same basal forebrain regions to exert arousal-enhancing (wake-promoting) actions. Recent studies also suggest arousal-enhancing actions of DA. The PI has initiated a research program that assesses the contribution of NE and DA to the arousal-enhancing actions of stimulants and identifies the neurocircuitry underlying these actions. Recent studies demonstrate potent arousal-enhancing actions of the peptides, hypocretins. Dysregulation of hypocretin neurotransmission appears to be an etiological factor in the arousal disorder, narcolepsy. Stimulants elicit an activation of hypocretin neurons, suggesting the participation of hypocretins in at least a subset of the behavioral actions of these drugs, including their therapeutic action in the treatment of narcolepsy. Utilizing a combination of behavioral, pharmacological, and anatomical methods, the proposed studies will provide novel information concerning the degree to which NE, DA and hypocretins participate in the behavioral effects of. Information obtained in these studies may provide insight into mechanisms underlying, and future treatment of, stimulant drug abuse, ADHD and narcolepsy.

Stimulant drug abuse is highly prevalent, constituting a major public health concern. To gain better insight into mechanisms contributing to stimulant drug abuse, the neurochemical mechanisms subserving the behavioral effects of these drugs have been intensively examined. Neurochemically, these drugs increase synaptic concentrations of dopamine (DA) and norepinephrine (NE). Evidence indicates that actions of DA within the striatum and nucleus accumbens are critical components of the rewarding and locomotor activating effects of stimulants. It is generally believed that NE serves a minimal contributory role in these behavioral actions of stimulants. However, recent observations by the PI indicate that previous studies may not have adequately addressed this issue. The rewarding effects of these drugs are superimposed upon an alert behavioral state (e.g. prolonged periods of waking/enhanced alertness). The ability of stimulants to maintain waking and enhance alertness has long been exploited and is a contributing factor to the widespread use of these drugs. However, the degree to which NE or DA participates in the "arousal"-enhancing actions of stimulants and which anatomical site(s) subserve such actions remains enigmatic. A variety of observations suggest that noradrenergic systems participates in the modulation of behavioral state. Previous studies by the PI demonstrated potent actions of the locus coeruleus (LC) on EEG and behavioral indices of waking via actions of beta-receptors located within structures located within the medial basal forebrain. Additional studies demonstrated potent arousal-enhancing effects of amphetamine when infused into these regions. These observations suggest that at least some of the arousal-enhancing actions of stimulants may be due to enhanced release of NE within the basal forebrain. Utilizing a combination of behavioral, pharmacological, and anatomical methods, the proposed studies will provide novel information concerning the degree to which NE participates in the behavioral effects of stimulants and the receptor mechanisms and circuitry involved in these actions. Information obtained in these studies may provide insight into mechanisms subserving, and treatment of, stimulant drug abuse.

DESCRIPTION (provided by applicant): Orexins are a newly identified peptide family comprised of two peptides, orexin-A and orexin-B, which are synthesized by a limited population of neurons located within the lateral and dorsal hypothalamus. Initially, these peptides were demonstrated to stimulate feeding, when administered in relatively high doses. However, orexin neurons project widely throughout the brain and spinal cord, including to regions associated with the regulation of behavioral state. Consistent with these observations, substantial evidence suggests dysregulation of orexin neurotransmission is associated with the sleep/arousal disorder, narcolepsy. Further, recent evidence suggests that these peptides exert an activating influence on forebrain and behavioral state. In preliminary studies, the PI has observed potent arousal-enhancing actions of orexin when administered into sleeping/resting animals, at doses substantially below those that elicit feeding. The neural mechanisms that underlie these arousal-enhancing actions remain unknown. Work by the PI demonstrates that the locus coeruleus (LC)-noradrenergic system exerts a potent activational influence on forebrain neuronal and behavioral activity states. These actions derive, in part, from actions of norepinephrine within a subset of basal forebrain structures. Given this, it is of interest that orexin-containing fibers innervate LC, these same basal forebrain structures, as well as other regions implicated in the regulation of behavioral state. The proposed studies will complete preliminary studies that characterize the dose-dependent effects of orexin-A and -B on behavioral state. Additionally, these studies will characterize the anatomical organization of the orexin efferent projection system. Finally, these studies will provide initial assessment of a number of potential neural mechanisms underlying orexin-enhanced arousal. Specifically, the extent to which orexins alter behavioral state via actions within certain basal forebrain and brainstem structures will be examined. These studies will provide a better understanding of the neurobiology of orexin, the neurobiology of sleep and waking, and the potential role of orexin in narcolepsy and other disorders of arousal.

Cognitive control of goal-directed behaviors likely involves the communication and computations across millions of cells in a distributed manner across multiple brain regions. To date, little is known regarding how the coordinated activity of these neurons represents cognitive processes involved in goal-directed behaviors, such as working memory, attention, and decision/response selection (i.e. the population code). To address this lacuna, these electrophysiological studies will record electrical signaling of neurons in rats within two fundamentally important brain regions, the prelimbic region of the frontal cortex (plPFC) and dorsal striatum (dSTR). A primary goal of this project is to relate this neural activity to animal performance in spatial delayed response tests of working memory using state-of-the-art computational strategies. Importantly, these studies will examine the distributed representations of task-related events within populations of plPFC and dSTR neurons as well as for the PFC-dSTR circuit as a whole under varying conditions associated with varying levels of performance (short delays, long delays, noise-stress). These studies are anticipated to further elucidate the neuronal codes and network circuitry that underlie higher cognitive function as measured in this task. In addition to the scientific knowledge gained by these studies, this project contains learning opportunities for undergraduates, graduate students, and post-doctoral fellows. A key theme in this work is the need for cross-disciplinary training in biology (neuroscience) and computational/engineering sciences. As part of our ongoing commitment to provide these educational opportunities, we have developed a neural analysis programming contest to 1) introduce students to computational neuroscience approaches, 2) educate and engage researchers outside the field of neuroscience in computational techniques and issues in neuroscience, and 3) build an open community and forum discussion for computational approaches in neuroscience.

DESCRIPTION (provided by applicant): Low doses of psychostimulants, including methylphenidate (MPH/Ritalin), are widely used clinically due to their behavioral-calming and cognition-enhancing actions. Less well-recognized is the fact that these drugs exert similar actions in both normal human and animal subjects. Of particular relevance to the proposed studies are the well-documented facilitatory actions of low- doses of MPH and other psychostimulants on prefrontal cortex (PFC)-dependent cognition (i.e. working memory and sustained attention). Despite these cognition-enhancing actions, these drugs possess certain risks, including toxicity and abuse/addiction. For this reason, there is much concern about the widespread use of these drugs, particularly in children. Moreover, these risks preclude use of these drugs in other disorders/conditions associated with relatively modest impairment in PFC- dependent cognition (i.e. normal aging, sleep deprivation). To better develop non-stimulant drugs for the treatment of ADHD and other disorders and conditions associated with impaired PFC- dependent cognition, it is important to understand the neural mechanisms responsible for the cognition-enhancing actions of low-dose psychostimulants. Surprisingly, little is known about the neural substrates underlying the behavioral/cognitive actions of low-dose stimulants. We recently demonstrated that at low doses that improve both working memory and sustained attention in rats, PFC catecholamine efflux displays a greater sensitivity than catecholamine efflux in a number of cortical and subcortical regions outside the PFC. Additional studies indicate that cognition-enhancing doses of MPH increase PFC neuronal responsivity, an effect not observed in the somatosensory cortex. Combined, these observations suggest a prominent role of the PFC in the cognition-enhancing actions of low-dose MPH. The proposed studies are designed to further test this hypothesis and to provide insight into the neural mechanisms that underlie these actions. These studies will use a combination of microdialysis measures of catecholamine release, electrophysiological measurement of PFC neuronal activity, pharmacological manipulations and tests PFC-dependent cognition. These studies will provide novel insight into the neurobiological mechanisms through which low-dose psychostimulants improve cognitive function. Additionally, these studies will provide important information for the development of new pharmacological treatments for ADHD and other disorders/conditions associated with PFC dysfunction. These studies will provide novel insight into the neural mechanisms that underlie the cognition- enhancing actions of low-dose psychostimulants as well as the neurobiology of higher cognitive function. Importantly, these studies will provide information necessary for the development of new pharmacological treatments lacking the potential adverse actions of psychostimulants for a variety of cognitive/behavioral disorders associated with prefrontal cortical dysfunction.

DESCRIPTION (provided by applicant): The prefrontal cortex (PFC) plays a pivotal role in higher cognitive processes that guide flexible goal-directed behavior, particularly under ambiguous and/or distracting conditions. These actions involve topographically organized frontostriatal projections. Frontostriatal dysfunction is implicated in a variety of disorders, including addiction, ADHD, and schizophrenia. Anatomical, modeling and limited in vitro evidence suggests that PFC-dependent function involves reverberatory (self-excitatory) activation of PFC neurons that involves recurrent circuitry and/or intracellular signaling cascades. Using a point-process, conditional intensity model we obtained the first empirical evidence that PFC neurons display reverberatory activity in vivo in rats engaged in a task of spatial working memory and that stress-related impairment in working memory is associated with a suppression of reverberatory activity. These and other observations indicate that reverberatory activity of PFC neurons represents a unique form of information coding that contributes to higher cognitive function. Catecholamines exert potent modulatory actions on PFC neuronal function that likely contribute to the therapeutic effects of drugs used to treat a variety of cognitive/behavioral disorders, including ADHD and schizophrenia. However, there are multiple neuromodulators found within the PFC, including corticotropin-releasing factor (CRF). Across cortical regions, the PFC contains a particularly high density of CRF receptors. Currently, we know little about the actions of PFC CRF on frontostriatal neuronal function, representing a significant gap in our understanding of the neurobiology of the PFC, CRF and goal-directed behavior. In preliminary studies, we observed that CRF acts locally within the PFC to impair PFC-dependent higher cognitive function while a CRF antagonist improve PFC- dependent cognition, similar to that seen with ADHD-related pharmacological treatments. Collectively, these observations suggest translationally-relevant actions of endogenous CRF signaling within the PFC. The goal of the proposed studies is to examine the effects of CRF signaling within the PFC on frontostriatal neuronal coding in rats engaged in a spatial working memory task. Methods developed and information gained in these studies will provide a solid foundation for the development of a comprehensive research program aimed at understanding the modulatory actions of CRF on frontostriatal circuit function. Ultimately, this research program will provide new insight into the neurobiology of frontostriatal-dependent cognition/behavior that may lead to novel treatment strategies for PFC dysfunction.

Project Summary Goal-directed behavior is dependent on a constellation of ?executive? cognitive and behavioral processes dependent on the prefrontal cortex (PFC) and extended frontostriatal circuitry. Dysregulation of PFC-dependent cognition and behavior is associated with numerous psychopathologies, including ADHD. Currently there is a dire need for improved treatments for frontostriatal dysregulation. For example, while psychostimulants are highly effective in the treatment of ADHD, they lack full efficacy across the broader patient population and are increasingly subject to abuse. Unfortunately, the development of novel pharmacological treatments for PFC dependent cognitive dysfunction is limited by a scarcity of alternative targets. From this perspective, it is of interest that corticotropin-releasing factor (CRF) and its receptors are prominent in the PFC. In recently completed studies, we demonstrated that CRF receptor blockade within the caudal dorsomedial PFC (dmPFC) improves working memory in male rats, similar to all approved drug treatments for ADHD. Thus, CRF may represent a novel target for the development of new treatments for PFC-dependent cognitive dysfunction. The proposed multidisciplinary studies will provide a better understanding of the broader cognitive actions of CRF neurotransmission in the PFC in males and females and identify the circuit mechanisms responsible for these actions. Aim 1 will determine the broader impact of PFC CRF receptors across PFC-dependent cognitive processes in both males and females using intra-PFC infusions of CRF and CRF antagonists. Aim 2 uses recently developed viral vector-based chemogenetic manipulations of PFC CRF neurons combined with intra-PFC infusions of a CRF antagonist to determine whether local neurons are a primary source of CRF for PFC CRF receptors. Finally, Aim 3 uses ensemble neuronal recordings to determine the extent to which PFC CRF receptors and neurons impair neuronal coding within the dorsomedial frontostriatal circuit. Collectively, these studies will provide novel insight into the neurobiology of frontostriatal-dependent cognition. In doing so, these studies may provide a better understanding of the neural bases of PFC cognitive dysfunction and lead to novel treatment strategies for PFC-dependent cognitive dysfunction.