Radhika Basheer, Ph.D. - US grants

DESCRIPTION (provided by applicant): The biological underpinnings of homeostatic sleep regulation are an important aspect of sleep research given the relevance of sleep deprivation (SD) to human health, well-being, and cognitive performance. More and more people either are forced to, due to vocational demands, or by choice, stay awake for long periods or at biologically non-optimal times of the day. Moreover, sleep loss-associated cognitive impairments are often observed in conditions such as depressive disorders, post-traumatic stress disorder, Alzheimer's and Parkinson's diseases. Central mechanisms that mediate the effects of SD causing attention and cognitive impairment as well as induction of homeostatic sleep response are critical to be understood to design treatment paradigms for alleviate such deleterious effects of sleep loss, and is close to the NIMH mission. One of the brain regions, the basal forebrain (BF), in addition to its important role in promoting wakefulness, is also recognized for its role i homeostatic sleep regulation as well as in attention and cognition. The BF consists of a variety of neurons that utilize acetylcholine or GABA or glutamate. The complexity of the neuronal composition in BF has long prevented a clear understanding of the causal role of each neuronal subtype on extracellular neurochemical alterations and modulation of cortical activity that underlies increased sleepiness and reduced alertness following prolonged neuronal activation during SD. Recent studies demonstrated that both cholinergic and parvalbumin (PARV) expressing GABAergic (PARV-pos GABA) neurons are active during wakefulness and are capable of modulating cortical activation. However, their distinct roles in sleep homeostasis are not clear. While neurotoxic lesions of cholinergic and GABAergic neurons have underlined the importance of these neurons in wakefulness and homeostatic sleep response, a direct cause and effect evaluation is best studied by selective manipulation of each neurotransmitter-specific neuronal cell types. The overall goals of this application is to discern the differences in the functional role of cholinergic and PARV-pos GABAergic neuronal activation in homeostatic sleep regulation. Using the state-of-the-art optogenetic technology to selectively manipulate the activities of cholinergic and PARV-GABA neurons combined with simultaneous polysomnographic recordings to monitor changes in cortical EEG and in vivo microdialysis for measuring extracellular neurochemical changes we will test the following model: Prolonged SD->BF cholinergic neuronal activation->increase extracellular NO and adenosine->inhibition of wake active cholinergic and non-cholinergic neurons->increased sleepiness. Successful completion of these exploratory studies will (1) validate a novel combinatorial method of performing optogenetics with in vivo microdialysis, (2) extend our understanding of the causal role of specific BF neuronal subtypes in modulating cortical EEG and homeostatic sleep response. PUBLIC HEALTH RELEVANCE: Sleep deprivation is a wide spread problem with negative impacts on performance efficiency, health and cognition. The current application proposes to use in vivo microdialysis with the state-of-the-art method of optogenetics to selectively manipulate two major wake-active neuronal cell types to discern their role in modulating the homeostatic sleep factors that increase the propensity to sleep and decrease attention and cognition. Understanding the neuronal components involved in mediating neurochemical changes is important towards designing targeted treatment plans to counteract the effects of sleep deprivation.

The broad objective of this study is to identify the neural substrate(s) underlying the homeostatic sleep response (HSR), i.e. enhanced sleepiness following prolonged sleep deprivation (SD). SD is experienced by many due to lifestyle or vocational demands and is accompanied by impaired cognition, increased impulsivity, and an increased likelihood of accidents. Furthermore, disrupted sleep is a common feature of many neuropsychiatric disorders. Thus, understanding the mechanisms underlying the HSR is critical to develop measures to combat the deleterious consequences of SD. Specifically, here we will address the central question: ?Are all neural wake-promoting systems equally important in triggering the HSR?? Our overarching hypothesis is that basal forebrain (BF) cholinergic neurons (ChAT+) are modulated by glutamate and play a privileged role in the HSR by causing the release of extracellular adenosine (ADex), which increases sleep by inhibiting wake-promoting BF neurons, and thereby adjusts the state of the system towards its' set point. Towards this goal, Aim 1, will test if BF cholinergic neurons, but not the brainstem pedunculopontine tegmental (PPT) cholinergic neurons, are required for HSR. Aim 2 will test the hypothesis that within BF, only those non- cholinergic wake-promoting neurons projecting to, and exciting, BF ChAT+ neurons will induce HSR. Aim 3 will test if stimulation of wake-promoting BF-vGluT2+ and PPT-vGluT2+ neurons will only induce HSR if BF ChAT+ neurons are intact, i.e. the integrity of BF ChAT+ neurons is necessary to trigger the HSR. Finally, Aim 4 will test the dual role of BF ChAT+ neurons in promoting arousal and sleep homeostasis. We will use our novel mouse `optodialysis' probes (Zant et al., 2016) that combine optical manipulation of selective neuronal populations with in vivo microdialysis for detecting local neurochemical changes and/or application of pharmacological agents. The successful completions of these investigations will further our understanding of the neural substrates necessary for inducing the HSR, and thus will help in developing targeted pharmacological interventions against the deleterious effects of sleep loss.