The basal forebrain (BF) is a highly complex brain region that is implicated in a wide range of higher-level neurobiological processes including, cognition, learning, memory and attention, virtually all of which operate on a basis of wakefulness. Dysfunction of BF circuitry is also implicated in the pathogenesis of a host of neuropsychiatric and neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, schizophrenia and the cognitive impairments of normal aging. In its most fundamental neurobiological context however, the BF (as an anatomical constituent of the "ascending reticular activating system") contains circuitry critical for maintaining behavioral arousal and an aroused cortex, which is the sine qua non for cognition and purposeful behaviors. Remarkably, however, the mechanisms and substrates by which the BF regulates EEG and neurobehavioral arousal remain poorly understood. Much of the difficulty in understanding the neurobiology of the BF is related to its high cellular heterogeneity and complex anatomical organization. In this project we plan to examine the in vivo role of cholinergic, GABAergic and glutamatergic neurons of the BF in the regulation of electrocortical and behavioral arousal. Each of these cell groups has been hypothesized to play an important role in regulating electrocortical and neurobehavioral arousal, although the respective role of each transmitter system in these processes is unresolved. We propose to examine, for the first time, the in vivo effects of cell-type specific lesions of each of these three BF transmitter systems on EEG and behavioral arousal using an adeno-associated viral (AAV) vector containing cre-recombinase injected into the BF of mice harboring loxP-modified alleles of either choline acetyltransferase (ChATflox/flox mice), the vesicular GABA transporter (Vgat flox/flox mice) or the vesicular glutamate transporter 2 (Vglut2 flox/flox mice). Collectively, these studies will provide important information regarding the substrates that are necessary to produce and maintain arousal, including the individual contribution of all three BF neurotransmitter system(s) to this process in a freely behaving, unrestrained animal. While the focal elimination of glutamate, GABA or cholinergic neurotransmission will potentially provide a significant advance in our knowledge regarding the long-term role of these BF transmitter systems in EEG and behavioral arousal, it is possible that there may be substantial compensation by the remaining neurotransmitter systems over time. To address this issue and, also, provide a second experimental model system for increasing the specificity of the linkage between selective transmitter disruption in the BF and EEG/behavioral outcomes, our laboratory has recently developed an AAV containing an ivermectin-gated chloride channel that permits selective and reversible silencing of specific neuronal subpopulations in vivo. By injecting this AAV into the BF of ChAT-IRES-Cre, Vgat-IRES-Cre and Vglut2-IRES- Cre mice we can examine the effects of acutely and reversibly silencing these neuronal subtypes, respectively, on the cortical EEG and other neurobehavioral measures in the freely behaving animal.
This program proposes to determine the respective in vivo role of three neurotransmitter systems comprising the basal forebrain, a highly complex area of the brain that is implicated in a wide-range of higher-level neurobiological processes. In addition to revealing the neurobiological role of the three basal forebrain transmitter systems in normal function, the results from the proposed studies may provide critical insight into the pathogenesis of a host of neuropsychiatric and neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, schizophrenia and the cognitive impairments of normal aging.
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