Christopher S. Colwell - US grants

learning; ethology; neurophysiology; hippocampus; circadian rhythms; long term potentiation; fear; hormone regulation /control mechanism; melatonin; conditioning; behavioral /social science research tag; laboratory rat; laboratory mouse; electrophysiology; experimental brain lesion;

DESCRIPTION (applicant's abstract): Most organisms, including humans, exhibit daily rhythms in their behavior and physiology. In most cases, these rhythms are generated by endogenous processes referred to as circadian oscillators. These oscillators provide temporal structure to an organism's physiological processes. Nearly all functions of the body show significant daily variations including arousal, cognition, learning, memory, motor performance and perception. This temporal variation obviously plays an important role in the body's homeostatic mechanisms and has a major impact on the function of the nervous system. In order to function adaptively, circadian oscillators must be synchronized to the environment and the daily cycle of light and dark is the dominant cue used by organisms, including humans, to synchronize their biological clocks to the environment. In humans, desynchronization results in symptoms of fatigue, gastrointestinal distress, and poor cognitive performance. Thus, a major goal of this research area, and the focus of this grant proposal, is to understand the mechanisms by which light acts to synchronize the circadian oscillator located in the suprachiasmatic nucleus (SCN). Previous work has shown that glutamate is a transmitter that conveys photic information to the SCN and the glutamate receptors play a critical role in mediating the response of the circadian system to photic stimulation. One of the primary goals of this proposal is to explore the possibility that glutamatergic retinal input to the SCN is rhythmic on a circadian time scale and to define the mechanisms underlying this daily regulation. Certainly understanding the mechanisms that mediate the long-term modulation of glutamatergic synaptic transmission are of general interest and importance in neuroscience research. In addition, a number of other related questions will be addressed. Is this rhythm restricted to cells in specific regions of the SCN or a general feature of synaptic communication in the SCN? Do anatomically defined cell populations within the SCN differ in their membrane properties and response to glutamatergic stimulation? Is there a daily rhythm in basal and glutamatergic-stimulated calcium levels in SCN cells? The presence of such rhythms would have important implications for information processing within the SCN but also for the cell biology of SCN neurons. Finally, the proposed work will determine whether a model developed to explain synchronization of molluscan circadian oscillators can be applied to the mammalian SCN.

DESCRIPTION (provided by applicant): Our long-term goal is to understand the mechanisms by which environmental signals regulate circadian oscillators as well as how circadian oscillators are coupled to each other, using neurons in the rodent suprachiasmatic nucleus (SCN) as a model system. A variety of evidence suggests that glutamate plays a critical role in the transmission of photic information from the environment to the SCN and that the peptide PACAP is a co-transmitter with glutamate at the RHT/SCN synaptic connection. A major goal of this application is to understand the mechanisms by which PACAP modulates glutamate-induced signaling in SCN neurons. We will present data indicating that PACAP enhances AMPA currents in SCN neurons from mice. Furthermore, data from a new line of transgenic animals in which the PACAP gene has been inactivated demonstrate a reduction in the magnitude of the effects of light on the circadian system. Thus, we feel confident that both glutamate and PACAP play a role, be it as yet undetermined, in mediating the effects of light on the circadian system. Many of the retino-recipient SCN neurons receiving this photic information themselves express the peptide VIP as well as GABA. These SCN cells synapse largely onto other SCN cells and presumably use these molecules to communicate photic information to other cells in the SCN. Thus, a second goal is to understand the mechanisms by which VIP modulates GABA-induced signaling pathways in SCN neurons. For this project, we will present data consistent with our hypothesis that VIP acts to modulate GABA currents in SCN neurons in mice. Encouragingly, data from a new line of transgenic animals in which the VIP gene has been inactivated demonstrate major disruptions in the circadian system that are consistent with VIP's role as a coupling agent within the SCN. By carrying out this research, we will address important questions about how SCN cells are coupled to the environment as well as how SCN cells are coupled to each other. In addition, we hope to use the SCN as model system to better understand the role of peptide co-transmitters in mediating cell-to-cell communication. These questions will be addressed using electrophysiological and calcium imaging techniques on SCN neurons in a mouse brain slice preparation. In addition, transgenic mice lacking PACAP and VIP will be analyzed with behavioral and anatomical tools. These newly developed mice are likely to prove a useful tool for circadian rhythms research.

[unreadable] DESCRIPTION (provided by applicant): The circadian system regulates many aspects of an organism's biology including sensory input, central processing, and motor output. We are particularly interested in the proposition that outputs of the circadian system modulate learning and memory functions. In our own work, we have found clear evidence for circadian variation in acquisition and recall of hippocampal-dependent contextual fear conditioning. In addition, we have found that a synaptic plasticity measured in the hippocampus (HP) is regulated on a circadian time scale and by melatonin. Finally, we and others have found evidence that clock genes including mPer1, mPer2, mBmal1 are expressed in the HP. The function of these clock genes in the HP is not yet known but a reasonable assumption is that these molecular oscillations serve to gate information from the SCN to hippocampal-specific rhythmic outputs. Several testable hypotheses form the basis of this proposal: 1) protein and message of the clock genes mPer1, mPer2, and mBmal1 will be rhythmically expressed in the HP of mice kept in constant conditions; 2) The peak expression of these genes in the HP will be out of phase with the SCN; 3) mPer2- deficient mice will exhibit phase advanced rhythms in gene expression in both HP and SCN while the VIP-deficient mice will exhibit disrupted rhythms in the SCN but not in the HP; 4) the loss of mPer2, mClock, and VIP will impact the recall of learned behaviors in both fear conditioning and radial arm maze. In testing these hypotheses, the present proposal will address a variety of issues including the mechanisms underlying the output from the SCN and the physiological basis for time of day variation in certain types of learning. Documenting a role for the circadian system in the control of learning may have broad implications for understanding temporal organization of human performance. Finally, we hope that the results obtained from the studies described in the present proposal will lay groundwork for future mechanistic work. Many patients with psychiatric and neurological disorders exhibit disturbances in their daily cycle of sleep and wake as part of their symptoms. These patients have difficulty sleeping at night and staying awake during the day. These patients also exhibit disturbances in their ability to learn and remember. These dysfunctions are not a causal to their disorder yet these symptoms have a major impact on the quality of life of the patient population and on the family members who care for the patients. Our long-term goal is to understand the mechanisms by which neurons in the mammalian suprachiasmatic nucleus (SCN) regulate the temporal patterning of learning and memory. We would then use this information to improve the learning and memory of the patient and through this mechanism improve the quality of life for a number of patient groups. Documenting a role for the circadian clock genes in the control of learning may have broad implications for understanding temporal organization of human performance. Finally, we hope that the results obtained from the studies described in the present proposal will lay groundwork for future mechanistic work. This line of research is novel and has the potential to contribute to our understanding of both the output of circadian system regulates other regions in the nervous system as well the mechanisms underlying the temporal organization of learned behavior. This line of research has not been previously funded, is exploratory in nature, and thus qualifies under the R21 format. [unreadable] [unreadable] [unreadable]

Disturbances in the daily sleep-wake cycle are a common feature experienced by individuals with neurodegenerative disorders. They have difficulty sleeping at night and staying awake during the day. These disturbances have a major impact on their quality of life as well as on the family members who care for them. Huntington's disease (HD) is the most common genetically determined neurodegenerative disease and we have documented that circadian rhythms are disrupted early in the disease progression in three distinct mouse models of HD. Using a mouse model of HD which expresses the human mutation (BACHD), we have successfully improved the behavioral and some of the autonomic deficits using a protocol that limits the daily food intake into a 6-hr window during the animal's active phase, and is thus named: time restricted feeding (TRF). This feeding/fasting cycle improved behaviorally defined sleep in the BACHD model when applied early in disease progression. To our knowledge, this is the first demonstration that TRF can improve sleep parameters in mice although earlier work has shown that a similar schedule can improve behavioral sleep patterns in Drosophila. A critical gap in our knowledge is whether TRF specifically alters the temporal pattern of sleep stages, sleep homeostasis or cortical up/down states reflecting slow wave activity. This proposal will employ electrophysiological and optical approaches to close this gap and determine if such treatments can be usefully employed in HD. Given the shared pathology including the formation of protein aggregates and cell death, treatment strategies that prove to be effective in HD are likely to be broadly beneficial in the management of neurodegenerative diseases.

Disturbances in the daily sleep-wake cycle are a common feature experienced by individuals with neurodegenerative disorders. They have difficulty sleeping at night and staying awake during the day. These disturbances have a major impact on their quality of life as well as on the family members who care for them. Huntington's disease (HD) is the most common genetically determined neurodegenerative disease and we have documented that circadian rhythms are disrupted early in the disease progression in three distinct mouse models of HD. Using a mouse model of HD which expresses the human mutation (BACHD), we have successfully improved the behavioral and some of the autonomic deficits using a protocol that limits the daily food intake into a 6-hr window during the animal's active phase, and is thus named: time restricted feeding (TRF). This feeding/fasting cycle improved behaviorally defined sleep in the BACHD model when applied early in disease progression. To our knowledge, this is the first demonstration that TRF can improve sleep parameters in mice although earlier work has shown that a similar schedule can improve behavioral sleep patterns in Drosophila. A critical gap in our knowledge is whether TRF specifically alters the temporal pattern of sleep stages, sleep homeostasis or cortical up/down states reflecting slow wave activity. This proposal will employ electrophysiological and optical approaches to close this gap and determine if such treatments can be usefully employed in HD. Given the shared pathology including the formation of protein aggregates and cell death, treatment strategies that prove to be effective in HD are likely to be broadly beneficial in the management of neurodegenerative diseases.