Disturbances in circadian rhythms contribute to a variety of diseases and impair mental and physical performance. Circadian rhythms in physiological and behavioral processes are generated by a molecular clock located in the suprachiasmatic nucleus. This clock receives environmental information from cues such as light and subsequently creates timing information that is sent to the rest of the organism. While the signaling pathways involved in this chain of information are poorly understood, evidence suggests a possible role for Ca2+ as a signaling molecule for both input to and output from the circadian clock. But the source of this Ca2+ is unknown. One model proposes that glutamate released from terminals of the retinohypothalamic tract activates NMDA receptors, which generate nitric oxide and release Ca2+ from ryanodine-sensitive stores. However, the release of Ca2+ from ryanodine-sensitive stores by glutamate or nitric oxide has not been directly demonstrated. NMDA receptor activation increases the nuclear Ca2+ concentration of SCN neurons. Nuclear Ca2+ regulates gene expression, including possibly clock gene expression. The long-term goal of this work is to characterize the functional properties of SCN neurons and how the circadian clock regulates these properties. This proposal will determine the roles that cytoplasmic and nuclear Ca2+ play as circadian input and output signals. Our central hypothesis is that changes in cytoplasmic and nuclear Ca2+ concentration are a critical step in light's regulation of the circadian clock. This proposal uses an innovative combination of fluorescent imaging techniques, cell culture, and electrophysiological recording techniques to study the regulation of Ca2+ in SCN neurons during different portions of the circadian day. This research will identify the early steps in the light-signaling pathway.
The Specific Aims of the proposal are: 1) Identify the mechanisms and circadian regulation of the increase of the cytoplasmic Ca2+ concentration produced by activating NMDA and AMPA receptors. 2) Determine the mechanisms and circadian phase dependence of the increase in the nuclear Ca2+ concentration produced by NMDA receptor activation. 3) Determine the role that PACAP plays in regulating changes in the cytoplasmic and nuclear Ca2+ concentration induced by NMDA and AMPA receptor activation. 4) Investigate whether the peak of the cytoplasmic Ca2+ rhythm precedes the peak of action potential firing frequency rhythm in SCN neurons. Together, these experiments will identify the early steps in the light-signaling pathway, thus contributing to a better understanding of the cellular basis of circadian rhythms.

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Research Project (R01)
Project #
5R01MH070922-02
Application #
6850773
Study Section
Biological Rhythms and Sleep Study Section (BRS)
Program Officer
Asanuma, Chiiko
Project Start
2004-03-01
Project End
2009-02-28
Budget Start
2005-03-01
Budget End
2006-02-28
Support Year
2
Fiscal Year
2005
Total Cost
$271,800
Indirect Cost
Name
Oregon Health and Science University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
096997515
City
Portland
State
OR
Country
United States
Zip Code
97239
Irwin, Robert P; Allen, Charles N (2010) Neuropeptide-mediated calcium signaling in the suprachiasmatic nucleus network. Eur J Neurosci 32:1497-506
Ruggiero, Linda; Allen, Charles N; Brown, R Lane et al. (2010) Mice with early retinal degeneration show differences in neuropeptide expression in the suprachiasmatic nucleus. Behav Brain Funct 6:36
Moldavan, Mykhaylo G; Allen, Charles N (2010) Retinohypothalamic tract synapses in the rat suprachiasmatic nucleus demonstrate short-term synaptic plasticity. J Neurophysiol 103:2390-9
Ruggiero, Linda; Allen, Charles N; Brown, R Lane et al. (2009) The development of melanopsin-containing retinal ganglion cells in mice with early retinal degeneration. Eur J Neurosci 29:359-67
Irwin, Robert P; Allen, Charles N (2009) GABAergic signaling induces divergent neuronal Ca2+ responses in the suprachiasmatic nucleus network. Eur J Neurosci 30:1462-75
Allen, Charles N (2008) Circadian rhythms, diet, and neuronal excitability. Epilepsia 49 Suppl 8:124-6
Hartwick, Andrew T E; Bramley, Jayne R; Yu, Jianing et al. (2007) Light-evoked calcium responses of isolated melanopsin-expressing retinal ganglion cells. J Neurosci 27:13468-80
Irwin, Robert P; Allen, Charles N (2007) Calcium response to retinohypothalamic tract synaptic transmission in suprachiasmatic nucleus neurons. J Neurosci 27:11748-57