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|Title:||Cholinergic regulation of a mammalian circadian clock|
|Doctoral Committee Chair(s):||Gillette, Martha U.|
|Department / Program:||Neuroscience|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||A cholinergic agonist, carbachol, has been shown to shift the phase of circadian rhythms in rodents when injected intracerebroventricularly. However, the site and receptor type mediating this action have been unknown. The suprachiasmatic nuclei (SCN), the primary circadian pacemaker in mammals, continue to show a circadian rhythm in neuronal activity in a hypothalamic brain slice. Using this in vitro preparation, we investigated the direct regulation of the SCN circadian pacemaker by cholinergics.
We found that the phase of the SCN activity rhythm was advanced by application of a microdrop of carbachol onto each SCN during the subjective night, but not day, with the largest phase advance of 6.5 hr induced at circadian time (CT) 18. The effect of carbachol at CT 18 was mimicked by acetylcholine and two muscarinic agonists, muscarine and McN-A-343 (MI selective), but not by nicotine, and was blocked by the muscarinic antagonists, atropine (0.1 $\mu$M) and pirenzepine (1 $\mu$M), not by a nicotinic antagonist. An M3-selective antagonist, 4-DAMP (1 $\mu$M), partially blocked the carbachol effect. Whole cell current clamp study revealed that the majority of the SCN neurons which responded to carbachol showed a hyperpolarization and an increase in membrane conductance, which can be blocked by atropine. These results demonstrate that carbachol acts directly on the SCN to reset the phase of its activity rhythm during the subjective night, through a muscarinic receptor, possibly an M1 subtype.
Since the phase response relationship for carbachol is almost identical to that for a cGMP analog reported previously, we tested whether cGMP signaling pathway mediates cholinergic input to the SCN pacemaker. Both the guanylyl cyclase (GC) inhibitor, LY83583, and the protein kinase G (PKG) inhibitor, KT5823, blocked the carbachol-induced phase advance at CT 18. Assays of PKG activity and cGMP levels demonstrated that carbachol (100 $\mu$M) increased PKG activity and cGMP concentration in the SCN slice. The increase in cGMP was blocked by 1 $\mu$M atropine, indicating the involvement of a muscarinic receptor. Together, these data revealed a specific pathway of cholinergic regulation of the SCN clock through a muscarinic receptor and the GC/cGMP/PKG signaling pathway.
|Rights Information:||Copyright 1995 Liu, Chen|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9624419|