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Carbachol injections into the intergeniculate leaflet induce nonphotic phase shifts
Sean W Cain1, Michael Verwey, Marta Szybowska
1Centre for Biological Timing and Cognition, Departments of Psychology, University of Toronto, 100 St. George Street, Room 4020, Toronto, Ontario, Canada M5S 3G3. swcain@hotmail.com
Brain Research
|October 9, 2007
Summary
Cholinergic input to the intergeniculate leaflet (IGL) induces nonphotic phase shifts in the mammalian circadian clock. This suggests a key role for muscarinic signaling in regulating circadian rhythms through arousal pathways.
Area of Science:
- Neuroscience
- Chronobiology
- Neurophysiology
Background:
- Nonphotic phase shifts of the mammalian circadian clock are mediated by the intergeniculate leaflet (IGL) projecting to the suprachiasmatic nucleus.
- Arousing stimuli, including wheel running and foot shock, can induce these phase shifts.
- Mesopontine cholinergic neurons are activated by arousing stimuli, suggesting a potential role in this process.
Purpose of the Study:
- To test the hypothesis that cholinergic input to the IGL mediates nonphotic phase shifts.
- To investigate the role of muscarinic signaling in circadian rhythm regulation.
Main Methods:
- Carbachol, a cholinergic agonist, was injected into the IGL of hamsters during subjective day (CT8).
- Phase shifts were measured following injections.
- The effect of a muscarinic antagonist, atropine, on carbachol-induced phase shifts was assessed.
Main Results:
- Carbachol injections into the IGL induced phase advances comparable to those caused by arousal stimuli.
- Control injections of saline or carbachol outside the IGL produced smaller shifts.
- Atropine pre-injections significantly reduced the phase advances induced by carbachol.
Conclusions:
- Muscarinic input to the intergeniculate leaflet (IGL) is sufficient to induce nonphotic phase shifts.
- Cholinergic pathways play a significant role in mediating circadian rhythm adjustments in response to arousal.
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