Cocaine modulates pathways for photic and nonphotic entrainment of the mammalian SCN circadian clock

Cocaine injection caused a 60% reduction in light-induced phase-delay shifts of circadian locomotor activity in mice.

• Cocaine was found to impair photic signaling in the master circadian clock of the mouse suprachiasmatic nucleus (SCN).
• A 1-hour phase-advance shift was observed at midday following cocaine administration, indicating a nonphotic effect.
• Blocking serotonin receptors with metergoline reduced phase shifts by 80%, suggesting a role for serotonin in this process.
• Cocaine application directly to the SCN induced 3.7-hour phase-advance shifts, while control substances had minimal effects.
• Cocaine's ability to induce phase shifts was completely inhibited by metergoline, but not by a dopamine receptor antagonist.
• Pre-treatment with a serotonin agonist prevented cocaine-induced phase shifts, further supporting the involvement of serotonergic mechanisms.

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