Potentiating action of MKC‐242, a selective 5‐HT1A receptor agonist, on the photic entrainment of the circadian activity rhythm in hamsters

MKC-242 (3 mg kg(-1), i.p.) significantly accelerated the re-entrainment of circadian rhythms in hamsters exposed to a new light-dark cycle.

• The selective 5-HT1A receptor agonist MKC-242 enhanced the phase advance of circadian rhythms induced by both low and high intensity light.
• In contrast, the 5-HT1A/5-HT7 receptor agonist 8-OH-DPAT suppressed phase advances at low light intensity.
• The effects of MKC-242 on light-induced phase advances were still observed when administered 20 or 60 minutes after light exposure.
• The action of MKC-242 was blocked by WAY100635, confirming its activation of 5-HT1A receptors.
• MKC-242 treatment resulted in decreased levels of 5-HIAA in the suprachiasmatic nuclei.
• These findings suggest that presynaptic activation of 5-HT1A receptors may play a role in enhancing photic entrainment.

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