Drugs that prevent mouse sleep also block light-induced locomotor suppression, circadian rhythm phase shifts and the drop in core temperature

Area of Science:

• Chronobiology
• Pharmacology
• Neuroscience

Background:

• Exposure to light during the active phase of nocturnal animals triggers responses like circadian rhythm phase shifts, reduced core body temperature (Tc), and suppressed activity.
• These light-induced responses are triggered by the stimulus, persist for a fixed duration, and do not require continuous light exposure.

Purpose of the Study:

• To investigate the effects of psychostimulant drugs (methamphetamine, modafinil, caffeine) on light-induced behavioral and physiological responses in mice.
• To determine if these drugs attenuate circadian phase shifts, core body temperature drops, and locomotor activity suppression caused by light exposure.

Main Methods:

• Mice were housed in constant darkness or a 12-h light:12-h dark cycle.
• Drugs (methamphetamine, modafinil, caffeine) or vehicle were administered at CT11.
• Mice were exposed to a brief light stimulus at CT13, and responses including phase shifts, Tc, and locomotor activity were measured.

Main Results:

• All tested psychostimulants (methamphetamine, modafinil, caffeine) significantly attenuated light-induced circadian phase delays (from ~60 min to 12-15 min).
• Drug pre-treatment abolished the light-induced drop in core body temperature and suppression of locomotor activity.
• While drugs generally increased activity, this effect did not account for the blockade of light responses.

Conclusions:

• Psychostimulant drugs effectively block multiple physiological and behavioral responses to acute light exposure in mice.
• The observed effects are independent of drug-induced hyperactivity, suggesting a direct interaction with light-signaling pathways.
• These findings highlight the complex interplay between psychostimulants, activity levels, sleep, core body temperature, and responses to light stimuli.