Effects of methamphetamine upon circadian rhythms in multiple unit activity inside and outside the suprachiasmatic nucleus in the golden hamster (Mesocricetus auratus)

To investigate the circadian system of the golden hamster, multiple unit activity (MUA) was recorded inside and outside the suprachiasmatic nucleus (SCN). MUA inside the SCN showed a daily rhythm with a daytime peak during a 24 h light-dark cycle (LD, 12:12), whereas MUA outside the SCN revealed a nighttime peak. The phase reversal of MUA between inside and outside the SCN in the golden hamster was similar to the rat which is also a nocturnal rodent. MUA rhythms to the lighting cycle started to freerun after methamphetamine administration. This result indicates that methamphetamine may affect directly the neural circadian oscillator to induce behavioral change.