Differential responses of circadian Per2 rhythms in cultured slices of discrete brain areas from rats showing internal desynchronisation by methamphetamine


Correspondence: Ken-ichi Honma, as above.

E-mail: kenhonma@med.hokudai.ac.jp


Chronic methamphetamine (MAP) treatment desynchronises the behavior rhythms of rats from light–dark cycles. Our previous study (Masubuchi et al., 2000) demonstrated the phase reversal of circadian rhythms in clock gene expression in several brain areas of rats treated with MAP. However, for technical reasons, it was not clear whether the phase shifts were the consequence of phase-shifted behavior rhythms or reflected phase shifts of extra-suprachiasmatic nucleus (SCN) oscillators in these areas. In the present study, circadian gene expression rhythms in discrete brain areas were continuously monitored in slice cultures of MAP-treated rats. Methamphetamine was given to rats carrying a Period2-dLuciferase reporter system via the drinking water for more than 2 weeks. When behavior rhythms were completely phase reversed, the brain was sampled for slice cultures and circadian bioluminescence rhythms were measured for 5 days in the SCN and four areas of the dopaminergic system, the olfactory bulb, caudate putamen, parietal cortex and substantia nigra. The circadian rhythms in the SCN and caudate putamen were not significantly phase shifted, whereas those in the parietal cortex and substantia nigra showed significant phase-delay shifts of 6–8 h and that in the olfactory bulb showed phase-advance shifts of ca. 8 h. Neither the period nor the amplitude of the circadian rhythm was changed by MAP treatment. These findings indicate that the extra-SCN oscillators in several brain areas are desynchronised from the SCN circadian pacemaker by MAP treatment in parallel with the desynchronisation of behavior rhythms in rats. As the direction and extent of phase shifts of circadian rhythms were different among the areas examined, the brain extra-SCN oscillators responded differentially to MAP.