Methamphetamine effects on rat circadian clock depend on actograph

Methamphetamine effects on the rest-activity rhythm were examined in 12 blinded rats using two different actographs, an Animex and a running-wheel. D-Methamphetamine was administered chronically by dissolving it in drinking water. During methamphetamine treatment, the rest-activity rhythm measured by an Animex showed a clear sign of relative coordination in addition to the general enhancement of activity level. Analyses of pre- and posttreatment activity rhythms revealed that neither the phase nor the period was affected by methamphetamine treatment. On the other hand, the circadian period was lengthened by methamphetamine treatment when locomotor activity was measured by a running-wheel. These results confirmed our previous findings that the chronic treatment of methamphetamine modified the expression of the circadian rhythms but did not affect the underlying oscillation when measured by an Animex, and further indicated that methamphetamine could affect the underlying oscillation when rats had free access to a running-wheel. It is concluded that the effects of methamphetamine on the circadian clock depend on actograph.