The Methamphetamine-Sensitive Circadian Oscillator (MASCO) in Mice

May 30, 2006Journal of biological rhythms

The body clock in mice that responds to methamphetamine

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Abstract

Chronic methamphetamine use lengthens the circadian period of locomotor activity rhythms in rats and induces rhythms in animals lacking a suprachiasmatic nucleus (SCN).

Chronic methamphetamine is associated with the presence of a methamphetamine-sensitive circadian oscillator (MASCO) that operates independently of the SCN.
Data from rat models show that the MASCO can produce circadian rhythms even in the absence of the SCN.
In intact mice, the interaction between MASCO and the SCN varies based on strain, sex, and dose.
SCN-lesioned mice exhibit strong free-running locomotor rhythms induced by methamphetamine, which can persist for up to 14 cycles after the drug is withdrawn.
The anatomical and molecular characteristics of the MASCO remain unidentified.

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The suprachiasmatic nucleus (SCN) orchestrates synchrony among many peripheral oscillators and is required for circadian rhythms of locomotor activity and many physiological processes. However, the unique effects of methamphetamine (MAP) on circadian behavior suggest the presence of an SCN-independent, methamphetamine-sensitive circadian oscillator (MASCO). Substantial data collected using rat models show that chronic methamphetamine dramatically lengthens circadian period of locomotor activity rhythms and induces rhythms in animals lacking an SCN. However, the anatomical substrate and the molecular components of the MASCO are unknown. The response to MAP is less well studied in mice, a model that would provide the genetic tools to probe the molecular components of this extra-SCN oscillator. The authors tested the effects of chronic MAP on 2 strains of intact and SCN-lesioned mice in constant dark and constant light. Furthermore, they applied various MAP availability schedules to SCN-lesioned mice to confirm the circadian nature of the underlying oscillator. The results indicate that this oscillator has circadian properties. In intact mice, the MASCO interacts with the SCN in a manner that is strain, sex, and dose dependent. In SCN-lesioned mice, it induces robust free-running locomotor rhythmicity, which persists for up to 14 cycles after methamphetamine is withdrawn. In the future, localization of the MASCO and characterization of its underlying molecular mechanism, as well as its interactions with other oscillators in the body, will be essential to a complete understanding of the organization of the mammalian circadian system.

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The Methamphetamine-Sensitive Circadian Oscillator (MASCO) in Mice

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