Methamphetamine induced locomotor rhythm entrains to restricted daily feeding in SCN lesioned rats.

Rats were lesioned in the SCN and treated with methamphetamine dissolved in drinking water. A robust rhythm appeared in spontaneous locomotor activity which was not affected by blinding. Periodic food restriction (RF) of a 24 hr period was imposed on SCN lesioned rats with free-access to food for 4 or 6 hr per day, while water was given ad lib. The locomotor rhythm induced by methamphetamine treatment was phase-set by RF immediately in most cases but with transients in some. The phase-angle difference (psi) between food presentation and the activity onset became more negative by increasing the dose of methamphetamine. Because there was a positive correlation between methamphetamine dose and the period of locomotor rhythm, the change in psi was most likely due to lengthening of the period. After the termination of the RF schedule, the locomotor rhythm started to free-run from the prior phase set by RF. These results indicate that the methamphetamine dependent locomotor rhythm entrains to RF.