Role of the suprachiasmatic nuclei in the circadian timing system of the squirrel monkey. I. The generation of rhythmicity

The circadian organization of squirrel monkey ( Saimiri sciureus) drinking behavior was evaluated before and after the placement of radiofrequency lesions which completely destroyed the suprachiasmatic nuclei (SCN) in 4 monkeys and partially ablated the SCN in another 4 animals. In continuous illumination (LL: 600 lux) prior to surgery, each monkey had a precise free-running circadian rhythm of drinking behavior with a period of 25.13 ± 0.21h(¯X±S.E.M.). By 4–6 weeks following the lesions, the temporal organization of drinking behavior had become disrupted, but a statistically significant free-running circadian rhythm was still detectable by time series analyses. Subsequently, the circadian organization of drinking behavior in 7 out of 8 monkeys gradually decayed with either no statistically significant rhythmicity or only weak circadian and/or ultradian rhythmicity detected by time series analyses by 10–92 weeks post-lesion. The remaining animal which maintained a statistically reliable free-running rhythm in drinking behavior received the least damage (