Involvement of the primary optic tracts in mediation of light effects on hamster orcadian rhythms

Abstract

1. The effects of primary optic tract (POT) interruption on entrainment of circadian rhythms have been studied in rats (Stephan and Zucker, 1972a; Moore and Eichler, 1972). These studies concluded that the POT are not involved in the mediation of photic entrainment. 2. The present study assessed the effects of POT interruption on entrainment, phase-shifting and free-runs of activity in male golden hamsters, Mesocricetus auratus. 3. Several hamsters that sustained complete bilateral POT interruptions showed unusually long active phases that extended into the light phase of the light-dark (LD) cycle, or showed a long phase lead of activity onset relative to the D phase. 4. The periods (τ) of the free-running rhythms of these hamsters were unusually long. The combination of long τ's and altered entrainment are not explicable in terms of alterations in light sensitivity according to predictions from the Circadian Rule. 5. An explanation for these results is possible in terms of alterations in the coupling of two oscillators. One model of entrainment (Pittendrigh, 1974) suggests that such coupling is involved in the control of both entrainment and the periodicity of free-running rhythms. © 1977 Springer-Verlag.