Masking of circadian activity rhythms in male golden hamsters by the presence of females

Summary Wheel-running activity was recorded in male golden hamsters (Mesocricetus auratus) that had been blinded by bilateral enucleation and then kept singly in cages in a continuously darkened cabinet (room 1). In an adjacent cabinet (room 2), sighted male and female hamsters were kept in a 12:12-h light-dark cycle. For time spans varying from 15 to 45 days, two females within their cages were transferred for 3 h each day from room 2 to room 1 at the same time of light-off in room 2. Afterwards, two sighted male hamsters were transferred to room 1 for 3 h each day for 28 days. For the last 70 days of the experiment, all blinded males were transferred permanently to room 2. There were three main results: (1) bilateral enucleation of the males in room 1 had no effect on phase or period of the free-running rhythm; (2) the rhythms of the blinded males were entrained neither by the 3-h daily presence of two females nor after the transfer into room 2; (3) the presence of females usually released activity in the males depending on the circadian phase at which the exposure to females occurred. The masking responses were maximal at the beginning of the activity time, and reached a minor second maximum approximately 9 to 12 h later.