Pineal gland influences period of circannual rhythms of ground squirrels.

Female golden-mantled ground squirrels were pinealectomized (Pinx) or Sham-Pinx at 70 days of age and maintained for more than 2 yr at 23 degrees C in a 10:14 light-dark photoperiod. Reproductive condition and body weight were recorded weekly and bi-weekly, respectively. Pinx and Sham-Pinx squirrels displayed circannual rhythms in body weight; the groups did not differ with respect to absolute magnitudes of annual peaks and troughs in body mass. The period of the circannual body weight cycle (measured peak to peak) was 27 and 58 days shorter in Pinx than in Sham-Pinx squirrels during the 1st and 2nd yr, respectively, after surgery. The onset of estrus during the second postoperative cycle occurred significantly earlier in Pinx than in Sham-Pinx squirrels. The pineal gland is not essential for the generation or expression of circannual or circadian cycles but may affect the period of some circannual rhythms.